硒镉高背景区茶叶中硒和砷、汞、镉的积累与浸出特征研究

Selenium, arsenic, mercury and cadmium in tea leaves and infusion of a green tea grown in an area with a high geological background of selenium and cadmium

为阐明地质高背景区微量元素的生物地球化学循环,以及其在农作物中的积累和潜在健康风险,探讨了硒镉高背景区茶叶中硒、砷、汞、镉4种微量元素的积累特征,分析了采集时间、叶片成熟度、炒制温度对微量元素含量的影响;以硒的最大浸出量为参考,研究了富硒茶最佳的冲泡条件,并对4种微量元素的浸出特征和健康风险进行了评价。结果表明,所有茶园土壤均达到高硒水平,其中46.67%的土壤硒过量。镉的含量远超土壤风险筛选值,且57.31%为可交换态。所有茶叶均达到富硒茶标准,而砷、汞、镉未出现超标。土壤硒对茶叶中重金属的积累没有明显的拮抗作用,反而会促进汞的积累。高温炒制导致茶叶中63.51%的硒损失,而采集时间和叶片成熟度对茶叶中砷、汞、镉的含量有显著影响。硒的浸出主要受冲泡温度和次数影响,最高仅有26.06%的硒能进入茶汤;砷主要受冲泡次数和时间影响,而汞主要受冲泡温度影响。茶汤中硒、砷、汞、镉的浸出量很低,目标危害系数远小于1,没有明显的健康风险。研究表明,地质高背景区微量元素在茶叶中的积累特征及相关的健康风险与人为污染区存在较大差异。

It is very important to highlight the biogeochemical cycle of trace elements and their accumulation in crops and potential health risks in high geological background areas.The accumulation of selenium(Se),arsenic(As),mercury(Hg)and cadmium(Cd)in tea leaves was investigated and the impacts of harvest season,leaf maturity and drying temperature on the concentrations of these trace elements were analyzed.The optimal tea making conditions were obtained based on the maximum leaching of Se in the infusion,and the leaching characteristics of 4 trace elements and associated health risks were evaluated.The results showed that soil Se ranged from high to excessive(46.67%)according to the landscape ecological background value of Se in China.The concentration of Cd in the soil was much higher than the risk screening value and the proportion of acid exchangeable Cd species was 57.31%.Tea samples were recognized as Se-rich tea and contained normal amounts of As,Hg and Cd,according to the national standards of China.Soil Se did not have any antagonistic effect on the accumulation of toxic metals.On the contrary,it was positively correlated with Hg concentration in the tea leaves.A high-temperature for drying resulted in a 63.51%loss of foliar Se,while harvest season and leaf maturity exhibited significant effects on the concentrations of As,Hg and Cd.The leaching of Se was mainly controlled by temperature and brewing times and only 26.06%of Se was leached into the infusion under the optimal conditions.In contrast,As and Hg in the infusion were mainly subjected to brewing times,duration and temperature.There was no obvious health risk in the consumption of Se-rich tea in this study because all the target hazard quotients(THQ)were less than 1.The results indicated that the accumulation of trace elements in tea leaves and the associated health risks in a high geological background area were different from those in polluted areas.