1. Haalbare technieken voor verantwoorde sanering van bodems verontreinigd met zware metalen Jaco Vangronsveld, Ann Ruttens, Wouter Geebelen, Jan Colpaert, Theo Thewys, Herman Clijsters Universiteit Hasselt, Centrum voor Milieukunde, Agoralaan, B-3590 Diepenbeek

2. SELECTION OF A REMEDIATION TECHNIQUE: a complex and site-specific process size, location and history of the site soil characteristics (texture, pH,...) type, physical and chemical state of the contaminants degree of pollution (concentration and distribution) desired final land use technical and financial means available environmental, legal, geographical and social issues

3. REMEDIATION TECHNOLOGIES: do one of two things: Remove the contaminants from the substratum: ‘site decontamination techniques’ (clean-up) Reduce the risk posed by the contaminants by reducing exposure (prevent the contaminants from being spread to the surroundings and the groundwater): ‘site stabilization techniques’ (isolation and/or immobilization/inactivation)

4. CLEAN-UP TECHNIQUES FOR METAL- CONTAMINATED SOILS: Most important clean-up techniques currently available: Classical techniques: excavation (followed by disposal at a disposal site) ex situ or in situ extraction or wet classification (by means of flotation or hydrocyclonic techniques) of excavated soil thermal treatment (e.g. evaporation of mercury) electroreclamation These techniques are primarily based on civil-engineering techniques and are expensive, environmentally invasive and labor intensive.

5. PHYTOTECHNOLOGIES AS AN ALTERNATIVE? What are “PHYTOTECHNOLOGIES’’ –Plant-based techniques for the removal, degradation or immobilization of dangerous/toxic contaminants from or in soils or water –!!! In many cases of phytoremediation, plants are not the ‘exclusive players in the game’. A very important role can be attributed to plant-associated bacteria and mycorrhiza.

6. PHYTOREMEDIATION: PLANTS AND THEIR ASSOCIATED MICROORGANISMS DO THE JOB Plants themselves contribute to the process (stabilize, accumulate, transform, degradate or volatilize) Plants “ameliorate” growing conditions for micro-organisms and vice versa In several cases plant associated bacteria and/or mycorrhizal fungi are doing an important or major part of ‘the job’

7. ADVANTAGES OF PHYTOTECHNOLOGIES ‘clean’sun-powered technology Is a passive and in situ technology Minimal disturbance of soil and environment High level of public acceptance Aesthetically pleasing Low capital and operating costs

8. DISADVANTAGES OF PHYTOTECHNOLOGIES Mostly much slower compared to ‘classical’ techniques Only bio-available fraction can be treated by plants and associated micro-organisms Limited to the rooting-zone

9. PHYTOREMEDIATION TECHNIQUES PHYTOEXTRACTION: extraction of metals using metal hyperaccumulating plants PHYTOSTABILIZATION: in situ metal inactivation by means of revegetation either with or without non-toxic metal- immobilizing or fertilizing soil amendments PHYTOVOLATILIZATION PHYTOTRANSFORMATION AND PHYTODEGRADATION PHYTOSTIMULATION: enhanced biodegradation in the rhizosphere

10. PLANT BASED STRATEGIES TESTED ON THE FIELD METALS –PHYTOSTABILIZATION: in situ metal inactivation by means of revegetation either with or without non-toxic metal-immobilizing or fertilizing soil amendments (immobilization/inactivation) –PHYTOEXTRACTION: extraction of metals using metal hyperaccumulating plants (clean-up) ORGANICS –RHIZO- AND PHYTODEGRADATON: plants and plant associated bacteria degrade organic contaminants in soil or undeep groundwater

11. PHYTOSTABILIZATION

12. Plant cover: reduces wind- and water erosion, percolation, human contact Incorporation of soil amendments that immobilize contaminants and improve plant development Metal sequestration in roots Plants chosen for low contaminant translocation Reduction of plant uptake and percolation Root uptake of non- immobilized contaminants

13. PHYTOSTABILIZATION !! is not a technology for real clean-up of contaminated soil but for stabilizing (inactivating) trace elements that are potentially toxic restoring plant cover and installation of a functioning ecosystem inhibition of lateral wind erosion, and reduction of trace element transfer to surface- and groundwater attenuation of the impact on site and to adjacent ecosystems reduce uptake of metals by plants and direct exposure of soil-heterotrophic living organisms (reduction of ‘bioavailability’)

14. ROLE OF SOIL AMENDMENTS IN PHYTOSTABILIZATION OF METAL- CONTAMINATED SOILS convert the soluble and pre-existing high-soluble solid phase forms to more geochemically stable solid phases resulting in a reduced ‘bioavailability’ (reduced phytotoxicity) of heavy metals

15. PLANTS FOR PHYTOSTABILIZATION should: be tolerant to metals and/or tolerant to specific growing conditions for a given site not accumulate contaminants in above-ground parts which could get in food chains have shallow roots to stabilize soil and take up soil water be easy to care for once established

