Screening the baseline fish bioconcentration factor of various types of surfactants using phospholipid binding data.

Fish bioconcentration factors (BCFs) are commonly used in chemical hazard and risk assessment. For neutral organic chemicals BCFs are positively correlated with the octanol-water partition ratio ( K _OW ), but K _OW is not a reliable parameter for surfactants. Membrane lipid-water distribution ratios ( D _MLW ) can be accurately measured for all kinds of surfactants, using phospholipid-based sorbents. This study first demonstrates that D _MLW values for ionic surfactants are more than 100 000 times higher than the partition ratio to fish-oil, representing neutral storage lipid. A non-ionic alcohol ethoxylate surfactant showed almost equal affinity for both lipid types. Accordingly, a baseline screening BCF value for surfactants (BCF _baseline ) can be approximated for ionic surfactants by multiplying D _MLW by the phospholipid fraction in tissue, and for non-ionic surfactants by multiplying D _MLW by the total lipid fraction. We measured D _MLW values for surfactant structures, including linear and branched alkylbenzenesulfonates, an alkylsulfoacetate and an alkylethersulfate, bis(2-ethylhexyl)-surfactants ( e.g. , docusate), zwitterionic alkylbetaines and alkylamine-oxides, and a polyprotic diamine. Together with sixty previously published D _MLW values for surfactants, structure-activity relationships were derived to elucidate the influence of surfactant specific molecular features on D _MLW . For 23 surfactant types, we established the alkyl chain length at which BCF _baseline would exceed the EU REACH bioaccumulation (B) threshold of 2000 L kg ^-1 , and would therefore require higher tier assessments to further refine the BCF estimate. Finally, the derived BCF _baseline are compared with measured literature in vivo BCF data where available, suggesting that refinements, most notably reliable estimates of biotransformation rates, are needed for most surfactant types.