Persistence of DDT in soils and on cotton leaves, at Mwea Tebere, Kenya

Abstract

Plots in 3 replicates at Mwea Tebere Cotton Research Station, on which cotton had been planted 1n October 1980 were treated with technical DDT at various application rates and at different times of the year. The soil and cotton leaves were then sampled over a period of 4-5 months for the determination of the levels of pesticide residues remaining. From the data obtained the persistence of P,P'-DDT and related compounds was determined. Rainfall and a1r temperatures were recorded through the period of study. Replicate 1, was treated in February 1981, when the area was hot and dry while replicate 3 and 4 were treated with insecricide in April, during the rains Replicate 2 was left untreated to act as a control. The rate of loss of P,P'-DDT and it's related compounds from soils at Mwea Tebere was found to be rapid under aJl the various climatic condi~ions operating during the course of thi~ research programm~. The losses seem to occur by a 2 step process, consistini~of a fast initial stage followed by a slower second stage. The times taken for the loss af various percentages of the initial amount of pesticide applied are calculated. The loss of P,P'-DDT, O,P'-DDT, P,P'-DDD ant P,P'-DDE from cotton leaves was found to take place rapidly and preferential loss of pesticide from the upper leaves was shown to take place under all climatic conditions observed. The data resulting from this study are analysed and discussed in relation to the various climatic conditions operating d~ring the period of the study