Progress 10/01/05 to 09/30/08
Outputs
OUTPUTS: As part if our investigation of the metal-accumulating ability of willow species in the field and greenhouse, we completed a series of hydroponic studies comparing 14 cultivars for their ability to tolerate metal phytotoxicity and to bioconcentrate cadmium and zinc. We tested the hypthotheses that different cultivars would have widely different tolerances to Zn and Cd and would have different capabilities to bioconcentrate these heavy metals. We observed a range of tolerance to foliar Zn and Cd, with some cultivars accumulating greater than 1000 mg/kg Zn and 70 mg/kg Cd in the leaves with no significant growth reduction. The uptake of Cd and Zn was highly correlated. From these studies, two promising willow species for phytoremediation of soils have been identified. These have the combined desirable properties of high uptake potential for Cd and Zn, high tolerance to metal toxicity, and rapid growth. Higher foliar Zn and Cd was not correlated to foliar total sulfur or foliar thiol S (as measured by XANES spectroscopy), suggesting that thiol S does not have a primary role in heavy metal tolerance of willow species, and therefore metallothioneins may not be involved in sequestering these metals into insoluble, non-toxic forms. Investigations were conducted to determine whether polyphenols, common secondary metabolic products of willows, are able to complex and detoxify Zn and Cd in willow leaves. However, exposure of the willows to Cd and Zn had no consistent effect on foliar concentrations of polyphenols, condensed tannins or leucoanthocyanin. There were species or cultivar differences in these secondary metabolic products, and one of the promising cultivars ("301") had markedly higher condensed tannins and leucoanthocyanin than the other two cultivars. These results, along with earlier measurements of S and thiol content of willow leaves, suggest that toxic metal exposure does not typically provoke a response in willows of increasing concentrations of biochemicals capable of complexing and detoxifying these metals. Nevertheless, as preliminary experiments showed that tannic acids complex both Zn and Cd at circumneutral pH, we hypothesize that the high tannin and polyphenol levels in willows may sequester these metals in the leaves, protecting the plant from toxicity. In terms of the usefulness of willow for extraction of Cd and Zn from soils, the foliar Zn and Cd were relatively easily extracted (> 80% efficiency) from ground leaf tissue by either a strong chelating agent (DTPA) or nitric acid, consistent with the suggested form of these metals as polyphenol complexes, which are expected to more labile than metallothionein complexes. The results therefore point to a simple way to chemically concentrate the heavy metals from willow tissues - extraction from the tissue by acid, followed by precipitation as a sulfide, hydroxide or carbonate. Plant tissues cleansed in this manner could then be returned to the soil, a process that would largely solve the disposal problem created by phytoremediation. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
By ameliorating the health of soils with the selective removal of toxic metals such as cadmium and zinc, phytoremediation using willows can render soils more suitable and productive for food and feed production, addressing the national goals of a safe food system and healthy, well-nourished population. In addition, there is potential to harvest the wood biomass for conversion to energy, thereby enhancing economic opportunity locally by producing a valuable crop on previously unproductive or contaminated land. This could have economic benefits for rural areas utilizing land that is not generally suitable for agronomic crops. The CSREES National Goal of greater harmony between agriculture and the environment, and the goal of the Cornell University Agricultural Experiment Station to improve agricultural productivity and environmental sustainability, is addressed by the fact that willow culture stabilizes the soil, limiting erosion, and provides a habitat for birds and other wildlife. Potential beneficiaries of this research include entrepreneurs interested in further developing phytoremediation using shrub willow for various types of contaminated sites, such as urban brownfields. There is an opportunity for individuals to select for willow species particularly efficient at scavenging toxic metals from soils, and to market these for site remediation and restoration. There may be potential for genetic engineering of willow plants with greater ability to bioconcentrate Cd and other metals, with the consequence that patented plant species can be marketed. Finally, the usual drawback of phytoremediation, the obstacle of disposing of large quantities of metal-contaminated plant material, was shown to be potentially minimized by chemical extraction and concentration of metals from the plant tissue.
Publications
- No publications reported this period
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Progress 10/01/06 to 09/30/07
Outputs
As part if our investigation of the phytoremediation potential of willow species in the field and greenhouse, we have completed biochemical characterization of three willow cultivars that have show promise for Cd and Zn hyperaccumulation in preliminary hydroponic experiments. A greenhouse hydroponic experiment was done with the cultivars S. purpurea ("Hotel") , S. eriocephala X exigua ("301") and S. alba ("Pseudo") , with controlled exposure to high Zn and Cd in the nutrient solution. Concentrations of Zn and Cd in the leaf tissue were as high as 600 mg/kg and 140 mg/kg after 8 weeks of growth. The Zn and Cd was relatively easily extracted (> 80% efficiency) from ground leaf tissue by either a strong chelating agent (DTPA) or nitric acid. As preliminary experiments using titration methods and infrared spectroscopy showed that tannic acids complex both Zn and Cd at circumneutral pH, the hypothesis was tested that the high tannin and polyphenol levels in willows could be
sequestering these metals in the leaves and protecting the plant from toxicity. However, exposure of the willows to Cd and Zn had no consistent effect on foliar concentrations of polyphenols, condensed tannins or leucoanthocyanin. However, there were species or cultivar differences in these secondary metabolic products, with "301" having markedly higher condensed tannins and leucoanthocyanin than the other two cultivars. These results, along with earlier measurements of S and thiol content of willow leaves, suggest that toxic metal exposure does not typically provoke a response in willows of increasing concentrations of biochemicals capable of complexing and detoxifying these metals.
