PERSISTENCE OF DDT AND NATURE OF BOUND RESIDUES IN SOIL AT HIGHER ALTITUDE

The persistence, metabolism, and binding of C-14-labeled and unlabeled p,p'-DDT in soil at higher altitude were studied for 1 year under field conditions at Dharmsala in Himachal Pradesh, India (elevation 1211 m above sea level, 32 degrees 15' N latitude and 76 degrees 15' E longitude). Hollow poly(vinyl chloride) cylinders (17.5 cm L and 10 cm i.d.) open at both ends were pushed into the ground, and the soil in each of them was treated with 8 mu Ci of [C-14]-p,p'-DDT and 10 mg of unlabeled p,p'-DDT. At every sampling time, three cylinders were dug out, and the soil in them was analyzed. About 64% of DDT was lost from these in 1 year. The half-life of DDT was 250 days. At zero time, p,p'-DDT accounted for 98% of the extractable residues, which gradually declined to about 29% in 1 year. The residues consisted mainly of p,p'-DDT and smaller proportions of p,p'-DDE, p,p'-DDD, and DDMU. p,p'-DDE was the major metabolite and accounted for 24% of the extractable residues after 365 days. DDD and DDMU accounted for a maximum of 6.4% and 2.5% in extractable residues after 35 and 305 days, respectively. Initially, the bound (unextractable) residues were very small but increased gradually to a maximum of 8.7% after 1 year. Soil-bound residues could be released from the soil by sulfuric acid without affecting the chemical nature of the residues. The chemically released residues consisted mainly of p,p'-DDT and smaller proportions of p,p'-DDE, p,p'DDD, and DDMU.