Dissolved Elemental Mercury [Hg(0)_aq] Reactions and Purgeability in the Presence of Organic and Inorganic Particulates

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This article references 53 other publications.

1. 1

   Amyot, M.; Gill, G. A.; Morel, F. M. M. Production and loss of dissolved gaseous mercury in coastal seawater. Environ. Sci. Technol. 1997, 31 (12), 3606– 3611,  DOI: 10.1021/es9703685

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   1

   Production and Loss of Dissolved Gaseous Mercury in Coastal Seawater

   Amyot, Marc; Gill, Gary A.; Morel, Francois M. M.

   Environmental Science and Technology (1997), 31 (12), 3606-3611CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

   The formation of dissolved gaseous Hg (DGM, mainly composed of elemental Hg, Hg0) in the surface ocean and its subsequent removal through volatilization is an important component of the global Hg cycle. We studied DGM prodn. and loss in the coastal waters of the Gulf of Mexico using 4-26 h in situ incubation expts. DGM prodn. was only induced in the presence of sunlight. Once produced, DGM was rapidly lost from soln. (with a 1st-order rate const. of k = 0.1/h), apparently as a result of oxidn. Lab. expts. showed that dissolved gaseous Hg0 could be rapidly oxidized in the presence of chloride. In the field, most DGM prodn. (∼60%) was assocd. with the dissolved and colloidal Hg(II) phases. Spiking of samples with inorg. Hg(II) prior to in situ incubation greatly increased DGM prodn. rates, suggesting that photoreducible Hg(II) complexes were limiting DGM prodn. Diurnally, DGM seems to be formed through photoprodn. in the morning; DGM prodn. halts when substrate is exhausted, and DGM levels decrease afterwards, presumably by oxidn. of Hg0.

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2. 2

   Amyot, M.; Mierle, G.; Lean, D.; McQueen, D. J. Effect of solar radiation on the formation of dissolved gaseous mercury in temperate lakes. Geochim. Cosmochim. Acta 1997, 61 (5), 975– 987,  DOI: 10.1016/S0016-7037(96)00390-0

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   2

   Effect of solar radiation on the formation of dissolved gaseous mercury in temperate lakes

   Amyot, Marc; Mierle, Greg; Lean, David; McQueen, Donald J.

   Geochimica et Cosmochimica Acta (1997), 61 (5), 975-987CODEN: GCACAK; ISSN:0016-7037. (Elsevier)

   The effect was assessed of solar radiation on the formation of dissolved gaseous mercury (DGM) in lake water samples incubated in situ. In temperate forested lakes, solar radiation induced the formation of DGM, whereas in Lake Erie, light had no effect. In lakes where photo-induced DGM prodn. was found, DGM concns. were higher near the surface, whereas in Lake Erie, DGM levels peaked in the metalimnion. In high DOC (dissolved oxygen concn.) lakes, removal of UVB radiation did not affect DGM prodn., whereas in a low DOC lake, DGM prodn. rates were significantly lower in the absence of UVB radiation, suggesting that DOC compds. are reducing the availability of UVB radiation for photoredn. of Hg. The relationship between light intensity and DGM prodn. was nonlinear in Ranger Lake, Ontario. Above ∼3 MJ m-2 total incident radiation, a plateau was reached at about 300 fM during the summer and about 150 fM during the fall. In this lake, a clear diel pattern of DGM levels was found which paralleled that for total solar radiation. Spiking of samples with Hg(II) prior to incubation in Ranger Lake greatly increased the DGM prodn. rate, suggesting that photo-reducible Hg(II) complexes were limiting DGM prodn. Filtration through GF/F filters or sterilization by heating prior to incubation did not decrease DGM prodn. rates, suggesting that agents promoting DGM formation in Ranger Lake were either dissolved or colloidal. DGM levels in outflows of two high DOC drainage lakes were higher than in inflows, confirming that the lakes were sites of DGM prodn.

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3. 3

   Mason, R. P.; Lawson, N. M.; Sheu, G. R. Mercury in the Atlantic Ocean: factors controlling air-sea exchange of mercury and its distribution in the upper waters. Deep-Sea Res. Part II 2001, 48 (13), 2829– 2853,  DOI: 10.1016/S0967-0645(01)00020-0

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   Mercury in the Atlantic Ocean: factors controlling air-sea exchange of mercury and its distribution in the upper waters

   Mason, R. P.; Lawson, N. M.; Sheu, G.-R.

   Deep-Sea Research, Part II: Topical Studies in Oceanography (2001), 48 (13), 2829-2853CODEN: DSROEK; ISSN:0967-0645. (Elsevier Science Ltd.)

   To further understand Hg cycling at the Earth's surface, results of recent measurements of Hg concn. and speciation in the upper ocean and marine boundary layer of the Atlantic Ocean are discussed. In water, dissolved gaseous Hg (DGHg) and total Hg measurements are reported; in the atm., total gaseous Hg, reactive gaseous Hg (RGHg), and particulate Hg measurements were made. These measurements allow estn. of gas evasion to the atm. and deposition to the ocean. In conjunction with field collections, incubation expts. on-board ship and in the lab. further examd. processes controlling oxidn. and redn. of Hg species in water. The results suggested that dry deposition of RGHg could be significant.

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4. 4

   Lalonde, J. D.; Amyot, M.; Kraepiel, A. M. L.; Morel, F. M. M. Photooxidation of Hg(0) in artificial and natural waters. Environ. Sci. Technol. 2001, 35 (7), 1367– 1372,  DOI: 10.1021/es001408z

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   Photooxidation of Hg(0) in artificial and natural waters

   Lalonde, Janick D.; Amyot, Marc; Kraepiel, Anne M. L.; Morel, Francois M. M.

   Environmental Science and Technology (2001), 35 (7), 1367-1372CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

   The oxidn. of volatile aq. Hg in aquatic systems may be important in reducing fluxes of Hg out of aquatic systems. The results of lab. and field expts. designed to identify the parameters that control the photooxidn. of Hg(aq) are reported and the possible importance of this process in aquatic systems is assessed. The concns. of elemental and total Hg were measured as a function of time in both artificial and natural waters irradiated with a UV-B lamp. No change in Hg speciation was obsd. in dark controls, while a significant decrease in Hg was obsd. in UV-B irradiated artificial solns. contg. both Cl- and benzoquinone. Significant photooxidn. rates were also measured in natural samples spiked with Hg(aq); the photooxidn. of Hg then follows pseudo first-order kinetics (k = 0.6 h-1). The previously obsd. Hg(II) photoredn. rates in natural waters could represent a net balance between Hg(II) photoredn. and Hg photooxidn. As calcd. from Hg photooxidn. rates, the dominant Hg sink is likely to be photooxidn. rather than volatilization from the water column during summer days.

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5. 5

   Hines, N. A.; Brezonik, P. L. Mercury dynamics in a small Northern Minnesota lake: water to air exchange and photoreactions of mercury. Mar. Chem. 2004, 90 (1–4), 137– 149,  DOI: 10.1016/j.marchem.2004.03.013

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   Mercury dynamics in a small Northern Minnesota lake. Water to air exchange and photoreactions of mercury

   Hines, Neal A.; Brezonik, Patrick L.

   Marine Chemistry (2004), 90 (1-4), 137-149CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)

   Hg speciation at a small seepage lake in Northern Minnesota was shown to be influenced by photoredn. and photooxidn. Fluxes of Hg0 from water to air were greatest in the warmer, sunnier months in 2001 to 2002; however, correlation with solar radiation was weak. The daytime evasional loss was generally from water to air and was estd. at 5.3 pmol m-2 h-1 for 2001 and 6.2 pmol m-2 h-1 for 2002 using a two-layer gas transfer model. Losses of Hg0(aq) in the dark over 10 days were obsd. in lake water (0.02 h-1), Milli-Q water, and HPLC grade water (0.002 h-1) and agreed with reported pseudo-first-order loss rates in the dark in other fresh waters. Using a Hg arc lamp, the pseudo-first-order loss rate of Hg0 in water from Spring Lake was found to range from 0.39 to 0.76 h-1. Other sinks for Hg0 exist through reaction with ozone, hydroxyl radical, and possibly singlet oxygen. A second-order reaction rate const. for Hg0(aq) and •OH of 1.0 × 109 M-1 s-1 was estd. based on data from expts. and the literature. Although less reactive, there is a higher steady state concn. of ozone in lake water compared to hydroxyl radical. Consequently, loss of Hg0(aq) by ozone may predominate. Potential oxidn. of Hg0(aq) by singlet O using rose bengal as a sensitizer could not distinguish between oxidn. by rose bengal and by singlet oxygen itself. Chloride enhanced the oxidn. of Hg0(aq) and should be considered in the Hg cycle in the ocean.

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6. 6

   Bouffard, A.; Amyot, M. Importance of elemental mercury in lake sediments. Chemosphere 2009, 74 (8), 1098– 1103,  DOI: 10.1016/j.chemosphere.2008.10.045

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   Importance of elemental mercury in lake sediments

   Bouffard, Ariane; Amyot, Marc

   Chemosphere (2009), 74 (8), 1098-1103CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)

   Mercury (Hg) redox changes in sediments are poorly studied and understood, even though they potentially control Hg availability for methylation and can alter sediment-water Hg exchange. Elemental Hg (Hg0) concns. in sediments of two Canadian Shield lakes were assessed by thermodesorption. Hg0 concns. in sediments varied between 6.3 and 60.3 pg g-1 (wet wt.) which represented 7.4-28.4% of total mercury (HgT) concn. Hg0 concns. were similar in both lakes. Hg0 was rapidly adsorbed on sediments in controlled adsorption expts. and surface sediments sampled in summer had a stronger affinity for Hg0 than deeper sediments and sediments sampled in fall. This adsorption was pos. correlated to org. matter content and neg. related to particle grain size, pH and oxygen concn. in overlying water. This study demonstrates that Hg0 is a prevalent species in sediments, but not in pore water, because of the high sorptive capacity of sediments towards Hg0. Its potential availability towards Hg methylating bacteria remains to be detd.

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7. 7

   Wang, Y. M.; Li, Y. B.; Liu, G. L.; Wang, D. Y.; Jiang, G. B.; Cai, Y. Elemental Mercury in Natural Waters: Occurrence and Determination of Particulate Hg(0). Environ. Sci. Technol. 2015, 49 (16), 9742– 9749,  DOI: 10.1021/acs.est.5b01940

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   Elemental Mercury in Natural Waters: Occurrence and Determination of Particulate Hg(0)

   Wang, Yongmin; Li, Yanbin; Liu, Guangliang; Wang, Dingyong; Jiang, Guibin; Cai, Yong

   Environmental Science & Technology (2015), 49 (16), 9742-9749CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

   Hg(0) is ubiquitous in water and involved in key Hg biogeochem. processes. It is extensively studied as a purgeable dissolved species, termed dissolved gaseous Hg (DGM). Little information is available regarding nonpurgeable particulate Hg(0) in water, Hg(0) bound to suspended particulate matter (SPM), which is presumably present due to high affinity of Hg(0) adsorption on solids. Using stable isotope tracer and isotope diln. (ID) techniques, we studied the occurrence and quantification of particulate Hg(0) after Hg(0) was spiked into natural waters, aiming to provide firsthand information on particulate Hg(0) in water. A considerable fraction of 201Hg(0) spiked in water (∼70% after 4 h equilibration) was bound to SPM and nonpurgeable, suggesting the occurrence of particulate Hg(0) in natural waters. A scheme, involving isotope diln., purge and trap, and inductively coupled plasma mass spectrometry detection, was proposed to quantify particulate Hg(0) by the difference between DGM and total Hg(0), detd. immediately and at equilibration after spiking ID Hg isotope, resp. The application of this newly established method revealed the presence of particulate Hg(0) in Florida Everglades water, as the detd. DGM levels (0.14-0.22 ng/L) were remarkably lower than total Hg(0) (0.41-0.75 ng/L).

