Bioaccumulation and sub-chronic toxicity of microplastic environmentally relevant concentrations in Etroplus...

Numerous ecosystem-based studies have explored microplastic pollution in brackish water environments. However, research on the bioaccumulation of microplastics in brackish water fish and their effects remains limited. The present study investigated the bioaccumulation and effects of polystyrene microplastics (PS-MPs) in juvenile brackish water fish, pearl spot (Etroplus suratensis). Fish were exposed to 0, 0.2, 2, and 4 mg/L of 1 µm-sized PS-MPs for 14 days. PS-MPs were found in the gastrointestinal tract, gills, liver, spleen, muscle, and brain, with the highest concentration in the intestine and the lowest in the brain. Exposure to PS-MPs led to elevated serum level of glucose, total protein, total cholesterol, serum glutamic-oxaloacetic transaminase (SGOT), serum glutamic-pyruvic transaminase (SGPT), and alkaline phosphatase (ALP). Antioxidant parameters such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and total antioxidant capacity (TAC) decreased, while malondialdehyde (MDA) level and protein carbonyl (PC) content increased. PS-MP exposure down-regulated hepatic expression of NRF2 and P53, increased cortisol levels, and up-regulated HSP70 gene expression in a dose-dependent manner. Additionally, PS-MPs down-regulated expression of IGF1 and CYP1A in the liver. This is the first comprehensive research that has revealed the extent to which PS-MPs accumulate in various tissues of brackish water fish species after being exposed to environmentally significant concentrations. It also demonstrates the associated toxicity in an array of antioxidant indicators.