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Study: Prions likely
more mobile in alkaline soils
March 19, 2007
Prions, the rogue proteins that
cause chronic wasting disease and similar maladies, may be more
mobile in soil that is more alkaline, suggests a new study by
University of Wisconsin-Madison researchers.
Prion protein modeled in 3-D.
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That finding has implications for the safe disposal of
carcasses of animals infected with chronic wasting disease, "mad
cow" disease, scrapie and other prion diseases. Prions from
those carcasses can remain infectious in the soil for at least
three years. Soil alkalinity varies considerably but can be
relatively high in older landfills, especially if lime is spread
on the carcasses to speed decomposition.
The UW-Madison research team found that as alkalinity
increases, prions are less likely to adhere to particles of
quartz, a common soil mineral, and are therefore expected to be
more mobile, explains Joel Pedersen, an assistant professor of
soil science.
Movement of prions in the soil could be a good or bad thing,
depending on the situation, Pedersen explains. For example, if
they move away from the surface, they're less likely to be
ingested by animals.
"Those that remain near the surface would more accessible
to animals and might therefore lead to the spread of chronic
wasting," he points out.
On the other hand, prions that are more mobile might be more
likely to migrate through a landfill, he adds.
"In a landfill, if prions are mobile, they could be
transported down through the waste, where they could enter the
landfill's leachate collection system, and from there be directed
to wastewater treatment plants. If prions survive wastewater
treatment, they would be released back into the environment in
treated water or in the sludge," Pedersen says.
However, Pedersen cautions that his findings are from a highly
simplified experimental system, and that any assessments about
the safety of landfilling carcasses would have to be based on
studies of how prions behave in municipal solid waste and the
soils used in landfills. The research team is now undertaking
such studies.
He also says that the findings don't necessarily mean that
it's a bad idea to bury carcasses with lime.
"The lime treatment could destroy some prions," he
says. "We don't know yet. It's only the prions that might
survive that might be more mobile."
The experiment that generated these findings involved mixing a
solution that included prions and pure quartz sand, letting it
stand for a specific period of time and then measuring how many
prions remained free in the solution. In a real-world setting the
prions would in be a mix of landfill materials, not just quartz,
and the soil solution would be percolating downward.
For the next set of experiments, the researchers are flowing
water through columns of materials like those found in carcass
disposal sites, including both soil and solid waste, Pedersen
explains.
Other members of the research team include Xin Ma, a
postdoctoral researcher in the UW-Madison's Department of Soil
Science; Craig Bensen in the Department of Civil and
Environmental Engineering; and Judd Aiken and Debbie McKenzie in
the Department of Comparative Biosciences.
Source: University of
Wisconsin, Madison
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