Persistence of imidacloprid and its major metabolites in sugarcane leaves and juice following its soil application

Abstract

The persistence and metabolism of imidacloprid in sugarcane leaves and juice were studied following application of imidacloprid @ 20 and 80 g a.i. ha⁻¹. Samples of sugarcane leaves were collected at various time intervals (7, 15, 30, 45, 60 and 90 days after treatment), whereas those of juice were collected at the time of harvest. The residues of imidacloprid and its metabolites (6-chloronicotinic acid, nitrosimine, imidacloprid-NTG, olefin, urea and 5-hydroxy) were quantified by high-performance liquid chromatograph. In leaves, the total imidacloprid residues were mainly constituted by the parent compound followed by 6-chloronicotinic acid metabolite. Total residues of imidacloprid and its metabolites were found to be 4.97 and 12.99 mg kg⁻¹ in sugarcane leaves collected 7 days after the application of imidacloprid @ 20 and 80 g a.i. ha⁻¹ respectively. At both the doses, these residues declined to below the detectable limit in the leaves after 90 days of application with the half-life values of 9.68 and 8.14 days of imidacloprid @ 20 and 80 g a.i. ha⁻¹ respectively. The total toxic residues of imidacloprid in sugarcane leaves were 0.90 and 6.29 mg kg⁻¹ at 7 days after treatment of imidacloprid @ 20 and 80 g a.i. ha⁻¹ respectively. The bioconcentration factor in sugarcane leaves was 0.35 and 1.03 in the lower and higher dose respectively at 7 days after treatment. The total residues followed the pseudo first order kinetics with R² of 0.9243 and 0.944 for recommended dose and four times the recommended dose, respectively. The residues of imidacloprid and its metabolites were not detected in samples of sugarcane juice.

Keywords:

• sugarcane
• imidacloprid
• metabolism
• HPLC
• residues

Acknowledgement

The authors are thankful to the Professor and Head, Department of Entomology, PAU, Ludhiana for providing the necessary research facilities.