Degradation of endosulfan in a clay soil from cotton farms of western Queensland.
The persistence and degradation of endosulfan isomers and their primary degradation product, endosulfan-sulfate, were studied in a clay soil from cotton farms of western Queensland. Endosulfan degradation in relation to soil moisture, temperature, day and night temperature fluctuation, waterlogging and re-application were studied. The results show that the degradation rates of both endosulfan isomers were greatly affected by changes in soil water content and temperature. Under a high water content-high temperature regime the concentration of alpha-endosulfan in the soil fell rapidly during the first 4 weeks of application, followed by a prolonged period of slower rate of degradation. Alpha endosulfan showed a bi-exponential form of degradation for all water content-temperature experiments except for extremes in both these two factors. In the submerged soils (and also in low-water content, low temperature, non-submerged experiments) no such rapid initial degradation of alpha-endosulfan was observed, and a single first-order rate equation describes the data. Degradation of beta-endosulfan was significantly slower than for the alpha-isomer under all conditions studied. A half-life of more than a year was recorded for the beta-isomer when both water content and temperature were low. The degradation of beta-endosulfan showed no sign of the bi-exponential function observed for alpha-isomer, and a single first order rate equation described the data obtained for each factor studied. Endosulfan-sulfate was the major degradation product in all non-submerged experiments. Its build up in the soil very closely followed the disappearance of alpha-endosulfan. Its highest build-up was in the high water content-low temperature experiments, but its persistence was primarily influenced by soil temperature. Both alpha and beta-isomers, and endosulfan sulfate, persisted longer in the submerged soil. Re-application of endosulfan, and day and night fluctuation of temperature had contrasting effects on the degradation of the two isomers. Both factors slowed down the degradation of alpha-endosulfan and enhanced that of beta-endosulfan, but their net effect was to prolong the overall persistence of this chemical in the soil. Submerged conditions reduced the net formation of endosulfan-sulfate and enhanced its degradation rate.
Ghadiri
H
H
Faculty of Environmental Sciences, Griffith University, Brisbane, 4111, Queensland, Australia. H.Ghadiri@mailbox.gu.edu.au
Rose
C W
CW
D000383:Agriculture; D000538:Aluminum Silicates; D001673:Biodegradation, Environmental; D000077215:Clay; D004726:Endosulfan / Q000737:chemistry*; D003368:Gossypium; D006801:Humans; D006843:Hydrocarbons, Chlorinated; D007306:Insecticides / Q000737:chemistry*; D011793:Queensland; D012989:Soil Pollutants; D013696:Temperature; D014867:Water
D000538:Aluminum Silicates; D006843:Hydrocarbons, Chlorinated; D007306:Insecticides; D012989:Soil Pollutants; D014867:Water; D004726:Endosulfan; D000077215:Clay