Phytoremediation of Mercury-Contaminated Mine Tailings by Induced Plant-Mercury Accumulation

Abstract

In most contaminated soils and mine tailings, mercury (Hg) is not readily available for plant uptake. A strategy for inducing Hg mobilization in soils to increase accumulation potential in plants was investigated to enhance Hg phytoremediation. Accumulation of Hg in the nickel hyperaccumulator Berkheya coddii, the salt-tolerant Atriplex canescens, and the nonaccumulators Brassica juncea and Lupinus sp. was studied by pot trials containing mine tailings treated with either soluble Hg or sulfur-containing ligands. Accumulation of Hg in shoots of B. coddii and A. canescens after addition of soluble Hg was lower than 10 mg/kg dry weight. The addition of ammonium thiosulfate (NH₄S₂O₃) to tailings mobilized Hg in substrates, as indicated by the elevated Hg concentrations in leachates from the pots of both species. Ammonium thiosulfate caused a significant increase in the Hg concentration in shoots of B. juncea. Conversely, Hg translocation to Lupinus sp. shoots was significantly reduced in the presence of this ligand. Mass balance calculations revealed a significant fraction of Hg was lost from the system. This unaccounted-for Hg may indicate Hg volatilization. The results suggest that there is potential for induced plant Hg accumulation for phytoremediation of Hg-contaminated sites. Issues of Hg leaching and volatilization, however, need to be addressed before this technology can be implemented in the field.