| Abstrakt: |
Imidaclopride (IMI) and Thiamethoxam (THI) were the neonicotinoids that were most frequently used in Andhra Pradesh in sweet lime orchards to control Helicoverpa armigera and Marucavitrata. Despite the frequent use of these insecticides, little is known about their behaviour and interaction in the soils of sweet lime orchards. The main objective of this study is to estimate the degradation of IMI and THI in soils from sweet lime orchards collected in and around Pulivendula, near Kadapa, using established kinetic models. A new, rapid, sensitive, precise, and validated "Ultra High Performance Liquid Chromatography Coupled with a Photodiode Array Detector" (UHPLC-PDA) is developed for the quantification of IMI and THI individually in agricultural soil samples by the QuEChERS extraction technique. The IMI and THI were sprayed on the sweet lime trees at a rate of 2 ml/l and 1.5 ml/l respectively. Soil samples were collected for analysis at 0 (within 1 hour), 1, 3, 5, and 10days time intervals after spraying on soil soils. Quantification was carried out utilizing a 40:60 (v/v) methanol/water mobile phase and a validated reverse-phase HPLC with a "PDA" detector at 272nm wavelength. Within the measured range of 0.05 to 1 ppm concentration, the calibration graphs of IMI and THI in methanol solvent were linear with an index of correlation greater than 0.996. Sprayed soil recovery ranges from 95% to 110% respectively, in respect of IMI and THI. The dissipation kinetics of IMI and THI was studied in logarithmic first-order kinetic models, for which the R2 was 0.948 and 0.997 respectively. The IMI residues were 1.91, 0.45, 0.31, and 0.07 ppm on days 0, 1, 3, and 5 after spraying, respectively, and were detected below detectable levels on day 10. The THI residues were 1.95, 0.93, 0.32, and 0.06 mg/kg respectively on 0, 1, 3, and 5 days after spraying, and were detected below detectable levels on day 10. [ABSTRACT FROM AUTHOR] |
