In vivo and in vitro assessment of absorption and disposition kinetics of bis[2-(perfluorohexyl)ethyl] phosphate in rats: food effect, physiologically-based modeling, and human exposure estimation.

Bis[2-(perfluorohexyl)ethyl] phosphate (6:2 diPAP) is a widely used per- and poly-fluoroalkyl substance of toxicological concern considering its environmental persistence and potential for human exposure. To establish a mechanistic basis for evaluating internal exposure, this study experimentally characterized the kinetics of 6:2 diPAP following intravenous and oral dosing in rats and developed a physiologically-based kinetic (PBK) model by integrating in vivo, in vitro, and in silico datasets. Following intravenous administration, 6:2 diPAP exhibited a long half-life (32.1 ± 4.3 h) and low clearance (86.2 ± 20.8 mL/h/kg), while oral dosing resulted in near-complete bioavailability. Its systemic exposure was substantially higher in fasted rats than in fed rats for both routes. Renal elimination was negligible, while biliary excretion accounted for 14.5% of the intravenous dose. The estimated hepatic clearance was 75.3 mL/h/kg in rats, based on an intrinsic clearance of 334 ± 56 mL/h/kg (i.e., a sum of metabolic clearance from rat liver S9 fractions and biliary clearance), supporting hepatic metabolism and biliary excretion as the primary elimination pathways. The developed PBK model adequately captured plasma concentration-time profiles for both fed and fasted rats. When extrapolated to human subgroups for reverse dosimetry to estimate external exposure levels corresponding to biomonitoring data, the PBK model indicated that the observed internal 6:2 diPAP concentrations are unlikely to originate solely from dietary sources. Collectively, these findings provide a mechanistic understanding of the absorption and disposition kinetics of 6:2 diPAP and support quantitative evaluation of its exposure and potential health risks in human populations.