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From: TSS (wt-d6-170.wt.net)
Subject: Carcass Disposal: A Comprehensive Review August 2004 (TSE)
Date: December 29, 2004 at 8:32 am PST
-------- Original Message --------
Subject: Carcass Disposal: A Comprehensive Review August 2004 (TSE)
Date: Wed, 29 Dec 2004 10:06:36 -0600
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy
To: BSE-L@LISTSERV.KALIV.UNI-KARLSRUHE.DE
##################### Bovine Spongiform Encephalopathy #####################
Carcass Disposal: A Comprehensive Review August 2004 snip... Ch. 2 Incineration 15
4.2 – TSE Disease Agents
Durability of TSE disease agents
The disease agents responsible for TSEs (e.g.,
scrapie, BSE, and CWD) are highly durable (Brown,
1998). For example, scientists have demonstrated
the persistent infectivity of the scrapie agent in soil,
and healthy sheep have contracted scrapie after
grazing on land that had served, three years earlier,
as pasture for scrapie-infected sheep (Brown &
Gajdusek, 1991). While incineration is used to
dispose of TSE-infected animals, including scrapieinfected
sheep and goats, (EU, 2003, p.7) the disease
agents responsible for TSEs (i.e., prions) are
extremely heat resistant. This raises important
questions about incineration’s suitability for disposing
of TSE-infected—or potentially TSE-infected—
carcasses.
One study subjected the scrapie agent to varying
time and temperature combinations—5 to 15 minutes
at 150 to 1000°C (302 to 1832°F). Temperatures of
600°C (1112°F) completely ashed the samples, but
some infectivity remained (Brown et al., 2000). The
UK Spongiform Encephalopathy Advisory Committee
(SEAC) has recently affirmed its belief that the risk
of infectivity from ash would be extremely small if
incineration was conducted at 850°C (1562°F)
(SEAC, 2003), and the European Commission
Scientific Steering Committee (SSC) recognizes the
same temperature as a standard for disposing of
TSE-infected material (SSC, 2003a).
Open-air burning
World-renowned TSE expert Dr. David Taylor
explains that open-air burning is imprecise and not
normally a legitimate TSE-related disposal option
because of doubts it can completely destroy TSE
infectivity (Taylor, 2001). For similar reasons, the
European Commission SSC argues that fixed-facility
incineration is preferred to open-air burning:
There is no reliable data to indicate the
extent of risk reduction that could be
achieved by open burning. It is reasonable
however to assume that overall it will be
rather less effective in reducing the
infectivity of BSE/TSE than well-conducted
incineration. Moreover the reproducibility of
the risk reduction is likely to be very variable
even at a single location.
(SSC, 2003b, p.4)
For now, open-air burning of TSE-infected
carcasses should be prohibited. For exceptional
cases in which open-air burning might include TSEincubating
carcasses (e.g., in the UK during 2001,
when open-air burning of FMD-infected carcasses
likely included some sheep and cattle incubating
scrapie and BSE), studies conclude that the risk of
TSE spread is acceptably low (7x10-7) (Taylor, 2001,
citing a risk assessment report by DNV Technica). It
should also be noted that open-air burning
temperatures have been greatly enhanced through
the use of PMFs (see section 3.1). In the Czech
Republic, for example, PMFs have been used to
reach temperatures (1200-1400°C, or 2192-2552°F)
capable of destroying TSE agents (Sobolev et al.,
1999; Sobolev et al., 1997). While promising,
environmental questions remain, and studies clearly
validating PMF-assisted destruction of the TSE
agent are needed (see section 7.3).
Fixed-facility incineration
Unlike open-air burning, fixed-facility incineration is
highly controlled, lends itself to validation for
reaching the requisite (850°C or 1562°F) TSEdestruction
temperature, and is a reliable method for
dealing with TSE-infected carcasses. While
alkaline-hydrolysis digestion has been widely
reported to be the most robust method for dealing
with TSEs (Grady, 2004), this is not entirely
accurate. Both fixed-facility incineration and alkaline
hydrolysis may be used to dispose of TSE-infected
material (Powers, 2003).
As discussed further in section 7.1, combinations of
fixed-facility incineration and rendering have been
used to manage risk in European countries that have
been home to BSE. Although all animals confirmed
to be TSE-infected are disposed of in fixed-facility
incinerators, other “at-risk” animals and material
have been disposed of by using a combination of
rendering and incineration. These include carcasses
or parts of carcasses suspected of TSE infection,
animals that have died on the farm (fallen stock), and,
in the UK, animals older than 30 months (DEFRA,
2003b; Herbert, 2001). The UK’s Over Thirty
Months Scheme (OTMS) is a precautionary policy
requiring the removal from the food chain and
destruction of cattle aged over 30 months, an age
above which it is thought animals are at greater risk
of developing BSE (MAFF, 1996). Under the OTMS,
carcasses are rendered and, at a great cost to the UK
government, the resultant MBM and tallow is stored
and then disposed of in fixed-facility incinerators. At
several of the incineration plants, including one
waste-management incinerator that was the subject
of an interview, energy is recovered from the MBM
and tallow and an EU subsidy is received
(Anonymous, 2003g; Hilliard, 2003; Scottish
Parliament, 2002; Shanks, 2001).
Air-curtain incineration
Air-curtain incinerators reportedly achieve higher
temperatures than open-air burning, and may reach
1600°F (~871°C) (G. Ford, 2003; McPherson
Systems Inc., 2003). Such claims, particularly as
they relate to reaching the requisite (850°C or
1562°F) TSE-destruction temperature, need to be
further substantiated (Scudamore et al., 2002, p.779).
Noting that “with wet wastes, such as CWDcontaminated
carcasses, temperatures...can fluctuate
and dip below recommended temperatures,” an
Environmental Protection Agency (EPA) Region 8
draft document hesitates to endorse air-curtain
incineration as a robust method for dealing with CWD
(Anonymous, 2003c, p.4). In the UK, the Department
for Environment, Food and Rural Affairs (DEFRA) has
conducted experiments to elucidate the temperatures
reached during air-curtain incineration in fireboxes;
but despite efforts that included the placement of
temperature probes in the carcass mass, researchers
could confirm only a range of attained temperatures
(600-1000°C, or 1112-1832°F). This information
may be a useful guide, but further studies to confirm
the temperatures reached are needed (Hickman,
2003).
5.1 – Air Pollution snip... see full text 31 pages; http://fss.k-state.edu/research/books/carcassdispfiles/PDF%20Files/CH%202%20-%20Incineration.pdf TSS ######### https://listserv.kaliv.uni-karlsruhe.de/warc/bse-l.html ##########
Carcass Disposal: A Comprehensive Review
http://fss.k-state.edu/research/books/carcassdispfiles/Carcass%20Disposal.html TSS
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