Successes and limitations of phytotechnologies at field scale : Outcomes, assessment and outlook from COST Action 859
Résumé
Purpose : Many agricultural and brownfield soils are polluted and more have become marginalised due to the introduction of new, risk-based legislation. The European Environment Agency estimates that there are at least 250,000 polluted sites in the member states that require urgent remedial action. There is also significant volumes of wastewaters and dredged polluted sediments. Phytotechnologies potentially offer a cost-effective in situ alternative to conventional technologies for remediation of low to medium-contaminated matrices, e.g. soils, sediments, tailings, solid wastes and waters. For further development, social and commercial acceptance, there is a clear requirement for up-to-date information on successes and failures of these technologies based on evidence from the field. This review reports the outcomes from several integrated experimental attempts to address this at both field and market level in the 29 countries participating in COST Action 859. Results and discussion : This review offers insight into the deployment of promising and emergent in situ phytotechnologies, for sustainable remediation and management of contaminated soils and water, that integrative research findings produced between 2004 and 2009 by members of COST Action 859. Many phytotechnologies are at the demonstration level, but relatively few have been applied in practice on large sites. They are not capable of solving all problems. Those options that may prove successful at market level are (a) phytoextraction of metals, As and Se from marginally contaminated agricultural soils, (b) phytoexclusion and phytostabilisation of metal- and As-contaminated soils, (c) rhizodegradation of organic pollutants and (d) rhizofiltration/rhizodegradation and phytodegradation of organics in constructed wetlands. Each incidence of pollution in an environmental compartment is different and successful sustainable management requires the careful integration of all relevant factors, within the limits set by policy, social acceptance and available finances. Many plant stress factors that are not evident in short-term laboratory experiments can limit the effective deployment of phytotechnologies at field level. The current lack of knowledge on physicochemical and biological mechanisms that underpin phytoremediation, the transfer of contaminants to bioavailable fractions within the matrices, the long-term sustainability and decision support mechanisms are highlighted to identify future R&D priorities that will enable potential end-users to identify particular technologies to meet both statutory and financial requirements. Conclusions : Multidisciplinary research teams and a meaningful partnership between stakeholders are primary requirements that determine long-term ecological, ecotoxicological, social and financial sustainability of phytotechnologies and to demonstrate their efficiency for the solution of large-scale pollution problems. The gap between research and development for the use of phytoremediation options at field level is partly due to a lack of awareness by regulators and problem owners, a lack of expertise and knowledge by service providers and contractors, uncertainties in long-term effectiveness and difficulties in the transfer of particular metabolic pathways to productive and widely available plants. Networks such as COST Action 859 are highly relevant to the integration of research activity, maintenance of projects that demonstrate phytoremediation at a practical field scale and to inform potential end-users on the most suitable techniques. Biomass for energy and other financial returns, biodiversity and ecological consequences, genetic isolation and transfer of plant traits, management of plant-microorganism consortia in terrestrial systems and constructed wetlands, carbon sequestration and soil and water multi-functionality are identified as key areas that need to be incorporated into existing phytotechnologies.