Fate of 14c‐P,P'‐DDT in Kenyan tropical soils

Abstract

The dissipation and degradation of 14C‐p,p'‐DDT in tropical soils of Nairobi were studied under field and laboratory conditions for a period of six months. DDT was found to dissipate much more rapidly from the soil under field conditions than reported for temperate regions. The dissipation curve was found to be biphasic; a rapid phase from 0–37 days after application and a slower phase from 51–172 days. Based on first order kinetics an overall half‐life of 65 days was calculated. The bound residues initially constituted a very small percentage (1.3%) of the applied pesticide and gradually increased to 5.9% after 64 days. The main degradation products extracted from the soil were p,p'‐DDE and a small percentage of p,p'‐DDD. While the amount of p,p'‐DDT decreased with time, there was a slow increase in the amount of p,p'‐DDE extracted from the soil.

The effects of solar radiation on the dissipation of 14C‐p,p'‐DDT from non‐sterile soil was also studied under laboratory conditions by quantifying the volatilization and mineralization of 14C‐p,p'‐DDT. It was found that volatilization was the major dissipation process and the dissipation rate was significantly increased by solar radiation.