Statistical analysis of a North American Wetland Database (NAWDB) allowed us to develop a mass loading model that was used to separate P assimilative capacity (defined as P absorption with no significant ecosystem change and no elevated P output) from storage capacity (maximum storage) in wetlands. Our analysis indicates that, given ample supplies of other nutrients, average P assimilative capacity (PAC) in North American wetlands is near 1 g m^-2 yr^-1. From this analysis, we proposed a “One Gram Assimilative Capacity Rule” for P loadings within natural freshwater wetlands if long-term storage of P, maintenance of community structure and function, and low P effluent concentrations are required. An Everglades test site supports our hypothesis that natural wetlands will lose native species, become P saturated in a few years, and export unacceptable amounts of phosphate when phosphorus loading exceeds PAC. Moreover, our findings clearly demonstrate that even P-limited wetlands have the capacity to assimilate low levels of P loadings without significant changes in ecosystem structure and function.

The formation of the benzo[a]pyrene (B[a]P) diones (B[a]P-1,6-dione, B[a]P-3,6-dione, B[a]P-6,12-dione) as the main products of oxidative degradation of B[a]P has been observed under atmospheric conditions in air particulate matter. Samples were collected at two different sites in Munich, Germany. Total B[a]P dione concentrations were determined by APCI/LC−MS and ranged between 8 and 605 pg m^-3. The formation of the direct mutagen B[a]P-epoxide was not observed. B[a]P dione concentrations did not correspond with B[a]P and total carbon concentrations, but showed a correlation with solar irradiation. B[a]P dione concentrations were higher on daytime filters compared to filters collected during the night. Lower concentrations of B[a]P diones were observed at the site with higher traffic contributions, suggesting a major role of atmospheric transport. Rapid, high-volume sampling indicates that the B[a]P dione formation is not dependent on B[a]P concentrations, but on photochemical conditions.

Reliable environmental resource estimates are essential to informed regional scale decisions regarding protection, restoration, and enhancement of natural resources. Reliable estimates depend on objective and representative sampling. Probability-based sampling meets these requirements and provides accuracy estimates (confidence limits). Non-probability-based (judgment or convenience) sampling often is biased, thus less reliable (no accuracy estimates), and potentially misleading. We compare results from a probability- and a non-probability-based Secchi transparency sampling of lakes in the northeastern geographic region of the United States and its three primary ecoregions. Results from these samplings are compared on the basis of sample representativeness relative to the regional lake population and subsequent reliability of lake condition estimates. Statistically derived sampling indicates the northeast lake population median lake size to be about 9.5 (± 2.3) ha and the Secchi disk transparency (SDT) to be about 2.4 (± 0.4) m. On the basis of judgment sampling estimates, the median SDT for lakes in the same area would be 4.2 m. However, only about 15% of the regional lake population based on statistically designed sampling estimates has a SDT ≥4.2 m. Estimate unreliability of this magnitude can have profound effects on lake management decisions. Thus, regional extrapolation of non-probability-based sampling results should be avoided.

A dilution source sampling system was used to quantify the organic air pollutant emissions from commercial-scale meat charbroiling operations. Emission rates of gas-phase volatile organic compounds, semivolatile organic compounds, and high molecular weight particle-phase organic compounds were simultaneously quantified on a single compound basis. Fine particle mass emission rates and fine particle elemental chemical composition were measured as well. Emission rates of 120 organic compounds, spanning carbon numbers from C₁ to C₂₉ were quantified including n-alkanoic acids, n-alkenoic acids, carbonyls, lactones, alkanes, aromatics, polycyclic aromatic hydrocarbons, alkenes, and steroids. Ethylene, formaldehyde, and acetaldehyde were found to be the predominant light gas-phase organic compounds emitted from the charbroiling operations. n-Alkanoic acids, n-alkenoic acids, and carbonyls made up a significant fraction of the quantified semivolatile and particle-phase organic compound emissions. Meat charbroiling is one of the few sources identified to date that contributes to the high molecular weight aldehydes measured in the urban atmosphere. Semivolatile and particle-phase organic compounds were collected for quantification by two simultaneous sampling protocols:  (1) quartz fiber filters followed by polyurethane foam (PUF) cartridges, and (2) XAD-coated annular denuders followed by quartz fiber filters and PUF cartridges. Good agreement was observed for the total mass emissions collected by the two different sampling procedures; however, the partitioning of the semivolatile organic compounds between the gas phase and particle phase, as measured by the two sampling procedures, showed significant differences for n-alkanoic acids, indicating that significant artifact adsorption of these compounds occurs to the filter in the filter/PUF sampling system.