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8. 8

   Zhang, H.; Lindberg, S. E. Air/water exchange of mercury in the Everglades I: the behavior of dissolved gaseous mercury in the Everglades Nutrient Removal Project. Sci. Total Environ. 2000, 259 (1–3), 123– 133,  DOI: 10.1016/S0048-9697(00)00577-5

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   8

   Air/water exchange of mercury in the Everglades I: the behavior of dissolved gaseous mercury in the Everglades Nutrient Removal Project

   Zhang, H.; Lindberg, S. E.

   Science of the Total Environment (2000), 259 (1-3), 123-133CODEN: STENDL; ISSN:0048-9697. (Elsevier Science Ireland Ltd.)

   From 1996 to 1998 we detd. dissolved gaseous mercury (DGM) in waters of the Everglades Nutrient Removal Project (ENR), a constructed wetlands. The concns. of DGM measured in these waters (mean 7.3±9.5 pg L-1) are among the lowest reported in the literature, and suggest a system often near or slightly above equil. with Hg in ambient air. DGM exhibited both seasonal and diel trends, peaking at midday and during the summer. A simple box budget model of DGM in waters of the Everglades was developed using an interactive spreadsheet based on a mass balance among light-induced redn. of HgII (prodn. of DGM), Hg0 oxidn. (removal), and Hg0 evasion in a box (water column) consisting of a surface region with sunlight available and a lower dark region. The modeling results suggest high sensitivity of hourly DGM concns. to DGM prodn. rates and initial DGM levels. The sensitivity to Hg0 oxidn. is lower than the sensitivity to DGM prodn. The model performance demonstrates successful simulations of a variety of DGM trends in the Everglades. In particular, it clearly demonstrates how it is possible to measure comparable rates of evasion over several Everglades sites with different DGM concns.

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9. 9

   Zhang, H.; Lindberg, S. E. Sunlight and iron(III)-induced photochemical production of dissolved gaseous mercury in fresh water. Environ. Sci. Technol. 2001, 35, 928– 935,  DOI: 10.1021/es001521p

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   9

   Sunlight and Iron(III)-Induced Photochemical Production of Dissolved Gaseous Mercury in Freshwater

   Zhang, Hong; Lindberg, Steve E.

   Environmental Science and Technology (2001), 35 (5), 928-935CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

   Mechanistic understanding of sunlight-induced natural processes for prodn. of dissolved gaseous Hg (DGM) in freshwaters has remained limited, and few direct field tests of the mechanistic hypotheses are available. We exposed ferric Fe salt-spiked fresh surface lake water (Whitefish Bay, Lake Superior, MI) in Teflon bottles and pond water (Oak Ridge, TN) in quartz bottles to sunlight in the field to infer if sunlight and Fe(III)-induced photochem. prodn. of DGM could mechanistically contribute partly to natural photochem. prodn. of DGM in freshwaters. We found that exposure of freshwater spiked with fresh Fe(III) (∼5 or 10μM) to sunlight led to repeatable, significantly larger increases in DGM prodn. (e.g., 380% in 1 h, 420% in 2 h, and 470% in 4 h for Whitefish Bay water) than exposure without the spike (e.g., 200% in 6 h). DGM increased with increasing exposure time and then often appeared to approach a steady state in the tests. Higher Fe(III) spike levels resulted in the same, or even less, DGM prodn. Storage of the water with or without Fe(III) spike in the dark after sunlight exposure led to significant, apparently 1st-order, decreases in DGM. These phenomena were hypothetically attributed to sunlight-induced photochem. prodn. of highly reducing org. free radicals through photolysis of Fe(III)-org. acid coordination compds. and subsequent redn. of Hg(II) to Hg(0) by the org. free radicals; the redn. was also accompanied by dark oxidn. of Hg(0) by photochem. originated oxidants (e.g., •OH). This study suggests that sunlight and Fe(III)-induced photochem. redn. of Hg(II) could be one of the mechanisms responsible for natural photochem. prodn. of DGM in freshwaters and that Fe species may be influential in mediating Hg chemodynamics and its subsequent toxicity in aquatic ecosystems.

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10. 10

    Hu, H.; Lin, H.; Zheng, W.; Tomanicek, S. J.; Johs, A.; Feng, X.; Elias, D. A.; Liang, L.; Gu, B. Oxidation and methylation of dissolved elemental mercury by anaerobic bacteria. Nature Geosci 2013, 6 (9), 751– 754,  DOI: 10.1038/ngeo1894

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    10

    Oxidation and methylation of dissolved elemental mercury by anaerobic bacteria

    Hu, Haiyan; Lin, Hui; Zheng, Wang; Tomanicek, Stephen J.; Johs, Alexander; Feng, Xinbin; Elias, Dwayne A.; Liang, Liyuan; Gu, Baohua

    Nature Geoscience (2013), 6 (9), 751-754CODEN: NGAEBU; ISSN:1752-0894. (Nature Publishing Group)

    Methylmercury is a neurotoxin that poses significant health risks to humans. Some anaerobic sulfate- and iron-reducing bacteria can methylate oxidized forms of mercury, generating methylmercury. One strain of sulfate-reducing bacteria (Desulfovibrio desulfuricans ND132) can also methylate elemental mercury. The prevalence of this trait among different bacterial strains and species remains unclear, however. Here, we compare the ability of two strains of the sulfate-reducing bacterium Desulfovibrio and one strain of the iron-reducing bacterium Geobacter to oxidize and methylate elemental mercury in a series of lab. incubations. Expts. were carried out under dark, anaerobic conditions, in the presence of environmentally relevant concns. of elemental mercury. We report differences in the ability of these organisms to oxidize and methylate elemental mercury. In line with recent findings, we show that D. desulfuricans ND132 can both oxidize and methylate elemental mercury. We find that the rate of methylation of elemental mercury is about one-third the rate of methylation of oxidized mercury. We also show that Desulfovibrio alaskensis G20 can oxidize, but not methylate, elemental mercury. Geobacter sulphurreducens PCA is able to oxidize and methylate elemental mercury in the presence of cysteine. We suggest that the activity of methylating and non-methylating bacteria may together enhance the formation of methylmercury in anaerobic environments.

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11. 11

    Colombo, M. J.; Ha, J.; Reinfelder, J. R.; Barkay, T.; Yee, N. Anaerobic oxidation of Hg(0) and methylmercury formation by Desulfovibrio desulfuricans ND132. Geochim. Cosmochim. Acta 2013, 112, 166– 177,  DOI: 10.1016/j.gca.2013.03.001

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    11

    Anaerobic oxidation of Hg(0) and methylmercury formation by Desulfovibrio desulfuricans ND132

    Colombo, Matthew J.; Ha, Juyoung; Reinfelder, John R.; Barkay, Tamar; Yee, Nathan

    Geochimica et Cosmochimica Acta (2013), 112 (), 166-177CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)

    The transformation of inorg. mercury (Hg) to methylmercury (MeHg) plays a key role in detg. the amt. of Hg that is bioaccumulated in aquatic food chains. An accurate knowledge of Hg methylation mechanisms is required to predict the conditions that promote MeHg prodn. in aquatic environments. In this study, we conducted expts. to examine the oxidn. and methylation of dissolved elemental mercury [Hg(0)] by the anaerobic bacterium Desulfovibrio desulfuricans ND132. Anoxic cultures of D. desulfuricans ND132 were exposed to Hg(0) in the dark, and samples were collected and analyzed for the loss of Hg(0), formation of non-purgeable Hg, and formation of MeHg over time. We found that D. desulfuricans ND132 rapidly transformed dissolved gaseous mercury into non-purgeable Hg, with bacterial cultures producing approx. 40 μg/L of non-purgeable Hg within 30 min, and as much as 800 μg/L of non-purgeable Hg after 36 h. Derivatization of the non-purgeable Hg in the cell suspensions to diethylmercury and anal. of Hg(0)-reacted D. desulfuricans ND132 cells using X-ray absorption near edge structure (XANES) spectroscopy demonstrated that cell-assocd. Hg was dominantly in the oxidized Hg(II) form. Spectral comparisons and linear combination fitting of the XANES spectra indicated that the oxidized Hg(II) was covalently bonded to cellular thiol functional groups. MeHg analyses revealed that D. desulfuricans ND132 produced up to 118 μg/L of methylmercury after 36 h of incubation. We found that a significant fraction of the methylated Hg was exported out of the cell and released into the culture medium. The results of this work demonstrate a previously unrecognized pathway in the mercury cycle, whereby anaerobic bacteria produce MeHg when provided with dissolved Hg(0) as their sole Hg source.

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12. 12

    Wang, Y. W.; Schaefer, J. K.; Mishra, B.; Yee, N. Intracellular Hg(0) Oxidation in Desulfovibrio desulfuricans ND132. Environ. Sci. Technol. 2016, 50 (20), 11049– 11056,  DOI: 10.1021/acs.est.6b03299

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    12

    Intracellular Hg(0) Oxidation in Desulfovibrio desulfuricans ND132

    Wang, Yuwei; Schaefer, Jeffra K.; Mishra, Bhoopesh; Yee, Nathan

    Environmental Science & Technology (2016), 50 (20), 11049-11056CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    The disposal of elemental mercury (Hg(0)) wastes in mining and manufg. areas has caused serious soil and groundwater contamination issues. Under anoxic conditions, certain anaerobic bacteria can oxidize dissolved elemental mercury and convert the oxidized Hg to neurotoxic methylmercury. In this study, we conducted expts. with the Hg-methylating bacterium Desulfovibrio desulfuricans ND132 to elucidate the role of cellular thiols in anaerobic Hg(0) oxidn. The concns. of cell-surface and intracellular thiols were measured, and specific fractions of D. desulfuricans ND132 were examd. for Hg(0) oxidn. activity and analyzed with extended X-ray absorption fine structure (EXAFS) spectroscopy. The exptl. data indicate that intracellular thiol concns. are approx. six times higher than those of the cell wall. Cells reacted with a thiol-blocking reagent were severely impaired in Hg(0) oxidn. activity. Spheroplasts lacking cell walls rapidly oxidized Hg(0) to Hg(II), while cell wall fragments exhibited low reactivity toward Hg(0). EXAFS anal. of spheroplast samples revealed that multiple different forms of Hg-thiols are produced by the Hg(0) oxidn. reaction and that the local coordination environment of the oxidized Hg changes with reaction time. The results of this study indicate that Hg(0) oxidn. in D. desulfuricans ND132 is an intracellular process that occurs by reaction with thiol-contg. mols.

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13. 13

    Mason, R. P.; Reinfelder, J. R.; Morel, F. M. M. Bioaccumulation of mercury and methylmercury. Water Air Soil Poll. 1995, 80 (1–4), 915– 921,  DOI: 10.1007/BF01189744

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    13

    Bioaccumulation of mercury and methylmercury

    Mason, R. P.; Reinfelder, J. R.; Morel, F. M. M.

