Dissipation Behavior Of Three Pesticides During Tea Cultivation And Manufacturing, And Their Transfer In Tea Brewing

Pesticide residue in tea has been attracted great attentions since it not only has negative effects on tea consumers, but also causes large economic losses of tea exports. Although acephate and dimethoate are registered pesticides in tea garden, their metabolites with high toxic could bring high risks to human health by tea drinking. Acephate, one of chiral pesticides, may demonstrated enantioselective dissipation behaviour. However, few studies have reported on enantioselevtivity of chiral pesticides in tea. Dicofol is one of the highly excessive pesticides in tea in our country at present and the reason is still unclear. Therefore, it is urgent to find out the persistence of these three pesticides from fresh tea leaves to tea brewing.In this study, a rapid method for acephate and methamidophos enantiomers, dimethoate, omethoate, and dicofol determination in tea matrices was developed and validated. Then residues levels and dynamic of these three pesticides in an open tea field ecosystem, persistence during tea manufacturing, and their transfer rates during tea brewing were investigated. The results are as follows:(1) A QuEChERS method for acephate and methamidophos enantiomers, dimethoate, omethoate, and dicofol was modified by comparing the extraction efficiency with the treatment of adding water into made tea for pre-soaking, the adsorption ratio of three adsorbents [including primary-secondary amine (PSA), graphitized carbon black (GCB), and octadecylsilane (C18)] on these pesticides, and the purification effects of these adsorbents on various tea matrices. Acephate and methamidophos enantiomers were finally well separated by a BGB-176 capillary column. Acephate and methamidophos enantiomers, dimethoate, and omethoate were determined by gas chromatography coupled with flame photometric detector (GC-FPD) using the external method. The recoveries for these pesticides were 50.8-57.5%,58.4-65.3%,80.4-85.2%, and 55.2-59.1%, respectively, with RSDs less then 7%, and LOQs were 0.015-0.30,0.01-0.30,0.008-0.05,0.03-0.10 mg/kg. Dicofol was determined by gas chromatography-tandem mass spectrometry (GC-MS/MS) with recoveries of 87.3-92.4%(RSD<7%). LOQs for dicolfol in fresh tea leaves, made tea and tea infusion were 0.01,0.05,0.02 mg/kg, respectively. The developed method mentioned above is not only quick and simple, but also stable and reliable, which fulfills the requirement of this study.(2) The initial deposits of (+)-acephate, (-)-acephate, dimethoate, and dicofol were 36.14,36.49, 34.44,11.82 mg/kg respectively, when acephate (30% EC), dimethaote (40% EC), and dicofol (20% EC) were sprayed on green tea shoots after dilution. All these pesticides dissipated following the first-order kinetics with half-lives of 1.8、1.9、1.1、2.2 d, respectively. The increase of methamidophos entiomers and omethoate indicated that acephate and dimethoate could degraded into high toxic metabolite, methamidophos and omethoate, respectively. Besides, significant enantioselectivity of both acephate and methamidophos was found during tea cultivation.(3) One bud and two leaves were picked on days 1 and 3 and then were submitted to green tea and black tea manufacturing immediately. Residues of acephate enantiomers, dimethoate, and dicofol on fresh tea leaves were partly dissipated and the total loss were 49.8-72.8%,47.1-68.9%,18.2-29.3%, respectively. Compared to green tea manufacturing, all these pesticides were preferred to dissipated during black tea manufacturing. Among all these stages of tea manufacturing, drying was mainly responsible for pesticides dissipation, leading to considerable losses of 50.8-79.2% in the total losses. Withering during black tea manufacturing and spreading during green tea manufacturing also showed some positive effects on pesticides dissipation. Chemical changes of acephate and dimethoate were taken place during tea manufactuting, causing increases of methamidophos and omethoate. However, enantioselectivity dissipation of acephate was only occurred during drying.(4) All the made tea samples obtained during tea manufacturing were underwent further brewing with boiled water. Residues in both green tea and black tea partly transferred into tea infusion. Results showed that only 0.8-1.9% of dicofol were transferred into tea infusion, while the transfer rates of the other four pesticides in this study (including acephate, methamidophos, dimethoate, and omethoate) were higher than 80%.