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

This study determined the sorption affinity to artificial phospholipid membranes ( KMW) for series of perfluorinated carboxylates (PFCAs), perfluorinated sulfonates (PFSAs), alkyl sulfates (C xSO4), and 1-alkanesulfonates (C xSO3). 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 KMW of perfluorinated and hydrogenated anions, respectively. PFSAs sorbed 0.90 log units stronger than analogue PFCAs; C xSO4 sorbed 0.75 log units stronger than analogue C xSO3 anions. The log KMW values for the octyl analogues increase in the order H(CH2)8SO3- (1.74) < H(CH2)8SO4- (2.58) < F(CF2)8CO2- (PFNA, 4.04) < F(CF2)8SO3- (PFOS, 4.88). Intrinsic partition ratios determined on a phospholipid coated HPLC column (IAM-HPLC) closely aligned with SSLM KMW values. COSMO-RS based molecular calculations of KMW aligned with SSLM KMW values for hydrogenated anions with C8-C14 alkyl chains but strongly underestimated CF2 and CH2 unit increments for C4-C8 based anions. Dividing the critical narcotic membrane burden of 100 mmol/kg by the experimental KMW 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.