DEGRADATION OF DDT UNDER WET HUMID AND DRY SUBHUMID AGRO-ECOSYSTEMS IN NIGERIA.

Abstract

Degradation and dissipation of DDT (Dichloro diphenyl-trichloro-ethane) were investigated at two locations, viz, Ilorin in the sub-humid Guinea Savanna and Ile-Ife in the wet humid Rain Forest Zones of Nigeria. These were monitored in soil within plastic cylinders (25cm x 10cm diameter), spaced 1.5m x .5m and driven into the soil leaving a cm above the ground level in order to prevent run off losses. Extractable and bound residues of DDT were determined using Thin Layer Chromatography (TLC) and Gas Liquid Chromatography (GLC).

The results showed that the pattern of dissipation of DDT were biphasic at the two locations. The rapid and phases of degradation occurred during the first 3 weeks and the 4th week to the end of the experiment respectively. While extractable residues decreased, bound residues increased with time at both locations up to the end of the experiments. The rates of dissipation during the rapid phase and throughout the whole period were higher at Ile-Ife with half-lives of 38 and 370 days than at Ilorin with half-lives of 41 and 388 days respectively. However, there was greater transformation of DDT into less toxic products, viz. dichloro-diphenyl-ethane (DDE) and dichlorodiphenyl-dichloro ethane (DDD) at Ilorin than Ile-Ife. Hence, DDT was found more persistent at Ile-Ife. The trend emphasised the importance of soil factors especially the presence of sorption sites due to organic matter and clay in determining the persistence of DDT. The binding of DDT and its degradation products to exchange sites could have deleterious effects on long-term sol fertility and productivity.