Microplastic-metal interactions and their toxicological effects in fish: A comprehensive review

• Metal-laden microplastics pose rising risks, yet their impact is understudied • >80% studies target PS+Cd/Cu, leaving other metal–plastic mixtures largely unexplored • Haematological, genotoxic, and behavioural responses to co-exposures are still unexamined • Mechanistic insights into plastic-metal interactions and toxicity pathways are lacking • Future studies must investigate diverse plastic–metal combinations under realistic conditions Rapid industrialization and population growth have escalated aquatic pollution, threatening biodiversity and human health worldwide. Microplastics (MPs) and metals persist as major pollutants that interact to form toxic mixtures, amplifying harm across aquatic food webs. Fish, ecologically vital and nutritionally important, are particularly at risk. Yet, understanding of the combined effects of MPs and metals remains limited. Most research focuses on single pollutants under artificial conditions, employing inconsistent methodologies and offering scant attention to long-term impacts or molecular mechanisms, thereby hindering accurate risk assessment. In this study, the co-exposure of MPs and metals in fish was reviewed, covering literature published between 2016 and 2025 (154 publications). Nevertheless, endpoints, such as bioaccumulation (8.67%), biochemical (15.33%), molecular (11.33%), and histological (9.33%) responses have been less investigated. Moreover, endpoints, including behaviour (4.00%), haematology (3.33%), and genotoxicity (1.33%) have largely been overlooked. It is worth noting that advanced cellular and molecular techniques, like omics technologies, are rarely employed. Although key pathways, such as caspase activation and apoptosis are documented in co-exposure studies, other cell death cascades remain understudied. Therefore, to address these gaps, future research should adopt more realistic exposure scenarios and diversify MP–metal combinations. To further strengthen the analysis, it should integrate pathway-specific molecular assessments. A holistic, mechanistically informed approach is essential to better understand the toxico-dynamics of co-pollutants and to guide effective ecological risk assessment and pollution mitigation strategies.