Gas- and particle-phase tailpipe emissions from late-model medium duty diesel trucks are quantified using a two-stage dilution source sampling system. The diesel trucks are driven through the hot-start Federal Test Procedure (FTP) urban driving cycle on a transient chassis dynamometer. Emission rates of 52 gas-phase volatile hydrocarbons, 67 semivolatile and 28 particle-phase organic compounds, and 26 carbonyls are quantified along with fine particle mass and chemical composition. When all C₁−C₁₃ carbonyls are combined, they account for 60% of the gas-phase organic compound mass emissions. Fine particulate matter emission rates and chemical composition are quantified simultaneously by two methods:  a denuder/filter/PUF sampler and a traditional filter sampler. Both sampling techniques yield the same elemental carbon emission rate of 56 mg km^-1 driven, but the particulate organic carbon emission rate determined by the denuder-based sampling technique is found to be 35% lower than the organic carbon mass collected by the traditional filter-based sampling technique due to a positive vapor-phase sorption artifact that affects the traditional filter sampling technique. The distribution of organic compounds in the diesel fuel used in this study is compared to the distribution of these compounds in the vehicle exhaust. Significant enrichment in the ratio of unsubstituted polycyclic aromatic hydrocarbons (PAH) to their methyl- and dimethyl-substituted homologues is observed in the tailpipe emissions relative to the fuel. Isoprenoids and tricyclic terpanes are quantified in the semivolatile organics emitted from diesel vehicles. When used in conjunction with data on the hopanes, steranes, and elemental carbon emitted, the isoprenoids and the tricyclic terpanes may help trace the presence of diesel exhaust in atmospheric samples.

The behavior of heavy metals (Cd, Cu, Zn, Cr, Pb), nutrients (organic C, P, and N parameters), and major ions was investigated during percolation of roof runoff water through an artificial infiltration site. The concentrations of the various components were determined in rainwater, roof runoff, and infiltrating water at various depths in the soil. The concentrations of most parameters in roof runoff were highest during the “first flush” at the beginning of rain events. Despite rapid infiltration caused by strong preferential flow, differences were still observed in infiltration behavior between individual compounds. Cl^-, NO₃^-, SO₄^2-, ortho-phosphate, and the major part of DOC behaved essentially conservatively during infiltration, whereas NH₄⁺ concentration decreased probably as a consequence of nitrification. The concentrations of Ca, Mg, Na, K, and alkalinity were regulated by dissolution of soil material. The change in concentrations of Cu, Cd, and Cr during infiltration was mostly due to the concentration dynamics of roof runoff inflow water with only limited retention by soil, indicating the high mobility of these metals in the unsaturated zone. In the short term, Pb and Zn showed the opposite behavior with strong retention in the upper soil layers as determined by the large decrease in their concentrations measured in the lysimeters compared with those in the runoff water. However, in the long term, zinc and lead were also transported through the deeper soil layers of the unsaturated zone. The high mobility of Cu and Cd can be attributed to complexation by ligands in solution, and of Cr to the presence of Cr(VI) species. The artificial infiltration site used in this study was designed according to recommended standards for water infiltration; nevertheless its design turned out to be sub-optimal for the retention of heavy metals and for some of the organic and inorganic compounds.

Coal tar is a dense nonaqueous phase liquid (DNAPL) of significant environmental concern due to its toxicity and persistence in the subsurface. The mobility and recoverability of subsurface coal tar is significantly influenced by its interfacial properties. This paper demonstrates the dependence of coal tar interfacial properties, such as interfacial tension and contact angle, on aqueous pH. Coal tar−water interfacial tension, quartz wettability, capillary pressure-fluid saturation relationships, and interfacial film presence or absence were experimentally determined in aqueous solutions of varying pH (3.4−12.4) at constant ionic strength (0.1 M). Interfacial tension varied as much as 25 dynes/cm, dramatically decreasing as pH was increased above 9. Contact angle results indicate that, as for most NAPLs, water wets quartz media under coal tar-advancing conditions over the entire pH range tested. However, unlike most NAPLs, coal tar wets quartz media under coal tar-receding conditions at acidic to neutral pH. At basic pH, quartz media remained water wet. These results were corroborated by capillary pressure versus saturation experiments, in which spontaneous imbibition of waterindicative of a water-wet systemoccurred only at basic pH. In addition, interfacial films formed at acidic to neutral pH, but not at basic pH, and whenever films were present, coal tar was observed to strongly adhere to quartz. The effects observed in this study are postulated to occur due to the presence in coal tar of asphaltenes, compounds that are considered responsible for the pH-dependence of interfacial properties and formation of semisolid interfacial films in crude oil−water−rock systems.

The fate and dechlorination kinetics of PCP and its intermediates were studied in two fluidized-bed reactors (FBRs) with methanogenic enrichments. The two FBRs were operated at a 1-day hydraulic retention time and fed lactate at 400 mg/L and pentachlorophenol (PCP) at 5 mg/L (18.8 μmol/L). PCP was meta-dechlorinated to 2,3,4,6-tetrachlorophenol (2346-TeCP). Approximately 75% of the 2346-TeCP was meta-dechlorinated to 2,4,6-trichlorophenol (246-TCP), followed by sequential o-chlorine removals to 4-monochlorophenol (4-MCP); the remaining 2346-TeCP was ortho-dechlorinated via 245-TCP to 3,4-dichlorophenol (34-DCP). Neither 34-DCP nor 4-MCP were dechlorinated throughout the 18-month testing period. In mixed-CP batch tests, CPs competed with each other, resulting in reduced dechlorination rates; competition was position-specific with respect to ortho- and meta-dechlorination reactions. Michaelis−Menten dechlorination kinetic coefficients and linear solid−liquid partition coefficients were determined for PCP, 2346-TeCP, 246-TCP, 245-TCP, 24-DCP, 34-DCP, and 4-MCP. These coefficients were used in a Michaelis−Menten, sequential dechlorination, competitive inhibition kinetic model that used the experimentally determined CP half-saturation coefficients (K_s) for respective inhibition coefficients. The model reasonably predicted CP concentra tions over time in batch tests fed 246-TCP or PCP. Without competitive inhibition, the model increasingly overestimated CP dechlorination rates with each successive dechlorination step and underestimated the time for dechlorination.

