Background: There is a concern that continued emissions of per- and polyfluoroalkyl substances (PFASs) may cause environmental and human health effects. PFASs are a broad class of man-made substances that have been produced and used in commercial products and industrial processes for more than 60 years, and are now widespread in human populations. Phasing out the manufacture of some types of PFASs started in the year 2000.

Objectives: To investigate whether concentrations of PFASs in humans and in the environment are changing significantly, and whether such changes can be related to implemented phase-outs or regulatory actions. Another aim is to understand why conflicting temporal trends may be reported.

Methods: A systematic review was conducted according to the guidelines by Collaboration for Environmental Evidence (CEE). Searches for primary research studies were performed in bibliographic databases, on the internet, through stakeholder contacts and in review bibliographies. As meta-analysis was not feasible, this review is focused on a narrative synthesis.

Results: Human concentrations of PFOS, PFDS, and PFOA are generally declining, while previously increasing concentrations of PFHxS have begun to level off. Rapid declines for PFOS-precursors have also been consistently observed. In contrast, limited data indicate that human concentrations of PFOS and PFOA are increasing in China. Human concentrations of longer-chained PFCAs (C9-C14) are generally increasing or show insignificant trends.

Conclusions: Declining trends in humans contrast with findings in wildlife and in abiotic environmental samples, suggesting that declining PFOS, PFOS-precursor and PFOA concentrations in humans likely resulted from removal of certain PFASs from commercial products or from food packaging. Increasing concentrations of long-chain PFCAs are likely due to increased use of alternative PFASs. For humans, more temporal trend studies are needed in regions where manufacturing is most intense, as the one human study available in China is much different than in North America or Europe. Temporal trends of PFASs in the southern hemisphere are largely uninvestigated.