Are synthetic chemicals irreversibly damaging future generations of men? New studies show that a host of common chemicals can negatively affect the sexual development of certain male animals by blocking androgens, or male sex hormones.

Experts from the Environmental Protection Agency (EPA) posited as early as the mid-1990s that synthetic chemicals -- human-made chemicals -- that have been introduced into the environment could disrupt the endocrine system and potentially impair male reproductive functions. Now, however, the federal agency has come out with more conclusive evidence in conjunction with the Chemical Industry Institute of Toxicology (CIIT). Both groups studied the effects of environmental synthetic chemicals on laboratory rats, and both have shown that the effects of these chemicals are much more insidious than was originally thought. The results, say both groups, have implications for human males.

Among other effects on laboratory animals, the EPA and the CIIT say that synthetic chemicals can act as "endocrine disruptors." The endocrine system consists of glands and hormones that guide the development, growth, reproduction, and behavior of human beings and most other animals. For instance, some of the disruptors mimic the female sex hormone estrogen, which can interfere with normal male hormonal development.

"We have found that some [synthetic chemicals] do block the action of male hormones in fetuses [of laboratory rats] so that some of them look like females," says Dr. Earl Gray, an androgen toxicologist with the EPA who has co-authored several studies on the subject. Sometimes the effects have been alarming. "We have seen males with undeveloped testicles and malformed penises," explains Dr. Gray, "and some have even been born with a vaginal pouch."

The critical window of vulnerability for young male animals appears to range from before birth to puberty, according to the studies. Dr. Gray has identified about ten antiandrogen chemicals that critically impair reproductive function. "We haven't defined the whole universe yet, but the list of chemicals keeps growing," he explains.

More research on the way

The U.S. government recently initiated a couple of projects to learn more about how common synthetic chemical products disrupt the endocrine system. The National Institutes of Health and the Centers for Disease Control and Prevention are collaborating on a project to improve human exposure assessment to environmental endocrine disruptors, while the EPA has also been given the authority to test protocols that would screen for endocrine effects.

"We will start off with a lot of chemicals -- 87,000 -- but only a small fraction of them will be screened and tested," said Gary E. Timm, senior technical advisor for the Office of Science Coordination and Policy at the EPA. "That's because a lot of the chemicals are produced at low volumes or aren't produced anymore. Others are used to make another substance and therefore result in low exposures, and some are polymers, which means the molecules are too large to get into the [human] system."

The EPA policy on endocrine disruptors is still evolving, but the agency has already taken regulatory action in regard to some chemicals. Familiar problem chemicals that have already been banned include PCBs and, of course, DDT. The agency notes that in the future, organochlorine pesticides (compounds that include chlorine) will be among the first to be screened.

What to look out for

A few of the more dangerous chemicals listed by Dr. Gray and in the CIIT study are commonly found in household or garden products. When shopping for such products, avoid those containing the chemicals listed below, which are suspected to act as endocrine disruptors and may soon be regulated or restricted by the EPA:

In addition, avoid contact with the following chemicals that are also suspected endocrine disruptors:

The long-term effects of such chemicals are not yet known, but the recent lab studies at the EPA and the CIIT suggest using caution. In addition to results from controlled studies, EPA researchers have long observed wildlife in ecosystems that have been contaminated by synthetic chemicals. They have found that the wildlife populations in such ecosystems exhibit a variety of reproductive alterations, including sex reversal in fish and egg shell thinning among eagles. Although scientists say conclusions about the impact of endocrine disrupters on human health can't yet be drawn from wildlife studies, they stress that there is reason for concern.

EPA experts on wildlife have concluded that "many compounds introduced into the environment by human activity are capable of disrupting the endocrine system of animals, including fish, wildlife, and humans. The consequence of such disruption can be profound because of the crucial role hormones play in controlling [growth and sexual] development."

Are men at risk?

"The American public would be wise to reduce their exposure to these chemicals," warns Paul Foster, a phthalate toxicologist at the CIIT who conducts research on endocrine disruptors and their relationship to masculinity. "We have dramatically increased our production, use, and distribution of a large number of chemicals. A lot of them have unknown properties ...We just don't know." The CIIT is a nonprofit organization that researches possible adverse effects of chemicals on human health.

More research needs to be performed to determine the potential for endocrine disruption as a result of the daily, low-dose exposure to common chemicals experienced by humans, suggests Timm. "Most of the research has been done [on lab animals] using high doses, but the responses we get from high doses may not be able to accurately predict dangers at much lower doses," he notes. One of the most vulnerable period of hormonal and sexual development occurs in utero, and Timm cautions that "adult [lab animal] responses don't predict what will happen in the womb."

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Related links:

Outside Link: Information on Endocrine Disruptors from the Environmental Protection Agency