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Genetically modified plants that can break down pollutants
may be an effective way to clean soil, contaminated by industrial
chemicals and explosives used by the military, according to
scientists.
Tests on six-inch tall GM poplar cuttings which had a gene
from a rabbit inserted into them, showed that they could remove
up to 91% of a chemical called trichloroethylene from
the water used in their feed. This chemical, used as an industrial
degreaser and one of the most common contaminants of ground
water, was broken down by the plants into harmless byproducts
more than 100 times faster than by unaltered plants.
"In view of their large size and extensive root systems,
these transgenic poplars may provide the means to effectively
clean sites contaminated with a variety of pollutants at much
faster rates - and at lower costs - than can be achieved with
current conventional techniques" - wrote Sharon Doty,
of the University of Washington, Seattle, in the Proceedings
of the National Academy of Sciences (PNAS).
The GM poplars also broke down other common environmental
pollutants such as chloroform - a byproduct of the
disinfection of drinking water - the solvent carbon tetrachloride
and vinyl chloride - used to make plastics.
Poplars use an enzyme called cytochrome P450 to break
down contaminants. Trichloroethylene is turned into
a harmless salt, water and carbon dioxide.
After Dr Doty's team inserted the gene into the tree from
a rabbit, they also produced P450, but at a much faster
rate. Ultimately, the scientists would like to manipulate
the plant's own genes to achieve the same goal.
Mammalian cytochrome P450 has been used in the past
to create GM plants that can detoxify herbicide-treated fields.
In 2005, Japanese scientists used a human gene to produce
rice plants capable of degrading a number of herbicides.
Another study, also published in the PNAS, demonstrated a
way to break down the military explosive RDX. "Widespread
contamination of land and ground water has resulted from the
use, manufacture and storage of the military explosive ...
RDX. This contamination has led to a requirement for
a sustainable, low-cost method to remediate this problem"
- wrote Neil Bruce, of the University of York. "One of
the biggest concerns of RDX as a pollutant is that
it migrates readily through soil into the ground water and,
subsequently, contaminates drinking water supplies."
His team genetically modified Arabidopsis plants to
express enzymes - called XplA and XplB - which
are known to break down RDX. At their best, the plants
reduced RDX concentrations from soil by up to 97% in
one week.
Though the GM plants may be an effective way to treat pollutants,
Dr Doty acknowledged that people might have concerns at the
thought of forests of GM trees. In the US and UK, such plants
can currently only be grown for research purposes.
"As researchers, we want to make sure such concerns
are addressed and risks minimised. In the case of contaminated
sites, we're already facing bad situations, where the use
of transgenic plants may reduce the known risks from carcinogens
and other hazardous pollutants in the environment. Our ultimate
goal is to provide a more rapid way to reduce the amount of
carcinogens - one that is affordable, so that many sites can
be treated.
Dr Doty added that poplars are fast growing and can grow
for several years without flowering, so there was a reduced
risk of their genes being transferred into wild populations
of the tree.
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