Dietary uptake and effects of decabromodiphenyl ether (DeBDE), a widely used flame retardant, were studied in rainbow trout. Fish were fed for 16, 49, or 120 days with control or DeBDE-treated food (7.5−10 mg of DeBDE/kg of body weight/day). One group was fed DeBDE for 49 days and then control diet for 71 days to study depuration. Chemical analyses were performed using GC/MS(ECNI). Several physiological and biochemical variables were also measured. DeBDE concentrations in muscle increased from <0.6 ng/g of fresh weight to 38 (±14) ng/g after 120 days. Corresponding liver concentrations were <5 and 870 (±219) ng/g of fresh weight. Several hexa- to nonabromodiphenyl ethers, present in both liver and muscle, increased in concentration with exposure length. These congeners originate from metabolism of DeBDE and/or selective uptake of minor components in the DeBDE product. After depuration, DeBDE concentrations declined significantly, but concentrations of some lower brominated congeners were unaffected. Liver body index and plasma lactate concentrations were higher in fish exposed for 120 days and in the depuration group, indicating delayed chronic effects, possibly from lower brominated congeners. DeBDE uptake (0.02−0.13%) and possible metabolism seem not to be major sources of tetra- and pentabromodiphenyl ethers found in wild fish.

This paper reports mass measurements, size distributions, and the transient response of tailpipe particulate emissions from 21 recent model gasoline vehicles. Transient measurements are made for the FTP drive cycle (and limited ECE tests) using a scanning mobility particle sizer and an electrical low-pressure impactor. The particles emitted in vehicle exhaust have diameters in the 10−300 nm diameter range, with a mean diameter of about 60 nm. Particle emissions during the drive cycles occur as narrow peaks that correlate with vehicle acceleration. Cold start emissions generally outweigh those from a hot start by more than a factor of 3. Particulate mass deduced from the transient distributions agrees semiquantitatively with gravimetric measurements. Tailpipe particulate emissions from the recent model gasoline vehicles tested are very low, with mass emission rates ranging downward from 7 mg/mi for a light-duty truck during the cold start phase of the FTP drive cycle to ≤0.1 mg/mi during phase 2 for nearly half of the test vehicles. Three high-mileage (>100 K mi) test vehicles exhibited similarly low particulate emission rates. The FTP-weighted 3-bag average is under 2 mg/mi for all the conventional gasoline vehicles tested.

We have characterized Pb speciation in selected tailings from the Leadville, CO, area using a variety of analytical techniques, including X-ray absorption fine structure (XAFS) spectroscopy. Samples from three locations were analyzed, including two chemically distinct tailings piles located within the city limits [Apache (pyrite-rich, low pH) and Hamms (carbonate-rich, near-neutral pH)] and tailings material deposited as overbank sediments along the Arkansas River approximately 13 km downstream from Leadville (Arkansas River tailings). Extended XAFS (EXAFS) spectra of these multicomponent samples were fit using linear combinations of model compound spectra. In accordance with pH differences among the samples, adsorbed Pb accounts for ∼50% of total Pb (Pb_T) in fine fractions of the near-neutral pH Hamms tailings, whereas Pb-bearing jarosites account for the majority of Pb_T in the fine fractions of the low pH Apache and Arkansas River tailings. EXAFS analyses following sequential extraction by MgCl₂ and EDTA show evidence of significant redistribution (readsorption) of Pb during the MgCl₂ extraction and for removal of adsorbed Pb and dissolution of Pb-carbonates during the EDTA extraction. Changes in Pb speciation with water extraction (dissolution of anglesite and precipitation of plumbojarosite) are observed in one sample of Arkansas River tailings. These molecular-scale results show that Pb speciation varies dramatically among environments in the Leadville area and that Pb occurs in a number of phases not amenable to definitive characterization by conventional microanalytical and/or chemical extraction techniques.

Remediation of groundwater contamination in unconsolidated aquifers by dissolved hydrophobic compounds (HOC) requires detailed information on the sorption parameters present in the sediments. Equilibrium sorption isotherms were measured for phenanthrene for a wide variety of lithocomponents (constituents of sand and gravel sediments) and unweathered rock fragments (limestones and sandstones). The lithocomponents were separated based on macroscopic appearance of different lithologies (e.g. limestones, sandstones, shales, mudstones, and igneous rocks) and characterized in terms of organic carbon content and specific surface area. In addition the organic matter (OM) was characterized using coal petrography methods (white and UV light microscopy). As confirmed by heat-treated samples sorption was solely due to OM. Organic carbon normalized sorption coefficients (K_OC) varied by almost 3 orders of magnitude among the samples investigated. The different origin and maturity of isolated organic matter (organic facies) is believed to be responsible. For example, extremely high K_OC values were found for particulate organic matter such as charcoal and coal particles which were preserved within the sandstone and limestone grains. In a second paper we report data on sorption kinetics of the samples used in this study (1).

