Multicellular living organisms and unmodified parts thereof and – Method of introducing a polynucleotide molecule into or...
Reexamination Certificate
1998-11-04
2001-11-06
Campell, Bruce R. (Department: 1661)
Multicellular living organisms and unmodified parts thereof and
Method of introducing a polynucleotide molecule into or...
C800S294000, C047S05810R
Reexamination Certificate
active
06313374
ABSTRACT:
BACKGROUND OF THE INVENTION
Domestication of plants for human consumption has resulted in altering most crops and crop-related plant's ability to uptake metals from the soil medium. The ultimate aim of many decades of plant breeding practices has been to reduce the accumulation of unfavourable substances in plant parts that are destined for human or animal consumption. However, a few wild and native plant species have, to date, retained their ability to uptake undesirable toxic substances from the growth medium on which they establish. Some of these plant species often accumulate very high concentrations of metal ions in their foliage. These plants are commonly classified as “hyperaccumulators”. Hyperaccumulators are plants which can accumulate toxic metal ions, such as nickel, copper, cobalt and lead at very high concentrations in shoot or root tissues (>0.1% of the dry matter). These plants are normally found growing in soils containing unusually high concentrations of these metals in special geological formations, for example, the presence of zinc accumulating Thlaspi plants growing in zinc-rich soils near the Germany and Belgium border. To date, only a handful of hyperaccumulating plant species have been identified for their potential to uptake different metal species (see Table A.).
The term phytoremediation refers to the effective utilization of such metal-hyperaccumulating plant species which have the ability to uptake, bind, and detoxify environmental contaminants, such as metal ions and organics, through plant-mediated biological, biochemical and physical means. The current focus of researchers is to identify and select better plant species for phytoremediation, species that can be classified as hyperaccumulators and that also possess a large biomass into which the plants can accumulate and sequester large quantities of toxic metal ions. The identified plants must be hardy and suitable for the temperate North American environment. As stated by Brown et al. (1995), the hyperaccumulation mechanism involves the translocation of the metals from soil to shoot tissues in excess of 100 mg/kg for Cadmium, 1,000 mg/kg for Nickel and 10,000 mg/kg for Zinc, Copper and Cobalt hyperaccumulators are defined as plants capable of accumulating more than 0.1% (1,000 mg/kg) of these metals in their dried tissue (Baker et al., 1988).
TABLE A
Metal concentrations in the known hyperaccumulator species
[concentration in harvestable material from plants
growing in contaminated soils (on dry weight basis)]
Concentration
Metal
Plant Species
[mg/kg in shoots]
Cd
Thlaspi caerulescens
1,800
Cu
Ipomea alpina
12,300
Co
Haumaniastrum robertii
10,200
Pb
T. rotundzfoliium
8,200
Mn
Macademia neurophylla
51,800
Ni
Psychotria douarrei
47,500
Sebertia acuminata
(25% by wt of dried sap)
Zn
T. caerulescens
51,600
The major limitations of utilizing these hyperaccumulating plant species for phytoremediation are:
a) Plants such as Thlaspi and Haumaniastrum are very small, with a very low plant biomass. Although these plants can uptake metals >1% of their dry weight (“DW”), their low biomass limits their ability to uptake large amounts of metal ions. For example, shoots of
T. rotundifolium
can accumulate up to 8200 mg/kg DW of Pb but these plants can only produce 5 to 50 mg of plant dry material during a 5 month growing period. Therefore, these plants would have to be grown over several growth cycles and seasons in order to achieve complete remediation of a site.
b) Plants such as Thlaspi and Haumaniastrum are very small in stature, and therefore are not amenable for harvesting using conventional farm machinery.
c) Plants such as Thlaspi and Haumaniastrum have a very slow growth habit (
Thlaspi rotundifolium
has a 5 month growth period). A long growth cycle would result in longer remediation periods.
d) Tree species such as
Sebertia acuminata
have a longer growth period but due to their tropical origin, they might not be able to over-winter in temperate environments, and hence may not be useful for phytoremediation purposes in North America.
e) All the hyperaccumulator plant species mentioned above have specific target metal species, which they are capable of accumulating in very large amounts in their plant parts. However, most of the contaminated soil sites have a mixture of metal contaminants. In the presence of such complex metal contaminants, it is very unlikely that these known hyperaccumulators will be able to survive and uptake large levels of the different metal ions. For example, petroleum industries land-farming sites in Sarnia, Ontario, Canada, have a mixture of about 15 different metal ions and organic contaminants in varying concentrations, depending on the location.
Among the hyperaccumulating plant species currently being considered for phytoremediation and which have been characterized in greenhouse and field conditions, the most promising ones are
Thlaspi caerulescens
and plants belonging to the Brassicaceae family.
The limitation of using plants belonging to the Brassicaceae family are:
a) Most of the currently identified plants are wild relatives of the cultivated crop species
Brassica napus
(canola). Due to the potential for cross-pollination between the wild-relatives and crop species, public acceptance of these plants for phytoremediation is questionable. This problem holds credence considering the potential for evolution of new weed-like species, which might interfere with current agricultural systems.
b) These plants set seeds readily and might assume weed-like characteristics after repeated growth in contaminated sites.
c) These plants have relatively larger biomass than Thlaspi sp. However, they still do not compare well with plants with denser foliage (larger biomass).
The ability of plants to extract metal ions from soils and accumulate or sequester those metals in their tissues can be tremendously improved by adjusting the pH of the soil and also by the addition of synthetic chelators to the growing media. These two elements increase the release (desorption) of metal ions from soil particles, thereby increasing the availability of those ions to the plant roots, resulting in increased rate of uptake. The limitations of using metal chelators are:
The addition of chelating agents to metal contaminated soils could bring in new problems regarding health, safety and environmental concerns. Addition of large amounts of chelates will result in rapid solubilization of different metal ions. Some of the metals released will be beneficial to plants and microflora of the soil. However, this will also increase the soil solution concentration of undesirable ions. Moreover, there is a larger risk of releasing large amounts of the solubilized toxic metals in the underground water systems. The use of chelates would increase the bioavailability and uptake of these toxic metals by the natural flora and fauna of the soil, thereby accelerating the spread of these metals in the ecosystems and in the different food chains.
SUMMARY OF THE INVENTION
The present invention provides a process for remediating a growth medium contaminated with metal ions. More specifically, this invention provides a process for remediating a growth medium contaminated with metal ions using Pelargonium sp. plants.
According to one aspect of the invention, there is provided a method for removing one or more species of metal from a metal contaminated growth medium, comprising growing a Pelargonium sp. plant in the growth medium for a time period sufficient for the plant root to uptake and accumulate metal in the root or shoot biomass.
In a further aspect of the invention, the method for removing one or more species of metal from a metal contaminated growth medium further comprises the extraction of essential aromatic oils or concentration of metals from the root or shoot biomass.
In another of its aspects, the invention provides a method for removing one or more species of metal from a growth medium (the growth medium is preferably metal contaminated) which comprises growing a Pe
KrishnaRaj Sankaran
Perras Michel R.
Saxena Praveen K.
Campell Bruce R.
Grunberg Anne Marie
Oppedahl & Larson LLP
University of Guelph
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