Assessment of heavy metals in Cypress (Thuja orientalis L.) in the Yazd Highway green belt

Dust storm is one of the criteria for air pollution, and pollution by Heavy Metal(HM) is one of the major environmental problems in the world. The objective of the present study was to assess some of HMs concentrations in the leaves and bark of cypress and atmospheric falling dust along the Yazd highway, Yazd Province, Iran. The total concentrations of cadmium (Cd), cobalt (Co), copper (Cu), nickle (Ni), lead (Pb), zinc (Zn), iron (Fe) and manganese (Mn) in the dust and plant samples were measured using atomic absorption spectrophotometry after digestion with acid. The results showed that the concentration of Zn and Cd metals in falling dust were the highest to the lowest, respectively. The distance from the highway significantly influenced the concentration of HMs in leaves and bark of the cypress tree. Moreover, the effect of HMs on the bark of this tree was higher than that of leaves, except for Cd, Co, Cu and Mn. Concentrations of Zn, Co, Ni and Fe increased with the increase in the distance from the highway due to multi-directional winds and the presence of other contaminants. The Pearson correlation analysis between the HMs found in the falling dust and Thuja orientalis L. showed that the input and controlling factors of these metals in the cypress tree were probably the same as the dust. The results further showed that the Thuja orientalis L. leaves with a metal accumulation index of 1973.16 mg/kg were more able to simultaneously absorb different metals. Therefore, since this green belt surrounds the Yazd urban area, it is expected that a significant amount of HMs will be absorbed by these trees.