If you look into the hidden dangers of BPA-lined aluminum cans, you will probably come to believe it safer to drink from non-BPA-containing plastic bottles, or, preferably, glass bottles. You may even come to reject *any* food that has been packaged in a BPA-lined can:

Bisphenol A is ingested by practically everyone who eats canned foods or drinks from a can or hard plastic water bottles.

Now a controversy is raging over the safety of widespread public exposure to the chemical, which is known to act like a synthetic female sex hormone. At the heart of the intense debate over bisphenol A is that it challenges the main tenet of modern toxicology, the idea that the dose makes the poison. Under this principle, a two-pack-a-day smoker is more at risk of cancer than a one-pack-a-day user, and the belief that rising doses make a substance more dangerous is the basis of all government regulations that seek to set safe exposures for harmful chemicals.

It seems obvious that a high dose of a poison would be more dangerous than a lower one, but bisphenol A is creating a stir because it doesn't follow this seemingly common-sense rule. Researchers say this oddity results from the fact that bisphenol A isn't a conventional harmful agent, such as cigarette smoke, but behaves in the unconventional way typical of hormones, where even vanishingly small exposures can be harmful. This is why some environmentalists and scientists contend that bisphenol A, which leaches in trace amounts from food and beverage packaging, is among the scariest manufactured substances in use.

Extrapolating from the results of animal experiments, they suspect bisphenol A has its fingerprints all over the unexplained human health trends emerging in recent decades hinting at something going haywire with sex hormones, including the early onset of puberty, declining sperm counts, and the huge increase in breast and prostate cancer, among other ailments.

Some researchers with close-up views of bisphenol A are so shocked by its ability to skew development in their laboratory animals, even at among the lowest doses ever used in experiments, they aren't waiting for the government to ban it. In their personal lives, they can't run away from products containing it fast enough. "I would love to see it banished off the face of the Earth," Dr. Patricia Hunt, a Washington State University geneticist, said.

She began ditching her bisphenol-A-containing products after discovering that mere traces of the chemical were able to scramble the eggs of her lab mice. In humans, similar damage would lead to miscarriages and birth defects, such as Down syndrome. "I thought, 'Oh my God,' " she said. "I'm going to throw out every piece of plastic in my kitchen."

Although it has been known, since a search for estrogenic drugs in the 1930s, to act like a sex hormone, bisphenol A has recently emerged as one extremely odd compound, perhaps the most unusual in widespread use. Research has found that it seems to turn modern toxicology on its head by being more dangerous at very low exposures than at high ones, a finding that is focusing attention on the possible health repercussions of the relatively small amounts leaching from consumer products.

Bisphenol A also has a bizarre pattern of research results, with the funding source of a study the best predictor of whether scientists find it harmful or safe. All major industry studies into bisphenol A's safety, and they number about a dozen, haven't found anything worrisome in low-dose exposures. However, about 90 per cent of studies by independent researchers over the past decade, numbering about 150, have found adverse effects, ranging from enlarged prostates to abnormal breast tissue growth.

Bisphenol A has been used in increasing amounts since the 1950s in food and beverage containers because it doesn't impart a plastic-like taste, although traces leach out. Plastics that use it are often identified by an industry triangle symbol and the number seven.

"At low doses hormones stimulate their own receptors," said Frederick vom Saal, a University of Missouri biologist and leading academic expert on bisphenol A. "At higher doses, they inhibit their responses."

Within the plastics industry, the idea that small amounts of bisphenol A are dangerous, perhaps more worrisome than larger amounts, isn't dismissed outright, but viewed as a something still at the stage of a hypothesis in need of further proof to be validated, Mr. Hentges said.

But Dr. vom Saal, pointing to the many studies finding harm, said the industry's position "is really stunning because you have this huge independent scientific literature showing adverse effects at stunningly low doses." Low doses come into play because hormones are active at minute, parts per trillion concentrations. (A part per trillion is the scientific equivalent of practically nothing, roughly equal to a grain of salt in a large swimming pool.) Surveys of how much bisphenol A comes out of cans and bottles into food have found parts per billion amounts, raising concerns that diet could cause exposures similar to natural hormone levels.

Like many scientists who've found health impacts from bisphenol A, Dr. vom Saal is personally so nervous about its safety that he doesn't eat canned food or use polycarbonate beverage containers any more. "We've done everything possible to try to limit our exposure to this," he said.

Dr. vom Saal helped make one of the earliest discoveries about low doses of bisphenol A, finding in 1997 that traces fed to mice caused a 30-per-cent increase in prostate size.

He's also tried to figure out why industry studies don't find the results that seem so readily apparent in the laboratories of academic scientists.

Dr. vom Saal contends that many industry experiments are flawed. In one case, he says a study funded by the plastics council and including researchers from GE, Dow, and Bayer, found no effects from low doses of bisphenol A, but used a strain of rats he says are hundreds of times less sensitive

to estrogenic drugs than humans.

Also check out:

www.newstarget.com/022548.html