Modeling 137Cs bioaccumulation in the salmon–resident killer whale food web of the Northeastern Pacific following the Fukushima Nuclear Accident

Abstract

To track the long term bioaccumulation of 137Cs in marine organisms off the Pacific Northwest coast of Canada, we developed a time dependent bioaccumulation model for 137Cs in a marine mammalian food web that included fish-eating resident killer whales. The model outcomes show that 137Cs can be expected to gradually bioaccumulate in the food web over time as demonstrated by the increase of the apparent trophic magnification factor of 137Cs, ranging from 0.76 after 1month of exposure to 2.0 following 30years of exposure. 137Cs bioaccumulation is driven by relatively rapid dietary uptake rates, moderate depuration rates in lower trophic level organisms and slow elimination rates in high trophic level organisms. Model estimates of the 137Cs activity in species of the food web, based on current measurements and forecasts of 137Cs activities in oceanic waters and sediments off the Canadian Pacific Northwest, indicate that the long term 137Cs activities in fish species including Pacific herring, wild Pacific salmon, sablefish and halibut will remain well below the current 137Cs-Canada Action Level for consumption (1000Bq/kg) following a nuclear emergency. Killer whales and Pacific salmon are expected to exhibit the largest long term 137Cs activities and may be good sentinels for monitoring 137Cs in the region. Assessment of the long term consequences of 137Cs releases from the Fukushima aftermath should consider the extent of ecological magnification in addition to ocean dilution.