    Water, Air, and Soil Pollution (1995), 80 (1-4), 915-21CODEN: WAPLAC; ISSN:0049-6979. (Kluwer)

    The factors controlling the accumulation of mercury in fish are poorly understood. The often invoked lipid soly. of MMHg is an inadequate explanation because inorg. Hg complexes, which are not bioaccumulated, are as lipid sol. as their MMHg analogs and, unlike other hydrophobic compds., MMHg in fish resides in protein rather than fat tissue. We show that passive uptake of the lipophilic complexes (primarily HgCl2 and CH3HgCl) results in high concns. of both inorg. and MMHg in phytoplankton. However, differences in partitioning within phytoplankton cells between inorg. mercury - which is principally membrane bound - and MMHg - which accumulates in the cytoplasm - lead to a greater assimilation of MMHg during zooplankton grazing. Most of the discrimination between inorg. and MMHg thus occurs during trophic transfer while the major enrichment factor is between water and phytoplankton. As a result, MMHg concns. in fish are ultimately detd. by water chem. which controls MMHg speciation and uptake at the base of the food chain.

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14. 14

    Chen, C. Y.; Dionne, M.; Mayes, B. M.; Ward, D. M.; Sturup, S.; Jackson, B. P. Mercury bioavailability and bioaccumulation in estuarine food webs in the gulf of Maine. Environ. Sci. Technol. 2009, 43 (6), 1804– 1810,  DOI: 10.1021/es8017122

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    14

    Mercury Bioavailability and Bioaccumulation in Estuarine Food Webs in the Gulf of Maine

    Chen, Celia Y.; Dionne, Michele; Mayes, Brandon M.; Ward, Darren M.; Sturup, Stefan; Jackson, Brian P.

    Environmental Science & Technology (2009), 43 (6), 1804-1810CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Marine food webs are important links between Hg in the environment and human exposure via consumption of fish. Estuaries contain sediment repositories of Hg and are also crit. habitat for marine fish and shellfish species consumed by humans. MeHg biotransfers from sites of prodn. in estuarine sediments to higher trophic levels via both benthic and pelagic pathways. The authors studied the potential for Hg biotransfer to estuarine food webs across a Hg contamination gradient in the Gulf of Maine. Despite the variation in sediment Hg concns. across sites ( > 100 fold), Hg concns. in biota ranged by only 2-4 fold for each species across sites. Sediment contamination alone explained some variation in Hg and MeHg concns. in biota across sites. However, biogeochem. and ecol. factors also explained significant variation in Hg bioaccumulation across species. Contaminated sites had higher total org. carbon concns. in sediments, which related to a decrease in Hg bioaccumulation (measured as biota-sediment concn. factors). Also, concns. of MeHg were higher in pelagic-feeding than benthic-feeding fauna (detd. from δ13C), indicating the importance of pelagic pathways in transferring MeHg. Lastly, the proportion of total Hg as MeHg increased with trophic level (measured as δ15N). These results reveal the importance of both biogeochem. and ecol. factors in detg. the bioavailability and trophic transfer of MeHg in estuarine food webs.

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15. 15

    Zhang, Y. X.; Soerensen, A. L.; Schartup, A. T.; Sunderland, E. M. A global model for methylmercury formation and uptake at the base of marine food webs. Global Biogeochemical Cycles 2020, 34 (2), e2019GB00634,  DOI: 10.1029/2019GB006348

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16. 16

    Amyot, M.; Southworth, G.; Lindberg, S. E.; Hintelmann, H.; Lalonde, J. D.; Ogrinc, N.; Poulain, A. J.; Sandilands, K. A. Formation and evasion of dissolved gaseous mercury in large enclosures amended with (HgCl2)-Hg-200. Atmos. Environ. 2004, 38 (26), 4279– 4289,  DOI: 10.1016/j.atmosenv.2004.05.002

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    16

    Formation and evasion of dissolved gaseous mercury in large enclosures amended with 200HgCl2

    Amyot, M.; Southworth, G.; Lindberg, S. E.; Hintelmann, H.; Lalonde, J. D.; Ogrinc, N.; Poulain, A. J.; Sandilands, K. A.

    Atmospheric Environment (2004), 38 (26), 4279-4289CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science B.V.)

    The mercury expt. to assess atm. loading in Canada and the United States (METAALICUS) aims at establishing the link between atm. deposition of mercury (Hg) and Hg concns. in fish. As part of this initiative, we conducted an enclosure expt. in Lake 239 (ON, Canada). Our goal was to follow over time dissolved gaseous mercury (DGM) concns., after the addn. of 200HgCl2, to assess post-depositional Hg dynamics. DGM concns. reached very high levels in surface waters (up to 6 ng l-1) during the days following the spike. This increase in DGM levels coincided with a decrease in total Hg in the enclosure. Photoredn. rates of Hg were high after spiking (1 ng l-1 h-1) and decreased by two orders of magnitude during the summer, with low rates obsd. in August (0.01 ng l-1 h-1). These low rates may be caused by photobleaching of dissolved org. carbon. Water-to-air Hg fluxes (evasion) were measured with a flux chamber and modeled using DGM; both methods yielded similar fluxes when using time-averaged DGM values. Together, these results indicate that, under certain conditions, large amts. of newly deposited Hg(II) may be converted to DGM by photochem. processes and lost by evasion across the air/water interface.

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17. 17

    Liang, X.; Lu, X.; Zhao, J.; Liang, L.; Zeng, E.; Gu, B. Stepwise reduction approach reveals mercury competitive binding and exchange reactions within natural organic matter and mixed organic ligands. Environ. Sci. Technol. 2019, 53, 10685– 10694,  DOI: 10.1021/acs.est.9b02586

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    17

    Stepwise Reduction Approach Reveals Mercury Competitive Binding and Exchange Reactions within Natural Organic Matter and Mixed Organic Ligands

    Liang, Xujun; Lu, Xia; Zhao, Jiating; Liang, Liyuan; Zeng, Eddy Y.; Gu, Baohua

    Environmental Science & Technology (2019), 53 (18), 10685-10694CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    The kinetics of mercuric ion (Hg2+) binding with heterogeneous naturally dissolved org. matter (DOM) has been hypothesized to result from competitive interactions among different org. ligands and functional groups of DOM for Hg2+. However, an exptl. protocol is lacking to det. Hg2+ binding with various competitive ligands and DOM, their binding strengths, and their dynamic exchange reactions. In this study, a stepwise redn. approach using ascorbic acid (AA) and stannous tin [Sn(II)] was devised to differentiate Hg(II) species in the presence of two major functional groups in DOM: the carboxylate-bound Hg(II) is reducible by both AA and Sn(II), whereas the thiolate-bound Hg(II) is reducible only by Sn(II). Using this operational approach, the relative binding strength of Hg2+ with selected org. ligands was found in the order dimercaptopropanesulfonate (DMPS) > glutathione (GSH) > penicillamine (PEN) > cysteine (CYS) > ethylenediaminetetraacetate > citrate, acetate, and glycine at the ligand-to-Hg molar ratio < 2. Dynamic, competitive ligand exchanges for Hg2+ from weak carboxylate to strong thiolate functional groups were obsd. among these ligands and within DOM, and the reaction depended on the relative binding strength and abundance of thiols and carboxylates, as well as reaction time. These results provide addnl. insights into dynamic exchange reactions of Hg2+ within multicompositional DOM in controlling the transformation and bioavailability of Hg(II) in natural aquatic environments.

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18. 18

    Du, H. X.; Gu, X.; Johs, A.; Yin, X. P.; Spano, T.; Wang, D. Y.; Pierce, E. M.; Gu, B. H. Sonochemical oxidation and stabilization of liquid elemental mercury in water and soil. J. Haz. Mater. 2023, 445, 130589,  DOI: 10.1016/j.jhazmat.2022.130589

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    18

    Sonochemical oxidation and stabilization of liquid elemental mercury in water and soil

    Du, Hongxia; Gu, Xin; Johs, Alexander; Yin, Xiangping; Spano, Tyler; Wang, Dingyong; Pierce, Eric M.; Gu, Baohua

    Journal of Hazardous Materials (2023), 445 (), 130589CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)

    Over 3000 mercury (Hg)-contaminated sites worldwide contain liq. metallic Hg [Hg(0)l] representing a continuous source of elemental Hg(0) in the environment through volatilization and solubilization in water. Currently, there are few effective treatment technologies available to remove or sequester Hg(0)l in situ. We investigated sonochem. treatments coupled with complexing agents, polysulfide and sulfide, in oxidizing Hg(0)l and stabilizing Hg in water, soil and quartz sand. Results indicate that sonication is highly effective in breaking up and oxidizing liq. Hg(0)l beads via acoustic cavitation, particularly in the presence of polysulfide. Without complexing agents, sonication caused only minor oxidn. of Hg(0)l but increased headspace gaseous Hg(0)g and dissolved Hg(0)aq in water. However, the presence of polysulfide essentially stopped Hg(0) volatilization and solubilization. As a charged polymer, polysulfide was more effective than sulfide in oxidizing Hg(0)l and subsequently stabilizing the pptd. metacinnabar (β-HgS) nanocrystals. Sonochem. treatments with sulfide yielded incomplete oxidn. of Hg(0)l, likely resulting from the formation of HgS coatings on the dispersed μm-size Hg(0)l bead surfaces. Sonication with polysulfide also resulted in rapid oxidn. of Hg(0)l and pptn. of HgS in quartz sand and in the Hg(0)l-contaminated soil. This research indicates that sonochem. treatment with polysulfide could be an effective means in rapidly converting Hg(0)l to insol. HgS ppts. in water and sediments, thereby preventing its further emission and release to the environment. We suggest that future studies are performed to confirm its tech. feasibility and treatment efficacy for remediation applications.

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19. 19

    Lee, J. Y.; Ju, Y. H.; Keener, T. C.; Varma, R. S. Development of cost-effective noncarbon sorbents for Hg0 removal from coal-fired power plants. Environ. Sci. Technol. 2006, 40 (8), 2714– 2720,  DOI: 10.1021/es051951l

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    19

    Development of Cost-Effective Noncarbon Sorbents for Hg0 Removal from Coal-Fired Power Plants

    Lee, Joo-Youp; Ju, Yuhong; Keener, Tim C.; Varma, Rajender S.

    Environmental Science & Technology (2006), 40 (8), 2714-2720CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Noncarbonaceous materials or mineral oxides (silica gel, alumina, mol. sieves, zeolites, and montmorillonite) were modified with various functional groups such as amine, amide, thiol, and urea, and active additives such as elemental sulfur, sodium sulfide, and sodium polysulfide to examine their potential as sorbents for the removal of elemental mercury (Hg0) vapor at coal-fired utility power plants. A no. of sorbent candidates such as amino-modified silica gel, urea moiety-modified silica gel, thiol moiety-modified silica gel, amide moiety-modified silica gel, sulfur-modified alumina, sulfur mol. sieve, sulfur-modified montmorillonite, sodium sulfide-modified montmorillonite, and sodium polysulfide-modified montmorillonite, were synthesized and tested in a lab-scale fixed-bed system under an argon flow for screening purposes at 70° and(or) 140°. Several functionalized silica materials reported in previous studies to effectively control heavy metals in the aq. phase showed insignificant adsorption capacities for Hg0 control in the gas phase, suggesting that mercury removal mechanisms in both phases are different. Among elemental sulfur-, sodium sulfide-, and sodium polysulfide-impregnated inorg. samples, sodium polysulfide-impregnated montmorillonite K 10 showed a moderate adsorption capacity at 70°, which can be used for sorbent injection prior to the wet FGD system.

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20. 20

    Fang, S. C. Sorption and transformation of mercury-vapor by dry soil. Environ. Sci. Technol. 1978, 12 (3), 285– 288,  DOI: 10.1021/es60139a004

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    20

    Sorption and transformation of mercury vapor by dry soil

    Fang, Sheng C.

    Environmental Science and Technology (1978), 12 (3), 285-8CODEN: ESTHAG; ISSN:0013-936X.

