University of Khartoum

Comparative Degradation of Some Pesticides by Microorganisms and Sunlight in the Sudan

Comparative Degradation of Some Pesticides by Microorganisms and Sunlight in the Sudan

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Title: Comparative Degradation of Some Pesticides by Microorganisms and Sunlight in the Sudan
Author: Ishag, Abdelaziz Sulieman Ahmed
Abstract: This study was conducted in the University of Khartoum, Faculty of Agriculture Department of Crop Protection to compare the potential efficiency of bio- and photo-degradation in the remediation of pesticide polluted soils, identify promising pesticide biodegrading microorganisms, characterize the degradation rates and identify the major degradation products, especially those of toxicological concern. Bacillus safensis strain FO-36bT, Bacillus subtilis subsp. inaquosorum strain KCTC13429T and Bacillus cereus strain ATCC14579T were isolated from pesticides-polluted storage soil in Hasahesa (Gezira irrigation scheme), Sudan, incubated with tested pesticides with periodic samples drawn for GC-FID and GC-MS analysis. The tested pesticides were also subject to direct and indirect (blended with natural and synthetic sensitizers) photolysis with periodic samples drawn for GC-FID and GC-MS analysis. The results indicated that both bio- and photo-degradation of tested pesticides followed the biphasic model. Alpha half-lives (days) of chlorpyrifos, malathion, dimethoate, pendimethalin, α-endosulfan and β-endosulfan in B. safensis culture were 2.13, 2.59, 9.5, 2.12, 7.32 and 8.62 days, respectively. Respective values in B. subtilis and B. cereus cultures were; 4.09, 4.33 days for chlorpyrifos; 2.99, 2.43 days for malathion; 9.53, 4.16 days for dimethoate; 1.6, 2.54 days for pendimethalin; 0.85, 2.54 days for α-endosulfan and 0.87, 2.8 days for β-endosulfan. The alpha half-lives (t1/2α) of direct photolysis of chlorpyrifos, malathion, dimethoate, pendimethalin, α-endosulfan and β-endosulfan over glass were; 1.99, 2.1, 9.35, 1.84, 6.72, and 2.47 days, while the respective values for soil surface were; 4.75, 10.77, 1.88, 3.32, 9.76 and 2.71 days. Alpha values for indirect (sensitized) photolysis over glass surface with β-carotene and benzophenone were 1.59 and 0.38 days for chlorpyrifos; 2.40 and 2.37 days for dimethoate; 1.6 and 1.63 days for pendimethalin; 2.28 and 1.56 days for α-endosulfan; 0.85 and 1.05 days for β-endosulfan, respectively. However the corresponding values of alpha half-lives (t1/2α) on soil surface for β-carotene and benzophenone sensitized photolysis were; 2.18; 2.19 days for chlorpyrifos; 4.40 and 3.74 days for dimethoate; 0.85, 0.87 days for malathion 2.26; 1.93 days for pendimethalin; 2.84, 2.20 days for α-endosulfan; 3.16, 2.88 days for β-endosulfan. The alpha half-live for malathion β-carotene sensitized photolysis over glass surface is 2.15 days while it was not possible to calculate its half-lives for benzophenone sensitized photolysis as the starting material was completely lost after three days. Meteorological factors did not have a significant impact on photolysis rates. Many metabolites were detected in the various bacterial cultures as well as under indirect photolysis over glass and soil surfaces, while no photoproducts were detected in the direct photolysis over both glass and soil surfaces. Based on the half-lives, the bacterial efficiency can be ordered as B. safensis > B. subtilis > B. cereus for chlorpyrifos; B. cereus > B. subtilis > B. safensis for malathion and dimethoate; B. cereus > B. safensis > B. subtilis for pendimethalin and B. subtilis > B. cereus > B. safensis for endosulfan. The degradation efficiency of different types of photolysis also can be ordered as benzophenone > β-carotene > direct exposure for all tested pesticides. Generally, the sunlight photolysis caused faster degradation in the organophosphorus insecticides (chlorpyrifos, malathion, and dimethoate) whereas biodegradation induced faster degradation in endosulfan and pendimethalin. The study suggested further investigations the efficiency of isolated organisms and/or sunlight photolysis on reducing the level of contamination in soil samples collected from the contaminated sites, isolation and identification of enzymes responsible for degradation and evaluation of the efficiency under different environmental conditions.
Description: 394 Pages
URI: http://khartoumspace.uofk.edu/123456789/25915


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