Behaviour of 14C-DDT in soil under field and laboratory conditions in Brazil

The fate of 14C-DDT in soil was studied during a year, under ambient and high temperatures in the laboratory, and in soil columns in the field. A loam soil, rich in organic matter (8.65%) was selected. In the laboratory test, the treated soil was contained in jars with foam (plugs as traps for volatile organics) in the top and the moisture content was maintained constant. Half of the jars were kept under ambient temperature and the other half maintained at 34 deg. C. The field test studied the mobility of 14C-DDT in soil columns at ambient climatic conditions. All samples were exhaustively extracted with methanol and wet combustions of extracted samples were done. Quantification of 14C was performed by liquid scintillation counting. One year after application, the recoveries were 82.18% at ambient temperature and 81.74% at 34 deg. C in the laboratory. Less than 1% was collected in the foam traps as volatilized materials. About one third of radiocarbon in the field columns dissipated in the first two weeks probably due to volatilization. After two weeks, dissipation was slow and 14C-activity declined to 47.8% (39.4% extractable and 8.4% bound) after 48 weeks. 14C-DDT was almost immobile, even under two rainy periods, because very little was detected below the 0-10 cm section. (author). 9 refs, 1 fig., 2 tabs