Summary of a 5-year lysimeter study on the time-dependent transfer of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu and ²⁴¹Am to crops from three contrasting soil types: 1. Transfer to the edible portion

Variations in the transfer of radionuclides to the edible parts of crops over a 5-year period are summarized in terms of their soil-to-plant concentration ratios. Loam, peat and sand soils were artificially contaminated with ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu and ²⁴¹Am in the winter of 1983/84, and placed in large containers out of doors. Carrot, cabbage and barley crops were grown in rotation in subsequent years and after harvesting were separated into edible and unpalatable portions for radiochemical analysis. Soil-to-plant concentration ratios were calculated and are discussed in terms of differences in uptake between nuclides, crops and soil types as a function of time. Radionuclide transfer from soils to crops was found to decrease in the order ⁹⁰Sr ≥ ¹³⁷Cs ≫ ²⁴¹Am {reversed tilde equals} ^239,240Pu. Transfer to barley grain was generally lower than to carrot flesh and cabbage hearts. Concentration ratios for ¹³⁷Cs were greatest for crops grown on peat soils, by up to an order of magnitude. In contrast, the concentration ratios for ⁹⁰Sr, ^239,240Pu and ²⁴¹Am were all lowest for crops grown in peat, again by up to an order of magnitude. Soil-to-plant concentration ratios generally remained unchanged for crops grown 3 or more years after contamination of the soil. For crops grown soon after contamination there was evidence for some reduction in radionuclide uptake with time. The sustained bioavailability of ¹³⁷Cs in peat soils was the main exception to this trend. Irrigation water with naturally enhanced levels of calcium reduced the soil-to-plant transfer of radiostrontium in mineral soils.