U of S Researchers to Study How Insects Could Help Clean Up Contaminated Soils

Posted July 28, 2004


FOR IMMEDIATE RELEASE - Wednesday, July 28, 2004 2004-07-13-OTHER

Insects Could Help Clean Up Contaminated Soils

An international collaboration between researchers from the University of
Saskatchewan and the University of California has shown for the first time
that insects can detoxify selenium in the environment. The work illustrates
the power of synchrotron analysis to determine how toxic elements change as
they are metabolized by different organisms in the environment.

The finding, featured as a cover story in a recent edition of Environmental
Science and Technology, looked at selenium, a naturally occurring element in
many soils. Though it is an essential micronutrient for humans and other
organisms, it is toxic at higher doses. Livestock pastured on
selenium-contaminated land can be poisoned when forage plants accumulate
high levels of selenium in their tissues.

The researchers began with alfalfa plants irrigated with water containing
selenate, a selenium-containing salt. They observed that the plants absorbed
the selenate and partially transformed it into organoselenium, a less toxic
form. Armyworms (a kind of caterpillar) feeding on the alfalfa converted the
remaining selenate into organoselenium in their tissues.

But something surprising happened when wasp parasites preyed upon the
armyworms. The adult wasps contained not only organoselenium but also
selenonium ions, an electrically charged and highly soluble form of the
element. Its presence was evidence that the wasps were detoxifying selenium
into a chemical form that was being released in the air and dissipated.

"When the insects pupated, there was evidence of methylation," says team
leader Helen Nichol "When you see trimethylated selenium, it suggests that
dimethylated forms were present and have evaporated. This is the first time
it's been shown that insects convert selenium into these forms."

For researchers in the emerging field of phytoremediation, that is, using
plants to clean up contaminated soils, the findings mean that insect pests
might actually aid the process.

Nichol says. "It turns out that insects could actually enhance the
remediation process and it is possible that certain insects might be even
better at it than the species we used."

The team used X-ray experimental facilities at the Stanford Synchrotron
Radiation Laboratory (SSRL) to track the movement of selenium from the soil
to alfalfa, through to beet armyworm caterpillars that eat the alfalfa and
wasps that prey upon the caterpillars.

"This is a very interesting marriage of ecology with bioinorganic
chemistry," Nichol says. "The best way to examine how an element changes its
chemistry as it moves up the food chain is with the synchrotron."

The synchrotron analysis was performed by Helen Nichol, Department of
Anatomy and Cell Biology and U of S Canada Research Chairs Graham George and
Ingrid Pickering, both synchrotron scientists in the Department of
Geological Sciences. Pickering and George previously pioneered the
application of synchrotron techniques to the study of selenium in
environmental and biological systems. Danel Vickerman and John Trumble from
the University of California at Riverside carried out the ecological and
behavioural aspects that were also crucial to the success of the project.

Nichol, George and Pickering are part of a growing group of U of S
researchers that are harnessing synchrotron light in their research. The
Canadian Light Source synchrotron (www.lightsource.ca), due to open on the U
of S campus this year, will offer this country's researchers a powerful new
tool to shed light on a host of questions in environmental, materials and
life sciences, including advanced pharmaceuticals.

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For more information, contact:

Helen Nichol
Department of Anatomy and Cell Biology
College of Medicine
University of Saskatchewan
(306) 966-4094
helen.nichol@usask.ca

Michael Robin
Research Communications
University of Saskatchewan
(306) 966-2427
michael.robin@usask.ca
www.usask.ca/research