Membrane-Water Partition Coefficients to Aid Risk Assessment of Perfluoroalkyl Anions and Alkyl Sulfates

Abstract

This study determined the sorption affinity to artificial phospholipid membranes (K MW ) for series of perfluorinated carboxylates (PFCAs), perfluorinated sulfonates (PFSAs), alkyl sulfates (C x SO 4 ), and 1-alkanesulfonates (C x SO 3 ). A sorbent dilution assay with solid supported lipid membranes (SSLM) showed consistent CF 2 unit increments of 0.59, and CH 2 unit increments of 0.53, for the log K MW of perfluorinated and hydrogenated anions, respectively. PFSAs sorbed 0.90 log units stronger than analogue PFCAs; C x SO 4 sorbed 0.75 log units stronger than analogue C x SO 3 anions. The log K MW values for the octyl analogues increase in the order H(CH 2 ) 8 SO 3 - (1.74) < H(CH 2 ) 8 SO 4 - (2.58) < F(CF 2 ) 8 CO 2 - (PFNA, 4.04) < F(CF 2 ) 8 SO 3 - (PFOS, 4.88). Intrinsic partition ratios determined on a phospholipid coated HPLC column (IAM-HPLC) closely aligned with SSLM K MW values. COSMO-RS based molecular calculations of K MW aligned with SSLM K MW values for hydrogenated anions with C 8 -C 14 alkyl chains but strongly underestimated CF 2 and CH 2 unit increments for C 4 -C 8 based anions. Dividing the critical narcotic membrane burden of 100 mmol/kg by the experimental K MW predicts lethal baseline toxicity concentrations (LC 50,narc ). The LC 50,narc coincides with the lowest reported acute LC 50 values for several anionic surfactants but were on average about an order of magnitude lower.