Characteristics Of Metals And Isotopic Tracing Research In Soil-tea System From Typical Tea Gardens In Fujian Province

In this paper,the main object is soil-tea system from Wuyi rock tea and Tieguanyin tea gardens in Fujian province.We determined 20 kinds of none REE(rare earth elements)such as Be,Mg,Al,V,Cr,Mn,Fe,Co and 15 kinds of REE in soils-tea system.The distribution of metals in soils and teas was analyzed,and the pollution degree of metals in soils and tea leaves was assessed.Modified BCR method was employed to extract the forms of metals in soils and to discuss the bioavailability of each metal.The enrichment characteristics of metals in different parts of tea plant were analyzed.The transfer factors of metals from soil to tea were calculated.The health risk of heavy metals was evaluated based on the contents of heavy metas in tea leaves and the extraction ratios of metals in made tea.Combined Pb,Sr and Nd isotopic compositions were determined to trace the sources of metals in the soil-tea system.The main results are as follows:(1)Soils in Wuyi rock tea and Tieguanyin tea garden soils present acidic property and meet the environmental conditions in the producing areas of pollution-free tea.The soil fertility is in ? grade.Contents of Be,Cr,Ni,Cs in soils from Wuyi rock tea gardens and contents of Mn in Tieguanyin tea gardens are all higher than the background values of soils in Fujian province.The distribution of metals is dispersed.The contents of REE follow Ordo-Hagan 's rule.?REE in soils are lower than the background values of soils in Fujian province,the average values of soils in China,and the average values of soils in the world.?LREE/?HREE is higher than rock and the average value in China.It shows that HREEs fractionate and LREEs enrich.Ce in soils is relative enrichment,but Eu loss.(2)Except for Pb and 4 kinds of REE(Ce,Sm,Eu,Gd),the other metals are main in residual forms.The proportions of residual forms for most elements in subsurface soils are higher than those in surface soils.The bioavailability factors show the order of Ce> Pb> Gd> Eu> Sm> Nd> Pr> Tb> La> Y> Dy> Cd> Ho> Er> Tm> Se> Yb> Mn> Lu> Ba> Co> Cu> Sr> U> Cs> Be> Ni> Rb> Zn> Mg> V> Fe> Al> As> Cr.Bioavailability factors for most elements in surface soils are higher than those in subsurface soils.(3)The results of accumulation index of elements show that all the studied metals in soils from rock tea and Tieguanyin tea gardens present no pollution level.A part of sites reach mild to moderate pollution level.The results of enrichment factor show that metals in soils present no pollution to slight pollution degree.A part of sites reach moderate pollution degree.The results of potential ecological hazard index show that 10 kinds of metals in soils appear mild ecological hazard.TS4,TS10,TH7,TH10 and TH18 show moderate potential ecological risk.TH25 appears high potential ecological risk.The other sites present low potential ecological risk.Cd shows high potential ecological hazards to pollution sites.These three assessment methods reach a consistent conclusion.(4)The highest content of metals in new leaves is Mg and the lowest content of metals is Tm.The highest content of metals in old leaves is Al and the lowest content of metals is Tm.Be,Al,V,Cr,Mn,Fe,As,Se,Sr,Ba,Pb,U and REE in old leaves are all higher than those in new leaves.Content of Mg,Co,Cu,Zn,Rb,Cs in new leaves are all higher than those in old leaves.Higher metals in tea leaves are associated with higher bioavailability in soils.The results of metals in different parts of tea plant show that the contents of Zn,Ni,Al,Mn,V,As,U and rare earth elements with even atomic number are all higher than other parts.The contents of metals in branch are not high and REE in stone(include seed husks and kernels)are almost unenriched.(5)The results of single pollution index and comprehensive pollution index show that metals in tea leaves are all at security level.The results of extraction rates of made-tea show that the highest contents of metals in twice immersion leaching are both Mg and the lowest contents of metals are both Be.The highest extraction rates are both Rb and the lowest extraction rates are both Fe.The leaching amounts of metals in the second immersion are much lower than those in the first immersion.The results of health risk assessment show that Mn in made-tea has non-carcinogenic risk and Ni has carcinogenic risk to human.Tea soup in twice immersion both have no non-carcinogenic risk to human.But Ni has carcinogenic risk to human.(6)The transfer factors of metals in rock tea gardens are similar to those in Tieguanyin tea gardens.The transfer factors of Be,Al,V,Cr,Mn,Fe,As,Sr,Cd,Ba,Pb,U and REE in old leaves are higher than those in new leaves.The transfer factors of Mg,Co,Ni,Cu,Zn,Rb,Cd,Cs in new leaves are higher than those in old leaves.Mn,Co,Cd,Pb,U and REE in new leaves are significantly correlated to their bioavailabilities in soils.Mn,Co,Cd,Pb,U and REE in old leaves are both significantly correlated to their bioavailabilities and total contents in soils.But Mg,Cr,Ni,Sr in old leaves are only significantly correlated to their bioavailabilities in soils.(7)Pb,Sr,Nd isotopic compostions were analyzed to trace the sources of metals in the soil-tea systems.The results show that Pb in soils and tea leaves mainly come from vehicle exhausted dusts and parent materials.Sr is mainly affected by vehicle exhausted dusts,coal burning dusts and parent materials.REE in tea leaves mainly come from parent soils,vehicle exhausted dusts and coal burning dusts.Combined Sr-Nd isotopes were used to distinguish new leaves in these four regional tea gardens.The results show that tea leaves in Wuyi rock tea gardens are distinguished to those in Tieguanyin tea gardens.However,the isotope ratios in tea leaves from Xiamen,Zhangzhou and Anxi tea gardens overlap each other,so these three tea gardens are indistinguishable.