陕南茶园茶叶品质分析及重金属含量现状评估

为了解陕南茶园茶叶品质及茶园重金属含量现状,以茶叶主产区为研究对象,采集了8个县区330个茶园土壤样品,测定分析了pH值和铅(Pb)、锌(Zn)、铜(Cu)、铬(Cr)、汞(Hg)、砷(As)、镉(Cd)等7种重金属含量;同时测定分析了33个茶园茶叶品质及茶叶和浸出液中重金属含量。结果表明,茶叶中茶多酚平均含量为25.58%,儿茶素平均总量为20.74%,茶氨酸含量均值为2.45%,游离氨基酸总量均值为4.86%。茶叶中各重金属含量差异较大,Pb为0.04～2.65 mg/kg、Zn为34.82～55.38 mg/kg、Cu为3.18～20.16 mg/kg、Cr为0.09～4.89 mg/kg、Hg为0.02～0.30 mg/kg、As为0.66～1.16mg/kg和Cd为0.02～0.19mg/kg;32茶园茶叶符合《无公害食品茶叶》(NY5244—2004)和NY659—2003标准,33个茶园茶叶Cu含量符合有机茶标准。浸出液中仅检测出Zn、Cu和Cr,平均浸出率分别为:32.65%、24.96%和10.50%。土壤中重金属Pb、Zn、Cu、Cr、Hg、As和Cd的平均含量分别为10.03、87.61、16.42、12.38、0.20、6.89和0.11 mg/kg,综合潜在生态风险指数平均值为95.4,潜在生态风险较低。

Analysis of tea quality and assessment of heavy metal content status in tea plantations of southern Shaanxi Province, China

Abstract: Accumulation of heavy metals in agricultural soils tends to increase crop uptake of heavy metals, and can adversely impact human health through food chains. In this study, we assessed the tea quality, heavy metal status, and the potential ecological risk of tea plantation soils and leaves in Hanzhong city, southern Shaanxi province, China. A total of 330 topsoil samples and 33 leaves samples were collected to analyze the concentrations of seven heavy metals (Pb, Zn, Cu, Cr, Hg, As, and Cd) and the pH level. Also, the tea quality and the content of heavy metals in tea leaves and leachate in 33 leaves samples were determined and analyzed. Results showed that the contents of tea polyphenols ranged from 22.23% to 27.55%, and the mean content of polyphenols was 25.58%. The contents of catechins ranged from 18.48% to 22.37%, the mean content of catechins was 20.74%. The contents of free amino acids ranged from 3.37% to 6.42%, and the mean amount of free amino acids was 4.86%. The contents of theanine ranged from 1.70% to 3.18%, and the mean content of theanine was 2.45%. The contents of heavy metals in tea leaves ranged from 0.02 mg/kg to 0.19 mg/kg for Cd, 3.18 mg/kg to 20.16 mg/kg for Cu, 0.035 mg/kg to 2.65 mg/kg for Pb, 0.09 mg/kg to 4.89 mg/kg for Cr, 0.02 mg/kg to 0.30 mg/kg for Hg, 0.66 mg/kg to 1.16 mg/kg for As, 34.82 mg/kg to 55.38 mg/kg for Zn. The heavy metals in tea leave samples almost conform to the relevant standards of pollution-free food tea except that the content of Hg in one sample exceeded the relevant standards of pollution-free food tea of 1.66%. The content of Cu was conformed to the relevant standards of organic tea. Among the contents of seven heavy metals, only Zn, Cu, and Cr were detected in the leaching solution, and the average leaching rates were 32.65%, 24.96%, and 10.50%, respectively. The soil analysis showed that the contents of heavy metals in soils ranged 0.03-0.32 mg/kg for Cd, 7.48-29.03 mg/kg for Cu, 2.45-29.16 mg/kg for Pb, 0.83 -27.76 mg/kg for Cr, 0.08-0.38 mg/kg for Hg, 2.31-13.97 mg/kg for As, 25.73-146.94 mg/kg for Zn. The averaged contents of Cd, Cu, Pb, Cr, Hg, As, and Zn were 0.11,16.42, 10.03, 12.38, 0.20, 6.89, and 87.61 mg/kg, respectively. The coefficient of variation of the different elements ranged from 29.16% to 52.24% and was 49.30% for Cd and 48.55% for Hg. In 5.76% of the samples, Cd concentrations exceeded the risk screening value of the environmental quality agricultural land soil pollution risk control standard (GB 15618-2018). The average single pollution index of Pb, Zn, Cu, Cr, Hg, As, and Cd were 2.32, 0.83, 4.26, 0.41, 44.46, 9.37, and 33.89, only the average single pollution index of Hg was over 40. The comprehensive potential ecological risk index ranged from 23.58 to 226.90, and the average potential ecological risk index was 95.4, the total samples at a low level of potential ecological risk. Thus, the tea plantations were in a low potential ecological risk level and good quality of tea leaves for 33 samples.