DISSIPATION AND DEGRADATION OF DDT, DDE AND PARATHION IN BRAZILIAN SOILS

The persistence of C-14-DDT was monitored in the field at two sites re presenting tropical and subtropical climates in Sao Paulo State. Persi stence of C-14-DDE and C-14-parathion was also studied in the subtropi cal region. In the extracts of soils treated with DDT, the main produc t was DDT. The amount of DDE was small and reached a maximum of 16% of the extractable radioactivity after 16 weeks, while DDD was detected only after 48 weeks. Bound C-14-residues increased slowly and amounted to about 10% after 48 weeks. Extracts from C-14-DDE-treated soils con tained only DDE after 48 weeks. C-14-DDT dissipated with a half-life o f over 200 weeks in both regions while C-14-DDE dissipated at a faster rate (T1/2 = 88 weeks). It seems likely that the long persistence of DDT in this study relates to the acidic nature of the soil. Parathion dissipated much faster and, the degradation products paraoxon and 4-ni trophenol, were identified after short periods. Bound residues increas ed with time to about 30% after 6 weeks, and remained almost constant. The half-life for C-14-parathion dissipation was 12 weeks.