Phytoremediation of Mercury-Contaminated Mine Sites: An Evaluation of Processes and Their Associated Risks

Phytoremediation embraces an array of low-cost plant-based technologies that could be potentially advantageous for remediation of Hg polluted soils, especially in developing countries, where artisanal and small-scale mining for gold extraction has left a legacy of Hg pollution. In this work, we thoroughly examine phytoremediation processes and their associated risks in metal-contaminated mine tailings of Brazil, China and New Zealand where Hg pollution caused by anthropogenic or ASM activities are of concern. We describe laboratory and greenhouse experiments where the effect of total Hg concentrations, plant species, and humic acids was investigated on Hg-induced phytoextraction and phytostabilisation. The results of a field-scale phytoextraction experiment in situ are also presented. We also evaluated the generation of Hg-containing leachates and Hg vapour emissions from plant pots enclosed in gas-tight volatilisation chambers. Altogether, these experiments provided a picture on the Hg transport and fate in the plant-soil-atmosphere continuum, which is a fundamental step towards risk assessment and decision making of available alternatives for the remediation and rehabilitation of Hg-contaminated mine sites.