Most aquifer materials are heterogeneous in terms of grain size distribution and petrography. To understand sorption kinetics, homogeneous subfractions, either separated from heterogeneous sands and gravels (lithocomponents) or fragments of fresh rocks, have to be studied. In this paper we present data on long-term sorption kinetics of phenanthrene for homogeneous samples consisting of one type of lithocomponents or fresh rock fragments in different grain sizes. Diffusion rate constants were determined in batch experiments using a numerical model for retarded intraparticle pore diffusion and correlated to grain size and intraparticle porosity of the lithocomponents. Sorption isotherms were nonlinear for all samples investigated (Kleineidam et al. (1)). The numerical model described the sorption kinetics very well for coarse sand and gravels. Tortuosity factors, which were obtained as final fitting factors, agreed with Archie's law predictions based on the intraparticle porosity. The dependency of sorptive uptake on grain size revealed that for smaller grains intrasorbent diffusion may become significant. This is attributed to relatively large particulate organic matter (POM) within the sedimentary rock fragments. Specifically, charcoal and coal particles, which were found in some of the sandstones, controlled the sorptive uptake rates.

There are few methods to effectively measure organic selenium [Se(−II)] in natural water and soil-sediment extracts. A method has been developed to determine organic Se(−II) in soil-sediment extracts and agricultural drainage water by using persulfate to oxidize organic Se(−II) and using manganese oxide as an indicator for oxidation completion. This method was used to determine Se speciation in eleven soil-sediments and four agricultural drainage water samples collected from the western United States. Results showed that organic Se(−II) can be quantitatively oxidized to selenite without changing the selenate concentration in the soil-sediment extract and agricultural drainage water and then quantified by hydride generation atomic absorption spectrometry. Recoveries of spiked organic Se(−II) and selenite were 96−105% in the soil-sediment extracts and 96−103% in the agricultural drainage water. Concentrations of soluble Se in the soil-sediment extracts were 0.0534−2.45 μg/g, of which organic Se(−II) accounted for 4.5−59.1%. Selenate is the dominant form of Se in agricultural drainage water, accounting for about 90% of the total Se. In contrast, organic Se(−II) was an important form of Se in the wetlands. These results showed that wetland sediments are more active in reducing selenate compared to evaporation pond sediments.

Subcritical water extraction was used as a tool to remove the carboxylic, aliphatic, and carbohydrate types of organic carbon from a humic soil. The rates and extents of soil organic carbon removal were quantified as functions of superheated water temperature, phase, and exposure time. The experimental data suggest that superheated water effects deoxygenation/aromatization reactions of soil organic matter that mimic those of geologically slow, natural diagenesis processes. Phenanthrene sorption and desorption equilibrium isotherms for the altered soils were measured. The sorption isotherms were characterized by increasing capacity and nonlinearity with increasing degree of polar functionality removal and simulated diagenesis of the soil organic matter.

Poly-l-aspartic acid (PLAsp), which consists of ca. 50 Asp residues in a linear polypeptide, has been immobilized on controlled pore glass (CPG) and evaluated for its selectivity and binding strength in the complexation of metal ions from aqueous solutions. The carboxylate side chain of Asp (pK_a = 5.4 ± 0.2) is thought to be primarily responsible for chelation of the target metals. Of the several metals evaluated, Eu³⁺, Ce³⁺, La³⁺, Cu²⁺, and Pb²⁺ exhibited good binding capacities. Quantitative determination of single-element capacities were determined for Cu²⁺ (12 ± 1 μmol/g PLAsp-CPG) and La³⁺ (7.1 ± 0.3 μmol/g PLAsp-CPG). Isotherms were constructed from breakthrough curves using a flow injection system. These curves were used to evaluate the effective site capacity and formation constants. A combination of moderate and strong binding sites for Pb²⁺ was detected, while moderate binding of Cd²⁺ was observed with a minimal number of strong binding sites. Several cations showed little to no binding by PLAsp-CPG (e.g., Na⁺, Ca²⁺, Mg²⁺, Mn²⁺, Co²⁺, and Ni²⁺). Propensity for metal binding seems to follow the trend seen for binding to carboxylates in such ligands as acetate. The polydentate binding available from the polypeptide chain significantly enhanced the binding strength with equilibrium constants in excess of 10⁸ observed for the strong binding sites. The binding selectivity was complementary, in many cases, with the results previously reported for poly-l-cysteine immobilized on CPG.

The accidental introduction and extremely rapid growth of the tropical alga Caulerpa taxifolia in the northern coastal waters of the Mediterranean sea represents an adaptive challenge for indigenous animal and plant species. Since first being detected near Monaco, it has spread to many areas, sometimes hundreds of kilometers away from the initial site of implantation. This alga is known to produce some repulsive toxic compounds such as caulerpenyne derivatives. In this study, specimens of Scorpaena porcus (a typical mediterranean fish) were maintained under laboratory conditions in the presence of this alga, and hepatic glutathione S-transferase and cytochrome P450 monooxygenases activities of fish were examined. The collective data indicate that the presence of Caulerpa taxifolia in the environment of these fish modifies the hydroxylation stereospecificity of hepatic microsomal cytochromes P450 toward steroid substrates. These results reflect changes in the relative levels of P450 isoforms in the liver and thus demonstrate the influence of Caulerpa taxifolia on the physiology of fish sharing space with this new alga. In addition, this phenomenon was found to be dependent on the contact time between the fish and the alga.

