Geochemical Characteristics Of Rare Earth Elements And Risk Assessment In Soil And Tea System Of Tieguanyin Tea Garden

Tea is one of the most popular drinks in the world.The soil environment quality and tea quality has drawn more attention.An investigation on natural geographical condition and social economic condition was conducted in Tieguanyin tea-producing areas.The main production area of Tieguanyin tea was selected for this study.Surface soils and vertical profile soils as well as tea leaves were collected.The total contents and available contents of rare earth elements(REEs)in soils and tea leaves were analyzed by ICP-MS,and the distribution,migration and accumulation of REEs in soils and tea leaves were studied.Assessment of REEs contamination in the soil of Tieguanyin tea gardens was conducted by the methods of geo-accumulation index and enrichment factor.The leachable rates of La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu and Y from eight kinds of Tieguanyin tea were investigated,and the individual health risk assessment was also conducted in the study.The main conclusions of the research were summarized as following:The contents of total REEs ranged from 57.34 to 525.11 mg·kg-1 in the surface soil,with the mean of 241.41 mg·kg-1.The contents of total REEs ranged from 132.83 to 383.64 mg·kg-1 in the subsurface soil,with the mean of 250.49 mg·kg-1.The contents of total REEs in the surface and subsurface soils were much higher than those in China(163.86 mg·kg-1)as well as in the world(153.80 mg·kg-1).The ratios of total light rare earth elements(LREEs)to heavy rare earth elements(HREEs)ranged from 7.460 to 22.09 in the surface soil,with the mean of 12.53.The ratios of LREE/HREE ranged from 2.830 to 11.24 in the subsurface soil,with the mean of 5.92.They were far greater than 1,indicating that LREEs and HREEs had obvious differentiation,and LREEs were relatively rich.Ce was relatively enriched and Eu was lost in the soil of Tieguanyin gardens.Correlation analysis showed that the available and total contents of REEs in soil had significantly positive correlation,and the available contents of REEs were controlled by the total contents of REE.The available contents of Eu were positively correlated with soil pH.The results of sequential extraction test showed that the speciation of REEs decreased in the order of residual> reducible> oxidizable> soluble.The contents of total REEs ranged from 153.10 to 217.40 mg·kg-1 in the vertical profile soil with the mean of 184.22 mg·kg-1,which was slight higher than those in China as well as in the world.Light rare earth elements and total rare earth elements kept similar distribution trend in the vertical soil,indicating that light rare earth elements were the main part of total rare earth elements.Correlation analysis showed that the correlation among light rare earth elements was highly significant and the correlation among heavy rare earth elements was highly significant,but the correlation between light rare earth elements and heavy rare earth elements was relatively weak.And the content of Eu was positively correlated with TC.Pollution of REEs in the soil of Tiegunayin tea gardens was evaluated based on the background values of REEs in the soil of Fujian province.The geo-accumulation index(Igeo)results indicated that the REEs showed no pollution.However,Er,Tm and Yb presented mild to moderate pollution in some samples.The local farmers and relevant departments should pay attention to this issue.Enrichment factor(EF)was applied to evaluate pollution of REEs.The EF values of REEs in soil were less than 2,suggesting that the REEs showed no pollution or slight pollution.Er,Tm and Yb reached moderate pollution level in some surface and subsurface soil samples.Tm was slightly larger than 2 in some horizons of vertical soil profile,implying moderate pollution level which was associated with human activities.The contents of the REEs differed significantly in Tieguanyin tea samples.La,Ce,Nd and Y were the major rare earth elements in the samples.Light rare earth elements and heavy rare earth elements had obvious differentiation and light rare earth elements were relatively rich.The distribution pattern of the REEs in the Tieguanyin teas and corresponding plantation soils were similar.The concentrations of REEs in old tea leaves were obviously higher than those in new tea leaves.The migration ability of REEs from soil to tea was weak,with the migration coefficient of less than 1 in most tea leaves.The tea leaves took up different REEs almost with equivalent abilities.But there was little correlation between the content of REEs in new and old tea leaves and the content of REEs in the soil.It showed that the content of REEs in tea was controlled not only by the content of REEs in the soil,but also by physiological property of the tea itself and anthropogenic influence.The health risk level of REEs in made Tieguanyin tea was evaluated based on the leaching rate of REEs from tea,combined with the intake dose of REEs through dringing tea-water.The results show that the maximum intake of REEs in the made Tieguanyin tea accounts for 0.31% of acceptable daily intake(ADI),less than 5.0% of ADI,which was issued by the Codex Alimentarius Commission(CAC).So the intake of tea is safe for people through dringing tea-water,although the contents of REEs in some Tieguanyin teas have exceeded the national standard limits.We should look at the problem calmly and scientifically.