Micro- and nanoplastics as vectors of aquatic pollutants and genotoxicity: An integrated review across aquatic and mammalian systems with special reference to the scenario in India.

Microplastics (MPs) and nanoplastics (NPs) are environmental pollutants with paramount implications for aquatic ecosystems and, through that route, human health, particularly due to their oxidative stress-mediated genotoxic potential. This review is a synthesis of findings from recent studies, with emphasis on the scenario in India, on the bioavailability, toxicological risks, and cellular mechanisms of MPs and NPs (MNPs) in various organisms, separately addressing evidence from aquatic models, including marine mussels, common carp, zebrafish, rotifers, etc., and mammalian systems relying essentially on in vitro studies. Key evidence indicates that MPs adsorb persistent organic pollutants like Polycyclic Aromatic Hydrocarbons (PAHs), enhancing their bioavailability and inducing oxidative stress, immunological alterations, and developmental toxicity, which are closely associated with DNA damage and chromosome instability. As regards aquatic organisms, combined exposure to MPs and heavy metals to fish models exacerbates biochemical disruptions and immune suppression, along with oxidative stress-linked genotoxic responses such as DNA strand breaks and micronucleus formation. Zebrafish embryos exhibit microcirculation dysfunction and pathological angiogenesis upon NP exposure. Mammalian cell studies reveal size-dependent cytotoxicity, with smaller NPs causing greater oxidative damage and membrane disruption, which triggers mitochondrial dysfunction, excessive ROS production, cell-cycle arrest, and activation of DNA damage response pathways, evidenced by micronucleus formation, chromosomal abnormalities, and oxidative DNA lesions. Overall, toxicity is influenced by particle size, charge and co-contaminants, with oxidative stress emerging as the central mechanism that connects cellular toxicity to genetic damage. This review underscores the urgent need for integrated, multidisciplinary approaches to assess the environmental and toxicological risks of MNPs with special emphasis on standardized genotoxicity assessment, while informing regulatory and mitigation strategies for the future.