Accumulation of heavy metals in the leaves of different tree species and its association with the levels of atmospheric PM(2.5)-bond heavy metals in Isfahan

Abstract

This study aimed to biomonitor air pollution by measuring heavy metals (HMs) accumulation levels in the leaves of common urban trees, Cupressus arizonica Greene, Melia azedarach L., Morus alba L. and Buxus colchica in different regions of Isfahan. Their association with the levels of PM(2.5) and PM(2.5)-bond HMs was also investigated. PM(2.5) were collected on a glass-fiber filter and measured by gravimetric method. The HM contents of the PM(2.5) and tree leaves were extracted and analyzed by ICP-OES. The average PM(2.5) concentrations in ambient air of all areas varied from 52.34 to 103.96 mug/m(3). The mean HMs levels in the leaves were in the following orderZn(31.2) > Cu(11.04) > Pb(4.38) > Ni(4.01) > Cr(3.03) > Co(0.61) > Cd(0.04) (mug/g). The highest level of HMs was detected in the leaves of Morus alba L., followed by Buxus colchica, Melia azedarach L. and Cupressus arizonica Greene. There was a significant correlation between the amounts of Pb and Cu in tree leaves and those in ambient PM(2.5) (p value </= 0.05). In conclusion, tree leaves can be used as a suitable bioindicator in the evaluation of air pollution. Morus alba L. compared to the other species can be confidently used for green space development. Isfahan is one of the most populated, industrialized cities in Iran experiencing serious air pollution. The currently operated air pollution monitoring stations in the city do not measure atmospheric heavy metals, a hazardous component of PM(2.5). To assess air pollution and level of exposure, biomonitor species such as tree leaves are the best tool due to their availability and low cost. Tree leaves can absorb and retain air pollutants. In this study, we found a good correlation between the concentration of heavy metals especially Pb and Cu in the leaves of commonly used tree species and their concentration in the airborne PM(2.5). Also, the results revealed that among the tree species, Morus alba L. retains more heavy metals followed by Buxus colchica, Melia azedarach L., and Cupressus arizonica Greene, which can be used for green space development.