16. PHYTOSTABILIZATION OF HEAVILY CONTAMINATED SITES Problem: –bare heavily contaminated acid sandy soil on zinc smelter sites –large bare surfaces due to aerial deposition of acids and metals from zinc smelters Strategy tested:: metal immobilization and restoration of plant cover

17. FIELD EXPERIMENT AT LOMMEL- MAATHEIDE Old pyrometallurgical zinc smelter site (1904-1974) Poor, acid, sandy soil Zn: 2800-20000 mg/kg Pb: 700-2000 mg/kg Cd: 10-70 mg/kg Cu: 400-2000 mg/kg

18. LOMMEL-MAATHEIDE 1990-2003

19. 1990, 2 weeks after sowing 1995 2002

20. FOLLOW-UP EVALUATIONS physico-chemical: general soil parameters, selective and sequential extractions, pore water... biological: bacteria, plants, invertebrates –toxicity and availability tests –evolution of biodiversity (plants, mycorrhiza, invertebrates, etc. )on the field effects on percolation

21. Total zinc concentration (mg/kg dry soil), water-extractable zinc(mg/kg dry soil) and ratio water-extractable zinc on total zinc concentration measured 5 years after the treatment

22. AM infection percentages in the roots of the grasses along the transect lines in the cyclonic ash treated and untreated site of the Maatheide; pH and total concentrations of Zn, Cd and Cu in the corresponding soil cores. Distance (m) %AM infection pHmg Zn kg -1 dry soil Treated 50817.312750 100697.93600 150767.41168 200387.69875 250377.913250 300657.64750 Untreated 2504.52400 10805.12080 15035.52720 200425.74960 250245.94160 300145.9800

23. ADVANTAGES OF IN SITU INACTIVATION AND PHYTOSTABILIZATION effective and durable inactivation strongly reduces leaching and ‘bioavailability’ subsequently vegetation can develop to physically stabilize the soil (elimination of wind/water erosion), reduce percolation and immobilize metals (effects on speciation) aesthetic profit (for heavily contaminated industrial sites) safer food production (kitchen gardens, agricultural soils) soil organic matter, soil structure not disturbed COST EFFECTIVE: 0.01-0.05 million Euro per ha

24. IN SITU IMMOBILIZATION Can also be used in kitchen- gardens and agricultural fields Metal uptake in vegetables and agricultural crops decreased Oldest ‘immobilization’ strategy: liming

25. PHYTOEXTRACTION OF METALS

26. PHYTOEXTRACTION Translocation to shoots Root uptake Increase of metal availability for plants (amendments, microflora, …) Harvesting Metal recuperation/ disposal of metal- enriched biomass Post-harvest processing: thermal, chemical or microbial

27. DESIRABLE CHARACTERS IN AN EFFECTIVE PHYTOEXTRACTION SPECIES Efficient metal accumulation in easily harvested plant parts Rapid growth coupled with proportionally rapid and high metal accumulation Tolerance to elevated soil metal levels that may be coupled with low macronutrient and soil organic matter content Ease of metal recovery/disposal

28. PHYTOEXTRACTION USING AGRICULTURAL-SYLVICULTURAL PLANTS Problem: > 280 km 2 soils containing increased Cd concentrations (1-10 mg/kg) –Agricultural soils –Kitchen gardens –Abandoned agricultural land Strategy tested: phytoextraction using crops, if possible with economical value: high biomass producing plants/oil delivering plants

29. FIELD EXPERIMENT:SPECIES UNDER INVESTIGATION: Willow and poplar: energy/pyrolysis Sunflower and Brassica: bio-oils/biofuel Tobacco: pyrolysis => High metal accumulation capacities

30. Small scale field experiment in spring 2003 (10 are) Aims: Screening metal accumulation different species/varieties/cultivars/clones Specific problems of the different species (pests, fertilization) Large scale field experiment in spring 2004 (2 hectare) Aims: Obtain results on a realistic field scale Sufficient biomass for energy/oil production and eventual metal recuperation

31. Experimental field: situated 500m NE of Umicore, Balen, former maize field mg/kg dry soil pH- KCl ZnCdCuPbAs field5.5 ±0.1 223 ± 17 5.0 ± 0.3 32 ± 3 198 ± 17 5.4 ± 0.7 Vlarebo (type II)6002.0200 45

32. 2003: 15 willow clones 2 clones known for high biomass production: Salix viminalis: STOTT en JORUNN 1 known metal accumulator: Salix dasyclados LODEN 2 commercially available Belgian clones: Salix fragilis BELGISCH ROOD Salix triandra NOIR DE VILLAINES 10 clones from own collection originating from metal contaminated soils 2 poplar clones HOOGVORST HAZENDANS

33. In practice: Cuttings of 20-40 cm Planting period: end april 2003 Planting distance: 1m20cm -12-24 With and without fertilization

