Epidemiological Findings

Abstract

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are man-made compounds which have been extensively used over the past 60 years. They are detectable globally in humans and animals. Among several PFAS compounds, perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonate (PFHxS), and perfluorononanoic acid (PFNA) have been most examined in epidemiological studies. In the United States PFOS is found at the highest levels in human serum, followed by PFOA. Median human serum levels are dropping for most PFAS in the US since phase out of production, but they are still being used in manufacturing a variety of products. PFHxS has a much longer elimination half-life [geometric mean: GM (GM: 7.3 years)] than PFOS (GM: 4.8 years) or PFOA (GM: 3.5 years). Serum PFOA concentration has been linked with increased serum lipids, and uric acid levels in occupational cohorts, a highly exposed community population, and general population studies. PFAS exposure has also been associated with adverse effects on thyroid homeostasis, liver enzymes, osteoarthritis, non-malignant kidney disease, and immunotoxicity, in some studies but the associations are inconsistent. Data are sparse but largely negative for Type 2 diabetes neurodegenerative disease, children’s cognition, adult CVD and stroke, immune function, liver disease, and obesity. Despite a large body of literature, and some positive findings regarding low birth weight, the data are overall inconsistent regarding reproductive/developmental outcomes in relation to PFAS. In conclusion current epidemiologic evidence suggests that there is an association between PFOA and six health outcomes: high cholesterol, ulcerative colitis, thyroid disease, testicular cancer, kidney cancer, and pregnancy-induced hypertension, although some of the findings come from only one large longitudinal study of a high exposed population, and have not been replicated elsewhere. Data remains limited for health effects of other PFAS. Longitudinal studies in populations with exposure above general background levels are needed to corroborate these results and increase our understanding of PFAS exposure and health outcomes.