Effective and ecological half-lives of (90)Sr and (137)Cs 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 (137)Cs and (90)Sr in rice and wheat. Effective half-lives (T(eff)) were calculated for rice ((137)Cs: 5.6 years; (90)Sr: 6.7 years) and wheat ((137)Cs: 3.5 years; (90)Sr: 6.2 years), respectively. In rice, (137)Cs exhibits a longer T(eff) because putrefaction processes will lead to the formation of NH(4)(+) 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.