Heavy Metal Accumulation and Distribution in Four Broadleaf and Coniferous Tree Species Cultivated at Mobarakeh Steel Company

Document Type : Complete scientific research article

Authors

1 M.Sc. Graduate in Forestry, Department of Forest Science and Engineering, Faculty of Natural Resources and Earth Sciences, Shahrekord University, Shahrekord, I. R. Iran

2 Department of forest sciences, Faculty of Natural Resources and Earth Science, Shahrekord University, Shahrekord, Iran.

3 PhD in Forest Science and Engineering, Department of Green Space, Mobarakeh Steel Company, Isfahan, I. R. Iran

4 Associate Professor, Department of Forestry, Faculty of Natural Resources and Marine Science, Tarbiat Modares University, Noor, I. R. Iran

Abstract

Background and objectives
Environmental contamination by heavy metals, particularly in industrial areas such as steel production facilities, poses a serious threat to ecosystem and human health. Phytoremediation is recognized as a sustainable and cost-effective approach for removing pollutants such as heavy metals from soil and water. Tree species, due to their extensive root systems, high biomass production, and perennial nature, are considered suitable candidates for long-term phytoremediation. This study investigated the capacity of four tree species Cupressus arizonica, Morus alba, Pinus eldarica, and Robinia pseudoacacia; grown in a heavy-metal-contaminated environment (the Mobarakeh Steel Complex) to accumulate and distribute heavy metals among roots, stems, branches, and leaves. The trees had grown for 17 years under similar conditions with drip irrigation in mixed stands within a single plot of approximately 0.5 ha. The main objectives were to evaluate organ-specific metal accumulation patterns, quantify the relative contribution of each organ to remediation, and determine the overall phytoremediation potential. The novelty of this study lies in providing an integrated analysis of metal concentration data together with actual biomass allocation patterns across the whole plant to achieve a more accurate assessment of species-specific remediation capacity.
Materials and Methods
Cadmium (Cd), copper (Cu), zinc (Zn), and iron (Fe) were selected due to their prominent occurrence in effluents and soils surrounding steel and metal smelting facilities. Five individuals of each species were randomly selected. Samples were separated into major plant organs, and after drying and grinding, metal concentrations were determined using flame atomic absorption spectrophotometry. Transfer factor (TF), biomass allocation, inter-metal correlations, and cumulative metal accumulation were calculated and analyzed using a general linear model.
Results
Cupressus arizonica (Zn: 223 mg·kg⁻¹; Cd: 6 mg·kg⁻¹) and Morus alba (Fe: 1336 mg·kg⁻¹; Cu: 55 mg·kg⁻¹) showed the highest metal concentrations, whereas Robinia pseudoacacia exhibited the lowest levels across organs. Leaves showed the highest TF values for all metals in all species. The highest Fe translocation was observed in Pinus eldarica leaves (TF = 27.86), followed by Morus alba (5.96) and Cupressus arizonica (3.69), while Cd and Zn generally showed TF values >1 in leaves. Copper translocation was species-dependent. Strong positive correlations among Cd, Cu, and Zn were detected in leaves of Morus (r = 0.85–0.96) and Robinia (r = 0.88–0.93), whereas no significant correlations were observed in Pinus. Pinus eldarica produced the highest total dry biomass (110 kg) with dominant allocation to stems (47%) and showed the greatest total metal accumulation, particularly for Cd, Cu, and Zn. Robinia pseudoacacia allocated the highest biomass share to roots (36%). Despite its low total biomass (30 kg), Morus alba exhibited high Fe and Cu accumulation in leaves. Metal concentrations in leaves of all species exceeded reported toxicity thresholds, indicating severe meta contamination stress.
Conclusion
The results demonstrate pronounced species-specific differences in heavy metal accumulation, translocation, and stabilization. Pinus eldarica is suitable for long-term metal stabilization due to high biomass production and metal storage in stems and roots, whereas Cupressus arizonica shows potential for combined stabilization and extraction through substantial foliar accumulation. Morus alba and Robinia pseudoacacia, despite lower biomass, are appropriate for restoration and management of moderately contaminated sites due to effective metal transfer to harvestable aerial organs. Accordingly, species selection in phytoremediation programs should be based on dominant metal type, contamination level, and management objectives (stabilization vs. extraction).

Keywords

Main Subjects

References

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Journal of Wood and Forest Science and Technology
Volume 33, Issue 1
March 2026
Pages 71-89

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