Influence of Amphibian Metamorphosis on the Biokinetics and Biodistribution of Radionuclides Cesium and Strontium

Amphibians currently face a global decline due to numerous stressors, including contaminated ecosystems. Radionuclides, while less prevalent than other anthropogenic contaminants, can pose a threat to aquatic environments due to their long physical half-lives and tendency to accumulate in organisms. This study investigated the accumulation, depuration, and biodistribution of ¹³⁴Cs and ⁸⁵Sr in amphibians through metamorphosis. Limnodynastes peronii tadpoles were exposed to dissolved ¹³⁴Cs and ⁸⁵Sr for 6 days and then depurated in clean water for up to 12 days. Whole-body Cs and Sr burdens were analyzed daily using gamma spectrometry. The biodistribution of radionuclides in tadpole tissues was also analyzed at three developmental stages (premetamorphosis, onset of metamorphic climax, and completion of metamorphosis). At the end of the depuration period, 49% of the initial ¹³⁴Cs and 67% of ⁸⁵Sr were retained. Cesium accumulated predominantly in the remains (i.e., muscle tissue and undissected organs) and gut, whereas Sr was found mainly in the remains and leg bones. The increased Cs and Sr concentrations in the remains and leg bones, respectively, at the completion of metamorphosis suggest the transference of these radionuclides from degenerating tissues, such as the tail. This research highlights the need to consider developmental stages in the assessment of contaminant impacts on amphibians.