34. Remark: Cd. conc. in maize on the same field is 2 mg/kg DM

35. 2004: Planting: 9-10 april 1.8 ha 17 willow clones 3 poplar clones

36. Species under investigation: - willow - poplar => pyrolysis-energy production - sunflower - Brassica napus => bio-oil, pyrolysis-energy production - tobacco=> pyrolysis-energy production Former use: -maize (high biomass production) =>alternative use: bio-ethanol; white biotechnology

37. *Zea mays cv Recolta *growth and biomass production OK (18 ton/ha) *metal concentrations: mg/kg DWZnCuCdPb Maize field33916.12.721.4 Threshold value feed (KB 21/4/’99) //1.145.5 Upper 25 cmremoval Cd g/ha/y decrease Cd conc. mg/kg /y ‘remediation period’(5=>2) Actual biomass48.60.016185 y

38. Upper 25 cmRemoval Cd g/ha/ydecrease Cd conc mg/kg /y ‘remediation period’(5=>2) Actual biomass prod. Production↑ 420.014215 y * Brassica sp. * Growth and biomassa production: OK (8.3 ton/ha) * Metal concentrations ‘best’ cultivar: mg/kg DWZnCuCdPb 6005.0

39. Nicotiana tabacum: *Fop (Forchheim Pereg) (4.3 ton/ha ): => NF Cu 7-15 ; NF Cu 10-2 Bag (Badisher Geudertheimer) => NB Cu 10-8; NB Cu 10-4 (8.4 ton/ha) *growth and biomass production OK (exception: Bag) *metal concentrations in ‘best’ cultivars: mg/kg DWZnCuCdPb Fop52524.621.049.9 NB CU 10-833917.310.433.9 Upper 25 cm (Fop/NB Cu) removal Cd g/ha/y decrease Cd conc. mg/kg /y ‘remediation period’(5=>2) Actual biomass production 90 / 880.030/0.029101 / 103

40. *Populus Cv Muur, Grimminge, Hoogvorst *growth and biomass production OK *metal concentration ‘best’ cv (HV) mg/kg DWZnCuCdPb leaf26428.228.517.4 twig4685.811.05.1 twig with leaves15557.019.811.3 Upper 25 cmCd removal g/ha/y decrease Cd conc. mg/kg /y remediation period (5=>2) Twig Twig with leaves 66 180 0.022 0.060 136 50 Supposed biomass production 6 ton/ha/j for twigs and 4 ton/ha/j leaves

41. mg/kg DWZnCuCdPb Leaf SVxS Tora SV Jorunn SV Christian SV Greger SF 5365 6004 5280 5523 5755 21.3 24.2 25.1 22.0 15.0 48.1 44.2 40.2 53.5 62.3 45.6 55.8 44.8 45.6 22.5 Twig SVxS Tora SV Jorunn SV Christian SV Greger SF 595 477 734 718 820 7.9 7.1 10.7 9.0 11.9 10.1 12.0 14.0 24.2 <10 *Metal concentations in willow: (! control leaf: Zn: 100-300;Cd:2-5, Pb <5 mg/kg DW)

42. Upper 25 cmCd removal g/ha/y decrease Cd conc. mg/kg /y Remediation period (5=>2) Twig (8 t/ha) SVxS Tora SV Jorunn SV Christian SV Greger SF (5 t/ha) 95 81 96 112 121 0.038 0.035 0.032 0.043 0.032 78 85 93 70 96 Twig with leaves (8+2.4= 10.4 t/ha) SVxS Tora SV Jorunn SV Christian SV Greger SF (5+1.5=6.5 t/ha) 211 187 192 240 215 0.070 0.062 0.064 0.080 0.071 43 48 47 37 42

43. First conclusions from field experiment: In the best case 40-60 years needed to reduce Cd content from 4.5 to 1 mg/kg

44. How to improve efficiency of phytoextraction? Choice of plant species/cultivar Genetic transformation of high biomass producing plants Increase mobility/plant availability of metals in soils, using (1) metal chelating agents (f.i. EDTA), (2) adjusting pH of soils (f.i. ammonium-nitrate, S-amendments,...), (3) siderophore producing rhizosphere bacteria Increase metal accumulation and translocation capacity in plants: metal chelating agents and metal accumulating endophytic bacteria

45. Improved cadmium uptake by Brassica juncea due to presence of root-associated Pseudomonas and Bacillus

46. FEASIBILITY OF METAL PHYTOEXTRACTION Plant-availability of metals and metal accumulation/translocation in plants are the limiting factors for a ‘quick’ remediation. Improvements at both levels are needed. Phyto-extraction of most metals will only be realistic when incorporated in a long-lasting system of sustainable agricultural/ sylvicultural use of contaminated soils (economical aspects!!)

47. GENERAL CONCLUSIONS Metal immobilization and phytostabilization: –Cheap and efficient if good soil amendments are available Metal phytoextraction: –Improvements of efficiency are needed –Should be incorporated in a long-lasting system of sustainable agricultural/ sylvicultural use of contaminated soils