Arsenic used in chicken feed may pose threat

Hopkins study explores risk to consumers, water

May 04, 2004|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

A prominent researcher at the Johns Hopkins Bloomberg School of Public Health says the poultry industry's widespread use of drugs to raise chickens is exposing people who eat them to more arsenic than previously estimated.

In a paper published yesterday in the journal Environmental Health Perspectives, Ellen K. Silbergeld said arsenic-laced drugs designed to keep the birds healthy might pose an increased risk of cancer for consumers and create manure that is contaminating Eastern Shore ground water.

Silbergeld's research essentially disputed the conclusions of a U.S. Department of Agriculture study, released in the journal in January, which concluded that the drugs did not pose a serious health problem.

She said the USDA underestimated the amount of arsenic found in chickens and used outdated data to estimate the health risks of ingesting arsenic.

"This paper had serious problems," Silbergeld said of the USDA report.

Her findings, based on data published by the USDA and other health experts, could have major implications for the Eastern Shore, where 10 percent of the nation's poultry is raised.

A spokesman for the poultry industry said concerns about arsenic in chicken feed are unfounded and that tests consistently show arsenic levels in chickens are well below standards set by the Food and Drug Administration.

"This study appears to be much ado about nothing," said Richard Lobb, a spokesman for the National Chicken Council.

But Silbergeld, a toxicologist who won a MacArthur Foundation "genius" grant in 1993 for her work linking mercury poisoning with infectious diseases, disagreed. She said arsenic in chicken feed creates potential problems in the meat produced and the ground water affected by the waste.

When chickens excrete arsenic in manure, sunlight breaks it down and it migrates to the soil, where it can contaminate ground water supplies, she said. She noted that Europe bans arsenic in chicken feed because of these health concerns.

"This is arsenic. We shouldn't lose sight of the sheer outrageousness of this," Silbergeld said.

Geologists have been closely monitoring arsenic levels in the Eastern Shore's water supply for years without finding serious hazards. Health officials in Queen Anne's, Talbot and Dorchester counties require new wells to be tested for arsenic because of concerns about contamination of the local aquifers, said David Bolton, program director of the hydrogeology section of the Maryland Geological Survey.

A recent U.S. Geological Survey study of the Pocomoke River Basin found slightly elevated levels of arsenic in shallow layers of ground water that could be the result of tainted manure, said Tracy Connell Hancock, a USGS hydrologist.

But she and Bolton said further studies are needed to prove any connection between the manure and arsenic in the water.

"Whether arsenic gets into the ground water from chicken waste is an open question that people are just beginning to investigate," Hancock said.

Arsenic is a heavy metal and poison that naturally occurs in trace amounts in drinking water, dust, wood and some foods. Daily exposures to lower levels have been associated with skin, respiratory and bladder cancers.

In recent years, the Environmental Protection Agency has tightened standards for arsenic in drinking water, reducing permissible levels to 10 micrograms per liter.

But in agriculture, arsenic is approved by the FDA as an ingredient in animal-feed supplements - it has been used for decades to promote growth and to kill parasites, such as cocciodosis, a killer of chickens.

Poultry growers feed arsenic to chickens in an antimicrobial drug known as Roxarsone, given when they're young to stave off infections and when they get older to help them grow. Most of the arsenic in Roxarsone leaves the animal as manure.

Researchers have known for years that some arsenic remains in the chickens, and the USDA has collected chickens from slaughterhouses to test their livers for arsenic since 1989.

In their study, published in January, USDA researchers reported that arsenic levels in chicken were four times higher than those of other meats and concluded that not all of the arsenic they consumed was being excreted.

Eating 2 ounces of chicken per day - the equivalent of a third to a half of a boneless breast - exposes a consumer to 3 to 5 micrograms of inorganic arsenic, the element's most toxic form.

People who eat a lot of chicken might ingest 10 times that amount, according to the USDA study. Even so, the scientists concluded, the levels were not high enough to raise serious alarms.

But Silbergeld said the study did not go far enough. She said the USDA findings are based on industry assumptions about how arsenic levels in chicken livers translate into levels in the parts of the chicken that humans consume in quantity.

Tamar Lasky, an epidemiologist formerly with the USDA, now concedes that the estimates in her January study may have been low. Given its preliminary nature, she said, she may have erred on the side of caution.

"We were deliberately conservative. We didn't want to exaggerate the numbers and have people writing in the press that there are huge numbers, in terms of arsenic levels in chicken," said Lasky, now with the National Institutes of Health.

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