The interplay between Cadmium and Zinc Induced Developmental Perturbations and Apoptosis in Daphnia Magna

Assessing combined toxicity provides a realistic and comprehensive approach to determining toxicological effects in aquatic species under environmentally relevant conditions. This study was conducted to understand the effects of single and combined metal mixtures on freshwater flea and Daphnia magna. Environmentally Relevant Concentrations (ERCs) of Cadmium (Cd) and Zinc (Zn) at a low dose (10μg/L) and high dose (30 μg/L) were employed for single and joint acute exposure (48 h) to investigate the associated mortality rate, heartbeat rate, growth rate, deformities rate, morphological changes and Apoptosis. Compared to a single exposure, the combined exposure of Cd and Zn induced elevated developmental toxicity, with pronounced bioaccumulation in the gut. Further, co-exposure showed the highest mortality (62%) in a dose-dependent treatment, compared to single-exposure groups. In all the treatments, the predominant morphological defects included missing tail, antenna, bioaccumulation, blood clotting, carapace alterations and shrinking organs, compared to the control group. However, faster bioaccumulation was observed after 12 h of Cd + Zn co-exposure. Furthermore, Acridine Orange (AO) staining revealed high Apoptosis, specifically in the head, antennae and gut or abdominal area in all samples. The Spearman correlation indicated a significant positive correlation between deformity and mortality rate in D. magna, suggesting the synergistic toxicity of Cd +Zn. In conclusion, single and mixture exposure to Cd + Zn at the ERC induced developmental impacts and Apoptosis in D. magna. Here, the combined toxicity assessment of heavy and trace metals mimics the realistic scenario, aiding authorities in further regulating the use of these elements and minimizing associated ecological health risks.