[USCC] Inactivation of prion wastes before discharge to sewage plants

[Helane Shields]

This is in response to Perry Beeman's 11/18/06 article in the Des Moines Register on incineration of prion infected tissue at the Ames, Iowa, National Animal Disease Center prior to discharge to city sewage plant.  The panel of 11 experts  concluded "cooking the wastes at 250 degrees Fahrenheit" (121 degrees Celsius) is adequate to inactivate prions.

To the contrary, Dr.Paul Brown, et al, Office of Research Facilities Development and Operations, NIH, US Dept. of HHS,  Bethesda, Maryland, published the following findings:  [Environ Sci Technol. 2004 Nov 15;38(22):6155-60]:

"We investigated the effectiveness of 15 min exposures to 600 and 1000 degrees C in continuous flow normal and starved-air incineration-like conditions to inactivate samples of pooled brain macerates from hamsters infected with the 263K strain of hamster-adapted scrapie with an infectivity titer in excess of 10(9) mean lethal doses (LD50) per g. "  (600 degrees Celsius= 1112 degrees Fahrenheit . . . . . 1000 degrees C = 1832 degrees F)."

"In a previous series of experiments (4), we showed that transmission could occur even after ashing infected tissue in a covered crucible at 600 °C: 
[1112 degrees F] the ash from one sample of fresh brain tissue heated for 15 min transmitted to five of 18 animals . . . "

" We conclude that at temperatures approaching 1000 degrees C under the air conditions and combustion times used in these experiments, contaminated tissues can be completely inactivated, with no release of infectivity into the environment from emissions. "

Thus National Institutes of Health scientists have concluded 250 degees Fahrenheit is inadequate to disinfect prion wastes -- and that 1000 degrees C -- equal to 1832 degrees Fahrenheit is necessary.

One statement in the news report was, however, quite true:  "If any infectious agents survived, they would be in sewage sludge that is spread on city-owned fields."

Helane Shields, PO Box 1133, Alton, NH 03809   Tel: 603-875-3842