Simulated Sea Level Rise in Coastal Peat Soils Stimulates Mercury MethylationClick to copy article linkArticle link copied!
- Bryce A. CookBryce A. CookDepartment of Environmental Toxicology, University of California Davis, One Shields Avenue, Davis, California 95616, United StatesMore by Bryce A. Cook
- Benjamin D. PetersonBenjamin D. PetersonDepartment of Environmental Toxicology, University of California Davis, One Shields Avenue, Davis, California 95616, United StatesMore by Benjamin D. Peterson
- Jacob M. OgorekJacob M. OgorekU.S. Geological Survey Mercury Research Laboratory, One Gifford Pinchot Drive, Madison, Wisconsin 53726, United StatesMore by Jacob M. Ogorek
- Sarah E. JanssenSarah E. JanssenU.S. Geological Survey Mercury Research Laboratory, One Gifford Pinchot Drive, Madison, Wisconsin 53726, United StatesMore by Sarah E. Janssen
- Brett A. Poulin*Brett A. Poulin*Email: [email protected]. Phone: +1 530 754 2454.Department of Environmental Toxicology, University of California Davis, One Shields Avenue, Davis, California 95616, United StatesMore by Brett A. Poulin
Abstract
Coastal wetlands are vulnerable to sea level rise with unknown consequences for mercury (Hg) cycling, particularly the potential for exacerbating neurotoxic methylmercury (MeHg) production and bioaccumulation in food webs. Here, the effect of sea level rise on MeHg formation in the Florida Everglades was evaluated by incubating peat cores from a freshwater wetland for 0–20 days in the laboratory at five salinity conditions (0.16–6.0 parts-per-thousand; 0.20–454 mg L–1 sulfate (SO42–)) to simulate the onset of sea level rise within coastal margins. Isotopically enriched inorganic mercury (201Hg(II)) was used to track MeHg formation and peat-porewater partitioning. In all five salinity treatments, porewaters became anoxic within 1 day and became progressively enriched in dissolved organic matter (DOM) of greater aromatic composition over the 20 days compared to ambient conditions. In the four highest salinity treatments, SO42– concentrations decreased and sulfide concentrations increased over time due to microbial dissimilatory SO42– reduction that was concurrent with 201Hg(II) methylation. Importantly, elevated salinity resulted in a greater proportion of produced Me201Hg observed in porewaters as opposed to bound to peat, interpreted to be due to the complexation of MeHg with aromatic DOM released from peat. The findings highlight the potential for enhanced production and mobilization of MeHg in coastal wetlands of the Florida Everglades due to the onset of saltwater intrusion.
This publication is licensed under
License Summary*
You are free to share(copy and redistribute) this article in any medium or format within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
Non-Commercial (NC): Only non-commercial uses of the work are permitted.
No Derivatives (ND): Derivative works may be created for non-commercial purposes, but sharing is prohibited.
*Disclaimer
This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials.
License Summary*
You are free to share(copy and redistribute) this article in any medium or format within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
Non-Commercial (NC): Only non-commercial uses of the work are permitted.
No Derivatives (ND): Derivative works may be created for non-commercial purposes, but sharing is prohibited.
*Disclaimer
This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials.
License Summary*
You are free to share(copy and redistribute) this article in any medium or format within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
Non-Commercial (NC): Only non-commercial uses of the work are permitted.
No Derivatives (ND): Derivative works may be created for non-commercial purposes, but sharing is prohibited.
*Disclaimer
This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials.
License Summary*
You are free to share(copy and redistribute) this article in any medium or format within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
Non-Commercial (NC): Only non-commercial uses of the work are permitted.
No Derivatives (ND): Derivative works may be created for non-commercial purposes, but sharing is prohibited.
*Disclaimer
This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials.
License Summary*
You are free to share(copy and redistribute) this article in any medium or format within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
Non-Commercial (NC): Only non-commercial uses of the work are permitted.
No Derivatives (ND): Derivative works may be created for non-commercial purposes, but sharing is prohibited.
*Disclaimer
This summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials.
Introduction
Methods
Results and Discussion
Porewater Chemistry of Peat Incubations
Figure 1
Figure 1. Porewater (A) redox potential (Eh) values at 6 cm depth from water surface compared to standard hydrogen electrode and porewater concentrations of (B) total iron (Fe), (C) sulfate (SO42–), (D) total sulfide (S2–), and (E) DOC concentration, (F) DOM decadic absorbance at 254 nm (α254), (G) DOM specific ultraviolet absorbance at 254 nm (SUVA254), and (H) DOM spectral slope ratio (SR). In panel A, data points with no error bars represent values of a single replicate (n = 1) and data points with error bars represent the average values of experimental replicates (n = 2) and error bars represent the average deviation from the mean. ORP measurements for the 0.50 ppt treatment are not reported. In panels B–H, data points at time points t = 1, 2, 3, 10, 13, and 15 and 0, 6, and 20 days present average values of experimental duplicates (n = 2) and triplicates (n = 3), respectively, and error bars represent the average deviation from the mean. Outlier values in DOC concentration were removed (n ≤ 1 per salinity treatment above 80 mg C L–1) for clarity.
Mercury Methylation in Peat Incubations
Figure 2
Figure 2. (A) Percentage of total 201Hg as porewater Me201Hg relative to the entire 201Hg pool and (B) percentage of all Hg species relative to the entire 201Hg pool (porewater and peat) vs incubation time from peat core experiments. Hashed bars represent porewater 201Hg species and solid bars represent peat 201Hg species. Yellow and orange bars represent Me201Hg and green and blue bars represent 201Hg(II). Data points present average values of experimental replicates (n = 2) and error bars represent the average deviation from the mean.
Figure 3
Figure 3. (A.) Porewater methylation efficiency presented as the percent of total porewater 201Hg as Me201Hg and distribution coefficients (log(Kd); L kg–1) of (B) 201Hg(II) and (C) Me201Hg as a function of incubation time. Data points present average values of experimental replicates (n = 2) and error bars represent the average deviation from the mean.
Biogeochemical Effects of Salinity Increases on Mercury Methylation in Peat Soils
Figure 4
Figure 4. Spearman’s rank correlation matrices for porewaters from treatment salinities (A) 0.16, (B) 0.25, (C) 0.50, (D) 1.0, and (E) 6.0 ppt. Darker red boxes at the intersection between two parameters indicate a stronger positive correlation; darker blue boxes represent a stronger negative correlation. Boxes at intersections between two significantly statistically correlated parameters (Spearman’s rank, p < 0.05) are represented as an open box. Boxes at intersections between two insignificantly statistically correlated parameters (Spearman’s rank, p > 0.05) are represented by a box with a black X symbol. S2– concentration correlations are omitted from panel A due to S2– being below the detection limit in all but one core at 0.16 ppt.
Figure 5
Figure 5. Linear correlation between the distribution coefficient of Me201Hg (log(Kd); L kg–1) and the DOM absorbance at 254 nm (α254, cm–1) for the four highest salinity treatments. Statistical outliers for distribution coefficient of Me201Hg (log(Kd); L kg–1) (n = 4 at 0.25 ppt) were identified and removed from the regression.
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsearthspacechem.4c00124.
Supporting Information on peat core collection (S1.1), porewater chemistry (S1.2), incubations (S1.3), water and peat analyses (S1.4), thermodynamic speciation calculations (S1.5), supporting interpretations (S2), and supporting figures and tables (S3) (PDF)
All data from incubations are provided in an xlsx file (XLSX)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.
Acknowledgments
Support was provided by the U.S. Geological Survey Greater Everglades Priority Ecosystems Science (GEPES) Program, a grant from The Everglades Foundation and VoLo Foundation, and the UC Davis Agricultural Experiment Station (AES). We thank three anonymous reviewers and D. P. Krabbenhoft (USGS) for providing constructive suggestions that improved the study. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
References
This article references 87 other publications.
- 1UN Environment. Global Mercury Assessment 2018; UN Environment Programme, Chemicals and Health Branch Geneva: Switzerland, 2019.Google ScholarThere is no corresponding record for this reference.
- 2Hsu-Kim, H.; Kucharzyk, K. H.; Zhang, T.; Deshusses, M. A. Mechanisms Regulating Mercury Bioavailability for Methylating Microorganisms in the Aquatic Environment: A Critical Review. Environ. Sci. Technol. 2013, 47, 2441– 2456, DOI: 10.1021/es304370gGoogle Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXitVKqu78%253D&md5=d8ee0c1dc6164c2b00390d3a6f18e18dMechanisms Regulating Mercury Bioavailability for Methylating Microorganisms in the Aquatic Environment: A Critical ReviewHsu-Kim, Heileen; Kucharzyk, Katarzyna H.; Zhang, Tong; Deshusses, Marc A.Environmental Science & Technology (2013), 47 (6), 2441-2456CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)A review is given. Hg is a potent neurotoxin for humans, particularly if the metal is in the form of methylmercury. Hg is widely distributed in aquatic ecosystems as a result of anthropogenic activities and natural earth processes. A 1st step toward bioaccumulation of MeHg in aquatic food webs is the methylation of inorg. forms of the metal, a process that is primarily mediated by anaerobic bacteria. We evaluate the current state of knowledge regarding the mechanisms regulating microbial Hg methylation, including the speciation of Hg in environments where methylation occurs and the processes that control Hg bioavailability to these organisms. MeHg prodn. rates are generally related to the presence and productivity of methylating bacteria and also the uptake of inorg. Hg to these microorganisms. Our understanding of the mechanisms behind methylation is limited due to fundamental questions related to the geochem. forms of Hg that persist in anoxic settings, the mode of uptake by methylating bacteria, and the biochem. pathway by which these microorganisms produce and degrade MeHg. In anoxic sediments and water, the geochem. forms of Hg (and subsequent bioavailability) are largely governed by reactions between Hg(II), inorg. sulfides, and natural org. matter. These interactions result in a mixt. of dissolved, nanoparticulate, and larger cryst. particles that cannot be adequately represented by conventional chem. equil. models for Hg bioavailability. We discuss recent advances in nanogeochem. and environmental microbiol. that can provide new tools and unique perspectives to help us solve the question of how microorganisms methylate Hg. An understanding of the factors that cause the prodn. and degrdn. of MeHg in the environment is ultimately needed to inform policy makers and develop long-term strategies for controlling Hg contamination.
- 3Bravo, A. G.; Cosio, C. Biotic Formation of Methylmercury: A Bio-Physico-Chemical Conundrum. Limnol. Oceanogr. 2020, 65, 1010– 1027, DOI: 10.1002/lno.11366Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhsF2jsbbO&md5=4675f727e8d286564851f04136326d14Biotic formation of methylmercury: A bio-physico-chemical conundrumBravo, Andrea G.; Cosio, ClaudiaLimnology and Oceanography (2020), 65 (5), 1010-1027CODEN: LIOCAH; ISSN:0024-3590. (John Wiley & Sons, Inc.)Mercury (Hg) is a natural and widespread trace metal, but is considered a priority pollutant, particularly its org. form methylmercury (MMHg), because of human's exposure to MMHg through fish consumption. Pioneering studies showed the methylation of divalent Hg (HgII) to MMHg to occur under oxygen-limited conditions and to depend on the activity of anaerobic microorganisms. Recent studies identified the hgcAB gene cluster in microorganisms with the capacity to methylate HgII and unveiled a much wider range of species and environmental conditions producing MMHg than previously expected. Here, we review the recent knowledge and approaches used to understand HgII-methylation, microbial biodiversity and activity involved in these processes, and we highlight the current limits for predicting MMHg concns. in the environment. The available data unveil the fact that HgII methylation is a bio-physico-chem. conundrum in which the efficiency of biol. HgII methylation appears to depend chiefly on HgII and nutrients availability, the abundance of electron acceptors such as sulfate or iron, the abundance and compn. of org. matter as well as the activity and structure of the microbial community. An increased knowledge of the relationship between microbial community compn., physico-chem. conditions, MMHg prodn., and demethylation is necessary to predict variability in MMHg concns. across environments.
- 4Wiener, J. G.; Krabbenhoft, D. P.; Heinz, G. H.; Scheuhammer, A. M. Ecotoxicology of Mercury. In Handbook of Ecotoxicology, 2nd ed.; Hoffman, D. J., Rattner, B. A., Burton, G. A., Cairns, J. C., Eds.; Lewis Publishers: Boca Raton, FL, 2003; pp 409– 463.Google ScholarThere is no corresponding record for this reference.
- 5Mahaffey, K. R.; Clickner, R. P.; Jeffries, R. A. Adult Women’s Blood Mercury Concentrations Vary Regionally in the United States: Association with Patterns of Fish Consumption (NHANES 1999–2004). Environ. Health Perspect. 2009, 117, 47– 53, DOI: 10.1289/ehp.11674Google ScholarThere is no corresponding record for this reference.
- 6Peterson, B. D.; Krabbenhoft, D. P.; McMahon, K. D.; Ogorek, J. M.; Tate, M. T.; Orem, W. H.; Poulin, B. A. Environmental Formation of Methylmercury Is Controlled by Synergy of Inorganic Mercury Bioavailability and Microbial Mercury-methylation Capacity. Environ. Microbiol. 2023, 25, 1409– 1423, DOI: 10.1111/1462-2920.16364Google ScholarThere is no corresponding record for this reference.
- 7Black, F. J.; Poulin, B. A.; Flegal, A. R. Factors Controlling the Abiotic Photo-Degradation of Monomethylmercury in Surface Waters. Geochim. Cosmochim. Acta 2012, 84, 492– 507, DOI: 10.1016/j.gca.2012.01.019Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XltFyqsbg%253D&md5=64db47969ddab5f72ce2e54cabab0ef5Factors controlling the abiotic photo-degradation of monomethylmercury in surface watersBlack, Frank J.; Poulin, Brett A.; Flegal, A. RussellGeochimica et Cosmochimica Acta (2012), 84 (), 492-507CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)Photo-decompn. is among the most important mechanisms responsible for degrading monomethylmercury (MMHg) in aquatic systems, but this process is not fully understood. We investigated the relative importance of different factors in controlling the rate of MMHg photo-decompn. in surface waters in expts. using DOM isolated from natural waters. We found no evidence of net abiotic prodn. of MMHg in any dark or light exposed treatments. The av. (mean ± s.d.) MMHg photo-decompn. rate const. for all light exposed samples using DOM concd. from three coastal wetlands was 0.0099 ± 0.0020 E-1/m2 (range of 0.006-0.015 E-1/m2) when expressed in photon flux from 330-700 nm. This was roughly 3-fold higher than the av. MMHg photo-decompn. rate const. in coastal seawater of 0.0032 ± 0.0010 E-1/m2. MMHg photo-degrdn. was highly wavelength dependent. The ratio of MMHg photo-decompn. rate consts., with respect to photon flux, was 400:37:1 for UVB:UVA:PAR. However, when integrated across the entire water column over which MMHg photo-demethylation occurs, PAR was responsible for photo-degrading more MMHg than UVB and UVA combined in the three wetland sites because of the more rapid attenuation of UV light with depth. MMHg half-lives in the wetlands were calcd. for the upper 250 cm where photo-degrdn. occurred, and ranged from 7.6 to 20 days under typical summer sunlight conditions at 37°N. Rates of MMHg photo-decompn. decreased with increasing salinity, and were 27% higher at a salinity of 5 than those at a salinity of 25. This difference could not be accounted for by changes in the complexation of MMHg by DOM and chloride. Differences in MMHg photo-degrdn. rate consts. of up to 18% were measured between treatments using DOM concd. from three different wetlands. Surprisingly, increasing DOM concn. from 1.5 to 11.3 mg OC L-1 had only a small (6%) effect on MMHg photo-decompn., which was much smaller than the 34% decrease predicted due to the attenuation of light at the higher DOM levels. This suggests that DOM plays an important role in MMHg photo-decompn. apart from mediating light levels and MMHg complexation. Expts. employing various scavengers implied that singlet oxygen and hydroxyl radicals were not involved in the photo-degrdn. of MMHg in the natural waters used. Varying concns. of Fe, Cu, and Mn had only small (≤11%) effects on rates of MMHg photo-decompn., and relatively high rates were measured in high purity water with no trace metals or DOM. These results demonstrate that MMHg photo-decompn. can occur via pathways not involving Fe, the photo-Fenton reaction, nitrate photolysis, or thiol complexation. Taken with previous studies, multiple reaction pathways appear to exist, and their importance varies as a function of water chem. and light wavelength.
- 8Blanchfield, P. J.; Rudd, J. W. M.; Hrenchuk, L. E.; Amyot, M.; Babiarz, C. L.; Beaty, K. G.; Bodaly, R. A. D.; Branfireun, B. A.; Gilmour, C. C.; Graydon, J. A.; Hall, B. D.; Harris, R. C.; Heyes, A.; Hintelmann, H.; Hurley, J. P.; Kelly, C. A.; Krabbenhoft, D. P.; Lindberg, S. E.; Mason, R. P.; Paterson, M. J.; Podemski, C. L.; Sandilands, K. A.; Southworth, G. R.; St Louis, V. L.; Tate, L. S.; Tate, M. T. Experimental Evidence for Recovery of Mercury-Contaminated Fish Populations. Nature 2022, 601, 74– 78, DOI: 10.1038/s41586-021-04222-7Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislGntbrJ&md5=6e9882bca58c8b9d134343d0a61e7f5eExperimental evidence for recovery of mercury-contaminated fish populationsBlanchfield, Paul J.; Rudd, John W. M.; Hrenchuk, Lee E.; Amyot, Marc; Babiarz, Christopher L.; Beaty, Ken G.; Bodaly, R. A. Drew; Branfireun, Brian A.; Gilmour, Cynthia C.; Graydon, Jennifer A.; Hall, Britt D.; Harris, Reed C.; Heyes, Andrew; Hintelmann, Holger; Hurley, James P.; Kelly, Carol A.; Krabbenhoft, David P.; Lindberg, Steve E.; Mason, Robert P.; Paterson, Michael J.; Podemski, Cheryl L.; Sandilands, Ken A.; Southworth, George R.; St Louis, Vincent L.; Tate, Lori S.; Tate, Michael T.Nature (London, United Kingdom) (2022), 601 (7891), 74-78CODEN: NATUAS; ISSN:1476-4687. (Nature Portfolio)Anthropogenic releases of mercury (Hg)1-3 are a human health issue4 because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorg. Hg in aquatic ecosystems, bioaccumulates to high concns. in fish consumed by humans5,6. Predicting the efficacy of Hg pollution controls on fish MeHg concns. is complex because many factors influence the prodn. and bioaccumulation of MeHg7-9. Here we conducted a 15-yr whole-ecosystem, single-factor expt. to det. the magnitude and timing of redns. in fish MeHg concns. following redns. in Hg addns. to a boreal lake and its watershed. During the seven-year addn. phase, we applied enriched Hg isotopes to increase local Hg wet deposition rates fivefold. The Hg isotopes became increasingly incorporated into the food web as MeHg, predominantly from addns. to the lake because most of those in the watershed remained there. Thereafter, isotopic addns. were stopped, resulting in an approx. 100% redn. in Hg loading to the lake. The concn. of labeled MeHg quickly decreased by up to 91% in lower trophic level organisms, initiating rapid decreases of 38-76% of MeHg concn. in large-bodied fish populations in eight years. Although Hg loading from watersheds may not decline in step with lowering deposition rates, this expt. clearly demonstrates that any redn. in Hg loadings to lakes, whether from direct deposition or runoff, will have immediate benefits to fish consumers.
- 9Bergamaschi, B. A.; Krabbenhoft, D. P.; Aiken, G. R.; Patino, E.; Rumbold, D. G.; Orem, W. H. Tidally Driven Export of Dissolved Organic Carbon, Total Mercury, and Methylmercury from a Mangrove-Dominated Estuary. Environ. Sci. Technol. 2012, 46, 1371– 1378, DOI: 10.1021/es2029137Google ScholarThere is no corresponding record for this reference.
- 10Gilmour, C. C.; Riedel, G. S.; Ederington, M. C.; Bell, J. T.; Gill, G.; Stordal, M.; Stordal, M. C. Methylmercury Concentrations and Production Rates across a Trophic Gradient in the Northern Everglades. Biogeochemistry 1998, 40, 327– 345, DOI: 10.1023/A:1005972708616Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXitlaku7g%253D&md5=9d124a2461c447e9f99d3e15da2fede8Methylmercury concentrations and production rates across a trophic gradient in the northern EvergladesGilmour, Cynthia C.; Riedel, G. S.; Ederington, M. C.; Bell, J. T.; Benoit, J. M.; Gill, G. A.; Stordal, M. C.Biogeochemistry (1998), 40 (2-3), 327-345CODEN: BIOGEP; ISSN:0168-2563. (Kluwer Academic Publishers)Methylmercury (MeHg) concns. and prodn. rates were examd. along with sulfur biogeochem. in Everglades sediments in Mar., July and Dec., 1995, as part of a large, multi-investigator study, the Aquatic Cycling of Mercury in the Everglades (ACME) project. The sites examd. constitute a trophic gradient, generated from agricultural runoff, across the Everglades Nutrient Removal (ENR) Area, which is a re-constructed wetland, and Water Conservation Areas (WCA) 2A, 2B and 3 in the northern Everglades. MeHg concns. and %MeHg (MeHg as a percent of total Hg) were lowest in the more eutrophic areas and highest in the more pristine areas in the south. MeHg concns. ranged from <0.1 ng gdwt-1 sediment in the ENR to 5 ng gdwt-1 in WCA3 sediments; and MeHg constituted <0.2% of total Hg (Hgτ) in ENR, but up to about 2% in two sites in WCA2B and WCA3. Methylation rates in surficial sediments, estd. using tracer-level injections of 203Hg(II) into intact sediment cores, ranged from 0 to 0.12 day-1, or about 1 to 10 ng g-1 d-1 when the per day values are multiplied by the ambient total Hg concn. Methylation was generally maximal at or within centimeters of the sediment surface, and was never obsd. in water overlying cores. The spatial pattern of MeHg prodn. generally matched that of MeHg concn. The coincident distributions of MeHg and its prodn. suggest that in situ prodn. controls concn., and that MeHg concn. can be used as an analog for MeHg prodn. In addn., the spatial pattern of MeHg in Everglades sediments matches that in biota, suggesting that MeHg bioaccumulation may be predominantly a function of the de novo methylation rate in surficial sediments. Sulfate concns. in surficial pore waters (up to 400 μm), microbial sulfate-redn. rates (up to 800 nm cc-1 day-1) and resultant pore water sulfide concns. (up to 300 μm) at the eutrophic northern sites were all high relative to most freshwater systems. All declined to the south, and sulfate concns. in WCA2B and in central WCA3 resembled those in oligotrophic lakes (50-100 μm). MeHg concn. and prodn. were inversely related to sulfate redn. rate and pore water sulfide. Control of MeHg prodn. in the northern Everglades appears to mimic that in an estuary, where sulfate concns. are high and where sulfide produced by microbial sulfate redn. inhibits MeHg prodn.
- 11Orem, W. H.; Fitz, C.; Krabbenhoft, D. P.; Poulin, B. A.; Varonka, M. S.; Aiken, G. R. Ecosystem-Scale Modeling and Field Observations of Sulfate and Methylmercury Distributions in the Florida Everglades: Responses to Reductions in Sulfate Loading. Aquat. Geochem. 2020, 26, 191– 220, DOI: 10.1007/s10498-020-09368-wGoogle ScholarThere is no corresponding record for this reference.
- 12Hurley, J. P.; Krabbenhoft, D. P.; Cleckner, L. B.; Olson, M. L.; Aiken, G. R.; Rawlik, P. S. System Controls on the Aqueous Distribution of Mercury in the Northern Florida Everglades. Biogeochemistry 1998, 40, 293– 310, DOI: 10.1023/A:1005928927272Google ScholarThere is no corresponding record for this reference.
- 13Cleckner, L. B.; Garrison, P. J.; Hurley, J. P.; Olson, M. L.; Krabbenhoft, D. P. Trophic Transfer of Methyl Mercury in the Northern Florida Everglades. Biogeochemistry 1998, 40, 347– 361, DOI: 10.1023/A:1005918101773Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXitlaku7k%253D&md5=dd1e4210055504b3a63fa040728e83fbTrophic transfer of methyl mercury in the northern Florida EvergladesCleckner, Lisa B.; Garrison, Paul J.; Hurley, James P.; Olson, Mark L.; Krabbenhoft, David P.Biogeochemistry (1998), 40 (2-3), 347-361CODEN: BIOGEP; ISSN:0168-2563. (Kluwer Academic Publishers)There are spatial differences in MeHg concns. in biota in Water Conservation Areas 2 and 3 in the Everglades, with higher concns. generally in the southern areas. Fish and hemipterans had the most MeHg on a wet wt. basis, with levels exceeding 30 ng/g. The magnitude of MeHg accumulation in biota varies seasonally and does not always appear to be assocd. with changes in water column concn. This is exemplified by periphyton, the base of the foodweb in the Everglades, at a high nutrient sampling site. Although limited in scope, MeHg concns. presented for biota provide insight into beginning to understand the dynamic nature of Hg transfer in the Everglades foodweb on a spatial and temporal basis.
- 14Dittmar, T.; Hertkorn, N.; Kattner, G.; Lara, R. J. Mangroves, a Major Source of Dissolved Organic Carbon to the Oceans. Global Biogeochem. Cycles 2006, 20, 2570, DOI: 10.1029/2005GB002570Google ScholarThere is no corresponding record for this reference.
- 15Rumbold, D. G.; Lange, T. R.; Richard, D.; DelPizzo, G.; Hass, N. Mercury Biomagnification through Food Webs along a Salinity Gradient Down-Estuary from a Biological Hotspot. Estuar. Coast Shelf Sci. 2018, 200, 116– 125, DOI: 10.1016/j.ecss.2017.10.018Google ScholarThere is no corresponding record for this reference.
- 16Buchanan, M. K.; Kulp, S.; Strauss, B. Resilience of U.S. Coastal Wetlands to Accelerating Sea Level Rise. Environ. Res. Commun. 2022, 4, 061001, DOI: 10.1088/2515-7620/ac6eefGoogle ScholarThere is no corresponding record for this reference.
- 17Zhao, X.; Rivera-Monroy, V. H.; Wang, H.; Xue, Z. G.; Tsai, C.-F.; Willson, C. S.; Castañeda-Moya, E.; Twilley, R. R. Modeling Soil Porewater Salinity in Mangrove Forests (Everglades, Florida, USA) Impacted by Hydrological Restoration and a Warming Climate. Ecol. Model. 2020, 436, 109292, DOI: 10.1016/j.ecolmodel.2020.109292Google ScholarThere is no corresponding record for this reference.
- 18Lagomasino, D.; Fatoyinbo, T.; Castañeda-Moya, E.; Cook, B. D.; Montesano, P. M.; Neigh, C. S. R.; Corp, L. A.; Ott, L. E.; Chavez, S.; Morton, D. C. Storm Surge and Ponding Explain Mangrove Dieback in Southwest Florida Following Hurricane Irma. Nat. Commun. 2021, 12, 4003, DOI: 10.1038/s41467-021-24253-yGoogle ScholarThere is no corresponding record for this reference.
- 19Parks, J. M.; Johs, A.; Podar, M.; Bridou, R.; Hurt, R. A.; Smith, S. D.; Tomanicek, S. J.; Qian, Y.; Brown, S. D.; Brandt, C. C.; Palumbo, A. V.; Smith, J. C.; Wall, J. D.; Elias, D. A.; Liang, L. The Genetic Basis for Bacterial Mercury Methylation. Science 2013, 339, 1332– 1335, DOI: 10.1126/science.1230667Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjvVaqtL8%253D&md5=67d2812c64b4f2b024bd58380b486787The genetic basis for bacterial mercury methylationParks, Jerry M.; Johs, Alexander; Podar, Mircea; Bridou, Romain; Hurt, Richard A., Jr.; Smith, Steven D.; Tomanicek, Stephen J.; Qian, Yun; Brown, Steven D.; Brandt, Craig C.; Palumbo, Anthony V.; Smith, Jeremy C.; Wall, Judy D.; Elias, Dwayne A.; Liang, LiyuanScience (Washington, DC, United States) (2013), 339 (6125), 1332-1335CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Methylmercury is a potent neurotoxin produced in natural environments from inorg. mercury by anaerobic bacteria. However, until now the genes and proteins involved have remained unidentified. Here, we report a two-gene cluster, hgcA and hgcB, required for mercury methylation by Desulfovibrio desulfuricans ND132 and Geobacter sulfurreducens PCA. In either bacterium, deletion of hgcA, hgcB, or both genes abolishes mercury methylation. The genes encode a putative corrinoid protein, HgcA, and a 2[4Fe-4S] ferredoxin, HgcB, consistent with roles as a Me carrier and an electron donor required for corrinoid cofactor redn., resp. Among bacteria and archaea with sequenced genomes, gene orthologs are present in confirmed methylators but absent in nonmethylators, suggesting a common mercury methylation pathway in all methylating bacteria and archaea sequenced to date.
- 20Poulin, B. A.; Ryan, J. N.; Tate, M. T.; Krabbenhoft, D. P.; Hines, M. E.; Barkay, T.; Schaefer, J.; Aiken, G. R. Geochemical Factors Controlling Dissolved Elemental Mercury and Methylmercury Formation in Alaskan Wetlands of Varying Trophic Status. Environ. Sci. Technol. 2019, 53, 6203– 6213, DOI: 10.1021/acs.est.8b06041Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXpsVejsLc%253D&md5=dcda1090684274c8891de727fe13394aGeochemical Factors Controlling Dissolved Elemental Mercury and Methylmercury Formation in Alaskan Wetlands of Varying Trophic StatusPoulin, Brett A.; Ryan, Joseph N.; Tate, Michael T.; Krabbenhoft, David P.; Hines, Mark E.; Barkay, Tamar; Schaefer, Jeffra; Aiken, George R.Environmental Science & Technology (2019), 53 (11), 6203-6213CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)The transformations of aq. inorg. divalent Hg (Hg(II)i) to volatile dissolved gaseous Hg (Hg(aq)) and toxic methylmercury (MeHg) govern Hg bioavailability and fate in northern ecosystems. This study quantified concns. of aq. Hg species (Hg(II)i, Hg(aq), MeHg) and relevant geochem. constituents in pore waters of 8 Alaskan wetlands that differ in trophic status (i.e., bog-to-fen gradient) to gain insight on processes controlling dark Hg(II)i redn. and Hg(II)i methylation. Regardless of wetland trophic status, pos. correlations were obsd. between pore water Hg(II)i and dissolved org. C (DOC) concns. The concn. ratio of Hg(aq) to Hg(II)i exhibited an inverse relation to Hg(II)i concn. A ubiquitous pathway for Hg(aq) formation was not identified based on geochem. data, but we surmise that dissolved org. matter (DOM) influences Hg retention in wetland pore waters by complexing Hg(II)i and decreasing the concn. of volatile Hg(aq) relative to Hg(II)i. There was no evidence of Hg(aq) abundance directly limiting Hg methylation. The concn. of MeHg relative to Hg(II)i was greatest in wetlands of intermediate trophic status, and geochem. data suggest Hg methylation pathways vary between wetlands. The insights on geochem. factors influencing aq. Hg speciation should be considered in context of the long-term fate of Hg in northern wetlands.
