Why are PFOS ecological surface water quality criteria so different between countries? A review of differences in...

Ecological surface water quality criteria (SWQC) for perfluorooctane sulfonic acid (PFOS) vary several orders of magnitude between jurisdictions. Such differences can undermine confidence in the SWQC and their scientific basis. The current study undertakes a sensitivity analysis to investigate the factors that drive the differences observed in the PFOS SWQC published by the United States, Australia, and Canada. Each jurisdiction follows a broadly similar three-step procedure when deriving SWQC: (1) selecting reliable ecotoxicological data from the literature (Variable 1, Study Selection); (2) extracting a suite of values that are protective of individual aquatic taxa (Variable 2, Data Reduction); and (3) deriving a final singular value that is protective of aquatic ecosystems (Variable 3, SWQC Derivation). We found substantial differences between the studies deemed reliable in each jurisdiction (Variable 1). Applying each jurisdiction's data reduction and SWQC derivation procedures (Variables 2 and 3) to the other jurisdictions' datasets showed generally comparable outcomes, except for Australia. Aspects of Australia's data reduction and SWQC derivation approach were unique and resulted in materially lower (i.e., greater than an order of magnitude difference) SWQC values. We suggest clarification of the scientific rationale behind the decision making for difference-driving steps and greater alignment between jurisdictions, based on sound scientific reasoning, to increase regulatory consistency and transparency and decrease overall uncertainty in promulgated SWQC.