Environ. Sci. Technol. 2007, 41, 1729-1734
Distribution and Abiotic Degradation of Chlorinated Solvents in Heated Field Samples JED COSTANZA* AND KURT D. PENNELL School of Civil and Environmental Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332-0512
The objective of this study was to evaluate the abiotic degradation of tetrachloroethylene (PCE) in contaminated soil and groundwater samples obtained from the Camelot Cleaners Superfund site, West Fargo, ND. The field samples were incubated at temperatures of 25, 55, 75, and 95 °C in sealed ampules containing aqueous, gas, and solid phases for periods of up to 75 days to simulate thermal treatment temperatures. Aqueous PCE concentrations increased with incubation temperature but remained constant over time. The degradation of dolomite to form CO2 facilitated the transfer of sorbed-phase PCE from the solid to the aqueous phase in heated ampules. While compounds associated with PCE degradation were detected in the heated ampules, these compounds were also detected in ampules with PCE-free Camelot soil and were attributed to soil diagenesis rather than PCE degradation. Trichloroethylene underwent hydrogenolysis to form cis-DCE at 95 °C, and TCE levels decreased with first-order half-lives of 157 days at 55 °C and 26 days at 95 °C. The relatively small decrease in total PCE levels after 75 days of heating at 95 °C suggests that abiotic degradation of PCE will not result in significant mass reduction during thermal treatment of the Camelot Cleaners Superfund site.
Introduction In situ thermal treatment technologies, such as electrical resistance heating, are capable of removing substantial quantities of chlorinated solvent mass from the subsurface (1, 2). Electrical heating of the subsurface results in warming of low-permeability soils, such as clays and silts, due to the preferential electrical conductance of these finer texture materials (1, 3). Raising the subsurface temperature increases the rate of chlorinated solvent mass transfer from nonaqueous and sorbed phases to mobile aqueous and gas phases, which can be recovered by water and vapor extraction systems. Thermal treatment involves heating subsurface environments for extended periods of time to facilitate the physical recovery of contaminants. However, the time to achieve remedial goals could be reduced if in situ degradation of contaminants to benign products was to occur. Hence, there is a need to understand, and potentially enhance, chemical reactions that could promote in situ contaminant destruction. Abiotic degradation of chlorinated solvents has been claimed to occur during thermal treatment (4) and could result in substantial reductions of contaminant mass beyond that recovered by physical processes. While the potential for abiotic degradation * Corresponding author phone: (404)385-4554; fax: (404)894-8266; e-mail:
[email protected]. 10.1021/es062419g CCC: $37.00 Published on Web 01/24/2007
2007 American Chemical Society
at elevated temperatures has been demonstrated using analytical grade chlorinated solvents and purified water (5, 6), evidence of abiotic degradation during thermal treatment of contaminated field sites is limited to anecdotal reports (7). Experimental evidence to support the degradation of PCE during thermal treatment is limited to three studies. The more recent study used a completely water-filled, gold-walled reactor operating at temperatures between 70 and 100 °C (5). For experiments conducted at 90 °C, the average firstorder half-life for TCE disappearance was 2.1 days, with only CO2 and chloride detected as reaction products. Although no data were published to document PCE disappearance, it was claimed that PCE degradation followed a similar pattern (4). Earlier studies on dissolved-phase PCE stability were conducted in 0.3 mL flame-sealed glass tubes maintained at temperatures ranging from 130 to 170 °C (8). On the basis of rate parameters reported for basic conditions, the firstorder half-life for PCE disappearance was estimated to be greater than 100 000 years at 90 °C. In addition, no changes in the aqueous concentration of PCE were observed in 1 mL glass bulbs containing either galena (PbS), pyrite (FeS2), or subsurface materials from Waterloo, Canada and Columbus, OH that were incubated at 106 °C for 72 h (9). Therefore, it is difficult to predict if a significant fraction of PCE will be destroyed during in situ thermal treatment based on these contradicting sets of experimental results. This study was performed to determine the rate and extent of chlorinated solvent degradation after heating contaminated soil and groundwater samples collected from the Camelot Cleaners Superfund site, West Fargo, ND. The site contained PCE-contaminated clay soil and the samples were collected prior to treating with electrical resistive heating. Soil samples were homogenized, loaded into 25 mL glass ampules, followed by the addition of groundwater, and then flame-sealed to create a batch of 110 ampules. The ampules were incubated at 25, 55, 75, and 95 °C, and ampule contents were sampled after 5, 17, 37, and 75 days to determine the reaction products and rates as a function of temperature. These data were used to determine the importance of chlorinated solvent degradation during thermal treatment of the field site.
