海洋環境における動物プランクトン中の東電福島第一原発由来放射性Csの動態

摘要

This study has focused on the temporal and spatial distribution of ~(137)Cs in zooplankton since the Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. FNPP-derived ~(137)Cs could have consequently accumulated within marine food webs via seawater intake and predator-prey interactions. We provide evidence of the temporal variability in ~(137)Cs concentrations in zooplankton samples collected in coastal waters off Miyagi, Fukushima and Ibaraki Prefectures, and in the western North Pacific Ocean (500-2100 ㎞ from the FNPP) after the accident. ~(137)Cs concentrations in zooplankton were high in the coastal waters and in the open ocean, and were two to four orders of magnitude higher than ~(137)Cs activities observed before the accident around Japan. Although taxonomic compositions of zooplankton were determined in order to elucidate reasons for the variation in ~(137)Cs concentrations, no relationship between the zooplankton community and ~(137)Cs concentration was clarified. Rather, ~(137)Cs concentrations in zooplankton might be influenced by the environmental radiocesium activity concentrations, that is, zooplankton exposed to seawater with high ~(137)Cs may have relatively high ~(137)Cs content. Concentration of ~(137)Cs in seawater and the apparent zooplankton-seawater concentration ratio (aCR) value measured in zooplankton well describes the progress of ~(137)Cs contamination in zooplankton from the beginning of the FNPP accident (dynamic non-equilibrium state) to the restoration phase (dynamic equilibrium state). The observed relation between ~(137)Cs in seawater and the aCR of zooplankton were good indicators of the progress of ~(137)Cs contamination in zooplankton from the beginning of the FNPP accident to the restoration phase.