BIOAVAILABILITY OF SOIL-BOUND RESIDUES OF DDT AND HCH TO CERTAIN PLANTS

The bioavailability of bound residues of C-14-labelled DDT and HCH in soil to gram, maize and rice plants was investigated using soil containing only bound residues or soil containing both extractable and bound residues of DDT and HCH. In general, the plants accumulated a low proportion of bound residues of DDT and HCH from soil. For example, gram and maize in 14 days and rice in 20 days accumulated 0.61, 0.13 and 0.05% of DDT and 0.95, 0.11 and 0.04% of HCH, respectively of the bound residues present in the soil. Plants accumulated 12-24-fold more DDT and 4-10-fold more HCH when grown in soil containing both bound and extractable residues. The roots accumulated a greater proportion of the insecticide residues than the shoots. DDT showed more binding with plant shoots while HCH revealed more binding with roots. The data also indicate that bound residues of DDT and HCH are mobilized to extractable forms in the soil upon ageing.