Experimental Procedures Materials. Methanol (Optima grade), mercuric chloride (certified ACS), hydrochloric acid (certified ACS), sulfuric acid (trace metals grade), hydroxylamine sulfate (99.98%), ferrous ammonium sulfate (certified ACS), and ferric chloride (certified ACS) were obtained from Fisher Scientific (Fair Lawn, NJ). Formate and glycolate solutions were prepared from 99% grade solids (ACROS Organics, Morris Plains, NJ), while acetate, oxalate, and sulfate solutions were prepared from ACS certified solids (Fisher Scientific, Fair Lawn, NJ). Ferrozine buffer [97%, 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p′-disulfonic acid monosodium salt hydrate], HEPES [99.5%, N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid)], methylene blue [98%, N,N-dimethyl-p-phenylenediamine hemioxalate salt], sodium sulfide (ACS reagent), and 1-butene (99+% grade) were obtained from Sigma-Aldrich (Milwaukee, WI). Field Samples. Soil and groundwater samples were obtained from the Camelot Cleaners Superfund site located in West Fargo, ND by personnel from Current Environmental Solutions (CES, Kennewick, WA). Two soil cores (ca. 1 kg each) were collected from a single borehole (E17) at 45 and 56 feet below ground surface (bgs) using a split-spoon sampler VOL. 41, NO. 5, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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with an acetate liner. The soil, classified as Fargo-Ryan silty clay (fine, smectitic, frigid, Typic Eqiaquerts), was gray, very sticky and plastic, and adhered to glass when wet. Groundwater (1.4 L) was collected from a monitoring well (PMW-10) screened from 45 to 60 feet bgs and located within 50 feet of E17. The contaminants present in methanol extracts of four subsamples from the 45 feet bgs soil core included 1082 ( 924 mg/kg of PCE, with less than 1 mg/kg of toluene and xylene. No contaminants were detected in the 56 feet bgs soil core or in the groundwater. Solids Preparation. The 45 feet bgs core was air-dried and homogenized to create a more uniform initial PCE content and to prevent wet soil from adhering to the ampule neck during loading. The core was dried in an autoclaved glass tray within a laminar flow hood for 12 h at room temperature (25 °C). The concentration of PCE in the soil after drying and homogenization was 14.7 ( 7.0 mg/kg based on methanol extracts of 12 randomly selected soil samples that were collected while loading the ampules. Ampule Preparation. Batch experiments were conducted in clear, 25 mL borosilicate glass ampules (Kimble-Kontes, Vineland, NJ). Prior to use, the ampules were autoclaved for 25 min at 121 °C and then rinsed with deionized water (>18 MΩ cm). The ampules were placed in a glass desiccator, evacuated under a vacuum of 750 mmHg for a period of 1 h, and then backfilled with argon gas. Each ampule was loaded with ca. 6 g of Camelot soil followed by 15 mL of Camelot groundwater. Prior to filling the ampules, the 1.4 L of groundwater was transferred to an autoclaved 2 L flask, and 0.6 L of deionized water was added to provide enough aqueous volume for 110 ampules. After adding soil and water, each ampule was temporarily sealed with aluminum foil and then permanently flame-sealed by melting the top 1 cm of the ampule neck with a propane-oxygen torch. Ampule Incubation. Ampules were incubated at 25, 55, 75, and 95 °C in custom-made enclosures that consisted of ice chests fitted with 1/4 in. i.d. copper tubing. The copper tubing was connected to constant temperature recirculation bath heaters (Neslab RTE-211 and RTE-111) filled with food grade mineral oil (STE Oil Co., San Marcos, TX). Enclosure temperatures were recorded every hour using a K-type thermocouple connected to a data logger (Campbell Scientific, Inc., Logan, UT). The average enclosure temperatures were 53.7 ( 0.6, 77.1 ( 0.5, and 96.7 ( 0.6 °C. Ampules were also stored at room temperature (25 ( 1 °C) in an enclosed container. Analytical Methods. The amount of PCE in methanol from soil extracts was determined using a Hewlett-Packard (HP) Model 6890 gas chromatograph (GC) equipped with a 30 m × 0.32 mm o.d. DB-5 column (Agilent Technologies, Palo Alto, CA) connected to an electron capture detector (ECD). Aqueous-phase concentrations of PCE were determined using a HP6890 GC equipped with a HP7694 headspace autosampler and a 60 m × 0.32 mm o.d. DB-624 column connected to a flame ionization detector (FID). The headspace autosampler was programmed to hold each sample at 70 °C for a period of 15 min prior to transferring the headspace gas to the GC inlet. Calibration standards were prepared by injecting small volumes of a 10 000 mg/L of PCE methanol stock solution into 100 mL volumetric flasks that contained deionized water chilled to a temperature of 4 °C. Gas-phase concentrations of CO and CO2 were determined using a HP6890 GC equipped with a heated gas sampling valve and a 250 µL sample loop, a 30 m × 0.32 mm o.d. Carboxen-1010 column (Supleco, Bellefonte, PA) connected to a custom-made methanizer and FID. Hydrogen concentrations were determined using a reduction gas analyzer (Trace Analytical, Menlo Park, CA). Aqueous-phase concentrations of formate, glycolate, sulfate, and chloride were determined using a Dionex DX-100 ion chromatograph 1730
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FIGURE 1. Concentration of PCE in the aqueous phase of Camelot ampules. Each bar represents the average of five ampules with error bars equal to one standard deviation. equipped with an AS14A IonPac column. Aqueous-phase concentrations of ferrous iron (Fe2+) and total iron (Fe2+ + Fe3+) were determined using the ferrozine method (10) after extraction in 0.5 M HCl for 10 min. The concentration of sulfides (e.g., H2S) was determined using the methylene blue method (11). Petrographic slides mounted with air-dried clay size ( 0.05, Figure 2). The fact that the aqueous-phase PCE concentrations increased with incubation temperature while the solid-phase concentrations remained relatively constant suggests that
FIGURE 2. Concentration of PCE in the solid phase of Camelot ampules. Each bar represents the average of five ampules with error bars equal to one standard deviation.
TABLE 1. Distribution Coefficients (Kd), Enthalpy of Sorption (∆Hs), and Isosteric Heat of Sorption (Qis) for PCE in Ampules Prepared with Camelot Cleaners Superfund Site Soil and Groundwater
d
temp (°C)
average Kd (L/kg)
25 55 75 95 ∆Hs (kJ/mol)c Qis (kJ/mol)d ∆Hs (kJ/mol)e
-2.3a ( 1.3b -1.4 ( 1.0 -1.1 ( 0.7 -0.9 ( 0.8 -12 ( 0.3 -7 ( 5 2(3
a Slope of C vs C . b ( standard error. c Slope of ln(K ) vs T-1. s w d Isosteric heat of sorption. e Slope of ln(Kd/γ) vs T-1.
PCE was strongly sorbed by the Camelot soil. Since the soil was air-dried prior to loading in the ampules, the readily desorbable fraction of PCE was removed by volatilization, leaving behind a more strongly sorbed or slow-desorbing PCE fraction (13). The total amount of PCE initially present in the 25 °C ampules was estimated to be 0.75 ( 0.08 µmol based on the mass of soil added to each ampule and the average concentration of PCE determined in methanol extracts from 12 randomly selected air-dried soil samples that were collected while loading the ampules. The total amount of PCE detected in the ampules after incubation at 25 °C, determined from aqueous samples and methanol extracts of water-wet soil, was 0.24 ( 0.14 µmol (n ) 25), which represents a PCE recovery of 32%. Tetrachloroethylene recovery increased with incubation temperature, ranging from 39 to 83% for ampules incubated at 55 °C, 66 to 120% for ampules at 75 °C, and 72 to 155% for ampules at 95 °C. The increase in PCE recovery with incubation temperature and poor recovery at 25 °C indicates that PCE was sorbed by a fraction of the Camelot soil that was not interrogated by methanol under water-wet conditions. Desorption isotherms were best fit using a linear partition model (see Figures S1 through S4, Supporting Information) to yield linear distribution coefficients (Kd) as a function of incubation time and temperature where the average coefficients are shown in Table 1. The Kd values (negative sign indicates desorption) for each incubation time were calculated from a linear regression analysis of solid-phase concentration (Cs) versus aqueous-phase concentration (Cw) for five ampules at each incubation temperature and duration. The solid-phase concentration was computed from the initial solid-phase PCE mass minus the mass measured in the aqueous phase. The Kd values obtained at 25 °C are within the range of values previously reported for PCE-
