Co-exposure toxicity of microplastic and sumithion in Nile tilapia – changes in growth, hematology, histopathology of internal tissues and immune-antioxidant genes expression

The widespread contamination of aquatic environment by microplastics (MP) and chemical pollutants, including pesticides, pose a severe threat to aquatic organisms. This research investigates the cumulative toxicity of polyamide microplastics (PA-MP) and the organophosphate pesticides sumithion (Sum) on Nile tilapia (Oreochromis niloticus). Over the course of 42 days, the fish were subjected to three exposure treatments; 10 mg/L PA-MP, 0.3 mg/L Sum, and a combined exposure to both (MP + Sum), including a control (without MP and Sum). The primary focus of this study was to evaluate growth parameters, hematological indices, tissue histopathology, and the expressions of genes linked to immune regulation and anti-oxidant responses. Co-exposure to MP + Sum led to a significant reduction in growth attributes including final body weight, weight gain, and specific growth rate (SGR), while impaired feed utilization may reflect diminished metabolic efficiency. Hematological analysis revealed a significant rise in blood glucose levels and a decline in the hemoglobin concentration in the co-exposure group, pointing to stress-induced metabolic imbalances. In addition, erythrocyte morphology exhibited notable alterations with common occurrences of karyopyknosis, nuclear bridges, and micronuclei, suggesting genotoxic effects. The histopathological changes observed in gill such as secondary lamellar degeneration, clubbing, hyperplasia of chloride cell, and intestinal tissues including degeneration of columnar epithelium, hyperplasia of intestinal mucosa, degeneration of lamina propria from epithelium, reinforced the severity of the combined exposure. The upregulation of immune-related genes like TNF-α, and IFN-γ, pointing to an inflammatory response, whereas the downregulation of IL-1β and SOD highlighted a declined in both antioxidant and immune-responses. This underscores the enhanced toxicity caused by the simultaneous exposure to microplastic and pesticide pollutants and highlights the urgent need for integrated approaches to pollution management in aquatic ecosystems to mitigate these synergistic effects.