Solid knowledge: Prions may stick in soil or sludge
 f prions, the proteins
at the heart of chronic-wasting disease, show up in wastewater treatment
plants, researchers at the University of Wisconsin-Madison will know
how to manage them. With funding from
the Environmental Protection Agency, Assistant
Professor Katherine (Trina) McMahon, Professor
Craig Benson, Veterinary Medicine Professor Judd Aiken and Soil
Science Assistant Professor Joel Pedersen are studying how prions behave—both
in solid-waste landfills and at water-treatment plants.
“We have no evidence
that there are any prions going into any wastewater treatment plants,”
says McMahon. “This is all a big ‘what if.’ What if
prions got into a wastewater treatment plant?”
Previous research has shown
that prions, unlike other proteins, are resistant to biodegradation,
says McMahon. Rather, they physically bind with solid particles, or
biosolids, in wastewater. “The particles are removed by gravity
in a wastewater treatment plant, so they just settle out—and the
clean water remaining at the top gets disinfected and discharged,”
she says.
That’s good news for
the streams and rivers receiving this treated water. But many plantssell
their biosolids, or “sludge” rich in nutrients such as nitrogen
and phosphorous, to farmers as organic fertilizer. They need to know
for certain that it is harmless. “For them, it’s a big economic
incentive to be able to land-apply the treated sludge,” says McMahon.
“If not, they have to landfill it.”
Landfilling potentially prion-laden
sludge is a temporary solution, since a pipeline carries the leachate,
or “goop” and water, from the landfill back to the water-treatment
plant. “They treat the leachate just like they would other sewage,”
says Benson. “That’s how they keep the nasty stuff from
the landfill out of groundwater.”
For those reasons, landfills
won’t accept the carcasses of deer suspected of having CWD. Some
of those carcasses are incinerated, but it’s an expensive process,
as is chemically treating them or storing them in refrigerated containers
while researchers learn more.
Benson’s group is studying
the fate of prions if carcasses are buried in a landfill. “Understanding
whether prions even get in the leachate in the first place is an issue,”
he says. “And then if there’s a way we can bury the carcasses
that keeps the prions in place—as opposed to getting into the
leachate—that’s desirable.”
His group is investigating
how prions migrate through a landfill as rain water infiltrates into
the waste. The researchers want to determine whether some soils used
to bury carcasses retain prions better than others. So far, their data
suggests that prions get “stuck” in finer-grained soils,
such as clay.
The process is somewhat like
rinsing pasta in a colander. “The water runs through it but the
prions get stuck in the mesh,” says McMahon.
If the researchers verify
that prions stick to soil components, it will be a substantial step
forward, she says. “In both landfills and wastewater treatment
plants, it’s much easier to deal with solid material than with
water, because water gets everywhere,” says McMahon. “You
can contain the solid material and deal with it.”
The threat of prions in landfills
and wastewater isn’t just a local one. Researchers have identified
dear or elk infected with CWD in Illinois, Colorado, Wyoming, Utah,
New Mexico, North Dakota, Nebraska and recently, New York.
When the group’s studies
conclude later this year and early next year, McMahon hopes the researchers
can give the EPA more than just information on which to base environmental
policy. “I’d like to be able to say with some confidence
to the EPA that you can do ‘X’ with your prion-contaminated
waste and be reasonably certain that you’re not going to have
it go out into the environment in an uncontrolled way,” she says.
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