How Good Is the Science Connecting Environmental Exposures to Health?


Are we ready to add our voice to concerns about environmental health? When is the science robust enough that providers routinely inquire about potentially dangerous exposures at health care visits? Professionals who accepted this scientific uncertainty yet wanted to protect public health addressed these questions in 1998 at the historic Wingspread Conference in Racine, Wisconsin, where they formalized a philosophy called the “precautionary principle.” The precautionary principle states:

“When an activity raises threats of harm to the environment or human health, precautionary measures should be taken, even if some cause and effect relationships are not fully established scientifically.”1

The issuance of the precautionary principle was a call to action for government and state agencies and health care providers.

Since the Wingspread Conference, the US government has charged a consortium of governmental agencies, including the Centers for Disease Control and Prevention (CDC) and the Environmental Protection Agency (EPA), to initiate a national program of biomonitoring of human exposure to chemicals. Although this is an important first step, the majority of the 100,000 chemicals used by industry in the United States have never undergone safety testing, so we do not know if they have a “safe” level of exposure.2 Moreover, even though the CDC is well on its way to tracking information and reporting trends and health effects,3 political lobbying still threatens to erode clean air standards and funding for The National Children's Study, a large prospective cohort study that will track environmental effects on children's health. This national study plans to follow more than 100,000 children from birth to age 21.4

We do know our bodies are being exposed, and in pregnant women, many of these chemicals are passing into the fetal environment. Pregnant women, children, and vulnerable populations are the most susceptible to environmental hazards. Evidence of adverse effects following fetal exposure to environmental toxins has been well documented historically. Studies of pregnant women exposed to diethylstilbestrol (DES) have undisputedly confirmed that maternal exposure can cause the development of cancer in the exposed offspring. The biologic plausibility for the greatest risk being during the embryonic and fetal period is exemplified, and the concern that long delays between exposure time and onset of disease add to the issues of uncertainty in the science. In July 2005, the Environmental Working Group, a nongovernmental organization, found an average of 287 contaminants in 10 samples of umbilical cord blood, with 180 of them known to cause cancer in humans or animals.5 The umbilical cord blood from these 10 babies harbored pesticides, consumer product ingredients, and wastes from burning coal, gasoline, and garbage.5

Recently reported evidence suggests that more than 300,000 newborns each year in the United States may have been exposed in utero to concentrations of methyl mercury dangerously above the daily reference dose (RfD) recommendation.6 Adverse neurologic sequela is associated with massive mercury exposure. The practical question today is how much fish do we need to eat and for how long before the likelihood for disease is significant?7 The FDA's fish advisories for pregnant women detail how consumption thresholds have been lowered from 2001 to the latest release in 2004.8 Moreover, challenges are underway to force the FDA advisory to lower recommended amounts of canned tuna consumption. Another change in the advisory may be forthcoming.9

Even in the face of “good” evidence, clinicians may hesitate to share environmental precautions with their clients because the environmental exposure cannot be avoided or because current information does not identify safe exposure levels. However, risk perception is a first step in initiating self-protective behaviors. If a person does not perceive risk from exposure to a substance, then self-protective actions will not take place. Nearly 90% of the participants in a consumer survey indicated belief that environmental exposures are important contributors to disease. Perhaps the time is right for more emphasis on this topic in health care visits.10

In 2004, the editorial board of this journal made a decision to dedicate this home study issue to environmental hazards and women's health, subscribing to the precautionary principle. This compilation of articles provides a review of the state of the science specifically addressing pesticide exposures, food and water safety, and breastfeeding and chemical exposure. We have included a resource guide to the Web-based databases that collate this science for clinicians who need access to clinically important updates on adverse effects of chemical exposures.

Uncertainty prevails, but credible science implicates environmental exposures as a source of disease in susceptible adults, and there are multiple implications for human development. The evidence provides clear direction for constructing justifiable recommendations on how to minimize exposures. Midwifery history in the United States has a tradition of advocacy and service for the most vulnerable populations. Our heritage is clear about our role in improving health in communities. In addition, women of reproductive age and mothers are an ideal audience to hear and heed this message, which can lead to improved health practices.