Distribution Characteristics Of Heavy Metals And Isotope Tracing In The Soil-Tea System Of Tea Garden In Anxi

Tea is one of the most popular beverage in the world, and soil is the major source of heavy metal elements of tea, so it has an great practical significance to study the pollution features of heavy metals in a soil-tea system and tracing its main source. In this study, the main object are heavy metal elements in Tie Guanyin tea garden soils and the leaves. We determined the content of heavy metal elements, and analysis the distribution of heavy metals and have a quality evaluation; analysis the correlation between heavy metal content in soils and tea, as well as the correlation between physical and chemical properties of soils and the heavy metals content in tea, and discuss the migration of heavy metals in soil-tea system; We use isotope tracer method to determine the main sources of Pb in soils and leaves, and calculate the contribution rate of Pb from the source to soils and tea. The main findings are as follows:The contents of Cr, Cd, Co, Cu, Ni, Zn, Pb, Sr, Nd, Fe, Mn and V elements in the surface soil(0~20cm) were 23.82(11.8~45.5), 0.3581(0.107~0.749), 6.774(1.96~15.1), 15.25(7.58~26.5), 7.815(4.28~18.3), 129.8(54.9~639), 46.82(22.6~82.1), 53.42(12.0~51.9), 38.33(10.1~71.9), 30914(13395~50621), 440.8(64~2582)�'� 67.44(31.8~127) mg/kg, respectively. The contents of elements in the deep soil(20~40cm) were 26.17(5.70~58.1), 0.2333(0.062~0.988), 8.307(1.76~20.2), 13.20(5.73~22.2), 8.811(2.67~18.6), 97.67(53.6~167), 40.93(17.1~76.7), 48.78(12.3~381), 39.64(13.7~83.8), 35341(14723~50691), 514.2(79.8~2294.8), 71.67(34.1~109) mg/kg, respectively. The contents of Cr and Cu elements in soils are lower than the national secondary standard of soils and the backgrounds in Fujian Province. The elements of Zn and Pb above the backgrounds and below the national secondary standard of soils, and Cd is higher than both the standards of soils. And other elements such as Co, Ni, Fe, V are below the background values of soil in Fujian Province, and Sr, Nd, Mn elements are higher than it.The experiments of extract the species of heavy metals in soil with an improved four-state BCR extraction method, and the results showed that, Cd mainly existedwith acid extractable fraction and residual fraction, Pb and Cu elements mainly existed with oxidizable fraction, and other elements mainly existed in residual fraction. The bioavailability analysis of heavy metals in soils shows that: Pb and Cd get higher biological availability, and followed by Cu, Mn elements.Evaluated the soils with geoaccumulation index showed that: most of the soils have not pollution or received a lesser pollution extent, but some places such as sites of S1~S8 in Guanqiao and S38~S39 in Changkeng had a varying degrees of enrichment of Cd and Mn. The potential ecological risk index of soil shows that: most of the soils are the lightest level, but some places such as S1~S8 sites of Guanqiao and S38~S39of Changkeng have contaminated by Cd, the highest pollution levels is highly contaminated in S6 site. Evaluation results of the two methods are consistent.The content of Cr, Cd, Co, Cu, Ni, Zn, Pb, Sr, Nd, Fe, Mn, V in tea leaves were0.1824(0.0737~0.3377)、0.0205(0.0043~0.0598)、0.3666(0.1218~1.266)、9.504(5.118~14.05)、2.828(1.103~4.508)、19.75(12.25~32.78)、0.4759(0.1326~1.531) g、18.59(3.965~55.35) 、 0.3804(0.019~1.575) 、 73.92(16.61~164.58) 、 985.8(196.9~2195)、0.2155(0.0234~0.6594) mg/kg, respectively. The average content of metal elements in old leaves were 0.5482(0.3389~1.074)、0.0288(0.0105~0.0504)、0.2675(0.0983~0.6398) 、 7.426(4.772~12.35) 、 3.633(1.729~7.343) 、 12.68(9.000~20.28)、2.207(0.7633~3.903)、49.92(14.10~176.8)、2.559(0.2049~8.471)、184.66(58.83~356.66) 、 2192(575.8~4870) 、 0.5888(0.1252~1.226) mg/kg,respectively. Single pollution index results show that young leaves has no pollution and old leaves reaches higher serious contaminated with Pb. The results of the comprehensive pollution index show that, young leaves get the security level and alert level for the old leaves. With an health risk assessment to commercial tea, the results shows that it has no negative impact on human health when normal drinking tea. The exposure assessment of heavy metal elements in tea shows that the risk of human health is negligible when drinking tea normally.The analysis of correlation between heavy metals contents in soil and tea shows that, Cr, Cu, Ni, Zn, Pb, Nd and Fe in tender tea was significant positive correlation with Nd in soil; Co of old leaves was significant positive correlation with Co in soil,Cr, Zn, Sr and Nd in old leaves was significant positive correlation with Nd elementsin soil. The analysis of correlation between physical and chemical properties of soil and heavy metals content of tea shows that, both p H of soil and organic matter content have little effect to the content of heavy metal leaves. Pb and Fe in old leaves was negative correlation with soil p H while other elements were positively correlated;Cr, Co, Zn and Mn in old tea was significantly negatively correlated with organic matter content of soil.The results of use isotope to identify the main source of Pb in soil indicate that both parent material which as natural sources and automobile exhaust dust which as anthropogenic sources contribute the Pb of soil, and the contribution rate is 76.69%and 23.31%, respectively; the main source of Pb in tea is also come from parent material and automobile exhaust dust, the contribution rate to young leaves is 21.08%and 78.92%, respectively, and contribution rate to old leaves is 36.19% and 63.81%,respectively. Compared to deep soil, surface soil had suffer more anthropogenic influence and its contribution to surface soil was 33.24%.