Abstract

Phytostabilisation with native plant species has been advocated as a cost-effective approach to rehabilitate mine tailings containing phytotoxic metal-bearing minerals. For this purpose, five Acacia species (natural colonisers) native to north-west Queensland region of Australia were investigated formetal uptake and root exudation characteristics in response to growth for 3 weeks in three differentmine tailings (Cu and Cu-Pb-Zn) differing in their degree ofweathering. Root tissues of the plant species grown in the three types of tailings accumulated up to 0.9 mg Cd kg(-1), 10mg Co kg(-1), 177mg Cu kg(-1), 38mg Pb kg(-1) and 4800mg Zn kg-1 (DW basis) -being suitable for phytostabilisation purposes. However, elevated levels of root exudates in rhizosphere tailings enhanced the bioavailability of metals, leading to the accumulation of high levels of some metals in Acacia shoots (e.g. shoot concentrations of 140 mg Zn kg(-1) in Acacia acradenia F. Muell. and 230 mg Zn kg-1 in Acacia hilliana Maiden). Positive correlations (P < 0.05) between citric acid levels and metal root uptakes suggested that citric acid production in these plant species may be the main driver for metal mobilisation. The results suggest that the native acacia species have the potential to mobilise metals (albeit in mineral forms) in the tailings, when used for phytostabilisation.