The Use of Alternative Techniques for Remediation of Polluted Sites andGroundwater in Flanders: Plant-based StrategiesJaco Vangronsveld1*and Daniël van der Lelie21Limburgs Universitair Centrum, Centre for Environmental Sciences, Universitaire Campus, B-3590 Diepenbeek, Belgium2Brookhaven National laboratory, Upton, New York 11973, USA* Corresponding author (jaco.vangronsveld@luc.ac.be)
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healthy and regenerating by vegetative means and by seed.Evaluations of soil physico-chemical parameters, potentialphytotoxicity, floristic and fungal diversity, and mycorrhizalinfection of the plant community 5, 7 and 10 years after theapplication of the soil additives indicated the sustainability ofmetal immobilization and the favourable benefits of this treat-ment on the environment (Vangronsveld et al. 1996, Boumanet al. 2001). Similar demonstration projects were performednear two other zinc smelters in the region (Overpelt and Balen),as well as in less contaminated kitchen gardens in order tostimulate public awareness of the concept.PhytoextractionOn a 3 ha field site containing 4 to 5 mg Cd/kg soil, differ-ent plant species (willow, poplar, tobacco, sunflower, Brassi-caceae, ...) were planted or sown in spring 2003. Repeatedcropping and harvest should lead to a gradual reduction oflabile soil metals. Metal contents in the plants and metalextraction efficiency show that remediation will be a long-term process. Both optimisation of extraction efficiency andimplementation in sustainable agricultural and silviculturalpractice are currently under investigation as part as a globalmanagement strategy.Phyto-rhizodegrationAbout 250 poplar trees were planted to contain a BTEX con-taminated groundwater plume on the site of a major car pro-duction plant in Genk (Belgium). In laboratory studies (Baracet al. 2004), the capacities of plants and their associated mi-croorganisms (both rhizospheric and endophytic) to degradethe contaminants present in the groundwater were studied.Monitoring wells were installed in the field. Three years afterplanting, the BTEX containing plume was cut off at the pop-lar plantation. Eventual seasonal variations are studied.ConclusionThe results of these field experiments illustrate that the useof plants for risk-management and remediation of contami-nated soils and groundwater clearly is promising. But, cer-tainly in case of metal contamination, the long-term dura-tion argues for the incorporation in current practices of landuse (agriculture, forestry,…) and landscape management.Remediation options currently applicable to contaminatedsoils and groundwater are frequently expensive, environ-mentally invasive and do not make cost-effective uses ofexisting resources. These techniques are based upon civilengineering methodologies, involving either the excavationand removal of contaminated soil (dig and dump), pumpand treat of contaminated groundwater or an ex situ treat-ment of the soil that drastically alters soil structure, biologicalactivity and subsequent function. Certainly in case of verylarge contaminated areas here is a clear need for cost-effec-tive, durable and validated alternative remediation strate-gies to those that are in current use. The focus of muchrecent experimental work has been directed towards theseends, developing techniques that exploit biological (plantand microorganisms) and chemical (use of metal-bindingagents) processes to reduce the inherent risk associated withcontaminated soils and groundwater. Strategies of this na-ture are generally classified under the generic heading of phy-toremediation.Experiments carried out in Flanders over the last decade, basedupon the above principles, show promise as viable soil treat-ment techniques. Field experiments were performed on metalcontaminated sandy soils in the vicinity of three old zinc smelt-ers. On the heavily contaminated old smelter sites, phytostabi-lisation was used. In case of the less contaminated surround-ings of these smelters, the use of different plant species wasstudied aiming a sustainable use and eventually, on the long-term, phytoextraction of the metals in excess. For the man-agement of a BTEX contaminated groundwater plume, theuse of poplar trees and associated microorganisms was inves-tigated on laboratory and on field scale.PhytostabilisationCyclonic ash was mixed (100 tons/ha) in the soil of theheavily contaminated zinc smelter site of Lommel-Maatheide(Belgium). Two grass species, Agrostis capillaris and Festucarubra, were sown. Physico-chemical and biological evalua-tions were made at different time intervals. The soil treat-ment on the old zinc smelter site was shown to reduce plantexposure to metals and to restore a vegetation cover at sev-eral sites (Vangronsveld et al. 1995). Even 12 years after thetreatment, vegetation on the 3 ha pilot plot is currently
