Inactivation of infectious prions in the environment: a mini-review

Infectious prions (PrP^TSE) contribute to horizontal transmission of transmissible spongiform encephalopathies. Specified risk material (SRM) wastes and wastewater generated from slaughterhouses and rendering plants represent a potential reservoir of PrP^TSE. Approved disposal practices for SRM that ensure destruction of PrP^TSE, including thermal or alkaline hydrolysis at 150°C–180°C under 4–12 atmospheres and incineration, gasification or combustion at 1000°C, are expensive and challenging to implement in commercial slaughter facilities. Consequently, a large portion of the SRM in Canada is rendered and buried in landfills, whereas they are incinerated at considerable cost in Europe. Alternatives for the disposal of these wastes have been proposed and include anaerobic digestion and composting. These biodegradative processes offer advantages in that they are less energy intensive, CH₄ can be used in cogeneration and the end products used as fertiliser. In addition, advanced ozonation of the liquid fraction of SRM may allow its direct release into wastewater streams. For these practices to be adopted, assessment of the extent of PrP^TSE inactivation during these processes is required. Moreover, multi-barrier use of these approaches (e.g., anaerobic digestion + composting or anaerobic digestion + ozone) may act synergistically to achieve an acceptable level of PrP^TSE inactivation.