contaminated field soils but are from 5 to 10 times greater than reported for soils with ca. 30% clay content (14). Heating the ampules caused decreases in the PCE distribution coefficient, where the average Kd values decreased by 1.6, 2.0, and 2.5 times, respectively, at 55, 75, and 95 °C relative to the value at 25 °C. The observed reductions in Kd values were similar to those for PCE in gravel-till soils, for which a 1.7 times decrease was reported upon increasing the temperature from 22 to 92 °C (15). The enthalpy of sorption (∆Hs, Table 1), calculated from a linear regression of ln Kd versus T-1 (i.e., van’t Hoff plot) for each incubation time, was greater than the +3 kJ/mol of heat of PCE dissolution (16), indicating a strong interaction between PCE and Camelot soil. The isosteric heats of sorption (Qis, Table 1), calculated from aqueous-phase PCE activity values (17), were less exothermic than those calculated from the van’t Hoff plot, although still indicated that PCE-soil interactions were important. The PCE activity values were calculated from the measured aqueous-phase PCE concentrations and the activity coefficient (γ) for each incubation temperature, which was determined from PCE solubility as a function of temperature (18). A modified van’t Hoff plot that used the linear distribution coefficient (Kd) divided by the activity coefficient (γ) was prepared to account for changes in PCE-water fugacity with increasing temperature as suggested by Mader et al. (19) and Farrell et al. (20). Correcting Kd with the activity coefficient resulted in heats of sorption that were endothermic on average and similar to the heat of PCE dissolution. The observation that PCE desorption from Camelot soil was best represented by a linear isotherm, combined with the slightly exothermic to slightly endothermic sorption energies after correcting for PCEwater solution enthalpy, suggest that PCE interacted with a mineral phase in the Camelot soil, rather than a hydrophobic organic phase such as soil organic matter (16). The soil sample collected from 45 feet bgs contained 1.11 ( 0.03 wt % CO2 based on a dry combustion analysis, which was the total carbon content (see Table S2, Supporting Information). However, the soil produced 1.58 ( 0.30 wt % CO2 after addition of 6 N HCl at room temperature, demonstrating that the source of CO2 was from carbonate minerals rather than soil organic matter (21). The concentrations of calcium (0.29 ( 0.01 wt %) and magnesium (0.26 ( 0.02 wt %) were consistent with the presence of dolomite [CaMg(CO3)2] and suggest that this was the source of CO2 in the dry combustion and acid dissolution analyses. The Camelot soil consisted of clay and silt size fractions, with 33% clay ( 0.05) suggests that the decrease in PCE content between 37 and 75 days at 95 °C was the result of a degradation process rather than variability in the initial PCE content. However, the average CO2 content in ampules incubated at 95 °C for 75 days was less than that observed after 37 days at 95 °C and in abiotic control ampules amended with mercuric chloride (Figure 3). On the basis of the correlation between PCE and CO2 ampule content, the lower CO2 content in the 95 °C ampules at 75 days suggests that there was less PCE initially present in the 75 day ampules incubated at 95 °C or that the PCE containing carbonate minerals were only partially degraded in the 75 day ampules as compared to the 37 day ampules. Chloride levels have been used to estimate rates of TCE degradation in ampule experiments conducted with lowchloride deionized water (6). The chloride levels in the Camelot ampules were ca. 300 mg/L, approximately 50 times greater than the amount of PCE (as chloride) initially present. Therefore, native chloride levels obscured the relatively small increases in chloride content that could be attributed to PCE degradation. Alternatively, CO, a product found during thermal degradation of TCE (6), could prove useful for monitoring PCE degradation. In fact, CO levels steadily increased in Camelot ampules incubated at 95 °C (Figure 4). Volatile organic compounds, in addition to PCE, were detected in the gas and aqueous-phase samples collected after 75 days of heating at 95 °C. These compounds included cis-1,2-dichloroethylene (cis-DCE), trans-1,2-dichlorothylene 1732
