New research on bisphenol A suggests that people are being exposed to the estrogen-mimicking chemical from a number of sources and not just food, as is commonly thought.
Scientists think there may be other sources because they have found unexpectedly high levels of the compound, used in the making of plastic, in people who have been fasting. This has led to speculation that people may be absorbing the chemical from such seemingly innocuous items as polyvinyl chloride (PVC) water pipes and carbonless cash-register receipts.
The research, published this week in the journal Environmental Health Perspectives, has major implications because regulators, including Health Canada, have assumed that almost all human exposure to bisphenol A (BPA) is the result of residue inadvertently ingested from food and beverage packaging.
This assumption may be wrong.
"If you look at populations of people, by 15 to 20 hours [of fasting] it should be practically gone, and it's not," says Richard Stahlhut, a postdoctoral fellow at the University of Rochester Medical Center in New York, who led the research team that announced the finding. "These high levels probably point to another source, and not a trivial source."
BPA from food is rapidly broken down by the liver into a biologically harmless form. Its half-life is about five hours, meaning that 50 per cent is metabolized in each time period of that length. But the researchers found that a group of people who fasted longer than 8.5 hours continued to have elevated amounts of BPA in their urine.
The amounts of the synthetic chemical were extremely small - typically in parts per billion - but estrogen is active at levels in parts per trillion, a thousand times less.
Dr. Stahlhut said another possible explanation is that people are accumulating BPA in their body fat, and during fasting the chemical is released. It is also possible that there is some combination of exposure from non-food items and releases from fat, he said.
Regardless of the source, Dr. Stahlhut says, people are being exposed to more BPA and for longer time periods than is commonly thought.
Health Canada said it will review the findings "and will take further action to protect Canadians' health if necessary."
Scientists have been studying BPA because it resembles estrogen, giving those who are exposed to it an extra amount of the female hormone. Studies have linked it to such conditions as breast cancer, heart disease and diabetes.
Last year, Health Canada said it would place BPA on the country's toxic substances list and ban its use in baby bottles, based on concerns that infants might be ingesting too much. The agency concluded that adults were at no risk, but estimated that about 90 per cent of exposure was from food.
Traces of BPA get into food because it is used to line tin cans and metal lids on glass jars.
Despite BPA's short half-life, surveys have found that almost everyone carries the chemical, a man-made substance not found in nature. The new research was based on a review conducted by the U.S. government in 2003 and 2004 that found 93 per cent of people tested had detectible amounts.
The data covered more than 1,400 people, who were asked not to eat for varying amounts of time before their urine was analyzed (they were allowed to drink fluids).
The industry group representing BPA makers played down the new research. "The conclusions and the implications that the authors present are speculative at best," said Steve Hentges, a spokesman for the American Chemistry Council.
Other researchers say the new finding is significant.
"This study profoundly challenges the assumptions of regulatory agencies about how we're exposed to bisphenol A," said Frederick vom Saal, a biology professor at the University of Missouri.
He speculated the BPA may be coming from products such as PVC water pipes. People may absorb it by drinking water or by breathing in water vapour while showering.
Dr. vom Saal has also tested carbonless paper and found BPA in it, too.
He said touching items such as cash-register and credit-card receipts may lead to some BPA being absorbed through the skin in much the same fashion as an estrogen patch delivers a dose of hormone.
He called on governments to reduce uncertainty over where the BPA in people originates by requiring companies to disclose whether the chemical is in their products.