    Five Montana soils of different characteristics, 5 clay minerals, and several others, e.g. straw, peat, humic acids, exhibited various degrees of sorption for Hg vapor. Among the clay minerals, illite [12173-60-3] had the highest sorption capacity, and kaolinite [1318-74-7] the lowest. Sorption of Hg by humic acid was the highest and by cellulose [9004-34-6] powder the lowest. Both org. matter and the mineral makeup of the soil play an important role in the wide range of Hg vapor sorption by the 5 Montana soils. The sorption phenomena are adequately described by the Freundlich-type equation. The sorption of Hg vapor did not reach its max. when the Hg vapor concn. was increased to 209 μg/m3 or the soils were continually exposed for 17 days. Only a small fraction of Hg sorbed, which was readily available for plant uptake, was transformed to Hg2+ form by these 5 soils. The major portion of the Hg sorbed by soils remained unidentified.

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21. 21

    Fang, S. C. Studies on the sorption of elemental mercury-vapor by soils. Arch. Environ. Contam. Toxicol. 1981, 10 (2), 193– 201,  DOI: 10.1007/BF01055621

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    21

    Studies on the sorption of elemental mercury vapor by soils

    Fang, Sheng C.

    Archives of Environmental Contamination and Toxicology (1981), 10 (2), 193-201CODEN: AECTCV; ISSN:0090-4341.

    Hg vapor sorption by 5 surface soils increased curvilinearly with the increase of soil moisture content until a max. was reached. A further increase of moisture content caused a decline in Hg sorption. The percentage moisture contents which gave maximal increase of 203Hg vapor sorption in these soils coincided quite closely with their water-holding capacity values at 1/3 bar. At 10-20% moisture content Hg sorption was 20-30% higher in nonsterile than sterile soils; thus, soil microorganisms may play a part in elemental Hg vapor sorption and subsequent transformation to mercuric form. Hg vapor diffused into both dry and moist soil columns, and the diffusion profile can be described by an exponential function of the form, y = ae-bx, where a is the adsorption characteristics of the soil, b is the diffusivity coeff., and x is the depth of soil. The diffusivity coeff. for Hg vapor varied with soil type and moisture content.

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22. 22

    Gu, B.; Bian, Y.; Miller, C. L.; Dong, W.; Jiang, X.; Liang, L. Mercury reduction and complexation by natural organic matter in anoxic environments. Proc. Natl. Acad. Sci. U.S.A. 2011, 108 (4), 1479– 1483,  DOI: 10.1073/pnas.1008747108

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    22

    Mercury reduction and complexation by natural organic matter in anoxic environments

    Gu, Baohua; Bian, Yongrong; Miller, Carrie L.; Dong, Wenming; Jiang, Xin; Liang, Liyuan

    Proceedings of the National Academy of Sciences of the United States of America (2011), 108 (4), 1479-1483, S1479/1-S1479/3CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)

    Hg(II) species form complexes with natural dissolved org. matter (DOM) such as humic acid (HA), and this binding is known to affect the chem. and biol. transformation and cycling of Hg in aquatic environments. Dissolved elemental Hg, Hg(0), is also widely obsd. in sediments and water. However, reactions between Hg(0) and DOM have rarely been studied in anoxic environments. Here, under anoxic dark conditions we show strong interactions between reduced HA and Hg(0) through thiolate ligand-induced oxidative complexation with an estd. binding capacity of ∼3.5 μmol Hg/g HA and a partitioning coeff. >106 mUg. We further demonstrate that Hg(II) can be effectively reduced to Hg(0) in the presence of as little as 0.2 mg/L reduced HA, whereas prodn. of Hg(0) is inhibited by complexation as HA concn. increases. This dual role played by DOM in the redn. and complexation of Hg is likely widespread in anoxic sediments and water and can be expected to significantly influence the Hg species transformations and biol. uptake that leads to the formation of toxic methylmercury.

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23. 23

    Zheng, W.; Liang, L.; Gu, B. Mercury reduction and oxidation by reduced natural organic matter in anoxic environments. Environ. Sci. Technol. 2012, 46, 292– 299,  DOI: 10.1021/es203402p

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    23

    Mercury Reduction and Oxidation by Reduced Natural Organic Matter in Anoxic Environments

    Zheng, Wang; Liang, Liyuan; Gu, Baohua

    Environmental Science & Technology (2012), 46 (1), 292-299CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Natural org. matter (NOM)-mediated redox cycling of elemental mercury Hg(0) and mercuric Hg(II) is critically important in affecting inorg. mercury transformation and bioavailability. However, these processes are not well understood, particularly in anoxic water and sediments where NOM can be reduced and toxic methylmercury is formed. Under dark anoxic conditions reduced org. matter (NOMre) simultaneously reduces and oxidizes Hg via different reaction mechanisms. Redn. of Hg(II) is primarily caused by reduced quinones. However, Hg(0) oxidn. is controlled by thiol functional groups via oxidative complexation, which is demonstrated by the oxidn. of Hg(0) by low-mol.-wt. thiol compds., glutathione, and mercaptoacetic acid, under reducing conditions. Depending on the NOM source, oxidn. state, and NOM:Hg ratio, NOM reduces Hg(II) at initial rates ranging from 0.4 to 5.5 h-1, which are about 2 to 6 times higher than those obsd. for photochem. redn. of Hg(II) in open surface waters. However, rapid redn. of Hg(II) by NOMre can be offset by oxidn. of Hg(0) with an estd. initial rate as high as 5.4 h-1. This dual role of NOMre is expected to strongly influence the availability of reactive Hg and thus to have important implications for microbial uptake and methylation in anoxic environments.

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24. 24

    Zheng, W.; Demers, J. D.; Lu, X.; Bergquist, B. A.; Anbar, A. D.; Blum, J. D.; Gu, B. H. Mercury stable isotope fractionation during abiotic dark oxidation in the presence of thiols and natural organic matter. Environ. Sci. Technol. 2019, 53 (4), 1853– 1862,  DOI: 10.1021/acs.est.8b05047

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    24

    Mercury Stable Isotope Fractionation during Abiotic Dark Oxidation in the Presence of Thiols and Natural Organic Matter

    Zheng, Wang; Demers, Jason D.; Lu, Xia; Bergquist, Bridget A.; Anbar, Ariel D.; Blum, Joel D.; Gu, Baohua

    Environmental Science & Technology (2019), 53 (4), 1853-1862CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Hg stable isotope fractionation has been widely used to trace Hg sources and transformations in the environment, although many important fractionation processes remain unknown. Here, we describe Hg isotope fractionation during the abiotic dark oxidn. of dissolved elemental Hg(0) in the presence of thiol compds. and natural humic acid. We observe equil. mass-dependent fractionation (MDF) with enrichment of heavier isotopes in the oxidized Hg(II) and a small neg. mass-independent fractionation (MIF) owing to nuclear vol. effects. The measured enrichment factors for MDF and MIF (ε202Hg and E199Hg) ranged from 1.10 to 1.56 and from -0.16 to -0.18‰, resp., and agreed well with theor. predicted values for equil. fractionation between Hg(0) and thiol-bound Hg(II). We suggest that the obsd. equil. fractionation was likely controlled by isotope exchange between Hg(0) and Hg(II) following the prodn. of the Hg(II)-thiol complex. However, significantly attenuated isotope fractionation was obsd. during the initial stage of Hg(0) oxidn. by humic acid and attributed to the kinetic isotope effect (KIE). This research provides addnl. exptl. constraints on interpreting Hg isotope signatures with important implications for the use of Hg isotope fractionation as a tracer of the Hg biogeochem. cycle.

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25. 25

    Hu, H.; Lin, H.; Zheng, W.; Rao, B.; Feng, X. B.; Liang, L.; Elias, D. A.; Gu, B. Mercury reduction and cell-surface adsorption by Geobacter sulfurreducens PCA. Environ. Sci. Technol. 2013, 47, 10922– 10930,  DOI: 10.1021/es400527m

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    25

    Mercury Reduction and Cell-Surface Adsorption by Geobacter sulfurreducens PCA

    Hu, Haiyan; Lin, Hui; Zheng, Wang; Rao, Balaji; Feng, Xinbin; Liang, Liyuan; Elias, Dwayne A.; Gu, Baohua

    Environmental Science & Technology (2013), 47 (19), 10922-10930CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Both redn. and surface adsorption of mercuric mercury [Hg-(II)] are found to occur simultaneously on G. sulfurreducens PCA cells under dark, anaerobic conditions. Redn. of Hg-(II) to elemental Hg(0) initially follows a pseudo-first order kinetics with a half-life of <2 h in the presence of 50 nM Hg-(II) and 1011 cells L-1 in a phosphate buffer (pH 7.4). Multiple gene deletions of the outer membrane cytochromes in this organism resulted in a decrease in redn. rate from ∼0.3 to 0.05 h-1, and redn. was nearly absent with heat-killed cells or in the cell filtrate. Adsorption of Hg-(II) by cells is found to compete with, and thus inhibit, Hg-(II) redn. Depending on the Hg to cell ratio, max. Hg-(II) redn. was obsd. at about 5 × 10-19 mol Hg cell-1, but redn. terminated at a low Hg to cell ratio (<10-20 mol Hg cell-1). This inhibitory effect is attributed to bonding between Hg-(II) and the thiol (-SH) functional groups on cells and validated by expts. in which the sorbed Hg-(II) was readily exchanged by thiols (e.g., glutathione) but not by carboxylate compds. such as ethylenediamine-tetraacetate (EDTA). We suggest that coupled Hg-(II)-cell interactions, i.e., redn. and surface binding, could be important in controlling Hg species transformation and bioavailability and should therefore be considered in microbial Hg-(II) uptake and methylation studies.

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26. 26

    Boszke, L.; Kowalski, A.; Glosinska, G.; Szarek, R.; Siepak, J. Environmental factors affecting speciation of mercury in the bottom sediments; an overview. Pol. J. Environ. Stud. 2003, 12 (1), 5– 13

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    26

    Environmental factors affecting speciation of mercury in the bottom sediments; an overview

    Boszke, L.; Kowalski, A.; Glosinska, G.; Szarek, R.; Siepak, J.

    Polish Journal of Environmental Studies (2003), 12 (1), 5-13CODEN: PJESE2; ISSN:1230-1485. (HARD Publishing Co.)

    A review concerning selected factors affecting Hg species distribution and behavior in bottom sediment is given. Topics discussed include: Hg species in bottom sediment; inorg. S and Hg species; microbiol. processes and Hg speciation; hydrobiol. aspects of Hg speciation; org. matter and Hg speciation; iron and manganese hydroxides and Hg speciation; redox conditions effect on Hg speciation; pH effect on Hg release from the environmental matrix; thermal effect (kinetic processes); and salt effect.

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27. 27

    Farrell, R. E.; Huang, P. M.; Germida, J. J. Biomethylation of mercury(II) adsorbed on mineral colloids common in freshwater sediments. Appl. Organomet. Chem. 1998, 12 (8–9), 613– 620,  DOI: 10.1002/(SICI)1099-0739(199808/09)12:8/9<613::AID-AOC769>3.0.CO;2-7

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    27

    Biomethylation of mercury(II) adsorbed on mineral colloids common in freshwater sediments

    Farrell, R. E.; Huang, P. M.; Germida, J. J.

    Applied Organometallic Chemistry (1998), 12 (8/9), 613-620CODEN: AOCHEX; ISSN:0268-2605. (John Wiley & Sons Ltd.)

