Migration And Source Analysis Of Metals In Soil-tea Plant System Of Tieguanyin Tea Garden

Tea is one of the three major beverages consumed worldwide,and it is consumed by more than 2 billion people.Drinking tea that contains metal pollutants over a long period will have adverse effects on human health.In this study,soil and tea plants from Tieguanyin tea plantations in Anxi County,Fujian Province were selected as study targets.The aims of this study were to(1)to investigate the metal(Li,V,Cr,Co,Ni,Cu,Zn,Sr,Mo,Cd,Sb,Ba,Tl,and Pb)pollution in the soil and tea plants by analyzing the total metal content,metal bioavailability,and characteristics of metal pollution in the soil-tea plant systems;(2)to observe the changes in the metal distribution in various parts of the tea plants and to determine the tea leaf quality in response to metal stress;and(3)to analyze the sources of metals in Tieguanyin tea plantations using the isotopic tracer technique and multivariate statistical analysis to provide the government with a conceptual framework and a scientific basis to make informed decisions about the prevention and control of metal pollution in the soil of tea plantations.The results of the present study were as follows:(1)The assessment of the physicochemical properties and metal contents of the soil and tea plants revealed severe acidification in the soil of the Tieguanyin tea plantations.The total organic C of the soil samples from most sampling points was classified as excellent.In the tea plantation soils,Cd,Pb,and Tl were the major pollution factors,with Cd posing a particularly high ecological risk.Severe pollution was found at three sampling points(HT1,HT2,and JD1)and two profiles(HTp and JDp)in Hutou Town and Jiandou Town.The changes in the profiles of the metals did not follow a specific pattern.Significant variations were found in the contents of Cu and Zn in roots;Mo,Cd,and Sb in stems;and Cr,Sr,Cd,and Ba in new leaves.The ability of new leaves to enrich metals from the soil was relatively weak.(2)Investigation of the metal speciation in the soil samples from the tea plantations revealed that Cd,Pb,and Cr had higher bioactivity.When observing the relationship between the physicochemical properties of the soil and metal bioactivities,soil with a higher acidity level or a lower organic content was found to have higher metal bioactivity.The total metal content did not exert a significant influence on the metal speciation.(3)The results of the Pb,Cd,and Zn stress experiments indicated that Pb and Cd mainly accumulated in the roots of the tea plant.A high concentration of pollutants in the soil resulted in considerable accumulation of Pb and Cd in the leaves and Zn in the stems.A high degree of metal stress led to a rapid decrease in the concentration of polyphenols and caffeine in the tea leaves,which resulted in lower quality tea.(4)The results of the tea leaf soaking experiment showed that the quality of water used for brewing influenced the metal concentration in the brewed tea.An analysis of the health risks posed by pollutants in tea plantation soil and brewed tea showed that the soil of the tea plantations did not pose a significant non-carcinogenic or carcinogenic risk to human health,brewed tea did not pose a significant carcinogenic risk,and Tl contamination in tea posed a non-carcinogenic risk.(5)The results of the multivariate statistical analysis showed that metals in the topsoil of the tea plantations mainly originated from the parent material as well as from agricultural and industrial activities.The parent material was the primary source of heavy metals in all profiles.Pollutants such as dust generated by industrial activities mainly landed on the tea plant roots.Stems were the most affected by agricultural activities.Metals from the parent material of the soil accounted for the largest proportion of the metals found in the new leaves of Tieguanyin tea plants.The Zn source in the new leaves was more difficult to identify because while Zn may originate from industrial activities,it may also originate from unknown sources.Cd does not easily move from the underground plant organs to the leaves.The distribution of heavy metals originating from the parent material was not consistent with the distribution of the topsoil in the region.An analysis of the spatial distribution of the various factors revealed the industrial layout of Anxi County.(6)The following results were obtained when an isotopic tracer technique and isotope mixing model with Pb and Sr isotopes were used to trace the sources of the heavy metals and to calculate the contribution rates of Pb and Sr.The isotopic composition in the topsoil mainly originated from the parent material and coal burning,with the parent material contributing 88% of the Pb on average.The metals in the profiles mainly originated from the parent material,with average contribution rates exceeding 90%.Human activity was the primary source of the heavy metals found in the various tea plant parts.Coal burning and the parent material contributed the most to heavy metal accumulation in the roots,while coal burning,agricultural activities,and dust from steel mills were the primary sources of heavy metals found in the stems and old leaves.New leaves mainly absorbed heavy metals from industrial and vehicle exhaust.