Because natural organic matter (NOM) can act as a carrier for contaminants, it is of great importance to understand its dynamic adsorption/desorption behavior. NOM is a mixture of organic molecules that vary both in chemical and physical properties. The adsorption/desorption behavior of a NOM mixture to the solid matrix cannot be adequately described using simple equilibrium sorption isotherms, like the Langmuir isotherm. Often adsorption/desorption hysteresis is found or “adsorption maxima” keep increasing slowly. In this paper a relatively simple model is developed to describe the kinetic adsorption/desorption of NOM. The model is calibrated using experimental data. Model simulations of experimental data show that adsorption/desorption hysteresis is an inherent property of a heterogeneous mixture of molecules. The composition and thus the properties of the mixture vary with the total amount of NOM added and with surface/volume ratios. Therefore the relationship between the overall adsorption and the overall solution concentration is nonunique and thus a nonthermodynamic isotherm. Although adsorption in terms of mass of carbon seems to reach equilibrium relatively fast, the distribution of individual components can still be far from equilibrium. This indicates that the composition of the NOM mixture may vary with time as well.

Both the primary chemical structure and the conformational structure of humic substances are still a matter of debate. A traditional assumption is that humic substances are large polymers and may present linear or coiled conformations according to solution properties. We studied the conformational changes of humic and fulvic acids of different chemical nature by high-pressure size-exclusion chromatography (HPSEC) after dissolution in mobile phases differing in composition but constant in ionic strength (I = 0.05). Modification of a neutral mobile phase (0.05 M NaNO₃, pH 7) by addition of methanol (4.6 × 10^-7 M, pH 6.97), hydrochloric acid (<2 × 10^-6 M, pH 5.54), and acetic acid (4.6 × 10^-7 M, pH 5.69) produced, in the order, a progressive decrease in molecular size. Size diminishing was shown by increasingly larger elution volumes at a refractive index detector and by concomitant reductions of peaks absorbance at a UV−vis detector. The decrease of molecular absorptivity (the phenomenon of hypochromism) proved that size reduction of dissolved humic substances was due more to disruption of an only apparent high-molecular-size arrangement into several smaller molecular associations than to coiling down of a macromolecular structure. The most significant conformational changes occurred in acidic mobile phases where hydrogen bondings formation was induced, suggesting that the large and easily disruptable humic conformation was held together predominantly by weak hydrophobic forces. The size of molecular association varied with humic samples indicating a close relation between humic chemical composition and stability of conformational structure. Our results show that humic substances in solution are loosely bound self-association of relatively small molecules, and intermolecular hydrophobic interactions are the predominant binding forces. The stability of such a conformation in solution is attributed to the entropy-driven tendency to exclude water molecules from humic association and thus decrease total molecular energy. This model of dissolved humic substances based on the reversible self-association of small molecules rather than on the macromolecular random coil represents a new understanding that should contribute to predict the environmental behavior of contaminants in association with natural organic matter.

The kinetics of the reactions between tetrachloromethane (CCl₄), 1,2-dichloroethane (C₂H₄Cl₂), or chlorobenzene (C₆H₅Cl) and sodium carbonate were investigated using evolved gas analysis−Fourier transform infrared spectroscopy. Sodium carbonate reacted with CCl₄ between 600 and 900 K to form over 90% carbon dioxide (CO₂) and less than 10% tetrachloroethene (C₂Cl₄). This reaction followed the three-dimensional diffusion mechanism and had an activation energy of 105 ± 10 kJ/ mol and a steric factor of 5000 ± 3000 min^-1. The reaction between C₂H₄Cl₂ and sodium carbonate produced CO₂, ethanal (C₂H₄O), water (H₂O), vinyl chloride (C₂H₃Cl), ethene (C₂H₄), and ethyne (C₂H₂) between 600 and 900 K from at least two different pathways. The product temperature profiles indicated that CO₂, C₂H₄O, and C₂H₃Cl were formed initially and that approximately 10% of the product is C₂H₄ at 900 K. The reaction kinetics followed the Ginstling−Brounshtein diffusion mechanism and had an activation energy of 100 ± 10 kJ/ mol and a steric factor of approximately 10⁴ min^-1. Benzene was produced from the reaction between chlorobenzene and sodium carbonate at temperatures above 800 K. This reaction followed the three-dimensional diffusion mechanism and had an activation energy of 80 ± 10 kJ/mol and a steric factor of approximately 500 min^-1.

