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 (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.