Study on bioaccumulation and histopathological effects of microplastic polystyrene on Goldfish (Carassius auratus)

 Microplastics are known to be emerging contaminants and there are widespread concerns about their potential toxic effects. Histopathological study is one of the appropriate methods in diagnosing the effects of environmental pollutants on aquatics. In this study, the accumulation and adsorption of polystyrene microplastics (PS-MPs) in the gills of Goldfish were identified and its toxic effects on gill histology were investigated. A total of 232 healthy, productive fish, with an average weight of 18.55±2.41 g, were selected. Microplastics were synthesized in two size ranges (0.25 and 8 μm) with two different functions (fluorescent and non-fluorescent). The experiments were performed in two stages. Initially, after the adaptation period, 64 fish were exposed to a constant concentration (PS-MPs) of 300 µg/L of both sizes (0.25 μm) and 8 (PS-MPs) fluorescent. Gill tissue was sampled at 24, 48 and 168 hours and samples were taken using a fluorescent microscope. Then, to determine the histopathological lesions, 168 fish were exposed to non-fluorescent microplastics at different concentrations (0,0.05, 0.5 and 5 ppm) for 28 days and were analyzed for histological lesions. After 168 hours of exposure at 300 µg/L of fluorescent particles, it was found that both dimensions (0.25 and 8 μm) were accumulated in gill tissue. The highest concentration of MP particles accumulated in gill tissue averaged in particles with dimensions of 8 (0.701±  0.098) μm and 0.25 (0.272 ±  0.046) μm, was determined as μg of gill dry weight per milligram. Examination of gill pathology revealed complications such as lamellar aneurysm, secondary blade epithelium protrusion, lamellar deviation, secondary blade connection, lamella shortening and paving in both size groups compared to the control group, but the severity of complications was different in each concentration. It can be concluded that although microplastics have accumulated in the gills of fish and have affected tissues, their potential toxic effects are largely unknown and further studies are needed.