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Mine tailings generated by artisanal gold mining constitute a major source of soil and water contamination in Sahelian regions, where agricultural land and water resources are particularly vulnerable. These tailings behave as environmental porous media in which water circulation, redox conditions and soil–plant interactions control the mobility, bioavailability and transfer of trace metals. In this context, phytoremediation represents a nature-based solution with the potential to limit metal transfer, although its effectiveness strongly depends on metal-specific behaviour within the soil porous matrix.
This study investigates the impact of phytoremediation on the mobility and speciation of iron (Fe) and zinc (Zn) in mine tailings, with particular emphasis on bioavailability and potential transfer towards pore water. A greenhouse pot experiment was conducted over an eighteen-month period using Chrysopogon zizanioides, a perennial grass widely recognised for its soil stabilisation and environmental remediation capacities. Polluted mine tailings and unpolluted reference soils were arranged in a completely randomised design. Changes in Fe and Zn binding forms within the soil porous system were assessed using the BCR sequential extraction procedure, distinguishing exchangeable, reducible, oxidisable and residual fractions.
After six months of phytoremediation, iron showed a strong predominance of the residual fraction, accounting for approximately 66.7% (± 0.5) of total Fe. This fraction is poorly mobile and weakly bioavailable, indicating effective Fe immobilisation within the mineral matrix and a limited risk of transfer towards pore water. Exchangeable, reducible and oxidisable Fe fractions remained marginal, highlighting the stabilising effect of phytoremediation on Fe behaviour in environmental porous media.
In contrast, zinc exhibited a more dynamic speciation pattern. Reducible and oxidisable fractions together represented nearly 60% (± 0.5) of total Zn, indicating a substantial pool of potentially mobilisable forms that are sensitive to changes in redox conditions and organic matter dynamics. Although the exchangeable Zn fraction remained comparatively low, it represents the most bioavailable pool and may contribute to plant uptake or downward migration within pore water. These results suggest that Zn mobility persists despite phytoremediation, implying that longer treatment periods or complementary stabilisation strategies may be required to effectively limit Zn transfer towards water resources.
Overall, this study highlights the contrasted responses of Fe and Zn to phytoremediation in mine tailings and demonstrates the importance of metal speciation for understanding soil–water–plant interactions in environmental porous media. Such insights are essential for assessing remediation efficiency and protecting agricultural soils and water resources in mining-impacted regions.
| References | Zhang, X., Liu, Y., Wang, Q., Chen, C., & Zhou, J. (2023). Sequential extraction insights into metal speciation dynamics under phytoremediation treatments. Environmental Pollution. Wani, Z. A., Ahmad, Z., Asgher, M., Bhat, J. A., Sharma, M., Kumar, A., Sharma, V., Kumar, A., Pant, S., Lukatkin, A. S., & Anjum, N. A. (2023). Phytoremediation of potentially toxic elements: role, status and concerns. Journal of Rehabilitation, 69(2), 43–48. Ure, A. M., Quevauviller, P., Muntau, H., & Griepink, B. (2013). An Account of the Improvement and Harmonization of Extraction Techniques Under the Auspices of the BCR of the Commission of the European Communities. International Journal of Speciation of Heavy Metals in Soils and Sediments. April 2013, 37 - 41. |
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| Country | Burkina Faso |
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