Wednesday, October 27, 2004

Livestock antibiotics found in waterways

Study detects chemicals near farms in Colorado river

By Jon Bonné MSNBC

Traces of antibiotics used to promote the health and increased growth of livestock and poultry are turning up in waterways, new research shows.

While testing at several sites along Colorado's Cache la Poudre River, aresearch team led by Ken Carlson, a Colorado State University civilengineering professor, discovered the presence of at least three antibioticsused only on food animals.

The compounds were not detected at the river's source near the ContinentalDivide, or near human waste treatment plants around Fort Colins, Colo. Butthey were found farther downriver close to large farms and feedlots. Thescientists' conclusion: Those operations were almost certainly the source.The livestock industry firmly insists it is able to manage the wasteproduced at such facilities.

"We're saying that doesn't appear to be completely the case," Carlson said."I think most people would agree ... these compounds should not be in our rivers."

Study is a first

A 2002 report by the U.S. Geological Survey highlighted the presence ofdozens of pharmaceuticals and other chemicals in the nation's streams andrivers, but this study appears to be the first time these chemicals havebeen pinpointed.

The three substances in question — monensin, salinomycin and narasin — areof interest because they are used exclusively in animal agriculture and arenot used on humans. Carlson found these substances not only in river waterbut in riverbed sediment as well, where concentrations of the antibioticswere up to 1,000 times greater than they were in the water.

The amounts found in the water are nearly infinitesimal, about 50 parts pertrillion at most. But their presence raises three concerns: a possiblecontamination of drinking water; an impact on fish and other aquatic animalssusceptible to long-term exposure; and the drugs' potential ability toprovide increased resistance to waterborne bacteria.

Monensin is given to cattle as a way to improve the health of their rumensand to help them grow more quickly. Salinomycin and narasin are usually usedto help reduce harmful bacteria in chickens' digestive tracts.

The environmental impact for any of the three is not clear, and is certainto prompt additional research and debate.

Industry questions findings

Gary Weber, executive director of regulatory affairs for the NationalCattlemen's Beef Association, questioned the study's methodology,particularly the detection of narasin at certain sites despite a lack ofnearby poultry farms. He believes the compounds may have been misidentifiedor may be from other sources.

"We just don't think it's from livestock operations at all," Weber said. "Wehave a question about what they're finding."

The three substances, part of a group of antibiotics known as ionophores,not only keep food animals healthy but can help them grow faster and withless feed.

Livestock and poultry producers have worked to minimize any remainingtraces, or residue, of these drugs from meat intended for human consumption.But most of them strongly support the use of ionophores as a regular part ofraising cattle and chickens.

Debate over definition of antibiotics

Many in the industry won't even acknowledge ionophores to be antibiotics,though the Food and Drug Administration classifies them as such. In 2003,members of the cattlemen's group sought to petition the FDA to reclassifyionophores as the bovine equivalent of a food supplement. They eased thatstance after an FDA guidance document concluded the human health impactswere likely minimal.

Though agricultural groups maintain these compounds are of no concern tohumans, there is little clear research about the long-term health impacts.

"While low concentrations are not necessarily a problem, we just don't knowenough to say, 'Oh, these are low concentrations. Let's not worry aboutthat,'" said Margaret Mellon, senior scientist at the Union of Concerned Scientists.

In larger doses, they have proven dangerous to animals for which they arenot approved. Monensin has been shown to cause poisoning in horses, andfirms that produce it warn against allowing them, or laying hens, anycontact with the drug. Pigs and turkeys exposed to narasin have also died. ANew Zealand farm worker fell seriously ill after exposure to salinomycingranules.

Worries over greater resistance

Ellen Silbergold, a Johns Hopkins University professor of environmentalhealth sciences who studies the impact of animal antibiotics on humans, saidthe largest worry is that otherwise harmless bacteria in streams andrivers — which concentrate in sediment, where the largest amounts ofantibiotics were detected — might develop better antibiotic resistance whenexposed to ambient levels of drugs used by livestock producers.

"The industry is obviously concerned about them because they're trying tokeep them out of our consumer products," Silbergold said.

While federal regulations focus on the toxicity of runoff and wasteemissions from large animal operations, there is little attention to theresidue from medicines, and little monitoring of less apparent sources ofpossible contamination, including the pools, or "lagoons," used by largelivestock operations to process animal waste.

In addition to animal medicines, Carlson found the presence of fivetetracycline antibiotics used in both human and veterinary medicine.

Ed Furlong, a USGS research chemist who helped produce the 2002 study, saidthe latest findings are helpful in narrowing possible sources ofcontamination and developing better water management policies, but shouldn'tbe used to start assigning blame.

He noted that the concentrations in the Colorado study are too small to havemuch direct human impact: "You'd need to drink about a million liters ofwater from these susceptible sites."

Carlson acknowledged it was not clear whether the antibiotics might beharmful, but he plans additional research to pinpoint exactly how thechemicals made their way into the river.

"There's really only one place they could be coming from," he said. "Now weneed to figure out how they're getting there."

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1 comment:

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