Dissipation and degradation of DDT, DDE and parathion in Brazilian soils

The persistence of 14C‐DDT was monitored in the field at two sites representing tropical and subtropical climates in Sao Paulo State. Persistence of 14C‐DDE and 14C‐parathion was also studied in the subtropical region. In the extracts of soils treated with DDT, the main product 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 14C‐residues increased slowly and amounted to about 10% after 48 weeks. Extracts from 14C‐DDE‐treated soils contained only DDE after 48 weeks. I4C‐DDT dissipated with a half‐life of over 200 weeks in both regions while 14C‐DDE dissipated at a faster rate (Tl/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‐nitrophenol, were identified after short periods. Bound residues increased with time to about 30% after 6 weeks, and remained almost constant. The half‐life for 14C‐parathion dissipation was 12 weeks.