Degradation of fluorotelomer alcohols: a likely atmospheric source of perfluorinated carboxylic acids

Human and animal tissues collected in urban and remote global locations contain persistent and bioaccumulative perfluorinated carboxylic acids (PFCAs). The source of PFCAs was previously unknown. Here we present smog chamber studies that indicate fluorotelomer alcohols (FTOHs) can degrade in the atmosphere to yield a homologous series of PFCAs. Atmospheric degradation of FTOHs is likely to contribute to the widespread dissemination of PFCAs. After their bioaccumulation potential is accounted for, the pattern of PFCAs yielded from FTOHs could account for the distinct contamination profile of PFCAs observed in arctic animals. Furthermore, polar bear liver was shown to contain predominately linear isomers (>99%) of perfluorononanoic acid (PFNA), while both branched and linear isomers were observed for perfluorooctanoic acid, strongly suggesting a sole input of PFNA from "telomer"-based products. The significance of the gas-phase peroxy radical cross reactions that produce PFCAs has not been recognized previously. Such reactions are expected to occur during the atmospheric degradation of all polyfluorinated materials, necessitating a reexamination of the environmental fate and impact of this important class of industrial chemicals.     

Partitioning of fluorotelomer alcohols to octanol and different sources of dissolved organic carbon

Interest in the environmental fate of fluorotelomer alcohols (FTOHs) has spurred efforts to understand their equilibrium partitioning behavior. Experimentally determined partition coefficients for FTOHs between soil/water and air/water have been reported, but direct measurements of partition coefficients for dissolved organic carbon (DOC)/water (K(doc)) and octanol/ water(K(ow)) have been lacking. Here we measured the partitioning of 8:2 and 6:2 FTOH between one or more types of DOC and water using enhanced solubility or dialysis bag techniques, and also quantified K(ow) values for 4:2 to 8:2 FTOH using a batch equilibration method. The range in measured log K(doc) values for 8:2 FTOH using the enhanced solubility technique with DOC derived from two soils, two biosolids, and three reference humic acids is 2.00-3.97 with the lowest values obtained for the biosolids and an average across all other DOC sources (biosolid DOC excluded) of 3.54 +/- 0.29. For 6:2 FTOH and Aldrich humic acid, a log K(doc) value of 1.96 +/- 0.45 was measured using the dialysis technique. These average values are approximately 1 to 2 log units lower than previously indirectly estimated K(doc) values. Overall, the affinity for DOC tends to be slightly lower than that for particulate soil organic carbon. Measured log K(ow) values for 4:2 (3.30 +/- 0.04), 6:2 (4.54 +/- 0.01), and 8:2 FTOH (5.58 +/- 0.06) were in good agreement with previously reported estimates. Using relationships between experimentally measured partition coefficients and C-atom chain length, we estimated K(doc) and K(ow) values for shorter and longer chain FTOHs, respectively, that we were unable to measure experimentally.     

High-resolution atmospheric modeling of fluorotelomer alcohols and perfluorocarboxylic acids in the North American troposphere

A high spatial and temporal resolution atmospheric model is used to evaluate the potential contribution of fluorotelomer alcohol (FTOH) and perfluorocarboxylate (PFCA) emissions associated with the manufacture, use, and disposal of DuPont fluorotelomer-based products in North America to air concentrations of FTOH, perfluorooctanoic acid (PFOA), and perfluorononanoic acid (PFNA) in North America and the Canadian Arctic. A bottom-up emission inventory for PFCAs and FTOHs was developed from sales and product composition data. A detailed FTOH atmospheric degradation mechanism was developed to simulate FTOH degradation to PFCAs and model atmospheric transport of PFCAs and FTOHs. Modeled PFCA yields from FTOH degradation agree with experimental smog-chamber results supporting the degradation mechanism used. Estimated PFCA and FTOH air concentrations and PFCA deposition fluxes are compared to monitoring data and previous global modeling. Predicted FTOH air concentrations are generally in agreement with available monitoring data. Overall emissions from the global fluorotelomer industry are estimated to contribute approximately 1-2% of the PFCAs in North American rainfall, consistent with previous global emissions estimates. Emission calculations and modeling results indicate that atmospheric inputs of PFCAs in North America from fluorotelomer-based products will decline by an order of magnitude in the near future as a result of current industry commitments to reduce manufacturing emissions and lower the residual fluorotelomer alcohol raw material and trace PFCA product content.     

