Research priorities for the environmental risk assessment of per- and polyfluorinated substances (PFAS).

Per- and polyfluorinated substances (PFAS) are a group of thousands ubiquitously applied persistent industrial chemicals. The field of PFAS environmental research is developing rapidly, but suffers from substantial biases towards specific compounds, environmental compartments, and organisms. The aim of this perspective was therefore to highlight current developments, and to identify knowledge gaps and subsequent research needs that would contribute to a comprehensive environmental risk assessment for PFAS. To this end, we consulted the open literature and databases, revealing that knowledge of the environmental fate of PFAS is based on the analysis of less than 1% of the compounds categorized as PFAS. Moreover, soils and suspended particulate matter (SPM) remain largely understudied. PFAS bioavailability, bioaccumulation and food web transfer studies also focus on a very limited number of compounds and are biased towards aquatic biota. Fish are predominantly studied, while aquatic invertebrates and macrophytes are included less frequently. The available ecotoxicity data revealed that only a few PFAS have been well-studied for their environmental hazards, and that PFAS ecotoxicity data are strongly biased towards aquatic organisms as well. This emphasizes the need to catch up with ecotoxicity studies in the terrestrial environment. Considering the persistency and bioaccumulation of PFAS, more chronic, multigeneration and community ecotoxicity studies are needed. Finally, we identified the urgent need to unravel the relationship between sorption, bioaccumulation and ecotoxicity on the one hand and molecular descriptors of PFAS chemical structures and physicochemical properties on the other, to enable prediction of exposure, bioaccumulation and toxicity.