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Abstract

The Fukushima nuclear accident on 11 March 2011 emerged as a global threat to the conservation of the Pacific Ocean, human health, and marine biodiversity. On April 11 (2011), the Fukushima nuclear plant reached the severity level 7, equivalent to that of the 1986-Chernobyl nuclear disaster. This accident was defined by the International Atomic Energy Agency as “a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures”.

Despite the looming threat of radiation, there has been scant attention and inadequate radiation monitoring. This is unfortunate, as the potential radioactive contamination of seafoods through bioaccumulation of radioisotopes (i.e. 137Cs) in marine and coastal food webs are issues of major concern for the public health of coastal communities. While releases of 137Cs into the Pacific after the Fukushima nuclear accident are subject to high degree of dilution in the ocean, 137Cs activities are also prone to concentrate in marine food-webs.

With the aim to track the long term fate and bioaccumulation of 137Cs in marine organisms of the Northwest Pacific, we assessed the bioaccumulation potential of 137Cs in a North West Pacific foodweb by developing, applying and testing a simulation time dependent bioaccumulation model in a marine mammalian food web that includes fish-eating resident killer whales (Orcinus orca) as the apex predator.

The model outcomes showed that 137Cs can be expected to bioaccumulate gradually over time in the food web as demonstrated through the use of the slope of the trophic magnification factor (TMF) for 137Cs, which was significantly higher than one (TMF > 1.0; p < 0.0001), ranging from 5.0 at 365 days of simulation to 30 at 10,950 days.

From 1 year to 30 years of simulation, the 137Cs activities predicted in the male killer whale were 6.0 to 182 times 137Cs activities in its major prey (Chinook salmon, Oncorhynchus tshawytscha).

Bioaccumulation of 137Cs was characterized by slow uptake and elimination rates in upper trophic level organisms and dominance of dietary consumption in the uptake of 137CS.

This modeling work showed that in addition to the ocean dilution of 137Cs, a magnification of this radionuclide takes place in the marine food web over time.