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The next big way to clean up toxic sites may be coaxing plants to become
janitors, a Michigan State University (USA) scientist says, February 2005.

Clayton Rugh, an assistant professor of crop and soil sciences, explains
that phytoremediation ? using plants to remove contaminants from the soil ?
is evolving.

In the early stages of this technology, plants were used like sponges,
soaking up toxic substances so they can be safely discarded. The next step,
Rugh says, is plants that act like a green Mr. Clean, with roots that make
detergents to break down toxins.

?What we?re looking at now are kind of ?Mop & Glo? plants,? Rugh said.
?These plants make detergents that secrete into the soil, making the plant a
kind of site custodian.?

Rugh spoke today at the American Association for the Advancement of Science
annual meeting at a session entitled ?Phytoremediation: New Solutions to
Pollution on Land and in the Sea.?

Rugh is collaborating with colleagues at the Institute of Genetics and
Cytology at Minsk, Belarus; the University of York in England; and the
Sainsbury Laboratory at Norwich Research Park, U.K., to work on strategies
to have plants produce biological detergent compounds ? called
biosurfactants ? that target the thorny environmental problems of
hydrophobic pollutants.

Hydrophobic pollutants present some of the most difficult remediation
challenges. These are chemicals like PCBs, pesticides and dioxins that cling
tightly to soil. They plague the environment because they are persistent,
dangerous in small concentrations, and yet are hard to remove. They usually
require large-scale, expensive dredging or aggressive chemical or thermal
treatments. Hydrophobic? which means water insoluble ? pollutants have
resisted early attempts at phytoremediation because plants can?t readily
absorb them.

Rugh and colleagues are having success with genetic engineering to create
plants that get to the root of the problem ? literally. The rhizosphere is
the world that surrounds plant roots, encompassing the bacteria, fungi, ?the
zone around a plant root that is biologically humming and pulsing with many
complex levels of biological interaction,? Rugh said.

The trick to make a common laboratory plant ? like tobacco ? into a janitor
is genetic engineering. Rugh said genes from bacteria that naturally produce
biological detergents are isolated and inserted into the plants. The plants
then gain the ability to release detergents that ?ultimately strip the toxic
compounds off the soil particles and into the rhizosphere, where they meet
their demise. If you change the soil chemistry properly, you really can
crank up the phytoremediation process.?

The plants and soil microbes can then convert the toxins to more benign
chemicals. ?We?re engineering tobacco plants to treat cancer-causing
pollutants,? Rugh said. ?Now there?s some beautiful irony.?

This method offers a cheaper, less ecologically disruptive alternative to
digging up enormous polluted sites.

?There are sites where we have no choice but to consider such alternatives,?
Rugh said. ?There are places impacted by these chemicals where it?s
impossible to dig them all up, dredge them or burn them. It?s not
economically possible; it simply will never happen and these sites will
continue to be problems for wildlife and people.?

Rugh?s research is supported by the Michigan Agricultural Experiment
Station. The MAES is one of the largest research organizations at MSU.
Founded in 1888, the MAES funds the work of nearly 400 scientists in five
colleges at MSU to enhance agriculture, natural resources and families and
communities in Michigan.

[newsroom.msu.edu]

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