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With the intention of avoiding the heavily polluted surface water supplies,
there is a growing current trend of drinking water from underground sources.
However, these are poisoned with arsenic. Now it has been proposed, that
genetically modified plants should be an effective tool in the cleanup of
arsenic-contaminated soils and groundwater, March 2005 by Katharina
Who wants to do without washing powder, shampoos and shower foam? They
bring us the cleanliness we long for. Nevertheless, the standard of living
of our affluent society has also some disadvantages. Many commonly-used
household products, such as builder and softer, tensides and
hair-conditioner, cannot be decomposed by sewage treatment plants, thus they
end up in rivers and lakes.
With the increased amount of polluted, surface water supplies, there is
currently a growing trend of obtaining drinking water from underground
sources. However, it turns out the underground sources are also polluted?by
Contaminated groundwater poisons people
Arsenic is a poison that can lead to skin lesions, cancers and other
symptoms. Since it naturally occurs in the soil, it can often be found in
groundwater. With a growing amount of people now drinking water from
underground sources, millions of people are thought to be at serious risk in
countries throughout the world.
Until now, arsenic-contaminated groundwater, drinking water and wastewater
was treated away from its place of contamination, commonly referred to as ex
situ clean up or treatment. Various physiochemical technologies such as
chemical precipitation, activated alumina and reverse osmosis were used for
the ex situ cleanup, but they have some drawbacks: they are expensive,
generate high volumes of toxic sludge and brine, and the water recovers
poorly. Therefore, new methods for ex situ and in situ (at the place, where
the water occurs naturally) remediation are needed.
Plants hunger for arsenic
A few years ago it was proposed that plants could be an effective tool in
arsenic cleanup. Transgenic plants have already been used to extract
contaminants such as metals and metalloids from soil, surface water,
groundwater, leachate and municipal industrial wastewater. The question was
then raise, if it worked for the other pollutants, why not for arsenic?
Spanish researchers around Carlos Garbisu, from the Basque Institute of
Agricultural Research and Development in Derio, have compiled the results
known so far from experiments in the cleanup of arsenic-contaminated soils
and waters. They published a review article on this subject matter in the
journal Environment International .
In the review article, Dr Garbisu mentioned that Chinese brake fern (Pteris
vittata) has been found to be a very effective plant for remediating
arsenic-contaminated soils and waters. It hyperaccumulates arsenic in its
shoots (fronds) to very high concentrations, up to 23,000 ?g arsenic per
gram plantmass. This fern not only accumulates arsenic, but even thrives on
arsenic, doubling its biomass in one week when subjected to 100 ppm arsenic.
The special mechanism in P. vittata in contrast to other plants, which do
not accumulate arsenic, is that it transports the arsenic from the roots to
the shoots. Thus in the end, up to 95% of the arsenic is accumulated in the
above-ground tissue of the plant.
By studying the molecular mechanisms of the uptake and transport of arsenic,
the corresponding genes could be identified and then be introduced in
fast-growing plants with a high biomass. These plants could then be used for
a fast cleanup of arsenic-contaminated soils.
Some of the initial ground work for producing genetically engineered plants
that can cleanse arsenic from contaminated water sources has already
started. Professor Richard B. Meagher?s team from the University of Georgia,
USA, developed the first transgenic system for removing arsenic from soil.
They inserted tow genes from the bacterium Escherichia coli into Arabidopsis
thaliana, a model-plant often used in biotechnological experiments. Being
genetically modified, the plants could accumulate 4- to 17-fold greater
fresh shoot weight, and 2- to 3-fold more arsenic per gram of tissue than
plants without the two genes.
Another approach for an arsenic clean up was carried out by Sandrine
Sauge-Merle and her team from the Département d?Ecophysiologie Végétale et
de la Microbiologie at the Laboratoire d?Ecophysiolgoie et de la
Photosynth?se at the Université de la Méditerrannée in
Saint-Paul-lez-Durance, France. They introduced a gene from A. thaliana in
E. coli. The gene encoded metal-binding factors. When E. coli colonies were
placed in the presence of arsenic, the cellular metal contents were
Similarly, Liping Nie and his team from the Department of Otolaryngology at
the University of California, USA, did experiments with genetically
engineered canola plants (Brassica napus cv.). In the presence of arsenate,
the transgenic canola plants grew approximately four-times more in mass than
non-transformed canola plants.
Plants clean contaminated water supplies
There is now a relatively new idea to cleanup arsenic-contaminated water by
rhizofiltration. This means that plants are used to absorb pollutants from
water. Researchers demonstrated, that P. vittata, grown in 600 ml of
groundwater, was able to reduce arsenic from 46 ppb to below 10 ppb in only
three days of growth. The standard for arsenic in drinking water has
recently been reduced from 50 to 10 ppb by the USEPA.
For the in situ remediation of contaminated groundwater, plants with deep
roots should be taken into account. Trees for example may be capable of
remediating deeper contaminants in soil or groundwater plumes. In
experiments with Tamarisk (Tamarix parviflora) and eucalyptus (Eucalyptus
camaldulensis), researchers discovered that the relatively high
concentrations of arsenic in soil and water did not significantly affect
tree growth and its ability to use water.
With several studies showing great potential for removing arsenic from
polluted soil and water, a solution that will help minimize arsenic
pollution of underground water is within sight?one that could prevent the
poisoning of millions of people world-wide.
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