FOR ENVIRONMENTALISTS and some public health experts, one of the most puzzling practices of modern agriculture is the addition of arsenic-based compounds to most chicken feed. The point of the practice is to promote growth, kill parasites that cause diarrhea, and improve pigmentation of chicken meat. But Tyson Foods, the U.S.'s largest poultry producer, stopped using arsenic compounds in 2004, and many high-end and organic growers raise chickens quite successfully without them. What's more, McDonald's has asked its suppliers not to use arsenic additives, and the European Union banned them in 1999.
Roxarsone—4-hydroxy-3-nitrobenzenearsonic acid—is by far the most common arsenic-based additive used in chicken feed. It is mixed in the diet of about 70% of the 9 billion broiler chickens produced annually in the U.S. In its original organic form, roxarsone is relatively benign. It is less toxic than the inorganic forms of arsenic-arsenite [As(III)] and arsenate [As(V)]. However, some of the 2.2 million lb of roxarsone mixed in the nation's chicken feed each year converts into inorganic arsenic within the bird, and the rest is transformed into inorganic forms after the bird excretes it.
According to the Environmental Protection Agency, long-term exposure to inorganic arsenic can cause bladder, lung, skin, kidney, and colon cancer, as well as deleterious immunological, neurological, and endocrine effects. Low-level exposures can lead to partial paralysis and diabetes. "None of this was known in the 1950s when arsenicals were first approved for use in poultry," says Ellen K. Silbergeld, a toxicologist at Johns Hopkins University Bloomberg School of Public Health.
Three different pathways exist by which roxarsone in chicken feed can contribute to human arsenic exposure. Roxarsone, or its breakdown products, ends up in chicken meat and adds to the dietary intake of arsenic; roxarsone excreted in chicken litter contaminates land and groundwater after the manure is spread on cropland; and the large amounts of poultry litter made into fertilizer pellets for home gardens and lawns contaminate homegrown produce with arsenic and expose the consumer to arsenic dust.
Last year, a team led by James A. Field of the department of chemical and environmental engineering at the University of Arizona reported that under anaerobic conditions, roxarsone is converted to inorganic arsenic within eight months after poultry litter is spread on fields (Environ. Sci. Technol. 2006, 40, 2951). "Roxarsone is not very toxic," Field says, "but in anaerobic environments, it is transformed into highly toxic forms."
In January, Partha Basu, associate professor of chemistry and biochemistry at Duquesne University and colleagues reported that microorganisms of the genus Clostridium in chicken litter rapidly transform roxarsone into inorganic arsenate under anaerobic conditions (Environ. Sci. Technol. 2007, 41, 818). "We see As(V) created in less than 10 days," Basu says, noting it "can be readily leached into groundwater."
Chicken manure introduces huge quantities of arsenic to agricultural fields. According to Donald L. Sparks, professor of marine studies at the University of Delaware, poultry litter is spread on land at the rate of 9 to 20 metric tons per hectare. Each year, he estimates, 20 to 50 metric tons of roxarsone in chicken litter is applied to fields on the Delmarva Peninsula, a region that includes parts of Delaware, Maryland, and Virginia.
A group led by Johns Hopkins' Silbergeld analyzed arsenic in tap water on the Delmarva Peninsula. It found higher levels of arsenic in areas where chicken litter is spread on fields and lower levels in areas where chicken manure is not spread. The research was reported at the Society of Toxicology meeting in late March.
One reason for the increasing concern about roxarsone is that the weight of evidence for arsenic as a carcinogen is much greater now than it was a decade ago. In 2001, EPA proposed reducing the maximum contaminant levels for arsenic in drinking water from 50 ppb to 10 ppb and required water systems to comply by January 2006. The agency took this action in response to three National Research Council reports that concluded the standard of 50 ppb posed unreasonable risks. And even the new lower maximum appears problematic. According to EPA estimates, the risk of cancer from 10 ppb of arsenic in tap water is 1 in 2,000, a 50-fold higher risk than that allowed for most other carcinogens.
Even though the drinking water standard for arsenic has been strengthened, the standards for arsenic residues in poultry-2,000 ppb for liver and 500 ppb for muscle-have remained unchanged for decades. Furthermore, neither the Food & Drug Administration nor the Department of Agriculture has actually measured the level of arsenic in the poultry meat that most people consume. USDA has measured it only in chicken livers.
In 2004, Tamar Lasky, an epidemiologist then at USDA's Food Safety & Inspection Service, estimated intake of arsenic from chicken consumption. To do this, she used liver measurements and a technical bulletin published by the roxarsone producer Alpharma. She concluded that the mean concentration in young chickens is 390 ppb, which is three to four times greater than arsenic levels in other types of poultry and meat from other animals.
Lasky also calculated that people ingest a mean of 1.3 to 5.2 ??g per day of inorganic arsenic from chicken alone. Those who eat much more chicken than average may ingest 21 to 31 ??g of inorganic arsenic per day, she wrote, which for some is greater than the tolerable daily intake recommended by the World Health Organization. Because per capita chicken consumption has more than doubled since the 1960s, it may be necessary to review the assumptions regarding the overall arsenic intake, Lasky observed.
THE ONLY PERSON who actually has obtained data on the arsenic content of chicken meat, other than livers, is David Wallinga, a physician and director of the food and health program at the Institute for Agriculture & Trade Policy. IATP, which is a research and advocacy organization in Minneapolis, tested raw chicken from Minnesota and California supermarkets.
Fifty-five percent of the 151 samples of raw chicken in these tests contained detectable arsenic ranging from 1.6 to 21.2 ppb, Wallinga wrote in a report. Nearly three-quarters of the samples from conventional producers had detectable levels of arsenic, but only one-third of samples from certified organic and other premium chicken suppliers had detectable levels. On the other hand, no arsenic was found in samples from Tyson and Foster Farms, which have both stopped using roxarsone. "As a physician, I find it ludicrous that we continue feeding arsenic to chickens now that we know it increases our cancer risk, and it's unnecessary for raising chickens," Wallinga says.
According to the Washington, D.C.-based National Chicken Council, Wallinga's report is not scientific and means very little. "There is no reason to believe that there are any human health hazards from this type of use" of arsenic-bearing feed additives, the council says. FDA's Center for Veterinary Medicine declined an opportunity for an interview about roxarsone.
Banning roxarsone in chicken feed would not eliminate all arsenic from chickens or the environment. Some poultry consume water from wells contaminated with natural arsenic. Some are raised on soil contaminated from heavy use of arsenical pesticides in past cotton cultivation. Arsenic also is released from coal-fired power plants. But banning the additive in feed would eliminate a substantial portion of arsenic from the human food chain and some of the arsenic in drinking water.
Even if regulators don't act, roxarsone may be on its way out because of lack of demand. There are reports that Bon Appétit Management Co., a $400 million food service company, may soon join McDonald's and Tyson Foods in prohibiting poultry suppliers from using the additive.