The post-Chernobyl budget of 137Cs and 90Sr in the Black Sea

Calculations of annual radionuclide budgets in the Black Sea for the period 1986–1995 have been carried out to estimate the contribution of radionuclides of Chernobyl origin to contamination of the Black Sea and to evaluate the various pathways by which 137Cs and 90Sr are introduced into the sea. The scale of radioactive contamination of the Black Sea as a result of the Chernobyl accident is close to that of weapons test contamination. In both cases, the main pathway of 137Cs and 90Sr input to the seawater was direct atmospheric fallout. River runoff brings relatively small amounts of 137Cs into the Black Sea. The river-derived share of 90Sr input reached 25% of its total input for the first 10 years after the accident and continues to grow. Decreases in the inventory of 137Cs and 90Sr in the seawater, caused by radioactive decay and their removal through the Bosporus Strait into the Marmara Sea, have been occurring since 1987. In 1994, the 90Sr inventory approached the pre-accident level. It is estimated that the 137Cs inventory will reach its pre-accident level by 2025–2030.