Mixture toxicity of perfluoroalkyl substances on the aquatic invertebrate Gammarus roeselii

• Different PFAS have additive toxicity in a mixture to Gammarus roeselii. • Sulphonic acid PFAS induce higher toxicity than carboxylic acid PFAS. • Toxicity of PFCAs increases with increasing perflourinated carbon chain length. • PFOA toxicity to Gammarus roeselii is more pronounced at higher temperatures. In recent years, PFAS (per- and polyfluoroalkyl substances) have been the focus of increasing attention due to their persistent, bioaccumulative and toxic properties. Given the variety of PFAS compounds, and potential interacting effects on biota, assessment of mixture toxicity is crucial in risk assessment. In this study, the acute toxic effects of the perfluorinated and polyfluorinated alkyl substances (PFAS), namely perfluorooctanoic acid (PFOA), perfluorosulfonic acid (PFOS), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) on the freshwater amphipod Gammarus roeselii were investigated for the first time, considering single and mixture effects at different ratios. Under acute exposure scenarios, a higher toxicity of the perfluoroalkyl carboxylic acids (PFCAs) with increasing chain length was demonstrated, with LC 50 values ranging from 9 to 65 mg/L. In addition, the toxicity of sulphonic acid derivatives (such as PFOS) was found to be five times higher than that of carboxylic acid derivatives (such as PFOA). The combination of different PFAS in mixtures showed a general additive toxicity effect, but the combination of a perfluorosulfonic acid (PFOS) with a perfluorocarboxylic acid (PFOA) suggests a slight synergistic effect. These results highlight the need for a better understanding of PFAS mixture effects, to improve environmental risk assessment and protection of aquatic health.