Radiocaesium contamination and dose rate estimation of terrestrial and freshwater wildlife in the exclusion zone of the Fukushima Dai-ichi Nuclear Power Plant accident

To characterise the radioactive contamination of terrestrial and freshwater wildlife caused by the Fukushima Dai-ichi Nuclear Power Plant accident, biological samples, namely, fungi, mosses, plants, amphibians, reptiles, insects, molluscs, and earthworms, were collected mainly from the forests of the exclusion zone in the Fukushima Prefecture from 2011 to 2012. Caesium-134 and ¹³⁷Cs were detected by gamma spectrometry in almost all the samples. Fungi, ferns, and mosses accumulated high amounts of radiocaesium, as they did in Chernobyl, with ¹³⁴Cs + ¹³⁷Cs activity concentrations of 10⁴–10⁶ Bq kg⁻¹ fresh mass (FM). Earthworms, amphibians, and the soft tissue of the garden snail Acusta despecta sieboldiana, also had levels as high as 10⁴–10⁵ Bq kg⁻¹ FM of ¹³⁴Cs + ¹³⁷Cs. Most of the estimated total (internal + external) dose rates to herbaceous plants, amphibians, insects, and earthworms were below the corresponding derived consideration reference levels (DCRLs) recommended by the ICRP. This suggests that, in most cases, there was little chance of deleterious effects of ionising radiation on these organisms in the exclusion zone for the first year after the accident, though the dose rates were underestimated mainly due to the lack of consideration of short-lived radionuclides. - Highlights: • Radioactive contamination in wildlife was studied in the Fukushima exclusion zone. • Mosses had the highest levels of accumulated radiocaesium. • Fungi, ferns, snails, earthworms, and amphibians were also highly contaminated. • Most of the estimated dose rates to wildlife were below the ICRP's DCRLs.