The relative importance of fecal and urinary excretion of perfluorooctane sulfonic acid and perfluorooctanoic acid after high exposure – An observational study in Ronneby, Sweden

Background: Many poly- and perfluoroalkyl substances (PFAS) are persistent and have long half-lives in the human body. However, there are limited data on the different routes of elimination. Most pharmacokinetic models assume that the urinary route dominates.

Objectives: Our aim was to investigate the relative importance of fecal and urinary elimination for linear perfluorooctane sulfonic acid (L-PFOS), branched PFOS and perfluorooctanoic acid (PFOA), and to estimate volumes of distributions (Vds).

Methods: Drinking water highly contaminated with PFAS from firefighting foam was distributed to many households in Ronneby, Sweden, from the 1980s to December 2013. In 2016, PFAS levels were measured in matched serum, feces and urine samples from 147 subjects. Daily urinary and fecal PFAS elimination was estimated through urinary creatinine elimination and dry fecal mass, respectively. Longitudinal serum PFAS elimination rates were used together with fecal and urinary elimination rates to estimate Vds.

Results: In 2016, the median serum concentrations were 100 ng/mL for L-PFOS and 10 ng/mL for PFOA. L-PFOS was eliminated primarily through feces, with a median urinary elimination of 91 ng/day and median fecal elimination of 364 ng/day. The branched PFOS had, similarly, a primarily fecal elimination. In contrast, PFOA had a slightly higher urinary elimination, with median urinary elimination of 26 ng/day and fecal elimination of 15 ng/day. Median Vds were estimated at 93 mL/kg for PFOS and 74 mL/kg for PFOA.

Conclusion: Fecal elimination was shown to be an important route for PFOS and PFOA elimination. Pharmacokinetic models need to take fecal elimination into consideration.