Effect of long-term application of pretilachlor on its persistence and residues in paddy crop

The effect of long-term application of pretilachlor to paddy in rice-wheat cropping system was investigated from 1997 to 2015. Additionally, in 2013, field experiment was also conducted where pretilachlor was applied to paddy field having no background of its application. The residues of pretilachlor were quantified using high-performance liquid chromatography (HPLC). The average recoveries of pretilachlor from paddy soil, paddy grain and straw samples ranged from 80.7% to 93.8% using HPLC with standard deviation less than 10%. The dissipation rate of pretilachlor in paddy soil followed first-order kinetics and half-life ranged from 9.58 to 21.19 days. In 2015, HPLC was compared with gas chromatography-tandem mass spectrometry (GC-MS/MS) for quantification of residues. Average recoveries of pretilachlor using GC-MS/MS from paddy soil, paddy grain and straw samples ranged from 81.4% to 98.3% with standard deviation less than 10%. Both HPLC and GC-MS/MS offered high reproducibility; however GC-MS/MS was more sensitive and the limit of detection was 3.0 and 1.0 ng g^-1 for HPLC and GC-MS/MS, respectively. At harvest, the residues of pretilachlor in the paddy soil and crop were below the maximum residue limit and no dangerous accumulation was observed after its prolonged application.