Jan. 30, 2008 -- Pouring boiling liquid into reusable water bottles or baby bottles made of polycarbonate plastic causes a much faster release of the estrogen-mimicking chemical bisphenol A, new research shows.
University of Cincinnati researchers reported that exposure to boiling water caused polycarbonate drinking bottles to release bisphenol A (BPA) up to 55 times more rapidly than exposure to cool or temperate water.
The jury is still out on whether BPA exposure poses a health risk to humans, even though the question was the subject of two expert panel reviews in the U.S. last year.
More than 6 billion pounds of bisphenol A are produced and used each year in the manufacture of the resins used to line food cans and in polycarbonate products. Almost everyone has measurable amounts of the man-made chemical in their blood, the CDC says.
It has long been known that BPA can cause genetic damage in lab animals, but it is not clear if the levels of leached BPA from polycarbonate bottles and other products are high enough to pose a threat to humans.
BPA at High Temperatures
Scott M. Belcher, PhD, who led the study team, tells WebMD that while there is little direct evidence that BPA poses a risk to humans, many experts believe that it does.
"The consensus of the scientific community is that there is a clear reason to proceed cautiously," he says.
But Steven G. Hentges, PhD, who is executive director of the American Chemical Council's Polycarbonate/BPA Global Group, disagrees.
Hentges tells WebMD that the finding that BPA leaching accelerates at high liquid temperatures is nothing new, having been reported in numerous previous studies.
"The bisphenol A levels seen under heating conditions are still extraordinarily low and far below levels that have been determined to be safe by government bodies," he says.
The popularity of reusable, plastic polycarbonate drinking bottles has grown with rising concerns about the environmental impact of disposable plastic bottles.
Plastic water and soda bottles manufactured for one-time use are not made with polycarbonate plastic. But many baby bottles and those hard water bottles sold in outdoor and athletic stores are.
Same Levels in New and Old Bottles
Belcher collected used polycarbonate water bottles from his local climbing gym and purchased new ones from a nearby outdoor activities store.
All the bottles were subjected to seven days of testing designed to simulate normal use during backpacking and camping conditions.
Whether they were new or used, the bottles released the same average amount of bisphenol A at the same rate when exposed to cool or temperate water.
"There is some thinking that the longer a bottle is used the more BPA it releases, but that isn't what we found," Belcher says.
But much higher levels of bisphenol A were released when the bottles were briefly exposed to boiling water. The rate of release after exposure to boiling water ranged from 8 to 32 nanograms per hour, compared with a range of 0.2 to 0.8 nanograms per hour under room-temperature conditions.
And the speed of release was 15 to 55 times faster, Belcher says.
He adds that the findings have made him reassess his own habits.
"I don't put hot tea or hot water in these bottles when I'm climbing anymore," he says. "And I have retired my polycarbonate French-press coffeemaker."
What the Experts Say
The two expert panels that recently weighed in on the safety of bisphenol A reached different conclusions.
The National Toxicology Program's Center for the Evaluation of Risks to Human Reproduction (CERHR) convened a 12-member panel made up of government and non-government scientists to review the scientific evidence.
The group concluded that bisphenol A exposure levels for most Americans were well within the Environmental Protection Agency's standards and found no major health risks associated with exposure.
The panel did express "some concern" that the chemical could cause behavioral and neurological problems in developing fetuses and young children, however.
Another panel made up of 38 researchers who have studied BPA concluded that levels of the chemical seen in humans are higher than those that caused adverse effects in animal studies.
The group also expressed confidence that even low doses of BPA can have biological effects.
Belcher, who served on the latter panel, says the group concluded that there was good reason for concern that bisphenol A can cause harm to humans at routine exposure levels.
Hentges says the panel was far from objective and their findings contradict those of other experts around the world.
"The very extensive research that has been done supports the safety of bisphenol A," he says. "That is the consensus of experts worldwide who have no stake in this."