- 21St Louis, V. L.; Rudd, J. W. M.; Kelly, C. A.; Beaty, K. G.; Flett, R. J.; Roulet, N. T. Production and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of Wetlands. Environ. Sci. Technol. 1996, 30, 2719– 2729, DOI: 10.1021/es950856hGoogle Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XksFGrsb0%253D&md5=6235494066b537ab8db4243105509b5dProduction and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of WetlandsSt. Louis, Vincent L.; Rudd, John W. M.; Kelly, Carol A.; Beaty, Ken G.; Flett, Robert J.; Roulet, Nigel T.Environmental Science and Technology (1996), 30 (9), 2719-2729CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Four terrestrial boreal forest catchments contg. different types of wetlands were studied to det. their strength as sources or sinks of methylmercury (MeHg) and total mercury (THg) to downstream ecosystems and to det. if patterns seen in one year were consistent over several years. All catchments were sinks for THg. The wetland type, percentage wetland area (0-25%), or annual water yield did not appear to have a consistent effect on the magnitude of this retention. Wetland areas of the catchments were always net sources of MeHg. Unlike for THg, there were large and consistent differences in the source strength among wetland types for MeHg. These differences appeared to be related to differences in the internal hydrol. of the wetlands. All types of wetlands were greater sources of MeHg during years of high water yield, but even during years of low flow, all wetland types were sources of MeHg. Thus, we conclude that wetlands are important sites of MeHg prodn. in boreal ecosystems on the long term. Upland areas of catchments were consistently sinks for MeHg, and so whole catchment sink/source values were strongly affected by the percentage of wetland areas within a catchment. Mass balance ests. of MeHg input from wetland areas to a lake indicate that the annual input of MeHg from wetlands is larger than the annual uptake of Hg by fish and is similar to the amt. of MeHg produced in the lake. Because of the predictable patterns between terrestrial catchments in their strength as sources or sinks of MeHg, it is possible to model inputs of MeHg from lake catchments with knowledge of the percentage wetland area in a catchment, the type of wetland contained in a catchment, and the annual water yield of a catchment.
- 22Mitchell, C. P. J.; Branfireun, B. A.; Kolka, R. K. Spatial Characteristics of Net Methylmercury Production Hot Spots in Peatlands. Environ. Sci. Technol. 2008, 42, 1010– 1016, DOI: 10.1021/es0704986Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXivF2nsw%253D%253D&md5=db8ddb47cbb9b424dba1b861ae975f40Spatial Characteristics of Net Methylmercury Production Hot Spots in PeatlandsMitchell, Carl P. J.; Branfireun, Brian A.; Kolka, Randall K.Environmental Science & Technology (2008), 42 (4), 1010-1016CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Many wetlands are sources of methylmercury (MeHg) to surface waters, yet little information exists about the distribution of MeHg within wetlands. Total mercury (THg) and MeHg in peat pore waters were studied in four peatlands in spring, summer, and fall 2005. Marked spatial variability in the distribution of MeHg, and %MeHg as a proxy for net MeHg prodn., was obsd., with highest values occurring in discrete zones. We denote these zones MeHg hot spots, defined as an area where the pore water %MeHg exceeded the 90th percentile of the data set (n = 463) or >22% of THg as MeHg. MeHg hot spots occurred near the interface between peatland and the upland watershed with few exceptions. The %MeHg in pore water was significantly less in peatland interiors compared to upland-peatland interface zones, with the significance of these differences related to the delineation of the boundary between the two areas. Although further research is necessary, our data suggest that the occurrence of MeHg hot spots is related to the transport of solutes in upland runoff to the peatland perimeter and not to the accumulation of MeHg in this zone as a result of transport from either the peatland interior or the surrounding upland watershed. These findings augment the understanding of peatland MeHg prodn. in upland-peatland watersheds, provide guidance for more accurate quantification of MeHg pool sizes in the landscape, and a spatial framework for the further study of mercury methylation processes in peatlands.
- 23Janssen, S. E.; Tate, M. T.; Poulin, B. A.; Krabbenhoft, D. P.; DeWild, J. F.; Ogorek, J. M.; Varonka, M. S.; Orem, W. H.; Kline, J. L. Decadal Trends of Mercury Cycling and Bioaccumulation within Everglades National Park. Sci. Total Environ. 2022, 838, 156031, DOI: 10.1016/j.scitotenv.2022.156031Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsFGqsLvM&md5=2dbae6214a64c8c838b8fead149144a8Decadal trends of mercury cycling and bioaccumulation within Everglades National ParkJanssen, Sarah E.; Tate, Michael T.; Poulin, Brett A.; Krabbenhoft, David P.; DeWild, John F.; Ogorek, Jacob M.; Varonka, Matthew S.; Orem, William H.; Kline, Jeffrey L.Science of the Total Environment (2022), 838 (Part_1), 156031CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)Mercury (Hg) contamination has been a persistent concern in the Florida Everglades for over three decades due to elevated atm. deposition and the system's propensity for methylation and rapid bioaccumulation. Given declines in atm. Hg concns. in the conterminous United States and efforts to mitigate nutrient release to the greater Everglades ecosystem, it was vital to assess how Hg dynamics responded on temporal and spatial scales. This study used a multimedia approach (water and biota) to examine Hg and methylmercury (MeHg) dynamics across a 76-site network within the southernmost portion of the region, Everglades National Park (ENP), from 2008 to 2018. Hg concns. across matrixes showed that air, water, and biota from the system were inextricably linked. Temporal patterns across matrixes were driven primarily by hydrol. and climatic changes in the park and no evidence of a decline in atm. Hg deposition from 2008 to 2018 was obsd., unlike other regions of the United States. In the Shark River Slough (SRS), excess dissolved org. carbon and sulfate were also consistently delivered from upgradient canals and showed no evidence of decline over the study period. Within the SRS a strong pos. correlation was obsd. between MeHg concns. in surface water and resident fish. Within distinct geog. regions of ENP (SRS, Marsh, Coastal), the geochem. controls on MeHg dynamics differed and highlighted regions susceptible to higher MeHg bioaccumulation, particularly in the SRS and Coastal regions. This study demonstrates the strong influence that dissolved org. carbon and sulfate loads have on spatial and temporal distributions of MeHg across ENP. Importantly, improved water quality and flow rates are two key restoration targets of the nearly 30-yr Everglades restoration program, which if achieved, this study suggests would lead to reduced MeHg prodn. and exposure.
- 24Mitchell, C. P. J.; Gilmour, C. C. Methylmercury Production in a Chesapeake Bay Salt Marsh. J. Geophys. Res. 2008, 113, G00C04, DOI: 10.1029/2008JG000765Google ScholarThere is no corresponding record for this reference.
- 25Bae, H.-S.; Dierberg, F. E.; Ogram, A. Syntrophs Dominate Sequences Associated with the Mercury Methylation-Related Gene HgcA in the Water Conservation Areas of the Florida Everglades. Appl. Environ. Microbiol. 2014, 80, 6517– 6526, DOI: 10.1128/AEM.01666-14Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslSiur7J&md5=a484e79d64cc90db832e89a07f7a7116Syntrophs dominate sequences associated with the mercury methylation-related gene hgcA in the water conservation areas of the Florida EvergladesBae, Hee-Sung; Dierberg, Forrest E.; Ogram, AndrewApplied and Environmental Microbiology (2014), 80 (20), 6517-6526, 11 pp.CODEN: AEMIDF; ISSN:1098-5336. (American Society for Microbiology)The mechanisms and rates of mercury methylation in the Florida Everglades are of great concern because of potential adverse impacts on human and wildlife health through mercury accumulation in aquatic food webs. We developed a new PCR primer set targeting hgcA, a gene encoding a corrinoid protein essential for Hg methylation across broad phylogenetic boundaries, and used this primer set to study the distribution of hgcA sequences in soils collected from three sites along a gradient in sulfate and nutrient concns. in the Northern Everglades. The sequences obtained were distributed in diverse phyla, including Proteobacteria, Chloroflexi, Firmicutes, and Methanomicrobia; however, hgcA clone libraries from all sites were dominated by sequences clustering within the order Syntrophobacterales of the Deltaproteobacteria (49 to 65 % of total sequences). DsrB mRNA sequences, representing active sulfate-reducing prokaryotes at the time of sampling, obtained from these sites were also dominated by Syntrophobacterales (75 to 89 %). Lab. incubations with soils taken from the site low in sulfate concns. also suggested that Hg methylation activities were primarily mediated by members of the order Syntrophobacterales, with some contribution by methanogens, Chloroflexi, iron-reducing Geobacter and non-sulfate-reducing Firmicutes inhabiting the sites. This suggests that prokaryotes distributed within clades defined by syntrophs are the predominant group controlling methylation of Hg in low-sulfate areas of the Everglades. Any strategy for managing mercury methylation in the Everglades should consider that net mercury methylation is not limited to the action of sulfate redn.
- 26Arndt, S.; Jørgensen, B. B.; LaRowe, D. E.; Middelburg, J. J.; Pancost, R. D.; Regnier, P. Quantifying the Degradation of Organic Matter in Marine Sediments: A Review and Synthesis. Earth Sci. Rev. 2013, 123, 53– 86, DOI: 10.1016/j.earscirev.2013.02.008Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXptFOns78%253D&md5=d24554d59bc546860eac339270b53cb8Quantifying the degradation of organic matter in marine sediments: A review and synthesisArndt, Sandra; Joergensen, B. B.; LaRowe, D. E.; Middelburg, J. J.; Pancost, R. D.; Regnier, P.Earth-Science Reviews (2013), 123 (), 53-86CODEN: ESREAV; ISSN:0012-8252. (Elsevier B.V.)A review. Quantifying the rates of biogeochem. processes in marine sediments is essential for understanding global element cycles and climate change. Because org. matter degrdn. is the engine behind benthic dynamics, deciphering the impact that various forces have on this process is central to detg. the evolution of the Earth system. Therefore, recent developments in the quant. modeling of org. matter degrdn. in marine sediments are critically reviewed. The first part of the review synthesizes the main chem., biol. and phys. factors that control org. matter degrdn. in sediments while the second part provides a general review of the math. formulations used to model these processes and the third part evaluates their application over different spatial and temporal scales. Key transport mechanisms in sedimentary environments are summarized and the math. formulation of the org. matter degrdn. rate law is described in detail. The roles of enzyme kinetics, bioenergetics, temp. and biomass growth in particular are highlighted. Alternative model approaches that quantify the degrdn. rate const. are also critically compared. In the third part of the review, the capability of different model approaches to extrapolate org. matter degrdn. rates over a broad range of temporal and spatial scales is assessed. In addn., the structure, functions and parameterization of more than 250 published models of org. matter degrdn. in marine sediments are analyzed. The large range of published model parameters illustrates the complex nature of org. matter dynamics, and, thus, the limited transferability of these parameters from one site to another. Compiled model parameters do not reveal a statistically significant correlation with single environmental characteristics such as water depth, deposition rate or org. matter flux. The lack of a generic framework that allows for model parameters to be constrained in data-poor areas seriously limits the quantification of org. matter degrdn. on a global scale. Therefore, we explore regional patterns that emerge from the compiled more than 250 org. matter rate consts. and critically discuss them in their environmental context. This review provides an interdisciplinary view on org. matter degrdn. in marine sediments. It contributes to an improved understanding of global patterns in benthic org. matter degrdn., and helps identify outstanding questions and future directions in the modeling of org. matter degrdn. in marine sediments.
- 27Yu, R. Q.; Reinfelder, J. R.; Hines, M. E.; Barkay, T. Syntrophic Pathways for Microbial Mercury Methylation. ISME J. 2018, 12, 1826– 1835, DOI: 10.1038/s41396-018-0106-0Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXmvFKgu7w%253D&md5=b52ed230d626973f761469b87d646344Syntrophic pathways for microbial mercury methylationYu, Ri-Qing; Reinfelder, John R.; Hines, Mark E.; Barkay, TamarISME Journal (2018), 12 (7), 1826-1835CODEN: IJSOCF; ISSN:1751-7362. (Nature Research)Exposure to dietary sources of methylmercury (MeHg) is the focus of public health concerns with environmental mercury (Hg) contamination. MeHg is formed in anoxic environments by anaerobic microorganisms. This process has been studied mostly with single-species culture incubations, although the relevance of such studies to Hg(II)-methylation in situ is limited because microbial activities in the environment are critically modulated by interactions among microbial functional groups. Here we describe expts. in which Hg(II)-methylation was examd. within the context of various microbial syntrophies. We show enhanced Hg(II)-methylation under conditions that established syntrophy by interspecies hydrogen and acetate transfer. Relative to activity of monocultures, interactions of Hg(II) methylating sulfate-reducing bacteria with a methanogen stimulated potential Hg(II)-methylation rates 2-fold to 9-fold, and with Syntrophobacter sp. 1.7-fold to 1.8-fold; those of a Hg(II) methylating Syntrophobacter sp. with a methanogen increased Hg(II)-methylation 2-fold. Under sulfate-depleted conditions, higher Hg(II)-methylation rates in the syntrophic incubations corresponded to higher free energy yields (ΔG°') than in the monocultures. Based on energetic considerations, we therefore propose that syntrophic microbial interactions are likely a major source of MeHg in sulfate- and iron-limited anoxic environments while in sulfate-replete environments, MeHg formation via sulfate redn. dominates.
- 28Luek, J. L.; Thompson, K. E.; Larsen, R. K.; Heyes, A.; Gonsior, M. Sulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic Matter. Sci. Rep. 2017, 7, 8829, DOI: 10.1038/s41598-017-09223-zGoogle Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cfpsleisw%253D%253D&md5=3f4c37a485ceba0a41f3797507fb787dSulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic MatterLuek Jenna L; Thompson Kaitlyn E; Heyes Andrew; Gonsior Michael; Thompson Kaitlyn E; Larsen Randolph KScientific reports (2017), 7 (1), 8829 ISSN:.Sulfate reduction plays an important role in altering dissolved organic matter (DOM) in estuarine and coastal sediments, although its role in the production of optically active chromophoric DOM (CDOM) and a subset of fluorescent DOM (FDOM) has not been previously investigated in detail. Freshwater sediment slurries were incubated anaerobically with added sulfate and acetate to promote sulfate-reducing bacteria. Ultraviolet visible (UV-Vis) absorbance and 3-dimensional excitation emission matrix (EEM) fluorescence spectra were measured over a five weeks anaerobic dark incubation period. Parallel Factor Analysis (PARAFAC) of FDOM determined components that increased significantly during dark and anaerobic incubation matching three components previously considered of terrestrially-derived or humic-like origin published in the OpenFluor database. The observed FDOM increase was strongly correlated (R(2) = 0.96) with the reduction of sulfate. These results show a direct experimental link between sulfate reduction and FDOM production, which impacts our understanding of coastal FDOM sources and early sediment diagenesis. As 3D fluorescence techniques are commonly applied to diverse systems, these results provide increasing support that FDOM can have many diverse sources not consistently captured by common classifications such as "humic-like" fluorescence.
- 29Aiken, G. R.; Gilmour, C. C.; Krabbenhoft, D. P.; Orem, W. Dissolved Organic Matter in the Florida Everglades: Implications for Ecosystem Restoration. Crit. Rev. Environ. Sci. Technol. 2011, 41, 217– 248, DOI: 10.1080/10643389.2010.530934Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXit1aqtLk%253D&md5=29a3020336d7c867e601283ad106a162Dissolved Organic Matter in the Florida Everglades: Implications for Ecosystem RestorationAiken, George R.; Gilmour, Cynthia C.; Krabbenhoft, David P.; Orem, WilliamCritical Reviews in Environmental Science and Technology (2011), 41 (Suppl. 1), 217-248CODEN: CRETEK; ISSN:1064-3389. (Taylor & Francis, Inc.)A review. Dissolved org. matter (DOM) in the Florida Everglades controls a no. of environmental processes important for ecosystem function including the absorption of light, mineral dissoln./pptn., transport of hydrophobic compds. (e.g., pesticides), and the transport and reactivity of metals, such as mercury. Proposed attempts to return the Everglades to more natural flow conditions will result in changes to the present transport of DOM from the Everglades Agricultural Area and the northern conservation areas to Florida Bay. In part, the restoration plan calls for increasing water flow throughout the Everglades by removing some of the manmade barriers to flow in place today. The land- and water-use practices assocd. with the plan will likely result in changes in the quality, quantity, and reactivity of DOM throughout the greater Everglades ecosystem. The authors discuss the factors controlling DOM concns. and chem., present distribution of DOM throughout the Everglades, the potential effects of DOM on key water-quality issues, and the potential utility of dissolved org. matter as an indicator of success of restoration efforts.
- 30Haitzer, M.; Aiken, G. R.; Ryan, J. N. Binding of Mercury(II) to Dissolved Organic Matter: The Role of the Mercury-to-DOM Concentration Ratio. Environ. Sci. Technol. 2002, 36, 3564– 3570, DOI: 10.1021/es025699iGoogle Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XltlWkurY%253D&md5=ad2cc1b382bec27bfed2f97a96d95f09Binding of Mercury(II) to Dissolved Organic Matter: The Role of the Mercury-to-DOM Concentration RatioHaitzer, Markus; Aiken, George R.; Ryan, Joseph N.Environmental Science and Technology (2002), 36 (16), 3564-3570CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)The binding of Hg(II) to dissolved org. matter (DOM; hydrophobic acids isolated from the Florida Everglades by XAD-8 resin) was measured over a wide range of Hg-to-DOM concn. ratios using an equil. dialysis ligand exchange method. Conditional distribution coeffs. (KDOM') detd. by this method were strongly affected by the Hg/DOM concn. ratio. At Hg/DOM ratios below approx. 1 μg of Hg/mg of DOM, we obsd. very strong interactions (KDOM' = 1023.2 ±1.0 L/kg at pH = 7.0 and I = 0.1), indicative of mercury-thiol bonds. Hg/DOM ratios above approx. 10 μg of Hg/mg of DOM, as used in most studies that have detd. Hg-DOM binding consts., gave much lower KDOM' values (1010.7 ±1.0 L/kg at pH = 4.9-5.6 and I = 0.1), consistent with Hg binding mainly to oxygen functional groups. These results suggest that the binding of Hg to DOM under natural conditions (very low Hg/DOM ratios) is controlled by a small fraction of DOM mols. contg. a reactive thiol functional group. Therefore, Hg/DOM distribution coeffs. used for modeling the biogeochem. behavior of Hg in natural systems need to be detd. at low Hg/DOM ratios.
- 31Gerbig, C. A.; Kim, C. S.; Stegemeier, J. P.; Ryan, J. N.; Aiken, G. R. Formation of Nanocolloidal Metacinnabar in Mercury-DOM-Sulfide Systems. Environ. Sci. Technol. 2011, 45, 9180– 9187, DOI: 10.1021/es201837hGoogle Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXht1ClsbzI&md5=9af24b8d68a6e618c50dff76fb24fa50Formation of Nanocolloidal Metacinnabar in Mercury-DOM-Sulfide SystemsGerbig, Chase A.; Kim, Christopher S.; Stegemeier, John P.; Ryan, Joseph N.; Aiken, George R.Environmental Science & Technology (2011), 45 (21), 9180-9187CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Direct detn. of Hg speciation in sulfide-contg. environments is confounded by low Hg concns. and poor anal. sensitivity. We report the results of expts. designed to assess Hg speciation at environmentally relevant ratios of Hg to dissolved org. matter (DOM) (i.e., <4 nmol Hg/mg DOM) by combining solid phase extn. using C18 resin with extended x-ray absorption fine structure (EXAFS) spectroscopy. Aq. Hg(II) and a DOM isolate were equilibrated in the presence and absence of 100μM total sulfide. In the absence of sulfide, Hg adsorption to the resin increased as the Hg:DOM ratio decreased and as the strength of Hg-DOM binding increased. EXAFS anal. indicated that in the absence of sulfide, Hg bonds with an av. of 2.4±0.2 S atoms with a bond length typical of Hg-org. thiol ligands (2.35 Å). In the presence of sulfide, Hg showed greater affinity for the C18 resin, and its chromatog. behavior was independent of Hg:DOM ratio. EXAFS anal. showed Hg-S bonds with a longer interat. distance (2.51-2.53 Å) similar to the Hg-S bond distance in metacinnabar (2.53 Å) regardless of the Hg:DOM ratio. For all samples contg. sulfide, the S coordination no. was below the ideal 4-coordinate structure of metacinnabar. At a low Hg:DOM ratio where strong binding DOM sites may control Hg speciation (1.9 nmol/mg) Hg was coordinated by 2.3±0.2 S atoms, and the coordination no. rose with increasing Hg:DOM ratio. The less-than-ideal coordination nos. indicate metacinnabar-like species on the nanometer scale, and the pos. correlation between Hg:DOM ratio and S coordination no. suggests progressively increasing particle size or cryst. order with increasing abundance of Hg with respect to DOM. In DOM-contg. sulfidic systems nanocolloidal metacinnabar-like species may form, and these species need to be considered when addressing Hg biogeochem.
- 32Poulin, B. A.; Gerbig, C. A.; Kim, C. S.; Stegemeier, J. P.; Ryan, J. N.; Aiken, G. R. Effects of Sulfide Concentration and Dissolved Organic Matter Characteristics on the Structure of Nanocolloidal Metacinnabar. Environ. Sci. Technol. 2017, 51, 13133– 13142, DOI: 10.1021/acs.est.7b02687Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1GrurbP&md5=5baa8a7d1bc3e9e9a9e56d895a05b1dfEffects of Sulfide Concentration and Dissolved Organic Matter Characteristics on the Structure of Nanocolloidal MetacinnabarPoulin, Brett A.; Gerbig, Chase A.; Kim, Christopher S.; Stegemeier, John P.; Ryan, Joseph N.; Aiken, George R.Environmental Science & Technology (2017), 51 (22), 13133-13142CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Understanding the speciation of divalent mercury (Hg(II)) in aquatic systems contg. dissolved org. matter (DOM) and sulfide is necessary to predict the conversion of Hg(II) to bioavailable methylmercury. We used X-ray absorption spectroscopy to characterize the structural order of mercury in Hg(II)-DOM-sulfide systems for a range of sulfide concn. (1-100 μM), DOM aromaticity (specific UV absorbance (SUVA254)), and Hg(II)-DOM and Hg(II)-DOM-sulfide equilibration times (4-142 h). In all systems, Hg(II) was present as structurally disordered nanocolloidal metacinnabar (β-HgS). β-HgS nanocolloids were significantly smaller or less ordered at lower sulfide concn., as indicated by under-coordination of Hg(II) in β-HgS. The size or structural order of β-HgS nanocolloids increased with increasing sulfide abundance and decreased with increasing SUVA254 of the DOM. The Hg(II)-DOM or Hg(II)-DOM-sulfide equilibration times did not significantly influence the extent of structural order in nanocolloidal β-HgS. Geochem. factors that control the structural order of nanocolloidal β-HgS, which are expected to influence nanocolloid surface reactivity and soly., should be considered in the context of mercury bioavailability.
- 33Graham, A. M.; Aiken, G. R.; Gilmour, C. C. Effect of Dissolved Organic Matter Source and Character on Microbial Hg Methylation in Hg-S-DOM Solutions. Environ. Sci. Technol. 2013, 47, 5746– 5754, DOI: 10.1021/es400414aGoogle Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmvVehs7w%253D&md5=614a5dc8029f5d5b2950d29d4fdb20f4Effect of Dissolved Organic Matter Source and Character on Microbial Hg Methylation in Hg-S-DOM SolutionsGraham, Andrew M.; Aiken, George R.; Gilmour, Cynthia C.Environmental Science & Technology (2013), 47 (11), 5746-5754CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Dissolved org. matter (DOM) is a key component of fate and transport models for most metals, including Hg. Using a suite of diverse DOM isolates, we demonstrated that DOM character, in addn. to concn., influences inorg. Hg (Hg(II)i) bioavailability to Hg-methylating bacteria. Using a model Hg-methylating bacterium, Desulfovibrio desulfuricans ND132, we evaluated Hg-DOM-sulfide bioavailability in washed-cell assays at environmentally relevant Hg/DOM ratios (∼1-8 ng Hg/mg C) and sulfide concns. (1-1000μM). All tested DOM isolates significantly enhanced Hg methylation above DOM-free controls (from ∼2 to >20-fold for 20 mg C/L DOM solns.), but high mol. wt./highly arom. DOM isolates and/or those with high S content were particularly effective at enhancing Hg methylation. Because these expts. were conducted under conditions of predicted supersatn. with respect to metacinnabar (β-HgS(s)), we attribute the DOM-dependent enhancement of Hg(II)i bioavailability to steric and specific chem. (e.g., DOM thiols) inhibition of β-HgS(s) growth and aggregation by DOM. Expts. examg. the role of DOM across a wide sulfide gradient revealed that DOM only enhances Hg methylation under fairly low sulfide conditions (.ltorsim.30μM), conditions that favor HgS nanoparticle/cluster formation relative to dissolved HgS species.
- 34Graham, A. M.; Aiken, G. R.; Gilmour, C. C. Dissolved Organic Matter Enhances Microbial Mercury Methylation under Sulfidic Conditions. Environ. Sci. Technol. 2012, 46, 2715– 2723, DOI: 10.1021/es203658fGoogle Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvVSrsrg%253D&md5=47c26725a3248a0854ac9f1320ba2c3aDissolved Organic Matter Enhances Microbial Mercury Methylation Under Sulfidic ConditionsGraham, Andrew M.; Aiken, George R.; Gilmour, Cynthia C.Environmental Science & Technology (2012), 46 (5), 2715-2723CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Dissolved org. matter (DOM) is generally thought to lower metal bioavailability in aquatic systems due to the formation of metal-DOM complexes that reduce free metal ion concns. However, this model may not be pertinent for metal nanoparticles, which are now understood to be ubiquitous, sometimes dominant, metal species in the environment. The effect of DOM on Hg bioavailability to microorganisms was examd. under conditions (0.5-5.0nM Hg and 2-10μM sulfide) that favor the formation of β-HgS(s) (metacinnabar) nanoparticles. We used the methylation of stable-isotope enriched 201HgCl2 by Desulfovibrio desulfuricans ND132 in short-term washed cell assays as a sensitive, environmentally significant proxy for Hg uptake. Suwannee River humic acid (SRHA) and Williams Lake hydrophobic acid (WLHPoA) substantially enhanced (2- to 38-fold) the bioavailability of Hg to ND132 over a wide range of Hg/DOM ratios (9.4 pmol/mg DOM to 9.4 nmol/mg DOM), including environmentally relevant ratios. Methylmercury (MeHg) prodn. by ND132 increased linearly with either SRHA or WLHPoA concn., but SRHA, a terrestrially derived DOM, was far more effective at enhancing Hg-methylation than WLHPoA, an aquatic DOM dominated by autochthonous sources. No DOM-dependent enhancement in Hg methylation was obsd. in Hg-DOM-sulfide solns. amended with sufficient l-cysteine to prevent β-HgS(s) formation. We hypothesize that small HgS particles, stabilized against aggregation by DOM, are bioavailable to Hg-methylating bacteria. Our lab. expts. provide a mechanism for the pos. correlations between DOC and MeHg prodn. obsd. in many aquatic sediments and wetland soils.
- 35Poulin, B. A.; Ryan, J. N.; Nagy, K. L.; Stubbins, A.; Dittmar, T.; Orem, W.; Krabbenhoft, D. P.; Aiken, G. R. Spatial Dependence of Reduced Sulfur in Everglades Dissolved Organic Matter Controlled by Sulfate Enrichment. Environ. Sci. Technol. 2017, 51, 3630– 3639, DOI: 10.1021/acs.est.6b04142Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjsFCktrg%253D&md5=509a7a6b72ad0068534b59cd1825165cSpatial Dependence of Reduced Sulfur in Everglades Dissolved Organic Matter Controlled by Sulfate EnrichmentPoulin, Brett A.; Ryan, Joseph N.; Nagy, Kathryn L.; Stubbins, Aron; Dittmar, Thorsten; Orem, William; Krabbenhoft, David P.; Aiken, George R.Environmental Science & Technology (2017), 51 (7), 3630-3639CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Sulfate inputs to the Florida Everglades stimulate sulfidic conditions in freshwater wetland sediments that affect ecol. and biogeochem. processes. An unexplored implication of sulfate enrichment is alteration of the content and speciation of sulfur in dissolved org. matter (DOM), which influences the reactivity of DOM with trace metals. Here, we describe the vertical and lateral spatial dependence of sulfur chem. in the hydrophobic org. acid fraction of DOM from unimpacted and sulfate-impacted Everglades wetlands using X-ray absorption spectroscopy and ultrahigh-resoln. mass spectrometry. Spatial variation in DOM sulfur content and speciation reflects the degree of sulfate enrichment and resulting sulfide concns. in sediment pore waters. Sulfur is incorporated into DOM predominantly as highly reduced species in sulfidic pore waters. Sulfur-enriched DOM in sediment pore waters exchanges with overlying surface waters and the sulfur likely undergoes oxidative transformations in the water column. Across all wetland sites and depths, the total sulfur content of DOM correlated with the relative abundance of highly reduced sulfur functionality. The results identify sulfate input as a primary determinant on DOM sulfur chem. to be considered in the context of wetland restoration and sulfur and trace metal cycling.
