Quantitative Estimation of Relative Contributions of Direct and Indirect Exposures to Perfluorooctane Sulfonate in Organisms Using the Isomer Profiling Technique

Abstract

It remains a big challenge to estimate the relative importance of direct vs indirect (via precursors) exposures of animals and humans to perfluorooctane sulfate (PFOS). In this study, fish as a biological model were exposed to PFOS and its typical precursor, perfluorooctane sulfonamide (PFOSA), singly and combined with different ratios in water for 76 days, followed by a 21-day depuration. Isomer-specific kinetic parameters including uptake, elimination, and biotransformation rates as well as bioconcentration factor (BCF) and biotransformation accumulation factor (BTAF) of PFOS were obtained based on single exposures. Single exposure to PFOS or PFOSA led to an opposite change in the % n-PFOS (increase vs decrease) in the fish blood. Based on the obtained kinetic parameters of each isomer, a quantitative model describing the relationship between % n-PFOS in blood and the relative concentration percentage of PFOSA in water was established. As verified by the coexposure tests, the model exhibited a promising performance in quantitative prediction of relative contribution of precursor exposure in water to the body burden of PFOS in fish. Field application of the model suggested that in addition to gill uptake, dietary exposure should be considered to generate more accurate results.