Current water quality guidelines may not protect wildlife from PFOS bioaccumulation in freshwater ecosystems

Accumulation of perfluorooctane sulfonate (PFOS) has been demonstrated in biota across the globe. Higher trophic-level air-breathing organisms that live in or depend on aquatic ecosystems are most at risk from PFOS and other bioaccumulative per- and polyfluoroalkyl substances (PFAS). Nonetheless, there are very few guidelines available for the protection of air-breathing wildlife. The Australian and New Zealand Guidelines for Fresh and Marine Water Quality provide Default Guideline Values (DGVs) for toxicants. These DGVs are based on traditional ecotoxicological tests that do not consider bioaccumulation. For chemicals known to bioaccumulate, the guidelines recommend a precautionary approach by applying the DGV that protects 99% of species. The PFAS National Environmental Management Plan (NEMP) provides Wildlife Diet Guidelines (WDGs) to protect mammals and birds that consume aquatic organisms. Other jurisdictions have developed Water Quality Criteria for the protection of wildlife via the use of dietary studies and combined with bioconcentration factors to back-calculate a safe concentration of PFOS in the water. As end users tend to use Water Quality Guidelines/Criteria as screening tools for further risk assessment, it is critically important to understand whether these PFOS guidelines effectively protect wildlife. In 2022-2023, water, sediment, and biota samples were collected over a year at eight sites in southeast Queensland, Australia. The dominant PFAS found in biota was PFOS, with the only other PFAS found in biota to be long-chain perfluorocarboxylic acids (PFCAs). Fifty percent of the sites had mean PFOS surface water concentrations that were below the draft Australian DGV, and yet all but one had biota concentrations that exceeded the NEMP WDGs. Bioaccumulation factors (BAFS) in fish were inversely related to concentrations of PFOS in water and showed a high variability within species and sites. Considering this, an interim field derived screening threshold is proposed for wildlife risk assessments.