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FIGURE 4. Amounts of CO and 1-butene in ampules incubated at 95 °C with PCE or PCE-free Camelot soil. (trans-DCE), TCE, 1-butene, benzene, and furan. Furan was identified based on its mass spectrum, while the other compounds were identified by their mass spectrum and capillary column retention time. Several of these compounds, including TCE, cis-DCE, and 1-butene, have been detected as products from the reductive dechlorination of PCE in experiments conducted with zerovalent iron (24). An additional experiment was conducted to evaluate the source of CO and 1-butene using PCE-free soil collected from 56 feet bgs at the Camelot site. Twenty-four ampules were prepared with the PCE-free Camelot soil and deionized water and then incubated at 25 and 95 °C for 75 days. The compounds detected in the PCE-free ampules included CO, CO2, 1-butene, and furan, with a small amount of benzene after 75 days at 95 °C. The amounts of CO formed in these PCE-free ampules were similar (p-values > 0.05) to those found in the ampules that contained PCE (Figure 4). Thus, CO production was attributed to soil diagenesis, rather than to PCE degradation in ampules heated to 95 °C. Carbon dioxide formed during in situ thermal treatment has also been suggested to represent the destruction of chlorinated solvents (4, 5). The concentration of CO2 in the PCE-free ampules incubated at 95 °C for 75 days was 3.6 times greater than in the ampules that contained PCEcontaminated Camelot soil and groundwater. Thus, the CO2 observed in ampules with PCE-contaminated Camelot soil was indicative of soil carbonate degradation, rather than degradation of chlorinated solvents. While the amounts of CO detected in PCE-contaminated and PCE-free ampules heated to 95 °C were similar (Figure 4), more 1-butene was detected in ampules containing PCE as compared to the PCE-free ampules. The difference in the amounts of 1-butene may have been due to PCE degradation or to differences in the aqueous-phase composition of ampules since the PCE-free ampules were filled with deionized water, while the ampules with PCE contained groundwater from the Camelot site. That is, the Camelot groundwater may have contained additional precursors necessary for 1-butene formation. Regardless of the formation pathway, the fact that 1-butene was detected in ampules with PCEfree Camelot soil renders this compound a poor indicator of PCE degradation under these conditions. The observation of 1-butene and furan in the PCE-free ampules demonstrates that soil organic matter was present in the Camelot soil. However, the levels of carbon as CO2 were 400-800 times greater than the amount of carbon associated with 1-butene and furan, which supports the conclusion that the primary source of CO2 was from carbonate degradation. Trichloroethylene was detected in the aqueous phase of ampules containing PCE-contaminated Camelot soil incubated at 55, 75, and 95 °C (Figure S5, Supporting Information)
FIGURE 5. Amount of PCE, TCE, and cis-DCE in aqueous phase of Camelot ampules incubated at 95 °C. Solid lines represent firstorder kinetic model fit by linear regression analysis. and may represent a PCE degradation product. Alternatively, TCE may have been present in the Camelot soil from 45 feet bgs but was only released as the carbonate in the soil was thermally degraded. In either case, the amount of TCE decreased with incubation time, with the greatest decay rate in ampules heated to 95 °C. First-order rate coefficients (k) (Figure S5, Supporting Information) increased with incubation temperature, indicating that the degradation followed the Arrhenius equation
k ) A exp
( ) -Ea RT
(1)