Impacts
By ameliorating the health of soils with the selective removal of toxic metals such as cadmium and zinc, phytoremediation using willows can render soils more suitable and productive for food and feed production, addressing the national goals of a safe food system and healthy, well-nourished population. In addition, there is potential to harvest the wood biomass for conversion to energy, thereby enhancing economic opportunity locally by producing a valuable crop on previously unproductive or contaminated land. This could have economic benefits for rural areas utilizing land that is not generally suitable for agronomic crops. The CSREES National Goal of greater harmony between agriculture and the environment, and the goal of the Cornell University Agricultural Experiment Station to improve agricultural productivity and environmental sustainability, is addressed by the fact that willow culture stabilizes the soil, limiting erosion, and provides a habitat for birds and
other wildlife. Potential beneficiaries of this research include entrepreneurs interested in further developing phytoremediation using shrub willow for various types of contaminated sites, such as urban brownfields. There is an opportunity for individuals to select for willow species particularly efficient at scavenging toxic metals from soils, and to market these for site remediation and restoration. There may be potential for genetic engineering of willow plants with greater ability to bioconcentrate Cd and other metals, with the consequence that patented plant species can be marketed.
Publications
- McBride, M.B. 2007. Trace metals and sulfur in soils and forage of a chronic wasting disease locus. Environmental Chemistry 4, 134-139.
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Progress 01/01/06 to 12/31/06
Outputs
As part if our investigation of the metal and sulfur-accumulating ability of willow species in the field and greenhouse, we have completed a series of hydroponic studies comparing 14 cultivars for their ability to tolerate metal phytotoxicity and to bioconcentrate cadmium, zinc and sulfur. We tested the hypthotheses that different cultivars would have widely different tolerances to Zn and Cd, would have different capabilities to bioconcentrate these heavy metals, and would accumulate higher tissue sulfur when exposed to these toxic metals. We observed a range of tolerance to foliar Zn and Cd, with some cultivars accumulating greater than 1000 mg/kg Zn and 70 mg/kg Cd in the leaves with no significant growth reduction. The uptake of Cd and Zn was highly correlated. However, higher foliar Zn and Cd was not correlated to foliar sulfur, even though S concentrations in different cultivars varied widely. It was concluded that S does not have a primary role in heavy metal
tolerance, and therefore metallothioneins may not be involved in sequestering these metals into insoluble, non-toxic forms. Investigations are underway to determine whether polyphenols, common secondary metabolic products of willows, are able to complex and detoxify Zn and Cd in willow leaves. From these initial studies, two promising willow species for phytoremediation of soils have been identified. These have the combined desirable properties of high uptake potential for Cd and Zn, high tolerance to metal toxicity, and rapid growth. These cultivars will be established at a well-characterized field site where soil Zn and Cd are at high concentrations because of a heavy application of metal-contaminated sewage sludge about 25 years ago. The willow will be harvested periodically and Zn and Cd determined in the above-ground biomass to determine effectiveness of willow in cleansing soils of these potentially toxic heavy metals.
Impacts
By ameliorating the health of soils with the selective removal of toxic metals such as cadmium and zinc, phytoremediation using willows can render soils more suitable and productive for food and feed production, addressing the national goals of a safe food system and healthy, well-nourished population. In addition, there is potential to harvest the wood biomass for conversion to energy, thereby enhancing economic opportunity locally by producing a valuable crop on previously unproductive or contaminated land. This could have economic benefits for rural areas utilizing land that is not generally suitable for agronomic crops. The CSREES National Goal of greater harmony between agriculture and the environment, and the goal of the Cornell University Agricultural Experiment Station to improve agricultural productivity and environmental sustainability, is addressed by the fact that willow culture stabilizes the soil, limiting erosion, and provides a habitat for birds and
other wildlife. Potential beneficiaries of this research include entrepreneurs interested in further developing phytoremediation using shrub willow for various types of contaminated sites, such as urban brownfields. There is an opportunity for individuals to select for willow species particularly efficient at scavenging toxic metals from soils, and to market these for site remediation and restoration. There may be potential for genetic engineering of willow plants with greater ability to bioconcentrate Cd and other metals, with the consequence that patented plant species can be marketed.
Publications
- No publications reported this period
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