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

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 1 month of exposure to 2.0 following 30 years 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 (1000 Bq/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. - Highlights: • A food web bioaccumulation model to assess the biomagnification of ¹³⁷Cs is developed. • Cesium 137 exhibits bioaccumulation over time as simulated by the model. • Predicted activities in marine biota are below ¹³⁷Cs-food consumption benchmarks. • Long-term monitoring of ¹³⁷Cs in the ocean will improve the model predictions.