Metal Removal Potential by Three Aquatic Plants in an Acid Mine Drainage Wetland

This study was conducted to gauge the metal bioaccumulation potential of hydrophytic vegetation in a wetland constructed in McCreary County, Kentucky, USA, to treat a cole mine effluent averaging 787 mg/L Fe, 12.6 mg/L Al, 10.9 mg/L Mn, and 2,244 mg/L acidity. Three dominant plant species, cattail (Typha latifolia), bulrush (Scirpus validus), and tickseed sunflower (Bidens aristosa), were sampled and analyzed for Al, Fe, and Mn, so that relationships could be drawn about their capability to bioaccumulate metals from the wastewater. Results showed that Al and Fe were retained-mainly in the roots of the plants, while Mn was more mobile throughout the plant. Iron bioaccumulation was similar for all three plant species at high metal concentration gradients, but somewhat reduced in T. latifolia at low concentration gradients. Scirpus validus appeared to be the most Al-tolerant species, considering its greater Al bioaccumulation potential at high metal concentration gradients. In spite of the high metal load and acidity of the water, there were no visible toxicity effects, but B. aristosa and to a lesser extent S. validus seemed to prefer low-mental concentration environments. All plants bioaccumulated some Al, Fe, and Mn, but their concentrations were fairly miniscule compared to overall metal retention by the wetland substrate. This suggests that the main plant contribution is through substrate stabilization, microbial attachment, and rhizosphere oxidation rather than phytoremediation. Therefore, plant selection criteria for high metal load wetlands should mainly be based on metal tolerance and rhizosphere surface area rather than metal bioaccumulation potential.