Phytotechnology has many potentially beneficial land uses, though for the most part the applications are still in the development stage. Several have been tested for the treatment of contamination, and in some cases successfully tried in the field, but generally they remain in the ‘novel and innovative’ category, lacking well-documented data on their performance under a variety of typical operating conditions. As a result, some researchers have voiced doubts, suggesting that the beneficial effects of plant utilisation, particularly in respect of phytoremediation, have been overstated. Some have argued that the reality may range from genuine enhancement to no effect, or even to a negative contribution under certain cir-cumstances and that the deciding factors have more to do with the nature of the site than the plants themselves. In addition, some technologies which have been successfully used on some sites may simply serve to complicate matters on others. One such approach which achieved commercial scale use in the USA, principally for lead remediation, required the addition of chemicals to induce metal take-up. Lead normally binds strongly to the soil particles and so its release was achieved by using chelating agents like ethylene diamine tetra acetic acid (EDTA), which were sprayed onto the ground. With the lead rendered biologically available, it can be taken up by plants and hence removed. However, dependent on the char-acter of the site geology, it has been suggested that this could also allow lead to percolate downwards through the soil, and perhaps ultimately into watercourses. While it may well be possible to overcome this potential problem, using accurate mathematical modelling, followed by the establishment of good hydraulic con-tainment as an adjunct to the process, or by running it in a contained biopile, it does illustrate one of the major practical limitations of plant bioengineering. The potential benefits of phytotechnology for inexpensive, large-scale land manage-ment are clear, but the lack of quantitative field data on its efficacy, especially compared with actively managed alternative treatment options, is a serious barrier to its wider adoption. In addition, the roles of enzymes, exudates and metabolites need to be more clearly understood and the selection criteria for plant species and systems for various contamination events requires better codification. Much research is underway in both public and the private sectors which should throw considerable light on these issue. Hopefully it will not be too long in the future before such meaningful comparisons can be drawn.
One area where phytoremediation may have a particular role to play, and one which might be amenable to early acceptance is as a polishing phase in combination with other clean-up technologies. As a finishing process follow-ing on from a preceding bioremediation or nonbiological method first used to deal with ‘hot-spots’, plant-based remediation could well represent an optimal low-cost solution. The tentative beginnings of this have already been tried in small-scale trials and techniques are being suggested to treat deeply located con-taminated groundwater by simply pumping to the surface and using it as the irrigant for carefully selected plant species, allowing them to biodegrade the pol-lutants. The lower levels of site intrusion and engineering required to achieve this would bring clear benefits to both the safety and economic aspects of the remediation operation.
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