Plastic pollution has become one of the most important environmental problems worldwide due to the extensive production, consumption, and persistence of plastic materials. Microplastics MPs , generally defined as plastic particles smaller than 5 mm, have emerged as widespread contaminants in marine, freshwater, coastal, and sedimentary environments. They originate either directly from products or industrial processes, known as primary microplastics, or through the fragmentation and degradation of larger plastic items, known as secondary microplastics. Their small size, persistence, high surface area to volume ratio, and ability to interact with other contaminants make microplastics particularly important emerging pollutants in aquatic ecosystems. Microplastics enter aquatic environments through domestic and industrial wastewater, urban runoff, atmospheric deposition, synthetic textile fibers, tire wear, fishing activities, and the degradation of larger plastic debris. Once released, their transport and environmental fate are influenced by particle size, shape, density, polymer type, weathering, biofilm formation, hydrodynamic conditions, and sediment characteristics. Microplastics have been detected throughout the water column and in sediments, demonstrating that their distribution is not restricted to surface waters. Aquatic organisms ranging from plankton and benthic invertebrates to fish can ingest microplastics directly or indirectly through contaminated food. Microplastic exposure has been associated with oxidative stress, inflammation, impaired growth, altered behavior, reproductive impairment, and physiological disturbances in aquatic organisms. In addition, plastic surfaces can be colonized by microorganisms, forming the aquatic “plastisphere”, which may influence microbial communities, nutrient cycling, pathogen dissemination, and antimicrobial resistance . Although laboratory studies provide substantial evidence of biological effects, ecological risks should be interpreted carefully because experimental concentrations and particle characteristics do not always reflect environmentally realistic conditions. Therefore, standardized monitoring, environmentally relevant experiments, improved waste management, reduction of plastic pollution at its source, and international cooperation are essential. This review evaluates the major sources, environmental fate, biological effects, food web interactions, ecological consequences, and management strategies associated with microplastics in aquatic ecosystems. Microplastics, aquatic ecosystems, nanoplastics, ecotoxicology, bioaccumulation. 70-76 Issue-5 Volume-10 Latife Ceyda Irkin