Mad cow disease-causing prions can survive conventional sewage treatment, according to a new study by University of Wisconsin-Madison scientists.
Prions — rogue misfolded proteins that cause mad cow disease, chronic wasting disease, and its human equivalent, variant Creutzfeldt- Jakob disease — are not degraded by standard wastewater decontamination and can end up in fertilizers, potentially contaminating crops.
Prions never have been reported in U.S. municipal sewage. But as a precaution, “we should keep prions out of wastewater treatment plants,” said Joel Pedersen, an environmental engineer at UW-Madison who led the study.
Prions are notoriously resilient to extreme heat, caustic chemicals and irradiation, but it wasn’t known how they would fare under the standard barrage of treatments applied to wastewater sludge.
However, it is unlikely the prions would be guzzled in treated tap water, expert says.
These findings cast doubt on the safety of biosolids, Pedersen said, though he noted that the water effluent was clean and prion-free.
Biosolids generally are thought to lack human pathogens and to be safe for agricultural applications. The Milwaukee Metropolitan Sewerage District makes a fertilizer called Milorganite from its Jones Island treatment plant’s biosolids. Madison makes its own biosolids fertilizer, called Metrogro.
“We’re looking at this research and asking what we can do to improve our systems,” said Jeff Spence, marketing director for Milorganite. “Based on the findings, there’s little or no risk in regard to these rogue proteins as it relates to biosolids.”
Since prions were restricted to the biosolids and not the water, the study “gives better confidence that (prions) could be sequestered in matter associated with solid materials,” and potentially removed, said Fran Kremer, a senior science adviser for the National Risk Management Research Laboratory of the Environmental Protection Agency, which partially funded the study.
