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By now, many environmentally conscious consumers are wary of bisphenol A, a chemical in food containers, plastic bottles and other household items.

A California state agency is wary, too, and will soon decide whether to call the compound a reproductive toxicant and place restrictions on it. In 2009, when it last took up the matter, a panel of experts said there wasn’t enough evidence.

Since then, a flurry of research in the Bay Area and across the nation has made deeper inroads into understanding the role that BPA may play in cardiovascular disease, neurodevelopment, infertility and other health conditions.

Scientists still don’t entirely understand BPA, which is believed to be an endocrine disruptor that mimics the hormone estrogen. But dozens of studies published in the last three or so years have brightened the spotlight on a chemical that scientists estimate exists in the bodies of 90 percent of the U.S. population.

“There’s a ton of new science that has come out that further supports BPA’s being a reproductive and developmental toxicant,” said Dr. Sarah Janssen, a senior scientist at the Natural Resources Defense Council, an advocacy group in San Francisco.

Chemical warnings

The group has petitioned California’s Environmental Protection Agency to add BPA to the state’s annual list of suspect chemicals under the consumer-safety law Proposition 65.

BPA leaches out of hard plastics, the linings of canned food and beverages, sales receipts and dental sealants. If it makes the list, manufacturers would be required by law to put warning labels on potentially hundreds of products that contain hazardous levels of BPA. Manufacturers that ignore the law could be hit with a flurry of lawsuits.

Chemical industry representatives, who are concerned that manufacturers will stop using BPA, sued the state last month in an attempt to keep the compound off the list. The American Chemistry Council, which did not return a request for comment for this story, argued in the lawsuit that the research cited by state regulators does not prove BPA poses serious health risks.

The U.S. Food and Drug Administration has expressed some concerns about the potential health risks of BPA, but believes that very low levels of exposure through food and drink are safe for humans.

A growing number of scientists have cast doubt on the idea that BPA is safe. Much of their work has been driven by the National Institute of Environmental Health Sciences, which has poured $30 million into BPA research since 2009.

Scientists involved in many of the 140 studies published so far have taken small steps toward understanding BPA’s effects on animals, with the intent of someday testing their findings on humans.

In a preliminary experiment on mice, researchers at the University of Missouri at Columbia raised the question of whether BPA can harm cognitive skills needed for reproduction.

The scientists fed female mice food laced with BPA or ethinyl estradiol, a synthetic estrogen similar to BPA. Their male offspring, compared with a control group, were significantly less willing or unable to widely explore and navigate through mazes – skills that males need to search for mates.

While scientists have tried to study BPA’s effects in people, they have found it difficult to prove conclusively that the chemical is harmful to health.

In the United Kingdom, for example, 760 initially healthy adults who had relatively high BPA concentrations in their urine ended up developing heart disease over a span of 10 years. But in a 2012 study, the researchers admitted they couldn’t be certain that BPA itself was responsible for triggering the disease.

In the Bay Area, scientists have mostly focused on BPA’s potential to harm people’s reproductive systems.

“There’s always room for doubt, as a scientist,” said Dr. Victor Y. Fujimoto, a professor of obstetrics and gynecology and reproductive sciences at UCSF. “But the evidence is mounting that BPA may very well be a reproductive toxin.”

Reproductive damage

Fujimoto’s research suggests that BPA may decrease chances of conception through in vitro fertilization. In 2011, he found that women with relatively high levels of BPA at the time of egg retrieval had lower fertilization rates.

Another study of women undergoing in vitro fertilization found that those with high levels of BPA produced less estrogen in response to fertility drugs they were taking than women with lower levels of the chemical. A balanced level of estrogen is essential for a woman seeking to get pregnant, and too much or too little can get in the way of the process.

Yet another study revealed troubling news for men with high levels of BPA. When their sperm were joined with their partner’s eggs during in vitro fertilization, the resulting embryos seemed to develop at a much slower rate than expected, Fujimoto said. He cautioned that the results were preliminary and based on a small sample of 27 couples.

“We’ve only begun to scratch the surface,” he said.

A UC Berkeley study in October concluded that BPA may alter thyroid hormones in pregnant women and newborn boys. The health effects were unclear, but the authors called the changes potentially alarming because thyroid hormones guide pre- and postnatal growth and brain development.

High levels of BPA have also been linked to decreased sexual function in men, decreased sperm count and vitality, and decreased birth weight in offspring.

“The bottom line is, we find that male workers who are exposed to high BPA, their sexual dysfunction risk is much higher … compared to male workers who were not exposed to BPA,” said Dr. De-Kun Li, a senior research scientist who has conducted a series of studies on the subject at Kaiser Permanente’s Division of Research in Oakland.

BPA may even alter boys’ genital development, Li and colleagues suggested in a 2011 study. They found that Chinese factory workers who were exposed to BPA at work during the time of pregnancy or conception gave birth to sons who had a shorter than expected distance between their genitals and anus. The study was based on 153 young boys.

Public health issue

Li recalls that when he started studying BPA in the mid-2000s, few studies on the subject involved humans. Now there are many more, and Li said they’ve compelled him to recommend that consumers avoid BPA whenever possible.

“If some chemicals (affect) only very small segments, the issue can wait. It may not be a big deal. People can wait a little longer for more evidence to be accumulated,” he said. But “if a large segment of the population is exposed, that potential for a public health disaster is much bigger.”

About the author

Stephanie M. Lee is a San Francisco Chronicle staff writer.