Biochar alleviates nanoplastics and bisphenol A mediated immunological, neurological and gut microbial toxicity in channel catfish Ictalurus punctatus

Nanoplastics (NPs) and bisphenol A (BPA), exhibit abundant industrial applications, are produced in large volumes and ubiquitously released into the environment, posing a serious threat to ecological and human health. Biochar has been extensively studied for its ability to mitigate the negative effects of contaminants on plants. Therefore, this study aims to investigate whether biochar co-exposure with polystyrene nanoplastics (PS-NPs, size 80 nm) and BPA mitigate their toxic impacts on Ictalurus punctatus and maintain its normal growth. The I. punctatus was exposed individually to PS-NPs (0.5 mg/L) and BPA (0.2 mg/L) as well as co-exposed to PS-NPs + biochar and BPA + biochar for 7 days. Results showed PS-NPs and BPA single exposure caused tissue damage in terms of hepatocyte swelling and gut villi diffusion, and induced oxidative stress. PS-NPs and BPA single exposures led to significant changes in enzymatic activities and genetic expressions of biomarkers related to the immune system, producing inflammatory response. It also led to dysregulation of neurotransmitter enzymes (ACH, ChAT, AChE) and overexpression of neuron genes, resulting in neurotoxicity. Moreover, there was an increase in the diversity and alteration in composition of the gut microbiota (Plesiomonas, Pseudomonas), resulting in dysbiosis of the gut microbiota. However, biochar presence (0.5 g/L) reduced the accumulation of PS-NPs and BPA in fish and contributed to various degrees of mitigation for the toxic impacts of PS-NPs and BPA. Overall, biochar helped to mitigate the negative effects of PS-NPs and BPA on oxidative stress, histopathology, immune system, neurological responses and gut microbiota. This study emphasized the potential of biochar to mitigate the negative impacts of NPs and BPA on aquatic organisms.