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Emerging
science on the impacts of
endocrine disruptors on intelligence and behavior.
During the nine months between conception and birth, the fetal brain is transformed from instructions in genes to a complex, highly differentiated mass of organized cells capable of interacting with the outside world and prepared for learning. Those first nine months lay the groundwork for all of what happens later in life. Get it wrong, and the consequences can diminish a person's capacity to participate in society and compete throughout life. Like virtually all development, the transformation is guided by natural chemical signals instructing cells to differentiate, form brain structures, forge links of immense complexity, and even to die (in a process that is thought to carefully prune unnecessary connections). Normal brain development is heavily influenced by a host of hormonal signalling systems. Thyroid hormones play a major role. The sex steroids (testosterone, estrogen, etc.) contribute to, among other things, sexual differentiate of brain centers, and thereby, to the development of sexual identity and sexual behaviors. Dependent upon natural hormone signals, brain development is therefore vulnerable to endocrine disruption. A rapidly increasing body of scientific research is revealing mechanisms of action, demonstrating impacts of disrupted development, and exploring links between intelligence, behavior and contamination experienced in the womb. What is emerging from this research is that brain and behavior are likely to be the most sensitive endpoints vulnerable to endocrine disruption. Many synthesized compounds in commercial use today, moreover, can derail neurological development. An important aspect of this research is the realization, discussed in OSF (Chapter 13), that small losses in intelligence might have large consequences for a society if they are experienced in a broad swath of the population. Follow the links below to discussions of this emerging research, including two excellent summaries (a book and a web report/publication) as well as many individual scientific papers. April 2003. Exposure in the womb to extremely low levels of bisphenol A alters sexual differentiation of the brain and behavior in rats. More... June 2002. Mice exposed to bisphenol A at one-fifth the level currently considered safe by the US EPA show altered maternal behavior toward pups. The changes involve less attentiveness, more time away and less nursing. These results suggest that current BPA standards may need to be strengthened by a factor of 5,000. This would make it difficult to employ BPA in many of its current, widespread uses. More... September 2002. Dutch scientists report that boys exposed prenatally to higher levels of PCBs and dioxin are more likely to show demasculinized play behaviors. Girls and boys exposed to modestly elevated dioxin levels demonstrate more feminized play behaviors. The scientists suggest that that these alterations in play result from endocrine disruption of the development of sex-specific behaviors. More...
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Schettler, T, J Stein, F Reich, and M Valenti. 2000. In Harms Way: Toxic threats to child development. A report by Greater Boston Physicians for Social Responsibility. Schettler et al. report on an epidemic of developmental, learning, and behavioral disabilities affecting America's children today. Nearly 12 million children (17%) in the United States under age 18 suffer from one or more learning, developmental, or behavioral disabilities. Scientific research points to contamination in the womb as a significant contributor to these problems. More... |
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Laessig, SA, MM McCarthy and EK Silbergeld. 1999. Neurotoxic effects of endocrine disruptors. Current Opinion in Neurology 12:745-751. Laessig et al. review the pathways by which endocrine disrupting compounds can exert neurologic effects during development. They argue that "because of the relative sensitivity of the developing CNS (central nervous system) to normal changes in gonadal hormone secretion, metabolism, and transport to the brain, it is possible that developmental neurotoxicity may be one of the more sensitive consequences of exposure to EDCs." One of their principle points of focus is sexual differentiation of the brain. They present original data from experiments exposing fetal mice to chlordecone, diesthylstilbestrol and bisphenol A, and show that chlordecone (but not BPA) at low levels produces a significant difference in a sexually-dimorphic part of the brain. |
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Christian, M and G Gillies. 1999. Developing hypothalamic dopaminergic neurones as potential targets for environmental estrogens. Journal of Endocrinology 160:R1-R6 Christian and Gillies report on the experiments with 17ß-estradiol and the estrogenic compound octylphenol that demonstrate the ability of both compounds to alter the metabolism of neuronal cells exposed in cell cultures at very low levels. The dose-response curves were non-monotonic. More...
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Porter, WP, JW Jaeger and IH Carlson. 1999. Endocrine, immune and behavioral effects of aldicarb (carbamate), atrazine (triazine) and nitrate (fertilizer) mixtures at groundwater concentrations. Toxicology and Industrial Health 15: 133-150. Porter et al. experiment with combinations of two common pesticides and a fertilizer, exposing adult male mice to mixtures and concentrations within the range of exposures regularly encountered in human drinking water in mid-West agricultural regions of the United States. Exposure was through voluntary consumption of drinking water. They found the mice became significantly more aggressive after exposures. More...
