"At least 500 of the chemicals that you carry in your body today are chemicals that no one was exposed to before the 1920s. And there is now undeniable evidence that a pregnant women shares some of these chemicals with the baby in her womb ," and at even higher concentrations with her baby when she breast feeds ," chemicals that, in many cases, interfere with the natural hormones that tell the baby how to develop."," Dr. Theo Colborn, author of Our Stolen Future, in her opening comments at the U.S. Department of the Interior's Conference on the Environment, March 2001.
The chemicals to which Colborn refers are endocrine disruptors, chemicals in our environment that might interfere with the human body's complex system of glands, hormones and cellular receptors that control internal functions. Although most researchers agree that large amounts of these chemicals adversely affect the endocrine system, the debate rages on when it comes to the lower doses to which humans generally are exposed.
Could such chemicals be responsible for today's declining sperm counts? For the increase seen in breast cancer rates? For learning and other developmental problems? Could you, as manufacturers of many of these chemicals, be at risk?
In a 1999 report, Endocrine Disruptors: A Scientific Perspective, the American Council on Science and Health (ACSH) concludes that "typical exposures to synthetic chemicals in the environment are not linked, in humans, to alleged endocrine-related health problems such as reductions in sperm counts and cancers of reproductive organs."
Other experts, however, insist we have much more to learn about the relationship between such exposures and human health.
Global Assessment of the State-of-the-Science of Endocrine Disruptors, a new report from the International Programme on Chemical Safety (IPCS), says "the evidence that human health has been adversely affected by exposure to EDCs [endocrine-disrupting chemicals] is generally weak." However, notes the study, sufficient evidence does exist that adverse effects have occurred as a result of exposure to EDCs in some wildlife species.
Because many concerns and scientific uncertainties remain, states the report, "studies on the potential effects posed by these chemicals should remain a high global priority requiring coordinated and strengthened international research strategies." Particularly urgent, concludes the report, is the need for studies in vulnerable populations such as infants and children because exposure during critical developmental periods might be associated with "irreversible effects."
Much of the uncertainty can be attributed to the complexity of EDC-related research.
"It's incredibly difficult to try to establish cause and effect," maintained Dr. Glen Van der Kraak, professor and chair of the Department of Zoology at the Guelph, Ontario-based University of Guelph and one of the report's editors. "We can't take volunteers and say: Drink these five gallons of bisphenyl-A this year, and we'll determine whether that's causing an adverse effect.'"
Van der Kraak told Chemical Processing that researchers need to perform additional epidemiological types of investigations. "We need to go into additional work that will point to the mechanisms by which chemicals are causing some of these effects," he said. "By following that mechanistic path, we may be able to identify markers or suitable tests that will help tease out responses that are due to one chemical [as opposed to] another stressor."
Much of today's research is going in the right direction, added Van der Kraak. "We went through a phase where people were using assays that would determine the potential of a compound to do something, to bind to the estrogen receptor," he said. "But now we're trying to go to the next step, trying to ask the question: Can we detect those kinds of responses in the real world?'"
Further confounding research efforts is the "unbelievably complicated" way in which the human population lives, stressed Van der Kraak. "How do we separate out responses that are not the ones affecting 75 percent of the people," he asked, "from a background rate of change?"
The U.S. Environmental Protection Agency (EPA) is just one of the many agencies performing research that one day could resolve some of the mysteries surrounding EDCs. In 1996, EPA formed the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC) to advise the agency on the design of an EDC screening and testing program. Based on EDSTAC recommendations, EPA's Endocrine Disruptor Methods Validation Subcommittee (EDMVS) now is developing and validating the assays needed for Tier 1 and Tier 2 of the agency's Endocrine Disruptor Screening Program.
Gary E. Timm, an EPA senior environmental scientist charged with implementation of the program, said one stumbling block has been "the difficulty of correlating low levels of exposure during fetal development with problems that are manifested only years later at adolescence or adulthood."
Timm said EPA "has an elaborate multi-year research agenda that is focusing on both wildlife and human health effects." The agency also is working to develop a better understanding of how chemicals affect the endocrine system, he added.
To read the IPCS report, visit the World Health Organization's Web site at www.who.int/pcs/pcs_new.html. Information about EPA's EDC research plan is available on the agency's Web site at www.epa.gov/epahome/resstrat.htm. CP