A model is presented that dynamically estimates the radiocesium activity in herbage from readily available soil parameters. Three key properties underlying the bioavailability of radiocesium in soils were estimated in the model: the labileradiocesium distribution coefficient (k{sub}dl), the solution K{sup}+ concentration (m{sub}K), and the radiocesium concentration factor (CF, Bqkg{sup}(-1) plant/Bq dm{sup}(-3) soil solution). These were determined as functions of the soil clay contentand exchangeable K status. The effect of time on radiocesium fixation was described by two first-order decay equations. The model was initially parametrized using radiocesium uptake data from a ryegrass pot trial Without further parameterization, themodel was then tested for a wide range of soil and crop combinations using a database of published and unpublished information from a variety of sources and covering contamination time periods of 0.5-11 years. Model predictions of activity concentrationsin crops were in generally good agreement with observed values.
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