SUMMARY OF A 5-YEAR LYSIMETER STUDY ON THE TIME-DEPENDENT TRANSFER OFCS-137, SR-90, PU-239, PU-240 AND AM-241 TO CROPS FROM 3 CONTRASTING SOIL TYPES .1. TRANSFER TO THE EDIBLE PORTION

Variations in the transfer of radionuclides to the edible parts of cro ps over a 5-year period are summarized in terms of their soil-to-plant concentration ratios. Loam, peat and sand soils were artificially con taminated with Cs-137, Sr-90, Pu-239,Pu-240 and Am-241 in the winter o f 1983/84, and placed in large containers out of doors. Carrot, cabbag e and barley crops were grown in rotation in subsequent years and afte r harvesting were separated into edible and unpalatable portions for r adiochemical analysis. Soil-to-plant concentration ratios were calcula ted and are discussed in terms of differences in uptake between nuclid es, crops and soil types as a function of time. Radionuclide transfer from soils to crops was found to decrease in the order Sr-90 greater-t han-or-equal-to Cs-137 >> Am-241 congruent-to Pu-239,Pu-240. Transfer to barley grain was generally lower than to carrot flesh and cabbage h earts. Concentration ratios for Cs-137 were greatest for crops grown o n peat soils, by up to an order of magnitude. In contrast, the concent ration ratios for Sr-90, Pu-239,Pu-240 and Am-241 were all lowest for crops grown in peat, again by up to an order of magnitude. Soil-to-pla nt concentration ratios generally remained unchanged for crops grown 3 or more years after contamination of the soil. For crops grown soon a fter contamination there was evidence for some reduction in radionucli de uptake with time. The sustained bioavailability of Cs-137 in peat s oils was the main exception to this trend. Irrigation water with natur ally enhanced levels of calcium reduced the soil-to-plant transfer of radiostrontium in mineral soils.