Congener-specific organic carbon-normalized soil and sediment-water partitioning coefficients for the C1 through C8 perfluoroalkyl carboxylic and sulfonic acids

Abstract

Organic carbon-normalized soil and sediment-water partitioning coefficients (Koc) were estimated for all C1 through C8 perfluoroalkyl carboxylic (PFCA) and sulfonic (PFSA) acid congeners. The limited experimental Koc data set for the straight chain C7 through C10 PFCAs and C8 and C10 PFSAs was correlated to SPARC and ALOGPS computationally estimated octanol-water partitioning/distribution constants and used to predict Koc values for both branched and linear C1 through C8 isomers. Branched and linear congeners in this homologue range are generally 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 estimating Koc values from octanol-water partitioning constants suggests that these equilibrium partitioning frameworks may be applicable towards modeling PFCA and PFSA environmental fate processes.