where A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the absolute temperature. A plot of ln(-k) versus T-1 (not shown) yielded an activation energy (Ea) of 44.5 kJ/mol. As compared to the activation energy reported for the degradation of TCE in aqueous-phase systems, the value from this experiment was similar to the 46.9 kJ/mol reported by Knauss et al. (5) but was 2.8 times lower than the 123.1 kJ/mol reported by Jeffers et al. (8). The pre-exponential factor (A) was ca. 500 times lower than reported by Knauss et al. (5), indicating that the presence of Camelot soil and gas phase decreased the rate of TCE degradation. In ampules incubated at 95 °C, the amount of cis-DCE increased with incubation time, coinciding with a decrease in the amount of TCE (Figure 5). This finding suggests that TCE underwent abiotic reductive dechlorination since a similar amount of cis-DCE was also noted in ampules amended with mercuric chloride (abiotic control). The degradation of TCE to cis-DCE was evident only in the 95 °C ampules, as no cis-DCE was detected in the ampules incubated at 55 or 75 °C. The observed transformation of TCE (C2HCl3) to cis-DCE (C2H2Cl2) requires a source of hydrogen as described by ∆
C2HCl3 + H2 98 C2H2Cl2 + HCl
(2)
The level of hydrogen (37.1 ( 12.6 ppmv) in the gas phase of the Camelot ampules incubated at 95 °C for 75 days was approximately 18 times greater than in ampules incubated at lower temperatures. The presence of the additional amount of hydrogen in the 95 °C ampules along with the added thermal energy resulted in TCE hydrogenolysis: the addition of hydrogen to TCE with the elimination of Cl to form cisDCE. This reaction (eq 2) was best fit using a first-order model that also included an initial amount of cis-DCE (0.017 µmol) as shown in Figure 5. The concentrations of other potential reductants, including ferrous iron (Fe2+) and sulfides, were
below the method detection limit. On the basis of the rate coefficients shown in Figure S5 (Supporting Information), the first-order half-lives of TCE were 157 days at 55 °C and 26 days at 95 °C. The rate of PCE degradation necessary to fit the observed TCE degradation at 95 °C (Figure 5) resulted in a PCE halflife of ca. 7000 days using a first-order kinetic model. On the basis of this finding, and the fact that PCE levels remained elevated even after 75 days of heating at 95 °C, it is reasonable to conclude that thermally induced PCE degradation will not be a significant treatment process during electrical resistive heating of the Camelot Cleaners Superfund site. On the other hand, if TCE is present or formed as a reaction product, it would be expected to degrade during treatment with the formation of cis-DCE once temperatures approach 95 °C.
Acknowledgments The authors thank Benaiah M. Jorgensen, Current Environmental Solutions (CES), for providing soil and groundwater samples and W. Crawford Elliott (Georgia Sate University) for assistance with XRD analysis. Support for this research was provided by CES and the Strategic Environmental Research and Development Program (SERDP) under Contract W912HQ-05-C-008 for Project ER-1419, “Investigation of Chemical Reactivity, Mass Recovery, and Biological Activity during Thermal Treatment of DNAPL”. This work has not been subject to SERDP review, and no official endorsement should be inferred.
Supporting Information Available Desorption isotherms for each incubation temperature, equilibrium coefficients (Kd) for each incubation time, results from soil chemical analyses, and disappearance of TCE with incubation time and temperature. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) Carrigan, C. R.; Nitao, J. J. Predictive and diagnostic simulation of in situ electrical heating in contaminated, low-permeability soils. Environ. Sci. Technol. 2000, 34, 4835-4841. (2) In situ thermal treatment of chlorinated solvents: Fundamentals and field applications; EPA 542-R-04-010.; U.S. Environmental Protection Agency, Office of Superfund Remediation and Technology Innovation: Washington, DC, 2004; pp 1-34. (3) Heron, G.; Van Zutphen, M.; Christensen, T. H.; Enfield, C. G. Soil heating for enhanced remediation of chlorinated solvents: A laboratory study on resistive heating and vapor extraction in a silty, low-permeable soil contaminated with trichloroethylene. Environ. Sci. Technol. 