Kurzbeschreibung
(Englisch)
|
In order to verify our results of several hydroponic, pot and laboratory experiments, we suggest to investigate the influence of additives (acidifying agents) such as Sulphur and Ammonium sulphate on one hand and an organic complexing agent like NTA on the other hand on mobile metal concentration in soil and, furthermore, on the plant concentrations either in edible or non-edible parts. This long term field study is carried out on an anthropogenically contaminated field site. The field experimental site has been selected in an area named Witzwil which received large amount of Bern city wastes for a period of 40 years (1913 to 1954). The area was selected on the basis of exceeding of trigger values of PAH and Metal.The field experiment will help to work out safe techniques applicable on fields. Further it will allow us to assess the influence of enhanced mobile metal concentration on their concentration in the biomass of rich agricultural crops and to investigate their distribution in edible and non-edible crop parts. An assessment is also made on the effect of crop rotation on the biodegradation of PAH. A comparison in pot experiment and/or literature study will be made to prepare a list of accumulator plants, excluder plants, metal resistant plants and metal sensitive plants. The knowledge gained is of great importance in regulation of food quality and to select the most efficient phytotechnologies to remediate contaminated diffusely polluted soils which are relatively inexpensive and ecological safe.
|
Partner und Internationale Organisationen
(Englisch)
|
EPF Lausanne Geotechnisches Institut AG, Bern AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IE, IL, IT, LT, LU, NL, NO, PL, PT, RO, SE, SI, SK, TR, UK
|
Abstract
(Englisch)
|
The general objectives of this study were: (I) to examine the potential of metal-solubilising soil amendments to enhane the phytoextraction of soil-polluting metals by high-biomass crop plants under field conditions over a time of more than one crop rotation, (II) to investigate the effect of metal-soil amendments on metal allocation within the plants, (III) to investigate the effect of soil metal-solubilizing amendments on the expression of selected genes involved in metal uptake and detoxification in field grown plants, and (IV) to test the potential of growth-promoting phytohormones to alleviate phytotoxicity of soil-polluting metals and to increase their phytoextraction by the combined application of phytohormones and chelating agents. Based on the available literature, in particular the following hypotheses were proposed and tested: (I) The application of ammonium sulphate fertilizer, elemental sulphur and NTA to metal contaminated soil can be used to increase the uptake of Cd, Cu and Zn by crop plants grown under field conditions in a realistic agronomic setting. The effects of ammonium sulphate fertilizer and elemental sulphur are expected to increase over time. (II) The three soil amendments increase metal uptake predominantly in leaves and stems, but not in the seeds of field grown crop plants. (III) Elemental sulphur applied to a Cd-contaminated soil will induce responses in the expression of genes involved in Cd detoxification and in sulphur uptake and assimilation of tobacco plants (predominantly in the roots) grown on such soil. (IV) Auxin applied to nutrient solutions and soil will alleviate metal toxicity to crop plants (in our case sunflower) and increase growth and metal uptake by the plants. This effect is also expected to work in combination with the application of metal-solubilising chelants (in our case EDDS). Heavy metal contamination of large areas of agricultural soil may cause health problems to human and animals because of the accumulation of metals in the food chain. Heavy metal stress to plants can furthermore decrease crop production. On the other hand, leaving low or moderately-contaminated land fallow may be wasting a precious natural resource, given the increasing shortage of fertile agricultural soil. Techniques to decontaminate polluted soils and to restore their fertility are in demand, therefore. Phytoextraction has been proposed as such a technique and has been investigated extensively but primarily in hydroponic and pot experiments. In the present study, we investigated the applicability of enhanced phytoextraction in a long-term field experiment that was carried out between 2000 and 2007 on a heavy-metal (Cd, Cu and Zn) contaminated former peat soil at Witzwil in the Bernese Seeland. We performed a crop rotation experiment with three high-biomass crop plants (maize, sunflowers and tobacco), as high biomass is needed for effective metal extraction and established cultivation techniques with the respective machinery are available for these agricultural crop plants. In order to increase the heavy-metal uptake of the plants, the following soil amendments were tested: (I) ammonium sulphate fertilizer, (II) elemental sulphur and (III) nitrilotriacetic acid (NTA), a biodegradable chelating agent. In a fourth treatment no amendments were applied for control. In the first six years of the study the amendments had only minor effects on metal uptake by the three crops. The differences between years were larger than the effects of the amendments, demonstrating the role of environmental factors that are difficult or even impossible to control. This variability also shows that the extrapolation of results from a single year to estimate remediation times is very questionable. Ammonium sulphate showed no effect at all, and NTA only increased Zn uptake by maize. Elemental sulphur increased Zn uptake in all three plants, but Cd uptake only in tobacco. The Cu uptake was not affected by any of three treatments. In the seventh and eighth year we discontinued the ammonium sulphate treatment, while we doubled the amount of applied NTA and sulphur. NTA still showed no effect, but the additional sulphur led to an amplified increase in Zn and Cd uptake by sunflower and tobacco. The extraction potential of tobacco came close to a level required to make phytoextraction a practical option. The predicted remediation time for Cd reached less than 50 years (instead of 240 years), given tobacco could be cultivated year after year and the Cd concentration in the soil would decrease linearly. Details are given in Results.
|
