Phytoremediation and rhizoremediation of organic soil contaminants: Potential and challenges
Karen E. Gerhardt, Xiao-Dong Huang, Bernard R. Glick, Bruce M. Greenberg
Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Over the past few decades there has been avid interest in developing in situ strategies for remediation of environmental contaminants. Major foci have been on persistent organic chemicals and metals. Phytoremediation, a strategy that uses plants to degrade, stabilize, and/or remove soil contaminants, has been extensively investigated. Rhizoremediation, a specific type of phytoremediation that involves both plants and their associated rhizosphere microbes, can occur naturally, or can be actuated by deliberately introducing specific microbes. These microbes can be contaminant degraders and/or can promote plant growth under stress conditions. Because initial phytoremediation research showed great promise as a cost-effective remedial strategy, considerable effort has been devoted to making the transition from the laboratory to commercialization. Despite our understanding of the mechanisms of remediation, and the success of studies in the laboratory and greenhouse, efforts to translate phytoremediation research to the field have proven challenging. Although there have been many encouraging results in the past decade, there have also been numerous inconclusive and unsuccessful attempts at phytoremediation in the field. There is a need to critically assess why remediation in the field is not satisfactory, before negative perceptions undermine the progress that has been made with this promising remedial strategy. Two general themes have emerged in the literature: (1) Plant stress factors not present in laboratory and greenhouse studies can result in significant challenges for field applications. (2) Current methods of assessing phytoremediation may not be adequate to show that contaminant concentrations are decreasing, although in many cases active remediation may be occurring. If phytoremediation is to become an effective and viable remedial strategy, there is a need to mitigate plant stress in contaminated soils. There is also a need to establish reliable monitoring methods and evaluation criteria for remediation in the field. This review will focus on the challenges and the potential of phytoremediation, particularly rhizoremediation, of organic contaminants from soils.