The Potential Of Some Indigenous Soil Microorganisms In Degradation Of The Insecticide Endosulfan Alpha And Beta Isomers

Abstract

Nine soil types from sites with various levels and history of contamination by insecticides were chosen as inoculums sources for the present studies. The presences of four groups of soil microorganisms in these soils were surveyed using selective media. The results indicated that organic nitrogen bacteria is more prevalent and found in all types of soils followed by inorganic nitrogen bacteria and actinomycetes, fungi and bacteria and actinomycetes which lives in poor media. Soil microorganisms isolated from the nine soil types showed great potential in degrading ^5; and ^6;-endosulfan in selective media after 15 days of incubation. Generally the results indicated that microorganisms isolated from highly contaminated soils had greater potential in degrading the two isomers of endosulfan. The effects of soil microorganisms isolated from highly polluted soil, on half-lives of ^5; and ^6;- endosulfan under condition of selective and carbon free media were re-studied for longer period. The results showed significant decrease in half-lives ranging between 58.4 – 81.9% in ^5;-endosulfan compared to 35.5 – 71.6% in ^6;-isomer. The effect of fertilizer activator on enhancing the microbial growth and capability in degrading ^5; and ^6;- endosulfan under soil conditions was studied. Results indicated that all activators caused significant increase in microbial counts especially the triple super phosphate. The accompanied reduction in half lives ranged between 20-73% with various levels of endosulfan sulphate generated. Microbial degradation at elevated concentration (500 mg/l) of endosulfan in carbon free was studied and the results showed that there were no significant differences in the reduction of half-lives between high (500 mg/l) and low (100 mg/l) concentration. Tolerant strains of bacteria and fungi from the soil of Rass Elfeel pesticide store (Mangil scheme) were isolated through consecutive exposure to elevated concentration of endosulfan under condition of carbon free media and the results showed that the most tolerant fungi (can tolerate up to1000 mg/l) was Aspergillus fumigates while the most tolerant bacteria was Bacillus sp. The comparative degradation of endosulfan by tolerant strains and their parents was studied under condition of soil and carbon free media. Results showed that parent strains (present in large number) showed faster decrease in half lives compared to tolerant strains (few numbers). However tolerant strains might have greater potential if they find a chance to propagate in massive numbers.