Urban versus remote air concentrations of fluorotelomer alcohols and other polyfluorinated alkyl substances in Germany

Neutral, volatile polyfluorinated alkyl substances (PFAS) were measured in environmental air samples at two different sites in Northern Germany in spring 2005. The sampling locations were chosen to cover a metropolitan and a rural site, the Hamburg city center, and Waldhof, a background monitoring site. An optimized and validated analytical protocol was used to analyze two sets of parallel high-volume air samples. For both sampling locations as well as for individual samples, field blanks were taken to monitor possible background contamination. Gas chromatography coupled to mass spectrometry using positive chemical ionization (GC/ PCI-MS) was used for quantitative analyses. This article describes the first air concentration data of volatile PFAS outside North America reported in the peer-reviewed literature. The wide distribution of fluorotelomer alcohols (FTOHs), fluorinated sulfonamides, and sulfonamidoethanols (FOSAs/FOSEs) in German environmental air is presented. Furthermore, two volatile PFAS, i.e., N-methyl fluorooctane sulfonamide (NMeFOSA) and 4:2 FTOH, were determined for the first time in environmental air. Minimum-maximum sigmaFTOH concentrations of 64-311 pg/m3 (remote) up to 150-546 pg/m3 (urban) and minimum-maximum sigmaFOSA + FOSE concentrations between 12 and 54 pg/m3 (remote) and 29 and 151 pg/m3 (urban) were determined. 8:2 FTOH and 6:2 FTOH were found to be the predominant POPs determined in Waldhof so far. Blank contamination was found to be negligible. A significant correlation was found with the ambient temperature for the partitioning of airborne FOSEs between the gaseous and particulate phase (R = 0.853), whereas FTOHs and FOSAs were almost exclusively found in the gaseous phase. Furthermore, highest airborne PFAS concentrations were determined at relatively high ambient temperatures. Correlation coefficients (R) for sigmaFTOH and sigmaFOSA + FOSE concentrations with temperature were 0.954 and 0.968, respectively. Finally, the PFAS concentrations determined in this study are set into context with levels of "classical" persistent organic pollutants (POPs) in the same region and PFAS data available for North America.     

Quantitation of gas-phase perfluoroalkyl surfactants and fluorotelomer alcohols released from nonstick cookware and microwave popcorn bags

Fluoropolymer dispersions are used for coating certain cookware products and food-contact packaging to impart oil and water repellency. Since salts of perfluorooctanoic acid (PFOA) are used as a processing aid in the manufacture of many fluoropolymers, it is necessary to determine if these compounds are still present as residuals after the process used to coat nonstick cookware or packaging, and could be released during typical cooking conditions. In this study, we identified and measured perfluoroalkyl carboxylates (PFCAs), particularly PFOA, and fluorotelomer alcohols (FTOHs; 6:2 FTOH and 8:2 FTOH), released from nonstick cookware into the gas phase under normal cooking temperatures (179 to 233 degrees C surface temperature). PFOA was released into the gas phase at 7-337 ng (11-503 pg/cm2) per pan from four brands of nonstick frying pans. 6:2 FTOH and 8:2 FTOH were found in the gas phase of four brands of frying pans, and the sources of FTOHs released from nonstick cookware are under investigation. We observed a significant decrease in gas-phase PFOA following repeated use of one brand of pan, whereas the other brand did not show a significant reduction in PFOA release following multiple uses. PFOA was found at >5 ng during the fourth use of both brands of pans. FTOHs were not found after the second use of either brand of pans. PFOA was found at 5-34 ng in the vapors produced from a prepacked microwave popcorn bag. PFOA was not found in the vapors produced from plain white corn kernels popped in a polypropylene container. 6:2 FTOH and 8:2 FTOH were measured in the vapors produced from one brand of prepacked microwave popcorn at 223 + 37 ng and 258 +/- 36 ng per bag, respectively, but not measured at >20 ng (LOQ) in the other two brands. On the packaging surface of one brand of microwave popcorn several PFCAs, including C5-C12, 6:2 FTOH, and 8:2 FTOH, were found at concentrations in the order of 0.5-6.0 ng/cm2. This study suggests that residual PFOA is not completely removed during the fabrication process of the nonstick coating for cookware. They remain as residuals on the surface and may be off-gassed when heated at normal cooking temperatures.     

