The influence of chain length on the sorption of C4-C10 perfluorocarboxylic acids during transport in a sand

The impact of chain length on the retention and transport of perfluorocarboxylic acids (PFCAs) in a quartz sand was investigated. Short-chain (C4-C7: PFBA, PFPeA, PFHxA, PFHpA) and long-chain (C8-C10: PFOA, PFNA, PFDA) PFCAs were selected as a representative homologous series. Miscible-displacement transport experiments were conducted under saturated conditions to characterize the magnitudes of sorption mediating retention and transport. Quantitative-structure/property-relationship (QSPR) analysis was applied to characterize the influence of molecular size on sorption. The transport of the long-chain PFCAs exhibited greater retardation than the short-chain PFCAs. The log of the equilibrium sorption coefficient (Kd) exhibited a biphasic relationship with carbon number and molar volume, with the magnitude of measured sorption for the short-chain significantly greater than would be predicted using the QSPR regression developed for the long-chain PFCAs. This is consistent with batch-measured data reported in the literature, and likely reflects the relative influence of different sorption mechanisms for the short-chain vs long-chain PFCAs.