    The effect of freshwater sediment components such as kaolinite, montmorillonite, and birnessite (δ-MnO2) on the biomethylation of Hg2+ in a synthetic growth medium (M-IIY) was assessed. Addns. of kaolinite or montmorillonite to media contg. [Hg(NO3)2; 12 μg Hg/mL] had no significant effect on either bacterial growth or prodn. of CH3Hg+. However, whereas adding birnessite resulted in only a small (∼4%) increase in bacterial growth, it also produced a significant decrease (∼50%) in CH3Hg+ prodn. Further, it was demonstrated that, with the exception of kaolinite, adsorption of Hg2+ onto sediment components before they were added to the M-IIY medium decreased its bioavailability, i.e., the amt. of CH3Hg+ produced from adsorbed Hg2+ was significantly lower than that produced from equiv. concns. of Hg(NO3)2 in the absence of mineral colloids. For montmorillonite, CH3Hg+ prodn. was decreased by 21% relative to the control system. Most striking was the case of birnessite, in which no CH3Hg+ was detected after a 25 h incubation period, and only very small quantities of CH3Hg+ (3-7 ng/L) were present in the medium after 336 h. These data demonstrated that mineral colloids common in freshwater sediments significantly affect the extent of biomethylation of Hg2+ adsorbed on their surfaces. Birnessite, in particular, is a very effective inhibitor of the biomethylation of surface-bound Hg2+. Therefore, it may be possible to reduce the severity of Hg pollution in some aquatic environments by adding a reactive MnO, such as birnessite, to the system and thereby to inhibit the transformation (methylation) of inorg. Hg2+ into the much more toxic CH3Hg+ species.

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28. 28

    Zhao, L.; Li, Y.; Zhang, L.; Zheng, J.; Pierce, E. M.; Gu, B. Mercury adsorption on minerals and its effect on microbial methylation. ACS Earth Space Chem. 2019, 3, 1338– 1345,  DOI: 10.1021/acsearthspacechem.9b00039

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    28

    Mercury Adsorption on Minerals and Its Effect on Microbial Methylation

    Zhao, Linduo; Li, Yunzi; Zhang, Lijie; Zheng, Jianqiu; Pierce, Eric M.; Gu, Baohua

    ACS Earth and Space Chemistry (2019), 3 (7), 1338-1345CODEN: AESCCQ; ISSN:2472-3452. (American Chemical Society)

    Adsorbed or solid-phase inorg. mercury [Hg(II)] is commonly assumed immobile or less bioavailable for microbial uptake, although recent studies suggest that mineral-adsorbed Hg(II) is at least partially available for cell uptake and methylation. This study examd. the adsorption of Hg(II) onto two ref. minerals, hematite and montmorillonite, and evaluated Hg(II) uptake and methylation by a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 in lab. incubations. Mineral-adsorbed Hg(II) on both hematite and montmorillonite was not only available for cell uptake and methylation but also resulted in a 2-3-fold increased methylmercury prodn. compared to the mineral-free incubation. An optimal Hg(II) methylation was obsd. at a low to moderate mineral/soln. ratio (1-5 g L-1) with fixed Hg(II) (25 nM) and cell concns. The result could be explained by decreased cellular immobilization of Hg(II) but enhanced close interactions between Hg(II) and cells both adsorbed or concd. on mineral surfaces, leading to increased methylation. However, a high mineral/soln. ratio inhibited Hg(II) methylation, likely as a result of a low Hg(II) coverage (per surface area) at high mineral loadings, which limit close contacts between Hg(II) and the cells. These results indicate that mineral-adsorbed Hg(II) may be directly available for microbial uptake or methylation, although whether the adsorption enhances or inhibits Hg(II) methylation may depend upon microniches, where Hg(II), microbes, and minerals co-exist in the natural environment. We suggest that future studies are performed to establish quant. relationships of bioavailable Hg(II) with not only the dissolved but also adsorbed Hg(II) species to improve model predictions of Hg(II) fate and transformations.

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29. 29

    Miller, C. L.; Liang, L.; Gu, B. Competitive ligand exchange reveals time dependant changes in the reactivity of Hg–dissolved organic matter complexes. Environ. Chem. 2012, 9 (6), 495– 501,  DOI: 10.1071/EN12096

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    29

    Competitive ligand exchange reveals time dependant changes in the reactivity of Hg-dissolved organic matter complexes

    Miller, Carrie L.; Liang, Liyuan; Gu, Baohua

    Environmental Chemistry (2012), 9 (6), 495-501CODEN: ECNHAA; ISSN:1449-8979. (CSIRO Publishing)

    Environmental contextMercury, a globally important pollutant, undergoes transformations in the environment to form methylmercury that is toxic to humans. Naturally occurring dissolved org. matter is a controller in these transformations, and we demonstrate that its strength of interaction with mercury is time dependent. These changes in complexation with dissolved org. matter are likely to affect mercury's reactivity in aquatic systems, thereby influencing how mercury is methylated and bioaccumulated. Mercury interactions with dissolved org. matter (DOM) are important in aquatic environments but the kinetics of Hg binding to and repartitioning within the DOM remain poorly understood. We examd. changes in Hg-DOM complexes using glutathione (GSH) titrns., coupled with stannous-reducible Hg measurements during Hg equilibration with DOM. In lab. prepd. DOM solns. and in water from a Hg-contaminated creek, a fraction of the Hg present as Hg-DOM complexes did not react to GSH addn. This unreactive Hg fraction increased with time from 13% at 1h to 74% after 48h of equilibration with a Suwannee River DOM. In East Fork Poplar Creek water in Oak Ridge, Tennessee, ∼58% of the DOM-complexed Hg was unreactive with GSH 1h after the sample was collected. This time-dependent increase in unreactive Hg suggests that Hg forms stronger complexes with DOM over time. Alternatively the DOM-complexed Hg may become more sterically protected from the ligand exchange reactions, as the binding environment changes within the DOM over time. These results have important implications to understanding Hg transformations in the natural environment, particularly in contaminated aquatic systems due to non-equil. interactions between Hg and DOM.

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30. 30

    Peretyazhko, T.; Sposito, G. Reducing capacity of terrestrial humic acids. Geoderma 2006, 137 (1–2), 140– 146,  DOI: 10.1016/j.geoderma.2006.08.004

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    30

    Reducing capacity of terrestrial humic acids

    Peretyazhko, Tanya; Sposito, Garrison

    Geoderma (2006), 137 (1-2), 140-146CODEN: GEDMAB; ISSN:0016-7061. (Elsevier B.V.)

    The role of terrestrial humic substances as electron shuttles in bioredn. processes has gained broad acceptance as recognition has grown that the ability to transfer electrons to humic materials is distributed widely among microorganisms in nature. A fundamental property of humic substances pertinent to their mediation of reductive transformations is the max. moles of electron charge they can transfer to an added oxidant, a parameter for which the name Reducing Capacity has been suggested. A no. of different operational definitions of this important parameter have appeared in the literature recently, leading to conflicting terminol. that has not heretofore been rationalized. In this paper, we present a consistent set of independent definitions of Reducing Capacity and develop lab. methodologies for applying them, illustrating our concepts and methods with representative International Humic Substances Society (IHSS) humic acids that have been widely studied in connection with electron shuttling. Our principal results are: (1) non-negligible Reducing Capacity for humic acid (HA) maintained under oxic conditions, indicating that important reductant functional groups persist in humic substances, and (2) Reducing Capacity of chem.-reduced HA equal, within exptl. precision, to that for microbially-reduced HA, indicating that chem. redn. can be used as a convenient lab. method to assess the capacity of HA to be reduced by microorganisms. Our results also demonstrate that complexed Fe contributes negligibly to the Reducing Capacity of HA. We further illustrate our proposed definitions by applying them to interpret some published field data on the Reducing Capacity profile of HA measured in a freshwater lake sediment exhibiting a pronounced redox zonation.

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31. 31

    Brooks, S. C.; Southworth, G. R. History of mercury use and environmental contamination at the Oak Ridge Y-12 Plant. Environ. Pollut. 2011, 159 (1), 219– 228,  DOI: 10.1016/j.envpol.2010.09.009

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    31

    History of mercury use and environmental contamination at the Oak Ridge Y-12 Plant

    Brooks, Scott C.; Southworth, George R.

    Environmental Pollution (Oxford, United Kingdom) (2011), 159 (1), 219-228CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)

    A review. Between 1950 and 1963 approx. 11 million kilograms of mercury (Hg) were used at the Oak Ridge Y-12 National Security Complex (Y-12 NSC) for lithium isotope sepn. processes. About 3% of the Hg was lost to the air, soil and rock under facilities, and East Fork Poplar Creek (EFPC) which originates in the plant site. Smaller amts. of Hg were used at other Oak Ridge facilities with similar results. Although the primary Hg discharges from Y-12 NSC stopped in 1963, small amts. of Hg continue to be released into the creek from point sources and diffuse contaminated soil and groundwater sources within Y-12 NSC. Mercury concn. in EFPC has decreased 85% from ∼2000 ng/L in the 1980s. In general, methylmercury concns. in water and in fish have not declined in response to improvements in water quality and exhibit trends of increasing concn. in some cases. Mercury discharges from an industrial plant have created a legacy contamination problem exhibiting complex and at times counter-intuitive patterns in Hg cycling.

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32. 32

    Gu, B.; Mishra, B.; Miller, C.; Wang, W.; Lai, B.; Brooks, S. C.; Kemner, K. M.; Liang, L. X-ray fluorescence mapping of mercury on suspended mineral particles and diatoms in a contaminated freshwater system. Biogeosciences 2014, 11 (18), 5259– 5267,  DOI: 10.5194/bg-11-5259-2014

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    There is no corresponding record for this reference.
33. 33

    Margel, S.; Hirsh, J. Reduction of organic mercury in water, urine, and blood by sodium-borohydride for direct determination of total mercury content. Clin. Chem. 1984, 30 (2), 243– 245,  DOI: 10.1093/clinchem/30.2.243

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    33

    Reduction of organic mercury in water, urine, and blood by sodium borohydride for direct determination of total mercury content

    Margel, Shlomo; Hirsh, Joseph

    Clinical Chemistry (Washington, DC, United States) (1984), 30 (2), 243-5CODEN: CLCHAU; ISSN:0009-9147.

    The optimal conditions for use of NaBH4 as the reducing agent before the direct detn. of Hg in water, urine, and blood by at. absorption spectroscopy were established. The effects of pH, temp., and CuSO4 concn. on the direct detn. of both org. and inorg. compds. of Hg were evaluated. Accurate and precise quantification of Hg requires that the pH be between 9.3 and 9.5, the reaction temp. >25°, the reaction time >1 min, and, for urine samples only, the CuSO4 concn. 10 μmol/L. The detection limit of the method is 1-2 ng and the precision is 3.8% for blood and 4.0% for urine.

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34. 34

    Kenduzler, E.; Ates, M.; Arslan, Z.; McHenry, M.; Tchounwou, P. B. Determination of mercury in fish otoliths by cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS). Talanta 2012, 93, 404– 410,  DOI: 10.1016/j.talanta.2012.02.063

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    34

    Determination of mercury in fish otoliths by cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS)

    Kenduzler, Erdal; Ates, Mehmet; Arslan, Zikri; McHenry, Melanie; Tchounwou, Paul B.

    Talanta (2012), 93 (), 404-410CODEN: TLNTA2; ISSN:0039-9140. (Elsevier B.V.)

