Effect of different sizes and concentrations of polystyrene microplastic on the histopathology of Goldfish (Carassius auratus)

Nowadays, the presence of microplastics in aquatic ecosystems is a serious challenge for aquatic animals. In this study, the accumulation of polystyrene microplastic (PS-MPs) and its toxic effects on histology of liver and intestines of goldfish was investigated. A total of 231 healthy fish with an average weight of 18.55±2.41 g was selected in the spring of 2019. Microplastic 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, 68 fish were exposed to a constant concentration (PS-MPs) of 300 µg/L of both 0.25 and 8 μm PS-MPs. Liver and intestinal tissue were sampled for 7 days and the samples were imaged using a fluorescent microscope. Then, 168 fish were exposed to non-fluorescent microplastics with different concentrations (0, 5, 0.5, 0.05 ppm) for 28 days to determine histopathological lesions. The results showed that both sizes can accumulate in liver and intestinal tissues. Examination of liver histopathology showed different complications such as bleeding, necrosis, cell swelling, bile stasis, thinning of the sinusoidal space and accumulation of blood compared to the control group, the severity of lesions increased with increasing concentrations in a group of size. There was no predictable trend, but the intensity of destruction was greater at 0.25 μm. Examination of intestinal tissue lesions showed different complications such as necrosis, loss of intestinal villi, vacuolation, villi decay and degeneration of epithelium in both size groups compared to the control group. In general, microplastics have destructive tissue effects on goldfish. Most tissue lesions were observed at the highest concentration (5 mg/l). The severity of particles with a size of 0.25 μm was higher than the size of 8 μm, with destructive effects observed first in the intestine and then in the liver.