Simultaneous Degradation of Mixed Insecticides by Mixed Fungal Culture Isolated from Sewage Sludge

Abstract

The degradation of mixed (DDT and chlorpyrifos) insecticides by mixed insecticide enriched cultures was investigated. The mixed fungal population was isolated from mixed insecticide acclimatized sewage sludge over a period of 90 days. Gas chromatography was used to detect the concentration of mixed insecticides and calculate the degradation efficiency. The results showed that the degradation capability of the mixed microbial culture was higher in low concentrations than in high concentrations of the mixed insecticides. After 12 weeks of incubation, mixed pesticide enriched cultures were able to degrade 79.5-94.4% of DDT and 73.6-85.9% of chlorpyrifos in facultative cometabolic conditions. The fungal strains isolated from the mixed microbial consortium were identified as Fusarium sp. isolates GFSM-4 (ITCC 6841) and GFSM-5 (ITCC 6842). The fungal culture GFSM-4 could not utilize mixed insecticides as source of carbon and nitrogen, probably due to high combined toxicity of the mixed insecticides. Liquid media deficient in carbon (1% mannitol) and nitrogen (0.1% sodium nitrate) source increased the degradation efficiency of DDT and chlorpyrifos to 69 and 45%, respectively. The media with normal carbon and deficient nitrogen (0.1% sodium nitrate) sources extensively increased the degradation efficiencies of DDT (94%) and chlorpyrifos (69.2%). Traces of p,p'-dichlorobenzophenone and desdiethylchlorpyrifos were observed in the liquid medium, which did not accumulate probably due to further rapid degradation. This fungal isolate (GFSM-4) was able to degrade simultaneously DDT (26.94%) and chlorpyrifos (24.94%) in sterile contaminated (50 mg of each insecticide kg(-1)) soil in aerobic conditions.