Concentration ratios of (238)U and (226)Ra 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 (238)U and (226)Ra 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 (238)U and (226)Ra levels were of interest: (i) pond and its shore (PO); (ii) low-level stream and its shore near overburden dump (OD); and (iii) uranium mill tailings pond and its shore (MP). The activity concentrations in both soil and water were PO ≈ OD < MP for (238)U, and PO < OD < MP for (226)Ra. Regarding the wildlife, (238)U was able to be determined for all samples, but the detection of (226)Ra 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.