- 36Graham, A. M.; Cameron-Burr, K. T.; Hajic, H. A.; Lee, C.; Msekela, D.; Gilmour, C. C. Sulfurization of Dissolved Organic Matter Increases Hg-Sulfide-Dissolved Organic Matter Bioavailability to a Hg-Methylating Bacterium. Environ. Sci. Technol. 2017, 51, 9080– 9088, DOI: 10.1021/acs.est.7b02781Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFKntL7M&md5=ad4090caaa270f6cab5e90df5c4b47cfSulfurization of Dissolved Organic Matter Increases Hg-Sulfide-Dissolved Organic Matter Bioavailability to a Hg-Methylating BacteriumGraham, Andrew M.; Cameron-Burr, Keaton T.; Hajic, Hayley A.; Lee, Connie; Msekela, Deborah; Gilmour, Cynthia C.Environmental Science & Technology (2017), 51 (16), 9080-9088CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Reactions of dissolved org. matter (DOM) with aq. sulfide (termed sulfurization) in anoxic environments can substantially increase DOM's reduced sulfur functional group content. Sulfurization may affect DOM-trace metal interactions, including complexation and metal-contg. particle pptn., aggregation, and dissoln. Using a diverse suite of DOM samples, we found that susceptibility to addnl. sulfur incorporation via reaction with aq. sulfide increased with increasing DOM arom.-, carbonyl-, and carboxyl-C content. The role of DOM sulfurization in enhancing Hg bioavailability for microbial methylation was evaluated under conditions typical of Hg methylation environments (μM sulfide concns. and low Hg-to-DOM molar ratios). Under the conditions of predicted metacinnabar supersatn., microbial Hg methylation increased with increasing DOM sulfurization, likely reflecting either effective inhibition of metacinnabar growth and aggregation or the formation of Hg(II)-DOM thiol complexes with high bioavailability. Remarkably, Hg methylation efficiencies with the most sulfurized DOM samples were similar (>85% of total Hg methylated) to that obsd. in the presence of L-cysteine, a ligand facilitating rapid Hg(II) biouptake and methylation. This suggests that complexes of Hg(II) with DOM thiols have similar bioavailability to Hg(II) complexes with low-mol.-wt. thiols. Overall, our results are a demonstration of the importance of DOM sulfurization to trace metal and metalloid (esp. mercury) fate in the environment. DOM sulfurization likely represents another link between anthropogenic sulfate enrichment and MeHg prodn. in the environment.
- 37Weishaar, J. L.; Aiken, G. R.; Bergamaschi, B. A.; Fram, M. S.; Fujii, R.; Mopper, K. Evaluation of Specific Ultraviolet Absorbance as an Indicator of the Chemical Composition and Reactivity of Dissolved Organic Carbon. Environ. Sci. Technol. 2003, 37, 4702– 4708, DOI: 10.1021/es030360xGoogle Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXotFCgtLY%253D&md5=69b76d997d8d1ecee868c741fe7582e0Evaluation of Specific Ultraviolet Absorbance as an Indicator of the Chemical Composition and Reactivity of Dissolved Organic CarbonWeishaar, James L.; Aiken, George R.; Bergamaschi, Brian A.; Fram, Miranda S.; Fujii, Roger; Mopper, KennethEnvironmental Science and Technology (2003), 37 (20), 4702-4708CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved org. carbon (DOC) concn. Our data indicate that SUVA, detd. at 254 nm, is strongly correlated with percent aromaticity as detd. by 13C NMR for 13 org. matter isolates obtained from a variety of aquatic environments. SUVA, therefore, is shown to be a useful parameter for estg. the dissolved arom. carbon content in aquatic systems. Expts. involving the reactivity of DOC with chlorine and tetramethylammonium hydroxide (TMAH), however, show a wide range of reactivity for samples with similar SUVA values. These results indicate that, while SUVA measurements are good predictors of general chem. characteristics of DOC, they do not provide information about the reactivity of DOC derived from different types of source materials. Sample pH, nitrate, and iron were found to influence SUVA measurements.
- 38Åkerblom, S.; Nilsson, M. B.; Skyllberg, U.; Björn, E.; Jonsson, S.; Ranneby, B.; Bishop, K. Formation and Mobilization of Methylmercury across Natural and Experimental Sulfur Deposition Gradients. Environ. Pollut. 2020, 263, 114398, DOI: 10.1016/j.envpol.2020.114398Google ScholarThere is no corresponding record for this reference.
- 39Mason, R. P.; Reinfelder, J. R.; Morel, F. M. M. Uptake, Toxicity, and Trophic Transfer of Mercury in a Coastal Diatom. Environ. Sci. Technol. 1996, 30, 1835– 1845, DOI: 10.1021/es950373dGoogle Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XisFansL4%253D&md5=5729dcd90feb7b4ee9bbe692faaa0cd4Uptake, Toxicity, and Trophic Transfer of Mercury in a Coastal DiatomMason, Robert P.; Reinfelder, John R.; Morel, Francois M. M.Environmental Science and Technology (1996), 30 (6), 1835-45CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)The studies of mercury speciation, toxicity, and phytoplankton uptake demonstrate that passive uptake of uncharged, lipophilic chloride complexes is the principal accumulation route of both methylmercury and inorg. mercury in phytoplankton. The predominance of methylmercury in fish, however, is a consequence of the greater trophic transfer efficiency of methyl- mercury than inorg. mercury. In particular, methylmercury in phytoplankton, which accumulates in the cell cytoplasm, is assimilated by zooplankton four times more efficiently than inorg. mercury, which is principally bound in phytoplankton membranes. On the basis of these results, the authors constructed a simple model of mercury accumulation in fish as a function of the overall octanol-water partition coeff. of methylmercury. The model can explain the variability of mercury concns. in fish within, but not among, different lake regions.
- 40Moye, H. A.; Miles, C. J.; Phlips, E. J.; Sargent, B.; Merritt, K. K. Kinetics and Uptake Mechanisms for Monomethylmercury between Freshwater Algae and Water. Environ. Sci. Technol. 2002, 36, 3550– 3555, DOI: 10.1021/es011421zGoogle Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XltFGis74%253D&md5=81849780f6e93b44a757517752726201Kinetics and Uptake Mechanisms for Monomethylmercury between Freshwater Algae and WaterMoye, H. Anson; Miles, Carl J.; Phlips, Edward J.; Sargent, Bethany; Merritt, Kristen K.Environmental Science and Technology (2002), 36 (16), 3550-3555CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Uptake kinetics of monomethylmercury chloride (MeHgCl) were measured for two species of green algae (Selenastrum capricornutum and Cosmarium botrytis), one blue-green algae (Schizothrix calcicola), and one diatom (Thalassiosira weissflogii), algal species that are commonly found in natural surface waters. Species differences were found with the two green algae giving the highest uptake rates, and one of them (Cosmarium) showing differences between cultures having widely different cell age (exponential vs. stationary), where increases in uptake rate for cells 30 days old were about 25 times greater than cells only 3 days old when wts. of cells were considered. Both Schizothrix and Thalassiosira exhibited nearly the same lower uptake rates, approx. 20 times lower than the two green algal species. Expts. with photosystem inhibitors, uncouplers, γ-radiation, light deprivation, and extended range uptake all point to an active transport mechanism for MeHgCl.
- 41Luengen, A. C.; Fisher, N. S.; Bergamaschi, B. A. Dissolved Organic Matter Reduces Algal Accumulation of Methylmercury. Environ. Toxicol. Chem. 2012, 31, 1712– 1719, DOI: 10.1002/etc.1885Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1GmtbvI&md5=db1bfccef37e6e81a87958b9eeb07bb6Dissolved organic matter reduces algal accumulation of methylmercuryLuengen, Allison C.; Fisher, Nicholas S.; Bergamaschi, Brian A.Environmental Toxicology and Chemistry (2012), 31 (8), 1712-1719CODEN: ETOCDK; ISSN:0730-7268. (Wiley-Blackwell)Dissolved org. matter (DOM) significantly decreased accumulation of methylmercury (MeHg) by the diatom Cyclotella meneghiniana in lab. expts. Live diatom cells accumulated 2 to 4 times more MeHg than dead cells, indicating that accumulation may be partially an energy-requiring process. Methylmercury enrichment in diatoms relative to ambient H2O was measured by a vol. concn. factor (VCF). Without added DOM, the max. VCF was 32 × 104, and the av. VCF (from 10 to 72 h) over all expts. was 12.6 × 104. At very low (1.5 mg L-1) added DOM, VCFs dropped by approx. half. At very high (20 mg L-1) added DOM, VCFs dropped 10-fold. Presumably, MeHg was bound to a variety of reduced S sites on the DOM, making it unavailable for uptake. Diatoms accumulated significantly more MeHg when exposed to transphilic DOM exts. than hydrophobic ones. However, algal lysate, a labile type of DOM created by resuspending a marine diatom in freshwater, behaved similarly to a refractory DOM isolate from San Francisco Bay. Addn. of 67 μM L-cysteine resulted in the largest drop in VCFs, to 0.28 × 104. Although the DOM compn. influenced the availability of MeHg to some extent, total DOM concn. was the most important factor in detg. algal bioaccumulation of MeHg.
- 42Zhang, K. Analysis of Non-Linear Inundation from Sea-Level Rise Using LIDAR Data: A Case Study for South Florida. Clim. Change 2011, 106, 537– 565, DOI: 10.1007/s10584-010-9987-2Google ScholarThere is no corresponding record for this reference.
- 43Park, J.; Stabenau, E.; Redwine, J.; Kotun, K. South Florida’s Encroachment of the Sea and Environmental Transformation over the 21st Century. J. Mar. Sci. Eng. 2017, 5, 31, DOI: 10.3390/jmse5030031Google ScholarThere is no corresponding record for this reference.
- 44Damseaux, F.; Kiszka, J. J.; Heithaus, M. R.; Scholl, G.; Eppe, G.; Thomé, J. P.; Lewis, J.; Hao, W.; Fontaine, M. C.; Das, K. Spatial Variation in the Accumulation of POPs and Mercury in Bottlenose Dolphins of the Lower Florida Keys and the Coastal Everglades (South Florida). Environ. Pollut. 2017, 220, 577– 587, DOI: 10.1016/j.envpol.2016.10.005Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1ygs7%252FI&md5=0bcc08ca521de180a9449f0ac9613daeSpatial variation in the accumulation of POPs and mercury in bottlenose dolphins of the Lower Florida Keys and the coastal Everglades (South Florida)Damseaux, France; Kiszka, Jeremy J.; Heithaus, Michael R.; Scholl, George; Eppe, Gauthier; Thome, Jean-Pierre; Lewis, Jennifer; Hao, Wensi; Fontaine, Michael C.; Das, KrishnaEnvironmental Pollution (Oxford, United Kingdom) (2017), 220 (Part_A), 577-587CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)The bottlenose dolphin (Tursiops truncatus) is an upper trophic level predator and the most common cetacean species found in nearshore waters of southern Florida, including the Lower Florida Keys (LFK) and the Florida Coastal Everglades (FCE). The objective of this study was to assess contamination levels of total mercury (T-Hg) in skin and persistent org. pollutants (PCBs, PBDEs, DDXs, HCHs, HCB, Σ PCDD/Fs and Σ DL-PCBs) in blubber samples of bottlenose dolphins from LFK (n = 27) and FCE (n = 24). PCBs were the major class of compds. found in bottlenose dolphin blubber and were higher in individuals from LFK (Σ 6 PCBs LFK males: 13,421 ± 7730 ng g-1 lipids, Σ 6 PCBs LFK females: 9683 ± 19,007 ng g-1 lipids) than from FCE (Σ 6 PCBs FCE males: 5638 ng g-1 ± 3627 lipids, Σ 6 PCBs FCE females: 1427 ± 908 ng g-1 lipids). These levels were lower than previously published data from the southeastern USA. The Σ DL-PCBs were the most prevalent pollutants of dioxin and dioxin like compds. (Σ DL-PCBs LFK: 739 ng g-1 lipids, Σ DL-PCBs FCE: 183 ng g-1 lipids) since PCDD/F concns. were low for both locations (mean 0.1 ng g-1 lipids for LFK and FCE dolphins). The toxicity equivalences of PCDD/Fs and DL-PCBs expressed as TEQ in LFK and FCE dolphins is mainly expressed by DL-PCBs (81% LFK - 65% FCE). T-Hg concns. in skin were significantly higher in FCE (FCE median 9314 ng g-1 dw) compared to LFK dolphins (LFK median 2941 ng g-1 dw). These concns. are the highest recorded in bottlenose dolphins in the southeastern USA, and may be explained, at least partially, by the biogeochem. of the Everglades and mangrove sedimentary habitats that create favorable conditions for the retention of mercury and make it available at high concns. for aquatic predators.
- 45Orem, W.; Gilmour, C.; Axelrad, D.; Krabbenhoft, D.; Scheidt, D.; Kalla, P.; McCormick, P.; Gabriel, M.; Aiken, G. Sulfur in the South Florida Ecosystem: Distribution, Sources, Biogeochemistry, Impacts, and Management for Restoration. Crit. Rev. Environ. Sci. Technol. 2011, 41, 249– 288, DOI: 10.1080/10643389.2010.531201Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXit1aqtLg%253D&md5=af643ff21f1100f16efe92527abbd800Sulfur in the South Florida Ecosystem: Distribution, Sources, Biogeochemistry, Impacts, and Management for RestorationOrem, William; Gilmour, Cynthia; Axelrad, Donald; Krabbenhoft, David; Scheidt, Daniel; Kalla, Peter; McCormick, Paul; Gabriel, Mark; Aiken, GeorgeCritical Reviews in Environmental Science and Technology (2011), 41 (Suppl. 1), 249-288CODEN: CRETEK; ISSN:1064-3389. (Taylor & Francis, Inc.)A review. Sulfur is broadly recognized as a water quality issue of significance for the freshwater Florida Everglades. Roughly 60% of the remnant Everglades has surface water sulfate concns. above 1 mg l-1, a restoration performance measure based on present sulfate levels in unenriched areas. Highly enriched marshes in the northern Everglades have av. sulfate levels of 60 mg l-1. Sulfate loading to the Everglades is principally a result of land and water management in South Florida. The highest concns. of sulfate (av. 60-70 mg l-1) in the ecosystem are in canal water in the Everglades Agricultural Area (EAA). Potential sulfur sources in the watershed are many, but geochem. data and a preliminary sulfur mass balance for the EAA are consistent with sulfur presently used in agricultural, and sulfur released by oxidn. of org. EAA soils (including legacy agricultural applications and natural sulfur) as the primary sources of sulfate enrichment in the EAA canals. Sulfate loading to the Everglades increases microbial sulfate redn. in soils, leading to more reducing conditions, greater cycling of nutrients in soils, prodn. of toxic sulfide, and enhanced methylmercury (MeHg) prodn. and bioaccumulation. Wetlands are zones of naturally high MeHg prodn., but the combination of high atm. mercury deposition rates in South Florida and elevated sulfate loading leads to increased MeHg prodn. and MeHg risk to Everglades wildlife and human consumers. Sulfate from the EAA drainage canals penetrates deep into the Everglades Water Conservation Areas, and may extend into Everglades National Park. Present plans to restore sheet flow and to deliver more water to the Everglades may increase overall sulfur loads to the ecosystem, and move sulfate-enriched water further south. However, water management practices that minimize soil drying and rewetting cycles can mitigate sulfate release during soil oxidn. A comprehensive Everglades restoration strategy should include redn. of sulfur loads as a goal because of the many detrimental impacts of sulfate on the ecosystem. Monitoring data show that the ecosystem response to changes in sulfate levels is rapid, and strategies for reducing sulfate loading may be effective in the near term. A multifaceted approach employing best management practices for sulfur in agriculture, agricultural practices that minimize soil oxidn., and changes to stormwater treatment areas that increase sulfate retention could help achieve reduced sulfate loads to the Everglades, with resulting benefits.
- 46Tate, M. T.; DeWild, J. F.; Ogorek, J. M.; Janssen, S. E.; Krabbenhoft, D. P.; Poulin, B. A.; Breitmeyer, S. E.; Aiken, G. R.; Orem, W. H.; Varonka, M. S. Chemical Characterization of Water, Sediments, and Fish from Water Conservation Areas and Canals of the Florida Everglades (USA), 2012 to 2019 ; U.S. Geological Survey Data Release, 2023, DOI: 10.5066/P976EGIX .Google ScholarThere is no corresponding record for this reference.
- 47Schall, T. N.; Ruiz, P. L.; Rutchey, K.; Irving, C.; McFee, D.; Caldecutt, K.; Maholland, B.; Bogina, V.; McCoy, C.; Shamblin, R. B.; Whelan, K. R. T. The Everglades National Park and Big Cypress National Preserve Vegetation Mapping Project: Interim Report-Shark River Slough/Long Pine Key (Region 1), Everglades National Park: Jacksonville District, Jacksonville, FL, 2020.Google ScholarThere is no corresponding record for this reference.
- 48Wilson, B. J.; Servais, S.; Mazzei, V.; Kominoski, J. S.; Hu, M.; Davis, S. E.; Gaiser, E.; Sklar, F.; Bauman, L.; Kelly, S.; Madden, C.; Richards, J.; Rudnick, D.; Stachelek, J.; Troxler, T. G. Salinity Pulses Interact with Seasonal Dry-down to Increase Ecosystem Carbon Loss in Marshes of the Florida Everglades. Ecol. Appl. 2018, 28, 2092– 2108, DOI: 10.1002/eap.1798Google ScholarThere is no corresponding record for this reference.
- 49Chambers, L. G.; Reddy, K. R.; Osborne, T. Z. Short-Term Response of Carbon Cycling to Salinity Pulses in a Freshwater Wetland. Soil Sci. Soc. Am. J. 2011, 75, 2000– 2007, DOI: 10.2136/sssaj2011.0026Google ScholarThere is no corresponding record for this reference.
- 50Servais, S.; Kominoski, J. S.; Charles, S. P.; Gaiser, E. E.; Mazzei, V.; Troxler, T. G.; Wilson, B. J. Saltwater Intrusion and Soil Carbon Loss: Testing Effects of Salinity and Phosphorus Loading on Microbial Functions in Experimental Freshwater Wetlands. Geoderma 2019, 337, 1291– 1300, DOI: 10.1016/j.geoderma.2018.11.013Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisVensb7K&md5=f34cbcc610f13ce1c1bb2b44c5238530Saltwater intrusion and soil carbon loss: Testing effects of salinity and phosphorus loading on microbial functions in experimental freshwater wetlandsServais, Shelby; Kominoski, John S.; Charles, Sean P.; Gaiser, Evelyn E.; Mazzei, Viviana; Troxler, Tiffany G.; Wilson, Benjamin J.Geoderma (2019), 337 (), 1291-1300CODEN: GEDMAB; ISSN:0016-7061. (Elsevier B.V.)Wetlands can store significant amts. of carbon (C), but climate and land-use change increasingly threaten wetland C storage potential. Carbon stored in soils of freshwater coastal wetlands is vulnerable to rapid saltwater intrusion assocd. with sea-level rise and reduced freshwater flows. In the Florida Everglades, unprecedented saltwater intrusion is simultaneously exposing wetlands soils to elevated salinity and phosphorus (P), in areas where C-rich peat soils are collapsing. To det. how elevated salinity and P interact to influence microbial contributions to C loss, we continuously added P (∼0.5 mg P d-1) and salinity (∼6.9 g salt d-1) to freshwater Cladium jamaicense (sawgrass) peat monoliths for two years. We measured changes in porewater chem., microbial extracellular enzyme activities, respiration rates, microbial biomass, root litter breakdown rates (k), and soil elemental compn. after short (57 d), intermediate- (392 d), and long-term (741 d) exposure. After 741 days, both β-1,4-glucosidase activity (P < 0.01) and β-1,4-cellobiosidase activity (P < 0.01) were reduced with added salinity in soils at 7.5-15 cm depth. Soil microbial biomass C decreased by 3.6× at 7.5-15 cm (P < 0.01) but not 0-7.5 cm depth (P > 0.05) with added salinity and was unaffected by added P. Soil respiration rates decreased after 372 d exposure to salinity (P = 0.05) and did not change with P exposure. Root litter k increased by 1.5× with added P and was unaffected by salinity exposure (P > 0.01). Soil %C decreased by approx. 1.3× after 741 days of salinity exposure compared to freshwater controls (P < 0.01). Elevated salinity and P accelerated wetland soil C loss primarily through leaching of DOC and increased root litter k. Our results indicate that freshwater wetland soils are sensitive to short- and long-term exposure to saltwater intrusion. Despite suppression of some soil microbial processes with added salinity, salt and P exposure appear to drive net C losses from coastal wetland soils.
- 51Gaiser, E.; Childers, D.; Travieso, R. Water Quality Data (Grab Samples) from the Shark River Slough, Everglades National Park (FCE LTER), Florida, USA, May 2001-Ongoing Ver 16; Environmental Data Initiative, 2022.Google ScholarThere is no corresponding record for this reference.
- 52Castaneda, E.; Rivera-Monroy, V. Abiotic Monitoring of Physical Characteristics in Porewaters and Surface Waters of Mangrove Forests from the Shark River Slough and Taylor Slough, Everglades National Park (FCE LTER), South Florida, USA, December 2000-Ongoing; Environmental Data Initiative, 2023.Google ScholarThere is no corresponding record for this reference.
- 53Aiken, G. R.; McKnight, D. M.; Thorn, K. A.; Thurman, E. M. Isolation of Hydrophilic Organic Acids from Water Using Nonionic Macroporous Resins. Org. Geochem. 1992, 18, 567– 573, DOI: 10.1016/0146-6380(92)90119-IGoogle Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XlvFyjtb4%253D&md5=06bb30fd942deb61a589d2d05ee876ddIsolation of hydrophilic organic acids from water using nonionic macroporous resinsAiken, G. R.; McKnight, D. M.; Thorn, K. A.; Thurman, E. M.Organic Geochemistry (1992), 18 (4), 567-73CODEN: ORGEDE; ISSN:0146-6380.A method for the isolation of hydrophilic org. acids from aquatic samples uses a 2-column array of XAD-8 and XAD-4 resins in series. The hydrophobic org. acids, composed primarily of aquatic fulvic acid, are removed from the sample on XAD-8, followed by the isolation of the more hydrophilic acids on XAD-4. For samples from a no. of diverse environments, more dissolved org. C was isolated on the XAD-8 resin (23-58%) than on the XAD-4 resin (7-25%). For these samples, the hydrophilic acids have lower C and H, higher O and N, and are lower in mol. wt. than the corresponding fulvic acids. The hydrophilic acids have lower arom. C and greater heteroaliph., ketone and carboxyl content than the fulvic acid.
- 54Pucher, M.; Wünsch, U.; Weigelhofer, G.; Murphy, K.; Hein, T.; Graeber, D. StaRdom: Versatile Software for Analyzing Spectroscopic Data of Dissolved Organic Matter in R. Water 2019, 11, 2366, DOI: 10.3390/w11112366Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXot1Oiurg%253D&md5=200d532b893b48e62574fdd993b99c19StaRdom: versatile software for analyzing spectroscopic data of dissolved organic matter in RPucher, Matthias; Wuensch, Urban; Weigelhofer, Gabriele; Murphy, Kathleen; Hein, Thomas; Graeber, DanielWater (Basel, Switzerland) (2019), 11 (11), 2366CODEN: WATEGH; ISSN:2073-4441. (MDPI AG)The roles of dissolved org. matter (DOM) in microbial processes and nutrient cycles depend on its compn., which requires detailed measurements and analyses. We introduce a package for R, called staRdom ("spectroscopic anal. of DOM in R"), to analyze DOM spectroscopic data (absorbance and fluorescence), which is key to deliver fast insight into DOM compn. of many samples. staRdom provides functions that standardize data prepn. and anal. of spectroscopic data and are inspired by practical work. The user can perform blank subtraction, diln. correction, Raman normalization, scatter removal and interpolation, and fluorescence normalization. The software performs parallel factor anal. (PARAFAC) of excitation-emission matrixes (EEMs), including peak picking of EEMs, and calcs. fluorescence indexes, absorbance indexes, and absorbance slope indexes from EEMs and absorbance spectra. A comparison between PARAFAC solns. by staRdom in R compared with drEEM in MATLAB showed nearly identical solns. for most datasets, although different convergence criteria are needed to obtain similar results and interpolation of missing data is important when working with staRdom. In conclusion, staRdom offers the opportunity for standardized multivariate decompn. of spectroscopic data without requiring software licensing fees and presuming only basic R knowledge.
- 55Helms, J. R.; Stubbins, A.; Ritchie, J. D.; Minor, E. C.; Kieber, D. J.; Mopper, K. Absorption Spectral Slopes and Slope Ratios as Indicators of Molecular Weight, Source, and Photobleaching of Chromophoric Dissolved Organic Matter. Limnol. Oceanogr. 2008, 53, 955– 969, DOI: 10.4319/lo.2008.53.3.0955Google ScholarThere is no corresponding record for this reference.
- 56Cook, B. A.; Janssen, S. E.; Tate, M. T.; Peterson, B. D.; Poulin, B. A. Mercury Methylation Assay Along a Salinity Gradient in Coastal Peat Soils in the Florida Everglades , U.S. Geological Survey Data Release, 2024, DOI: 10.5066/P139NMHU .Google ScholarThere is no corresponding record for this reference.
- 57NIST. NIST Standard Reference Database 46, Ver 4.0. Critical Stability Constants of Metal Complexes Database; National Institute of Standards and Technology, 1997.Google ScholarThere is no corresponding record for this reference.
- 58NIST. NIST Standard Reference Database 13, Ver 1. 0. NIST JANAF Thermochemical Tables; National Institute of Standards and Technology, 1985.Google ScholarThere is no corresponding record for this reference.
- 59Davison, W. The Solubility of Iron Sulphides in Synthetic and Natural Waters at Ambient Temperature. Aquat. Sci. 1991, 53, 309– 329, DOI: 10.1007/BF00877139Google ScholarThere is no corresponding record for this reference.
- 60Nordstrom, D. K.; Plummer, L. N.; Langmuir, D.; Busenberg, E.; May, H. M.; Jones, B. F.; Parkhurst, D. L. Revised Chemical Equilibrium Data for Major Water-Mineral Reactions and Their Limitations. In Chemical Modeling of Aqueous Systems II; ACS Symposium Series; American Chemical Society, 1990; Vol. 416, pp 398– 413.Google ScholarThere is no corresponding record for this reference.
- 61Drott, A.; Björn, E.; Bouchet, S.; Skyllberg, U. Refining Thermodynamic Constants for Mercury(II)-Sulfides in Equilibrium with Metacinnabar at Sub-Micromolar Aqueous Sulfide Concentrations. Environ. Sci. Technol. 2013, 47, 4197– 4203, DOI: 10.1021/es304824nGoogle Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjslSgt7o%253D&md5=5509af631efe40d228fbcc3988efa4b1Refining Thermodynamic Constants for Mercury(II)-Sulfides in Equilibrium with Metacinnabar at Sub-Micromolar Aqueous Sulfide ConcentrationsDrott, A.; Bjoern, E.; Bouchet, S.; Skyllberg, U.Environmental Science & Technology (2013), 47 (9), 4197-4203CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)An important issue in Hg biogeochem. is to explore the effect of aq. Hg(II) forms on bacterial uptake, and subsequent MeHg formation, under Fe(III) and sulfate reducing conditions. The success of this is dependent on relevant information on the thermodn. stability of Hg-sulfides. We detd. the soly. of a com. available HgS(s) phase, which was shown by x-ray diffraction to be a mixt. of 83% metacinnabar and 17% cinnabar. At aq. sulfide concns. 0.060-84μM, well below levels in previous studies, we report a soly. product (log Ksp ±SE) of -36.8±0.1 (HgS(s) + H+ = Hg2+ + HS-, I = 0, T =25°, pH 6-10, n =20) for metacinnabar. This value is 0.7 log units higher than previous ests. Complementing our data with data from Paquette and Helz (1997), we took advantage of a large data set (n =65) covering a wide range of aq. sulfide (0.06μM-140mM) and pH (1-11). On the basis of this, we report refined formation consts. (±SE) for the 3 aq. Hg(II)-sulfide species proposed by Schwarzenbach and Widmer (1963): Hg2+ + 2HS- = Hg(SH)20; log K =39.1±0.1, Hg2+ + 2HS- = HgS2H- + H+; log K =32.5±0.1, Hg2+ + 2HS- = HgS22- + 2H+; log K =23.2±0.1. Our refined log K values differ from previous ests. by 0.2-0.6 log units. At the low sulfide concns. in our study we could rule out the value of -10.0 for the reaction HgS(s) + H2O = HgOHSH(aq) as reported by Dyrssen and Wedborg (1991). By establishing a soly. product for the most environmentally relevant HgS(s) phase, metacinnabar, and extending the range of aq. sulfide concns. to sub-micromolar levels, relevant for soils, sediments, and waters, this study decreases the uncertainty in stability consts. for Hg-sulfides, thereby improving the basis for understanding the bioavailability and mobility of Hg(II) in the environment.
- 62Haitzer, M.; Aiken, G. R.; Ryan, J. N. Binding of Mercury(II) to Aquatic Humic Substances: Influence of PH and Source of Humic Substances. Environ. Sci. Technol. 2003, 37, 2436– 2441, DOI: 10.1021/es026291oGoogle Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjtlGlt70%253D&md5=8f50e9319e1214795a4d19dd843692dcBinding of Mercury(II) to Aquatic Humic Substances: Influence of pH and Source of Humic SubstancesHaitzer, Markus; Aiken, George R.; Ryan, Joseph N.Environmental Science and Technology (2003), 37 (11), 2436-2441CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Conditional distribution coeffs. (KDOM') for Hg(II) binding to seven dissolved org. matter (DOM) isolates were measured at environmentally relevant ratios of Hg(II) to DOM. The results show that KDOM' values for different types of samples (humic acids, fulvic acids, hydrophobic acids) isolated from diverse aquatic environments were all within 1 order of magnitude (1022.5 ±1.0-1023.5 ±1.0 L/kg), suggesting similar Hg(II) binding environments, presumably involving thiol groups, for the different isolates. KDOM' values decreased at low pHs (4) compared to values at pH 7, indicating proton competition for the strong Hg(II) binding sites. Chem. modeling of Hg(II)-DOM binding at different pH values was consistent with bidentate binding of Hg(II) by one thiol group (pKa = 10.3) and one other group (pKa = 6.3) in the DOM, which is in agreement with recent results on the structure of Hg(II)-DOM bonds obtained by extended x-ray absorption fine structure spectroscopy (EXAFS).
- 63Amirbahman, A.; Reid, A. L.; Haines, T. a.; Kahl, J. S.; Arnold, C. Association of Methylmercury with Dissolved Humic Acids. Environ. Sci. Technol. 2002, 36, 690– 695, DOI: 10.1021/es011044qGoogle Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XksVeltg%253D%253D&md5=d9f902a2569221142f9446c5ca70d0f4Association of Methylmercury with Dissolved Humic AcidsAmirbahman, Aria; Reid, Andrew L.; Haines, Terry A.; Kahl, J. Steven; Arnold, CedricEnvironmental Science and Technology (2002), 36 (4), 690-695CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Sorption of methylmercury (MeHg) to three different humic acids was studied as a function of pH and humic concn. The extent of sorption did not show a strong pH dependence within the pH range of 5-9. Below pH 5, a decrease in adsorption for all humic samples was obsd. The exptl. data for equil. sorption of MeHg were modeled using a discrete log K spectrum approach with three weakly acidic functional groups. The modeling parameters, which were the equil. binding consts. and the total binding capacities, represented the data well at all MeHg and humic concns. and pH values for a given humic sample. The estd. binding consts. for complexes of MeHg with humic acids were similar in magnitude to those of MeHg with thiol-contg. compds., suggesting that binding of MeHg involves the thiol groups of humic acids. The results show that only a small fraction of the reduced sulfur species in humic substances may take part in binding MeHg, but in most natural systems, this subfraction is considerably higher in concn. than ambient MeHg. The model developed here can be incorporated into speciation models to assess the bioavailability of MeHg in the presence of dissolved org. matter and competing ligands such as chloride and sulfide.