Atmospheric lifetime and global warming potential of a perfluoropolyether

Perfluoropolyethers (PFPEs) are a family of perfluorinated fluids used mainly in industrial applications. Lower molecular weight commercial PFPE fractions have boiling points ranging between 55 and 270 degrees C, and have the potential to escape into the atmosphere. To improve our understanding of the atmospheric chemistry of PFPEs, a distilled fraction of a commercial mixture containing perfluoropolymethylisopropyl ethers (PFPMIEs) was introduced into an atmospheric chamber system. Relative rate techniques were used to determine upper limits for the rate constants for reactions of OH and Cl with PFPMIE in 700 Torr of air at 296 K. The reactivity of PFPMIE with Cl was less than 2 x 10(-17) cm3 molecule(-1) s(-1), while the reactivity with OH was less than 6.8 x 10(-16) cm3 molecule(-1) s(-1), indicating low reactivity in the troposphere. Consequently, the lifetime of PFPMIE should be limited bytransport to the mesosphere, where photolysis by Lyman-alpha radiation at 121.6 nm will be efficient. By analogy to perfluorinated alkanes, the lower limit for the total atmospheric lifetime is 800 years. PFPMIE was shown to have instantaneous radiative forcing of 0.65 W m(-2) ppb(-1), which corresponds to a global warming potential on a 100 year time scale of 9000 relative to CO2 and 1.95 relative to CFC-11.     

Concentrations, distribution, and persistence of fluorotelomer alcohols in sludge-applied soils near Decatur, Alabama, USA

Soil samples were collected for fluorotelomer alcohol (FTOH) analyses from six fields to which sludge had been applied and one "background" field that had not received sludge. Ten analytes in soil extracts were quantified using GC/MS. Sludge-applied fields had surface soil FTOH concentrations exceeding levels found in the background field. For 8:2nFTOH, which can degrade to perfluorooctanoic acid, impacted surface-soils ranged from 5 to 73 ng/g dry weight, clearly exceeding the background field in which 8:2nFTOH was not detected. The highest [FTOH] generally was 10:2nFTOH, which had concentrations of <5.6 to 166 ng/g. For the first time, we document the persistence of straight-chained primary FTOHs (n-FTOHs) and branch-chained secondary FTOHs (sec-FTOHs), which are transformation products of n-FTOHs, in field soils for at least five years after sludge application. Ratios of sec-FTOHs to n-FTOHs were highest for 7:2sFTOH/8:2nFTOH (～50%) and decreased with increasing chain length to a minimum for the longest-chained analytes, 13:2sFTOH/14:2nFTOH (～10%). Disappearance half-lives for FTOHs, calculated with these data, ranged from 0.85 to 1.8 years. These analytical results show that the practice of sludge application to land is a pathway for the introduction of FTOHs and, accordingly, their transformation products, perfluorocarboxylic acids, into the environment.     

Quantitative determination of perfluorochemicals and fluorotelomer alcohols in plants from biosolid-amended fields using LC/MS/MS and GC/MS

Analytical methods for determining perfluorochemicals (PFCs) and fluorotelomer alcohols (FTOHs) in plants using liquid chromatography/tandem mass spectrometry (LC/MS/MS) and gas chromatography/mass spectrometry (GC/MS) were developed, and applied to quantify a suite of analytes in plants from biosolid-amended fields. Dichloromethane-methanol and ethylacetate were chosen as extracting solutions for PFCs and FTOHs, respectively. Nine perfluorocarboxylic acids (PFCAs), three perfluorosulfonic acids (PFSAs), and ten FTOHs were monitored. Most PFCAs and perfluorooctanesulfonate (PFOS) were quantifiable in plants grown in contaminated soils, whereas PFCs went undetected in plants from two background fields. Perfluorooctanoic acid (PFOA) was a major homologue (～10-200 ng/g dry wt), followed by perfluorodecanoic acid (～3-170 ng/g). [PFOS] in plants (1-20 ng/g) generally was less than or equal to most [PFCAs]. The site-specific grass/soil accumulation factor (GSAF = [PFC](Grass)/[PFC](Soil)) was calculated to assess transfer potentials from soils. Perfluorohexanoic acid had the highest GSAF (= 3.8), but the GSAF decreased considerably with increasing PFCA chain length. Log-transformed GSAF was significantly correlated with the PFCA carbon-length (p < 0.05). Of the measured alcohols, 8:2nFTOH was the dominant species (≤1.5 ng/g), but generally was present at ≥10× lower concentrations than PFOA.     

