Microplastic (MP) pollution is a growing concern and is now one of the most important scientific issues in the field of ecology and environment. Previous studies have shown that the ingestion of MPs is widespread among many aquatic species, including fish, crustaceans, and marine mammals. In aquatic organisms, MPs can cause a wide range of toxic effects, including growth inhibition,
histopathological changes, oxidative stress, metabolic disturbances, behavioral changes, inflammatory reactions, and others. The toxicity of MPs is exacerbated by their ability to adsorb and transport chemical pollutants and pathogens, posing additional risks to aquatic organisms and humans in the food chain. The toxic effects of MPs in marine ecosystems are currently beingextensively investigated. However, less attention has been paid to freshwater organisms, and as a consequence, the ecotoxicological effects of MPs in these ecosystems have not been sufficiently investigated. Given that freshwater ecosystems are direct reservoirs and transporters of MPs, and are also characterized by lower water volumes and a greater dependence on anthropogenic activities, freshwater biota are at a higher risk of exposure to MPs. The thesis will include experimental studies on the toxicity of various polymer types of MPs, nanoplastics, and tire wear particles to salmonids, which are one of the main sources of MP pollution in the environment. Cytogenetic, biochemical, hematological, and biological parameters will be assessed to evaluate the toxic potential of MPs for salmonids at different stages of their development and to predict the mechanisms of toxicity. The results will be useful for the development or adjustment of current guidelines for the assessment of exposure to complex stressors and environmental risk, and may contribute to the improvement of monitoring programs for aquatic ecosystems. The research may also contribute to the integration of biological-chemical monitoring, leading to a better understanding of the cause-effect relationships between environmental pollution (as a causal factor) and changes in biodiversity and ecological status in aquatic ecosystems. Additionally, the research could provide a basis for the application of new criteria, the development of practical guidelines for the assessment of biological impacts of MPs, and could contribute to methodological advances in evaluating the status of aquatic ecosystems.