S-Metolachlor Degradation Efficiency Using Indigenous Soil Micro-Organism

Abstract

S-metolachlor is a pre-emergent persistent acetanilide herbicide used to control annual grasses and broadleaf weeds. Health advisory level (HAL) of S-metolachlor by US EPA is 0.525 mg/L in drinking water. The objective of the study was to isolate indigenous soil micro-organism having potential to degrade S-metolachlor. The bacterial culture capable of degrading S-metolachlor was isolated from soil by using enrichment technique. Isolated bacterial culture was identified as Pseudomonas sp. by using morphological and biochemical characteristics. Molecular identification of Pseudomonas sp. was done with the help of Polymerase Chain Reaction (PCR). The isolated soil micro-organism was ultimately identified as Pseudomonas aeruginosa. For biodegradation studies a bench scale reactor system was established. Set-up was run on ambient conditions at different S-metolachlor concentrations (10, 20 and 50µg/ml). Minimal Salt medium (MSM) having S-metolachlor as the sole carbon source was used to determine degradation potential of isolated bacterial strain. Optical density and total organic carbon content were used to determine degradation efficiency by increase in absorbance (at 600nm) and decrease in total organic carbon with time. Gas Chromatography was used to determine the concentration of S-metolachlor at varied time intervals. By inoculating Pseudomonas aeruginosa in the medium maximum degradation that is 62.5% was achieved within 120 hours. Optimized concentration and time for the bench scale bioreactor was found to be 20µg/ml at 72 hours respectively at ambient conditions.