Products marketed for infants or billed as "microwave safe" release toxic doses of the chemical bisphenol A when heated, an analysis by the Journal Sentinel has found.

The newspaper had the containers of 10 items tested in a lab - products that were heated in a microwave or conventional oven. Bisphenol A, or BPA, was found to be leaching from all of them.

The amounts detected were at levels that scientists have found cause neurological and developmental damage in laboratory animals. The problems include genital defects, behavioral changes and abnormal development of mammary glands. The changes to the mammary glands were identical to those observed in women at higher risk for breast cancer.

The newspaper's test results raise new questions about the chemical and the safety of an entire inventory of plastic products labeled as "microwave safe." BPA is a key ingredient in common household plastics, including baby bottles and storage containers. It has been found in 93% of Americans tested.

The newspaper tests also revealed that BPA, commonly thought to be found only in hard, clear plastic and in the lining of metal food cans, is present in frozen food trays, microwaveable soup containers and plastic baby food packaging.

Food companies advise parents worried about BPA to avoid microwaving food in plastic containers, especially those with the recycling No. 7 stamped on the bottom.

But the Journal Sentinel's testing found BPA leaching from containers with different recycling numbers, including Nos. 1, 2 and 5.

"There is no such thing as safe microwaveable plastic," said Frederick vom Saal, a University of Missouri researcher who oversaw the newspaper's testing.

The American Chemistry Council disputed the findings, saying publishing the results amounts to a "serious disservice by drawing a conclusion about product safety that simply cannot be drawn from either this study or the overall body of scientific research."

Food company officials say the doses detected in the tests are so low that they are insignificant to human health.

"These levels are EXTREMELY low," wrote John Faulkner, director of brand communications for Campbell Soup Co. Tests of the company's Just Heat & Enjoy tomato soup showed its container leached some of the lowest levels of BPA found. "In fact, you might just be able to find similar levels in plain old tap water due to 'background' levels. We are talking 40 to 60 parts per trillion (ppt). What is 40 to 60 ppt? 40 to 60 seconds in 32,000 years!"

But the Journal Sentinel identified several peer-reviewed studies that found harm to animals at levels similar to those detected in the newspaper's tests - in some cases, as low as 25 parts per trillion. Scientists with an expertise in BPA say the findings are cause for concern, especially considering how vulnerable a baby's development is and how even tiny amounts of BPA can trigger cell damage.

Harm done during this critical window of development is irreparable and can be devastating, they say.

"This is stuff that shouldn't be in our babies' and infants' bodies," said Patricia Hunt, a professor at Washington State University who pioneered studies linking BPA to cancer.

Scientists say BPA and other chemicals that disrupt the endocrine system do not act like other toxins that become more potent as their doses increase. BPA behaves like a hormone. It mimics estrogen with effects that are ultra-potent. Even tiny amounts can trigger cell change.

Nira Ben-Jonathan, a professor at the University of Cincinnati whose studies found that BPA interferes with chemotherapy, said the chemical's effects might not be immediately obvious, but can be devastating over time.

"They used to say DDT was safe, too," Ben-Jonathan said.

The Journal Sentinel's tests were done to determine the prevalence of BPA in a typical modern diet for babies and small children.

Based on the test results, the newspaper then estimated the amount of BPA a child might consume and compared it with low-dose amounts of BPA used by researchers in animal studies.

In what is believed to be the first analysis of its kind by a newspaper, the Journal Sentinel found that an average 1-month-old girl is exposed to the same amount of BPA that caused mammary gland changes in mice. Those same changes in humans can lead to breast cancer.

Unregulated labels

The label "microwave safe" is stamped on thousands of products sold across the country. But that is not an official designation regulated by the government.

Companies are able to place it on their products without any official testing by the Food and Drug Administration.

BPA makes its way into food from plastic packaging when those containers are heated.

In the Journal Sentinel's tests, the highest amounts of leaching were found in two items: a can of Enfamil liquid infant formula and a Rubbermaid plastic food-storage container. The lowest levels, trace amounts, were found to be leaching from disposable frozen-food containers.

Hunt, the Washington State University scientist, called the levels found leaching from the plastic food-storage containers "real doozies."

It is likely that the newspaper's tests underestimated the amounts of BPA that normally would be leaching from reusable products, BPA experts say. All products the newspaper had tested were new. Studies show that as products age and are repeatedly heated and washed, they are more likely to leach higher amounts of BPA.

"You can't see this happening," vom Saal said. "You can't taste it, you can't smell it, but you are getting dosed at a higher and higher amount."

Also, testers did not examine the food in those containers for BPA levels. They replaced food with a mixture of water and alcohol, a standard laboratory practice that makes measuring easier and more accurate. But that also eliminates other variables that are in the food, such as fats and acids that are more likely to encourage BPA to leach.

BPA's effects also can be magnified by other chemicals in the plastic. This has been proved in one experiment after another, said vom Saal, who has become a vocal critic of the chemical industry. While BPA is potentially dangerous to all humans, scientists are especially concerned about how the chemical affects fetuses and newborns, whose systems are not developed. Babies up to age 12 months or so can't metabolize BPA as efficiently as adults.

But no one is more exposed to BPA than a newborn. A newborn's small size means that he or she gets a more concentrated dose of the chemical. Many products that contain BPA - such as baby bottles, infant formula, some pacifiers and toys - are marketed for mothers and newborns.