    A method based on cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS) has been developed for detn. of inorg. mercury, Hg(II), and total mercury in fish otoliths. NaBH4 was used as the only reducing agent and its concn. was optimized across an acidity gradient to selectively reduce Hg(II) without affecting methylmercury, CH3Hg(I). Inorg. Hg was quant. reduced to elemental Hg0 with 1 × 10-4% (m/v) NaBH4. CH3Hg(I) required a min. of 0.5% (m/v) NaBH4 for complete redn. Increasing the HCl concn. of soln. to 5% (vol./vol.) improved the selectivity toward Hg(II) as it decreased the signals from CH3Hg(I) to baseline levels. Potassium ferricyanide soln. was the most effective in eliminating the memory effects of Hg compared with a no. of chelating and oxidizing agents, including EDTA, gold chloride, thiourea, cerium ammonium nitrate and 2-mercaptoethylamine chloride. The relative std. deviation (RSD) was less than 5% for 1.0 μg L-1 Hg(II) soln. The detection limits were 4.2 and 6.4 ng L-1 (ppt) for Hg(II) and total Hg, resp. Sample dissoln. conditions and recoveries were examd. with ultra-pure CaCO3 (99.99%) spiked with Hg(II) and CH3HgCl. Methylmercury was stable when dissoln. was performed with up to 20% (vol./vol.) HCl at 100 °C. Recoveries from spiked solns. were higher than 95% for both Hg(II) and CH3Hg(I). The method was applied to the detn. of Hg(II) and total Hg concns. in the otoliths of red emperor (CRM 22) and Pacific halibut. Total Hg concn. in the otoliths was 0.038 ± 0.004 μg g-1 for the red emperor and 0.021 ± 0.003 μg g-1 for the Pacific halibut. Inorg. Hg accounted for about 25% of total Hg indicating that Hg in the otoliths was predominantly org. mercury (e.g., methylmercury). However, as opposed to the bioaccumulation in tissues, methylmercury levels in otoliths was very low suggesting a different route of uptake, most likely through the deposition of methylmercury available in the water.

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35. 35

    Zhang, L.; Liang, X.; Wang, Q.; Zhang, Y.; Yin, X.; Lu, X.; Pierce, E. M.; Gu, B. Isotope exchange between mercuric [Hg(II)] chloride and Hg(II) bound to minerals and thiolate ligands: implications for enriched isotope tracer studies. Geochim. Cosmochim. Acta 2021, 292, 468– 481,  DOI: 10.1016/j.gca.2020.10.013

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    35

    Isotope exchange between mercuric [Hg(II)] chloride and Hg(II) bound to minerals and thiolate ligands: Implications for enriched isotope tracer studies

    Zhang, Lijie; Liang, Xujun; Wang, Quanying; Zhang, Yaoling; Yin, Xiangping; Lu, Xia; Pierce, Eric M.; Gu, Baohua

    Geochimica et Cosmochimica Acta (2021), 292 (), 468-481CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)

    Enriched mercury (Hg) stable isotopes have been widely used as tracers in field and lab. investigations of Hg(II) biogeochem. transformations such as methylation and demethylation. Few studies, however, have considered concurrent isotope exchange reactions between newly spiked and pre-existing Hg(II) in environmental matrixes, which may alter redistribution and thus transformation of the spiked and pre-existing Hg(II). Using enriched 198Hg [as mercuric Hg(II) or HgCln species], this study investigated isotope exchange between 198Hg and pre-existing Hg(II) bound to metacinnabar (β-HgS), sediments, low-mol.-wt. (LMW) thiols, and dissolved org. matter (DOM). The impact of isotope exchange on methylmercury prodn. in the presence of org. ligands was also evaluated with an iron-reducing bacterium Geobacter sulfurreducens PCA in a phosphate buffered soln. (pH 7.4). We found that spiked 198Hg readily exchanged with mineral-bound ambient Hg(II) despite concurrent Hg(II) adsorption and immobilization on the solids. Rapid exchange (<3 min) was also obsd. between spiked 198Hg and 200Hg pre-equilibrated with LMW thiols and DOM in soln. While the exchange did not cause net changes in Hg(II) chem. speciation, it resulted in redistribution of Hg(II) isotopes bound to the ligands and thus an apparently similar methylation rate and magnitude of the spiked 198Hg and pre-existing 200Hg by PCA cells when 198Hg and 200Hg were added at 1:1 ratio. These observations underscore the importance of isotope exchange when an enriched Hg isotope is applied in environmental matrixes, as the exchange could potentially lead to biased rate calcns. of Hg(II) transformation and bioaccumulation and thus risk assessments of new Hg(II) input to the natural ecosystems.

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36. 36

    Wang, Q.; Zhang, L.; Liang, X.; Yin, X.; Zhang, Y.; Zheng, W.; Pierce, E. M.; Gu, B. Rates and mechanisms of isotope exchange between dissolved elemental Hg(0) and Hg(II)-bound to organic and inorganic ligands. Environ. Sci. Technol. 2020, 54, 15534– 15545,  DOI: 10.1021/acs.est.0c06229

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    36

    Rates and dynamics of mercury isotope exchange between dissolved elemental Hg(0) and Hg(II) bound to organic and inorganic ligands

    Wang, Quanying; Zhang, Lijie; Liang, Xujun; Yin, Xiangping; Zhang, Yaoling; Zheng, Wang; Pierce, Eric M.; Gu, Baohua

    Environmental Science & Technology (2020), 54 (23), 15534-15545CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Mercury (Hg) isotope exchange is a common process in biogeochem. transformations of Hg in the environment, but it is unclear whether and at what rates dissolved elemental Hg(0)aq may exchange with divalent Hg(II) bound to various org. and inorg. ligands in water. Using enriched stable isotopes, we investigated the rates and dynamics of isotope exchange between 202Hg(0)aq and 201Hg(II) bound to org. and inorg. ligands with varying chem. structures and binding affinities. Time-dependent exchange reactions were followed by isotope compositional changes using both inductively coupled plasma mass spectrometry and Zeeman cold vapor at. absorption spectrometry. Rapid, spontaneous isotope exchange (<1 h) was obsd. between 202Hg(0)aq and 201Hg(II) bound to chloride (Cl-), ethylenediaminetetraacetate (EDTA), and thiols, such as cysteine (CYS), glutathione (GSH), and 2,3-dimercaptopropanesulfonic acid (DMPS) at a thiol ligand-to-Hg(II) molar ratio of 1:1. Without external reductants or oxidants, the exchange resulted in transfer of two electrons and redistribution of Hg isotopes bound to the ligand but no net changes of chem. species in the system. However, an increase in the ligand-to-Hg(II) ratio decreased the exchange rates due to the formation of 2:1 or higher thiol:Hg(II) chelated complexes, but had no effects on exchange rates with 201Hg(II) bound to EDTA or Cl-. The exchange between 202Hg(0)aq and 201Hg(II) bound to dissolved org. matter (DOM) showed an initially rapid followed by a slower exchange rate, likely resulting from Hg(II) complexation with both low- and high-affinity binding functional groups on DOM (e.g., carboxylates vs bidentate thiolates). These results demonstrate that Hg(0)aq readily exchanges with Hg(II) bound to various ligands and highlight the importance of considering exchange reactions in exptl. enriched Hg isotope tracer studies or in natural abundance Hg isotope studies in environmental matrixes.

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37. 37

    Zhang, L.; Wu, S.; Zhao, L.; Lu, X.; Pierce, E. M.; Gu, B. Mercury sorption and desorption on organo-mineral particulates as a source for microbial methylation. Environ. Sci. Technol. 2019, 53, 2426– 2433,  DOI: 10.1021/acs.est.8b06020

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    37

    Mercury Sorption and Desorption on Organo-Mineral Particulates as a Source for Microbial Methylation

    Zhang, Lijie; Wu, Shan; Zhao, Linduo; Lu, Xia; Pierce, Eric M.; Gu, Baohua

    Environmental Science & Technology (2019), 53 (5), 2426-2433CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    In natural freshwater and sediments, mercuric mercury (Hg(II)) is largely assocd. with particulate minerals and orgs., but it remains unclear under what conditions particulates may become a sink or a source for Hg(II) and whether the particulate-bound Hg(II) is bioavailable for microbial uptake and methylation. In this study, we investigated Hg(II) sorption-desorption characteristics on three organo-coated hematite particulates and a Hg-contaminated natural sediment and evaluated the potential of particulate-bound Hg(II) for microbial methylation. Mercury rapidly sorbed onto particulates, esp. the cysteine-coated hematite and sediment, with little desorption obsd. (0.1-4%). However, the presence of Hg-binding ligands, such as low-mol.-wt. thiols and humic acids, resulted in up to 60% of Hg(II) desorption from the Hg-laden hematite particulates but <6% from the sediment. Importantly, the particulate-bound Hg(II) was bioavailable for uptake and methylation by a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under anaerobic incubations, and the methylation rate was 4-10 times higher than the desorption rate of Hg(II). These observations suggest direct contacts and interactions between bacterial cells and the particulate-bound Hg(II), resulting in rapid exchange or uptake of Hg(II) by the bacteria. The results highlight the importance of Hg(II) partitioning at particulate-water interfaces and the role of particulates as a significant source of Hg(II) for methylation in the environment.

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38. 38

    Yin, X.; Wang, L.; Zhang, L.; Chen, H.; Liang, X.; Lu, X.; DiSpirito, A. A.; Semrau, J.; Gu, B. Synergistic effects of a chalkophore, methanobactin, on microbial methylation of mercury. Appl. Environ. Microbiol. 2020, 86, e00122-20,  DOI: 10.1128/AEM.00122-20

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    There is no corresponding record for this reference.
39. 39

    Lu, X.; Zhao, J.; Liang, X.; Zhang, L.; Liu, Y.; Yin, X.; Li, X.; Gu, B. The application and potential artifacts of Zeeman cold vapor atomic absorption spectrometry in mercury stable isotope analysis. Environ. Sci. Technol. Lett. 2019, 6, 165– 170,  DOI: 10.1021/acs.estlett.9b00067

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    39

    The Application and Potential Artifacts of Zeeman Cold Vapor Atomic Absorption Spectrometry in Mercury Stable Isotope Analysis

    Lu, Xia; Zhao, Jiangtao; Liang, Xujun; Zhang, Lijie; Liu, Yurong; Yin, Xiangping; Li, Xiangkai; Gu, Baohua

    Environmental Science & Technology Letters (2019), 6 (3), 165-170CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)

    Zeeman cold vapor at. absorption spectrometry (CVAAS) has been widely used for environmental mercury (Hg) detection and quantification for decades, but little is known about its utility and potential artifacts in analyzing Hg with varying isotope compns. We show that each Hg isotope responds differently by CVAAS anal., with 200Hg and 202Hg isotopes exhibiting signal intensities ∼10 times greater than those of 198Hg and 201Hg isotopes. However, all Hg isotopes show a linear correlation between Hg concn. and signal intensity, validated by both measurements and theor. simulations. Zeeman CVAAS could thus offer a convenient, inexpensive tool for detg. Hg isotopes, particularly in using one or two enriched Hg isotopes for tracing Hg biogeochem. transformations, such as partitioning, ion exchange, sorption-desorption, and methylation-demethylation in environmental matrixes. We also caution that care must be taken when CVAAS is used for quantifying Hg in samples with changing isotope compns. to avoid measurement errors.

