Trace elements in tree rings and their environmental effects: A case study in Xi’an City

Using wet digested method and ICP mass spectrometer, we analyzed the concentration of five trace elements (Cd, Mn, P, Zn and Pb) for the tree rings from both urban and suburbs of Xi’an. At the urban sampling site, one Chinese mahogany ( Toona sinensis ) disc and one phoenix tree ( Firmiana simplex ) disc were sampled from a steelworks in Xi’an City. At the suburb site, a Chinese mahogany disc was collected from a village in the south of the City. In addition, some soils near the roots of the sampled trees were collected. The analysis results indicate that the concentration of each of the five elements in annual rings has a positive correlation with the production of the steelworks. Statistical calculations show that Pb and Mn elements were stable without lag effects. That means these two elements do not move between rings. Cd displayed one year moving, P two years and Zn three years. These results are quite similar to those found by other methods.