Fate and behavior of microplastics in freshwater systems

The extensive utilization and mismanagement of plastic have led to the ubiquitous presence of microplastics in the environment. The freshwater system has received much attention recently due to the prevalence of high concentrations of microplastics concerning marine systems. Rivers, streams, lakes, and estuaries situated proximate to urban and industrial areas are undoubtedly prone to high amounts of microplastic contamination via wastewater effluents, agricultural runoffs, floods, and storm water. In some cases, even remote freshwater sources do not escape from microplastic pollution due to the input pathways flown across urban stretches. The distribution and fate of microplastics in the freshwater are affected by the physicochemical properties of the plastic particle, such as the size, shape, density, color, polymer type, and the natural processes such as biofouling, heteroaggregation, and weathering. Microplastics eventually enter into the marine waters, enabling their settlement in deep oceanic sediments or consumption by marine biota. Besides, particle dispersion and their transport pathways are governed by hydrological, geographical, and meteorological factors of the freshwater system. These factors are effectively utilized and assessed through models to predict their fate and distribution in the aquatic system, that is, Lagrangian transport model, Global NEWS model, Nano DUFLOW model, and INCA contaminants model. In freshwater, microplastics are eventually taken up by a wide variety of freshwater biota, initiated from primary producers at the base of the food chain up to higher trophic predatory animals. The interaction could lead to trophic transfer and bioaccumulation of microplastics over the food chain, posing hazardous toxicological effects on all trophic levels.