ABSTRACT

The Fukushima Dai-ichi Nuclear Power Plant (DNPP) accident has caused serious contamination of the marine environment from atmospheric fallout deposition and the direct discharges of highly radioactive liquid wastes. In contrast to the immediate intensive studies on the distributions of released fission products, such as ¹³¹I, ¹³⁴Cs and ¹³⁷Cs, information on the possible contamination by actinides in the marine environment is quite limited. In this study, we report the first data-set on the distribution of Pu isotopes in surface sediments in the Pacific 30 km off Fukushima after the Fukushima DNPP accident. Activities of ^239+240Pu and ²⁴¹Pu, and atom ratios of ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu in surface sediments collected in July-August, 2011 were analyzed to make a quick assessment on the environmental impact of the possible Pu contamination. The observed ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios are comparable to those previously reported in marine sediments in the western North Pacific and its marginal seas, and in Japanese estuaries before the accident. The Pu contamination from the Fukushima DNPP accident was not observed in marine sediments outside the 30 km zone.