Cadmium bioaccumulation dynamics during amphibian development and metamorphosis

Cadmium pollution poses a significant threat to aquatic ecosystems due to its propensity to bioaccumulate and cause toxicity. This study assessed the complex dynamics of cadmium uptake, accumulation and distribution across anuran development to provide new insights into the fate of cadmium burdens during metamorphosis and compare the susceptibility of different life stages to cadmium accumulation. Tadpoles of various developmental stages were exposed to dissolved 109-cadmium and depurated in clean water in a series of experiments. Temporal changes in whole-body and tissue concentrations were analysed using gamma spectroscopy, and anatomical distributions were visualised using autoradiography. Results showed that animals exposed at the onset of metamorphic climax (forelimb emergence) retained significantly less cadmium than animals exposed through larval stages. After exposure, cadmium partitioned predominantly in the skin, gills and remains of metamorphs, whereas larvae accumulated cadmium predominately through their gut. This shows a shift in the primary route of uptake at the onset of climax, which relates to the structural and functional changes of uptake sites through metamorphosis. During climax, some cadmium was redistributed in tissues developing de novo, such as the forelimbs, and concentrated in the regressing tail. Our findings highlight the need for stage-specific considerations in assessing exposure risks. Environmental implications Cadmium is classified as a hazardous substance of high priority due to its persistence, toxicity, and tendency to accumulate in living organisms. This research provides new insights into the accumulation dynamics of cadmium during anuran metamorphosis, emphasising the importance of considering development when assessing exposure risks. This is important as amphibians are among the most threatened animal groups and are found to be more vulnerable to some stressors during metamorphic stages. Additionally, our findings highlight the significance of understanding the fate of contaminant burdens through ontogeny, as toxicants can be transferred across ecosystem boundaries through predation and metamorphosis.