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Global Soils: BelgiumMolecular Tools for Bioremediation251The OVAM (Public Waste Agency of the Flemish Region,responsible for soil remediation in Flanders) is stimulatingresearch on and field applications of these alternative reme-diation strategies.ReferencesBarac T, Borremans B, Provoost A, Oeyen L, Colpaert JV, Vangrons-veld J, Taghavi S, van der Lelie D (2004): Engineered endo-phytic bacteria improve phytoremediation of water-soluble vola-tile organic pollutants. (Submitted Nature Biotechnology)Bouwman L, Bloem J, Römkens PFAM, Boon GT, Vangronsveld J(2001): Beneficial effect of the growth of metal tolerant grasson biological and chemical parameters in copper- and zinc con-taminated sandy soils. Minerva Biotech 13, 19–26Vangronsveld J, Colpaert J, Van Tichelen K (1996): Reclamation of abare industrial area contaminated by non-ferrous metals: Physico-chemical and biological evaluation of the durability of soil treat-ment and revegetation. Environmental Pollution 94, 131–140Vangronsveld J, Van Assche F, Clijsters H (1995): Reclamation of abare industrial area, contaminated by non-ferrous metals: Insitu metal immobilization and revegetation. Environmental Pol-lution 87, 51–59Global Soils: BelgiumThe Application of Molecular Tools to Follow up BioremediationJoke Geets1,2, Jaco Vangronsveld1, L. Diels2and Daniel van der Lelie3*1 Limburgs Universitair Centrum, Environmental Biology, Universitaire Campus, B-3590 Diepenbeek, Belgium2 Vito, Flemish Institute for Technological Research, Department of Environmental Technology, Boeretang 200, B-2400 Mol, Belgium3 Brookhaven National Laboratory, Biology Department, Building 463, Upton, NY11973-5000, USA* Corresponding author (vdlelied@bnl.gov)developmental phase, as well as during the actual bioreme-diation treatment. At the lab-scale, these PCR based tech-niques will demonstrate the presence of active microbialcommunities and identify the 'key players' whose activitiesare crucial for a successful remediation strategy. They willalso become important management tools to follow up theefficiency of bioremediation processes, especially when ap-plying in situ remediation. When combined with batch, col-umn and pilot studies, they can be used as part of theremediation startup phase to define optimal process condi-tions: comparison of the bacterial community compositionand activity for different process conditions with their re-spective metal removal or xenobiotic degradation efficiencywill predict the success or failure of the final remediation,and will facilitate the selection of optimal process condi-tions. Once the bioremediation strategy is being applied, themonitoring methods can be used for the follow up, and as adecision tool for necessary process adjustments.The only limitation for large scale, high throughput appli-cation of microbial monitoring as part of a managementstrategy for the remediation of contaminated sites is the costprice of the analysis as well as the need for specialized laborand equipment. However, due to the recent developmentsof tests for the detection of pathogens, it can be envisagedthat cheap tests for the detection of specific groups of envi-ronmentally important microorganisms or their functions,such as Sulfate Reducing Bacteria, will become available inthe near future. As a result of this development, monitoringtools will become an integrated part of the managementdecision system for the remediation of contaminated siteswhen efficient, cost-effective and reliable bioremediationtechnologies are applied.During the last decades, major advances have been made inunderstanding the mechanisms of interactions between mi-croorganisms and pollutants, and in the application of spe-cialized microorganisms for the in situ and ex situ treatmentof organic xenobiotics, heavy metal and radionuclide con-taminated soils, wastes and groundwater. The efficiency ofbioremediation depends on the presence and activities ofthe microorganisms involved which is, in turn, affected byenvironmental conditions, operational parameters and thelocal composition of the overall microbial community com-position. Hence, when opting for a biological remediationstrategy, important questions to be answered as part of theoverall remediation strategy include: (i) are microorganismswith the desired characteristics and activities present at thecontaminated site and at what densities, (ii) what is theiractivity, (iii) and how is the microbial community composi-tion and functioning influenced by environmental param-eters and process conditions? Recently, molecular and non-molecular methods for the identification and characterizationof bacteria and their specific properties have been used toassess the composition and activity of microbial communi-ties found at contaminated sites or in the rhizosphere ofplants. For the future, these techniques contain the promiseto be applied as complementary tools to classical chemicaland physiological analytical methods (pollutant concentra-tions and speciation, redox potential, etc.) to monitor thespatial and temporary changes in microbial community com-position and functioning during bioremediation processes.Molecular and microbial monitoring tools, when combinedwith batch, column and pilot studies, enable the optimiza-tion and follow-up of the biological processes during theJSS – J Soils & Sediments 3 (4) 2003