Rachel’s News #757, November 28, 2002
[This essay first appeared in SAN FRANCISCO MEDICINE, November 2002. See http://www.sfms.org/sfm/ for other important work. In the text, I have added explanatory notes inside square brackets, and the sub-headings have been added as well. For additional documents and discussions related to these topics, see http://www.OurStolenFuture.org and http://www.ProtectingOurHealth.org . –Peter Montague, editor]
by John Peterson Myers*
Four decades ago in SILENT SPRING, Rachel Carson wove together a fabric of evidence suggesting that parts of the modern chemical revolution were having unintended consequences, undermining human and wildlife health in unexpected ways.[1] At the time that fabric was more Chantilly lace than Afghan rug, with the scientific pattern defined as much by the holes as by the threads of connecting evidence.
Her thesis was compelling, nonetheless. It launched the modern environmental movement. It stimulated a new branch of government focused on environmental impacts. It led to bans of DDT and, since then, a host of other chemicals. Most recently it spurred in 2001 a global treaty, the Stockholm Convention, that requires phase-out and elimination of twelve persistent organic pollutants. And it forced new scientific questions to be asked about links between contamination and health.
We’re in the Midst of a Scientific Revolution
Now four decades later, we are midstream in the scientific revolution that her work helped foment. The revolution arises from scientific discoveries which establish that many chemicals — both from the natural world and synthesized in laboratories — interfere with the biochemical messaging systems that direct the biological development of plants and animals, including humans.[2,3]
Chemicals Can Disrupt Biological Signals
Virtually all biological development is under the control of various biochemical messaging systems that are involved in the chain of events leading to gene activation and expression. Hormones and growth factors, among others, are key elements of these message systems. Normal healthy development depends on the successful initiation of genetic instructions by hormones and growth factors, among others, which are key elements in these message systems. Disruption can cause immediate effects, ranging from conspicuous teratological [birth defect] impacts to subtle functional disabilities that may not be evident until decades after exposure.
Research now demonstrates that a wide array of chemicals can disrupt these messages without damaging the genes themselves. Much attention has focused on disruption of hormonal signaling, which has become known as endocrine disruption.[4]
Chemicals Can Impair Growth and Development
Investigation of developmental disruption has burgeoned during the past decade because of research funding by European, Japanese and North American governments. New results are published virtually every week in journals like ENVIRONMENTAL HEALTH PERSPECTIVES, HUMAN REPRODUCTION, TOXICOLOGY, and ENVIRONMENTAL SCIENCE AND TECHNOLOGY.
For example, a study published in September 2002 by a research group in the Netherlands documented associations between variations in background levels of in utero [in the womb] exposure to certain organochlorine chemicals and gender-specific play behavior in children.[5] Boys with relatively higher levels of PCB exposure were less likely to engage in play behaviors typical for boys; girls more likely to engage in play behavior typical for boys. Boys with relatively higher levels of dioxin were more likely to engage in more feminine play behaviors, as were girls.
These findings are especially noteworthy because the levels of exposure were not that high, but instead represented variations around background levels common in European women. Moreover, these outcomes are consistent with experiments carried out with laboratory animals examining exposure impacts on sex-specific behaviors.
The same research group had recently published studies demonstrating impacts of in utero [in the womb] exposure on cognitive development and immune system function.[6,7,8] Their groundbreaking studies rest on detailed tracking of the development of a cohort [group] of individuals beginning with measurements of the mother’s serum [blood] contamination during pregnancy, with careful attention paid to potential confounding variables.
A Revolution in Thinking about Health & Environment
New results like these are legion.[9] They are forcing a series of conceptual shifts upon toxicology as it integrates these new findings with long-standing assumptions. These shifts are summarized in Table 1. The text below examines several in greater detail.
