Persistence and transformation of thiamethoxam, a neonicotinoid insecticide, in soil of different agroclimatic zones of India.

摘要

The persistence and transformation of thiamethoxam were investigated in 4 soils of different agroclimatic regions of India: loamy sand (Bangalore, Karnataka), sandy clay loam (Pantnagar, Uttar Pradesh), silty clay loam (Punjab) and sandy loam (Delhi). The half life of thiamethoxam in these soils ranged from 11 to 26 days. The initial recovery of insecticide after 5 days did not show much difference in 4 soils but after that somewhat faster degradation was observed in sandy clay loam soil (32.9%) in comparison to 22-26% in other 3 soils. A slow dissipation was observed in loamy sand and only 55.7% of thiamethoxam dissipated in 30 days compared to 81.6, 78.8 and 69.5% in sandy clay loam, silty clay loam and sandy loam soils, respectively. Linear plots of log residues against time showed that the dissipation followed a first order rate kinetics. The half life of thiamethoxam in loamy sand (acidic, pH 6.4) was 25.5 days compared to 11.5-16.9 days in 3 soils (alkaline pH). Percentage of organic carbon (OC) was also found to be a responsible factor for the dissipation of thiamethoxam in soil. The dissipation was 81.6% in sandy clay loam with high OC (0.84%) compared to loamy sand with low OC (0.4%) where dissipation was only 55.7% in 30 days. Among 3 alkaline soils, the fastest dissipation (81.6%) was observed in sandy clay loam, which had the highest OC content though its pH (7.5) was less than the other 2 soils. Between the 2 soils of similar alkaline pH again the dissipation was found affected by OC concent when 78.8% dissipation was observed in silty clay loam (0.7% OC) in comparison to 60.4% in sandy loam (0.5% OC)..