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

This study determined the sorption affinity to artificial phospholipid membranes (K-MW) for series of perfluorinated carboxylates (PFCAs), perfluorinated sulfonates (PFSAs), alkyl sulfates (CxSO4), and 1-alkanesulfonates (CxSO3). A sorbent dilution assay with solid supported lipid membranes (SSLM) showed consistent CF2 unit increments of 0.59, and CH2 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; CxSO4 sorbed 0.75 log units stronger than analogue CxSO3 anions. The log K-MW values for the octyl analogues increase in the order H(CH2)(8)SO3- (1.74) < H(CH2)(8)SO4- (2.58) < F(CF2)(8)CO2- (PFNA, 4.04) < F(CF2)(8)SO3- (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 CF2 and CH2 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 (LC50,narc). The LC50,narc coincides with the lowest reported acute LC50 values for several anionic surfactants but were on average about an order of magnitude lower.