Aerobic soil biodegradation of 8:2 fluorotelomer stearate monoester

A laboratory investigation on the biotransformation of 8:2 fluorotelomer stearate monoester (8:2 FTS) in aerobic soils was conducted by monitoring the loss of 8:2 FTS, production of 8:2 fluorotelomer alcohol (8:2 FTOH) and stearic acid, which would be released by cleavage of the ester linkage, and subsequent degradation products from FTOH for 80 d. Soil microcosms were extracted with ethyl acetate followed by two heated 90/10 v/v acetonitrile/200 mM NaOH extractions. 8:2 FTS was degraded with an observed half-life (t(1/2)) of 10.3 d. The rate of 8:2 FTS biotransformation substantially decreased after 20 d with 22% of 8:2 FTS still remaining on day 80. No biotransformation of 8:2 FTS occurred in autoclaved soil controls, which remained sterile with 102 ± 6% recovery, through day 20. 8:2 FTOH was generated with cleavage of the ester linkage of 8:2 FTS followed by a rapid decline (t(1/2) ~ 2 d) due to subsequent biodegradation. All the expected 8:2 FTOH degradation products were detected including 8:2 fluorotelomer unsaturated and saturated carboxylic acids, 7:2s FTOH, 7:3 acid, and three perfluoroalkyl carboxylic acids with the most prominent being perfluorooctanoic acid (PFOA). PFOA consistently increased over time reaching 1.7 ± 0.07 mol % by day 80. Although cleavage of the ester linkage was evidenced by 8:2 FTOH production, an associated trend in stearic acid concentrations was not clear because of complex fatty acid metabolism dynamics in soil. Further analysis of mass spectrometry fragmentation patterns and chromatography supported the conclusion that hydrolysis of the ester linkage is predominantly the first step in the degradation of 8:2 FTS with the ultimate formation of terminal products such as PFOA.     

Quantitative determination of fluorotelomer sulfonates in groundwater by LC MS/MS

Aqueous film-forming foams (AFFF) are complex mixtures containing fluorocarbon- and hydrocarbon-based surfactants that are used to fight hydrocarbon-fueled fires. The military is the largest consumer of AFFF in the United States, and fire-training activities conducted at military bases have led to groundwater contamination by unspent fuels and AFFF chemicals. A direct-injection, liquid-chromatography tandem mass spectrometry (LC MS/MS) method was developed to quantify a suite of fluorotelomer sulfonate surfactants in groundwater collected from military bases where fire-training activities were conducted. The 4:2, 6:2, and 8:2 fluorotelomer sulfonates were detected and quantified in groundwater from two of the three military bases. The total fluorotelomer sulfonate concentrations observed at Wurtsmith AFB, MI, and Tyndall AFB, FL, ranged respectively from below quantitation (< or = 0.60) to 182 microg/L and from 1100 to 14,600 microg/L. Analyses of a fluorotelomer-based AFFF concentrate by negative ion fast atom bombardment/mass spectrometry and LC MS/MS analyses indicate that the AFFF concentrate contains only a small amount of fluorotelomer sulfonates and that fluoroalkylthioamido sulfonates are the main anionic fluorosurfactant in the mixtures. More research is needed to determine the fate of fluoroalkylthioamido sulfonates in the environment.     

Influence of Asian and Western United States urban areas and fires on the atmospheric transport of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and fluorotelomer alcohols in the Western United States

Atmospheric measurements of semivolatile organic compounds (SOCs) were made at Mt Bachelor Observatory (MBO), located in Oregon's Cascade Range, to understand the trans-Pacific and regional transport of SOCs from urban areas. High volume air sampling (approximately 644 m3 for 24 h periods) of both the gas and particulate phases was conducted from April 19, 2004 to May 13, 2006 (n = 69); including NASA's INTEX-B campaign in spring 2006 (n = 34 of 69). Air mass back trajectories were calculated and were used to calculate source region impact factors (SRIFs), the percentage of time the sampled air mass resided in a given source region. Particulate-phase polycyclic aromatic hydrocarbon (PAH) concentrations at MBO increased with the percentage of air mass time in Asia and, in conjunction with other data, provided strong evidence that particulate-phase PAHs are emitted from Asia and undergo trans-Pacific atmospheric transport to North America. Gas-phase PAH and fluorotelomer alcohol (FTOH) concentrations significantly increased with the percentage of air mass time in California's urban areas, whereas retene and polychlorinated biphenyl (PCB) concentrations increased with the percentage of air mass time in Oregon and during regional fire events. In addition, sigma(gas-phase) PAH, retene, and levoglucosan concentrations were significantly correlated (p-value < 0.001) with sigma(PCB) concentrations, suggesting that increased atmospheric PCB concentrations were associated with fires due to the volatilization of stored PCBs from soil and vegetation.     