The current sulfur-impregnated activated carbons are extremely costly sorbents in mercury control technologies. In this regard, the present study offers a cheaper alternative by using a natural silicate, sepiolite, as sulfur substrate. Sepiolite is a fibrous hydrated magnesium silicate clay that is very cheap (around $100/t of the 0.6−0.8-mm fraction) and abundant with unique textural and structural characteristics:  S_BET, 150−350 m² g^-1; pore volume, 0.3−0.8 cm³ g^-1; density, ∼0.8 g cm^-3. Samples of 10% S supported on monolithic sepiolite have been used to retain 90 ppm mercury in air at 320 K and ambient pressure. The experimentation has been effected in a dynamic system at fluid velocities in the 4.7−18.8 cm s^-1 range. A comparative study of the performance of three different monoliths against a fixed-bed reactor of powders of 0.026-cm size is made. Under the work conditions, the process is governed by mass transfer, which on fresh solids fits the expression Sh = 0.075Re^4/3 for powders and Sh = 0.766 (Re Sc d L^-1)^0.483 for monoliths. In the work, the importance of the adsorbents texture and, consequently, of the monoliths preparative method is demonstrated:  the capacity per mass unity of the samples is better when impregnation is the last preparation step because porosity is better preserved and sulfur is more uniformly distributed.

Dense, nonaqueous phase liquids (DNAPLs) are separate phase compounds that commonly contaminate groundwater supplies. Miscible displacement methods using surfactants and alcohols to recover the DNAPLs have been proposed, but concerns have been raised about mobilizing the DNAPLs deeper into previously uncontaminated media. In this paper, the concerns are addressed by reducing DNAPL density prior to elimination of interfacial tension. Laboratory-measured equilibrium phase behavior demonstrates the ability of 2-butanol to reverse the density contrast between tetrachloroethene (PCE) and water prior to miscibility, resulting in a DNAPL phase less dense than the aqueous phase. Laboratory experiments using an upward gradient flow cell demonstrate that 2-butanol, introduced as an aqueous solution to a PCE pool suspended within a water-saturated sandpack, partitions strongly into the PCE. Pools of PCE exposed to 1 pore volume of water saturated with 2-butanol and subsequently recovered by miscible displacements with 1-propanol showed that between 56.6% and 97.6% of the DNAPL mass was recovered for total alcohol complements of between 0.24 and 1.0 pore volume. In all two-phase samples produced, the NAPL phase was less dense than the aqueous phase. Analysis of a static DNAPL pool shows that the use of a 2-butanol preflood may prevent the downward mobilization predicted to occur for more conventional alcohol floods.

Composite membranes of a block copolymer of styrene and butadiene (S−B−S) were cast on highly porous, hydrophobic thin films of PTFE and used for the separation and recovery of volatile organic compounds (VOCs) from aqueous solutions by pervaporation. Trichloroethane, trichloroethylene, and toluene were the VOCs selected for testing the efficacy of these membranes. An analysis of the pervaporation data showed that the liquid film boundary layer offered the main mass transfer resistance to permeation. The separation factor for the VOCs was as high as 5000 at near-ambient temperatures but decreased substantially at higher temperatures. The water flux was practically independent of the solute concentration. But it increased more rapidly with an increase in temperature as compared to the organic flux, thereby reducing the separation factor. Also, the separation of a multicomponent mixture from the aqueous feed could be predicted well from single-component data.

The relationship between biomass growth and degradation of polynuclear aromatic hydrocarbons (PAHs) in soil, and subsequent toxicity reduction, was evaluated in 10 in-vessel, bench-scale compost units. Field soil was acquired from the Reilly Tar and Chemical Company Superfund site in St. Louis Park, MN (Reilly soil) and brought to the U.S. Environmental Protection Agency Test and Evaluation Facility in Cincinnati, OH for a 12-week composting study. Five separate amendment conditions were applied in duplicate to Reilly soil to stimulate varying degrees of biomass growth. Amendments included standard nutrients (SN) adjusted to C:N:P = 100:5:1, based on total organic carbon, plus 1% cow manure, modified OECD nutrients adjusted to C:N:P = 100:5:1 plus 1% cow manure, SN plus 1% activated sludge, SN plus 5% activated sludge, and SN plus 5% autoclaved sludge. All reactors contained 30% (w/w) corn cobs. All amendment conditions resulted in decreased concentrations of PAHs with two to four rings in their molecular structure. No reduction in concentrations of five- or six-ring PAHs occurred during the 12-week study. No significant differences resulted between the final concentrations achieved through any of the amendment conditions. Starting concentrations of total PAHs ranged from 1606 to 4445 mg/kg, and final concentrations ranged from 888 to 1556 mg/kg in the reactors. Contaminant concentration plateaus appeared in all treatment curves by the eighth week. Once a concentration plateau was attained, little further PAH removal occurred during the remaining treatment, and all treatments moved closer to a similar concentration plateau value. Therefore, percent removal of PAHs from Reilly soil correlated with starting PAH concentrations but not with final concentrations. Rates of removal of PAHs during the first 4 weeks of compost treatment correlated strongly with starting PAH concentration but did not correlate with reactor biomass concentration. Several toxicity bioassays in earthworms and plants were used to evaluate the efficacy of compost biomass to reduce toxicity of PAH-contaminated soil. Earthworms (Lumbricus terrestris and Eisenia fetida andrei) were exposed to contaminated soil mixed with artificial soil in 6% to 100% dilutions (w/w), and survival was assessed after 14 days. Seed germination and root elongation tests were evaluated in lettuce and oats, and genotoxicity (mitotic aberrations) testing was performed on Allium cepa (onion). Composting of PAH contaminated soil decreased toxicity to earthworms and oat roots but had no significant effect on lettuce root toxicity. Untreated soil evoked genotoxicity in the Allium assay. After composting, no significant genotoxicity was observed in Reilly soil. Two challenges for future research on compost treatment of soils contaminated with PAHs involve increasing the removal of five- and six-ring compounds and achieving total removal that plateaus at a lower level. Whether this can be achieved by optimizing compost biomass development is uncertain. Continued evaluation of the amount and physiological status of compost biomass may provide information on the long-term ability of composting to destroy large PAHs.

