Oxidative stress, neurotoxicity, and intestinal microbial regulation after a chronic zinc exposure: an experimental study on adult zebrafish (Danio rerio)

Zinc is one of the heavy metals present in textile wastewater with high concentrations. However, the chronic toxic effects of zinc on aquatic vertebrates are still ambiguous. Zinc accumulation in zebrafish after chronic zinc exposure and toxic effects on the intestines, muscles, and gills were investigated in this study. The results showed that a significant accumulation of zinc in the intestine, muscle, and gill was observed after 25 d of zinc exposure. The toxic effects of zinc were mainly in the form of zinc-induced oxidative stress in zebrafish, potential neurotoxicity, and changes in intestinal microbes. Significant changes in the levels of superoxide dismutase, catalase, metallothionein, glutathione, and malondialdehyde indicated that zinc damaged the antioxidant system of adult zebrafish. Zinc exposure resulted in a significant decrease in acetylcholinesterase activity and abnormal neural signaling. Furthermore, zinc exposure resulted in increased intestinal microbial richness and decreased the Simpson index in adult zebrafish. At the phylum and genus levels, the predominant microbes in the intestine are altered by zinc. In summary, this study provides an analysis of the toxic effects of chronic zinc exposure on adult zebrafish and the potential mechanisms, which are important for assessing the dual effects of zinc on aquatic organisms.