年轮化学示踪技术及在重现矿区重金属污染历史中的应用

Dendrochemistry Application as a Tool for Biomonitoring Environmental Pollution of Mining Areas

矿区自然分布的树木从环境中吸收重金属元素,并在形成层发育过程中将重金属元素储存在年轮中,通过分析年轮中重金属元素含量的变化特征,可以半定量判定不同污染途径对年轮中重金属元素的贡献率,进而重现矿区环境变迁历史。本文综述了国内外年轮化学在环境污染分析中的应用案例,针对影响年轮化学分析精度的各种环境因素,结合矿区污染特征,探讨了如何提高年轮化学在矿区大气污染和土壤污染研究中的分析精度。随着年轮中重金属元素分析手段的不断改进,年轮化学将在矿区污染监测方面发挥越来越重要的作用。

The trees,naturally growing in the mining areas,can uptake heavy metals from air,soil,and irrigation water.The pathways of heavy metals entering the trees might be roots,barks,and leaves.After entering the trees,heavy metals will deposit in the tree-rings during cambium development.The long-term fluctuations of element contents in tree rings can be analysed by the laser ablation system coupled to an inductively coupled plasma mass spectrometer.Therefore,the pollution processes of mining areas can be recorded by the variation of heavy metal concentrations in the tree-rings,and the influential ratios of different pollution routes can be semi-quantitatively determined.Cases of applications of dendrochemistry in biomonitoring of air,water and soil pollution were reviewed in this article.Based on the point pollution characteristics of mining areas,the possibility of applying dendrochemistry for pollution monitoring was discussed.Aiming to improve the accuracy of research of atmospheric and soil pollution in mining areas by dendrochemistry,different influential factors of heavy metal concentrations in tree rings,such as tree species,selective uptake of elements by trees,climate variation and nutrient providing,were reviewed.Geostatistics,stable isotope tracer,and synchrotron radiation X-ray fluorescence can improve the accuracy of dendrochemistry for environmental pollution recording.Atmospheric dispersion model predicting ground-level concentrations from a point source of metal emissions,such as smelters,can be calibrated on tree rings in order to reconstruct the spatial and temporal Pb-contamination pattern.Dating of the historical record has been achieved using isotopic analysis,for example 210Pb and 137Cs.With the development of analytical techniques of heavy metals in tree rings,dendrochemistry will play a more important role in pollution monitoring in mining areas.This review highlights the strong potential for dendrochemistry to combine with other approaches in environmental research.