TiO2-induced heterogeneous photodegradation of a fluorotelomer alcohol in air

Degradation of C4F9C2H4OH in air over TiO2 particles was examined in this first report of gas-solid heterogeneous photochemical degradation of fluorotelomer alcohols (FTOHs), which may be precursors of perfluorocarboxylic acids (PFCAs) in the environment. Photoirradiation (>290 nm) of C4F9C2H4OH in air flowing over TiO2 produced CO2, via C4F9CH2CHO, C4F9CHO, CnF(2n+1)COF (n=2 and/or 3), and COF2, in that order. X-ray photoelectron spectroscopy of the Ti02 surface showed a decrease in the amount of fluorine bonded to carbon and an increase in the amount of F- as the degradation of C4F9C2H4OH in air proceeded. Of the carbon content in the initial C4F9C2H4OH (78.8 ppmv), 90.7% was transformed to CO2, and the predominant fluorine species produced on the TiO2 surface was F-. Fluorotelomer unsaturated acids, which are considered to be toxic and have been observed in the biodegradation of FTOHs, did notform. Increased relative humidity in the air accelerated the decomposition of the reaction intermediates, which led to increased CO2 and F- formation. This result indicates that humidity is a key factor for counteracting FTOHs in indoor air. Although perfluoroalkyl substances such as PFCAs in water reportedly undergo little photodegradation over TiO2, our data show that mineralization of C4F9C2H4OH in air can be achieved with TiO2.     

Effect of fluorotelomer alcohol chain length on aqueous solubility and sorption by soils

Fluorotelomer alcohols (FTOHs) are a group of polyfluorinated alkyl chemicals that have been widely studied as precursorsto perfluorocarboxylates such as perfluorooctanoic acid and for which knowledge on their fate in soils is sparse. The solubility and sorption by soil of the homologous 4:2 to 10:2 FTOHs were measured in water or cosolvent/ water solutions. For the smaller 4:2 and 6:2 FTOHs, solubility and sorption could be measured adequately in aqueous systems although transformation was apparent even in gamma-irradiated and autoclaved systems. Sorption coefficients estimated by measuring both sorbed and solution-phase concentrations were not significantly affected by the biotransformation process. The use of cosolvents was employed for probing the behavior of the longer-chain FTOHs with limited aqueous solubility. A single log-linear correlation between aqueous solubility and modified McGowan molar volumes resulted for the n-alkanols and FTOHs. Soil organic carbon (OC) consistently appeared to be the key soil property influencing sorption of the FTOHs while the perfluorocarbon chain length was the dominant structural feature influencing solubility and sorption. Each CF2 moiety decreased the aqueous solubility by -0.78 log units (compared to 0.60 log units for each CH2 addition in hydrogenated primary alcohols), and increased OC-normalized sorption coefficients (Koc) by -0.87 log units. Good log-log linear correlations between Koc and both octanol-water partition coefficients and solubility were observed for the FTOHs.     

Biotransformation of 8:2 fluorotelomer alcohol in soil and by soil bacteria isolates

The microbial transformation of 8:2 fluorotelomer alcohol (FTOH) to perfluorocarboxylic acids, including the globally detected perfluorooctanoic acid (PFOA), has recently been confirmed to occur in mixed bacteria cultures, activated sludge, and soil. However, little is known to date about the microbes involved in the transformation. In the present study, the effect of three carrier solvents (ethanol, octanol, and 1,4-dioxane), which may serve as carbon sources, on the aerobic degradation rate of 8:2 FTOH and metabolite distribution was evaluated both in a clay loam soil and in two pure soil bacterial cultures. Biodegradation pathways appeared similar regardless of the solvent; however, significant differences in 8:2 FTOH degradation rates were observed: 1,4-dioxane > ethanol > octanol. In the presence of 1,4-dioxane, which is not easily biodegraded, 8:2 FTOH degradation was the fastest With octanol, which is a structural analogue of 8:2 FTOH, the transformation was inhibited, but upon depletion of octanol, 8:2 FTOH was biodegraded. In the pure culture study, two soil bacterial strains, Pseudomonas species OCY4 and OCW4, enriched from soil using octanol as a sole carbon source, also transformed 8:2 FTOH without prior exposure or acclimation to 8:2 FTOH. Increased biomass resulting from octanol metabolism did increase 8:2 FTOH transformation rates; however, 8:2 FTOH could not support bacterial growth, indicating the transformation by pure cultures was via cometabolic processes.     