- 64Zeng, T.; Arnold, W. A.; Toner, B. M. Microscale Characterization of Sulfur Speciation in Lake Sediments. Environ. Sci. Technol. 2013, 47, 1287– 1296, DOI: 10.1021/es303914qGoogle Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslGguw%253D%253D&md5=3187923ac5c2a87bb1b522e63849cedfMicroscale Characterization of Sulfur Speciation in Lake SedimentsZeng, Teng; Arnold, William A.; Toner, Brandy M.Environmental Science & Technology (2013), 47 (3), 1287-1296CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Prairie pothole lakes (PPLs) are naturally sulfur-enriched wetlands in the glaciated prairie region of North America. High sulfate levels and dynamic hydrogeochem. in combination render PPLs a unique environment to explore the speciation of sedimentary S. The goals were to define and quantify the solid-phase S pools in PPL sediments and track seasonal dynamics of S speciation. A quant. x-ray microprobe method was developed based on S 1s x-ray absorption near-edge structure (XANES) spectroscopy and multienergy x-ray fluorescence mapping. Three S pools, pyritic S, reduced org. S (org. mono- and disulfide), and oxidized S (inorg. sulfate, ester sulfate, and sulfonate)-were identified in PPL sediments. No significant seasonal variation was evident for total S, but S speciation showed a seasonal response. During the spring-summer transition, the reduced org. S decreased from 55 to 15 mol%, with a concomitant rise in the oxidized S. During the summer-fall transition, the trend reversed and the reduced org. S grew to 75 mol% at the expense of the oxidized S. The pyritic S, on the other hand, remained relatively const. (∼22 mol%) over time. The seasonal changes in S speciation have strong potential to force the cycling of elements such as Hg in prairie wetlands.
- 65Bates, A. L.; Spiker, E. C.; Holmes, C. W. Speciation and Isotopic Composition of Sedimentary Sulfur in the Everglades, Florida, USA. Chem. Geol. 1998, 146, 155– 170, DOI: 10.1016/S0009-2541(98)00008-4Google ScholarThere is no corresponding record for this reference.
- 66Gilmour, C.; Krabbenhoft, D.; Orem, W.; Aiken, G. Appendix 2B-1%: Influence of Drying and Rewetting on Mercury and Sulfur Cycling in Everglades and STA Soils, 2004 Everglades consolidated report for the South Florida Water Management District: West Palm Beach, FL, 2004.Google ScholarThere is no corresponding record for this reference.
- 67Sleighter, R. L.; Chin, Y.-P.; Arnold, W. A.; Hatcher, P. G.; McCabe, A. J.; McAdams, B. C.; Wallace, G. C. Evidence of Incorporation of Abiotic S and N into Prairie Wetland Dissolved Organic Matter. Environ. Sci. Technol. Lett. 2014, 1, 345– 350, DOI: 10.1021/ez500229bGoogle Scholar67https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVSnsbnP&md5=4768a281e0723bbd225bb3001acc464bEvidence of Incorporation of Abiotic S and N into Prairie Wetland Dissolved Organic MatterSleighter, Rachel L.; Chin, Yu-Ping; Arnold, William A.; Hatcher, Patrick G.; McCabe, Andrew J.; McAdams, Brandon C.; Wallace, Grant C.Environmental Science & Technology Letters (2014), 1 (9), 345-350CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)Wetlands in the prairie pothole region of North America, which are among the most threatened ecosystems in the world, provide many services, ranging from waterfowl habitats to pesticide attenuation to carbon sequestration. The dissolved org. matter (DOM) that occurs within these wetlands, in surface waters and sediment porewaters, was examd. by mol.-level techniques. While it contains components typical of DOM from surface and subsurface waters, both sulfidic and nitrogenous org. mols. are significantly more abundant in this DOM pool than in other natural waters and show distribution patterns that exactly mimic the pattern obsd. for DOM that is comprised of only carbon, hydrogen, and oxygen. This indicates that incorporation of N and S within DOM is abiotic and nonspecific, likely involving hydrogen sulfide, polysulfides, and N-contg. nucleophiles.
- 68Chambers, L. G.; Davis, S. E.; Troxler, T.; Boyer, J. N.; Downey-Wall, A.; Scinto, L. J. Biogeochemical Effects of Simulated Sea Level Rise on Carbon Loss in an Everglades Mangrove Peat Soil. Hydrobiologia 2014, 726, 195– 211, DOI: 10.1007/s10750-013-1764-6Google ScholarThere is no corresponding record for this reference.
- 69Weston, N. B.; Vile, M. A.; Neubauer, S. C.; Velinsky, D. J. Accelerated Microbial Organic Matter Mineralization Following Salt-Water Intrusion into Tidal Freshwater Marsh Soils. Biogeochemistry 2011, 102, 135– 151, DOI: 10.1007/s10533-010-9427-4Google ScholarThere is no corresponding record for this reference.
- 70Weston, N. B.; Dixon, R. E.; Joye, S. B. Ramifications of Increased Salinity in Tidal Freshwater Sediments: Geochemistry and Microbial Pathways of Organic Matter Mineralization. J. Geophys. Res.: Biogeosci. 2006, 111, G01009, DOI: 10.1029/2005JG000071Google ScholarThere is no corresponding record for this reference.
- 71Sholkovitz, E. R. Flocculation of Dissolved Organic and Inorganic Matter during the Mixing of River Water and Seawater. Geochim. Cosmochim. Acta 1976, 40, 831– 845, DOI: 10.1016/0016-7037(76)90035-1Google ScholarThere is no corresponding record for this reference.
- 72Poulin, B. A.; Aiken, G. R.; Nagy, K. L.; Manceau, A.; Krabbenhoft, D. P.; Ryan, J. N. Mercury Transformation and Release Differs with Depth and Time in a Contaminated Riparian Soil during Simulated Flooding. Geochim. Cosmochim. Acta 2016, 176, 118– 138, DOI: 10.1016/j.gca.2015.12.024Google Scholar72https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpvVah&md5=76a66daa27c7b1a49bb022bde1c08f5eMercury transformation and release differs with depth and time in a contaminated riparian soil during simulated floodingPoulin, Brett A.; Aiken, George R.; Nagy, Kathryn L.; Manceau, Alain; Krabbenhoft, David P.; Ryan, Joseph N.Geochimica et Cosmochimica Acta (2016), 176 (), 118-138CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)Riparian soils are an important environment in the transport of mercury in rivers and wetlands, but the biogeochem. factors controlling mercury dynamics under transient redox conditions in these soils are not well understood. Mercury release and transformations in the Oa and underlying A horizons of a contaminated riparian soil were characterized in microcosms and an intact soil core under satn. conditions. Pore water dynamics of total mercury (HgT), methylmercury (MeHg), and dissolved gaseous mercury (Hg0(aq)) along with selected anions, major elements, and trace metals were characterized across redox transitions during 36 d of flooding in microcosms. Next, HgT dynamics were characterized over successive flooding (17 d), drying (28 d), and flooding (36 d) periods in the intact core. The obsd. mercury dynamics exhibit depth and temporal variability. At the onset of flooding in microcosms (1-3 d), mercury in the Oa horizon soil, present as a combination of ionic mercury (Hg(II)) bound to thiol groups in the soil org. matter (SOM) and nanoparticulate metacinnabar (β-HgS), was mobilized with org. matter of high mol. wt. Subsequently, under anoxic conditions, pore water HgT declined coincident with sulfate (3-11 d) and the proportion of nanoparticulate β-HgS in the Oa horizon soil increased slightly. Redox oscillations in the intact Oa horizon soil exhausted the mobile mercury pool assocd. with org. matter. In contrast, mercury in the A horizon soil, present predominantly as nanoparticulate β-HgS, was mobilized primarily as Hg0(aq) under strongly reducing conditions (5-18 d). The concn. of Hg0(aq) under dark reducing conditions correlated pos. with byproducts of dissimilatory metal redn. (.sum.(Fe,Mn)). Mercury dynamics in intact A horizon soil were consistent over two periods of flooding, indicating that nanoparticulate β-HgS was an accessible pool of mobile mercury over recurrent reducing conditions. The concn. of MeHg increased with flooding time in both the Oa and A horizon pore waters. Temporal changes in pore water constituents (iron, manganese, sulfate, inorg. carbon, headspace methane) all implicate microbial control of redox transitions. The mobilization of mercury in multiple forms, including HgT assocd. with org. matter, MeHg, and Hg0(aq), to pore waters during periodic soil flooding may contribute to mercury releases to adjacent surface waters and the recycling of the legacy mercury to the atm.
- 73Weber, F. A.; Voegelin, A.; Kretzschmar, R. Multi-Metal Contaminant Dynamics in Temporarily Flooded Soil under Sulfate Limitation. Geochim. Cosmochim. Acta 2009, 73, 5513– 5527, DOI: 10.1016/j.gca.2009.06.011Google Scholar73https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtVKjsrfP&md5=11aee3f2ce48531c15a75f2da40f7606Multi-metal contaminant dynamics in temporarily flooded soil under sulfate limitationWeber, Frank-Andreas; Voegelin, Andreas; Kretzschmar, RubenGeochimica et Cosmochimica Acta (2009), 73 (19), 5513-5527CODEN: GCACAK; ISSN:0016-7037. (Elsevier B.V.)The authors investigated the dynamics of copper, cadmium, lead, zinc, and nickel in a contaminated freshwater floodplain soil (gleyic fluvisol of Mulde River floodplain near Mulderstein, Germany under a realistic sulfate-limited flooding regime in microcosm expts. They found that most contaminants were initially mobilized by processes driven by the reductive dissoln. of Fe(III) and Mn(IV, III) (hydr)oxides. Subsequently, bacterial sulfate respiration resulted in the transformation of the entire available sulfate (2.3 mmol/kg) into chromous reducible sulfur (CRS). Cu K-edge X-ray absorption fine structure (XAFS) spectroscopy revealed that the soil Cu speciation changed from predominantly Cu(II) bound to soil org. matter (SOM) intermittently to 14% metallic Cu(0) and subsequently to 66% copper sulfide (CuxS). These CuxS ppts. accounted for most of the formed CRS, suggesting that CuxS was the dominant sulfide phase formed in the flooded soil. Sequential metal extns., in agreement with CRS results, suggested that easily mobilizable Cd was completely and Pb partially sequestered in sulfide ppts., controlling their dissolved concns. to below detection limits. In contrast, Zn and Ni (as well as Fe) were hardly sequestered into sulfide phases, so that micromolar levels of dissolved Zn and Ni (and millimolar dissolved Fe(II)) persisted in the reduced soil. The finding that Cu, Cd, and Pb were sequestered (but hardly any Zn, Ni, and Fe) is consistent with the thermodynamically predicted sulfide ladder following the increasing soly. products of the resp. metal sulfides. The observation that Cd and Pb were sequestered in sulfides despite the presence of remaining SOM-bound Cu(II) suggested that the kinetics of Cu(II) desorption, diffusion, and/or CuxS pptn. interfered with the sulfide ladder. It is concluded that the dynamics of multiple metal contaminants are intimately coupled under sulfate limitation by the relative thermodn. stabilities and formation kinetics of the resp. metal sulfides.
- 74D’Andrilli, J.; Junker, J. R.; Smith, H. J.; Scholl, E. A.; Foreman, C. M. DOM Composition Alters Ecosystem Function during Microbial Processing of Isolated Sources. Biogeochemistry 2019, 142, 281– 298, DOI: 10.1007/s10533-018-00534-5Google Scholar74https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXnvVygtLY%253D&md5=c34326e0f884988c113568d307c71b0aDOM composition alters ecosystem function during microbial processing of isolated sourcesD'Andrilli, Juliana; Junker, James R.; Smith, Heidi J.; Scholl, Eric A.; Foreman, Christine M.Biogeochemistry (2019), 142 (2), 281-298CODEN: BIOGEP; ISSN:0168-2563. (Springer)Dynamics of dissolved org. matter (DOM) in ecosystems are controlled by a suite of interacting phys., chem., and biol. factors. Growing recognition of the assocns. between microbial communities and metab. and intrinsic DOM characteristics, highlight the potential importance of microbe-DOM relationships to modulate the role and fate of DOM, yet these relationships are difficult to isolate because they often operate across confounding environmental gradients. In a controlled lab. incubation (44 days), we integrated DOM bulk and mol. characterization, bacterial abundances, microbial assemblage compn., nutrient concns., and cellular respiration to discern the structural dynamics of biol. processing among DOM sources from different allochthonous litters (grass, deciduous leaves, and evergreen needles). We identified two periods, consistent among DOM sources, where processing dynamics differed. Further, bulk fluorescent analyses showed shifts from low to high excitation and emission wavelengths, indicating the biol. prodn. of more complex/degraded materials over time. Mol. level analyses revealed similar temporal patterns among DOM sources in the prodn. and consumption of individual chem. components varying in reactivity and heteroat. content. Despite these similarities, total carbon (C) removed and carbon dioxide (CO2) accumulation differed by ∼ 20% and 25% among DOM sources. This range in C processing was apparently tied to key chem. properties of the DOM (e.g., initial DOM compn., N content, and labile nature) as well as differential reorganization of the microbial populations that decompd. the DOM. We conclude that the prodn., transformation, and consumption of C in aquatic ecosystems is strongly dependent on the source and character of DOM as well as the structure of the microbial communities present, both of which change as DOM is processed over time. It is crucial that stream C processing models represent this complexity accurately.
- 75Herzog, S. D.; Persson, P.; Kvashnina, K.; Kritzberg, E. S. Organic Iron Complexes Enhance Iron Transport Capacity along Estuarine Salinity Gradients of Baltic Estuaries. Biogeosciences 2020, 17, 331– 344, DOI: 10.5194/bg-17-331-2020Google Scholar75https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtlaqs7%252FF&md5=afdfea378e0fa13c9816dc62a17a896eOrganic iron complexes enhance iron transport capacity along estuarine salinity gradients of Baltic estuariesHerzog, Simon David; Persson, Per; Kvashnina, Kristina; Kritzberg, Emma SofiaBiogeosciences (2020), 17 (2), 331-344CODEN: BIOGGR; ISSN:1726-4189. (Copernicus Publications)Rivers discharge a notable amt. of dissolved Fe (1.5 x 109 mol yr-1) to coastal waters but are still not considered important sources of bioavailable Fe to open marine waters. The reason is that the vast majority of particular and dissolved riverine Fe is considered to be lost to the sediment due to aggregation during estuarine mixing. Recently, however, several studies demonstrated relatively high stability of riverine Fe to salinity-induced aggregation, and it has been proposed that organically complexed Fe (Fe-OM) can "survive" the salinity gradient, while Fe (oxy)hydroxides are more prone to aggregation and selectively removed. In this study, we directly identified, by X-ray absorption spectroscopy, the occurrence of these two Fe phases across eight boreal rivers draining into the Baltic Sea and confirmed a significant but variable contribution of Fe-OM in relation to Fe (oxy)hydroxides among river mouths. We further found that Fe-OM was more prevalent at high flow conditions in spring than at low flow conditions during autumn and that Fe-OM was more dominant upstream in a catchment than at the river mouth. The stability of Fe to increasing salinity, as assessed by artificial mixing expts., correlated well to the relative contribution of Fe-OM, confirming that org. complexes promote Fe transport capacity. This study suggests that boreal rivers may provide significant amts. of potentially bioavailable Fe beyond the estuary, due to org. matter complexes.
- 76Nagy, K. L.; Manceau, A.; Gasper, J. D.; Ryan, J. N.; Aiken, G. R. Metallothionein-like Multinuclear Clusters of Mercury(II) and Sulfur in Peat. Environ. Sci. Technol. 2011, 45, 7298– 7306, DOI: 10.1021/es201025vGoogle Scholar76https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXps1Oit7k%253D&md5=92e29669be9712d22568bfadfbc07c28Metallothionein-Like Multinuclear Clusters of Mercury(II) and Sulfur in PeatNagy, Kathryn L.; Manceau, Alain; Gasper, Jarrod D.; Ryan, Joseph N.; Aiken, George R.Environmental Science & Technology (2011), 45 (17), 7298-7306CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Strong Hg(II)-S (Hg-SR) bonds in natural org. matter, which influence Hg bioavailability, are difficult to characterize. We report evidence for 2 new Hg-SR structures using x-ray absorption spectroscopy in peats from the Florida Everglades with added Hg. The 1st, obsd. at a mole ratio of org. reduced S to Hg (Sred/Hg) between 220 and 1140, is a Hg4Sx type of cluster with each Hg atom bonded to 2 S atoms at 2.34 Å and one S at 2.53 Å, and all Hg atoms 4.12 Å apart. This model structure matches those of metal-thiolate clusters in metallothioneins, but not those of HgS minerals. The 2nd, with one S atom at 2.34 Å and ∼6 C atoms at 2.97 to 3.28 Å, occurred at Sred/Hg between 0.80 and 4.3 and suggests Hg binding to a thiolated arom. unit. The multinuclear Hg cluster indicates a strong binding environment to cysteinyl S that might impede methylation. Along with a linear Hg(SR)2 unit with Hg-S bond lengths of 2.34 Å at Sred/Hg of about 10-20, the new structures support a continuum in Hg-SR binding strength in natural org. matter.
- 77Marvin-DiPasquale, M.; Agee, J.; McGowan, C.; Oremland, R. S.; Thomas, M.; Krabbenhoft, D.; Gilmour, C. C. Methyl-Mercury Degradation Pathways: A Comparison among Three Mercury-Impacted Ecosystems. Environ. Sci. Technol. 2000, 34, 4908– 4916, DOI: 10.1021/es0013125Google Scholar77https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXnt1Kjsbo%253D&md5=21400d52af6589cde05ef778eafc47fdMethyl-Mercury Degradation Pathways: A Comparison among Three Mercury-Impacted EcosystemsMarvin-DiPasquale, Mark; Agee, Jennifer; McGowan, Chad; Oremland, Ronald S.; Thomas, Martha; Krabbenhoft, David; Gilmour, Cynthia C.Environmental Science and Technology (2000), 34 (23), 4908-4916CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)We examd. microbial methylmercury (MeHg) degrdn. in sediment of the Florida Everglades, Carson River (NV), and San Carlos Creek (CA), 3 freshwater environments that differ in the extent and type of mercury contamination and sediment biogeochem. Degrdn. rate const. (kdeg) values increased with total Hg (Hgt) contamination both among and within ecosystems. The highest kdeg's (2.8-5.8/day) were obsd. in San Carlos Creek, at acid mine drainage impacted sites immediately downstream of the former New Idria mercury mine, where Hgt was 4.5-21.3 ppm (dry wt.). A reductive degrdn. pathway (presumably mer-detoxification) dominated degrdn. at these sites, as indicated by the nearly exclusive prodn. of 14CH4 from 14C-MeHg, under both aerobic and anaerobic conditions. At the upstream control site, and in the less contaminated ecosystems (e.g. the Everglades), kdeg's were low (≤0.2/day) and oxidative demethylation (OD) dominated degrdn., as evident from 14CO2 prodn. kdeg increased with microbial CH4 prodn., org. content, and reduced S in the Carson River system and increased with decreasing pH in San Carlos Creek. OD assocd. CO2 prodn. increased with pore-water SO42- in Everglades samples but was not attributable to anaerobic methane oxidn., as has been previously proposed. This ecosystem comparison indicates that severely contaminated sediments tend to have microbial populations that actively degrade MeHg via mer-detoxification, whereas OD occurs in heavily contaminated sediments as well but dominates in those less contaminated.
- 78Cleckner, L. B.; Gilmour, C. C.; Hurley, J. P.; Krabbenhoft, D. P. Mercury Methylation in Periphyton of the Florida Everglades. Limnol Oceanogr 1999, 44, 1815– 1825, DOI: 10.4319/lo.1999.44.7.1815Google Scholar78https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnsVWisbo%253D&md5=a90be6e3b49133dd504edea42f59cfa5Mercury methylation in periphyton of the Florida EvergladesCleckner, Lisa B.; Gilmour, Cynthia C.; Hurley, James P.; Krabbenhoft, David P.Limnology and Oceanography (1999), 44 (7), 1815-1825CODEN: LIOCAH; ISSN:0024-3590. (American Society of Limnology and Oceanography)Trophic accumulation of mercury (Hg) in aquatic ecosystems is of global concern due to health effects assocd. with eating fish with elevated Hg levels. The methylated form of Hg bio-accumulates so it is important to understand how inorg. Hg is transformed to methylmercury in the environment. Here, a new site for Hg methylation, the periphyton communities that are prevalent in the Florida Everglades, is described. It is hypothesized that periphyton communities that support an active microbial sulfur cycle support Hg methylation. This new methylation site has implications for trophic transfer of methylmercury since periphyton can be the base of the food web in aquatic ecosystems.
- 79Qian, J.; Skyllberg, U.; Frech, W.; Bleam, W. F.; Bloom, P. R.; Petit, P. E. Bonding of Methyl Mercury to Reduced Sulfur Groups in Soil and Stream Organic Matter as Determined by X-Ray Absorption Spectroscopy and Binding Affinity Studies. Geochim. Cosmochim. Acta 2002, 66, 3873– 3885, DOI: 10.1016/S0016-7037(02)00974-2Google Scholar79https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XotlKisbk%253D&md5=98684179b2a63dd97efdcf2f38bd482bBonding of methyl mercury to reduced sulfur groups in soil and stream organic matter as determined by x-ray absorption spectroscopy and binding affinity studiesQian, Jin; Skyllberg, Ulf; Frech, Wolfgang; Bleam, William F.; Bloom, Paul R.; Petit, Pierre EmmanuelGeochimica et Cosmochimica Acta (2002), 66 (22), 3873-3885CODEN: GCACAK; ISSN:0016-7037. (Elsevier Science Inc.)We combined synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy and binding affinity studies to det. the coordination, geometry, and strength of Me mercury, CH3Hg (II), bonding in soil and stream org. matter. Samples of org. soil (OS), potentially sol. org. substances (PSOS) from the soil, and org. substances from a stream (SOS) draining the soil were taken along a short "hydrol. transect. "We detd. the sum of concns. of highly reduced org. S groups (designated Org-SRED), such as thiol (RSH), disulfane (RSSH), sulfide (RSR), and disulfide (RSSR), using sulfur K-edge XANES. Org-SRED varied between 27% and 64% of total S in our samples. Hg LIII-edge EXAFS anal. were detd. on samples added CH3Hg (II) to yield CH3Hg (II)/Org-SRED ratios in the range 0.01-1.62. At low ratios, Hg was assocd. to one C atom (the Me group) at an av. distance of 2.03 ± 0.02 A and to one S atom at an av. distance of 2.34 ± 0.03 A, in the first coordination shell. At calcd. CH3Hg(II)/Org-SRED ratios above 0.37 in OS, 0.32 in PSOS, and 0.24 in SOS, the org. S sites were satd. by CH3Hg+, and O (and/or N) atoms were found in the first coordination shell of Hg at an av. distance of 2.09 ± 0.01 A. Based on the assumption that RSH (and possibly RSSH) groups take part in the complexation of CH3Hg+, whereas RSSR and RSR groups do not, approx. 17% of total org. S consisted of RSH (+ RSSH) functionalities in the org. soil. Corresponding figures for samples PSOS and SOS were 14% and 9%, resp. Competitive complexation of CH3Hg+ by halide ions was used to det. the av. binding strength of native concns. of CH3Hg (II) in the OS sample. Using data for Org-SRED, calcd. surface complexation consts. were in the range from 1016.3 to 1016.7 for a model RSH site having an acidity const. of mercaptoacetic acid. These values compare favorably with identically defined stability consts. (log K1) for the binding of Me mercury to thiol groups in well-defined org. compds.
- 80Peterson, B. D.; Poulin, B. A.; Krabbenhoft, D. P.; Tate, M. T.; Baldwin, A. K.; Naymik, J.; Gastelecutto, N.; McMahon, K. D. Metabolically Diverse Microorganisms Mediate Methylmercury Formation under Nitrate-Reducing Conditions in a Dynamic Hydroelectric Reservoir. ISME J. 2023, 17 (10), 1705– 1718, DOI: 10.1038/s41396-023-01482-1Google ScholarThere is no corresponding record for this reference.
- 81Peterson, B. D.; McDaniel, E. A.; Schmidt, A. G.; Lepak, R. F.; Janssen, S. E.; Tran, P. Q.; Marick, R. A.; Ogorek, J. M.; Dewild, J. F.; Krabbenhoft, D. P.; McMahon, K. D. Mercury Methylation Genes Identified across Diverse Anaerobic Microbial Guilds in a Eutrophic Sulfate-Enriched Lake. Environ. Sci. Technol. 2020, 54, 15840– 15851, DOI: 10.1021/acs.est.0c05435Google Scholar81https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitlyrs7bI&md5=167e120eb1fe79ed5386c72d69b9d335Mercury methylation genes identified across diverse anaerobic microbial guilds in a eutrophic sulfate-enriched lakePeterson, Benjamin D.; McDaniel, Elizabeth A.; Schmidt, Anna G.; Lepak, Ryan F.; Janssen, Sarah E.; Tran, Patricia Q.; Marick, Robert A.; Ogorek, Jacob M.; DeWild, John F.; Krabbenhoft, David P.; McMahon, Katherine D.Environmental Science & Technology (2020), 54 (24), 15840-15851CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Mercury (Hg) methylation is a microbially mediated process that converts inorg. Hg into bioaccumulative, neurotoxic methylmercury (MeHg). The metabolic activity of methylating organisms is highly dependent on biogeochem. conditions, which subsequently influences MeHg prodn. However, our understanding of the ecophysiol. of methylators in natural ecosystems is still limited. Here, we identified potential locations of MeHg prodn. in the anoxic, sulfidic hypolimnion of a freshwater lake. At these sites, we used shotgun metagenomics to characterize microorganisms with the Hg-methylation gene hgcA. Putative methylators were dominated by hgcA sequences divergent from those in well-studied, confirmed methylators. Using genome-resolved metagenomics, we identified organisms with hgcA (hgcA+) within the Bacteroidetes and the recently described Kiritimatiellaeota phyla. We identified hgcA+ genomes derived from sulfate-reducing bacteria, but these accounted for only 22% of hgcA+ genome coverage. The most abundant hgcA+ genomes were from fermenters, accounting for over half of the hgcA gene coverage. Many of these organisms also mediate hydrolysis of polysaccharides, likely from cyanobacterial blooms. This work highlights the distribution of the Hg-methylation genes across microbial metabolic guilds and indicate that primary degrdn. of polysaccharides and fermn. may play an important but unrecognized role in MeHg prodn. in the anoxic hypolimnion of freshwater lakes.
- 82Jones, D. S.; Walker, G. M.; Johnson, N. W.; Mitchell, C. P. J.; Coleman Wasik, J. K.; Bailey, J. V. Molecular Evidence for Novel Mercury Methylating Microorganisms in Sulfate-Impacted Lakes. ISME J. 2019, 13, 1659– 1675, DOI: 10.1038/s41396-019-0376-1Google Scholar82https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVyrtbrJ&md5=2d385401e87ae623883b59d5dadcd729Molecular evidence for novel mercury methylating microorganisms in sulfate-impacted lakesJones, Daniel S.; Walker, Gabriel M.; Johnson, Nathan W.; Mitchell, Carl P. J.; Coleman Wasik, Jill K.; Bailey, Jake V.ISME Journal (2019), 13 (7), 1659-1675CODEN: IJSOCF; ISSN:1751-7362. (Nature Research)Methylmercury (MeHg) is a bioaccumulative neurotoxin that is produced by certain anaerobic microorganisms, but the abundance and importance of different methylating populations in the environment is not well understood. We combined mercury geochem., hgcA gene cloning, rRNA methods, and metagenomics to compare microbial communities assocd. with MeHg prodn. in two sulfate-impacted lakes on Minnesota's Mesabi Iron Range. The two lakes represent regional endmembers among sulfate-impacted sites in terms of their dissolved sulfide concns. and MeHg prodn. potential. rRNA amplicon sequencing indicates that sediments and anoxic bottom waters from both lakes contained diverse communities with multiple clades of sulfate reducing Deltaproteobacteria and Clostridia. In hgcA gene clone libraries, however, hgcA sequences were from taxa assocd. with methanogenesis and iron redn. in addn. to sulfate redn., and the most abundant clones were from unknown groups. We therefore applied metagenomics to identify the unknown populations in the lakes with the capability to methylate mercury, and reconstructed 27 genomic bins with hgcA. Some of the most abundant potential methylating populations were from phyla that are not typically assocd. with MeHg prodn., including a relative of the Aminicenantes (formerly candidate phylum OP8) and members of the Kiritimatiellaeota (PVC superphylum) and Spirochaetes that, together, were more than 50% of the potential methylators in some samples. These populations do not have genes for sulfate redn., and likely degrade org. compds. by fermn. or other anaerobic processes. Our results indicate that previously unrecognized populations with hgcAB are abundant and may be important for MeHg prodn. in some freshwater ecosystems.
- 83Chambers, L. G.; Steinmuller, H. E.; Breithaupt, J. L. Toward a Mechanistic Understanding of “Peat Collapse” and Its Potential Contribution to Coastal Wetland Loss. Ecology 2019, 100, e02720 DOI: 10.1002/ecy.2720Google ScholarThere is no corresponding record for this reference.
- 84McCarter, C. P. R.; Sebestyen, S. D.; Coleman Wasik, J. K.; Engstrom, D. R.; Kolka, R. K.; Jeremiason, J. D.; Swain, E. B.; Monson, B. A.; Branfireun, B. A.; Balogh, S. J.; Nater, E. A.; Eggert, S. L.; Ning, P.; Mitchell, C. P. J. Long-Term Experimental Manipulation of Atmospheric Sulfate Deposition to a Peatland: Response of Methylmercury and Related Solute Export in Streamwater. Environ. Sci. Technol. 2022, 56, 17615– 17625, DOI: 10.1021/acs.est.2c02621Google ScholarThere is no corresponding record for this reference.
