Residual behavior and dietary risk assessment of chlorothalonil and its metabolite 4-hydroxy chlorothalonil in Panax notoginseng

To ensure the safe use of chlorothalonil and clarify the residual behavior of chlorothalonil and its metabolite 4-hydroxy chlorothalonil in P. notoginseng, the supervised field trials were conducted in the main producing areas of P. notoginseng in Yunnan Province, including Qiubei, Guangnan, Mile and Shilin in 2017. In addition, analytical methods were established for the determination of chlorothalonil and 4-hydroxy chlorothalonil in P. notoginseng using gas chromatography (GC-ECD) and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), respectively. Chlorothalonil in samples were extracted with V (ethyl acetate) : V (n-hexane) = 2 : 8 mixed solvent, cleaned-up by silica gel solid phase extraction column, and detected by GC-ECD. 4-Hydroxy chlorothalonil was extracted with acetonitrile, cleaned-up by N-propyl ethylenediamine (PSA) dispersible solid phase extraction, and detected by UPLC-MS/MS. Both analytes were quantified with external standard method. Satisfactory recoveries of 93%-98%, relative standard deviations (RSDs) of 3%-6%, and limit of quantity (LOQ) of 0.05 mg/kg for chlorothalonil, and satisfactory recoveries of 75%-94%, RSDs of 3%-9%, and LOQ of 0.02 mg/kg for 4-hydroxy chlorothalonil were obtained in P. notoginseng root and fibrous root. The dissipation experiments in Qiubei and Guangnan showed that the half-life of chlorothalonil was 8.4-8.5 d, and the half-life of 4-hydroxy chlorothalonil was 16.5-17.3 d on P. notoginseng plant. However, the dissipation of chlorothalonil and 4-hydroxy chlorothalonil in the underground root system of P. notoginseng did not conform to the first-order kinetic model. It was observed that, within 45 days after the application, the residues of chlorothalonil decreased slowly, while the residues of 4-hydroxy chlorothalonil increased slowly, and both followed a fluctuating trend. The terminal residue experiments in the above 4 sites showed that when 40% chlorothalonil suspension applied for 3-4 times with an interval of 7 d at doses of 2 400 and 3 600 g (a.i)/hm², the residues of chlorothalonil and 4-hydroxy chlorothalonil were <0.05-3.14 mg/kg and 0.19-1.54 mg/kg in root, and 0.085-0.760 mg/kg and 0.46-4.48 in fibrous root, respectively, 21 d after the last application. The results of the risk assessment of dietary intake revealed it would not pose an unacceptable risk to the health of the general population. Given that the national estimated daily intake (NEDI) of chlorothalonil was 0.967 mg, its risk quotient (RQ%) was 76.8%. Given that NEDI of 4-hydroxy chlorothalonil was 0.012 mg, its RQ% is 2.4%.