Contamination Source And Risk Assessment Of Pyrrolizidine Alkaloids In Tea

Pyrrolizidine alkaloids(PAs)are a kind of natural toxins produced by secondary metabolites of plants,among which 1,2-unsaturated pyrrolizidine alkaloids and most pyrrolizidine alkaloid N-oxides have multiple toxic effects,which can threaten human health by contaminating food from plant sources.At present,domestic and foreign studies have found that PAs are commonly detected in tea,but the contamination source and risk assessment in tea have not been reported.In this study,ultra-high performance liquid chromatography tandem mass spectrum(UPLC-MS/MS)was used to establish a method for the detection of 15 common PAs in the tea plantation system(weeds-soil-tea fresh leaves-dried tea).Through the determination and analysis of PAs in the tea plantation system of six major tea producing regions in Anhui Province,the contamination condition of PAs in tea plantations was clarified,and the contamination source of PAs in tea was further explored,so as to provide scientific guidance for the safety control of tea plantations.The risk assessment of PAs contamination in tea was carried out by using the margin of exposure(MOE),which provided a theoretical reference for formulating the safe drinking limit standard of tea and ensuring the quality and safety of tea.The main results of this study were as follows:1.The methods of sampling treatment and UPLC-MS/MS determination for 15 PAs in weeds,soil,tea fresh leaves and dried tea were optimized and developed.The recoveries of 15 PAs were investigated in the tea plantation system.The average recoveries range of15 PAs was 71.03%-119.72%,RSDs were all lower than 9.09%.The LODs of 15 PAs range from 0.1 μg/kg to 0.5 μg/kg,and LOQs range from 0.01 mg/kg to 0.02 mg/kg.The method had a high sensitivity and good separation degree.The peak area of 15 PAs samples showed a good linear relationship with their concentrations.The method could be used to detect weeds,soil,tea fresh leaves and real tea samples.2.The content of PAs in tea plantation samples was determined by UPLC-MS/MS.PAs were detected in 59 of 88 green tea samples,with a detection rate of 67.05%.A total of 10 PAs were detected,and the highest content of total PAs was found in No.12 green tea sample from the major tea producing region in No.5,which was 90.50 μg/kg.PAs were detected in 35 of 37 weed samples,with a detection rate of 94.59%,and all 15 PAs were detected.The highest content of total PAs was found in the major tea producing region in No.4: Ageratum conyzoides L.,which was 74707.75 μg/kg.PAs were detected in 21 of 37 soil samples,with a detection rate of 56.76%.A total of 11 PAs were detected,and the highest content of total PAs was found in the major tea producing region in No.3: soil of the Crassocephalum crepidioides(Benth.)S.Moore,which was 204.39 μg/kg.PAs were detected in 14 of 31 tea fresh leaves,with a detection rate of 45.16%,and a total of 5 PAs were detected.The highest content of total PAs was found in the major tea producing region in No.5: tea fresh leaves near the Dendranthema morifolium(Ramat.)Tzvelev.,which was 171.60 μg/kg.3.The contamination source of PAs in tea plantation system with the major tea producing region in No.5 as the key area was investigated,and the PAs contamination condition was analyzed emphatically.Im,Im NO,Jb NO,Sn NO,Sp NO and Sk were all detected in tea plantation.Among them,Im,Im NO and Jb NO could migrate to soil through weeds and be absorbed by the root of tea plant through soil.Then they were further migrated to tea fresh leaves and finally remained in finished tea.Sn NO,Sp NO and Sk could be transferred to soil by weeds,but they were not detected in tea fresh leaves and finished tea.4.The margin of exposure method was used to assess the risk of PAs contamination in tea.The MOE values corresponding to different points of PAs in tea were all greater than 10000,indicating that the contamination risk of tea in our province was low.In this study,No.12 green tea sample from the major tea producing region in No.5 was also selected to carry out the tea immersion experiment.It was found that the leaching rate of Im and Im NO was 12.72% and 7.63%,and the MOE value was higher than 10000,indicating a low concern of PAs for public health.