Accumulation of heavy metals in the leaves of different tree species and its association with the levels of atmospheric PM2.5-bond heavy metals in Isfahan.

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 μg/m³. 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) (μg/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.