Exposure for babies can be exaggerated by the fact that many have diets exclusively made up of liquid baby formula from cans lined with BPA.

Babies who drink liquid formula from bottles made with BPA are effectively getting a super-dose of the chemical, said Hunt, the Washington State University scientist.

The U.S. surgeon general has advised that breast milk is the healthiest food for newborns, though BPA has been found in breast milk, too.

Less than one-third of babies are breastfed until they are 3 months old, and just one in 10 is exclusively breastfed to 6 months, a 2004 study by the U.S. Centers for Disease Control and Prevention found.

Gail McCarver, a physician at the Medical College of Wisconsin who led the National Toxicology Program's investigation of BPA earlier this year, declined to be interviewed for this article.

But McCarver said at an FDA hearing in September that she is particularly concerned about premature babies who are exposed to plastic tubing in hospitals.

The government should be protecting the smallest, most vulnerable baby, not just the average child, she said. Four million babies are born in the United States each year, and roughly 500,000 are born prematurely.

Christina Deppoleto, 36, of Hartland says she does her best to protect her 18-month-old son, Carson. Deppoleto, interviewed recently at the Milwaukee County Zoo, said she was troubled to hear about the newspaper's test results - especially findings that showed BPA to be leaching from "microwave safe" containers.

"I try to be a good consumer and a good parent," she said. "But you have to be able to trust the labels."

Reviewing scientific studies

The newspaper examined all the published literature on BPA spanning two decades. A total of 21 studies have looked at effects on mammals at doses that were similar to the amounts found leaching from the products. All but four concluded that BPA caused damage to animals.

In one 2006 study, pregnant mice were exposed to BPA from the eighth day of pregnancy to the 16th, a period critical for the development of neurons that regulate sexual behavior.

Scientists found the female offspring had fewer such neurons than usual. Their activity levels dropped and mirrored that of their brothers.

In another experiment, newborn mice were fed BPA at doses common in human diets. They were found to have changes in the patterns of their mammary glands at the time of puberty. They had more ducts and duct extensions, more developed fat areas and additional cell changes associated with a more mature gland. The consequences of this early alteration in breast tissue development are likely to increase vulnerability to breast cancer later in life, the scientists found.

Animals tested were fed BPA through pumps under the skin that regularly administered the chemical. Some critics say that method exaggerates the chemical's effects. But others say it is an acceptable method because newborns are constantly feeding.

Scientists also add that the Journal Sentinel analysis of how much BPA a baby might ingest is just a small window into a child's typical day of exposure.

Studies have shown the chemical can be absorbed through the skin. And babies also put items other than food in their mouths, including pacifiers and toys that might contain the chemical.

The findings have disturbed and angered parents and consumer advocates who say the government needs to do a better job of protecting people from potentially harmful chemicals.

"The safety of this compound is in major question, and our government is not taking steps to address this," said Urvashi Rangan, senior analyst for Consumers Union, a watchdog group that regularly tests products. "Consumers shouldn't have to be the guinea pigs here."

Canada has declared BPA a toxin and is moving to ban it from baby bottles, infant formula and other children's products. But U.S. regulators have been conflicted.

The National Toxicology Program has expressed concern about the chemical for fetuses, newborns and young children. But the FDA has declared it to be safe. That assessment, however, was found to be flawed, and the FDA since has reopened its examination.

The conflict has further heightened consumer anxiety about how much BPA, if any, is safe.

Bradley Kirschner, a pediatrician at Children's Hospital of Wisconsin and the father of three young girls, said his patients are increasingly concerned about the chemical.

"If an entire country is banning it, that makes it hard to ignore," he said.

Parents are confused, he said. And he is not certain how to advise them.

"If you ask, 'Should a baby sleep on his back?' I can tell you what to do," he said. "But this is muddy."

Kirschner said he would like a more definitive answer from U.S. regulators about whether BPA is safe.

Increasingly, consumer groups are calling for BPA to be banned. Last month, the consumer watchdog Environmental Working Group sent letters to infant formula makers, asking them to stop packaging their products in containers made with BPA.

The attorneys general in New Jersey, Connecticut and Delaware sent letters to 11 companies that make baby bottles and baby formula containers, asking that they voluntarily stop using BPA.

Six U.S. senators have called for a federal ban on the chemical, and more than 35 lawsuits have been filed in recent years against companies using BPA, claiming the chemical has caused physical harm.

Companies are beginning to proactively back away from BPA. In April, after Canada's announcement of a ban, several corporations said they would stop producing and selling certain products made with BPA. The companies and retailers include Nalgene, Wal-Mart, Toys "R" Us, Playtex and CVS pharmacies.

But plenty of products designed for heating food still contain BPA.

Many companies that use BPA now include safety information about the chemical on their Web sites. But those sites maintain that BPA is safe at low doses. Their claims are based largely on studies that were paid for by the chemical industry.

Jackie Chesney, a grandmother from Spring Grove, Ill., said she assumes a certain level of safety in products that are allowed to be sold.

"You should think the things you are using would be safe," Chesney said as she strolled through the Milwaukee County Zoo with her daughter and grandchildren.

Chesney said things have changed a lot since her children were small. There is so much more plastic these days, and food is more likely to be individually wrapped, she said.

The proliferation of plastic worries her.

"Yes, it's handy and convenient," she said. "But at what cost?"