Uptake and Metabolism of Thiamethoxam in Wheat and its Persistence in Soil
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Date
2021
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Punjab Agricultural University, Ludhiana
Abstract
The persistence and metabolism of thiamethoxam in wheat and soil was studied following
thiamethoxam application as seed treatment and foliar application. Wheat and soil samples
were analyzed by Liquid Chromatography-Tandem Mass Spectrometry. During 2018-19, total
residues of thiamethoxam and its metabolites were found to be 2.64 and 9.75 mg kg-1 in wheat
leaves collected at 20 days after seed treatment with thiamethoxam-Cruiser 70WS @ 0.7 and
2.8 g a.i. kg-1, respectively, however, during 2019-20, the residues were 2.52 and 9.71 mg
kg-1, respectively, and reached below limit of quantification (LOQ) at 90 days after seed
treatment for both the dosages during both the years. In soil samples, these residues were
found to be below LOQ after 45 days after seed treatment for both the dosages during both
the years. During 2018-19, the initial deposits of thiamethoxam and its metabolites were
found to be 3.69 and 14.03 mg kg-1 in leaves collected at 0 (2hrs after application) day after
foliar application of thiamethoxam-Actara 25WG @ 12.5 and 50.0 g a.i. ha-1, respectively,
however, during 2019-20, the residues were 3.79 and 14.36 mg kg-1, respectively. The residue
in leaves reached below LOQ at 30 and 45 days after foliar application of thiamethoxam @
12.5 and 50.0 g a.i. ha-1, respectively. These residues in soil dissipated to below LOQ after 30
days after foliar application for both the dosages during both the years. The samples of straw
and grain did not reveal the presence of thiamethoxam residues at harvest during both the
years. Microbial isolates isolated from soil, Bacillus safensis, B. pumilus, B. megaterium, B.
velezensis, Aspergillus sp., Cladosporium velox, Aspergillus flavus, Streptomyces sp. 1 and
Streptomyces sp. 2. screened for thiamethoxam degradation were found to be effective in
degradation of thiamethoxam. Thiamethoxam degradation in soils amended with 50, 100 and
150 mg kg-1 thiamethoxam was 86.68 to 89.41 per cent, 97.99 to 98.70 per cent and 85.99 to
87.63 per cent by Bacillus safensis, Aspergillus sp. and Streptomyces sp. 1, respectively,
which were the most efficient microbial isolates.
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Citation
Rasool, Rozy (2021). Uptake and Metabolism of Thiamethoxam in Wheat and its Persistence in Soil (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.