Dose rate estimation of freshwater wildlife inhabiting irrigation ponds in restricted areas of the Fukushima Dai-ichi Nuclear Power Plant accident

To assess risks of ionising radiation to freshwater environments in the exclusion zone of the Fukushima Dai-ichi Nuclear Power Plant accident, absorbed dose rates to aquatic organisms possibly inhabiting irrigation ponds were estimated using the ERICA Assessment Tool from the 134Cs and 137Cs radioactivity monitoring data from 2013 to 2017. In each year, the total dose rates to benthic organisms were in the same or higher levels compared with those to pelagic organisms. Among pelagic organisms, total dose rates to amphibian, bird and pelagic fish were two orders of magnitude higher than those to plankton. Total dose rates to insect larva, which attained a maximum of 130 μGy h-1, were higher than those to the other benthic organisms. The dose rates to benthic organisms increased from 2013 to 2015 and remained constant thereafter. In 50–93 % ponds, dose rates to at least one taxon of freshwater organisms, all of which were benthic organisms, exceeded the ERICA screening level (10 μGy h-1). Comparison of the estimated dose rates with the ICRP’s derived consideration reference levels suggests that radioactive contamination was not likely to damage amphibians, birds, pelagic fish, benthic fish, crustaceans, and insect larvae, except for a limited number of the most severely contaminated ponds