Letter to the editors regarding “The conundrum of the PFOA human half-life, an international collaboration”

Campbell et al. (2022) propose that many studies estimating the human half-life of perfluorooctanoic acid (PFOA) are significantly confounded by lack of accounting for ongoing exposures, which would inflate estimates, and by the presence of branched isomers, which could deflate estimates for linear PFOA. The authors suggest that the most accurate estimate comes from a single study, Zhang et al. (2013), of PFOA urinary clearance in the general population. However, a critical review of published human observational studies presents no such conundrum. Studies of larger, highly-exposed populations with longer follow-up periods provide reliable half-life estimates >2 years, consistent with empirical and modeled serum:drinking water ratio data not discussed herein due to space constraints. Thus, the weight of evidence strongly supports a human PFOA half-life >2 years.