- 85Mitchell, C. P. J.; Branfireun, B. A.; Kolka, R. K. Assessing Sulfate and Carbon Controls on Net Methylmercury Production in Peatlands: An in Situ Mesocosm Approach. Appl. Geochem. 2008, 23, 503– 518, DOI: 10.1016/j.apgeochem.2007.12.020Google Scholar85https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXjtVChsbo%253D&md5=9a06fc7e0957d5dc4c5b3eec9eba37e9Assessing sulfate and carbon controls on net methylmercury production in peatlands: An in situ mesocosm approachMitchell, Carl P. J.; Branfireun, Brian A.; Kolka, Randall K.Applied Geochemistry (2008), 23 (3), 503-518CODEN: APPGEY; ISSN:0883-2927. (Elsevier Ltd.)The transformation of atmospherically deposited inorg. Hg to the toxic, org. form methylmercury (MeHg) is of serious ecol. concern because MeHg accumulates in aquatic biota, including fish. Research has shown that the Hg methylation reaction is dependent on the availability of SO4 (as an electron acceptor) because SO4-reducing bacteria (SRB) mediate the biotic methylation of Hg. Much less research has investigated the possible org. C limitations to Hg methylation (i.e. from the perspective of the electron donor). Although peatlands are long-term stores of org. C, the C derived from peatland vegetation is of questionable microbial lability. This research investigated how both SO4 and org. C control net MeHg prodn. using a controlled factorial addn. design in 44 in situ peatland mesocosms. Two levels of SO4 addn. and energetic-equiv. addns. (i.e. same no. of electrons) of a no. of org. C sources were used including glucose, acetate, lactate, coniferous litter leachate, and deciduous litter leachate. This study supports previous research demonstrating the stimulation of MeHg prodn. from SO4 input alone (∼200 pg/L/day). None of the addns. of org. C alone resulted in significant MeHg prodn. The combined addn. of SO4 and some org. C sources resulted in considerably more MeHg prodn. (∼500 pg/L/day) than did the addn. of SO4 alone, demonstrating that the highest levels of MeHg prodn. can be expected only where fluxes of both SO4 and org. C are delivered concurrently. When compared to a no. of pore water samples taken from two nearby peatlands, MeHg concns. resulting from the combined addn. of SO4 and org. C in this study were similar to MeHg "hot spots" found near the upland-peatland interface. The formation of MeHg "hot spots" at the upland-peatland interface may be dependent on concurrent inputs of SO4 and org. C in runoff from the adjacent upland hillslopes.
- 86Chambers, L. G.; Guevara, R.; Boyer, J. N.; Troxler, T. G.; Davis, S. E. Effects of Salinity and Inundation on Microbial Community Structure and Function in a Mangrove Peat Soil. Wetlands 2016, 36, 361– 371, DOI: 10.1007/s13157-016-0745-8Google ScholarThere is no corresponding record for this reference.
- 87Ulus, Y.; Tsui, M. T.-K.; Sakar, A.; Nyarko, P.; Aitmbarek, N. B.; Ardón, M.; Chow, A. T. Declines of Methylmercury along a Salinity Gradient in a Low-Lying Coastal Wetland Ecosystem at South Carolina, USA. Chemosphere 2022, 308, 136310, DOI: 10.1016/j.chemosphere.2022.136310Google ScholarThere is no corresponding record for this reference.
Cited By
This article has not yet been cited by other publications.
Article Views
Altmetric
Citations
Article Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.
Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.
The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.
Recommended Articles
Abstract
Figure 1
Figure 1. Porewater (A) redox potential (Eh) values at 6 cm depth from water surface compared to standard hydrogen electrode and porewater concentrations of (B) total iron (Fe), (C) sulfate (SO42–), (D) total sulfide (S2–), and (E) DOC concentration, (F) DOM decadic absorbance at 254 nm (α254), (G) DOM specific ultraviolet absorbance at 254 nm (SUVA254), and (H) DOM spectral slope ratio (SR). In panel A, data points with no error bars represent values of a single replicate (n = 1) and data points with error bars represent the average values of experimental replicates (n = 2) and error bars represent the average deviation from the mean. ORP measurements for the 0.50 ppt treatment are not reported. In panels B–H, data points at time points t = 1, 2, 3, 10, 13, and 15 and 0, 6, and 20 days present average values of experimental duplicates (n = 2) and triplicates (n = 3), respectively, and error bars represent the average deviation from the mean. Outlier values in DOC concentration were removed (n ≤ 1 per salinity treatment above 80 mg C L–1) for clarity.
Figure 2
Figure 2. (A) Percentage of total 201Hg as porewater Me201Hg relative to the entire 201Hg pool and (B) percentage of all Hg species relative to the entire 201Hg pool (porewater and peat) vs incubation time from peat core experiments. Hashed bars represent porewater 201Hg species and solid bars represent peat 201Hg species. Yellow and orange bars represent Me201Hg and green and blue bars represent 201Hg(II). Data points present average values of experimental replicates (n = 2) and error bars represent the average deviation from the mean.
Figure 3
Figure 3. (A.) Porewater methylation efficiency presented as the percent of total porewater 201Hg as Me201Hg and distribution coefficients (log(Kd); L kg–1) of (B) 201Hg(II) and (C) Me201Hg as a function of incubation time. Data points present average values of experimental replicates (n = 2) and error bars represent the average deviation from the mean.
Figure 4
Figure 4. Spearman’s rank correlation matrices for porewaters from treatment salinities (A) 0.16, (B) 0.25, (C) 0.50, (D) 1.0, and (E) 6.0 ppt. Darker red boxes at the intersection between two parameters indicate a stronger positive correlation; darker blue boxes represent a stronger negative correlation. Boxes at intersections between two significantly statistically correlated parameters (Spearman’s rank, p < 0.05) are represented as an open box. Boxes at intersections between two insignificantly statistically correlated parameters (Spearman’s rank, p > 0.05) are represented by a box with a black X symbol. S2– concentration correlations are omitted from panel A due to S2– being below the detection limit in all but one core at 0.16 ppt.
Figure 5
Figure 5. Linear correlation between the distribution coefficient of Me201Hg (log(Kd); L kg–1) and the DOM absorbance at 254 nm (α254, cm–1) for the four highest salinity treatments. Statistical outliers for distribution coefficient of Me201Hg (log(Kd); L kg–1) (n = 4 at 0.25 ppt) were identified and removed from the regression.
References
This article references 87 other publications.
- 1UN Environment. Global Mercury Assessment 2018; UN Environment Programme, Chemicals and Health Branch Geneva: Switzerland, 2019.There is no corresponding record for this reference.
- 2Hsu-Kim, H.; Kucharzyk, K. H.; Zhang, T.; Deshusses, M. A. Mechanisms Regulating Mercury Bioavailability for Methylating Microorganisms in the Aquatic Environment: A Critical Review. Environ. Sci. Technol. 2013, 47, 2441– 2456, DOI: 10.1021/es304370g2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXitVKqu78%253D&md5=d8ee0c1dc6164c2b00390d3a6f18e18dMechanisms Regulating Mercury Bioavailability for Methylating Microorganisms in the Aquatic Environment: A Critical ReviewHsu-Kim, Heileen; Kucharzyk, Katarzyna H.; Zhang, Tong; Deshusses, Marc A.Environmental Science & Technology (2013), 47 (6), 2441-2456CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)A review is given. Hg is a potent neurotoxin for humans, particularly if the metal is in the form of methylmercury. Hg is widely distributed in aquatic ecosystems as a result of anthropogenic activities and natural earth processes. A 1st step toward bioaccumulation of MeHg in aquatic food webs is the methylation of inorg. forms of the metal, a process that is primarily mediated by anaerobic bacteria. We evaluate the current state of knowledge regarding the mechanisms regulating microbial Hg methylation, including the speciation of Hg in environments where methylation occurs and the processes that control Hg bioavailability to these organisms. MeHg prodn. rates are generally related to the presence and productivity of methylating bacteria and also the uptake of inorg. Hg to these microorganisms. Our understanding of the mechanisms behind methylation is limited due to fundamental questions related to the geochem. forms of Hg that persist in anoxic settings, the mode of uptake by methylating bacteria, and the biochem. pathway by which these microorganisms produce and degrade MeHg. In anoxic sediments and water, the geochem. forms of Hg (and subsequent bioavailability) are largely governed by reactions between Hg(II), inorg. sulfides, and natural org. matter. These interactions result in a mixt. of dissolved, nanoparticulate, and larger cryst. particles that cannot be adequately represented by conventional chem. equil. models for Hg bioavailability. We discuss recent advances in nanogeochem. and environmental microbiol. that can provide new tools and unique perspectives to help us solve the question of how microorganisms methylate Hg. An understanding of the factors that cause the prodn. and degrdn. of MeHg in the environment is ultimately needed to inform policy makers and develop long-term strategies for controlling Hg contamination.
- 3Bravo, A. G.; Cosio, C. Biotic Formation of Methylmercury: A Bio-Physico-Chemical Conundrum. Limnol. Oceanogr. 2020, 65, 1010– 1027, DOI: 10.1002/lno.113663https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhsF2jsbbO&md5=4675f727e8d286564851f04136326d14Biotic formation of methylmercury: A bio-physico-chemical conundrumBravo, Andrea G.; Cosio, ClaudiaLimnology and Oceanography (2020), 65 (5), 1010-1027CODEN: LIOCAH; ISSN:0024-3590. (John Wiley & Sons, Inc.)Mercury (Hg) is a natural and widespread trace metal, but is considered a priority pollutant, particularly its org. form methylmercury (MMHg), because of human's exposure to MMHg through fish consumption. Pioneering studies showed the methylation of divalent Hg (HgII) to MMHg to occur under oxygen-limited conditions and to depend on the activity of anaerobic microorganisms. Recent studies identified the hgcAB gene cluster in microorganisms with the capacity to methylate HgII and unveiled a much wider range of species and environmental conditions producing MMHg than previously expected. Here, we review the recent knowledge and approaches used to understand HgII-methylation, microbial biodiversity and activity involved in these processes, and we highlight the current limits for predicting MMHg concns. in the environment. The available data unveil the fact that HgII methylation is a bio-physico-chem. conundrum in which the efficiency of biol. HgII methylation appears to depend chiefly on HgII and nutrients availability, the abundance of electron acceptors such as sulfate or iron, the abundance and compn. of org. matter as well as the activity and structure of the microbial community. An increased knowledge of the relationship between microbial community compn., physico-chem. conditions, MMHg prodn., and demethylation is necessary to predict variability in MMHg concns. across environments.
- 4Wiener, J. G.; Krabbenhoft, D. P.; Heinz, G. H.; Scheuhammer, A. M. Ecotoxicology of Mercury. In Handbook of Ecotoxicology, 2nd ed.; Hoffman, D. J., Rattner, B. A., Burton, G. A., Cairns, J. C., Eds.; Lewis Publishers: Boca Raton, FL, 2003; pp 409– 463.There is no corresponding record for this reference.
- 5Mahaffey, K. R.; Clickner, R. P.; Jeffries, R. A. Adult Women’s Blood Mercury Concentrations Vary Regionally in the United States: Association with Patterns of Fish Consumption (NHANES 1999–2004). Environ. Health Perspect. 2009, 117, 47– 53, DOI: 10.1289/ehp.11674There is no corresponding record for this reference.
- 6Peterson, B. D.; Krabbenhoft, D. P.; McMahon, K. D.; Ogorek, J. M.; Tate, M. T.; Orem, W. H.; Poulin, B. A. Environmental Formation of Methylmercury Is Controlled by Synergy of Inorganic Mercury Bioavailability and Microbial Mercury-methylation Capacity. Environ. Microbiol. 2023, 25, 1409– 1423, DOI: 10.1111/1462-2920.16364There is no corresponding record for this reference.
- 7Black, F. J.; Poulin, B. A.; Flegal, A. R. Factors Controlling the Abiotic Photo-Degradation of Monomethylmercury in Surface Waters. Geochim. Cosmochim. Acta 2012, 84, 492– 507, DOI: 10.1016/j.gca.2012.01.0197https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XltFyqsbg%253D&md5=64db47969ddab5f72ce2e54cabab0ef5Factors controlling the abiotic photo-degradation of monomethylmercury in surface watersBlack, Frank J.; Poulin, Brett A.; Flegal, A. RussellGeochimica et Cosmochimica Acta (2012), 84 (), 492-507CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)Photo-decompn. is among the most important mechanisms responsible for degrading monomethylmercury (MMHg) in aquatic systems, but this process is not fully understood. We investigated the relative importance of different factors in controlling the rate of MMHg photo-decompn. in surface waters in expts. using DOM isolated from natural waters. We found no evidence of net abiotic prodn. of MMHg in any dark or light exposed treatments. The av. (mean ± s.d.) MMHg photo-decompn. rate const. for all light exposed samples using DOM concd. from three coastal wetlands was 0.0099 ± 0.0020 E-1/m2 (range of 0.006-0.015 E-1/m2) when expressed in photon flux from 330-700 nm. This was roughly 3-fold higher than the av. MMHg photo-decompn. rate const. in coastal seawater of 0.0032 ± 0.0010 E-1/m2. MMHg photo-degrdn. was highly wavelength dependent. The ratio of MMHg photo-decompn. rate consts., with respect to photon flux, was 400:37:1 for UVB:UVA:PAR. However, when integrated across the entire water column over which MMHg photo-demethylation occurs, PAR was responsible for photo-degrading more MMHg than UVB and UVA combined in the three wetland sites because of the more rapid attenuation of UV light with depth. MMHg half-lives in the wetlands were calcd. for the upper 250 cm where photo-degrdn. occurred, and ranged from 7.6 to 20 days under typical summer sunlight conditions at 37°N. Rates of MMHg photo-decompn. decreased with increasing salinity, and were 27% higher at a salinity of 5 than those at a salinity of 25. This difference could not be accounted for by changes in the complexation of MMHg by DOM and chloride. Differences in MMHg photo-degrdn. rate consts. of up to 18% were measured between treatments using DOM concd. from three different wetlands. Surprisingly, increasing DOM concn. from 1.5 to 11.3 mg OC L-1 had only a small (6%) effect on MMHg photo-decompn., which was much smaller than the 34% decrease predicted due to the attenuation of light at the higher DOM levels. This suggests that DOM plays an important role in MMHg photo-decompn. apart from mediating light levels and MMHg complexation. Expts. employing various scavengers implied that singlet oxygen and hydroxyl radicals were not involved in the photo-degrdn. of MMHg in the natural waters used. Varying concns. of Fe, Cu, and Mn had only small (≤11%) effects on rates of MMHg photo-decompn., and relatively high rates were measured in high purity water with no trace metals or DOM. These results demonstrate that MMHg photo-decompn. can occur via pathways not involving Fe, the photo-Fenton reaction, nitrate photolysis, or thiol complexation. Taken with previous studies, multiple reaction pathways appear to exist, and their importance varies as a function of water chem. and light wavelength.
- 8Blanchfield, P. J.; Rudd, J. W. M.; Hrenchuk, L. E.; Amyot, M.; Babiarz, C. L.; Beaty, K. G.; Bodaly, R. A. D.; Branfireun, B. A.; Gilmour, C. C.; Graydon, J. A.; Hall, B. D.; Harris, R. C.; Heyes, A.; Hintelmann, H.; Hurley, J. P.; Kelly, C. A.; Krabbenhoft, D. P.; Lindberg, S. E.; Mason, R. P.; Paterson, M. J.; Podemski, C. L.; Sandilands, K. A.; Southworth, G. R.; St Louis, V. L.; Tate, L. S.; Tate, M. T. Experimental Evidence for Recovery of Mercury-Contaminated Fish Populations. Nature 2022, 601, 74– 78, DOI: 10.1038/s41586-021-04222-78https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislGntbrJ&md5=6e9882bca58c8b9d134343d0a61e7f5eExperimental evidence for recovery of mercury-contaminated fish populationsBlanchfield, Paul J.; Rudd, John W. M.; Hrenchuk, Lee E.; Amyot, Marc; Babiarz, Christopher L.; Beaty, Ken G.; Bodaly, R. A. Drew; Branfireun, Brian A.; Gilmour, Cynthia C.; Graydon, Jennifer A.; Hall, Britt D.; Harris, Reed C.; Heyes, Andrew; Hintelmann, Holger; Hurley, James P.; Kelly, Carol A.; Krabbenhoft, David P.; Lindberg, Steve E.; Mason, Robert P.; Paterson, Michael J.; Podemski, Cheryl L.; Sandilands, Ken A.; Southworth, George R.; St Louis, Vincent L.; Tate, Lori S.; Tate, Michael T.Nature (London, United Kingdom) (2022), 601 (7891), 74-78CODEN: NATUAS; ISSN:1476-4687. (Nature Portfolio)Anthropogenic releases of mercury (Hg)1-3 are a human health issue4 because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorg. Hg in aquatic ecosystems, bioaccumulates to high concns. in fish consumed by humans5,6. Predicting the efficacy of Hg pollution controls on fish MeHg concns. is complex because many factors influence the prodn. and bioaccumulation of MeHg7-9. Here we conducted a 15-yr whole-ecosystem, single-factor expt. to det. the magnitude and timing of redns. in fish MeHg concns. following redns. in Hg addns. to a boreal lake and its watershed. During the seven-year addn. phase, we applied enriched Hg isotopes to increase local Hg wet deposition rates fivefold. The Hg isotopes became increasingly incorporated into the food web as MeHg, predominantly from addns. to the lake because most of those in the watershed remained there. Thereafter, isotopic addns. were stopped, resulting in an approx. 100% redn. in Hg loading to the lake. The concn. of labeled MeHg quickly decreased by up to 91% in lower trophic level organisms, initiating rapid decreases of 38-76% of MeHg concn. in large-bodied fish populations in eight years. Although Hg loading from watersheds may not decline in step with lowering deposition rates, this expt. clearly demonstrates that any redn. in Hg loadings to lakes, whether from direct deposition or runoff, will have immediate benefits to fish consumers.
- 9Bergamaschi, B. A.; Krabbenhoft, D. P.; Aiken, G. R.; Patino, E.; Rumbold, D. G.; Orem, W. H. Tidally Driven Export of Dissolved Organic Carbon, Total Mercury, and Methylmercury from a Mangrove-Dominated Estuary. Environ. Sci. Technol. 2012, 46, 1371– 1378, DOI: 10.1021/es2029137There is no corresponding record for this reference.
- 10Gilmour, C. C.; Riedel, G. S.; Ederington, M. C.; Bell, J. T.; Gill, G.; Stordal, M.; Stordal, M. C. Methylmercury Concentrations and Production Rates across a Trophic Gradient in the Northern Everglades. Biogeochemistry 1998, 40, 327– 345, DOI: 10.1023/A:100597270861610https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXitlaku7g%253D&md5=9d124a2461c447e9f99d3e15da2fede8Methylmercury concentrations and production rates across a trophic gradient in the northern EvergladesGilmour, Cynthia C.; Riedel, G. S.; Ederington, M. C.; Bell, J. T.; Benoit, J. M.; Gill, G. A.; Stordal, M. C.Biogeochemistry (1998), 40 (2-3), 327-345CODEN: BIOGEP; ISSN:0168-2563. (Kluwer Academic Publishers)Methylmercury (MeHg) concns. and prodn. rates were examd. along with sulfur biogeochem. in Everglades sediments in Mar., July and Dec., 1995, as part of a large, multi-investigator study, the Aquatic Cycling of Mercury in the Everglades (ACME) project. The sites examd. constitute a trophic gradient, generated from agricultural runoff, across the Everglades Nutrient Removal (ENR) Area, which is a re-constructed wetland, and Water Conservation Areas (WCA) 2A, 2B and 3 in the northern Everglades. MeHg concns. and %MeHg (MeHg as a percent of total Hg) were lowest in the more eutrophic areas and highest in the more pristine areas in the south. MeHg concns. ranged from <0.1 ng gdwt-1 sediment in the ENR to 5 ng gdwt-1 in WCA3 sediments; and MeHg constituted <0.2% of total Hg (Hgτ) in ENR, but up to about 2% in two sites in WCA2B and WCA3. Methylation rates in surficial sediments, estd. using tracer-level injections of 203Hg(II) into intact sediment cores, ranged from 0 to 0.12 day-1, or about 1 to 10 ng g-1 d-1 when the per day values are multiplied by the ambient total Hg concn. Methylation was generally maximal at or within centimeters of the sediment surface, and was never obsd. in water overlying cores. The spatial pattern of MeHg prodn. generally matched that of MeHg concn. The coincident distributions of MeHg and its prodn. suggest that in situ prodn. controls concn., and that MeHg concn. can be used as an analog for MeHg prodn. In addn., the spatial pattern of MeHg in Everglades sediments matches that in biota, suggesting that MeHg bioaccumulation may be predominantly a function of the de novo methylation rate in surficial sediments. Sulfate concns. in surficial pore waters (up to 400 μm), microbial sulfate-redn. rates (up to 800 nm cc-1 day-1) and resultant pore water sulfide concns. (up to 300 μm) at the eutrophic northern sites were all high relative to most freshwater systems. All declined to the south, and sulfate concns. in WCA2B and in central WCA3 resembled those in oligotrophic lakes (50-100 μm). MeHg concn. and prodn. were inversely related to sulfate redn. rate and pore water sulfide. Control of MeHg prodn. in the northern Everglades appears to mimic that in an estuary, where sulfate concns. are high and where sulfide produced by microbial sulfate redn. inhibits MeHg prodn.
- 11Orem, W. H.; Fitz, C.; Krabbenhoft, D. P.; Poulin, B. A.; Varonka, M. S.; Aiken, G. R. Ecosystem-Scale Modeling and Field Observations of Sulfate and Methylmercury Distributions in the Florida Everglades: Responses to Reductions in Sulfate Loading. Aquat. Geochem. 2020, 26, 191– 220, DOI: 10.1007/s10498-020-09368-wThere is no corresponding record for this reference.
- 12Hurley, J. P.; Krabbenhoft, D. P.; Cleckner, L. B.; Olson, M. L.; Aiken, G. R.; Rawlik, P. S. System Controls on the Aqueous Distribution of Mercury in the Northern Florida Everglades. Biogeochemistry 1998, 40, 293– 310, DOI: 10.1023/A:1005928927272There is no corresponding record for this reference.
- 13Cleckner, L. B.; Garrison, P. J.; Hurley, J. P.; Olson, M. L.; Krabbenhoft, D. P. Trophic Transfer of Methyl Mercury in the Northern Florida Everglades. Biogeochemistry 1998, 40, 347– 361, DOI: 10.1023/A:100591810177313https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXitlaku7k%253D&md5=dd1e4210055504b3a63fa040728e83fbTrophic transfer of methyl mercury in the northern Florida EvergladesCleckner, Lisa B.; Garrison, Paul J.; Hurley, James P.; Olson, Mark L.; Krabbenhoft, David P.Biogeochemistry (1998), 40 (2-3), 347-361CODEN: BIOGEP; ISSN:0168-2563. (Kluwer Academic Publishers)There are spatial differences in MeHg concns. in biota in Water Conservation Areas 2 and 3 in the Everglades, with higher concns. generally in the southern areas. Fish and hemipterans had the most MeHg on a wet wt. basis, with levels exceeding 30 ng/g. The magnitude of MeHg accumulation in biota varies seasonally and does not always appear to be assocd. with changes in water column concn. This is exemplified by periphyton, the base of the foodweb in the Everglades, at a high nutrient sampling site. Although limited in scope, MeHg concns. presented for biota provide insight into beginning to understand the dynamic nature of Hg transfer in the Everglades foodweb on a spatial and temporal basis.
- 14Dittmar, T.; Hertkorn, N.; Kattner, G.; Lara, R. J. Mangroves, a Major Source of Dissolved Organic Carbon to the Oceans. Global Biogeochem. Cycles 2006, 20, 2570, DOI: 10.1029/2005GB002570There is no corresponding record for this reference.
- 15Rumbold, D. G.; Lange, T. R.; Richard, D.; DelPizzo, G.; Hass, N. Mercury Biomagnification through Food Webs along a Salinity Gradient Down-Estuary from a Biological Hotspot. Estuar. Coast Shelf Sci. 2018, 200, 116– 125, DOI: 10.1016/j.ecss.2017.10.018There is no corresponding record for this reference.
- 16Buchanan, M. K.; Kulp, S.; Strauss, B. Resilience of U.S. Coastal Wetlands to Accelerating Sea Level Rise. Environ. Res. Commun. 2022, 4, 061001, DOI: 10.1088/2515-7620/ac6eefThere is no corresponding record for this reference.
- 17Zhao, X.; Rivera-Monroy, V. H.; Wang, H.; Xue, Z. G.; Tsai, C.-F.; Willson, C. S.; Castañeda-Moya, E.; Twilley, R. R. Modeling Soil Porewater Salinity in Mangrove Forests (Everglades, Florida, USA) Impacted by Hydrological Restoration and a Warming Climate. Ecol. Model. 2020, 436, 109292, DOI: 10.1016/j.ecolmodel.2020.109292There is no corresponding record for this reference.
- 18Lagomasino, D.; Fatoyinbo, T.; Castañeda-Moya, E.; Cook, B. D.; Montesano, P. M.; Neigh, C. S. R.; Corp, L. A.; Ott, L. E.; Chavez, S.; Morton, D. C. Storm Surge and Ponding Explain Mangrove Dieback in Southwest Florida Following Hurricane Irma. Nat. Commun. 2021, 12, 4003, DOI: 10.1038/s41467-021-24253-yThere is no corresponding record for this reference.
- 19Parks, J. M.; Johs, A.; Podar, M.; Bridou, R.; Hurt, R. A.; Smith, S. D.; Tomanicek, S. J.; Qian, Y.; Brown, S. D.; Brandt, C. C.; Palumbo, A. V.; Smith, J. C.; Wall, J. D.; Elias, D. A.; Liang, L. The Genetic Basis for Bacterial Mercury Methylation. Science 2013, 339, 1332– 1335, DOI: 10.1126/science.123066719https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjvVaqtL8%253D&md5=67d2812c64b4f2b024bd58380b486787The genetic basis for bacterial mercury methylationParks, Jerry M.; Johs, Alexander; Podar, Mircea; Bridou, Romain; Hurt, Richard A., Jr.; Smith, Steven D.; Tomanicek, Stephen J.; Qian, Yun; Brown, Steven D.; Brandt, Craig C.; Palumbo, Anthony V.; Smith, Jeremy C.; Wall, Judy D.; Elias, Dwayne A.; Liang, LiyuanScience (Washington, DC, United States) (2013), 339 (6125), 1332-1335CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Methylmercury is a potent neurotoxin produced in natural environments from inorg. mercury by anaerobic bacteria. However, until now the genes and proteins involved have remained unidentified. Here, we report a two-gene cluster, hgcA and hgcB, required for mercury methylation by Desulfovibrio desulfuricans ND132 and Geobacter sulfurreducens PCA. In either bacterium, deletion of hgcA, hgcB, or both genes abolishes mercury methylation. The genes encode a putative corrinoid protein, HgcA, and a 2[4Fe-4S] ferredoxin, HgcB, consistent with roles as a Me carrier and an electron donor required for corrinoid cofactor redn., resp. Among bacteria and archaea with sequenced genomes, gene orthologs are present in confirmed methylators but absent in nonmethylators, suggesting a common mercury methylation pathway in all methylating bacteria and archaea sequenced to date.
- 20Poulin, B. A.; Ryan, J. N.; Tate, M. T.; Krabbenhoft, D. P.; Hines, M. E.; Barkay, T.; Schaefer, J.; Aiken, G. R. Geochemical Factors Controlling Dissolved Elemental Mercury and Methylmercury Formation in Alaskan Wetlands of Varying Trophic Status. Environ. Sci. Technol. 2019, 53, 6203– 6213, DOI: 10.1021/acs.est.8b0604120https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXpsVejsLc%253D&md5=dcda1090684274c8891de727fe13394aGeochemical Factors Controlling Dissolved Elemental Mercury and Methylmercury Formation in Alaskan Wetlands of Varying Trophic StatusPoulin, Brett A.; Ryan, Joseph N.; Tate, Michael T.; Krabbenhoft, David P.; Hines, Mark E.; Barkay, Tamar; Schaefer, Jeffra; Aiken, George R.Environmental Science & Technology (2019), 53 (11), 6203-6213CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)The transformations of aq. inorg. divalent Hg (Hg(II)i) to volatile dissolved gaseous Hg (Hg(aq)) and toxic methylmercury (MeHg) govern Hg bioavailability and fate in northern ecosystems. This study quantified concns. of aq. Hg species (Hg(II)i, Hg(aq), MeHg) and relevant geochem. constituents in pore waters of 8 Alaskan wetlands that differ in trophic status (i.e., bog-to-fen gradient) to gain insight on processes controlling dark Hg(II)i redn. and Hg(II)i methylation. Regardless of wetland trophic status, pos. correlations were obsd. between pore water Hg(II)i and dissolved org. C (DOC) concns. The concn. ratio of Hg(aq) to Hg(II)i exhibited an inverse relation to Hg(II)i concn. A ubiquitous pathway for Hg(aq) formation was not identified based on geochem. data, but we surmise that dissolved org. matter (DOM) influences Hg retention in wetland pore waters by complexing Hg(II)i and decreasing the concn. of volatile Hg(aq) relative to Hg(II)i. There was no evidence of Hg(aq) abundance directly limiting Hg methylation. The concn. of MeHg relative to Hg(II)i was greatest in wetlands of intermediate trophic status, and geochem. data suggest Hg methylation pathways vary between wetlands. The insights on geochem. factors influencing aq. Hg speciation should be considered in context of the long-term fate of Hg in northern wetlands.
- 21St Louis, V. L.; Rudd, J. W. M.; Kelly, C. A.; Beaty, K. G.; Flett, R. J.; Roulet, N. T. Production and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of Wetlands. Environ. Sci. Technol. 1996, 30, 2719– 2729, DOI: 10.1021/es950856h21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XksFGrsb0%253D&md5=6235494066b537ab8db4243105509b5dProduction and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of WetlandsSt. Louis, Vincent L.; Rudd, John W. M.; Kelly, Carol A.; Beaty, Ken G.; Flett, Robert J.; Roulet, Nigel T.Environmental Science and Technology (1996), 30 (9), 2719-2729CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Four terrestrial boreal forest catchments contg. different types of wetlands were studied to det. their strength as sources or sinks of methylmercury (MeHg) and total mercury (THg) to downstream ecosystems and to det. if patterns seen in one year were consistent over several years. All catchments were sinks for THg. The wetland type, percentage wetland area (0-25%), or annual water yield did not appear to have a consistent effect on the magnitude of this retention. Wetland areas of the catchments were always net sources of MeHg. Unlike for THg, there were large and consistent differences in the source strength among wetland types for MeHg. These differences appeared to be related to differences in the internal hydrol. of the wetlands. All types of wetlands were greater sources of MeHg during years of high water yield, but even during years of low flow, all wetland types were sources of MeHg. Thus, we conclude that wetlands are important sites of MeHg prodn. in boreal ecosystems on the long term. Upland areas of catchments were consistently sinks for MeHg, and so whole catchment sink/source values were strongly affected by the percentage of wetland areas within a catchment. Mass balance ests. of MeHg input from wetland areas to a lake indicate that the annual input of MeHg from wetlands is larger than the annual uptake of Hg by fish and is similar to the amt. of MeHg produced in the lake. Because of the predictable patterns between terrestrial catchments in their strength as sources or sinks of MeHg, it is possible to model inputs of MeHg from lake catchments with knowledge of the percentage wetland area in a catchment, the type of wetland contained in a catchment, and the annual water yield of a catchment.