Laboratory-scale two-dimensional aquifer physical model studies were conducted to qualitatively assess how changes in air injection rate, air injection pulsing, and chemical type affect the rate and extent of removal by in situ air sparging. In this work, the treatment of immiscible-phase source zones in coarse media has been simulated. To provide a basis for comparison, equivalent unsaturated-soil soil vapor extraction-like simulation experiments were also conducted. Results suggest that, (i) initially, removal occurs from within saturated zone air flow channels at rates similar to those observed for soil vapor extraction, (ii) during this initial period, removal rates are proportional to air flow rate and equilibrium chemical vapor concentrations, (iii) while increased air injection rates improve volatilization rates in the short-term, the long-term cumulative removal efficiency may not be affected unless the saturated zone air flow distribution changes significantly with flow rate, (iv) pulsing the air injection can improve the long-term cumulative removal efficiency, and (v) while short-term removal efficiency improves with increasing flow rate and vapor pressure, the long-term removal efficiency appears to improve with increasing solubility.

Ability of copper/cupric compound mixtures to remove iodide from solution was investigated to predict sorption of radioactive iodine in the environment and to assess their use in a nuclear reprocessing method. Thermodynamic calculations were performed to study the stability of such mixtures in solution and to obtain equilibrium constants of Cu(0)/Cu(II)/I^- and Cu(0)/Cu(II)/Cl^- systems. Both calculations and experimental results showed that a Cu(0)/Cu₃(OH)₂(CO₃)₂ (azurite) mixture selectively uptakes iodide ions (initial concentrations: 10^-2 and 10^-1 M) in the presence of 10^-1 M chloride ions. Reaction of iodide with copper powder and azurite crystal or copper plate and azurite powder have also been investigated, leading to precipitation of CuI onto massive copper phase. The different solids were separately analyzed by XPS and MEB-EDX, giving some insight in the uptake mechanism. It is proposed that soluble copper released by the cupric compound is reduced at the surface of metallic copper, leading to a preferential precipitation of CuI on copper surface.

The microtransport of polycyclic aromatic hydrocarbons (PAHs) in airborne diesel soot particles over time scales ranging from 0.18 s to 11.9 h was studied via a smog chamber experiment and simulated using radial diffusion models. The sorption of the PAHs by particles over long time periods (i.e., minutes to hours) was studied by monitoring the gas and particle-phase concentrations in the chamber over the course of the experiment (11.9 h). Additionally, the desorption of PAHs from particles over short time scales (i.e., tenths of seconds to several seconds) was observed by passing the aerosol through a large gas-phase stripping device and a sampling denuder to remove the aerosol's gas phase, thus causing the PAHs to desorb from the particles. The results of each experimental test were compared to simulation results using a one-layer model and four dual-impedance radial diffusion models. The dual-impedance models were able to closely reproduce the experimental results of each test, while the one-layer model produced poor fits to the experimental data, especially for the rapid desorption tests. The low values of the resulting optimized apparent diffusion coefficients (∼10^-19−10^-11 cm²/s) indicate significant impedance to microtransport beyond simple free-liquid diffusion. The mechanisms responsible for these impedances are explored. The results of this study indicate that a dual-impedance radial diffusion model is a useful tool for predicting the microtransport of PAHs in diesel soot particles (and probably other types of carbonaceous particles containing a significant organic fraction) over a wide range of time scales.

The atmospheric degradation of three chlorofluorocarbon (CFC) replacement compounds, namely HFC-134a, HCFC-123, and HCFC-124, results in the formation of trifluoroacetic acid (TFA). Concentrations of TFA were determined in precipitation and surface water samples collected in California and Nevada during 1996−1997. Terminal lake systems were found to have concentrations 4−13 times higher than their calculated yearly inputs, providing evidence for accumulation. The results support dry deposition as the primary contributor of TFA to surface waters in arid and semiarid environments. Precipitation samples obtained from three different locations contained 20.7−1530 ng/L with significantly higher concentrations in fogwater (median = 689 ng/L) over rainwater (median = 63.7 ng/L). Elevated levels of TFA were observed for rainwater collected in Nevada (median = 136 ng/L) over those collected in California (median = 49.5 ng/L), indicating continual uptake and concentration as clouds move from a semiarid to arid climate. Thus several mechanisms exist, including evaporative concentration, vapor−liquid phase partitioning, lowered washout volumes of atmospheric deposition water, and dry deposition, which may lead to elevated concentrations of TFA in atmospheric and surface waters above levels expected from usual rainfall washout.