1998, 32, 1474-1481. (4) Knauss, K. G.; Copenhaver, S. C.; Aines, R. D. Hydrous pyrolysis/ oxidation process for in situ destruction of chlorinated hydrocarbon and fuel hydrocarbon contaminants in water and soil. U.S. Patent 6,127,592, October 3, 2000. (5) Knauss, K. G.; Dibley, M. J.; Leif, R. N.; Mew, D. A.; Aines, R. D. Aqueous oxidation of trichloroethylene (TCE): A kinetic analysis. Appl. Geochem. 1999, 14, 531-541. (6) Costanza, J.; Davis, E. L.; Mulholland, J. M.; Pennell, K. D. Abiotic degradation of trichloroethylene under thermal remediation conditions. Environ. Sci. Technol. 2005, 39, 6825-6830. (7) Beyke, G. Heat enhanced bioremediation of chlorinated solvents using electrical resistance heating; Presented at The 4th International Conference on Oxidation and Reduction Technologies for In Situ Treatment of Soil and Groundwater: Chicago, IL, 2005. (8) Jeffers, P. M.; Ward, L. M.; Woytowitch, L. M.; Wolfe, N. L. Homogeneous hydrolysis rate constants for selected chlorinated methanes, ethanes, ethenes, and propanes. Environ. Sci. Technol. 1989, 23, 965-969. (9) Jeffers, P. M.; Coty, P.; Luczak, S.; Wolfe, N. L. Halocarbon hydrolysis ratessA search for ionic strength and heterogeneous effects. J. Environ. Sci. Health, Part A 1994, 29, 821-831. VOL. 41, NO. 5, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1733
(10) Stookey, L. L. FerrozinesA new spectrophotometric reagent for iron. Anal. Chem. 1970, 42, 7 and 779. (11) Haddad, P. R.; Heckenberg, A. L. Trace determination of sulfide by reversed-phase ion-interaction chromatography using precolumn derivatization. J. Chromatogr. 1988, 447, 2 and 415420. (12) Davis, E. L. How heat can enhance in situ soil and aquifer remediation; United States Environmental Protection Agency EPA/540/S-97/502. U. S. Environmental Protection Agency, Technology Innovation Office of Solid Waste and Emergency Response: Washington, DC, 1997; pp 1-18. (13) Li, J.; Werth, C. J. Slow desorption mechanisms of volatile organic chemical mixtures in soil and sediment micropores. Environ. Sci. Technol. 2004, 38, 440-448. (14) Delle Site, A. Factors affecting sorption of organic compounds in natural sorbent/water systems and sorption coefficients for selected pollutants. A review. J. Phys. Chem. Ref. Data 2001, 30, 187-439. (15) Sleep, B. E.; McClure, P. D. The effect of temperature on adsorption of organic compounds to soils. Can. Geotech. J. 2001, 38, 46-52. (16) Schwarzenbach, R. P.; Gschwend, P. M.; Imboden, D. M. Environmental Organic Chemistry, 2nd ed.; John Wiley and Sons, Inc.: Hoboken, NJ, 2003; Table 5.3, p 143. (17) Huang, W.; Weber, W. J., Jr. Thermodynamic considerations in the sorption of organic contaminants by soils and sediments. 1. The isosteric heat approach and its application to model inorganic sorbents. Environ. Sci. Technol. 1997, 31, 32383243.
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(18) Knauss, K. G.; Dibley, M. J.; Leif, R. N.; Mew, D. A.; Aines, R. D. The aqueous solubility of trichloroethene (TCE) and tetrachloroethene (PCE) as a function of temperature. Appl. Geochem. 2000, 15, 501-512. (19) Mader, B. T.; Uwe-Goss, K.; Eisenreich, S. J. Soprtion of nonionic, hydrophobic organic chemicals to mineral surfaces. Environ. Sci. Technol. 1997, 31, 1079-1086. (20) Farrell, J.; Hauck, B.; Jones, M. Thermodynamic investigation of trichloroethylene adsorption in water-saturated microporous adsorbents. Environ. Toxicol. Chem. 1999, 18, 1637-1642. (21) Loeppert, R. H.; Suarez, D. L. Carbonate and Gypsum. In Methods of soil analysis, Part 3; Sparks, D. L., Page, A. L., Helmke, P. A., Loeppert, R. H., Soltanpour, P. N., Tabatabai, M. A., Johnston, C. T., Sumner, M. E., Eds.; SSSA Book Series 5, SSSA: Madison, WI, 1996; pp 451-455. (22) Jackson, M. L. Soil chemical analysis: Advanced course, revised 2nd ed.; Parallel Press, University of Wisconsin-Madison Libraries: Madison, WI, 2005; p 44. (23) Aggarwal, V.; Li, H.; Boyd, S. A.; Teppen, B. J. Enhanced sorption of trichloroethene by smectite clay exchanged with Cs+. Environ. Sci. Technol. 2006, 40, 894-899. (24) Arnold, W. A.; Roberts, A. L. Pathways and kinetics of chlorinated ethylene and chlorinated acetylene reaction with Fe(0) particles. Environ. Sci. Technol. 2000, 34, 1794-1805.
Received for review October 9, 2006. Revised manuscript received December 15, 2006. Accepted December 16, 2006. ES062419G
