Ecological Risk of Radiocesium Contamination and Dose Rate Estimation in Anuran Tadpole in Aquatic Environments

Radioactive cesium contamination in inland water bodies following the Fukushima Nuclear Power Plant accident in Japan has persisted for over a decade, potentially causing chronic effects on aquatic biota. This study aimed to understand the transfer factors influenced by environmental parameters and the resulting dose rates of radiocesium in tadpole larvae between river and lake ecosystems. In total, 2830 tadpoles from river ecosystem and 3056 tadpoles from lake ecosystem were analyzed in 80 and 33 composite samples respectively from Fukushima region. The relative effects of environmental parameters in radiocesium concentration ratio in tadpole larvae were compared between river and lake ecosystems using the generalized linear model. The average radiocesium concentration ratio in tadpole did not significantly vary between river and lake ecosystems (i.e., 6063.69 L/kg and 6071.59 L/kg respectively). While water depth exhibited a negative correlation as a prominent parameter affecting radiocesium transfer in lake ecosystems, environmental factors like water depth, temperature, and suspended solids showed significant impact in radiocesium transfer in tadpoles within river ecosystems, as revealed by generalized linear model analysis. Though algae and detritus materials significantly contribute to tadpole larvae nutrition in aquatic habitats, the multivariate analysis did not identify significant variables. Sediment emerged as a common factor facilitating the high transfer rate of radiocesium in tadpoles within aquatic environments. Observations estimated dose rates of radiocesium below 1 µGyh ^-1 in both river and lake ecosystems. However, tadpoles in the river ecosystem experienced higher radiocesium dose rates than those in lake ecosystems (i.e., 0.15 and 0.09 µGyh ^-1 respectively). This highlights the vulnerability of tadpoles in aquatic environments to external sources of radiocesium present in these habitats.