In vitro interactions of biological nucleophiles with fluorotelomer unsaturated acids and aldehydes: fate and consequences

Fluorotelomer unsaturated aldehydes and acids (FTUALs and FTUCAs) are intermediate metabolites that form from the biotransformation of fluorotelomer-based chemicals. FTUALs and FTUCAs have been previously suggested to contribute to the toxicity associated with human exposure to fluorotelomer compounds by covalently binding to biological nucleophiles. However, the extent of their reactivity has only been assessed with glutathione. The purpose of the present study was to assess the reactivity of these intermediate metabolites with a series of nucleophilic amino acids and model proteins. In vitro experiments were carried out in an aqueous buffer system to determine the reactivity of nucleophilic amino acids with FTUCAs and FTUALs having varying fluorinated chain lengths. Using (19)F NMR spectroscopy to monitor the disappearance of the FTUCAs and FTUAL signals and the production of a fluoride signal, reaction rate constants were determined under pseudo-first-order conditions. The FTUCAs reacted only with cysteine with the following second order rate constants: 3.63 (± 1.37) × 10(-5) min(-1) mM(-1) (4:2 FTUCA), 1.19 (± 0.91) × 10(-5) min(-1) mM(-1) (6:2 FTUCA), and 4.56 (± 0.94) × 10(-5) min(-1) mM(-1) (8:2 FTUCA). The FTUALs were significantly more reactive than any of the FTUCAs with reactivity decreasing in the following order: cysteine > histidine > lysine > arginine. The following second-order rate constants were obtained: 5.7 (± 4.2) × 10(-4) min(-1) mM(-1) (histidine), 4.3 (± 1.4) × 10(-4) min(-1) mM(-1) (lysine), and 1.4 (± 0.73) × 10(-4) min(-1) mM(-1) (arginine). FTUCAs and FTUALs were also reacted with model proteins to assess their potential for forming covalent adducts. Electrospray ionization mass spectrometry (ESI-MS) was used to investigate the stoichiometry of FTUCAs and FTUALs covalently bound to apomyoglobin (ApoMg) and human serum albumin (HSA). FTUCAs were not reactive, whereas two measurable FTUAL adducts were formed with both ApoMg and HSA at each of the FTUAL chain lengths (6:2, 8:2, and 10:2). This is the first study to probe the reactivity of FTUALs and FTUCAs with nucleophiles other than glutathione, further elucidating possible FTUAL and FTUCA fate within biological systems.     

Solubility and sorption by soils of 8:2 fluorotelomer alcohol in water and cosolvent systems

The solubility and sorption by five soils of 8:2 fluorotelomer alcohol (FTOH) were measured from water and cosolvent/ water solutions. Aqueous solubility and soil-water distribution coefficients (Kd,w, L kg(-1)) were extrapolated from cosolvent data using a log-linear cosolvency model and compared to direct aqueous measurements. Liquid chromatography tandem mass spectrometry with electrospray ionization was employed to analyze the 8:2 FTOH in solutions and soil extracts. The cosolvent-extrapolated water solubility is 0.224 mg L(-1), in good agreement with the measured value of 0.194 mg L(-1). All sorption isotherms were generally linear regardless of cosolvent composition or soil organic carbon (OC) content. Kd,w values extrapolated from cosolvent data were similar but consistently higher than those measured in aqueous solutions. The latter was hypothesized to be due to dissolved OC (DOC) in the aqueous slurries. An average log KDOC of 5.30 was estimated and supported by DOC and Kd,w measurements at two soil-water ratios. Sorption appeared to be driven by hydrophobic partitioning with a log KOC value of 4.13 +/- 0.16. Irreversible sorption was also observed and appeared to be related to OC content, with the extraction efficiency reduced from 85% to 45% with increasing contact time from 3 to 72 h for the highest OC soil.