Using plane tree leaves for biomonitoring of dust borne heavy metals: A case study from Isfahan, Central Iran

Limited studies have been conducted on atmospheric dust pollution due to high cost of instrumental monitoring and difficulties in associated sampling methods. In this study, the possibility of using leaves of plane tree (Platanus orientalis L.) as a bioindicator of atmospheric pollution was evaluated by determining the composition of heavy elements in both the tree leaves and the atmospheric dust. Plane tree leaves were sampled monthly for 7 consecutive months (May to Nov.; T1-T7) from 21 different sites in the city of Isfahan, central Iran. Atmospheric dust samples were also collected from the same sites on glass trays simultaneously, except for T1. Concentrations of Cu, Fe, Mn, Ni, Pb, and Zn were determined in both the washed (WL) and unwashed leaves (UL) as well as in the atmospheric dust samples. Elemental concentrations in the dust samples deposited on the leaves were determined by subtracting metal concentrations in UL from those in WL. Significant amounts of heavy metals were detected in UL taken from all sites at all the sampling times except for T7 before which time a heavy rain had fallen. Statistically significant correlations were found between the heavy metal concentrations in the atmospheric dust and the dust deposited on the leaves (UL-WL) except for Pb in T4 and T5 sampling times. The spatial distribution maps of heavy metal concentrations in atmospheric dust followed almost the same pattern as those in plant leaf dust. The results showed that plane tree leaves have a great potential for use as an indicator of air pollution for all the heavy metals investigated except for Pb. This passive dust sampling and pollution accumulating method appears to be an easy, inexpensive, and accessible approach for the detection of atmospheric heavy metals.