Microplastics and PFAS as ubiquitous pollutants affect potencies of highly toxic chemicals in mixtures

Pollutants usually occur as mixtures in the environment, where they affect each other's toxicity even at non-toxic concentrations. Despite the environmental relevance of interactions in complex mixtures, they remain severely understudied. Therefore, this study aimed to assess how PFAS and microplastics (MPs) as ubiquitous pollutants at (non-)toxic concentrations affect the potencies of highly toxic chemicals in mixtures. Experiments were performed to assess the toxicity of perfluorobutane sulfonamide (FBSA), linear low-density polyethylene MPs (0-50 µm), chlorpyrifos and imidacloprid to the reproduction of the springtail Folsomia candida in Lufa 2.2 soil, as single compounds, binary and ternary mixtures. FBSA at non-toxic concentrations showed dose-dependent synergism with imidacloprid, but antagonism with chlorpyrifos. Synergism only occurred in the ternary mixtures dominated by FBSA at non-toxic concentrations and imidacloprid. MPs and toxic concentrations of FBSA were antagonistic in all mixtures. In conclusion, MPs and FBSA affected insecticide toxicity, and assuming concentration addition for the hazard assessment of ternary mixtures is generally precautionary. Ternary interactions could not be reliably predicted from binary interactions, and ratio-specific interactions may be overlooked. This emphasizes the need to include experimental mixture toxicity data for a realistic risk assessment of complex chemical mixtures.