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

This study aimed to biomonitor air pollution by measuring heavy metals (HMs) accumulation levels in the leaves of common urban trees, <i>Cupressus arizonica Greene</i>, <i>Melia azedarach</i> L., <i>Morus alba</i> L. and <i>Buxus colchica</i> 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 <i>Morus alba</i> L<i>.,</i> followed by <i>Buxus colchica, Melia azedarach</i> L. and <i>Cupressus arizonica Greene</i>. There was a significant correlation between the amounts of Pb and Cu in tree leaves and those in ambient PM_2.5 (<i>p</i> value ≤ 0.05). In conclusion, tree leaves can be used as a suitable bioindicator in the evaluation of air pollution. <i>Morus alba</i> L. compared to the other species can be confidently used for green space development.