A revised and improved toxicokinetic model to simulate serum concentrations of bioaccumulative PFAS

Minnesota has been grappling with public health issues regarding exposure to per- and polyfluoroalkyl substances (PFAS) since 2002. For some PFAS, the traditional paradigm for developing health-based water guidance values (HBGVs) is inadequate due to their tendency to accumulate within the body and to transfer from mother to newborn via placental transfer and breastfeeding. In 2017, the Minnesota Department of Health (MDH) developed an Excel-based model to simulate daily serum PFAS concentrations over a lifetime of exposure to facilitate the derivation of HBGVs for bioaccumulative PFAS. Model results compare favorably to data on breastfed infants, who represent a susceptible and highly exposed population. Since 2017, new data have emerged that warranted a re-evaluation of key model parameters. Here, we present a revised and updated version of the 2017 model and assess the impact of the updates on the model results for perfluorooctanoate (PFOA). Updates to the model’s calculations and input parameters resulted in a 57% reduction in peak modeled PFOA serum concentrations in 1-year-old infants compared to the original model. However, the significantly lower epidemiologic-based reference serum concentration of 0.93 ng/mL (compared to the laboratory animal-based value of 130 ng/mL used in 2017) resulted in a decrease in the noncancer guidance value from 35 to 0.24 ng/L. Currently available serum PFOA data indicate that at drinking water concentrations at or below ~1 ng/L, drinking water would not be a major source of PFOA exposure compared to non-water sources.