Concentration ratios of ²³⁸U and ²²⁶Ra for insects and amphibians living in the vicinity of the closed uranium mine at Ningyo-toge, Japan

There is still a scarcity of data on the transfer of naturally occurring radionuclides to wildlife in various ecosystems. In the present study, concentration ratios (CR_wo-media) of ²³⁸U and ²²⁶Ra were obtained for grasshoppers, frogs and newts in terrestrial and freshwater ecosystems. Soil, water and animal samples were collected for 2 years in the vicinity of the closed uranium mine at Ningyo-toge, Japan. Three sites with different ²³⁸U and ²²⁶Ra levels were of interest: (1) pond and its shore (PO); (2) low-level stream and its shore near overburden dump (OD); and (3) uranium mill tailings pond and its shore (MP). The activity concentrations in both soil and water were PO approx. = OD < MP for ²³⁸U, and PO < OD < MP for ²²⁶Ra. Regarding the wildlife, ²³⁸U was able to be determined for all samples, but the detection of ²²⁶Ra was observed only for part of the samples. The means and standard deviations of CR_wo-soil or CR_wo-water were then calculated and may indicate the insignificant dependence of CR_wo-media on environmental conditions characterized by the tested sites. The present data on CR_wo-media were compared to the corresponding data or surrogate data from the IAEA's database, showing both agreement and discrepancy. Our data contribute to enhancing the available data for those radionuclides and animals. In particular, the transfer to amphibians, one of the main links in common food webs, is reported here for the first time.