Assessment of radiological dose rates in passerine birds after the Fukushima nuclear accident according to their life stage

Abstract

In this paper we present Caesium (¹³⁴Cs and ¹³⁷Cs) activity concentrations as measured during two life stages of passerine birds collected in Fukushima prefecture one year after the nuclear accident. We examined various adult specimens (i.e. Varied Tit Poecile varius, Oriental Greenfinch Chloris sinica and Eurasian Tree Sparrow Passer montanus) and un-hatched eggs of Japanese Tit Parus minor, and we subsequently estimated internal and external dose rates (and thus total dose rate) received by these organisms. We showed that the contribution of external dose rate to the total dose rate varied in relation to life stage (i.e., whether adult or egg) and to the contamination of the main surrounding micro-habitats in which the organisms spent most of their time (i.e., nest material for eggs, and air and soil for adults). In the un-hatched eggs, the external dose rate was higher than the internal one and was mostly driven by the nest material, the difference reaching about four orders of magnitude, because nest material was mainly composed of mosses, which are known to retain high quantities of radionuclides. In addition, estimated total dose rates were drastically greater than the ambient dose rates measured in the field. Our study underlined the importance of performing detailed dose analysis and of carefully considering the ecology of the species studied in future field cases when assessing radiation exposure effects on wildlife, in order to better predict potential harmful biological effects on individuals.