| Abstract: | Soils from an orchard sprayed annually (1953-1969) with technical DDT (77% pp′DDT and 22 % pp′DDT) were analysed for residues from 1964 until 1969. The amount of DDT found after 17 years was 21 %pp′DDTout of 27.1 kg/ha applied, and 7 % of pp′DDT out of 7.6 kg/ha. The vertical distribution of residues (pp′DDT, pp′DDE, pp′TDE and pp′DDT) showed a linear relationship between log amount and depth, with approximately 80% in the top 10 cm of soil. At depths from 50 to 210 cm, residue values were too small to be determined (i.e. < 1 ng/g dry wt). The surface distribution in the orchard showed a systematic pattern of circular areas of residues, with maximum values centred at each trunk (7.5 μg/g) and decreasing rapidly to each alley (1.9 ug/g). The levels of pp′DDT had reached a steady state (3-4 kg/ha) and the half-life time was calculated as 3.0 j′ears. pp′DDE (1.8 kg/ha) was the main metabolite of pp′DDT. Small amounts of pp′TDE were also found, pp′DDT was less persistent than pp′DDT, with a half-life time of 1.5 years. |
