This is to respond to the issue raised by Dr.Rufus Chaney of prions in treated municipal sewage sludge “biosolids”.
Both risk assessments on prions in sewage sludge (Gale, et al, 2001, and Yamamoto, et al, 2006) agree:
Prions from SRM (specified risk materials such as brains and spinal cords) of infected animals processed at abattoirs
may pass through drains into sewage treatment plants.
The wastewater treatment process does not inactivate infectious prions and reconcentrates
those prions in the treated sewage sludge “biosolids”.
Spreading the sludge as fertilizer may expose animals including livestock to transmissible spongiform encephalopathies (TSEs).
However, as a basis for their conclusions, both Gale and Yamamoto rely on incorporation of the sewage sludge into the soil
to dilute the infectious prions.
Gale: “For pasture land, a grazing restriction of three weeks applies and the treated sludge must be deep injected or ploughed down immediately after application.”
Yamamoto: “The level of sludge-derived fertilizer ingested by cattle was considered to be very low since the fertilizer is mixed with ground soil, . . . “
In the United States (US), top dressing sewage sludge “biosolids” on hay fields, dairy pastures and grazing lands is common practice.
Thus, there is no incorporation to dilute the prions in the sludge.
Further, both Yamamoto and Gale consider the only prion source to be tiny amounts of Bovine Spongiform Encephalopathy (BSE)
infected SRM (specified risk material) passing through drain screens and/or filters in abattoirs to the sewage plant.
Neither Yamamoto nor Gale consider other sources of prions which are present here in the US including Chronic Wasting Disease (CWD)
and human prions from Creutzfeldt Jakob Disease (CJD).
CWD, a transmissible infectious prion disease similar to BSE, is spreading and has infected farmed and/or wild deer and elk,
(and frequently both) in Montana, Wyoming, Colorado, South Dakota, Nebraska, Kansas, Oklahoma,
New Mexico, Minnesota, Wisconsin, Illinois, and has moved east to West Virginia and New York
Shedding of the CWD prions in feces and urine is considered a plausible route for transmission and environmental contamination.
(Williams, et al 2002)
Infectious CWD prions are also found in muscle tissue. (Angers, et al 2006)
Disposal of infected CWD carcasses in landfills is common:
“We want to reiterate that disposing of potentially contaminated CWD carcasses and wastes in MSWLFs (Municipal Solid Waste Landfills )
that are compliant with 40 CFR 258 standards is and remains an acceptable option.” (EPA memo, Nov. 12, 2004)
“In most instances the (landfill) leachate is transferred to a wastewater treatment plant (WWTP) for treatment.”
“Once that leachate (from landfill) reaches the wastewater treatment plant the suspended solids will be separated
from the effluent. Those suspended solids will then be termed "sludge" or biosolids.”
“Land application of municipal sludge that potentially contains CWD PrP-res (prions) may result
in the presence of CWD PrP-res in surface soils.” (WIDNR, 2002; EPA Reg. 8, 2005)
Prions can survive for years in soil (Brown, et al 1991). Animals can become infected from prions in soil.
(Miller, et al 2004)
Between 2 and 25% of the 4.5 million cases of Alzheimer’s Disease and senile dementia victims in the US
are actually infected with sporadic CJD. (Manuelidis, et al, 1989; Boller, et al, 1989, 1995;
Harrison, 1991; Teixeira, 1995; Warren, et al, 2005) creating the reality that many thousands of CJD victims
are shedding infectious prions into public sewers to end up in both Class B and Class A sludge compost.
Prions have been found in the blood and urine of CJD victims. (Gabizon, et al, 2001; Reichl, et al 2002) .
Undertakers and medical facilities routinely discharge CJD infected blood and body fluids into public sewers.
(Yale; UC Davis, CDC)
Prions can cross the intestinal barrier by riding piggyback on ferritin, a protein normally absorbed by the intestine.
Because ferritin shares considerable homology across species, these data suggest that PrPSc-associated proteins,
in particular ferritin, may facilitate PrPSc uptake in the intestine from distant species,
leading to a carrier state in humans. (Singh, et al 2004)
“ . . . enteric infection at early as well as later stages of (CJD) disease, and regardless of the route of agent entry,
implicates potential environmental spread by fecal matter.” (Radebold, et al 2001)
Class B sewage sludge “biosolids” is expected to be pathogenic.
EPA allows land applied sludge “biosolids” to contain fecal coliform up to 2 million CFU/gram.
But the EPA and waste industry promote the use of “pathogen-free” Class A sludge “biosolids” compost on playgrounds,
ball fields, public parks, and home flower and vegetable gardens.
. “Pathogen free” is clearly not the case when the Class A sludge compost can contain infectious human and animal prions.
Not only are livestock and wildlife at risk from ingesting prion infected soil and sludge,
but humans, and particularly children, are especially at risk because their hand to mouth behavior
results in the ingestion of dirt (Robischon, 1971; LaGoy, 1987; Binder, et al 1986; Gerba, et al 2002 ; CDC, Callahan, 2004).
The EPA guidelines and disclosures on pathogens in Class A sludge “biosolids” compost need to be revisited.
Helane Shields, Alton, NH