Letter to the Editor on Bil et al. 2021 "Risk Assessment of Per‐ and Polyfluoroalkyl Substance Mixtures: A Relative Potency Factor Approach".

Per- and polyfluoroalkyl substances (PFAS) represent a group of compounds of which some are known as "substances of very high concern", "substances that are persistent, bioaccumulative, and toxic", and/or "substances that are persistent, mobile, and toxic." Goodrum et al. (2021), for example, considered concentration addition- and RPF-based methods as inappropriate at this time for PFAS risk assessment due to dissimilarities in the dose-response curves. The EFSA established in this opinion a tolerable weekly intake (TWI) of 4.4 ng EFSA-4 PFAS/kg body weight/week for exposure to the sum of four PFAS congeners: perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), and perfluorohexane sulfonic acid (PFHxS). For some PFAS, linear dose-responses were observed for the whole dose range tested, and for other PFAS, such responses were seen especially for the lowest dose levels. [Extracted from the article]