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Experts soothe worries about using bone, blood meal
January 7, 2004 The Oregonian by Kym Pokorny
Concern about mad cow disease is expanding past the meat counter as gardeners worry that bone and blood meal sprinkled on their soil could make them sick.
Experts say scientific evidence is scant or nonexistent on the danger of such products made from rendered cow parts, but add there's an easy way to play it safe: Don't use them.
"If you're worried about using bone meal in the garden, use a mask," says Rich Baer, a plant pathologist and rosarian. "If you're really worried, don't use it."
Safety concerns about bone meal have turned into something of an urban legend, according to Dalton Hobbs, spokesman for the Oregon Department of Agriculture, but he knows of no evidence that bovine spongiform encephalopathy (BSE) can be contracted by inhaling bone meal dust.
"One would think there is a theoretical possibility, but that has not been documented as a form of spreading BSE," he says.
The same goes for plants taking up the prion protein that causes BSE and passing it on to humans who eat them.
"I've never even heard anyone hypothesize on that," says Baer, who has degrees in plant pathology and plant physiology. "Protein molecules tend to be fairly large. Plants don't tend to absorb anything of that size through their cell walls."
So far, research shows that BSE is spread in cattle through feed containing diseased animal byproducts. People seem to get the human form of BSE by eating meat from infected cattle, though only certain parts. The prion protein that's thought to cause BSE has been found in the brain, spinal cord and small intestine of beef, according to Hobbs, but not in blood, bone, milk or muscle (which is most of the meat we eat).
Parts of the cow (hooves, bones and innards) that don't end up in the grocery store for human consumption are sent to rendering facilities, where they're boiled down, ground up and made into any number of products, including bone meal and blood meal sold as plant nutrients. The new U.S. Department of Agriculture regulations restricting "downers," cows that can't stand or walk, from being slaughtered for human consumption don't apply to bone meal production.
"No one's said a thing about what we put in our gardens," says Dona Koepke, a gardener in Lake Oswego. "I just bought a huge thing of organic fertilizer and part of it was bone meal. I hadn't thought about it before, but if it's made from diseased tissue, can it be taken up by plants, how long does it stay in the ground?
"We think we're doing something good for our garden, but are we?"
Plants need three major nutrients to survive: nitrogen, phosphorus and potassium. Bone meal provides an organic source of phosphorus, needed for root development, and a little nitrogen, used by the plant for healthy growth. Blood meal is a good source of nitrogen. But there are alternatives.
Sales of blood meal at Concentrates, a Portland distributor of organic products, have dropped by about half since the discovery of mad cow disease in Great Britain more than a decade ago, according to manager Heather Havens. But a big reason for that decline is the increased availability of feather meal, which not only offers nitrogen but offers it in a form that's released slower than blood meal. And it's cheaper.
Bone meal, on the other hand, continues to sell well, she says. Sales dipped a bit during Britain's scare and then leveled off.
"It works well and has been used for so long. It's almost like a folk remedy. I think people will always use it," Havens says.
But they don't have to. "People who have reservations have switched to fish bone meal," she says. "You get more phosphorus per dollar, per pound at no risk."
The Royal Horticulture Society recommended in 1996 that gardeners wear face masks to avoid inhaling bone meal dust. "Any dust that you're working with, whether it's sanding the woodwork inside the house or working with lime in the front yard, it's best not to inhale," says Jan McNeilan, horticulture agent for Oregon State University Extension Service. "A simple mask would take care of that."
The thing to remember, according to Hobbs, is that the risk of getting BSE is minimal. "Only 200 people have contracted it and of those, 150 were in England where they had 200,000 infected cattle. That's a huge reservoir of infected meat. We've found one.
"Honestly, the chances of getting killed using a rototiller are a lot greater."
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