- 22Mitchell, C. P. J.; Branfireun, B. A.; Kolka, R. K. Spatial Characteristics of Net Methylmercury Production Hot Spots in Peatlands. Environ. Sci. Technol. 2008, 42, 1010– 1016, DOI: 10.1021/es070498622https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXivF2nsw%253D%253D&md5=db8ddb47cbb9b424dba1b861ae975f40Spatial Characteristics of Net Methylmercury Production Hot Spots in PeatlandsMitchell, Carl P. J.; Branfireun, Brian A.; Kolka, Randall K.Environmental Science & Technology (2008), 42 (4), 1010-1016CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Many wetlands are sources of methylmercury (MeHg) to surface waters, yet little information exists about the distribution of MeHg within wetlands. Total mercury (THg) and MeHg in peat pore waters were studied in four peatlands in spring, summer, and fall 2005. Marked spatial variability in the distribution of MeHg, and %MeHg as a proxy for net MeHg prodn., was obsd., with highest values occurring in discrete zones. We denote these zones MeHg hot spots, defined as an area where the pore water %MeHg exceeded the 90th percentile of the data set (n = 463) or >22% of THg as MeHg. MeHg hot spots occurred near the interface between peatland and the upland watershed with few exceptions. The %MeHg in pore water was significantly less in peatland interiors compared to upland-peatland interface zones, with the significance of these differences related to the delineation of the boundary between the two areas. Although further research is necessary, our data suggest that the occurrence of MeHg hot spots is related to the transport of solutes in upland runoff to the peatland perimeter and not to the accumulation of MeHg in this zone as a result of transport from either the peatland interior or the surrounding upland watershed. These findings augment the understanding of peatland MeHg prodn. in upland-peatland watersheds, provide guidance for more accurate quantification of MeHg pool sizes in the landscape, and a spatial framework for the further study of mercury methylation processes in peatlands.
- 23Janssen, S. E.; Tate, M. T.; Poulin, B. A.; Krabbenhoft, D. P.; DeWild, J. F.; Ogorek, J. M.; Varonka, M. S.; Orem, W. H.; Kline, J. L. Decadal Trends of Mercury Cycling and Bioaccumulation within Everglades National Park. Sci. Total Environ. 2022, 838, 156031, DOI: 10.1016/j.scitotenv.2022.15603123https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsFGqsLvM&md5=2dbae6214a64c8c838b8fead149144a8Decadal trends of mercury cycling and bioaccumulation within Everglades National ParkJanssen, Sarah E.; Tate, Michael T.; Poulin, Brett A.; Krabbenhoft, David P.; DeWild, John F.; Ogorek, Jacob M.; Varonka, Matthew S.; Orem, William H.; Kline, Jeffrey L.Science of the Total Environment (2022), 838 (Part_1), 156031CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)Mercury (Hg) contamination has been a persistent concern in the Florida Everglades for over three decades due to elevated atm. deposition and the system's propensity for methylation and rapid bioaccumulation. Given declines in atm. Hg concns. in the conterminous United States and efforts to mitigate nutrient release to the greater Everglades ecosystem, it was vital to assess how Hg dynamics responded on temporal and spatial scales. This study used a multimedia approach (water and biota) to examine Hg and methylmercury (MeHg) dynamics across a 76-site network within the southernmost portion of the region, Everglades National Park (ENP), from 2008 to 2018. Hg concns. across matrixes showed that air, water, and biota from the system were inextricably linked. Temporal patterns across matrixes were driven primarily by hydrol. and climatic changes in the park and no evidence of a decline in atm. Hg deposition from 2008 to 2018 was obsd., unlike other regions of the United States. In the Shark River Slough (SRS), excess dissolved org. carbon and sulfate were also consistently delivered from upgradient canals and showed no evidence of decline over the study period. Within the SRS a strong pos. correlation was obsd. between MeHg concns. in surface water and resident fish. Within distinct geog. regions of ENP (SRS, Marsh, Coastal), the geochem. controls on MeHg dynamics differed and highlighted regions susceptible to higher MeHg bioaccumulation, particularly in the SRS and Coastal regions. This study demonstrates the strong influence that dissolved org. carbon and sulfate loads have on spatial and temporal distributions of MeHg across ENP. Importantly, improved water quality and flow rates are two key restoration targets of the nearly 30-yr Everglades restoration program, which if achieved, this study suggests would lead to reduced MeHg prodn. and exposure.
- 24Mitchell, C. P. J.; Gilmour, C. C. Methylmercury Production in a Chesapeake Bay Salt Marsh. J. Geophys. Res. 2008, 113, G00C04, DOI: 10.1029/2008JG000765There is no corresponding record for this reference.
- 25Bae, H.-S.; Dierberg, F. E.; Ogram, A. Syntrophs Dominate Sequences Associated with the Mercury Methylation-Related Gene HgcA in the Water Conservation Areas of the Florida Everglades. Appl. Environ. Microbiol. 2014, 80, 6517– 6526, DOI: 10.1128/AEM.01666-1425https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslSiur7J&md5=a484e79d64cc90db832e89a07f7a7116Syntrophs dominate sequences associated with the mercury methylation-related gene hgcA in the water conservation areas of the Florida EvergladesBae, Hee-Sung; Dierberg, Forrest E.; Ogram, AndrewApplied and Environmental Microbiology (2014), 80 (20), 6517-6526, 11 pp.CODEN: AEMIDF; ISSN:1098-5336. (American Society for Microbiology)The mechanisms and rates of mercury methylation in the Florida Everglades are of great concern because of potential adverse impacts on human and wildlife health through mercury accumulation in aquatic food webs. We developed a new PCR primer set targeting hgcA, a gene encoding a corrinoid protein essential for Hg methylation across broad phylogenetic boundaries, and used this primer set to study the distribution of hgcA sequences in soils collected from three sites along a gradient in sulfate and nutrient concns. in the Northern Everglades. The sequences obtained were distributed in diverse phyla, including Proteobacteria, Chloroflexi, Firmicutes, and Methanomicrobia; however, hgcA clone libraries from all sites were dominated by sequences clustering within the order Syntrophobacterales of the Deltaproteobacteria (49 to 65 % of total sequences). DsrB mRNA sequences, representing active sulfate-reducing prokaryotes at the time of sampling, obtained from these sites were also dominated by Syntrophobacterales (75 to 89 %). Lab. incubations with soils taken from the site low in sulfate concns. also suggested that Hg methylation activities were primarily mediated by members of the order Syntrophobacterales, with some contribution by methanogens, Chloroflexi, iron-reducing Geobacter and non-sulfate-reducing Firmicutes inhabiting the sites. This suggests that prokaryotes distributed within clades defined by syntrophs are the predominant group controlling methylation of Hg in low-sulfate areas of the Everglades. Any strategy for managing mercury methylation in the Everglades should consider that net mercury methylation is not limited to the action of sulfate redn.
- 26Arndt, S.; Jørgensen, B. B.; LaRowe, D. E.; Middelburg, J. J.; Pancost, R. D.; Regnier, P. Quantifying the Degradation of Organic Matter in Marine Sediments: A Review and Synthesis. Earth Sci. Rev. 2013, 123, 53– 86, DOI: 10.1016/j.earscirev.2013.02.00826https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXptFOns78%253D&md5=d24554d59bc546860eac339270b53cb8Quantifying the degradation of organic matter in marine sediments: A review and synthesisArndt, Sandra; Joergensen, B. B.; LaRowe, D. E.; Middelburg, J. J.; Pancost, R. D.; Regnier, P.Earth-Science Reviews (2013), 123 (), 53-86CODEN: ESREAV; ISSN:0012-8252. (Elsevier B.V.)A review. Quantifying the rates of biogeochem. processes in marine sediments is essential for understanding global element cycles and climate change. Because org. matter degrdn. is the engine behind benthic dynamics, deciphering the impact that various forces have on this process is central to detg. the evolution of the Earth system. Therefore, recent developments in the quant. modeling of org. matter degrdn. in marine sediments are critically reviewed. The first part of the review synthesizes the main chem., biol. and phys. factors that control org. matter degrdn. in sediments while the second part provides a general review of the math. formulations used to model these processes and the third part evaluates their application over different spatial and temporal scales. Key transport mechanisms in sedimentary environments are summarized and the math. formulation of the org. matter degrdn. rate law is described in detail. The roles of enzyme kinetics, bioenergetics, temp. and biomass growth in particular are highlighted. Alternative model approaches that quantify the degrdn. rate const. are also critically compared. In the third part of the review, the capability of different model approaches to extrapolate org. matter degrdn. rates over a broad range of temporal and spatial scales is assessed. In addn., the structure, functions and parameterization of more than 250 published models of org. matter degrdn. in marine sediments are analyzed. The large range of published model parameters illustrates the complex nature of org. matter dynamics, and, thus, the limited transferability of these parameters from one site to another. Compiled model parameters do not reveal a statistically significant correlation with single environmental characteristics such as water depth, deposition rate or org. matter flux. The lack of a generic framework that allows for model parameters to be constrained in data-poor areas seriously limits the quantification of org. matter degrdn. on a global scale. Therefore, we explore regional patterns that emerge from the compiled more than 250 org. matter rate consts. and critically discuss them in their environmental context. This review provides an interdisciplinary view on org. matter degrdn. in marine sediments. It contributes to an improved understanding of global patterns in benthic org. matter degrdn., and helps identify outstanding questions and future directions in the modeling of org. matter degrdn. in marine sediments.
- 27Yu, R. Q.; Reinfelder, J. R.; Hines, M. E.; Barkay, T. Syntrophic Pathways for Microbial Mercury Methylation. ISME J. 2018, 12, 1826– 1835, DOI: 10.1038/s41396-018-0106-027https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXmvFKgu7w%253D&md5=b52ed230d626973f761469b87d646344Syntrophic pathways for microbial mercury methylationYu, Ri-Qing; Reinfelder, John R.; Hines, Mark E.; Barkay, TamarISME Journal (2018), 12 (7), 1826-1835CODEN: IJSOCF; ISSN:1751-7362. (Nature Research)Exposure to dietary sources of methylmercury (MeHg) is the focus of public health concerns with environmental mercury (Hg) contamination. MeHg is formed in anoxic environments by anaerobic microorganisms. This process has been studied mostly with single-species culture incubations, although the relevance of such studies to Hg(II)-methylation in situ is limited because microbial activities in the environment are critically modulated by interactions among microbial functional groups. Here we describe expts. in which Hg(II)-methylation was examd. within the context of various microbial syntrophies. We show enhanced Hg(II)-methylation under conditions that established syntrophy by interspecies hydrogen and acetate transfer. Relative to activity of monocultures, interactions of Hg(II) methylating sulfate-reducing bacteria with a methanogen stimulated potential Hg(II)-methylation rates 2-fold to 9-fold, and with Syntrophobacter sp. 1.7-fold to 1.8-fold; those of a Hg(II) methylating Syntrophobacter sp. with a methanogen increased Hg(II)-methylation 2-fold. Under sulfate-depleted conditions, higher Hg(II)-methylation rates in the syntrophic incubations corresponded to higher free energy yields (ΔG°') than in the monocultures. Based on energetic considerations, we therefore propose that syntrophic microbial interactions are likely a major source of MeHg in sulfate- and iron-limited anoxic environments while in sulfate-replete environments, MeHg formation via sulfate redn. dominates.
- 28Luek, J. L.; Thompson, K. E.; Larsen, R. K.; Heyes, A.; Gonsior, M. Sulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic Matter. Sci. Rep. 2017, 7, 8829, DOI: 10.1038/s41598-017-09223-z28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cfpsleisw%253D%253D&md5=3f4c37a485ceba0a41f3797507fb787dSulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic MatterLuek Jenna L; Thompson Kaitlyn E; Heyes Andrew; Gonsior Michael; Thompson Kaitlyn E; Larsen Randolph KScientific reports (2017), 7 (1), 8829 ISSN:.Sulfate reduction plays an important role in altering dissolved organic matter (DOM) in estuarine and coastal sediments, although its role in the production of optically active chromophoric DOM (CDOM) and a subset of fluorescent DOM (FDOM) has not been previously investigated in detail. Freshwater sediment slurries were incubated anaerobically with added sulfate and acetate to promote sulfate-reducing bacteria. Ultraviolet visible (UV-Vis) absorbance and 3-dimensional excitation emission matrix (EEM) fluorescence spectra were measured over a five weeks anaerobic dark incubation period. Parallel Factor Analysis (PARAFAC) of FDOM determined components that increased significantly during dark and anaerobic incubation matching three components previously considered of terrestrially-derived or humic-like origin published in the OpenFluor database. The observed FDOM increase was strongly correlated (R(2) = 0.96) with the reduction of sulfate. These results show a direct experimental link between sulfate reduction and FDOM production, which impacts our understanding of coastal FDOM sources and early sediment diagenesis. As 3D fluorescence techniques are commonly applied to diverse systems, these results provide increasing support that FDOM can have many diverse sources not consistently captured by common classifications such as "humic-like" fluorescence.
- 29Aiken, G. R.; Gilmour, C. C.; Krabbenhoft, D. P.; Orem, W. Dissolved Organic Matter in the Florida Everglades: Implications for Ecosystem Restoration. Crit. Rev. Environ. Sci. Technol. 2011, 41, 217– 248, DOI: 10.1080/10643389.2010.53093429https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXit1aqtLk%253D&md5=29a3020336d7c867e601283ad106a162Dissolved Organic Matter in the Florida Everglades: Implications for Ecosystem RestorationAiken, George R.; Gilmour, Cynthia C.; Krabbenhoft, David P.; Orem, WilliamCritical Reviews in Environmental Science and Technology (2011), 41 (Suppl. 1), 217-248CODEN: CRETEK; ISSN:1064-3389. (Taylor & Francis, Inc.)A review. Dissolved org. matter (DOM) in the Florida Everglades controls a no. of environmental processes important for ecosystem function including the absorption of light, mineral dissoln./pptn., transport of hydrophobic compds. (e.g., pesticides), and the transport and reactivity of metals, such as mercury. Proposed attempts to return the Everglades to more natural flow conditions will result in changes to the present transport of DOM from the Everglades Agricultural Area and the northern conservation areas to Florida Bay. In part, the restoration plan calls for increasing water flow throughout the Everglades by removing some of the manmade barriers to flow in place today. The land- and water-use practices assocd. with the plan will likely result in changes in the quality, quantity, and reactivity of DOM throughout the greater Everglades ecosystem. The authors discuss the factors controlling DOM concns. and chem., present distribution of DOM throughout the Everglades, the potential effects of DOM on key water-quality issues, and the potential utility of dissolved org. matter as an indicator of success of restoration efforts.
- 30Haitzer, M.; Aiken, G. R.; Ryan, J. N. Binding of Mercury(II) to Dissolved Organic Matter: The Role of the Mercury-to-DOM Concentration Ratio. Environ. Sci. Technol. 2002, 36, 3564– 3570, DOI: 10.1021/es025699i30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XltlWkurY%253D&md5=ad2cc1b382bec27bfed2f97a96d95f09Binding of Mercury(II) to Dissolved Organic Matter: The Role of the Mercury-to-DOM Concentration RatioHaitzer, Markus; Aiken, George R.; Ryan, Joseph N.Environmental Science and Technology (2002), 36 (16), 3564-3570CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)The binding of Hg(II) to dissolved org. matter (DOM; hydrophobic acids isolated from the Florida Everglades by XAD-8 resin) was measured over a wide range of Hg-to-DOM concn. ratios using an equil. dialysis ligand exchange method. Conditional distribution coeffs. (KDOM') detd. by this method were strongly affected by the Hg/DOM concn. ratio. At Hg/DOM ratios below approx. 1 μg of Hg/mg of DOM, we obsd. very strong interactions (KDOM' = 1023.2 ±1.0 L/kg at pH = 7.0 and I = 0.1), indicative of mercury-thiol bonds. Hg/DOM ratios above approx. 10 μg of Hg/mg of DOM, as used in most studies that have detd. Hg-DOM binding consts., gave much lower KDOM' values (1010.7 ±1.0 L/kg at pH = 4.9-5.6 and I = 0.1), consistent with Hg binding mainly to oxygen functional groups. These results suggest that the binding of Hg to DOM under natural conditions (very low Hg/DOM ratios) is controlled by a small fraction of DOM mols. contg. a reactive thiol functional group. Therefore, Hg/DOM distribution coeffs. used for modeling the biogeochem. behavior of Hg in natural systems need to be detd. at low Hg/DOM ratios.
- 31Gerbig, C. A.; Kim, C. S.; Stegemeier, J. P.; Ryan, J. N.; Aiken, G. R. Formation of Nanocolloidal Metacinnabar in Mercury-DOM-Sulfide Systems. Environ. Sci. Technol. 2011, 45, 9180– 9187, DOI: 10.1021/es201837h31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXht1ClsbzI&md5=9af24b8d68a6e618c50dff76fb24fa50Formation of Nanocolloidal Metacinnabar in Mercury-DOM-Sulfide SystemsGerbig, Chase A.; Kim, Christopher S.; Stegemeier, John P.; Ryan, Joseph N.; Aiken, George R.Environmental Science & Technology (2011), 45 (21), 9180-9187CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Direct detn. of Hg speciation in sulfide-contg. environments is confounded by low Hg concns. and poor anal. sensitivity. We report the results of expts. designed to assess Hg speciation at environmentally relevant ratios of Hg to dissolved org. matter (DOM) (i.e., <4 nmol Hg/mg DOM) by combining solid phase extn. using C18 resin with extended x-ray absorption fine structure (EXAFS) spectroscopy. Aq. Hg(II) and a DOM isolate were equilibrated in the presence and absence of 100μM total sulfide. In the absence of sulfide, Hg adsorption to the resin increased as the Hg:DOM ratio decreased and as the strength of Hg-DOM binding increased. EXAFS anal. indicated that in the absence of sulfide, Hg bonds with an av. of 2.4±0.2 S atoms with a bond length typical of Hg-org. thiol ligands (2.35 Å). In the presence of sulfide, Hg showed greater affinity for the C18 resin, and its chromatog. behavior was independent of Hg:DOM ratio. EXAFS anal. showed Hg-S bonds with a longer interat. distance (2.51-2.53 Å) similar to the Hg-S bond distance in metacinnabar (2.53 Å) regardless of the Hg:DOM ratio. For all samples contg. sulfide, the S coordination no. was below the ideal 4-coordinate structure of metacinnabar. At a low Hg:DOM ratio where strong binding DOM sites may control Hg speciation (1.9 nmol/mg) Hg was coordinated by 2.3±0.2 S atoms, and the coordination no. rose with increasing Hg:DOM ratio. The less-than-ideal coordination nos. indicate metacinnabar-like species on the nanometer scale, and the pos. correlation between Hg:DOM ratio and S coordination no. suggests progressively increasing particle size or cryst. order with increasing abundance of Hg with respect to DOM. In DOM-contg. sulfidic systems nanocolloidal metacinnabar-like species may form, and these species need to be considered when addressing Hg biogeochem.
- 32Poulin, B. A.; Gerbig, C. A.; Kim, C. S.; Stegemeier, J. P.; Ryan, J. N.; Aiken, G. R. Effects of Sulfide Concentration and Dissolved Organic Matter Characteristics on the Structure of Nanocolloidal Metacinnabar. Environ. Sci. Technol. 2017, 51, 13133– 13142, DOI: 10.1021/acs.est.7b0268732https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1GrurbP&md5=5baa8a7d1bc3e9e9a9e56d895a05b1dfEffects of Sulfide Concentration and Dissolved Organic Matter Characteristics on the Structure of Nanocolloidal MetacinnabarPoulin, Brett A.; Gerbig, Chase A.; Kim, Christopher S.; Stegemeier, John P.; Ryan, Joseph N.; Aiken, George R.Environmental Science & Technology (2017), 51 (22), 13133-13142CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Understanding the speciation of divalent mercury (Hg(II)) in aquatic systems contg. dissolved org. matter (DOM) and sulfide is necessary to predict the conversion of Hg(II) to bioavailable methylmercury. We used X-ray absorption spectroscopy to characterize the structural order of mercury in Hg(II)-DOM-sulfide systems for a range of sulfide concn. (1-100 μM), DOM aromaticity (specific UV absorbance (SUVA254)), and Hg(II)-DOM and Hg(II)-DOM-sulfide equilibration times (4-142 h). In all systems, Hg(II) was present as structurally disordered nanocolloidal metacinnabar (β-HgS). β-HgS nanocolloids were significantly smaller or less ordered at lower sulfide concn., as indicated by under-coordination of Hg(II) in β-HgS. The size or structural order of β-HgS nanocolloids increased with increasing sulfide abundance and decreased with increasing SUVA254 of the DOM. The Hg(II)-DOM or Hg(II)-DOM-sulfide equilibration times did not significantly influence the extent of structural order in nanocolloidal β-HgS. Geochem. factors that control the structural order of nanocolloidal β-HgS, which are expected to influence nanocolloid surface reactivity and soly., should be considered in the context of mercury bioavailability.
- 33Graham, A. M.; Aiken, G. R.; Gilmour, C. C. Effect of Dissolved Organic Matter Source and Character on Microbial Hg Methylation in Hg-S-DOM Solutions. Environ. Sci. Technol. 2013, 47, 5746– 5754, DOI: 10.1021/es400414a33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmvVehs7w%253D&md5=614a5dc8029f5d5b2950d29d4fdb20f4Effect of Dissolved Organic Matter Source and Character on Microbial Hg Methylation in Hg-S-DOM SolutionsGraham, Andrew M.; Aiken, George R.; Gilmour, Cynthia C.Environmental Science & Technology (2013), 47 (11), 5746-5754CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Dissolved org. matter (DOM) is a key component of fate and transport models for most metals, including Hg. Using a suite of diverse DOM isolates, we demonstrated that DOM character, in addn. to concn., influences inorg. Hg (Hg(II)i) bioavailability to Hg-methylating bacteria. Using a model Hg-methylating bacterium, Desulfovibrio desulfuricans ND132, we evaluated Hg-DOM-sulfide bioavailability in washed-cell assays at environmentally relevant Hg/DOM ratios (∼1-8 ng Hg/mg C) and sulfide concns. (1-1000μM). All tested DOM isolates significantly enhanced Hg methylation above DOM-free controls (from ∼2 to >20-fold for 20 mg C/L DOM solns.), but high mol. wt./highly arom. DOM isolates and/or those with high S content were particularly effective at enhancing Hg methylation. Because these expts. were conducted under conditions of predicted supersatn. with respect to metacinnabar (β-HgS(s)), we attribute the DOM-dependent enhancement of Hg(II)i bioavailability to steric and specific chem. (e.g., DOM thiols) inhibition of β-HgS(s) growth and aggregation by DOM. Expts. examg. the role of DOM across a wide sulfide gradient revealed that DOM only enhances Hg methylation under fairly low sulfide conditions (.ltorsim.30μM), conditions that favor HgS nanoparticle/cluster formation relative to dissolved HgS species.
- 34Graham, A. M.; Aiken, G. R.; Gilmour, C. C. Dissolved Organic Matter Enhances Microbial Mercury Methylation under Sulfidic Conditions. Environ. Sci. Technol. 2012, 46, 2715– 2723, DOI: 10.1021/es203658f34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvVSrsrg%253D&md5=47c26725a3248a0854ac9f1320ba2c3aDissolved Organic Matter Enhances Microbial Mercury Methylation Under Sulfidic ConditionsGraham, Andrew M.; Aiken, George R.; Gilmour, Cynthia C.Environmental Science & Technology (2012), 46 (5), 2715-2723CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Dissolved org. matter (DOM) is generally thought to lower metal bioavailability in aquatic systems due to the formation of metal-DOM complexes that reduce free metal ion concns. However, this model may not be pertinent for metal nanoparticles, which are now understood to be ubiquitous, sometimes dominant, metal species in the environment. The effect of DOM on Hg bioavailability to microorganisms was examd. under conditions (0.5-5.0nM Hg and 2-10μM sulfide) that favor the formation of β-HgS(s) (metacinnabar) nanoparticles. We used the methylation of stable-isotope enriched 201HgCl2 by Desulfovibrio desulfuricans ND132 in short-term washed cell assays as a sensitive, environmentally significant proxy for Hg uptake. Suwannee River humic acid (SRHA) and Williams Lake hydrophobic acid (WLHPoA) substantially enhanced (2- to 38-fold) the bioavailability of Hg to ND132 over a wide range of Hg/DOM ratios (9.4 pmol/mg DOM to 9.4 nmol/mg DOM), including environmentally relevant ratios. Methylmercury (MeHg) prodn. by ND132 increased linearly with either SRHA or WLHPoA concn., but SRHA, a terrestrially derived DOM, was far more effective at enhancing Hg-methylation than WLHPoA, an aquatic DOM dominated by autochthonous sources. No DOM-dependent enhancement in Hg methylation was obsd. in Hg-DOM-sulfide solns. amended with sufficient l-cysteine to prevent β-HgS(s) formation. We hypothesize that small HgS particles, stabilized against aggregation by DOM, are bioavailable to Hg-methylating bacteria. Our lab. expts. provide a mechanism for the pos. correlations between DOC and MeHg prodn. obsd. in many aquatic sediments and wetland soils.
- 35Poulin, B. A.; Ryan, J. N.; Nagy, K. L.; Stubbins, A.; Dittmar, T.; Orem, W.; Krabbenhoft, D. P.; Aiken, G. R. Spatial Dependence of Reduced Sulfur in Everglades Dissolved Organic Matter Controlled by Sulfate Enrichment. Environ. Sci. Technol. 2017, 51, 3630– 3639, DOI: 10.1021/acs.est.6b0414235https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjsFCktrg%253D&md5=509a7a6b72ad0068534b59cd1825165cSpatial Dependence of Reduced Sulfur in Everglades Dissolved Organic Matter Controlled by Sulfate EnrichmentPoulin, Brett A.; Ryan, Joseph N.; Nagy, Kathryn L.; Stubbins, Aron; Dittmar, Thorsten; Orem, William; Krabbenhoft, David P.; Aiken, George R.Environmental Science & Technology (2017), 51 (7), 3630-3639CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Sulfate inputs to the Florida Everglades stimulate sulfidic conditions in freshwater wetland sediments that affect ecol. and biogeochem. processes. An unexplored implication of sulfate enrichment is alteration of the content and speciation of sulfur in dissolved org. matter (DOM), which influences the reactivity of DOM with trace metals. Here, we describe the vertical and lateral spatial dependence of sulfur chem. in the hydrophobic org. acid fraction of DOM from unimpacted and sulfate-impacted Everglades wetlands using X-ray absorption spectroscopy and ultrahigh-resoln. mass spectrometry. Spatial variation in DOM sulfur content and speciation reflects the degree of sulfate enrichment and resulting sulfide concns. in sediment pore waters. Sulfur is incorporated into DOM predominantly as highly reduced species in sulfidic pore waters. Sulfur-enriched DOM in sediment pore waters exchanges with overlying surface waters and the sulfur likely undergoes oxidative transformations in the water column. Across all wetland sites and depths, the total sulfur content of DOM correlated with the relative abundance of highly reduced sulfur functionality. The results identify sulfate input as a primary determinant on DOM sulfur chem. to be considered in the context of wetland restoration and sulfur and trace metal cycling.
- 36Graham, A. M.; Cameron-Burr, K. T.; Hajic, H. A.; Lee, C.; Msekela, D.; Gilmour, C. C. Sulfurization of Dissolved Organic Matter Increases Hg-Sulfide-Dissolved Organic Matter Bioavailability to a Hg-Methylating Bacterium. Environ. Sci. Technol. 2017, 51, 9080– 9088, DOI: 10.1021/acs.est.7b0278136https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFKntL7M&md5=ad4090caaa270f6cab5e90df5c4b47cfSulfurization of Dissolved Organic Matter Increases Hg-Sulfide-Dissolved Organic Matter Bioavailability to a Hg-Methylating BacteriumGraham, Andrew M.; Cameron-Burr, Keaton T.; Hajic, Hayley A.; Lee, Connie; Msekela, Deborah; Gilmour, Cynthia C.Environmental Science & Technology (2017), 51 (16), 9080-9088CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Reactions of dissolved org. matter (DOM) with aq. sulfide (termed sulfurization) in anoxic environments can substantially increase DOM's reduced sulfur functional group content. Sulfurization may affect DOM-trace metal interactions, including complexation and metal-contg. particle pptn., aggregation, and dissoln. Using a diverse suite of DOM samples, we found that susceptibility to addnl. sulfur incorporation via reaction with aq. sulfide increased with increasing DOM arom.-, carbonyl-, and carboxyl-C content. The role of DOM sulfurization in enhancing Hg bioavailability for microbial methylation was evaluated under conditions typical of Hg methylation environments (μM sulfide concns. and low Hg-to-DOM molar ratios). Under the conditions of predicted metacinnabar supersatn., microbial Hg methylation increased with increasing DOM sulfurization, likely reflecting either effective inhibition of metacinnabar growth and aggregation or the formation of Hg(II)-DOM thiol complexes with high bioavailability. Remarkably, Hg methylation efficiencies with the most sulfurized DOM samples were similar (>85% of total Hg methylated) to that obsd. in the presence of L-cysteine, a ligand facilitating rapid Hg(II) biouptake and methylation. This suggests that complexes of Hg(II) with DOM thiols have similar bioavailability to Hg(II) complexes with low-mol.-wt. thiols. Overall, our results are a demonstration of the importance of DOM sulfurization to trace metal and metalloid (esp. mercury) fate in the environment. DOM sulfurization likely represents another link between anthropogenic sulfate enrichment and MeHg prodn. in the environment.
- 37Weishaar, J. L.; Aiken, G. R.; Bergamaschi, B. A.; Fram, M. S.; Fujii, R.; Mopper, K. Evaluation of Specific Ultraviolet Absorbance as an Indicator of the Chemical Composition and Reactivity of Dissolved Organic Carbon. Environ. Sci. Technol. 2003, 37, 4702– 4708, DOI: 10.1021/es030360x37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXotFCgtLY%253D&md5=69b76d997d8d1ecee868c741fe7582e0Evaluation of Specific Ultraviolet Absorbance as an Indicator of the Chemical Composition and Reactivity of Dissolved Organic CarbonWeishaar, James L.; Aiken, George R.; Bergamaschi, Brian A.; Fram, Miranda S.; Fujii, Roger; Mopper, KennethEnvironmental Science and Technology (2003), 37 (20), 4702-4708CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved org. carbon (DOC) concn. Our data indicate that SUVA, detd. at 254 nm, is strongly correlated with percent aromaticity as detd. by 13C NMR for 13 org. matter isolates obtained from a variety of aquatic environments. SUVA, therefore, is shown to be a useful parameter for estg. the dissolved arom. carbon content in aquatic systems. Expts. involving the reactivity of DOC with chlorine and tetramethylammonium hydroxide (TMAH), however, show a wide range of reactivity for samples with similar SUVA values. These results indicate that, while SUVA measurements are good predictors of general chem. characteristics of DOC, they do not provide information about the reactivity of DOC derived from different types of source materials. Sample pH, nitrate, and iron were found to influence SUVA measurements.
