Laboratory and field studies on the fate of 1,3,6,8-tetrachlorodibenzo-p-dioxin in soil and sediments

The fate of carbon-14-ring-labelled 1,3,6,8-TCDD was studied in small field plots of sandy loam soil and in the laboratory with pond and lake sediment. Duplicate soil samples were extracted with hexane and acetone. The aqueous phase was further extracted with dichloromethane. Analysis was by thin layer chromatography. Losses from field soils were greater than from the laboratory soil/water incubations. Total carbon-14 at 0-5 cm depth was 95 per cent after 20 days and 56 per cent after 131 days. Unextractable radioactivity was determined by combustion of extracted soil and was 2 to 15 per cent of total carbon-14. Throughout the 495 days of study, more than 97.5 per cent of extractable radioactivity was in the form of intact 1,3,6,8-TCDD. Negligible amounts of carbon-14 were detected at 5-10 cm depth suggesting that the reduction in radioactivity was not due to movement in the soil. During the 675 day laboratory study more than 80 per cent of the radioactivity was extractable and this did not decrease with time. Almost all of the carbon-14 was 1,3,6,8-TCDD. Unextractable radioactivity in the sediments was low; 3.1 per cent for lake sediments and 8.6 per cent for pond sediments. Unidentified polar products in soil and sediment extracts had similar characteristics to those observed in sediment and pure culture incubations of 2,3,7,8-TCDD.