Academic journal article Forum for Applied Research and Public Policy

The State of the Debate: While Scientists Agree That Some Synthetic Chemicals Can Mimic Hormones, Consensus on a Course of Action Remains Elusive

Academic journal article Forum for Applied Research and Public Policy

The State of the Debate: While Scientists Agree That Some Synthetic Chemicals Can Mimic Hormones, Consensus on a Course of Action Remains Elusive

Article excerpt

In the past decade, there has been growing concern that environmental chemicals may be disrupting normal endocrine processes. Since the developing fetus is highly influenced by hormones that orchestrate male and female sexual development, transient and low-level exposure of the developing fetus to chemicals that could interfere with normal sexual differentiation could result in sexual ambiguity, abnormalities of the reproductive organs, cancer of the reproductive system, and reduced fertility.

This toxicity stems largely from the capacity of the chemical to act like a hormone (hormone agonist), block the action of a hormone (hormone antagonist), and alter the natural, or endogenous, hormone levels (hormone modulator). While scientists agree on the ability of these chemicals to mimic, block, or alter hormones, consensus dissolves when they consider whether chemicals found in the environment actually elicit endocrine-disrupting toxicity, particularly in humans.

In fact, a variety of laboratory studies have demonstrated that some chemicals can cause endocrine-disrupting effects, and wildlife populations with documented exposure to environmental toxicants have demonstrated abnormal development of the reproductive system. Some researchers have concluded from this evidence that environmental contaminants are responsible for reported declines in sperm count, increased incidence of breast and prostate cancer, and other hormonally influenced conditions in the human population.

To date, however, the notion that environmental chemicals disrupt endocrine processes and result in disease and dysfunction in people remains a hypothesis, though these chemicals clearly have the potential to do so. While researchers agree that some environmental chemicals elicit endocrine-disrupting toxicity, existing evidence is insufficient to establish whether such effects are currently occurring in humans.

Half the Man

At a congressional hearing held in 1993 to address the issue of environmental endocrine disruption, Dr. Louis Guillette from the University of Florida won the attention of legislators by declaring that "every man in this room is half the man that his grandfather was." Dr. Guillette was referring to the reputed decline in sperm counts in the human population.

Congress ultimately decided that the issue warranted attention and in 1996 enacted the Food Quality Protection Act and the Safe Drinking Water Act. These two measures mandated that the U.S. Environmental Protection Agency develop and implement testing procedures for the screening of chemicals for endocrine-disrupting properties by 1999.

Was the enactment of these pieces of legislation based upon good science or strong emotions? Many argue that the science was inadequate to support the policy and that the policy is now driving the science. Others argue that the science was sufficient to provide a foundation for the resulting policy decision. Equally disconcerting is our lack of understanding of the magnitude of the problem. However, a tragic and well-documented human experiment provided additional support for those who maintain that there is indeed cause for concern.

From the 1940s to the 1960s, the synthetic hormone diethylstilbestrol (DES) was prescribed to pregnant women to prevent miscarriage. DES is estrogenic; that is, like many reputed environmental endocrine disruptors, it acts like the female hormone 17-[Beta]-estradiol.

While mothers tolerated the drug well, their daughters at maturity experienced an increased incidence of numerous problems, including reproductive tract deformities, menstrual irregularities, vaginal cancer, and poor prognosis for pregnancy.(1) These tragic consequences of fetal exposure to exogenous estrogen confirmed concerns that the developing fetus is highly susceptible to such toxicity.

The Legacy of DDT

Toxicity induced by exposures to hormone disruptors in the environment is not new to science. …

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