Long-term effective decrease of cesium concentration in foodstuffs after nuclear fallout.

The long-term decrease in activity concentrations in various foodstuffs relevant for the long-term ingestion dose after a nuclear fallout is reviewed. The effective decrease observed in various countries of Central Europe after the Chernobyl accident are compared to the effective decrease observed after the atmospheric nuclear weapons testing. The presentation also includes the short-term decline immediately after fallout and the time course in the first year, which are relevant to the first year ingestion dose. The initial effective decrease is dominantly controlled by plant growth and follows an approximate half-life of 4.2 d in lettuce and spinach, and 10.5 d in grass during the growing season, resulting in an effective half-life of 33 d in milk. In order to avoid artifacts due to local fallout or plant variations or differences in the metabolism of single animals, the sampling of each foodstuff was spread over very large areas of production and a large number of samples including investigations in several individual provinces. The long-term decrease over the following years, which is vital for the long-term internal exposure, is slower but still follows an effective half-life for different foodstuffs: milk = 1.4-2.2 y, vegetables = 1.4-2.7 y, potatoes = 2.0-2.6 y, cereals = 3.0-3.4 y, and fruit = 1.2-1.6 y. Differences observed between the different products and areas are discussed. Half-lives in milk vary between three central-European countries from 708 d (Austria), to 663 d (Germany), to 538 d (Czechia). The observed effective half-life is much shorter than observed after nuclear weapons testing where a half-life of approximately 4.5-4.9 y was observed, which is explained by the weapons tests' fallout lasting for several years compared to the single short-term fallout after the Chernobyl accident.