Das Projekt "Biologische Dekontamination schwermetallbelasteter Boeden mit Hyperakkumulatoren: Beeinflussung der Schwermetallaufnahme im Wurzelraum" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich (ETHZ), Institut für Terrestrische Ökologie ITOE durchgeführt. Remediation of heavy-metal polluted agricultural soils requires gentle methods, i.e. methods by which the fertility of the soil is fully restored. This means that harsh methods such extraction of metal pollutants by strong acids or soil washing are not applicable as they do not only remove the pollutants, but also destroy the physical and chemical basis of soil fertility, e.g. soil structure and cation exchangers, as well. Soil cleaning by methal harvesting through accumulator plants is a promising technique for the gentle remediation of heavy metal contaminated soils. Up to now one major problem of this technique has been however the comparatively low productivity of candidate accumulator plants under field conditions. In this project we investigate possibilities to improve the efficiency of this method by enhancing the availability of the pollutants for the roots of the accumulator plants, i.e. by applying mobilizing additives such as chelator agents or by optimizing root growth through classical agricultural techniques such as soil preparation, fertilization and harvesting regimes. Leading Questions: Can metal-accumulating plants be used to clean-up heavy-metal polluted calcareous soils for agricultural or similar re-use?
Das Projekt "Biologische Sanierung schwermetallverseuchter Boeden unter Verwendung hyperakkumulierender Pflanzen: Beeinflussung der Aufnahme von Schwermetallen im Wurzelbereich" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Terrestrische Ökologie, Fachbereich Bodenschutz durchgeführt. Remediation of heavy-metal polluted agricultural soils requires gentle methods, i.e. methods by which the fertility of the soil is fully restored. This means that harsh methods such as the extraction of metals by strong acids or soil washing are not applicable as they do not only remove the pollutants, but also destroy the physical and chemical basis of soil fertility, e.g. soil structure and cation exchange sites. As soil cleaning by metal harvesting through accumulator plants had shown to be a promising, but not yet sufficiently effective technique for the gentle remediation of heavy metal contaminated soils, we investigated possibilities to increase the efficiency of phytoextraction by enhancing the phytoavailability of the metals cadmium, zinc and copper for various metal-polluted agricultural soils of Switzerland. We focussed on two innovative approaches. In the first approach we evaluated the possibility to enhance metal phytoavailability by the addition of elemental sulphur to the soil. The other approach started out from the completely innovative idea to exploit natural siderophores as agents to enhance metal availability. Elemental sulphur application was very effective in solubilizing Zn and Cd in calcareous soil and even more in acidic soil. Unfortunately, however, the effect on plant uptake was much weaker than on the solubility of the metals in the soil. Still, metal uptake in plants grown on calcareous soil under field conditions was increased up a factor of 8. Additional field trials performed at other locations in Switzerland showed that the conditions at Dornach were particularly difficult for phytoremediation. At the current state-of-the-art, clean-up of metal-polluted soils by phytoextraction would require still several decades also the other investigated sites, however. The siderophore studies were performed with model systems consisting of soil mineral suspensions, addressing the lack of a fundamental study of the interactions between siderophore, metals and soil constituents. Desferrioxamine B (DFOB) was used as a model siderophore. For comparison, analogous experiments were performed with citrate and NTA. The results show that the effect of such ligands can be mobilizing as well as immobilizing, depending on soil conditions. While the effects in the model system could be under-stood in terms of chemical speciation modelling, it was found that they did not fully explain the effects observed with field soil samples, suggesting that the model system did not fully represent the dominant features of the real soil. However, the experiments opened up new perspectives for the use of siderophores worth to be further investigated.