Per- and polyfluoroalkyl substances: toxicokinetics, exposure and health risks

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals containing stable per- or polyfluoroalkyl groups. Recent epidemiological studies have shown that PFAS cause health risks even at low concentrations. This review outlines the toxicokinetics, exposure and health risks of PFAS, with a focus on perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and long-chain perfluoroalkyl carboxylic acids (LC-PFCAs). These compounds are known to interact with various proteins in vivo, including the peroxisomal proliferator-activated receptor-α (PPARα). PFOA and PFOS have been identified as carcinogenic. It is known that PFOA and PFOS are transported by transporters such as organic anion transporter. Significant species differences in the behavior of these compounds exist, with much longer half-lives in humans than in mice and rats. One of the reasons that the half-lives of PFOA and PFOS are long in humans is that their renal clearance is low in humans. For animal toxicity experiments, it is essential that the doses in animal experiments are converted to equivalent doses in humans using pharmacokinetic models. Compared with PFOA, some LC-PFCAs have longer half-lives and accumulate more in the liver. Although tap water is a source of exposure to PFAS, the most common exposure source is food, with seafood being an important source for exposure to PFAS in Japan. PFOS and PFOA concentrations in human blood in Japan have been decreasing in recent years. However, according to clinical guidance published in 2022 by the United States National Academies, most Japanese residents are still in the medium risk group (PFAS concentration in plasma or serum is greater than 2 ng/mL and less than 20 ng/mL) or above. Further research is needed to help reduce exposure, and further risk assessments are required.