Dissipation Kinetics and Risk Assessment of Spirodiclofen and Tebufenpyrad in Aster scaber Thunb

The dissipation kinetics of spirodiclofen and tebufenpyrad after their application on Aster scaber Thunb were studied for 10 days, including the pre-harvest intervals. Spirodiclofen and tebufenpyrad were used in two greenhouses in Taean-gun, Chungcheongnam province (Field 1) and Gwangyang-si, Jeollanam province (Field 2), Republic of Korea. Samples were taken at 0, 1, 3, 5, 7, and 10 days after pesticide application. The method validations were performed utilizing liquid chromatography (LC)-tandem mass spectrometry (MS/MS). The recoveries of the studied pesticides ranged from 82.0–115.9%. The biological half-lives of spirodiclofen and tebufenpyrad were 4.4 and 3.8 days in Field 1, and 4.5 and 4.2 days in Field 2, respectively. The pre-harvest residue limits (PHRLs; 10 days before harvesting) of Aster scaber were 37.6 mg/kg (Field 1) and 41.2 mg/kg (Field 2) for spirodiclofen, whereas the PHRLs were 7.2 (Field 1) and 3.6 (Field 2) for tebufenpyrad. The hazard quotient for both pesticides at pre-harvest intervals was less than 100% except in the case of spirodiclofen (0 day).