The relative importance of faecal and urinary excretion of PFAS and implications for epidemiological studies

BACKGROUND AND AIM Some per- and polyfluoroalkyl substances (PFAS) are persistent with long half-lives. Elimination rates and half-lives for PFAS have been described in animal and human studies, but there is little data on the importance of different routes of excretion, and many reviews have assumed that the renal route is primary. The aim is therefore to address the magnitude of faecal vs renal excretion for PFAS in a population highly exposed to PFAS. METHODS Municipal drinking water contaminated with PFAS was distributed to many households in Ronneby, Sweden. The source was firefighting foam used nearby since the mid-1980s. Clean water was provided from December, 2013. Faeces and urine samples have been collected from over 200 participants in the serum biomonitoring programme with parallel measurements of multiple PFAS, including: perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS), linear perfluorooctane sulfonate (L-PFOS) and branched PFOS. This study will estimate the distribution of individual excretion rates by the two routes in this population based on concurrent measured PFAS in serum, blood, and faeces. Preliminary data presented here are for 51 subjects with repeated blood measurements between 2014 and 2018, in a half-life study. RESULTS For PFOA median concentrations were 10 ng/ml in serum, 0.02 ng/ml in urine and 0.6 ng/g dry weight in faeces, corresponding to estimated elimination rates of 28 and 17 ng/day via urine and faeces respectively. Faecal elimination was generally less than urinary, median ratio 0.45. Equivalent median faecal/urinary daily elimination ratios were 0.18 for PFHxS and 3.65 for PFOS. CONCLUSIONS Faecal elimination is important and for some PFAS, eg L-PFOS, far outweighs renal elimination. This has implications for epidemiological studies using serum concentration, as measured levels are sensitive to gut excretion rates, and variation in this rate has the potential to confound associations with some outcomes studied. KEYWORDS PFAS, Biomonitoring