Dispersion and fate of ⁹⁰Sr in the Northwestern Pacific and adjacent seas: Global fallout and the Fukushima Dai-ichi accident

The 3D compartment model POSEIDON-R was applied to the Northwestern Pacific and adjacent seas to simulate the transport and fate of ⁹⁰Sr in the period 1945–2010 and to perform a radiological assessment on the releases of ⁹⁰Sr due to the Fukushima Dai-ichi nuclear accident for the period 2011–2040. The contamination due to runoff of ⁹⁰Sr from terrestrial surfaces was taken into account using a generic predictive model. A dynamical food-chain model describes the transfer of ⁹⁰Sr to phytoplankton, zooplankton, molluscs, crustaceans, piscivorous and non-piscivorous fishes. Results of the simulations were compared with observation data on ⁹⁰Sr for the period 1955–2010 and the budget of ⁹⁰Sr activity was estimated. It was found that in the East China Sea and Yellow Sea the riverine influx was 1.5% of the ocean influx and it was important only locally. Calculated concentrations of ⁹⁰Sr in water, bottom sediment and marine organisms before and after the Fukushima Dai-ichi accident are in good agreement with available experimental measurements. The concentration of ⁹⁰Sr in seawater would return to the background levels within one year after leakages were stopped. The model predicts that the concentration of ⁹⁰Sr in fish after the Fukushima Dai-ichi accident shall return to the background concentrations only 2 years later due to the delay of the transfer throughout the food web and specific accumulation of ⁹⁰Sr. The contribution of ⁹⁰Sr to the maximal dose rate due to the FDNPP accident was three orders of magnitude less than that due to ¹³⁷Cs, and thus well below the maximum effective dose limits for the public. - Highlights: • A box model with a dynamical food-chain model for the NW Pacific was applied. • The transport and fate of ⁹⁰Sr in sea were simulated for the period 1945–2040. • Marine exposure pathways for ⁹⁰Sr were assessed for the Fukushima Dai-ichi accident. • Simulations confirm the presence of leak of ⁹⁰Sr with a ⁹⁰Sr/¹³⁷Cs ratio of about 1. • ⁹⁰Sr human dose was 3 orders of magnitude less than that from ¹³⁷Cs