Effective and ecological half-lives of 90Sr and 137Cs observed in wheat and rice in Japan

Published pre-Fukushima food monitoring data from 1963 to 1995 were used to study the long-term presence of Cs-137 and Sr-90 in rice and wheat. Effective half-lives (T (eff)) were calculated for rice (Cs-137: 5.6 years; Sr-90: 6.7 years) and wheat (Cs-137: 3.5 years; Sr-90: 6.2 years), respectively. In rice, Cs-137 exhibits a longer T (eff) because putrefaction processes will lead to the formation of NH4 (+) ions that are efficient ion exchangers for mineral-adsorbed cesium ions, hence making it more readily available to the plant. Knowledge on the long-term behavior of radiocesium and radiostrontium will be important for Japanese food-safety campaigns after the Fukushima nuclear accident.