Super Trees

Noreastah noreastah at acadia.net
Sun Oct 11 00:40:07 EST 1998


>Hybrid poplar trees suck up heavy metals and solvents
>Eds: Hold for release at 5 p.m. EDT.
>By JOSEPH B. VERRENGIA
>AP Science Writer
>Cleaning up polluted industrial sites may not require billion-dollar
>government programs. Instead, scientists suggest, plant a poplar tree.
>Laboratory-designed hybrids of the fast-growing poplar tree have been
found
>to act like 100-foot straws that suck contamination from soil and
>groundwater.
>In a process known as phytoremediation, the tree either safely stores
the
>chemicals in its tissues or metabolizes them into apparently less
volatile
>compounds. Then the tree releases these byproducts through its leaves
as
>vapor into the atmosphere.
>This natural cleanup takes several years to complete. But tests show
the
>method is inexpensive and might work at least as well as high-tech soil

>roasting and groundwater filtering, while keeping the site green and
>attractive.
>Researchers say phytoremediation eventually may transform the way
industry
>and government agencies treat long-term pollution problems, which are
>estimated to top $200 billion nationwide.
>Still unknown, however, is whether the chemical byproducts generated by
the
>poplars really are less harmful, or if diluting them in the atmosphere
only
>creates another hazard.
>''We may soon be using trees to heal the hurt inflicted on the Earth,''

>said David E. Salt, an environmental chemist at Northern Arizona
University
>in Flagstaff. ''But would we simply be exchanging soil pollution for
air
>pollution?''
>In one study, published in the October issue of the journal Nature
>Biotechnology, researchers at the University of Georgia took a gene
from a
>strain of bacteria that enables it tolerate high levels of ionic
mercury, a
>highly toxic version of the heavy metal.
>They modified the merA gene and inserted it into the genetic code of
the
>yellow poplar. Laboratory tests showed the genetically engineered
poplar
>had a tenfold increase in mercury resistance and also its ability to
>transport it through its roots and tissues, reduce it to a less
volatile
>form and release it into the air. The genetic hybrid has not yet been
>planted in field tests.
>The yellow poplar, also known as the tulip poplar, is one of the
largest
>and most commercially valuable hardwood trees. It grows primarily east
of
>the Mississippi River.
>Environmental scientists favor it for phytoremediation for the same
reasons
>that make the tree popular with commercial foresters, plywood
manufacturers
>and neighborhood landscapers.
>It grows up to 15 feet per year and absorbs 25 gallons of water a day.
Its
>broad green leaves measure 6 inches square, providing plenty of leaf
>surface to release processed contaminants. It has an extensive root
system.
>And it's resistant to everything from gypsy moths to toxic wastes.
>In a study published in the October issue of the Journal of
Environmental
>Engineering, scientists at the University of Missouri-Rolla and the
>University of Iowa report that more conventional poplar trees
effectively
>reduce high soil levels of atrazine, a farm fertilizer.
>Other remediation technologies strip the soil of vital nutrients and
>microorganisms, so nothing can grow on the site even if it has been
>decontaminated, they said.
>''Phytoremediation simultaneously restores soil health and revegeates
>during the cleansing process,'' said co-author Joel G. Burken of the
>University of Missouri-Rolla.
>One of the nation's largest phytoremediation experiments is being
conducted
>in Oregon. In 1984, a tanker truck skidded on icy Interstate 5 near
Central
>Point, spilling hundreds of gallons of the solvent TCE.
>Conventional cleanup efforts spanning 13 years failed to remove the
>solvent, a suspected carcinogen, from the surrounding soil and
groundwater.
>In 1997, University of Washington scientists planted 800 hybrid
poplars.
>The results will not be available for several years. But in laboratory
>simulations, the Washington team said, poplars reduced TCE
concentrations
>by 97 percent.
>
>
>
>





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