European officials recently took another step in the difficult process of regulating - and potentially banning - endocrine-disrupting chemicals, a growing concern because of links to health problems including infertility, birth defects, diabetes and cancer.

In June, the European Commission, the executive arm of the European Union, presented the world's first legal framework for scientific criteria to classify the chemicals.

Rebecca Simmons, deputy director of the Center of Excellence in Environmental Toxicology at the University of Pennsylvania and attending neonatologist at Children's Hospital of Philadelphia, spoke to us recently about these chemicals.

She and another Penn research scientist and professor, Marisa Bartolomei, have worked together for several years on a project involving one endocrine disruptor, in particular, bisphenol A, or BPA, used in plastics and many other everyday products.

What is the endocrine system, and what are endocrine-disrupting chemicals?
The endocrine system is made up of many organs that control aspects of our body function and physiology. One of the major endocrine systems is reproduction. Another obviously very important one is the thyroid hormone system, which regulates many aspects of neurological function, cardiac function and metabolic function.

Endocrine-disrupting chemicals can interfere with this system. Examples of reproductive effects are problems like endometriosis and decreased fertility. These chemicals also can affect neurological systems and have adverse effects on the immune system. Lastly, they're linked to increased incidence of breast cancer and prostate cancer. They're not good.

What are specific examples of some of the most worrisome ones?
A historical example is DES - diethylstilbestrol - that women took to prevent miscarriages. That was one of the best-studied endocrine-disrupting chemicals years ago. It caused rare forms of vaginal cancers in both some of the women taking it and their offspring. It also impaired the development of reproductive systems in the offspring. It is no longer in use.

Another example is DDT, which has been banned in the United States.

Now, it's hard to say which of these chemicals are the worst. We are exposed to so many endocrine disruptors. Many of us are most worried about something called polychlorinated biphenyls, PCBs, which have been linked to cancers. Probably the most common use was in piping in buildings. PCBs have been banned in Europe, and there are many states in the U.S. that have banned them. So production has decreased dramatically. But they have a very long half-life.

There are a whole lot of other ones that haven't been banned, and they are found in many everyday products. They include plasticizers (chemicals added to plastics to make them more flexible), pesticides and flame retardants. People are exposed to them because they're eating out of a tin can or microwaving in plastic dishes, because they are kids wearing pajamas, women putting on lipstick, and people spraying their back yard with pesticides. We still produce several billion pounds of endocrine-disrupting chemicals every year.

BPA has been a focus because it's so ubiquitous. Although it is banned for use in baby bottles, it is found in plastic bottles, the lining of metal food cans, some detergents, dental sealants and cash register receipts. If you had your urine tested, you'd find BPA in it.

Is there evidence that we are actually being harmed?
The evidence is strong, but it's circumstantial. Say you take a population, and of all the people that are obese, a significant number had higher-than-normal levels of BPA in their urine. It doesn't mean that BPA caused it. But it's obviously worrisome enough that Europe has banned it.

I think that the data are unequivocal that endocrine-disrupting chemicals cause problems in animals. We see fish in rivers with high levels of endocrine-disrupting chemicals, and the fish are abnormal in terms of their reproductive tracts. Those sorts of animal studies, combined with epidemiology studies, make us very worried.

Why is it important to watch what Europe is doing?
Certainly, the European action could provide a blueprint for similar action in the U.S. It's also important because so many countries with diverse populations and diverse economies feel that there is strong evidence that these chemicals are harmful to human health and potentially have implications for the next generation.

There were a number of studies in Europe, many funded by the European Union. They were done in many countries with large numbers of subjects. They measured levels of a variety of endocrine-disrupting chemicals in urine and blood, and then they looked at different outcomes, such as breast cancer, prostate cancer. They looked at people's weight gain and body-mass index. Those conditions were linked to much higher levels of a variety of endocrine-disrupting chemicals. Coupled with animal studies, these results strongly suggest that there's a link with a number of adverse outcomes.

The European Commission, using those data, took note of that. They now want to ban some of these chemicals.

Tell us about your own research.
We are looking at the transgenerational effects of endocrine disruptors on metabolic outcomes - on the development of obesity and type 2 diabetes.

We use an animal model of BPA exposure and give female mice BPA in very low doses - doses that achieve levels that are observed in humans - prior to pregnancy and during pregnancy. We only expose the mom. We make sure the offspring have no BPA in their food, cages or water.

Then we look at the offspring. We look at their weight and their body-mass index, and we determine whether or not they develop the mouse equivalent of diabetes. So far, we know that the effects persist into the second generation - the grandchildren. Next, we want to look at whether it persists into the great-grandchildren, the third generation.

If it goes away after the second generation, that's reassuring. It means that once we ban these chemicals and they are finally out of our environment, the effects won't persist.

Many of these products are helpful to us as a society. Dental sealants - those are useful. Pesticides - we do need some pesticides. But when you get rid of one endocrine disruptor, sometimes the chemical companies produce something that may be just as bad. Raising awareness of endocrine disruptors is really important, because we hope it will force chemical companies to test new products to determine whether or not they have endocrine-disrupting properties.