Toxicity of microplastics and per- and polyfluoroalkyl substances in sentinel freshwater models, Daphnia, Zebrafish and unicellular green algae: A systemic review

Microplastics (MP) and per- and poly-fluoroalkyl substances (PFAS) are persistent environmental contaminants that raise concern due to their potential toxicity to ecosystems and human health. Despite their widespread co-occurrence in freshwater environments, their individual and combined effects on aquatic biota remain poorly understood. This study applied a systematic workflow to identify and analyse 68 relevant studies from over 4,000 screened on the toxicity of MP and/or PFAS in three key freshwater ecotoxicology models: Daphnia , zebrafish, and unicellular green algae. The review highlights differences between acute and chronic exposure effects, emphasizing the need for chronic studies to capture life-cycle impacts. Findings indicate that MP toxicity varies based on shape, size, and polymer type, with chronic exposure at environmentally relevant concentrations showing greater toxicity than acute exposure. Studies on combined toxicity suggest that MP-associated chemicals exacerbate toxic effects, raising concerns as "virgin" MP are rare in natural environments. For PFAS, Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were the most studied and widely detected contaminants, with PFOS exhibiting greater toxicity. Few studies showed that some “newer” PFAS have similar toxicity to PFOS and PFOA, while mixtures of PFAS displayed synergistic effects on freshwater organisms. Notably, only one recent study assessed the combined toxicity of PFAS and MP in Daphnia , highlighting a critical research gap. This review identifies key knowledge gaps and research priorities to advance understanding of MP and PFAS mixtures, supporting efforts to protect freshwater ecosystems and public health. • PFAS mixtures exhibited synergistic toxic effects on Daphnia and zebrafish. • Increased toxicity/bioconcentration of PFAS with increasing carbon chain length. • Newer PFAS, PFOS and PFOA alternatives, displayed similar toxic effects on aquatic biota. • Mixtures of MPs + associated chemicals display higher toxicity than MPs alone. • MPs shapes, sizes and polymer type contribute to their toxicity on aquatic biota.