Mercury Contaminated Sites: A Review of Remedial Solutions

The physio-chemical characteristics of mercury have made it a favourable component for many industrial and agricultural applications. Significant anthropogenic Hg sources include fossil fuel combustion, the chloralkali industry and pharmaceuticals. Modifications to industrial practices and stricter regulations have led to emission reductions in many countries; however, this has been countered by the increased use of Hg for gold amalgamation, particularly in tropical, developing countries. Under any of these circumstances, varying quantities and forms of Hg have been inevitably released to environments where it can pose a risk to human and ecological health. Given the unique behaviour of Hg, remediation of Hg contaminated sites can be complicated and costly. This paper reviews commonly employed and emerging techniques to mitigate Hg pollution and describes key design considerations and concerns associated with each method. Well-established ex-situ (external) techniques, such as physical separation and thermal treatment of excavated materials, are discussed in theory and practice. Potential in-situ (i.e. in place) Hg recovery methods, such as soil vapour extraction combined with soil heating and the use of leaching agents, are also explored. Finally, containment strategies are described for sites where more conclusive measures cannot be employed.