Thesis (M.Sc.)--Chulalongkorn University, 2014

Dichlorvos (2,2-dimethyl dichlorovinyl phosphate) is one of the major organophosphate insecticides. It has been widely used to control various insect pests. There is possibility of dichlorvos contamination to the environment. This study aimed on biodegradation of dichlorvos. Dichlorvos-degrading consortium and pure cultures were enriched from contaminated soil. Dichlorvos degradation under different dichlorvos concentrations (50, 100, 200, 400 and 800 mg/L) and pHs (pH 4, 5, 6, 7 and 8) was focused. In addition, the degradation kinetic estimation and metabolic intermediate monitoring were conducted. A consortium and pure cultures well utilize dichlorvos. Three selected isolates were identified as Klebsiella sp. strain DV1 (DV1), Enterobacter sp. strain DV2 (DV2) and Klebsiella pneumoniae strain DV3 (DV3). Under different dichlorvos concentrations, abiotic process (hydrolysis) could remove dichlorvos for 0.10-0.28 1/d while biodegradation (with hydrolysis) by a consortium and pure cultures well degraded dichlorvos with rate constance of 0.17-0.28 and 0.24-0.43 1/d, respectively. At high dichlorvos concentrations (more than 400 mg/L), microbial degradation could enhance the dichlorvos removal. For effect of pH, hydrolysis well removed dichlorvos at pH of 7 to 8 (0.67-0.80 1/d) while the dichlorvos removal at pHs ranging from 4 to 6 was 0.04 to 0.30 1/d. At acidic pHs, biodegradation (with hydrolysis) by a consortium, DV1, DV2 and DV3 reduced dichlorvos of 0.06-0.13, 0.05-0.38, 0.07-0.40 and 0.07-0.38, respectively. During the dichlorvos degradation experiment, three metabolites including 2-chloroethyl dimethyl phosphate, triethyl phosphate and trimethyl phosphate were detected in both abiotic (hydrolysis) and biodegradation processes. It could say that abiotic process by hydrolysis reaction influenced dichlorvos degradation. Biodegradation could improve the removal performance, espicailly under the conditions with high contaminated concentration or acidic pH. The consortium and isolates are efficient in dichlorvos degradation and have potential for dichlorvos remediation.