How Safe Are Microwaveable Plastics For That “Bun in the Oven”?

I love leftovers. Toss them in the microwave and voilà: a piping hot meal. I own scads of plastic containers for this express purpose, but I’m starting to wonder just how microwave-safe they really are. Many reusable plastic containers contain bisphenol-A (BPA), one of several chemicals called endocrine disruptors that may interfere with the body’s natural hormonal processes. Hormones control everything from when I get my period to the gender of any fetus I might someday carry, so it’s no huge surprise that BPA can mess with the reproductive system.

But what freaks me out the most is that scientists aren’t spending much time figuring out what BPA could do to me. That’s because they’re more worried that it could be a problem for my future children. Or maybe even my grandkids.

In 2005 the Centers for Disease Control found BPA in the urine of 95% of 397 randomly sampled citizens, indicating that pretty much everyone’s exposed. Small wonder. BPA is everywhere: in the polycarbonate plastic of baby bottles and tableware; in the resin that lines most food cans and milk cartons; and in dental sealants, to name a few examples. Small amounts can leach from containers into our food – especially during heating. From there, they enter the bloodstream through our intestinal tract, allowing them free travel throughout the body, disrupting the normal function of glands and organs.

Researchers already knew that hormone-like chemicals in the environment affected the reproductive systems of wildlife, particularly in fish and amphibians. But it was a lab accident in 1998 that first showed how BPA might affect the next generation. Researchers at Case Western University were studying a condition where cells have the wrong number of chromosomes. They noticed an odd eightfold increase in the abnormality in eggs from their young female mice. Detective work revealed that a lab technician had washed the water bottles with an unusually strong detergent, causing them to degrade and BPA to leach into the mice’s drinking water. Follow-up research confirmed that the chromosomal abnormalities were related to low-level BPA exposure. These missteps in the genetic code, called aneuploidy, can result in Down’s syndrome and other genetic birth defects. In many cases they cause spontaneous abortion.

But even if I give birth to a child whose chromosomes are normal, she may not be out of the woods. In 2005, endocrinologists at Tufts University School of Medicine and Universidad Nacional del Litoral in Santa Fe, Argentina, found that female mice whose mothers had been exposed to low doses of BPA developed denser mammary glands when they hit puberty and that as adults they were more sensitive to estrogens from any source. Both characteristics are risk factors for breast cancer in women. And it’s not only our daughters we need to worry about: Male babies of exposed mice may produce less sperm when they reach adulthood.

My exposure to BPA might even affect my grandchildren. That’s because a woman’s eggs are created in her ovaries before she’s even born. So if I get pregnant with a little girl, all the cells she will need to create her own kids will be inside her while she’s still inside me. Last month, the Case Western University researchers reported that BPA exposure increased chromosomal abnormalities in the eggs of a mouse’s female pups before they were born.

Of course, nobody’s saying that what happens in mice will happen in humans. A 2006 report by the American Council on Science and Health argues that much of the evidence on BPA comes from experiments conducted on rodents or in test tubes and therefore holds little relevance for our complex human physiology. BPA levels have been correlated with ovarian cysts and miscarriages in Japanese women, but that doesn’t mean BPA was the cause. Waiting around to document the effects of our current exposures will literally take generations.

We do know that exposure to endocrine disruptors during pregnancy can devastate the reproductive capabilities of a child years after it’s born. From 1947–1971, many women were prescribed diethylstilbestrol (DES), a synthetic estrogen that was intended to prevent miscarriage. Although later studies showed that DES had no effect on the rates of miscarriage, they did show that daughters of women who took DES were more likely than their peers to develop rare vaginal and cervical cancers, have structural abnormalities such as fibrous ridges in the vagina and have trouble conceiving. Effects on DES sons are less clear-cut but might include noncancerous growths in their testicles and reproductive tract abnormalities. The National Cancer Institute is still studying the grandchildren of women who took DES, to figure out whether they are affected too.

Those doses of DES were much higher than the environmental levels of BPA we’re exposed to today. Despite the ubiquity of BPA, our exposure is probably only billionths of a gram per kilogram of our body weight. Most agencies say that research results aren’t consistent enough to confirm that BPA is harmful. In 2006, an expert panel concluded in the journal “Critical Reviews in Toxicology” that BPA posed no reproductive risk, and listed hundreds of studies showing no effect of the chemical on a diverse collection of outcomes. The E.U. Scientific Committee on Toxicity, Ecotoxicity and the Environment, and Japanese regulators have also concluded that there is not enough evidence to regulate. While the U.S. National Toxicology Program is working on a new assessment, California, Maryland and Minnesota have considered and rejected a ban on BPA. A San Francisco ordinance banning the manufacture, sale or distribution of baby-related items containing BPA was supposed to go into effect last month, but is being held up by a court challenge from a coalition including area retailers, toy manufacturers, and the American Chemicals Council.

Even if regulators are right, the plastics industry’s behavior gives me the willies. One industry-funded study reported no negative effects in BPA-exposed mice, but declined to tell readers that their control animals, mice exposed to DES, weren’t affected either. This effectively means that their experimental setup was flawed, since they weren’t able to measure effects where scientists are certain they exist. In 2001 the U.S. National Toxicology Program pointed to an industry-funded study that noted no major differences between their experimental and control animals – and to another that reported nonsignificant results which were later found to be significant when reanalyzed. A 2004 report by the Harvard Center for Risk Assessment and funded by the American Plastics Council concluded that there wasn’t enough evidence to show that BPA was harmful. The same study was later criticized by one of its own investigators for not including all the available research.

It all sounds a bit “Children of Men”-esque, but if BPA and other endocrine disruptors are screwing with our eggs, the most probable outcome is that they just won’t be viable. Infertility rates have been on the rise recently, and a 2005 report from the Centers for Disease Control identified women under 25 as the fastest-growing segment of the U.S. population with fertility woes. Perfectly plausible theories about the advancing age of new mothers and the higher numbers of obese women in our population account for some of the phenomenon, but 10% of all infertility is still medically unexplained.

At 30 years old, I’m one of those confused young modern women trying to get my career off the ground while a nagging fear says I should hurry up and have kids before my ovaries turn into raisins. Bringing leftovers to work and carrying around a reusable water bottle always made me feel like a thrifty, eco-friendly, health-aware modern gal. The possibility that I might struggle to conceive because of it is unsettling, no matter how uncertain the evidence.