Microplastics as Emerging One Health Threats: A Molecular and Ecotoxicological Review Across Aquatic Life with Emphasis on Fish

Microplastics (MPs) are increasingly detected environmental contaminants in both marine and freshwater ecosystems, with reported concentrations ranging from a few to thousands of particles per cubic meter depending on location and methodology. Although growing evidence suggests potential risks to aquatic organisms, the extent of their ecological and biological impacts is still under active investigation. Their size, persistence and capacity to transport chemical additives and co-contaminants allow them to enter biological systems by ingestion and respiration. When ingested, MPs cause oxidative stress, inflammation, and metabolic disorders, resulting in the destruction of vital tissues in major body organs including liver, gills, intestines, and brain. They also change gene expression, cause endocrine and immune pathway perturbation, induce apoptosis, and cause gut microbiome dysbiosis, all of which worsen the health and survival of the organism. MPs also serve as vectors of heavy metals, antibiotics, pesticides, and pathogens and enhance toxicity due to the Trojan horse effect and enable bioaccumulation in food webs. Due to their widespread presence in water, soil, air, and food, MP pollution has direct effects on human, animal, and ecosystem health. This review synthesizes current knowledge on the sources of MPs, the mode of exposure, and the mechanism of toxicity and new ecological implications. It also presents mitigation measures, and stresses a One Health paradigm as the key to taking concerted action on the international level to minimize MP pollution and protect both the environment and human health.