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40. 40

    Zhang, L.; Kang-Yun, C.; Lu, X.; Chang, J.; Liang, X.; Pierce, E. M.; Semrau, J.; Gu, B. Adsorption and intracellular uptake of mercuric mercury and methylmercury by methanotrophs and methylating bacteria. Environ. Pollut. 2023, 331, 121790,  DOI: 10.1016/j.envpol.2023.121790

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    40

    Adsorption and intracellular uptake of mercuric mercury and methylmercury by methanotrophs and methylating bacteria

    Zhang, Lijie; Kang-Yun, Christina S.; Lu, Xia; Chang, Jin; Liang, Xujun; Pierce, Eric M.; Semrau, Jeremy D.; Gu, Baohua

    Environmental Pollution (Oxford, United Kingdom) (2023), 331 (Part_1), 121790CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)

    The cell surface adsorption and intracellular uptake of mercuric mercury Hg(II) and methylmercury (MeHg) are important in detg. the fate and transformation of Hg in the environment. However, current information is limited about their interactions with two important groups of microorganisms, i.e., methanotrophs and Hg(II)-methylating bacteria, in aquatic systems. This study investigated the adsorption and uptake dynamics of Hg(II) and MeHg by three strains of methanotrophs, Methylomonas sp. strain EFPC3, Methylosinus trichosporium OB3b, and Methylococcus capsulatus Bath, and two Hg(II)-methylating bacteria, Pseudodesulfovibrio mercurii ND132 and Geobacter sulfurreducens PCA. Distinctive behaviors of these microorganisms towards Hg(II) and MeHg adsorption and intracellular uptake were obsd. The methanotrophs took up 55-80% of inorg. Hg(II) inside cells after 24 h incubation, lower than methylating bacteria (>90%). Approx. 80-95% of MeHg was rapidly taken up by all the tested methanotrophs within 24 h. In contrast, after the same time, G. sulfurreducens PCA adsorbed 70% but took up <20% of MeHg, while P. mercurii ND132 adsorbed <20% but took up negligible amts. of MeHg. These results suggest that microbial surface adsorption and intracellular uptake of Hg(II) and MeHg depend on the specific types of microbes and appear to be related to microbial physiol. that requires further detailed investigation. Despite being incapable of methylating Hg(II), methanotrophs play important roles in immobilizing both Hg(II) and MeHg, potentially influencing their bioavailability and trophic transfer. Therefore, methanotrophs are not only important sinks for methane but also for Hg(II) and MeHg and can influence the global cycling of C and Hg.

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41. 41

    Zheng, W.; Lin, H.; Mann, B. F.; Liang, L.; Gu, B. Oxidation of dissolved elemental mercury by thiol compounds under anoxic conditions. Environ. Sci. Technol. 2013, 47, 12827– 12834,  DOI: 10.1021/es402697u

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    41

    Oxidation of dissolved elemental mercury by thiol compounds under anoxic conditions

    Zheng, Wang; Lin, Hui; Mann, Benjamin F.; Liang, Liyuan; Gu, Baohua

    Environmental Science & Technology (2013), 47 (22), 12827-12834CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Mercuric ion, Hg2+, forms strong complexes with thiolate compds. that commonly dominate Hg-(II) speciation in natural freshwater. However, reactions between dissolved aq. elemental mercury (Hg(0)aq) and org. ligands in general, and thiol compds. in particular, are not well studied although these reactions likely affect Hg speciation and cycling in the environment. In this study, we compared the reaction rates between Hg(0)aq and a no. of selected org. ligands with varying mol. structures and sulfur (S) oxidn. states in dark, anoxic conditions to assess the role of these ligands in Hg(0)aq oxidn. Significant Hg(0)aq oxidn. was obsd. with all thiols but not with ligands contg. no S. Compds. with oxidized S (e.g., disulfide) exhibited little or no reactivity toward Hg(0)aq either at pH 7. The rate and extent of Hg(0)aq oxidn. varied greatly depending on the chem. and structural properties of thiols, thiol/Hg ratios, and the presence or absence of electron acceptors. Smaller aliph. thiols and higher thiol/Hg ratios resulted in higher Hg(0)aq oxidn. rates than larger arom. thiols at lower thiol/Hg ratios. The addn. of electron acceptors (e.g., humic acid) also led to substantially increased Hg(0)aq oxidn. Our results suggest that thiol-induced oxidn. of Hg(0)aq is important under anoxic conditions and can affect Hg redox transformation and bioavailability for microbial methylation.

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42. 42

    Lamborg, C. H.; Tseng, C. M.; Fitzgerald, W. F.; Balcom, P. H.; Hammerschmidt, C. R. Determination of the mercury complexation characteristics of dissolved organic matter in natural waters with ″reducible Hg″ titrations. Environ. Sci. Technol. 2003, 37, 3316– 3322,  DOI: 10.1021/es0264394

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    42

    Determination of the Mercury Complexation Characteristics of Dissolved Organic Matter in Natural Waters with "Reducible Hg" Titrations

    Lamborg, Carl H.; Tseng, Chun-Mao; Fitzgerald, William F.; Balcom, Prentiss H.; Hammerschmidt, Chad R.

    Environmental Science and Technology (2003), 37 (15), 3316-3322CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    A new method for the detn. of the concn. and conditional stability const. of dissolved org. matter that binds mercury has been developed using an in vitro assay of reducible Hg. The technique is a wet chem. analog of electrochem. approaches now in use for ligand studies of many other trace transition metals in natural waters. Ligand characteristics are obtained from addns. of ionic Hg to buffered lake water, river water, and seawater and detn. of the wet chem. reducible fraction following equilibration of the spike. This approach is robust, as demonstrated by (i) anal. using three reducing agents of varying strengths, (ii) replicate analyses, (iii) comparison to well-characterized complexing species (chloride and EDTA) using a competitive ion-exchange resin, and (iv) kinetic studies. The results indicate that Hg-complexing equiv. are present in the dissolved phase (<0.2 μm) ranging from <1 to >60nN concns. and with log conditional stability consts. (log K') in the range of 21-24. Only one ligand class was found in the natural waters analyzed. There was indirect evidence for a class of org. ligands that formed reducible complexes with Hg in freshwater. Such ligand characteristics indicate that the vast majority of ionic inorg. Hg dissolved in freshwater and coastal saltwaters is assocd. with org. complexes. Concns., affinities, and kinetics implicate multidentate chelation sites as the principal complexing moieties for Hg and discourage the use of humic carboxylic acids as a proxy for the ligands/functional groups.

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43. 43

    Miller, C.; Southworth, G.; Brooks, S. C.; Liang, L.; Gu, B. Kinetic controls on the complexation between mercury and dissolved organic matter in a contaminated environment. Environ. Sci. Technol. 2009, 43, 8548– 8553,  DOI: 10.1021/es901891t

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    43

    Kinetic Controls on the Complexation between Mercury and Dissolved Organic Matter in a Contaminated Environment

    Miller, Carrie L.; Southworth, George; Brooks, Scott; Liang, Liyuan; Gu, Baohua

    Environmental Science & Technology (2009), 43 (22), 8548-8553CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    The interaction of Hg with dissolved natural org. matter (NOM) under equil. conditions is the focus of many studies but the kinetic controls on Hg-NOM complexation in aquatic systems have often been overlooked. We examd. the rates of Hg-NOM complexation both in a contaminated Upper East Fork Poplar Creek (UEFPC) in Oak Ridge, Tennessee, and in controlled lab. expts. using reducible Hg (HgR) measurements and C18 solid phase extn. techniques. Of the filterable Hg at the headwaters of UEFPC, >90% was present as HgR and this fraction decreased downstream but remained >29% of the filterable Hg at all sites. The presence of higher HgR concns. than would be predicted under equil. conditions in UEFPC and in expts. with a NOM isolate suggests that kinetic reactions are controlling the complexation between Hg and NOM. The slow formation of Hg-NOM complexes is attributed to competitive ligand exchange among various moieties and functional groups in NOM with a range of binding strengths and configurations. This study demonstrates the need to consider the effects of Hg-NOM complexation kinetics on processes such as Hg methylation and solid phase partitioning.

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44. 44

    Dong, W.; Bian, Y.; Liang, L.; Gu, B. Binding constants of mercury and dissolved organic matter determined by a modified ion exchange technique. Environ. Sci. Technol. 2011, 45 (8), 3576– 3583,  DOI: 10.1021/es104207g

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    44

    Binding Constants of Mercury and Dissolved Organic Matter Determined by a Modified Ion Exchange Technique

    Dong, Wenming; Bian, Yongrong; Liang, Liyuan; Gu, Baohua

    Environmental Science & Technology (2011), 45 (8), 3576-3583CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    Ion-exchange techniques have been widely used for detg. the conditional stability consts. (logK) between dissolved org. matter (DOM) and various metal ions in aq. solns. An exception is Hg2+ whose exceedingly strong binding with reduced S or thiol-like functional groups in DOM makes the ion exchange reactions difficult. Using a Hg-selective thiol resin, we developed a modified ion-exchange technique which overcomes this limitation. This technique allows not only the detn. of binding consts. between Hg2+ and DOM of varying origins, but also the discrimination of complexes with varying coordination nos. [i.e., 1:1 and 1:2 Hg:thiol-ligand (HgL) complexes]. Measured logK values of 4 selected DOM isolates varied slightly, 21.9-23.6 for 1:1 HgL complexes, and 30.1-31.6 for 1:2 HgL2 complexes. These results suggest similar binding modes that are likely occurring between Hg2+ and key thiolate functional groups in DOM particularly at a relatively low Hg to DOM ratio. Future studies should further elucidate the nature and precise stoichiometries of binding between Hg2+ and DOM at environmentally relevant concns.

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45. 45

    Skyllberg, U.; Qian, J.; Frech, W. Combined XANES and EXAFS study on the bonding of methyl mercury to thiol group in soil and aquatic organic matter. Phys. Scr. 2005, T115, 894– 896,  DOI: 10.1238/Physica.Topical.115a00894

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    45

    Combined XANES and EXAFS study on the bonding of methyl mercury to thiol groups in soil and aquatic organic matter

    Skyllberg, U.; Qian, J.; Frech, W.

    Physica Scripta, T (2005), T115 (12th X-Ray Absorption Fine Structure International Conference (XAFS12), 2003), 894-896CODEN: PHSTER; ISSN:0281-1847. (Royal Swedish Academy of Sciences)

    The authors combined x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopy to det. the coordination chem. of Me mercury (MeHg) in natural org. matter from an org. soil (OS), potentially sol. org. matter extd. from the soil (PSOS) and in a humic stream draining the soil (SOS). The sum of concns. of highly reduced org. S groups (Org-SRED), such as thiol (RSH), sulfide (RSR) and disulfide (RSSR), was 39, 42 and 47% of total S in SOS, PSOS and OS, resp. No traces of inorg. sulfides were detected. Hg LIII-edge EXAFS anal. of samples with added MeHg yielded MeHg/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 Å and to one S atom at an av. distance of 2.34 ± 0.03 Å, in the first coordination shell. At higher MeHg/Org-SRED ratios RSH groups were satd. and O and/or N atoms gradually took part in the bonding. Based on the assumption that RSH is the only S group accounting for the very strong complexation of MeHg, approx. 17% of total org. S consisted of RSH groups in the org. soil, 14% in potentially sol. org. matter extd. from soil and 9% in aquatic org. matter.

