The impact of microplastics and copper on sex ratio and oxidative stress: analysis in zebrafish intestine, gonad and brain

The increasing prevalence of emerging pollutants, such as microplastics and heavy metals, poses a major threat to aquatic ecosystems. This study aimed to investigate the individual and combined effects of copper (Cu), polyethylene (PE) and polystyrene (PS) microplastics on embryonic development and sexual differentiation in zebrafish (Danio rerio), as well as biochemical responses in target organs. Exposure trials revealed that copper, at environmentally relevant concentrations, caused high embryonic mortality, developmental delays, and altered heart rates. PE exposure alone induced sublethal effects, including a feminisation trend in sex differentiation. Co-exposure amplified these adverse outcomes, confirming a synergistic interaction. Histological analyses revealed disruptions in sexual differentiation, while biochemical assays demonstrated organ-specific responses. The brain appeared highly vulnerable to copper neurotoxicity, the gonads showed limited antioxidant adaptation, and the intestine displayed subtle but significant changes. These findings highlight the ecological relevance of multi-contaminant exposure scenarios and reinforce zebrafish as a powerful model for toxicological studies. Overall, the interaction between microplastics and heavy metals may compromise reproductive success and population sustainability in aquatic organisms.