Effective half-lives of radiocesium in terrestrial plants observed after nuclear power plant accidents. In: Impact of Cesium on Plants and the Environment

Information on “how fast radiocesium could be removed from plants” is important to decide measures after contamination. To express the decreasing rate, effective half-life (Teff) can be used; Teff is defined as the time required for a 50% decline of radiocesium in an individual plant or plant population in a natural ecosystem. There are four major radioactivity decrease process in plants when terrestrial environment is contaminated with radiocesium. (1) Removal of radiocesium attached to plant surface by rain and wind (weathering effect), (2) plant mass increase at growing season (dilution effect), (3) removal of radiocesium by shedding leaves and fruits (elimination effect) and (4) decrease of bioavailable radiocesium fraction in soil (aging effect). It is difficult to separate these processes, however, since radiocesium decreasing trend fits well with exponential curves (usually a combination of two exponential curves), effective half-lives (Teff) are reported. This paper summarizes terrestrial plant Teff data in woody and herbaceous plants observed after Fukushima nuclear accident and also compared the data observed after the Chernobyl power plant accident