- 38Åkerblom, S.; Nilsson, M. B.; Skyllberg, U.; Björn, E.; Jonsson, S.; Ranneby, B.; Bishop, K. Formation and Mobilization of Methylmercury across Natural and Experimental Sulfur Deposition Gradients. Environ. Pollut. 2020, 263, 114398, DOI: 10.1016/j.envpol.2020.114398There is no corresponding record for this reference.
- 39Mason, R. P.; Reinfelder, J. R.; Morel, F. M. M. Uptake, Toxicity, and Trophic Transfer of Mercury in a Coastal Diatom. Environ. Sci. Technol. 1996, 30, 1835– 1845, DOI: 10.1021/es950373d39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XisFansL4%253D&md5=5729dcd90feb7b4ee9bbe692faaa0cd4Uptake, Toxicity, and Trophic Transfer of Mercury in a Coastal DiatomMason, Robert P.; Reinfelder, John R.; Morel, Francois M. M.Environmental Science and Technology (1996), 30 (6), 1835-45CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)The studies of mercury speciation, toxicity, and phytoplankton uptake demonstrate that passive uptake of uncharged, lipophilic chloride complexes is the principal accumulation route of both methylmercury and inorg. mercury in phytoplankton. The predominance of methylmercury in fish, however, is a consequence of the greater trophic transfer efficiency of methyl- mercury than inorg. mercury. In particular, methylmercury in phytoplankton, which accumulates in the cell cytoplasm, is assimilated by zooplankton four times more efficiently than inorg. mercury, which is principally bound in phytoplankton membranes. On the basis of these results, the authors constructed a simple model of mercury accumulation in fish as a function of the overall octanol-water partition coeff. of methylmercury. The model can explain the variability of mercury concns. in fish within, but not among, different lake regions.
- 40Moye, H. A.; Miles, C. J.; Phlips, E. J.; Sargent, B.; Merritt, K. K. Kinetics and Uptake Mechanisms for Monomethylmercury between Freshwater Algae and Water. Environ. Sci. Technol. 2002, 36, 3550– 3555, DOI: 10.1021/es011421z40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XltFGis74%253D&md5=81849780f6e93b44a757517752726201Kinetics and Uptake Mechanisms for Monomethylmercury between Freshwater Algae and WaterMoye, H. Anson; Miles, Carl J.; Phlips, Edward J.; Sargent, Bethany; Merritt, Kristen K.Environmental Science and Technology (2002), 36 (16), 3550-3555CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Uptake kinetics of monomethylmercury chloride (MeHgCl) were measured for two species of green algae (Selenastrum capricornutum and Cosmarium botrytis), one blue-green algae (Schizothrix calcicola), and one diatom (Thalassiosira weissflogii), algal species that are commonly found in natural surface waters. Species differences were found with the two green algae giving the highest uptake rates, and one of them (Cosmarium) showing differences between cultures having widely different cell age (exponential vs. stationary), where increases in uptake rate for cells 30 days old were about 25 times greater than cells only 3 days old when wts. of cells were considered. Both Schizothrix and Thalassiosira exhibited nearly the same lower uptake rates, approx. 20 times lower than the two green algal species. Expts. with photosystem inhibitors, uncouplers, γ-radiation, light deprivation, and extended range uptake all point to an active transport mechanism for MeHgCl.
- 41Luengen, A. C.; Fisher, N. S.; Bergamaschi, B. A. Dissolved Organic Matter Reduces Algal Accumulation of Methylmercury. Environ. Toxicol. Chem. 2012, 31, 1712– 1719, DOI: 10.1002/etc.188541https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1GmtbvI&md5=db1bfccef37e6e81a87958b9eeb07bb6Dissolved organic matter reduces algal accumulation of methylmercuryLuengen, Allison C.; Fisher, Nicholas S.; Bergamaschi, Brian A.Environmental Toxicology and Chemistry (2012), 31 (8), 1712-1719CODEN: ETOCDK; ISSN:0730-7268. (Wiley-Blackwell)Dissolved org. matter (DOM) significantly decreased accumulation of methylmercury (MeHg) by the diatom Cyclotella meneghiniana in lab. expts. Live diatom cells accumulated 2 to 4 times more MeHg than dead cells, indicating that accumulation may be partially an energy-requiring process. Methylmercury enrichment in diatoms relative to ambient H2O was measured by a vol. concn. factor (VCF). Without added DOM, the max. VCF was 32 × 104, and the av. VCF (from 10 to 72 h) over all expts. was 12.6 × 104. At very low (1.5 mg L-1) added DOM, VCFs dropped by approx. half. At very high (20 mg L-1) added DOM, VCFs dropped 10-fold. Presumably, MeHg was bound to a variety of reduced S sites on the DOM, making it unavailable for uptake. Diatoms accumulated significantly more MeHg when exposed to transphilic DOM exts. than hydrophobic ones. However, algal lysate, a labile type of DOM created by resuspending a marine diatom in freshwater, behaved similarly to a refractory DOM isolate from San Francisco Bay. Addn. of 67 μM L-cysteine resulted in the largest drop in VCFs, to 0.28 × 104. Although the DOM compn. influenced the availability of MeHg to some extent, total DOM concn. was the most important factor in detg. algal bioaccumulation of MeHg.
- 42Zhang, K. Analysis of Non-Linear Inundation from Sea-Level Rise Using LIDAR Data: A Case Study for South Florida. Clim. Change 2011, 106, 537– 565, DOI: 10.1007/s10584-010-9987-2There is no corresponding record for this reference.
- 43Park, J.; Stabenau, E.; Redwine, J.; Kotun, K. South Florida’s Encroachment of the Sea and Environmental Transformation over the 21st Century. J. Mar. Sci. Eng. 2017, 5, 31, DOI: 10.3390/jmse5030031There is no corresponding record for this reference.
- 44Damseaux, F.; Kiszka, J. J.; Heithaus, M. R.; Scholl, G.; Eppe, G.; Thomé, J. P.; Lewis, J.; Hao, W.; Fontaine, M. C.; Das, K. Spatial Variation in the Accumulation of POPs and Mercury in Bottlenose Dolphins of the Lower Florida Keys and the Coastal Everglades (South Florida). Environ. Pollut. 2017, 220, 577– 587, DOI: 10.1016/j.envpol.2016.10.00544https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1ygs7%252FI&md5=0bcc08ca521de180a9449f0ac9613daeSpatial variation in the accumulation of POPs and mercury in bottlenose dolphins of the Lower Florida Keys and the coastal Everglades (South Florida)Damseaux, France; Kiszka, Jeremy J.; Heithaus, Michael R.; Scholl, George; Eppe, Gauthier; Thome, Jean-Pierre; Lewis, Jennifer; Hao, Wensi; Fontaine, Michael C.; Das, KrishnaEnvironmental Pollution (Oxford, United Kingdom) (2017), 220 (Part_A), 577-587CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)The bottlenose dolphin (Tursiops truncatus) is an upper trophic level predator and the most common cetacean species found in nearshore waters of southern Florida, including the Lower Florida Keys (LFK) and the Florida Coastal Everglades (FCE). The objective of this study was to assess contamination levels of total mercury (T-Hg) in skin and persistent org. pollutants (PCBs, PBDEs, DDXs, HCHs, HCB, Σ PCDD/Fs and Σ DL-PCBs) in blubber samples of bottlenose dolphins from LFK (n = 27) and FCE (n = 24). PCBs were the major class of compds. found in bottlenose dolphin blubber and were higher in individuals from LFK (Σ 6 PCBs LFK males: 13,421 ± 7730 ng g-1 lipids, Σ 6 PCBs LFK females: 9683 ± 19,007 ng g-1 lipids) than from FCE (Σ 6 PCBs FCE males: 5638 ng g-1 ± 3627 lipids, Σ 6 PCBs FCE females: 1427 ± 908 ng g-1 lipids). These levels were lower than previously published data from the southeastern USA. The Σ DL-PCBs were the most prevalent pollutants of dioxin and dioxin like compds. (Σ DL-PCBs LFK: 739 ng g-1 lipids, Σ DL-PCBs FCE: 183 ng g-1 lipids) since PCDD/F concns. were low for both locations (mean 0.1 ng g-1 lipids for LFK and FCE dolphins). The toxicity equivalences of PCDD/Fs and DL-PCBs expressed as TEQ in LFK and FCE dolphins is mainly expressed by DL-PCBs (81% LFK - 65% FCE). T-Hg concns. in skin were significantly higher in FCE (FCE median 9314 ng g-1 dw) compared to LFK dolphins (LFK median 2941 ng g-1 dw). These concns. are the highest recorded in bottlenose dolphins in the southeastern USA, and may be explained, at least partially, by the biogeochem. of the Everglades and mangrove sedimentary habitats that create favorable conditions for the retention of mercury and make it available at high concns. for aquatic predators.
- 45Orem, W.; Gilmour, C.; Axelrad, D.; Krabbenhoft, D.; Scheidt, D.; Kalla, P.; McCormick, P.; Gabriel, M.; Aiken, G. Sulfur in the South Florida Ecosystem: Distribution, Sources, Biogeochemistry, Impacts, and Management for Restoration. Crit. Rev. Environ. Sci. Technol. 2011, 41, 249– 288, DOI: 10.1080/10643389.2010.53120145https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXit1aqtLg%253D&md5=af643ff21f1100f16efe92527abbd800Sulfur in the South Florida Ecosystem: Distribution, Sources, Biogeochemistry, Impacts, and Management for RestorationOrem, William; Gilmour, Cynthia; Axelrad, Donald; Krabbenhoft, David; Scheidt, Daniel; Kalla, Peter; McCormick, Paul; Gabriel, Mark; Aiken, GeorgeCritical Reviews in Environmental Science and Technology (2011), 41 (Suppl. 1), 249-288CODEN: CRETEK; ISSN:1064-3389. (Taylor & Francis, Inc.)A review. Sulfur is broadly recognized as a water quality issue of significance for the freshwater Florida Everglades. Roughly 60% of the remnant Everglades has surface water sulfate concns. above 1 mg l-1, a restoration performance measure based on present sulfate levels in unenriched areas. Highly enriched marshes in the northern Everglades have av. sulfate levels of 60 mg l-1. Sulfate loading to the Everglades is principally a result of land and water management in South Florida. The highest concns. of sulfate (av. 60-70 mg l-1) in the ecosystem are in canal water in the Everglades Agricultural Area (EAA). Potential sulfur sources in the watershed are many, but geochem. data and a preliminary sulfur mass balance for the EAA are consistent with sulfur presently used in agricultural, and sulfur released by oxidn. of org. EAA soils (including legacy agricultural applications and natural sulfur) as the primary sources of sulfate enrichment in the EAA canals. Sulfate loading to the Everglades increases microbial sulfate redn. in soils, leading to more reducing conditions, greater cycling of nutrients in soils, prodn. of toxic sulfide, and enhanced methylmercury (MeHg) prodn. and bioaccumulation. Wetlands are zones of naturally high MeHg prodn., but the combination of high atm. mercury deposition rates in South Florida and elevated sulfate loading leads to increased MeHg prodn. and MeHg risk to Everglades wildlife and human consumers. Sulfate from the EAA drainage canals penetrates deep into the Everglades Water Conservation Areas, and may extend into Everglades National Park. Present plans to restore sheet flow and to deliver more water to the Everglades may increase overall sulfur loads to the ecosystem, and move sulfate-enriched water further south. However, water management practices that minimize soil drying and rewetting cycles can mitigate sulfate release during soil oxidn. A comprehensive Everglades restoration strategy should include redn. of sulfur loads as a goal because of the many detrimental impacts of sulfate on the ecosystem. Monitoring data show that the ecosystem response to changes in sulfate levels is rapid, and strategies for reducing sulfate loading may be effective in the near term. A multifaceted approach employing best management practices for sulfur in agriculture, agricultural practices that minimize soil oxidn., and changes to stormwater treatment areas that increase sulfate retention could help achieve reduced sulfate loads to the Everglades, with resulting benefits.
- 46Tate, M. T.; DeWild, J. F.; Ogorek, J. M.; Janssen, S. E.; Krabbenhoft, D. P.; Poulin, B. A.; Breitmeyer, S. E.; Aiken, G. R.; Orem, W. H.; Varonka, M. S. Chemical Characterization of Water, Sediments, and Fish from Water Conservation Areas and Canals of the Florida Everglades (USA), 2012 to 2019 ; U.S. Geological Survey Data Release, 2023, DOI: 10.5066/P976EGIX .There is no corresponding record for this reference.
- 47Schall, T. N.; Ruiz, P. L.; Rutchey, K.; Irving, C.; McFee, D.; Caldecutt, K.; Maholland, B.; Bogina, V.; McCoy, C.; Shamblin, R. B.; Whelan, K. R. T. The Everglades National Park and Big Cypress National Preserve Vegetation Mapping Project: Interim Report-Shark River Slough/Long Pine Key (Region 1), Everglades National Park: Jacksonville District, Jacksonville, FL, 2020.There is no corresponding record for this reference.
- 48Wilson, B. J.; Servais, S.; Mazzei, V.; Kominoski, J. S.; Hu, M.; Davis, S. E.; Gaiser, E.; Sklar, F.; Bauman, L.; Kelly, S.; Madden, C.; Richards, J.; Rudnick, D.; Stachelek, J.; Troxler, T. G. Salinity Pulses Interact with Seasonal Dry-down to Increase Ecosystem Carbon Loss in Marshes of the Florida Everglades. Ecol. Appl. 2018, 28, 2092– 2108, DOI: 10.1002/eap.1798There is no corresponding record for this reference.
- 49Chambers, L. G.; Reddy, K. R.; Osborne, T. Z. Short-Term Response of Carbon Cycling to Salinity Pulses in a Freshwater Wetland. Soil Sci. Soc. Am. J. 2011, 75, 2000– 2007, DOI: 10.2136/sssaj2011.0026There is no corresponding record for this reference.
- 50Servais, S.; Kominoski, J. S.; Charles, S. P.; Gaiser, E. E.; Mazzei, V.; Troxler, T. G.; Wilson, B. J. Saltwater Intrusion and Soil Carbon Loss: Testing Effects of Salinity and Phosphorus Loading on Microbial Functions in Experimental Freshwater Wetlands. Geoderma 2019, 337, 1291– 1300, DOI: 10.1016/j.geoderma.2018.11.01350https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisVensb7K&md5=f34cbcc610f13ce1c1bb2b44c5238530Saltwater intrusion and soil carbon loss: Testing effects of salinity and phosphorus loading on microbial functions in experimental freshwater wetlandsServais, Shelby; Kominoski, John S.; Charles, Sean P.; Gaiser, Evelyn E.; Mazzei, Viviana; Troxler, Tiffany G.; Wilson, Benjamin J.Geoderma (2019), 337 (), 1291-1300CODEN: GEDMAB; ISSN:0016-7061. (Elsevier B.V.)Wetlands can store significant amts. of carbon (C), but climate and land-use change increasingly threaten wetland C storage potential. Carbon stored in soils of freshwater coastal wetlands is vulnerable to rapid saltwater intrusion assocd. with sea-level rise and reduced freshwater flows. In the Florida Everglades, unprecedented saltwater intrusion is simultaneously exposing wetlands soils to elevated salinity and phosphorus (P), in areas where C-rich peat soils are collapsing. To det. how elevated salinity and P interact to influence microbial contributions to C loss, we continuously added P (∼0.5 mg P d-1) and salinity (∼6.9 g salt d-1) to freshwater Cladium jamaicense (sawgrass) peat monoliths for two years. We measured changes in porewater chem., microbial extracellular enzyme activities, respiration rates, microbial biomass, root litter breakdown rates (k), and soil elemental compn. after short (57 d), intermediate- (392 d), and long-term (741 d) exposure. After 741 days, both β-1,4-glucosidase activity (P < 0.01) and β-1,4-cellobiosidase activity (P < 0.01) were reduced with added salinity in soils at 7.5-15 cm depth. Soil microbial biomass C decreased by 3.6× at 7.5-15 cm (P < 0.01) but not 0-7.5 cm depth (P > 0.05) with added salinity and was unaffected by added P. Soil respiration rates decreased after 372 d exposure to salinity (P = 0.05) and did not change with P exposure. Root litter k increased by 1.5× with added P and was unaffected by salinity exposure (P > 0.01). Soil %C decreased by approx. 1.3× after 741 days of salinity exposure compared to freshwater controls (P < 0.01). Elevated salinity and P accelerated wetland soil C loss primarily through leaching of DOC and increased root litter k. Our results indicate that freshwater wetland soils are sensitive to short- and long-term exposure to saltwater intrusion. Despite suppression of some soil microbial processes with added salinity, salt and P exposure appear to drive net C losses from coastal wetland soils.
- 51Gaiser, E.; Childers, D.; Travieso, R. Water Quality Data (Grab Samples) from the Shark River Slough, Everglades National Park (FCE LTER), Florida, USA, May 2001-Ongoing Ver 16; Environmental Data Initiative, 2022.There is no corresponding record for this reference.
- 52Castaneda, E.; Rivera-Monroy, V. Abiotic Monitoring of Physical Characteristics in Porewaters and Surface Waters of Mangrove Forests from the Shark River Slough and Taylor Slough, Everglades National Park (FCE LTER), South Florida, USA, December 2000-Ongoing; Environmental Data Initiative, 2023.There is no corresponding record for this reference.
- 53Aiken, G. R.; McKnight, D. M.; Thorn, K. A.; Thurman, E. M. Isolation of Hydrophilic Organic Acids from Water Using Nonionic Macroporous Resins. Org. Geochem. 1992, 18, 567– 573, DOI: 10.1016/0146-6380(92)90119-I53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XlvFyjtb4%253D&md5=06bb30fd942deb61a589d2d05ee876ddIsolation of hydrophilic organic acids from water using nonionic macroporous resinsAiken, G. R.; McKnight, D. M.; Thorn, K. A.; Thurman, E. M.Organic Geochemistry (1992), 18 (4), 567-73CODEN: ORGEDE; ISSN:0146-6380.A method for the isolation of hydrophilic org. acids from aquatic samples uses a 2-column array of XAD-8 and XAD-4 resins in series. The hydrophobic org. acids, composed primarily of aquatic fulvic acid, are removed from the sample on XAD-8, followed by the isolation of the more hydrophilic acids on XAD-4. For samples from a no. of diverse environments, more dissolved org. C was isolated on the XAD-8 resin (23-58%) than on the XAD-4 resin (7-25%). For these samples, the hydrophilic acids have lower C and H, higher O and N, and are lower in mol. wt. than the corresponding fulvic acids. The hydrophilic acids have lower arom. C and greater heteroaliph., ketone and carboxyl content than the fulvic acid.
- 54Pucher, M.; Wünsch, U.; Weigelhofer, G.; Murphy, K.; Hein, T.; Graeber, D. StaRdom: Versatile Software for Analyzing Spectroscopic Data of Dissolved Organic Matter in R. Water 2019, 11, 2366, DOI: 10.3390/w1111236654https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXot1Oiurg%253D&md5=200d532b893b48e62574fdd993b99c19StaRdom: versatile software for analyzing spectroscopic data of dissolved organic matter in RPucher, Matthias; Wuensch, Urban; Weigelhofer, Gabriele; Murphy, Kathleen; Hein, Thomas; Graeber, DanielWater (Basel, Switzerland) (2019), 11 (11), 2366CODEN: WATEGH; ISSN:2073-4441. (MDPI AG)The roles of dissolved org. matter (DOM) in microbial processes and nutrient cycles depend on its compn., which requires detailed measurements and analyses. We introduce a package for R, called staRdom ("spectroscopic anal. of DOM in R"), to analyze DOM spectroscopic data (absorbance and fluorescence), which is key to deliver fast insight into DOM compn. of many samples. staRdom provides functions that standardize data prepn. and anal. of spectroscopic data and are inspired by practical work. The user can perform blank subtraction, diln. correction, Raman normalization, scatter removal and interpolation, and fluorescence normalization. The software performs parallel factor anal. (PARAFAC) of excitation-emission matrixes (EEMs), including peak picking of EEMs, and calcs. fluorescence indexes, absorbance indexes, and absorbance slope indexes from EEMs and absorbance spectra. A comparison between PARAFAC solns. by staRdom in R compared with drEEM in MATLAB showed nearly identical solns. for most datasets, although different convergence criteria are needed to obtain similar results and interpolation of missing data is important when working with staRdom. In conclusion, staRdom offers the opportunity for standardized multivariate decompn. of spectroscopic data without requiring software licensing fees and presuming only basic R knowledge.
- 55Helms, J. R.; Stubbins, A.; Ritchie, J. D.; Minor, E. C.; Kieber, D. J.; Mopper, K. Absorption Spectral Slopes and Slope Ratios as Indicators of Molecular Weight, Source, and Photobleaching of Chromophoric Dissolved Organic Matter. Limnol. Oceanogr. 2008, 53, 955– 969, DOI: 10.4319/lo.2008.53.3.0955There is no corresponding record for this reference.
- 56Cook, B. A.; Janssen, S. E.; Tate, M. T.; Peterson, B. D.; Poulin, B. A. Mercury Methylation Assay Along a Salinity Gradient in Coastal Peat Soils in the Florida Everglades , U.S. Geological Survey Data Release, 2024, DOI: 10.5066/P139NMHU .There is no corresponding record for this reference.
- 57NIST. NIST Standard Reference Database 46, Ver 4.0. Critical Stability Constants of Metal Complexes Database; National Institute of Standards and Technology, 1997.There is no corresponding record for this reference.
- 58NIST. NIST Standard Reference Database 13, Ver 1. 0. NIST JANAF Thermochemical Tables; National Institute of Standards and Technology, 1985.There is no corresponding record for this reference.
- 59Davison, W. The Solubility of Iron Sulphides in Synthetic and Natural Waters at Ambient Temperature. Aquat. Sci. 1991, 53, 309– 329, DOI: 10.1007/BF00877139There is no corresponding record for this reference.
- 60Nordstrom, D. K.; Plummer, L. N.; Langmuir, D.; Busenberg, E.; May, H. M.; Jones, B. F.; Parkhurst, D. L. Revised Chemical Equilibrium Data for Major Water-Mineral Reactions and Their Limitations. In Chemical Modeling of Aqueous Systems II; ACS Symposium Series; American Chemical Society, 1990; Vol. 416, pp 398– 413.There is no corresponding record for this reference.
- 61Drott, A.; Björn, E.; Bouchet, S.; Skyllberg, U. Refining Thermodynamic Constants for Mercury(II)-Sulfides in Equilibrium with Metacinnabar at Sub-Micromolar Aqueous Sulfide Concentrations. Environ. Sci. Technol. 2013, 47, 4197– 4203, DOI: 10.1021/es304824n61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXjslSgt7o%253D&md5=5509af631efe40d228fbcc3988efa4b1Refining Thermodynamic Constants for Mercury(II)-Sulfides in Equilibrium with Metacinnabar at Sub-Micromolar Aqueous Sulfide ConcentrationsDrott, A.; Bjoern, E.; Bouchet, S.; Skyllberg, U.Environmental Science & Technology (2013), 47 (9), 4197-4203CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)An important issue in Hg biogeochem. is to explore the effect of aq. Hg(II) forms on bacterial uptake, and subsequent MeHg formation, under Fe(III) and sulfate reducing conditions. The success of this is dependent on relevant information on the thermodn. stability of Hg-sulfides. We detd. the soly. of a com. available HgS(s) phase, which was shown by x-ray diffraction to be a mixt. of 83% metacinnabar and 17% cinnabar. At aq. sulfide concns. 0.060-84μM, well below levels in previous studies, we report a soly. product (log Ksp ±SE) of -36.8±0.1 (HgS(s) + H+ = Hg2+ + HS-, I = 0, T =25°, pH 6-10, n =20) for metacinnabar. This value is 0.7 log units higher than previous ests. Complementing our data with data from Paquette and Helz (1997), we took advantage of a large data set (n =65) covering a wide range of aq. sulfide (0.06μM-140mM) and pH (1-11). On the basis of this, we report refined formation consts. (±SE) for the 3 aq. Hg(II)-sulfide species proposed by Schwarzenbach and Widmer (1963): Hg2+ + 2HS- = Hg(SH)20; log K =39.1±0.1, Hg2+ + 2HS- = HgS2H- + H+; log K =32.5±0.1, Hg2+ + 2HS- = HgS22- + 2H+; log K =23.2±0.1. Our refined log K values differ from previous ests. by 0.2-0.6 log units. At the low sulfide concns. in our study we could rule out the value of -10.0 for the reaction HgS(s) + H2O = HgOHSH(aq) as reported by Dyrssen and Wedborg (1991). By establishing a soly. product for the most environmentally relevant HgS(s) phase, metacinnabar, and extending the range of aq. sulfide concns. to sub-micromolar levels, relevant for soils, sediments, and waters, this study decreases the uncertainty in stability consts. for Hg-sulfides, thereby improving the basis for understanding the bioavailability and mobility of Hg(II) in the environment.
- 62Haitzer, M.; Aiken, G. R.; Ryan, J. N. Binding of Mercury(II) to Aquatic Humic Substances: Influence of PH and Source of Humic Substances. Environ. Sci. Technol. 2003, 37, 2436– 2441, DOI: 10.1021/es026291o62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjtlGlt70%253D&md5=8f50e9319e1214795a4d19dd843692dcBinding of Mercury(II) to Aquatic Humic Substances: Influence of pH and Source of Humic SubstancesHaitzer, Markus; Aiken, George R.; Ryan, Joseph N.Environmental Science and Technology (2003), 37 (11), 2436-2441CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Conditional distribution coeffs. (KDOM') for Hg(II) binding to seven dissolved org. matter (DOM) isolates were measured at environmentally relevant ratios of Hg(II) to DOM. The results show that KDOM' values for different types of samples (humic acids, fulvic acids, hydrophobic acids) isolated from diverse aquatic environments were all within 1 order of magnitude (1022.5 ±1.0-1023.5 ±1.0 L/kg), suggesting similar Hg(II) binding environments, presumably involving thiol groups, for the different isolates. KDOM' values decreased at low pHs (4) compared to values at pH 7, indicating proton competition for the strong Hg(II) binding sites. Chem. modeling of Hg(II)-DOM binding at different pH values was consistent with bidentate binding of Hg(II) by one thiol group (pKa = 10.3) and one other group (pKa = 6.3) in the DOM, which is in agreement with recent results on the structure of Hg(II)-DOM bonds obtained by extended x-ray absorption fine structure spectroscopy (EXAFS).
- 63Amirbahman, A.; Reid, A. L.; Haines, T. a.; Kahl, J. S.; Arnold, C. Association of Methylmercury with Dissolved Humic Acids. Environ. Sci. Technol. 2002, 36, 690– 695, DOI: 10.1021/es011044q63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XksVeltg%253D%253D&md5=d9f902a2569221142f9446c5ca70d0f4Association of Methylmercury with Dissolved Humic AcidsAmirbahman, Aria; Reid, Andrew L.; Haines, Terry A.; Kahl, J. Steven; Arnold, CedricEnvironmental Science and Technology (2002), 36 (4), 690-695CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Sorption of methylmercury (MeHg) to three different humic acids was studied as a function of pH and humic concn. The extent of sorption did not show a strong pH dependence within the pH range of 5-9. Below pH 5, a decrease in adsorption for all humic samples was obsd. The exptl. data for equil. sorption of MeHg were modeled using a discrete log K spectrum approach with three weakly acidic functional groups. The modeling parameters, which were the equil. binding consts. and the total binding capacities, represented the data well at all MeHg and humic concns. and pH values for a given humic sample. The estd. binding consts. for complexes of MeHg with humic acids were similar in magnitude to those of MeHg with thiol-contg. compds., suggesting that binding of MeHg involves the thiol groups of humic acids. The results show that only a small fraction of the reduced sulfur species in humic substances may take part in binding MeHg, but in most natural systems, this subfraction is considerably higher in concn. than ambient MeHg. The model developed here can be incorporated into speciation models to assess the bioavailability of MeHg in the presence of dissolved org. matter and competing ligands such as chloride and sulfide.
- 64Zeng, T.; Arnold, W. A.; Toner, B. M. Microscale Characterization of Sulfur Speciation in Lake Sediments. Environ. Sci. Technol. 2013, 47, 1287– 1296, DOI: 10.1021/es303914q64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslGguw%253D%253D&md5=3187923ac5c2a87bb1b522e63849cedfMicroscale Characterization of Sulfur Speciation in Lake SedimentsZeng, Teng; Arnold, William A.; Toner, Brandy M.Environmental Science & Technology (2013), 47 (3), 1287-1296CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Prairie pothole lakes (PPLs) are naturally sulfur-enriched wetlands in the glaciated prairie region of North America. High sulfate levels and dynamic hydrogeochem. in combination render PPLs a unique environment to explore the speciation of sedimentary S. The goals were to define and quantify the solid-phase S pools in PPL sediments and track seasonal dynamics of S speciation. A quant. x-ray microprobe method was developed based on S 1s x-ray absorption near-edge structure (XANES) spectroscopy and multienergy x-ray fluorescence mapping. Three S pools, pyritic S, reduced org. S (org. mono- and disulfide), and oxidized S (inorg. sulfate, ester sulfate, and sulfonate)-were identified in PPL sediments. No significant seasonal variation was evident for total S, but S speciation showed a seasonal response. During the spring-summer transition, the reduced org. S decreased from 55 to 15 mol%, with a concomitant rise in the oxidized S. During the summer-fall transition, the trend reversed and the reduced org. S grew to 75 mol% at the expense of the oxidized S. The pyritic S, on the other hand, remained relatively const. (∼22 mol%) over time. The seasonal changes in S speciation have strong potential to force the cycling of elements such as Hg in prairie wetlands.
- 65Bates, A. L.; Spiker, E. C.; Holmes, C. W. Speciation and Isotopic Composition of Sedimentary Sulfur in the Everglades, Florida, USA. Chem. Geol. 1998, 146, 155– 170, DOI: 10.1016/S0009-2541(98)00008-4There is no corresponding record for this reference.
- 66Gilmour, C.; Krabbenhoft, D.; Orem, W.; Aiken, G. Appendix 2B-1%: Influence of Drying and Rewetting on Mercury and Sulfur Cycling in Everglades and STA Soils, 2004 Everglades consolidated report for the South Florida Water Management District: West Palm Beach, FL, 2004.There is no corresponding record for this reference.
