A new study by researchers at the University of Wisconsin in Madison, US, have shown that that infectious prions - thought to be the causative agents in mad cow disease and human vCJD - can survive wastewater decontamination and wind up in fertiliser, potentially contaminating fruit and vegetables.
Microbiologist Joel Pedersen, of the University of Wisconsin in Madison, US, who led the study, said that the prions would be present in such low quantities that they are unlikely to pose a health threat, but as a precaution, 'we should prevent the entry of prions into wastewater treatment plants.'
He said that prions could end up in wastewater treatment plants through slaughterhouse drains, hunted game cleaned in a sink, or humans with vCJD shedding prions in their urine or faeces.
Prior studies have suggested that prions can survive heat treatment and caustic chemicals.
However, to see how prions fare during sewage treatment, Pedersen's research team spiked sludge from a local treatment plant with infectious prions, and then subjected the toxic brew to a typical wastewater treatment regimen.
This typically involves three weeks of filtration, separation and incubation with microbes that break down contaminants in the sludge, resulting in clean water and 'biosolids' free of most human pathogens, which can be used as a fertiliser.
When Pedersen's team tested the sewage soup at various stages, they found the water was clean, but the biosolids were contaminated with prions.
"The sludge digestion seems to have no effect on the prion protein," New Scientist quoted him, as saying.