Radiocaesium transfer from volcanic soils to Swiss chard, cabbage and sweet corn

The root uptake of radiocaesium by different plant parts of Swiss chard (Beta vulgaris L. var. cicla), cabbage (Brassica oleracea L. var. capitata) and sweet corn (Zea mays L. var. saccharata) and the potential influence of K-fertilising on the transfer behaviour was studied in allophanic volcanic soils (umbric andosol and dystric fluvisol) in Chile under temperate climate and heavy rainfall conditions (∼2660 mm y⁻¹) over several vegetation periods. The soils were spiked homogeneously to 0.20 m depth with 100 kBq ¹³⁴Cs m⁻² and activity concentrations measured. The transfer factor (TF, on a dry mass basis) to Swiss chard had a clear exponential decrease within each crop year for both soil types, either K-fertilised or unfertilised. The highest values of the TFs to Swiss chard were at the beginning of the harvests, and the half-times of TF decrease ranged between 52 and 137 d for umbric andosol and between 40 and 164 d for dystric fluvisol. Over the five seasons there was no consistent ageing effect based on TF in either soil types for the three studied crops. The effect of ¹³⁴Cs foliar uptake by Swiss chard from resuspended soil was estimated to account for about 70% (external leaves) and 30% (internal leaves) increase in the TF for the K-unfertilised umbric andosol, and showed an ambiguous behaviour for the K-fertilised umbric andosol. Consequently foliar uptake does not explain the 370 and 500% increase of the TF to Swiss chard leaves determined during the third growing period in the umbric andosol without and with K-fertilisation, respectively. Therefore an uncertainty factor of 3–5 is recommended to be taken into account when using this parameter for dose calculations. The TF to Swiss chard was found to be higher than previously reported values. The TF to cabbage and sweet corn plant parts was found to be within the range of previously reported values. Normal K-fertilisation resulted in about 2.4-fold reduction in ¹³⁴Cs TF to Swiss chard, 2.3-fold to sweet corn and 3.0-fold to cabbage.