Congener specific organic carbon normalized soil and sediment-water partitioning coefficients for the C1 through C8 perfluorinated alkylsulfonic and alkylcarboxylic acids

Sierra Rayne,Kaya Forest

doi:10.1038/npre.2009.3011.1

Abstract

AbstractOrganic carbon normalized soil and sediment-water partitioning (Koc) coefficients were estimated for all C1 through C8 perfluorinated alkylsulfonic acid (PFSA) and alkylcarboxylic acids (PFCA) congeners. The limited experimental Koc dataset for the straight chain C7 through C10 PFCAs and C8 and C10 PFSAs was correlated to SPARC and ALOGPS computationally estimated octanol-water partitioning constants and used to predict Koc values for both branched and linear C1 through C8 isomers. All branched and linear congeners in this homologue range are expected to have Koc values>1, leading to their accumulation in organic matter on sediments and soils, retardation during ground and pore water flow, and the preferential association with dissolved organic matter in aquatic systems. Both increasing perfluoroalkyl chain length and linearity increase Koc values with substantial intra- and inter-homologue variation and interhomologue mixing. Variability in Koc values among the PFCA and PFSA congeners will likely lead to an enrichment of more linear and longer chain isomers in organic matter fractions, resulting in aqueous phases fractionated towards shorter chain branched congeners. The expected magnitude of fractionation will require inclusion in source apportionment models and risk assessments. A comparison of representative established quantitative structure property relationships for estimated Koc values from octanol-water partitioning constants suggests that equilibrium partitioning frameworks may be applicable towards modeling PFCA and PFSA environmental fate processes and warrants further study using other partitioning coefficients for which suitable experimental data is available.

Highlights

Only two datapoints were available for the perfluorinated alkylsulfonic acid (PFSA), similar slopes were observed for the Kow,SPARC and Doctanol,SPARC values across both Perfluoroalkyl acids (PFAs) classes but the PALOGPS slope was substantially higher for the PFSAs compared to the perfluoroalkyl carboxylic acids (PFCAs) (Fig. 2(b)): log10 Koc (L kgoc-1) = 0.453 × log10 Kow,SPARC – 0.561; log10 Koc (L kgoc-1) = 0.439 × log10 Doctanol,SPARC – 1.181; and log10 Koc (L kgoc-1) = 4.082 × log10 PALOGPS – 14.627
Using these regression equations for the PFCAs, Kow,SPARC, Doctanol,SPARC, and PALOGPS values were calculated for all C1 through C8 congeners and the corresponding Koc values estimated via negative linear extrapolation of the relationship observed for the straight chain C7 through C10 isomers (Fig. 3)
Both the Kow,SPARC and Doctanol,SPARC approaches predict that almost all C1 through C8 PFCAs and PFSAs will have log10 Koc values >0 (with the limited exceptions of C4 PFSA 1 and C5 PFSA 3 using the Doctanol,SPARC approach) and should accumulate in sediments and soils

Summary

Introduction

Perfluoroalkyl acids (PFAs) such as the perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs) (Fig. 1) are well established as contaminants widely distributed in the environment that display the capacity for long range transport, bioaccumulation, persistence, and a range of toxicological effects.[1,2,3,4,5,6,7] Longer chain (≥C2) PFCAs and all PFSAs are currently thought to arise solely from the use of commercial perfluorinated surfactants, whereas the C1 PFCA (trifluoroacetic acid; TFA) is both used itself in industry and can be formed via the oxidative degradation of various precursors such as hydrofluorocarbons, anesthetics, trifluoromethylbenzene based pesticides, and waste incineration.[8,9,10] It has been suggested that continuous low level TFA releases from biological and/or geological sources must be present to account for the mass of this compound (ca. 250 to 300 million tons) in global oceans, whereas terrestrial, freshwater, and atmospheric reservoirs are primarily anthropogenically derived.[8,11,12] In general, total PFSA and PFCA concentrations in surface and ground waters and marine systems range widely from the low ng L-1 to low mg L-1 levels depending on age and the proximity to point and nonpoint sources of contamination. [3,7,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74] Wastewaters from semiconductor fabrication plants using photolithographic techniques have the highest reported PFA levels to date, with concentrations reaching well into the mg L-1 range,[75] and even up to g L-1 levels.[76]. 250 to 300 million tons) in global oceans, whereas terrestrial, freshwater, and atmospheric reservoirs are primarily anthropogenically derived.[8,11,12] In general, total PFSA and PFCA concentrations in surface and ground waters and marine systems range widely from the low ng L-1 to low mg L-1 levels depending on age and the proximity to point and nonpoint sources of contamination.

Methods

Results

Conclusion