Measurement and evaluation of heavy metal accumulation in soil and leaves of three tree species (Azadirachta indica, Conocarpus Erectus L. and Prosopis juliflora) in Bandar Abbas

Document Type : Original Article


1 Department of Watershed Management Science and Engineering, Faculty of Agriculture and Natural Resources, University of Hormozgan, Bandar Abbas, Iran

2 Marine Science Research Institute, Kish International Campus, University of Tehran, Kish, Iran

3 Department Environmental Planning, Management and Education, Faculty of Environment, University of Tehran, Tehran, Iran


Introduction: Emissions of particulate matter from car exhaust, tire wear, engine lubricants and street fence wear contain heavy metals, which are dangerous for the urban ecosystem. However, most of the particles are deposited on the canopy and soil of plants, which are absorbed by them. Pollution-resistant species with a high capacity to absorb suspended particles can be used to remove suspended particles from the urban environment. For this reason, in this study, concentrations of heavy metals in the leaves and soil of tree species in Bandar Abbas were measured and evaluated. Also, species with the highest potential for adsorption of heavy metals were identified.
 Material and methods: First, three tree species including Azadirachta indica, Conocarpus and Prosopis juliflora were selected as the dominant plants in Bandar Abbas and in 30 points of the fields with 5 points of the non-polluted environment outside the city (control), and sampled from the surface soil and leaves of these species. After preparing and digesting the samples, the concentration of heavy metals (cadmium, manganese, zinc and lead) emitted from urban traffic was measured using atomic absorption spectrometry in soil and tree leaf samples. Next, the difference in heavy metal concentrations between tree species was analyzed by ANOVA and between soil and leaves and between urban and control environments was analyzed by t-student test. Then, to determine the tree species with high accumulation of heavy metals, two indices of heavy metal accumulation (BCF) and bioaccumulation index (MAI) were used.
Results and discussion: The results showed that the pattern of heavy metals in soil and leaves of tree species was Mn> Zn> Pb> Cd. The maximum concentrations of heavy metals in the soil and leaves were detected in Conocarpus, Azadirachta indica and Prosopis juliflora, respectively. Spatially, the highest concentration of heavy metals in the sampling points was related to Imam Hossein Street. However, the minimum concentration of heavy metals was observed in the Persian Gulf Street. The concentrations of Mn and Pb in the soil of plant species were different and their differences were significant at 95% level, but the concentration of Cd and Zn was not different in the soil of tree species. Pb, Mn and Zn concentrations were not different in the shoots of the studied tree species and their differences were not significant at the 95% level. However, the concentration of Cd in the shoots of the species was different and the difference between the species was significant at the 95% level. There was a significant difference in the concentration of heavy metals between soil and leaves at 95 and 99%. Also, the concentration of heavy metals in soil and leaves between urban and control fields was significantly different at 95%. The pattern of the BCF index in all species was Zn> Pb> Mn> Cd and heavy metals had moderate accumulation for tree species. Bioaccumulation index (MAI) showed that Conocarpus had the highest adsorption potential of heavy metals and the lowest adsorption potential was observed in Prosopis juliflora.
Conclusion: Conocarpus, by absorbing pollutants from urban traffic, purifies the polluted air of Bandar Abbas; However, Prosopis juliflora, which is one of the migratory trees in the city of Bandar Abbas, with strong and deep roots, dries up the surface and groundwater of the region. On the other hand, its potential to absorb urban air pollutants is weak. Therefore, despite their resistance to drought and heat, Conocarpus trees have a high potential to purify urban pollution and can replace Prosopis juliflora.


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