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A Multi-Process Phytoremediation System for Decontamination of Soils
and Its Applications to Alleviating Crop Plant Stress
Bruce M. Greenberg, Xiao-Dong Huang, and Bernard R. Glick
Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1
Contact information:
Bruce M. Greenberg
Xiao-Dong Huang
[email protected]
[email protected]
519-888-4567 x3209
519-888-4567 x5085
Fax: 519-746-0614
Web: http://sciborg.uwaterloo.ca/~greenber/
Background:
Effective remediation processes for persistent organic pollutants (POPs) and metals are a significant need
in today’s industrialized environment. Examples of organic contaminants of concern are polycyclic aromatic
hydrocarbons (PAHs), total petroleum hydrocarbons (TPHs) and pesticides. Metals of concern include copper,
cadmium, nickel, lead, zinc and arsenic. The levels of these contaminants are increasing in the environment due
to anthropogenic release. Their toxicity, mutagenicity and carcinogenicity pose significant problems, especially
in soils when a change in land usage is envisioned. We have developed an effective multi-process
phytoremediation system (MPPS) (plant-based bioremediation). The system is applicable to any soil system
where plant growth is feasible. An added benefit of the MPPS we have developed is significantly increased
general plant stress tolerance. This includes tolerance to heat, drought, moisture and salt.
A number of techniques have been investigated for remediation of POPs and/or metals from soils.
However, they are either ineffective, too slow, too costly or too cumbersome. For instance, assuming a 10-acre
contaminated site, off-site solidification/stabilization would cost ~$12 million, soil washing would cost ~$6
million, an asphalt cap or a soil cap would cost ~$1 million. In situ microbial bioremediation has been attempted,
however low biomass usually limits the efficacy of such systems, and it is not useful for metals. Conversely,
phytoremediation holds great promise and has received recent attention for remediation of POPs and metals in
soils.
Methodology:
Phytoremediation has the following advantages: it is suitable for large, medium and small sites; it is
“green” and solar driven; it is low in cost. The problem: the plants often grow slowly due to chemical toxicity,
and thus do not provide sufficient biomass for “rapid” remediation. Our multi-process system has overcome
this problem.
To improve the remediation process, multiple complimentary techniques that target different aspects of
POP and metal removal have been combined. The result is an enhanced multi-process phytoremediation system
with improved and accelerated remediation kinetics. This leads to more rapid and more complete removal of
POPs and metals from soil. Importantly, the multi-process system not only removes POPs from the soils, but
generally results in their metabolism to non-toxic molecules. It also brings metals into biomass that can be
removed from the soil.
The process:
 Land farming: For aeration, physical volatilization, and photochemical degradation.
 Microbial remediation: Bacteria that start the degradation of organic contaminants.
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Phytoremediation (plant growth) with plant growth promoting rhizobacteria (PGPR): Rapid
growth of plants including roots, for effective partitioning of POPs and metals out of the
soil.
Why it works:
 The complementary processes build on each other so that remediation is rapidly initiated
and is sustained throughout the growth season.
 The PGPR prevent production of stress ethylene and they synthesize auxin. This promotes
vigorous root growth under stress conditions.
 With PGPR the large amount of root biomass in the soil allows for effective partitioning of
contaminants out of the soil.
 Multiple physical and biological processes result in high rates of metabolism of POPs and
sequestering of metals.
Other applications of the plant/PGPR combination:
 Provides tolerance to heat, drought, moisture and salt stress.
 May provide tolerance for agronomic processes such as transplanting.
 Provides a system for salt remediation.
 Confers herbicide tolerance and allows for remediation.
Successes:
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> 90 % of Creosote in spiked soil at 2 g/kg was removed in a single 4-month growth season. This
included high molecular weight recalcitrant PAHs.
50 % of PAHs were removed in 4 months from an industrial brownfield soil from Dundas,
ON contaminated since World War II with PAHs (500 ppm, ≥ 4 rings)
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> 90 % of TPHs (90 g/kg) were removed from weathered contaminated soils acquired from
Imperial Oil. This was accomplished in two 4-month growth seasons and included the major
toxic fractions of petroleum (C15-50, CCME fractions 3 and 4).
Metals (Cu, Pb and Cd) were removed from spiked soils. They were isolated to the root tissue.
2004 and 2005: Completed field test at Imperial Oil on soil contaminated with oil sludge (100 to
150 g/kg). The field test worked exceptionally well. Remediation rates on par with greenhouse
trials (40 to 60 % remediation in one 4-month season, including CCME fractions 3 and 4).
2005: Field tests at two oil contaminated sites in Alberta were successful.
2005: Field tests for removal of DDT were performed in Summer/Fall 2005. Plants grew well
with improved growth with PGPR. DDT analysis is underway.
Have observed tolerance to salt stress.
Based on our results, we can confidently predict that sites heavily contaminated with POPs and/or metals
can be remediated in 2 to 5 years. The cost of such a clean up would be a fraction of the cost of other remediation
practices.
The Next Step:
We are ready to deploy our multi-process phytoremediation system on contaminated soil sites. We are
also ready to test our system more extensively for other stresses. We are currently entertaining proposals from
partners with suitable sites to apply our system. Please contact us to determine if your site is a good candidate for
our system.