Degradation of Organochlorine Pesticides in Soils Under Controlled Environment and Outdoor Conditions

Abstract

The degradation rates of four organochlorine pesticides in a clay soil were studied in the growth chamber and in the outdoor environment. The soil was aged with aldrin, dieldrin, endrin and chlordane at different concentrations. For controlled environment experiments, the soil was incubated at 30°C and with moisture contents of 10% (-7000 kPa), 19% (-320 kPa), 24% (-70 kPa) and 33% (-13 kPa). The degradation of all four pesticides in the soil samples with a controlled water content of 10% was slower than in the wetter soils. Over the range of higher water contents investigated, there was no significant trend in degradation rate. Thus, the sensitivity to soil moisture of all four organochlorine pesticides is generally low. First-order rate equations best described the degradation of pesticides from the soil during the course of this study. The rate constants were different for different pesticides. For each pesticide, two rate constants have been defined, one for the lower 10% water content (-7000 kPa) and one for all higher water contents investigated. With the soil kept at a constant temperature of 30°C, degradation rates were much higher and the half-lives of all pesticides 3-5 times shorter than for the same soil under the variable temperature of outdoor conditions. Applying endosulfan to the soil significantly reduced the rates of degradation of both aldrin and dieldrin, indicating possible toxic effect of this pesticide on the micro-organisms responsible for the degradation of the aged organochlorine pesticides already in the soil.