Biodegradation of Chlorpyrifos in Paddy Rice Soil in the Mekong Delta, Vietnam
Truong Quoc TatObjective: Chlorpyrifos (CP) is an organophosphate insecticide. High toxicity makes it a potential source of soil pollution when used in agriculture. This study aimed to assess the anaerobic digestion of CP, the diversity of chlorpyrifos-degrading bacteria in soil, and the mechanism of CP decomposition.
Materials and Methods: Four soil samples were collected from paddy rice fields in Vietnam to evaluate the degradation of CP by anaerobic bacteria. The experiment was conducted in 50 mL microcosms containing 30 mL mineral salt medium, 10 g soil, and 35 mg/kg CP. The concentration of CP was determined using an high performance liquid chromatography.The intermediate products of CP were identified using a gas chromatography–mass spectrometry.
Results: Our bacterial communities in the soil samples anaerobically degraded CP. The rate of CP degradation was doubled after increasing the bacterial density during incubation. The percentage of CP degradation within a 4-month incubation period was significantly higher in the two bacterial communities isolated from alluvial soil than in acid soil. Four bacterial communities were found to degrade CP through the anaerobic reduction of chloride. The intermediate products resulting from the decomposition of CP by these soil bacterial communities were identified as O, O-diethyl-3, 6-dichloro-2-pyridyl phosphorothioate; 3,5,6-trichloro2-pyridinol; O, O-diethyl-O (3,5,6-trichloro-2-pyridyl) phosphate. This shows the presence of the Chloroflexi bacterial phylum in the soil samples.
Conclusion: There is the presence of a group of anaerobic bacteria capable of decomposing CP in soil specialised in rice cultivation, opening up the potential to improve polluted soil by biological means.
