The Food and Drug Administration said Wednesday that some chicken meat may contain small amounts of arsenic, though the agency is stressing that the amount is too tiny to be dangerous to people who eat it.

The FDA said Wednesday that a new study developed by the agency shows that an ingredient in chicken feed that contains arsenic, called Roxarsone, may make its way into parts of the bird that are eaten. Previous studies have indicated that the arsenic was eliminated with chicken waste.

Pfizer Inc., which makes the feed ingredient, said Wednesday that it will pull it off the market in the United States. Had the company not stopped sales, the FDA could have eventually banned the product since it contains a known carcinogen.

Many poultry producers have already stopped feeding their birds the ingredient, which has been used since the 1940s to kill parasites and promote growth.

The FDA said that people should not stop eating chicken that may have been fed the drug. Michael Taylor, FDA's deputy commissioner for foods, said the study raised "concerns of a very low but completely avoidable exposure to a carcinogen."

Pfizer said in a statement that a subsidiary, Alpharma LLC, is suspending sales next month in response to the FDA findings. The company said it is waiting a month so producers have time to transition their birds off the drug. The ingredient will also be pulled off the market for swine and turkeys, though the FDA only studied chickens.

Scott Brown, of Pfizer Animal Health's Veterinary Medicine Research and Development division, said the company also sells the ingredient in about a dozen other countries. He said Pfizer is reaching out to regulatory authorities in those countries and will decide whether to sell it on an individual basis.

In the study of 100 chickens, the FDA found that chickens that had eaten the Roxarsone had higher levels of inorganic arsenic _ as opposed to organic arsenic, which is naturally occurring _ in their livers than chickens which had not eaten the Roxarsone. Inorganic arsenic is more toxic than the naturally occurring form.

The agency attempted to study levels of arsenic found in chicken muscle _ breasts and legs, for example _ in addition to the livers but that test ran into complications. An agency official said Wednesday that they would expect about 40 times less arsenic to be found in the muscle than in the liver.

Roxarsone has long been a concern for environmental and consumer groups worried about its presence in chicken waste and the resulting effects on human health in areas with high chicken production. Maryland state lawmakers have attempted to force a ban in that state, saying the arsenic ends up in the Chesapeake Bay.

"Arsenic in chicken production poses a risk not only to human health, but to the environment," said Michael Hansen, a senior scientist with Consumers Union, which publishes Consumer Reports. "We need to get arsenic out of food production altogether."

Consumers Union and other groups praised the FDA's move but asked the agency to go further and encourage bans of other animal drugs that contain arsenic. The FDA said it is looking at another drug made by Pfizer, Nitarsone, which contains arsenic and is fed to chickens and turkeys but is used much less frequently than Roxarsone. Officials said they are in talks with the company about that drug but do not have any data specific to it.

The National Chicken Council, which represents companies that produce and process chickens, said in a statement that the ingredient has been used to maintain good health in chickens for many years, and that it is used in "many, but not all" flocks.

"Chicken is safe to eat," the group said.