Study On The Process Of Reside And Accumulation Of Heavy Metals In Tea

Tea is a health drink with traditional cultural background in China, and also is an important cash crop. The southwest region in China is the tea country of origin in the world, mainly distributed in Sichuan, Chongqing, Guizhou, and etc. Those regions have advantages of well natural conditions and little environmental pollution, and are beneficial to grow tea trees and produce famous tea of health security. In recent years, industrial "three wastes" are discharged largely with the development of the village and township enterprises, and the excessive use of fertilizers and pesticides in the tea gardens, the soil surroundings in those areas are polluted by heavy metals to some extents, which involve in the rising of the contents of heavy metals in teas, and thus give a direct threat to human health.In this thesis, the pollution backgrounds of heavy metals were investigated in teas and tea-garden soils in southwest region, and the pollution status of heavy metals were evaluated using the single-factor pollution index and Nemerow pollution index, and thus the health quality of the teas and tea-garden soils were analyzed in order to provide the basic data for the sustainable development of tea industry in the region. Based on the background investigation, and combined with the imperative monitoring items in the healthy quality standard of tea in our country, four heavy metals (Cu, Pb, Cr and Cd) were selected as pillutants in this study. The dynamic characteristics of the residual generation and accumulation of heavy metals in tea examined and discussed with the chage of culture time and the added levels of heavy metals by using liquid cultivation and potted experiment, the transport and transform rules of heavy metals in tea tree were studied in the different growth environments, and the bioavalability of the four heavy metals in soil were analyzed. Based on the main influence factors on the residues of heavy metals, the mathematical model of the relationship between the residue of heavy metals in tea and exogenous concentration of heavy metals, the cumulative rate constant and culture time was established, and the process of residual generation and accumulation of heavy metal in tea was revealed. This study can provide theoretics foundation to know the residual problem of the heavy metals in tea in southwest region and prevent the pollution of heavy metals in tea scientically.The main achievements were summarized as follows.1. The background investigation of heavy metals in tea garden: the contents of six kinds of heavy metals in tea and the tea-garden soil in southwest region were in the scope of appropriate quality standards, with the single-factor pollution indices and Nemerow pollution indices of less than 1.0. However, the comprehensive pollution indices of soils in Leshan and chuan-tea groups were reached 0.69, and close to the upper limit (0.70) of security rank. Generally speaking, tea and the tea-garden soil were not polluted by the six heavy metals (Cd, Cr, Cu, Pb, As, and Hg), and thus the environmental quality of tea and the tea-garden soil are good.2. The dynamic characteristics of residual accumulation of heavy metal in tea tree were studied by liquid cultivation in different culture period. The results showed that the absorption amounts of the four heavy metals (Pb, Cu, Cd, and Cr) were quite different in different parts of the tea tree, and the sequence of all the four heavy metals were root > stem > leaf. The activity of the four heavy metals in tea tree was low, most of the them were fixed by root of the tea tree, the proportion of transportation into stem and leaf was low, and the sequence of the four heavy metals in tea leaf was Cu > Cr > Pb > Cd. In addition, the accumulative amounts of the four heavy metals in tea leaf were related to the concentrations of the added four heavy metals in alimentation fluid and culture time.3. The process of residual accumulation of heavy metals in tea tree were studied by potted cultivation in different culture period. The results showed that the absorption amounts of the four heavy metals (Pb, Cu, Cd, and Cr) were quite different in different parts of the tea tree, and the sequence of all the four heavy metals were root > stem > leaf. The activity of the four heavy metals in tea tree was low, most of them were fixed by root of the tea tree, and the sequence of the four heavy metals in tea leaf was Cr >Cu > Cd > Pb. In addition, the accumulative amounts of the four heavy metals in tea leaf were related to the concentrations of the added four heavy metals in soil and culture time. The first-order kinetic equation was obtained as lnC_t = kt + A to describe the accumulative process of heavy metals in tea leaf with culture time, where C_t is the concentration of heavy metals in tea (mg/kg), / is the culture time (d), and k is the accumulative rate constant of heavy metals. The accumulative rate constant of Cr was maximum, while that of Cd is minimum among the four heavy metals. There were some relationships between the absorption of heavymetals in tea tree and pH of the soil, and the amounts of available heavy metals in soil.