We report the results of a 1995 study in which Fourier transform infrared (FTIR) gas-phase spectrometry was employed to measure the concentrations of four organic compounds (tetrahydrofuran, toluene, 2-butanone, and cyclohexanone) in the gas stream of an industrial solvent recovery unit. The goals of the study were to demonstrate that the extractive FTIR technique is (a) suitable for compliance measurements of the four individual compound concentra tions and (b) an accurate substitute for flame ionization detection determinations of the total hydrocarbon content of the gas stream. The U.S. Environmental Protection Agency (EPA) provides guidance on this type of study in its Method 301, which lists specific procedures and statistical criteria, and in several recently published documents describing FTIR quality assurance/quality control measures. The EPA reviews of the procedures and results indicate that both goals of the study were met according to EPA standards.

A new 20-L glass chamber for the determination of VOC emissions from construction materials and consumer products under controlled air velocity and turbulence is described. Profiles of air velocity and turbulence, obtained with precisely positioned hot wire anemometric probes, show that the velocity field is homogeneous and that air velocity is tightly controlled by the fan rotation speed; this overcomes the problem of selecting representative positions to measure air velocity above a test specimen. First tests on material emissions show that the influence of air velocity on the emission rate of VOCs is negligible for sources limited by internal diffusion (e.g., PVC tile) and strong for sources limited by evaporation. In a velocity interval from 0.15 to 0.30 m s^-1, an emission rate increase of 50% has been observed for pure n-decane and 1,4-dichlorobenzene and of 30% for 1,2-propanediol from a water-based paint. In contrast, no measurable influence of turbulence could be observed during vaporization of 1,4-dichlorobenzene within a 3-fold turbulence interval. Investigations still underway show that the chamber has a high recovery (i.e., low adsorption) for the heavier VOC (TXIB), even at low concentrations (∼20 μg m^-3).

Complexation by dissolved humic substances has an important influence on trace metal behavior in natural systems. Unfortunately, few analytical techniques are available with adequate sensitivity and selectivity to measure free metal ions reliably at the low concentrations under which they occur in natural waters. In the past, differential pulse anodic stripping voltammetry with a thin mercury film rotating disk glassy carbon electrode (DPASV-TMF-RDGCE) has been used to measure complexation capacities and conditional metal−ligand binding constants in oceanic and estuarine waters. In contrast, few studies have been conducted to validate DPASV's use in freshwaters. The current study compares DPASV and Cu ion-selective electrode (CuISE) methods for measuring free copper, complexation capacities, and conditional binding constants on samples of synthetic and isolated natural organics. Titration data show that DPASV and CuISE are able to measure similar amounts of labile copper when the two methods' detection windows overlap. Furthermore, the greater sensitivity of DPASV allows it to measure free copper at lower concentrations, which correlated well with CuISE data extrapolated into that same region. This strong correlation between these analytical methods provides positive evidence for the use of DPASV (TMF-RDGCE) in measuring free Cu²⁺, complexation capacities, and conditional binding constants in freshwaters.

Development of a microprobe technique to determine Pb isotope ratios within the growth layers of mammal teeth could have widespread applications in Pb toxicology, Pb pollution tracing, and human and animal ecology. Here, the SHRIMP II ion microprobe is shown to possess sufficient sensitivity, accuracy, and precision to satisfactorily determine Pb isotope ratios in the canine tooth cementum of a walrus (Odobenus rosmarus rosmarus), with a sampling resolution of 130 μm. The tooth layers were estimated to contain only 1−3 μg/g Pb. By combining multiple replicates (N = 10−30) within each annual layer, the ±1 SE uncertainty was typically ±1% for ²⁰⁶Pb/²⁰⁷Pb and ±0.5% for ²⁰⁸Pb/²⁰⁷Pb. Significant isotopic differences were found between layers deposited at age 10 and ages 2, 27, and 30. This result, together with corroborative data on excised cementum fragments analyzed by thermal ionization mass spectrometry, indicates that the animal migrated into different geological terrains several times during its life. There was no evidence of exchange between the Pb deposited in early growth layers and more recent ambient Pb.

Residues of butyltin compounds, including mono- (MBT), di- (DBT) and tributyltins (TBT), were measured in human blood collected from central Michigan, U.S.A. MBT, DBT, and TBT were detected in 53, 81, and 70% of the 32 blood samples examined. Concentrations of butyltins were in the order of MBT > DBT ≥ TBT, with total butyltin concentrations ranging from less than the limit of detection to 101 ng/mL. Exposure of humans to butyltin compounds used as stabilizers or as biocides in household articles has been regarded as a source in addition to the ingestion of contaminated foodstuffs. There was no significant difference in concentrations of butyltin compounds between sexes. Concentrations of butyltin compounds did not exhibit pronounced age-dependency, which is different from those observed for persistent pollutants such as polychlorinated biphenyls (PCBs). In general, concentrations of butyltins measured in blood were less than that affected human natural killer lymphocytes (a primary immune defense against tumor and virally infected cells). The toxicological significance of the concentrations of butyltins observed in this study is unknown. However, the potential for sporadic incidences of great exposure and possible synergistic effect on immune function when exposed in mixtures suggest a need for further investigations to evaluate sources and effects of butyltins in humans.