At the same time that you're buttering your morning toast, you also may be slathering it with the tiny amounts of the flame retardant PBDE.

In a study to be published Tuesday in the journal Environmental Health Perspectives, researchers found that each of 10 samples of butter purchased at five Dallas grocery stores contained various types of PBDEs.

Although it was a limited sampling and the amounts were small enough to be measured in trillionths of a gram per gram of butter, lead researcher Arnold Schecter said the concentration was the highest found so far in food.

"This is a brominated flame retardant. It should not be in butter at all," said Schecter, professor of environmental and occupational health sciences at the University of Texas School of Public Health in Dallas.

Schecter said the study results showed a need for federal oversight, including a broad food-testing program.

He and his colleagues have been looking at chemical contamination in food for several years, their work funded by the Pfeiffer Research Foundation in Short Hills, N.J.

One butter sample in particular stood out, with levels significantly higher than the other nine samples. Researchers then tested the wrapper and concluded that most or all of the sample's contamination came from there.

"It's an indication that there's contamination in food packaging, and this could relate to more than just butter," said Sonya Lunder, senior analyst at the Environmental Working Group, a national nonprofit that seeks to limit chemical exposure in humans.

PBDEs have been used as flame retardants in foam products and electronics equipment.

Animal studies have linked ingestion of PBDEs with hormone changes in adult rodents and neurobehavior changes in young rodents. Health officials have not calculated safe ingestion limits for humans, but national health studies have detected its presence in their blood.

Researchers had thought the exposure route was breathing dust contaminated with PBDEs that migrated from couch cushions and televisions, for instance. Schecter said this study suggested another exposure route.

PBDEs - polybrominated diphenyl ethers - are fat-soluble, so are more likely to be found in foods rich in animal fats, such as dairy products and meats. They are persistent in the environment, and they tend to "bioaccumulate" as they progress through the food chain.