A new study indicates that bisphenol A (BPA), a chemical used in plastic bottles and can linings that has been linked to heart disease, diabetes and liver failure, may linger in the body far longer than previously believed.

Environmental health scientist Richard Stahlhut of the University of Rochester Medical Center and his colleagues discovered that even those who had been fasting for 24 hours still had high BPA levels in their urine, using a U.S. Centers for Disease Control and Prevention (CDC) survey of 1,469 adults.

Stahlhut says that it appears that the amount of BPA in the body drops relatively rapidly from four to nine hours after exposure, but then levels out. "After the nine hours or so," he says, "it stops doing what it's supposed to and the decline goes flat."

Previous research had suggested that levels of BPA, which mimics the female hormone estrogen in the human body, declined by 50 percent every five hours after it was ingested in foods or water it had leached into from plastic containers. But the new research indicates that the chemical declines initially but then sticks around, making it potentially more harmful.

"This suggests substantial nonfood exposure, accumulation in body tissues such as fat, or both," the researchers wrote in their paper released today by Environmental Health Perspectives.

That may explain why 93 percent of Americans carry BPA in their bodies, according to the CDC, or it could be that exposure is coming through different routes than food, such as the polyvinyl chloride (PVC) pipes often used for water lines in modern homes.

"It makes you wonder what percentage of [exposure] really is food. If half of it isn't food then we've underestimated [human] exposure by half. That might matter," Stahlhut says.

The U.S. National Institutes of Health's National Toxicology Program—a government program that coordinates federal studies of chemicals' adverse effects—warns that BPA exposure may lead to abnormal development in infants and the Canadian government last year banned its use in baby bottles. But the American Chemistry Council, U.S. Food and Drug Administration and the U.S. Environmental Protection Agency maintain that BPA is safe.

Some preliminary studies have shown that the chemical can persist in human fat tissue and trigger a drop in adiponectin, a hormone excreted by fat that helps control sugar levels in the blood. "This would be good news," Stahlhut says. "If BPA is part of this huge increase in obesity and diabetes, you should celebrate because, unlike PCBs, if we stop BPA exposure it will go away."

But the first step on that road will be figuring out exactly how BPA typically gets into the human body as well as how the body processes it—something scientists thought they already knew. "If I go to a diner and they serve me a Coke in a polycarbonate glass, I drink from it. But I don't mess with the stuff at home," Stahlhut says. "I've been in this long enough to know that we don't know anything."