Modelling the accumulation of 137Cs by Atlantic bluefin tuna (Thunnus thynnus) after a hypothetical nuclear accident in the Northwest Atlantic Ocean

The potential accumulation of radionuclides in migratory fish following nuclear accidents is a concern for marine ecology and human consumption. We developed and applied a Lagrangian numerical model coupled with a four-level food web uptake module to simulate the transport and bioaccumulation of 137 Cs in Atlantic bluefin tuna ( Thunnus thynnus ) in the Northwest Atlantic Ocean, following hypothetical Fukushima-like releases from three coastal nuclear power plants in eastern North America. Tuna trajectories were obtained from electronic tagging data, and 137 Cs transfers from water and prey were modelled daily at each tuna location. Simulations show that even when tuna pass through contaminated water and food patches, the resulting 137 Cs concentrations in their flesh remain low, with maximum values around 1 Bq/kg wet weight. These concentrations are well below international safety limits and often below typical background levels. The study confirms that the rapid movement of migratory species limits radionuclide uptake, suggesting that tuna consumption would remain safe even in the event of such accidents. • This is the first study simulating radionuclide uptake by NW Atlantic bluefin tuna. • Migration-based models show tuna absorb minimal 137 Cs even in contaminated waters. • Rapid tuna movement limits radionuclide bioaccumulation, keeping flesh levels low. • Peak 137 Cs levels in tuna stay below food safety limits in all simulated scenarios. • Findings stress considering species mobility in radiological risk assessments. assessments.