Temporal Changes in ¹³⁷Cs Concentrations in Fish, Sediments, and Seawater off Fukushima Japan

We analyzed publicly available data of Fukushima ¹³⁷Cs concentrations in coastal fish, in surface and bottom waters, and in surface marine sediments and found that within the first year of the accident pelagic fish lost ¹³⁷Cs at much faster rates (mean of ∼1.3% d^-1) than benthic fish (mean of ∼0.1% d^-1), with benthopelagic fish having intermediate loss rates (mean of ∼0.2% d^-1). The loss rates of ¹³⁷Cs in benthic fish in the first year were more comparable to the decline of ¹³⁷Cs concentrations in sediments (0.03% d^-1), and the declines in pelagic fish were more comparable to the declines in seawater. Retention patterns of ¹³⁷Cs in pelagic fish were comparable to that in laboratory studies of fish in which there were no sustained ¹³⁷Cs sources, whereas the benthopelagic and benthic fish species retained ¹³⁷Cs to a greater extent, consistent with the idea that there is a sustained additional ¹³⁷Cs source for these fish. These field data, based on 13 511 data points in which ¹³⁷Cs was above the detection limit, are consistent with conclusions from laboratory experiments that demonstrate that benthic fish can acquire ¹³⁷Cs from sediments, primarily through benthic invertebrates that contribute to the diet of these fish.