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46. 46

    Song, Y.; Jiang, T.; Liem-Nguyen, V.; Sparrman, T.; Bjorn, E.; Skyllberg, U. Thermodynamics of Hg(II) bonding to thiol groups in suwannee river natural organic matter resolved by competitive ligand exchange, Hg L-III-edge EXAFS and H-1 NMR spectroscopy. Environ. Sci. Technol. 2018, 52 (15), 8292– 8301,  DOI: 10.1021/acs.est.8b00919

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    46

    Thermodynamics of Hg(II) Bonding to Thiol Groups in Suwannee River Natural Organic Matter Resolved by Competitive Ligand Exchange, Hg LIII-Edge EXAFS and 1H NMR Spectroscopy

    Song, Yu; Jiang, Tao; Liem-Nguyen, Van; Sparrman, Tobias; Bjoern, Erik; Skyllberg, Ulf

    Environmental Science & Technology (2018), 52 (15), 8292-8301CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    A mol. level understanding of the thermodn. and kinetics of the chem. bonding between mercury, Hg(II), and natural org. matter (NOM) assocd. thiol functional groups (NOM-RSH) is required if bioavailability and transformation processes of Hg in the environment are to be fully understood. This study provides the thermodn. stability of the Hg(NOM-RS)2 structure using a robust method in which cysteine (Cys) served as a competing ligand to NOM (Suwannee River 2R101N sample) assocd. RSH groups. The concn. of the latter was quantified to be 7.5 ± 0.4 μmol g-1 NOM by Hg LIII-edge EXAFS spectroscopy. The Hg(Cys)2 mol. concn. in chem. equil. with the Hg(II)-NOM complexes was directly detd. by HPLC-ICPMS and losses of free Cys due to secondary reactions with NOM was accounted for in expts. using 1H NMR spectroscopy and 13C isotope labeled Cys. The log K ± SD for the formation of the Hg(NOM-RS)2 mol. structure, Hg2+ + 2NOM-RS- = Hg(NOM-RS)2, and for the Hg(Cys)(NOM-RS) mixed complex, Hg2+ + Cys- + NOM-RS- = Hg(Cys)(NOM-RS), were detd. to be 40.0 ± 0.2 and 38.5 ± 0.2, resp., at pH 3.0. The magnitude of these consts. was further confirmed by 1H NMR spectroscopy and the Hg(NOM-RS)2 structure was verified by Hg LIII-edge EXAFS spectroscopy. An important finding is that the thermodn. stabilities of the complexes Hg(NOM-RS)2, Hg(Cys)(NOM-RS) and Hg(Cys)2 are very similar in magnitude at pH values <7, when all thiol groups are protonated. Together with data on 15 low mol. mass (LMM) thiols, as detd. by the same method (Liem-Ngyuen et al. Thermodn. stability of mercury(II) complexes formed with environmentally relevant low-mol.-mass thiols studied by competing ligand exchange and d. functional theory. Environ. Chem. 2017, 14, (4), 243-253.), the consts. for Hg(NOM-RS)2 and Hg(Cys)(NOM-RS) represent an internally consistent thermodn. data set that we recommend is used in studies where the chem. speciation of Hg(II) is detd. in the presence of NOM and LMM thiols.

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47. 47

    Yu, C. H. Interference from Soluble Iron on Mercury Determination in Water by Cold Vapor Atomic Absorption Spectrometry (CV-AAS) with Sodium Borohydride as Reductant. Anal. Sci. 2021, 37 (8), 1181– 1184,  DOI: 10.2116/analsci.20N035

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    47

    Interference from soluble iron on mercury determination in water by cold vapor atomic absorption spectrometry (CV-AAS) with sodium borohydride as reductant

    Yu, Chunhai

    Analytical Sciences (2021), 37 (8), 1181-1184CODEN: ANSCEN; ISSN:1348-2246. (Japan Society for Analytical Chemistry)

    This study demonstrated the signal enhancement interference from sol. iron (Fe) during mercury (Hg) detn. in water by cold vapor at. absorption spectrometry (CV-AAS) using sodium borohydride (NaBH4) as reductant. In the presence of 50 mg L-1 sol. Fe, Hg values will be overestimated by around 25%. The reason for the Hg signal enhancement is still unclear, but it is speculated to be attributable to the catalyst function for the equil. redn. reaction between Hg2+ and BH4- from the at. Fe formed at the same time. Using the matrix matching calibration stds. prepd. in 50 mg L-1 Fe soln., the problem of Hg overestimation could be minimized. This study also indicated that stannous chloride (SnCl2), another common reductant for Hg anal., does not suffer from the overestimation problem from sol. Fe in the presence of NaBH4.

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48. 48

    Choe, K. Y.; Gill, G. A. Distribution of particulate, colloidal, and dissolved mercury in San Francisco Bay estuary. 2. Monomethyl mercury. Limnol. Oceanogr. 2003, 48 (4), 1547– 1556,  DOI: 10.4319/lo.2003.48.4.1547

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    48

    Distribution of particulate, colloidal, and dissolved mercury in San Francisco bay estuary. 2. Monomethyl mercury

    Choe, Key-Young; Gill, Gary A.

    Limnology and Oceanography (2003), 48 (4), 1547-1556CODEN: LIOCAH; ISSN:0024-3590. (American Society of Limnology and Oceanography)

    Phase speciation and estuarine behavior of monomethyl mercury (MeHg) were detd. in surface water of San Francisco Bay Estuary in Sept.-Oct. 2000 (low flow) and Mar. 2001 (high flow). Colloidally-assocd. MeHg was isolated using a cross-flow ultrafiltration method with a nominal mol. wt. cutoff of 1 kDa. Filter-passing MeHg was 57 ± 18% of MeHg in unfiltered water in fall and 39 ± 12% in spring. Colloidal MeHg averaged 34 ± 11% of filter-passing MeHg in fall and 56 ± 15% in spring. Significantly higher particle-water partition coeffs. were obsd. between colloidal and dissolved MeHg (log KC = 5.6 ± 0.3, n = 21) vs. those between particulate and dissolved MeHg (log KP = 4.9 ± 0.5, n = 21), suggesting MeHg is preferentially assocd. with colloidal matter. Strong correlations of MeHg with org. C content in filter-passing, colloidal, and dissolved fractions confirmed the importance of org. matter in the MeHg cycle. Abs. and relative (as a percentage of Hg) MeHg concns. were highest in river water end-member under both flow regimes, suggesting river-borne MeHg is the major source of MeHg introduced to the estuary. A non-conservative estuarine mixing model suggested significant amts. of colloidal and dissolved MeHg are removed in the estuary under both flow regimes, in marked contrast to Hg, which had a source within the estuary under low flow conditions.

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    Aiken, G. R.; Gilmour, C. C.; Krabbenhoft, D. P.; Orem, W. Dissolved organic matter in the Florida Everglades: Implications for ecosystem restoration. Crit Rev. Env Sci. Tec 2011, 41, 217– 248,  DOI: 10.1080/10643389.2010.530934

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50. 50

    Aiken, G. R.; Hsu-Kim, H.; Ryan, J. N. Influence of dissolved organic matter on the environmental fate of metals, nanoparticles, and colloids. Environ. Sci. Technol. 2011, 45 (8), 3196– 3201,  DOI: 10.1021/es103992s

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    Influence of Dissolved Organic Matter on the Environmental Fate of Metals, Nanoparticles, and Colloids

    Aiken, George R.; Hsu-Kim, Heileen; Ryan, Joseph N.

    Environmental Science & Technology (2011), 45 (8), 3196-3201CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    A review discussing the nature of dissolved org. matter (DOM), trace metal complexation by DOM, role of DOM in altering transformations between metals and inorg. ligands, influence of DOM on colloids, and the effect of DOM on engineered nanomaterials entering the environment. Much of recent work involving DOM and engineered nanomaterials has shown that DOM slow aggregation of nanoparticle suspensions and inhibits the deposition of nanoparticles in satd. porous media. The alteration of interfacial chem. by DOM and the kinetics of nanoparticle aggregation, deposition, and dissoln. are relevant for most pollution scenarios. A crit. area for future advances is related to photoreactivity of metals, nanoparticles, and DOM. Interactions of DOM with sunlight are important drivers for a no. of reactions in surface waters that control metal speciation and surface chem. of colloids.

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51. 51

    Larsen, L. G.; Harvey, J. W.; Crimaldi, J. P. Morphologic and transport properties of natural organic floc. Water Resource Research 2009, 45, W01410,  DOI: 10.1029/2008WR006990

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    51

    Morphologic and transport properties of natural organic floc

    Larsen, Laurel G.; Harvey, Judson W.; Crimaldi, John P.

    Water Resources Research (2009), 45 (1), W01410/1-W01410/13CODEN: WRERAQ; ISSN:0043-1397. (American Geophysical Union)

    The morphol., entrainment, and settling of suspended aggregates ("floc") significantly impact fluxes of org. carbon, nutrients, and contaminants in aquatic environments. However, transport properties of highly org. floc remain poorly understood. In this study detrital floc was collected in the Florida Everglades from two sites with different abundances of periphyton for use in a settling column and in racetrack flume entrainment expts. Although Everglades flocs are similar to other org. aggregates in terms of morphol. and settling rates, they tend to be larger and more porous than typical mineral flocs because of biostabilization processes and relatively low prevailing shear stresses typical of wetlands. Flume expts. documented that Everglades floc was entrained at a low bed shear stress of 1.0 × 10-2 Pa, which is considerably smaller than the typical entrainment threshold of mineral floc. Because of similarities between Everglades floc and other org. floc populations, floc transport characteristics in the Everglades typify the behavior of floc in other org.-rich shallow-water environments. Highly org. floc is more mobile than less org. floc, but because bed shear stresses in wetlands are commonly near the entrainment threshold, wetland floc dynamics are often transport-limited rather than supply limited. Org. floc transport in these environments is therefore governed by the balance between entrainment and settling fluxes, which has implications for ecosystem metab., materials cycling, and even landscape evolution.

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    Hurley, 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. Biogeochem 1998, 40 (2–3), 293– 310,  DOI: 10.1023/A:1005928927272

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    52

    System controls on the aqueous distribution of mercury in the northern Florida Everglades

    Hurley, James P.; Krabbenhoft, David P.; Cleckner, Lisa B.; Olson, Mark L.; Aiken, George R.; Rawlik, Peter S., Jr.

    Biogeochemistry (1998), 40 (2-3), 293-311CODEN: BIOGEP; ISSN:0168-2563. (Kluwer Academic Publishers)

    The forms and partitioning of aq. Hg species in the canals and marshes of the northern Florida Everglades exhibit strong spatial and temporal variability. In canals feeding Water Conservation Area (WCA) 2A, unfiltered total Hg (HgTU) is <3 ng/L and relatively const. In contrast, MeHg exhibited a strong seasonal pattern, with highest levels entering WCA-2A marshes during July. Stagnation and reduced flows also lead to particle enrichment of MeHg. In the marshes of WCA-2A, 2B and 3A, HgTu is usually <5 ng/L with no consistent north-south patterns. However, for individual dates, aq. unfiltered MeHg levels increase from north to south with generally lowest levels in the eutrophied regions of northern WCA-2A. A strong relation between filtered Hg species and dissolved org. C (DOC), evident for rivers draining wetlands in Wisconsin, was not apparent in the Everglades, suggesting either differences in the binding sites of DOC between the 2 regions, or non-org. Hg complexation in the Everglades.

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    Revis, N. W.; Osborne, T. R.; Holdsworth, G.; Hadden, C. Mercury in soil - a method for assessing acceptable limits. Arch. Environ. Contam. Toxicol. 1990, 19 (2), 221– 226,  DOI: 10.1007/BF01056090

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    53

    Mercury in soil: a method for assessing acceptable limits

    Revis, N. W.; Osborne, T. R.; Holdsworth, G.; Hadden, C.

    Archives of Environmental Contamination and Toxicology (1990), 19 (2), 221-6CODEN: AECTCV; ISSN:0090-4341.

    Acceptable limits for Hg in soil were detd. at a site with Hg contamination after measuring the soil concn. of total Hg, the species of Hg, and the intestinal absorption of HgS by mice. The total concn. of Hg at this site ranged 0.5-3000 ppm. Of the total Hg present, 88% was identified as HgS, 0.01% as MeHg+ and 7% as elemental Hg. Intestinal absorption studies in mice following the intubation of 203HgS showed that 0.4% of the intubated dose was absorbed. An acceptable limit for Hg in soil at this site was estd. to be 722 ppm on the basis of based on results of this study; on reports in the literature on the intestinal and pulmonary absorption of Hg species from air, water, and food; and on the normal intake of total Hg in humans reported by the World Health Organization. With a safety factor of 10 this limit would be reduced to 72 ppm.

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