| slaughterhouse waste |
| Friday, 13 July 2007 | |
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researchers to test slaughterhouse waste water for disease agent article by: Margaret Munro, CanWest News Service
Brains, eyes, tonsils and other select tissues from older cattle - even bone dust generated when their spines are split open - will be diverted out of the food chain to meet new federal rules that go into effect Thursday in an effort to eradicate mad cow disease, or bovine spongiform encephalopathy, caused by infectious proteins called prions. But the water that pours down the drains at slaughterhouses and rendering plants continues to be considered risk-free. "It's not contaminated," says Freeman Libby, an official with the Canadian Food Inspection Agency, who likens it to "normal waste water going down your sink drain." Mike Belosevic, a University of Alberta microbiologist, however, is not convinced. "They are making a huge assumption," Belosevic says, noting there are "zero data" to back up claims that water from slaughterhouses and rendering plants is free of prions. "The point is no one has even looked." He stresses the risk is "infinitesimally small," given that only 10 cases of the mad cow disease have turned up so far in Canada. But the possibility of prions entering and persisting in waste water cannot be discounted, says Belosevic, who is leading a $2 million project to learn more about the water used in cattle-processing facilities. Currently, saws, knives and other equipment are washed or hosed off after use to remove tissues that will be diverted into a special waste stream as part of a multi-million-dollar effort to eradicate mad cow disease in Canada. The tissues, called "specified risk material," or SRM, are where infectious prions can concentrate. Prions are rogue proteins that induce abnormal folding of other proteins, leading to fatal brain-wasting diseases such as mad cow, scrapie in sheep and Creutzfeldt-Jakob disease in humans. More than 100,000 tonnes of such SRM is generated in Canada every year, the bulk of it in Alberta. Until now it has been processed like other cattle waste, most of it ending up in pet food and feed for non-ruminant animals such as chickens, and as fertilizer and bone meal. Once the new ban comes into effect, most of Canada's SRM will be taken to rendering plants in Calgary and reduced to dry meal. It will then be hauled to a Coronation, Alta., landfill and buried, according to officials at the rendering company that will be handling the material. During rendering, the wastes are compressed and "dewatered." "Along with that squeeze of water you may release prions," says Belosevic, who explains the proteins can persist for years and may be "bioaccumulating" in waste water ponds. "Say you had a rendering plant and two or three infectious animals came through in a year," he says. "You may find it in leachates from that rendering plant." Federal and Alberta research networks are financing Belosevic's project, called "prion inactivation in the environment." Over the next two years, the researchers will look for prions in waste water from rendering plants and slaughterhouses. Belosevic says the team is working with industrial partners, but declined to identify the companies or plants involved. He says hunting for the infectious particles is not easy. Interpreting the results of the tests could be even trickier, as it's unclear if prions in water can lead to the disease. "That's a question for the risk assessors," says Belosevic. His team is more interested in finding out if the prions are slipping through - and if they are, in deactivating them. The only proven ways of destroying prions are with high-temperature incineration, or a combination of heat, chemicals and high pressure. Composting is another option, although it isn't thought to completely destroy prions. A Canadian Food Inspection Agency team in Ottawa recently reported that heat and microbial processes generated by burying infected material reduces the number of prions, but doesn't completely eliminate them. "We don't anticipate composting is going to be so effective that it will totally destroy the prions, but it could decrease the infectivity," says Belosevic. Even so, there is talk of composting SRM. Several small slaughterhouses in northwestern Ontario are proposing to pool their waste at one compost site, says Libby, who is national director of the food inspection agency's feed ban task force. Restrictions will, however, be put on the use of any compost made with SRM, he says, noting that it will not be allowed on grazing land or gardens, although it might be permitted on Christmas tree farms and golf courses. Belosevic, meanwhile, sees more promise in a chemical process, called advanced oxidation, that might be able to deform the proteins and render them non-infectious. To test their ideas in the lab, the researchers are busy rounding up a supply of prions. Earlier this year, they infected 30 hamsters with scrapie at a secure federal laboratory in Ottawa and hope to harvest billions of prions. They also have a line on prions from elk, infected with chronic wasting disease that are part of a research project in Lethbridge, Alta. And they are working on a new "amplification" technique to generate even more of the rogue proteins, which they will use to test inactivation techniques in their Edmonton laboratory. Belosevic says the hope is to have a "way of dealing with prions in waste water, if and when we find them." © CanWest News Service 2007 |
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