In Vivo and In Vitro Assessment of Bis[2-(perfluorohexyl)ethyl] Phosphate Kinetics in Rats: Food Effect and Physiologically-Based Modeling

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 human exposure. To establish a mechanistic basis for evaluating internal exposure and associated risks, this study obtained experimental data on 6:2 diPAP kinetics following intravenous and oral dosing in rats and performed physiologically-based kinetic (PBK) modeling by integrating in vivo/in vitro/in silico datasets. Following intravenous administration, 6:2 diPAP exhibited a long half-life (32.1±4.3 h) and slow clearance (86.2±20.8 mL/h/kg), while oral administration resulted in near-complete bioavailability. Its systemic exposure was substantially higher in fasted rats than in non-fasted rats for both routes. Renal elimination was negligible, while biliary excretion accounted for 14.5% of the intravenous dose. The calculated hepatic clearance was 75.3 mL/h/kg (based on an intrinsic clearance of 334±56 mL/h/kg, 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 PBK model adequately captured plasma concentration-time profiles in non-fasted and fasted rats. This study provides experimental evidence and mechanistic insights into the absorption and disposition of 6:2 diPAP in rats, establishing a foundation for future exposure extrapolation and quantitative risk assessment.