Feasibility of biodegradation of Azamethiphos; odour and fly controlling chemical used in open solid waste dumpsite at Karadiyana, Colombo, Sri Lanka

Azamethiphos (AZA) is an organophosphorus pesticide used to control flies and odour. Karadiyana is an open dumpsite in Colombo which creates problems like unpleasant odour and flies which have led to heavy use of AZA. Thus, the present study was aimed to isolate and characterize AZA degrading bacteria from the dumpsite. AZA was extracted from soil samples using the Solid Phase Extraction method and quantified by the High- Performance Liquid Chromatography. Soil and water recovery of AZA was recorded as 94.65 ± 0.13 mg L^-1 and 94.02 ± 0.09 mg L^-1 respectively. Partitioning coefficient values and high sorption coefficient values depicted AZA is likely to be in sorbed status combining with organic matter rather than being in an insoluble status. The bacteria; Bacillus graminis, Corynebacterium sp., Enterobactor sp., Micrococcus sp. and Lactobacillus sp. were identified as AZA degraders and complete removal of AZA was achieved at 10 days of incubation following the half-life time of 6, 2, 5, 5 and 3 days, respectively. The highest degradation rate (0.681 d^-1) was recorded after 2 days of incubation with Corynebacterium sp. The most effective temperature was 33 °C and Lactobacillus sp. showed efficient degradation of AZA compared to the other isolates. The photo-oxidation effect on the removal of AZA was found to be low (47 %) compared with bacteria degradation (85 %). Hence, the result of the study showed that microbial degradation is the major path of removal of AZA from the environment considering only the natural routes of degradation.