- 67Sleighter, R. L.; Chin, Y.-P.; Arnold, W. A.; Hatcher, P. G.; McCabe, A. J.; McAdams, B. C.; Wallace, G. C. Evidence of Incorporation of Abiotic S and N into Prairie Wetland Dissolved Organic Matter. Environ. Sci. Technol. Lett. 2014, 1, 345– 350, DOI: 10.1021/ez500229b67https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVSnsbnP&md5=4768a281e0723bbd225bb3001acc464bEvidence of Incorporation of Abiotic S and N into Prairie Wetland Dissolved Organic MatterSleighter, Rachel L.; Chin, Yu-Ping; Arnold, William A.; Hatcher, Patrick G.; McCabe, Andrew J.; McAdams, Brandon C.; Wallace, Grant C.Environmental Science & Technology Letters (2014), 1 (9), 345-350CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)Wetlands in the prairie pothole region of North America, which are among the most threatened ecosystems in the world, provide many services, ranging from waterfowl habitats to pesticide attenuation to carbon sequestration. The dissolved org. matter (DOM) that occurs within these wetlands, in surface waters and sediment porewaters, was examd. by mol.-level techniques. While it contains components typical of DOM from surface and subsurface waters, both sulfidic and nitrogenous org. mols. are significantly more abundant in this DOM pool than in other natural waters and show distribution patterns that exactly mimic the pattern obsd. for DOM that is comprised of only carbon, hydrogen, and oxygen. This indicates that incorporation of N and S within DOM is abiotic and nonspecific, likely involving hydrogen sulfide, polysulfides, and N-contg. nucleophiles.
- 68Chambers, L. G.; Davis, S. E.; Troxler, T.; Boyer, J. N.; Downey-Wall, A.; Scinto, L. J. Biogeochemical Effects of Simulated Sea Level Rise on Carbon Loss in an Everglades Mangrove Peat Soil. Hydrobiologia 2014, 726, 195– 211, DOI: 10.1007/s10750-013-1764-6There is no corresponding record for this reference.
- 69Weston, N. B.; Vile, M. A.; Neubauer, S. C.; Velinsky, D. J. Accelerated Microbial Organic Matter Mineralization Following Salt-Water Intrusion into Tidal Freshwater Marsh Soils. Biogeochemistry 2011, 102, 135– 151, DOI: 10.1007/s10533-010-9427-4There is no corresponding record for this reference.
- 70Weston, N. B.; Dixon, R. E.; Joye, S. B. Ramifications of Increased Salinity in Tidal Freshwater Sediments: Geochemistry and Microbial Pathways of Organic Matter Mineralization. J. Geophys. Res.: Biogeosci. 2006, 111, G01009, DOI: 10.1029/2005JG000071There is no corresponding record for this reference.
- 71Sholkovitz, E. R. Flocculation of Dissolved Organic and Inorganic Matter during the Mixing of River Water and Seawater. Geochim. Cosmochim. Acta 1976, 40, 831– 845, DOI: 10.1016/0016-7037(76)90035-1There is no corresponding record for this reference.
- 72Poulin, B. A.; Aiken, G. R.; Nagy, K. L.; Manceau, A.; Krabbenhoft, D. P.; Ryan, J. N. Mercury Transformation and Release Differs with Depth and Time in a Contaminated Riparian Soil during Simulated Flooding. Geochim. Cosmochim. Acta 2016, 176, 118– 138, DOI: 10.1016/j.gca.2015.12.02472https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpvVah&md5=76a66daa27c7b1a49bb022bde1c08f5eMercury transformation and release differs with depth and time in a contaminated riparian soil during simulated floodingPoulin, Brett A.; Aiken, George R.; Nagy, Kathryn L.; Manceau, Alain; Krabbenhoft, David P.; Ryan, Joseph N.Geochimica et Cosmochimica Acta (2016), 176 (), 118-138CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)Riparian soils are an important environment in the transport of mercury in rivers and wetlands, but the biogeochem. factors controlling mercury dynamics under transient redox conditions in these soils are not well understood. Mercury release and transformations in the Oa and underlying A horizons of a contaminated riparian soil were characterized in microcosms and an intact soil core under satn. conditions. Pore water dynamics of total mercury (HgT), methylmercury (MeHg), and dissolved gaseous mercury (Hg0(aq)) along with selected anions, major elements, and trace metals were characterized across redox transitions during 36 d of flooding in microcosms. Next, HgT dynamics were characterized over successive flooding (17 d), drying (28 d), and flooding (36 d) periods in the intact core. The obsd. mercury dynamics exhibit depth and temporal variability. At the onset of flooding in microcosms (1-3 d), mercury in the Oa horizon soil, present as a combination of ionic mercury (Hg(II)) bound to thiol groups in the soil org. matter (SOM) and nanoparticulate metacinnabar (β-HgS), was mobilized with org. matter of high mol. wt. Subsequently, under anoxic conditions, pore water HgT declined coincident with sulfate (3-11 d) and the proportion of nanoparticulate β-HgS in the Oa horizon soil increased slightly. Redox oscillations in the intact Oa horizon soil exhausted the mobile mercury pool assocd. with org. matter. In contrast, mercury in the A horizon soil, present predominantly as nanoparticulate β-HgS, was mobilized primarily as Hg0(aq) under strongly reducing conditions (5-18 d). The concn. of Hg0(aq) under dark reducing conditions correlated pos. with byproducts of dissimilatory metal redn. (.sum.(Fe,Mn)). Mercury dynamics in intact A horizon soil were consistent over two periods of flooding, indicating that nanoparticulate β-HgS was an accessible pool of mobile mercury over recurrent reducing conditions. The concn. of MeHg increased with flooding time in both the Oa and A horizon pore waters. Temporal changes in pore water constituents (iron, manganese, sulfate, inorg. carbon, headspace methane) all implicate microbial control of redox transitions. The mobilization of mercury in multiple forms, including HgT assocd. with org. matter, MeHg, and Hg0(aq), to pore waters during periodic soil flooding may contribute to mercury releases to adjacent surface waters and the recycling of the legacy mercury to the atm.
- 73Weber, F. A.; Voegelin, A.; Kretzschmar, R. Multi-Metal Contaminant Dynamics in Temporarily Flooded Soil under Sulfate Limitation. Geochim. Cosmochim. Acta 2009, 73, 5513– 5527, DOI: 10.1016/j.gca.2009.06.01173https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtVKjsrfP&md5=11aee3f2ce48531c15a75f2da40f7606Multi-metal contaminant dynamics in temporarily flooded soil under sulfate limitationWeber, Frank-Andreas; Voegelin, Andreas; Kretzschmar, RubenGeochimica et Cosmochimica Acta (2009), 73 (19), 5513-5527CODEN: GCACAK; ISSN:0016-7037. (Elsevier B.V.)The authors investigated the dynamics of copper, cadmium, lead, zinc, and nickel in a contaminated freshwater floodplain soil (gleyic fluvisol of Mulde River floodplain near Mulderstein, Germany under a realistic sulfate-limited flooding regime in microcosm expts. They found that most contaminants were initially mobilized by processes driven by the reductive dissoln. of Fe(III) and Mn(IV, III) (hydr)oxides. Subsequently, bacterial sulfate respiration resulted in the transformation of the entire available sulfate (2.3 mmol/kg) into chromous reducible sulfur (CRS). Cu K-edge X-ray absorption fine structure (XAFS) spectroscopy revealed that the soil Cu speciation changed from predominantly Cu(II) bound to soil org. matter (SOM) intermittently to 14% metallic Cu(0) and subsequently to 66% copper sulfide (CuxS). These CuxS ppts. accounted for most of the formed CRS, suggesting that CuxS was the dominant sulfide phase formed in the flooded soil. Sequential metal extns., in agreement with CRS results, suggested that easily mobilizable Cd was completely and Pb partially sequestered in sulfide ppts., controlling their dissolved concns. to below detection limits. In contrast, Zn and Ni (as well as Fe) were hardly sequestered into sulfide phases, so that micromolar levels of dissolved Zn and Ni (and millimolar dissolved Fe(II)) persisted in the reduced soil. The finding that Cu, Cd, and Pb were sequestered (but hardly any Zn, Ni, and Fe) is consistent with the thermodynamically predicted sulfide ladder following the increasing soly. products of the resp. metal sulfides. The observation that Cd and Pb were sequestered in sulfides despite the presence of remaining SOM-bound Cu(II) suggested that the kinetics of Cu(II) desorption, diffusion, and/or CuxS pptn. interfered with the sulfide ladder. It is concluded that the dynamics of multiple metal contaminants are intimately coupled under sulfate limitation by the relative thermodn. stabilities and formation kinetics of the resp. metal sulfides.
- 74D’Andrilli, J.; Junker, J. R.; Smith, H. J.; Scholl, E. A.; Foreman, C. M. DOM Composition Alters Ecosystem Function during Microbial Processing of Isolated Sources. Biogeochemistry 2019, 142, 281– 298, DOI: 10.1007/s10533-018-00534-574https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXnvVygtLY%253D&md5=c34326e0f884988c113568d307c71b0aDOM composition alters ecosystem function during microbial processing of isolated sourcesD'Andrilli, Juliana; Junker, James R.; Smith, Heidi J.; Scholl, Eric A.; Foreman, Christine M.Biogeochemistry (2019), 142 (2), 281-298CODEN: BIOGEP; ISSN:0168-2563. (Springer)Dynamics of dissolved org. matter (DOM) in ecosystems are controlled by a suite of interacting phys., chem., and biol. factors. Growing recognition of the assocns. between microbial communities and metab. and intrinsic DOM characteristics, highlight the potential importance of microbe-DOM relationships to modulate the role and fate of DOM, yet these relationships are difficult to isolate because they often operate across confounding environmental gradients. In a controlled lab. incubation (44 days), we integrated DOM bulk and mol. characterization, bacterial abundances, microbial assemblage compn., nutrient concns., and cellular respiration to discern the structural dynamics of biol. processing among DOM sources from different allochthonous litters (grass, deciduous leaves, and evergreen needles). We identified two periods, consistent among DOM sources, where processing dynamics differed. Further, bulk fluorescent analyses showed shifts from low to high excitation and emission wavelengths, indicating the biol. prodn. of more complex/degraded materials over time. Mol. level analyses revealed similar temporal patterns among DOM sources in the prodn. and consumption of individual chem. components varying in reactivity and heteroat. content. Despite these similarities, total carbon (C) removed and carbon dioxide (CO2) accumulation differed by ∼ 20% and 25% among DOM sources. This range in C processing was apparently tied to key chem. properties of the DOM (e.g., initial DOM compn., N content, and labile nature) as well as differential reorganization of the microbial populations that decompd. the DOM. We conclude that the prodn., transformation, and consumption of C in aquatic ecosystems is strongly dependent on the source and character of DOM as well as the structure of the microbial communities present, both of which change as DOM is processed over time. It is crucial that stream C processing models represent this complexity accurately.
- 75Herzog, S. D.; Persson, P.; Kvashnina, K.; Kritzberg, E. S. Organic Iron Complexes Enhance Iron Transport Capacity along Estuarine Salinity Gradients of Baltic Estuaries. Biogeosciences 2020, 17, 331– 344, DOI: 10.5194/bg-17-331-202075https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtlaqs7%252FF&md5=afdfea378e0fa13c9816dc62a17a896eOrganic iron complexes enhance iron transport capacity along estuarine salinity gradients of Baltic estuariesHerzog, Simon David; Persson, Per; Kvashnina, Kristina; Kritzberg, Emma SofiaBiogeosciences (2020), 17 (2), 331-344CODEN: BIOGGR; ISSN:1726-4189. (Copernicus Publications)Rivers discharge a notable amt. of dissolved Fe (1.5 x 109 mol yr-1) to coastal waters but are still not considered important sources of bioavailable Fe to open marine waters. The reason is that the vast majority of particular and dissolved riverine Fe is considered to be lost to the sediment due to aggregation during estuarine mixing. Recently, however, several studies demonstrated relatively high stability of riverine Fe to salinity-induced aggregation, and it has been proposed that organically complexed Fe (Fe-OM) can "survive" the salinity gradient, while Fe (oxy)hydroxides are more prone to aggregation and selectively removed. In this study, we directly identified, by X-ray absorption spectroscopy, the occurrence of these two Fe phases across eight boreal rivers draining into the Baltic Sea and confirmed a significant but variable contribution of Fe-OM in relation to Fe (oxy)hydroxides among river mouths. We further found that Fe-OM was more prevalent at high flow conditions in spring than at low flow conditions during autumn and that Fe-OM was more dominant upstream in a catchment than at the river mouth. The stability of Fe to increasing salinity, as assessed by artificial mixing expts., correlated well to the relative contribution of Fe-OM, confirming that org. complexes promote Fe transport capacity. This study suggests that boreal rivers may provide significant amts. of potentially bioavailable Fe beyond the estuary, due to org. matter complexes.
- 76Nagy, K. L.; Manceau, A.; Gasper, J. D.; Ryan, J. N.; Aiken, G. R. Metallothionein-like Multinuclear Clusters of Mercury(II) and Sulfur in Peat. Environ. Sci. Technol. 2011, 45, 7298– 7306, DOI: 10.1021/es201025v76https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXps1Oit7k%253D&md5=92e29669be9712d22568bfadfbc07c28Metallothionein-Like Multinuclear Clusters of Mercury(II) and Sulfur in PeatNagy, Kathryn L.; Manceau, Alain; Gasper, Jarrod D.; Ryan, Joseph N.; Aiken, George R.Environmental Science & Technology (2011), 45 (17), 7298-7306CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Strong Hg(II)-S (Hg-SR) bonds in natural org. matter, which influence Hg bioavailability, are difficult to characterize. We report evidence for 2 new Hg-SR structures using x-ray absorption spectroscopy in peats from the Florida Everglades with added Hg. The 1st, obsd. at a mole ratio of org. reduced S to Hg (Sred/Hg) between 220 and 1140, is a Hg4Sx type of cluster with each Hg atom bonded to 2 S atoms at 2.34 Å and one S at 2.53 Å, and all Hg atoms 4.12 Å apart. This model structure matches those of metal-thiolate clusters in metallothioneins, but not those of HgS minerals. The 2nd, with one S atom at 2.34 Å and ∼6 C atoms at 2.97 to 3.28 Å, occurred at Sred/Hg between 0.80 and 4.3 and suggests Hg binding to a thiolated arom. unit. The multinuclear Hg cluster indicates a strong binding environment to cysteinyl S that might impede methylation. Along with a linear Hg(SR)2 unit with Hg-S bond lengths of 2.34 Å at Sred/Hg of about 10-20, the new structures support a continuum in Hg-SR binding strength in natural org. matter.
- 77Marvin-DiPasquale, M.; Agee, J.; McGowan, C.; Oremland, R. S.; Thomas, M.; Krabbenhoft, D.; Gilmour, C. C. Methyl-Mercury Degradation Pathways: A Comparison among Three Mercury-Impacted Ecosystems. Environ. Sci. Technol. 2000, 34, 4908– 4916, DOI: 10.1021/es001312577https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXnt1Kjsbo%253D&md5=21400d52af6589cde05ef778eafc47fdMethyl-Mercury Degradation Pathways: A Comparison among Three Mercury-Impacted EcosystemsMarvin-DiPasquale, Mark; Agee, Jennifer; McGowan, Chad; Oremland, Ronald S.; Thomas, Martha; Krabbenhoft, David; Gilmour, Cynthia C.Environmental Science and Technology (2000), 34 (23), 4908-4916CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)We examd. microbial methylmercury (MeHg) degrdn. in sediment of the Florida Everglades, Carson River (NV), and San Carlos Creek (CA), 3 freshwater environments that differ in the extent and type of mercury contamination and sediment biogeochem. Degrdn. rate const. (kdeg) values increased with total Hg (Hgt) contamination both among and within ecosystems. The highest kdeg's (2.8-5.8/day) were obsd. in San Carlos Creek, at acid mine drainage impacted sites immediately downstream of the former New Idria mercury mine, where Hgt was 4.5-21.3 ppm (dry wt.). A reductive degrdn. pathway (presumably mer-detoxification) dominated degrdn. at these sites, as indicated by the nearly exclusive prodn. of 14CH4 from 14C-MeHg, under both aerobic and anaerobic conditions. At the upstream control site, and in the less contaminated ecosystems (e.g. the Everglades), kdeg's were low (≤0.2/day) and oxidative demethylation (OD) dominated degrdn., as evident from 14CO2 prodn. kdeg increased with microbial CH4 prodn., org. content, and reduced S in the Carson River system and increased with decreasing pH in San Carlos Creek. OD assocd. CO2 prodn. increased with pore-water SO42- in Everglades samples but was not attributable to anaerobic methane oxidn., as has been previously proposed. This ecosystem comparison indicates that severely contaminated sediments tend to have microbial populations that actively degrade MeHg via mer-detoxification, whereas OD occurs in heavily contaminated sediments as well but dominates in those less contaminated.
- 78Cleckner, L. B.; Gilmour, C. C.; Hurley, J. P.; Krabbenhoft, D. P. Mercury Methylation in Periphyton of the Florida Everglades. Limnol Oceanogr 1999, 44, 1815– 1825, DOI: 10.4319/lo.1999.44.7.181578https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXnsVWisbo%253D&md5=a90be6e3b49133dd504edea42f59cfa5Mercury methylation in periphyton of the Florida EvergladesCleckner, Lisa B.; Gilmour, Cynthia C.; Hurley, James P.; Krabbenhoft, David P.Limnology and Oceanography (1999), 44 (7), 1815-1825CODEN: LIOCAH; ISSN:0024-3590. (American Society of Limnology and Oceanography)Trophic accumulation of mercury (Hg) in aquatic ecosystems is of global concern due to health effects assocd. with eating fish with elevated Hg levels. The methylated form of Hg bio-accumulates so it is important to understand how inorg. Hg is transformed to methylmercury in the environment. Here, a new site for Hg methylation, the periphyton communities that are prevalent in the Florida Everglades, is described. It is hypothesized that periphyton communities that support an active microbial sulfur cycle support Hg methylation. This new methylation site has implications for trophic transfer of methylmercury since periphyton can be the base of the food web in aquatic ecosystems.
- 79Qian, J.; Skyllberg, U.; Frech, W.; Bleam, W. F.; Bloom, P. R.; Petit, P. E. Bonding of Methyl Mercury to Reduced Sulfur Groups in Soil and Stream Organic Matter as Determined by X-Ray Absorption Spectroscopy and Binding Affinity Studies. Geochim. Cosmochim. Acta 2002, 66, 3873– 3885, DOI: 10.1016/S0016-7037(02)00974-279https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XotlKisbk%253D&md5=98684179b2a63dd97efdcf2f38bd482bBonding of methyl mercury to reduced sulfur groups in soil and stream organic matter as determined by x-ray absorption spectroscopy and binding affinity studiesQian, Jin; Skyllberg, Ulf; Frech, Wolfgang; Bleam, William F.; Bloom, Paul R.; Petit, Pierre EmmanuelGeochimica et Cosmochimica Acta (2002), 66 (22), 3873-3885CODEN: GCACAK; ISSN:0016-7037. (Elsevier Science Inc.)We combined synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy and binding affinity studies to det. the coordination, geometry, and strength of Me mercury, CH3Hg (II), bonding in soil and stream org. matter. Samples of org. soil (OS), potentially sol. org. substances (PSOS) from the soil, and org. substances from a stream (SOS) draining the soil were taken along a short "hydrol. transect. "We detd. the sum of concns. of highly reduced org. S groups (designated Org-SRED), such as thiol (RSH), disulfane (RSSH), sulfide (RSR), and disulfide (RSSR), using sulfur K-edge XANES. Org-SRED varied between 27% and 64% of total S in our samples. Hg LIII-edge EXAFS anal. were detd. on samples added CH3Hg (II) to yield CH3Hg (II)/Org-SRED ratios in the range 0.01-1.62. At low ratios, Hg was assocd. to one C atom (the Me group) at an av. distance of 2.03 ± 0.02 A and to one S atom at an av. distance of 2.34 ± 0.03 A, in the first coordination shell. At calcd. CH3Hg(II)/Org-SRED ratios above 0.37 in OS, 0.32 in PSOS, and 0.24 in SOS, the org. S sites were satd. by CH3Hg+, and O (and/or N) atoms were found in the first coordination shell of Hg at an av. distance of 2.09 ± 0.01 A. Based on the assumption that RSH (and possibly RSSH) groups take part in the complexation of CH3Hg+, whereas RSSR and RSR groups do not, approx. 17% of total org. S consisted of RSH (+ RSSH) functionalities in the org. soil. Corresponding figures for samples PSOS and SOS were 14% and 9%, resp. Competitive complexation of CH3Hg+ by halide ions was used to det. the av. binding strength of native concns. of CH3Hg (II) in the OS sample. Using data for Org-SRED, calcd. surface complexation consts. were in the range from 1016.3 to 1016.7 for a model RSH site having an acidity const. of mercaptoacetic acid. These values compare favorably with identically defined stability consts. (log K1) for the binding of Me mercury to thiol groups in well-defined org. compds.
- 80Peterson, B. D.; Poulin, B. A.; Krabbenhoft, D. P.; Tate, M. T.; Baldwin, A. K.; Naymik, J.; Gastelecutto, N.; McMahon, K. D. Metabolically Diverse Microorganisms Mediate Methylmercury Formation under Nitrate-Reducing Conditions in a Dynamic Hydroelectric Reservoir. ISME J. 2023, 17 (10), 1705– 1718, DOI: 10.1038/s41396-023-01482-1There is no corresponding record for this reference.
- 81Peterson, B. D.; McDaniel, E. A.; Schmidt, A. G.; Lepak, R. F.; Janssen, S. E.; Tran, P. Q.; Marick, R. A.; Ogorek, J. M.; Dewild, J. F.; Krabbenhoft, D. P.; McMahon, K. D. Mercury Methylation Genes Identified across Diverse Anaerobic Microbial Guilds in a Eutrophic Sulfate-Enriched Lake. Environ. Sci. Technol. 2020, 54, 15840– 15851, DOI: 10.1021/acs.est.0c0543581https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitlyrs7bI&md5=167e120eb1fe79ed5386c72d69b9d335Mercury methylation genes identified across diverse anaerobic microbial guilds in a eutrophic sulfate-enriched lakePeterson, Benjamin D.; McDaniel, Elizabeth A.; Schmidt, Anna G.; Lepak, Ryan F.; Janssen, Sarah E.; Tran, Patricia Q.; Marick, Robert A.; Ogorek, Jacob M.; DeWild, John F.; Krabbenhoft, David P.; McMahon, Katherine D.Environmental Science & Technology (2020), 54 (24), 15840-15851CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Mercury (Hg) methylation is a microbially mediated process that converts inorg. Hg into bioaccumulative, neurotoxic methylmercury (MeHg). The metabolic activity of methylating organisms is highly dependent on biogeochem. conditions, which subsequently influences MeHg prodn. However, our understanding of the ecophysiol. of methylators in natural ecosystems is still limited. Here, we identified potential locations of MeHg prodn. in the anoxic, sulfidic hypolimnion of a freshwater lake. At these sites, we used shotgun metagenomics to characterize microorganisms with the Hg-methylation gene hgcA. Putative methylators were dominated by hgcA sequences divergent from those in well-studied, confirmed methylators. Using genome-resolved metagenomics, we identified organisms with hgcA (hgcA+) within the Bacteroidetes and the recently described Kiritimatiellaeota phyla. We identified hgcA+ genomes derived from sulfate-reducing bacteria, but these accounted for only 22% of hgcA+ genome coverage. The most abundant hgcA+ genomes were from fermenters, accounting for over half of the hgcA gene coverage. Many of these organisms also mediate hydrolysis of polysaccharides, likely from cyanobacterial blooms. This work highlights the distribution of the Hg-methylation genes across microbial metabolic guilds and indicate that primary degrdn. of polysaccharides and fermn. may play an important but unrecognized role in MeHg prodn. in the anoxic hypolimnion of freshwater lakes.
- 82Jones, D. S.; Walker, G. M.; Johnson, N. W.; Mitchell, C. P. J.; Coleman Wasik, J. K.; Bailey, J. V. Molecular Evidence for Novel Mercury Methylating Microorganisms in Sulfate-Impacted Lakes. ISME J. 2019, 13, 1659– 1675, DOI: 10.1038/s41396-019-0376-182https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVyrtbrJ&md5=2d385401e87ae623883b59d5dadcd729Molecular evidence for novel mercury methylating microorganisms in sulfate-impacted lakesJones, Daniel S.; Walker, Gabriel M.; Johnson, Nathan W.; Mitchell, Carl P. J.; Coleman Wasik, Jill K.; Bailey, Jake V.ISME Journal (2019), 13 (7), 1659-1675CODEN: IJSOCF; ISSN:1751-7362. (Nature Research)Methylmercury (MeHg) is a bioaccumulative neurotoxin that is produced by certain anaerobic microorganisms, but the abundance and importance of different methylating populations in the environment is not well understood. We combined mercury geochem., hgcA gene cloning, rRNA methods, and metagenomics to compare microbial communities assocd. with MeHg prodn. in two sulfate-impacted lakes on Minnesota's Mesabi Iron Range. The two lakes represent regional endmembers among sulfate-impacted sites in terms of their dissolved sulfide concns. and MeHg prodn. potential. rRNA amplicon sequencing indicates that sediments and anoxic bottom waters from both lakes contained diverse communities with multiple clades of sulfate reducing Deltaproteobacteria and Clostridia. In hgcA gene clone libraries, however, hgcA sequences were from taxa assocd. with methanogenesis and iron redn. in addn. to sulfate redn., and the most abundant clones were from unknown groups. We therefore applied metagenomics to identify the unknown populations in the lakes with the capability to methylate mercury, and reconstructed 27 genomic bins with hgcA. Some of the most abundant potential methylating populations were from phyla that are not typically assocd. with MeHg prodn., including a relative of the Aminicenantes (formerly candidate phylum OP8) and members of the Kiritimatiellaeota (PVC superphylum) and Spirochaetes that, together, were more than 50% of the potential methylators in some samples. These populations do not have genes for sulfate redn., and likely degrade org. compds. by fermn. or other anaerobic processes. Our results indicate that previously unrecognized populations with hgcAB are abundant and may be important for MeHg prodn. in some freshwater ecosystems.
- 83Chambers, L. G.; Steinmuller, H. E.; Breithaupt, J. L. Toward a Mechanistic Understanding of “Peat Collapse” and Its Potential Contribution to Coastal Wetland Loss. Ecology 2019, 100, e02720 DOI: 10.1002/ecy.2720There is no corresponding record for this reference.
- 84McCarter, C. P. R.; Sebestyen, S. D.; Coleman Wasik, J. K.; Engstrom, D. R.; Kolka, R. K.; Jeremiason, J. D.; Swain, E. B.; Monson, B. A.; Branfireun, B. A.; Balogh, S. J.; Nater, E. A.; Eggert, S. L.; Ning, P.; Mitchell, C. P. J. Long-Term Experimental Manipulation of Atmospheric Sulfate Deposition to a Peatland: Response of Methylmercury and Related Solute Export in Streamwater. Environ. Sci. Technol. 2022, 56, 17615– 17625, DOI: 10.1021/acs.est.2c02621There is no corresponding record for this reference.
- 85Mitchell, C. P. J.; Branfireun, B. A.; Kolka, R. K. Assessing Sulfate and Carbon Controls on Net Methylmercury Production in Peatlands: An in Situ Mesocosm Approach. Appl. Geochem. 2008, 23, 503– 518, DOI: 10.1016/j.apgeochem.2007.12.02085https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXjtVChsbo%253D&md5=9a06fc7e0957d5dc4c5b3eec9eba37e9Assessing sulfate and carbon controls on net methylmercury production in peatlands: An in situ mesocosm approachMitchell, Carl P. J.; Branfireun, Brian A.; Kolka, Randall K.Applied Geochemistry (2008), 23 (3), 503-518CODEN: APPGEY; ISSN:0883-2927. (Elsevier Ltd.)The transformation of atmospherically deposited inorg. Hg to the toxic, org. form methylmercury (MeHg) is of serious ecol. concern because MeHg accumulates in aquatic biota, including fish. Research has shown that the Hg methylation reaction is dependent on the availability of SO4 (as an electron acceptor) because SO4-reducing bacteria (SRB) mediate the biotic methylation of Hg. Much less research has investigated the possible org. C limitations to Hg methylation (i.e. from the perspective of the electron donor). Although peatlands are long-term stores of org. C, the C derived from peatland vegetation is of questionable microbial lability. This research investigated how both SO4 and org. C control net MeHg prodn. using a controlled factorial addn. design in 44 in situ peatland mesocosms. Two levels of SO4 addn. and energetic-equiv. addns. (i.e. same no. of electrons) of a no. of org. C sources were used including glucose, acetate, lactate, coniferous litter leachate, and deciduous litter leachate. This study supports previous research demonstrating the stimulation of MeHg prodn. from SO4 input alone (∼200 pg/L/day). None of the addns. of org. C alone resulted in significant MeHg prodn. The combined addn. of SO4 and some org. C sources resulted in considerably more MeHg prodn. (∼500 pg/L/day) than did the addn. of SO4 alone, demonstrating that the highest levels of MeHg prodn. can be expected only where fluxes of both SO4 and org. C are delivered concurrently. When compared to a no. of pore water samples taken from two nearby peatlands, MeHg concns. resulting from the combined addn. of SO4 and org. C in this study were similar to MeHg "hot spots" found near the upland-peatland interface. The formation of MeHg "hot spots" at the upland-peatland interface may be dependent on concurrent inputs of SO4 and org. C in runoff from the adjacent upland hillslopes.
- 86Chambers, L. G.; Guevara, R.; Boyer, J. N.; Troxler, T. G.; Davis, S. E. Effects of Salinity and Inundation on Microbial Community Structure and Function in a Mangrove Peat Soil. Wetlands 2016, 36, 361– 371, DOI: 10.1007/s13157-016-0745-8There is no corresponding record for this reference.
- 87Ulus, Y.; Tsui, M. T.-K.; Sakar, A.; Nyarko, P.; Aitmbarek, N. B.; Ardón, M.; Chow, A. T. Declines of Methylmercury along a Salinity Gradient in a Low-Lying Coastal Wetland Ecosystem at South Carolina, USA. Chemosphere 2022, 308, 136310, DOI: 10.1016/j.chemosphere.2022.136310There is no corresponding record for this reference.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsearthspacechem.4c00124.
Supporting Information on peat core collection (S1.1), porewater chemistry (S1.2), incubations (S1.3), water and peat analyses (S1.4), thermodynamic speciation calculations (S1.5), supporting interpretations (S2), and supporting figures and tables (S3) (PDF)
All data from incubations are provided in an xlsx file (XLSX)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.