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| MacLusky,
NJ, TJ Brown, S Schantz, BW Seo and RE Peterson. 1998. Hormonal
interactions in the effects of halogenated aromatic hydrocarbons of
the developing brain. Toxicology and Industrial Health 14:185-208.
As discussed in Our Stolen Future (Chapter 7), RE Peterson's lab has shown that extremely low doses of dioxin experienced in utero can disturb reproductive function and behavior in adulthood (Mably et al. 1992a,b,c). Here, MacLusky et al. show that fetal exposure to a low level of dioxin (0.7 µg/kg or 0.7 ppb) "disturbed sexual differentiation of reproductive behavior, potentiating the expression of feminine sexual behavior and reducing masculine behavior." They also studied cognitive function in rats exposed in utero. Here their experiments revealed an enhancement in rat performance in maze tests comparing treated animals to controls. Treated animals committed significantly fewer errors.
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| Williams,
C. 1997. Terminus Brain: The environmental threats to human
intelligence. Cassell, London and Herndon VA. ISBN 0-304-33857-5.
261pp.
Williams presents data and analyses indicating that millions of people around the world have experienced declines in intelligence and increases in dysfunctional behavior because of two interacting factors: exposure (especially in the womb and early in life) to contaminants and dietary deficiencies in critical micronutrients like iodine. This insight is crucial to identifying barriers to economic development and prosperity, especially in the developing world. More... |
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| The
Erice Statement:
A multidisciplinary group of international experts gathered in November
1995 in Erice, Sicily, to evaluate current science on the neural,
endocrine and behavioral effects of endocrine disrupting compounds.
authors. A 1998 anthropological study of children living in rural Mexico by Elizabeth Guillette and her colleagues suggests that children exposed to high levels of agricultural pesticides have difficulty performing simple motor tasks. |
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| More
than a decade ago, Joseph and Sandra Jacobson began a study looking
at whether a mother's consumption of Lake Michigan fish, which
contain significant levels of PCBs and other man-made contaminants,
had any effect on her children. As we discussed in Chapter 10
of Our Stolen Future, they did find measurable losses in motor
coordination, short term memory, and verbal skills as they tracked
the development of the children born to women who had eaten two or
three fish meals a month in the 6 years prior to pregnancy. A new
study they published in the New England Journal
of Medicine in September 1996 takes this landmark series of studies
deeper into the impacts of contamination on intellectual development
by documenting significant IQ deficits and reading impairment at
age 11 linked to in utero PCB exposure. |
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Koopman-Esseboom, C, N Weisglas, MAJ de Ridder, CG Van der Paauw, LGM Th Tuinstra, PJJ Sauer. 1996. Effects of Polychlorinated Biphenyls/Dioxin Exposure and Feeding Type on Infant's Mental and Psychomotor Development Pediatrics 97: 700-706. Koopman-Esseboom
and colleagues demonstrate that typical background levels of PCBs
in women are having a small, but measurable, negative effect on
children's development. In this investigation, the researchers compared
a child's scores on psychomotor development tests with PCBs levels
in its mother's blood during the last month of pregnancy and found
that the children born to women with higher PCB levels lagged behind
in tests given at three months of age. More
. . . |
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| Lonky,
E, J Reihman, T Darvill, J Mather and H Daly. 1996. Neonatal behavioral
assessment scale performance in humans influenced by maternal consumption
of environmentally contaminated Lake Ontario Fish. Journal of
Great Lakes Research 22(2)198-212.
Lonky et al. studied a cohort of children born to 243 mothers who had eaten varying amounts of fish from Lake Ontario in their lifetime prior to pregnancy. "Despite relatively low levels of fish consumption, newborns in the high-exposure group scored significantly more poorly than those in the low-exposure and control groups on measurements of neonatal behavior." |
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| vom
Saal, F, S Nagel, P Palanza, M Boechler, S Parmigiani and W Welshons.
1995. Estrogenic Pesticides: Binding Relative to Estradiol in MCF-7
Cells and Effects of Exposure During Fetal Life on Subsequent Territorial
Behavior in Male Mice. Toxicology Letters 77:343-350.
Fetal mice were exposed in utero to low doses of DES, o,p'-DDT and methoxychlor and then examined during adulthood for the rate of territorial marking in a novel territory. Each chemical had a strong, dose dependent effect upon this element of behavior, with increases above controls evident at all levels tested. According to vom Saal et al.; "It is well established that during fetal life, hormones have marked effects on subsequent social behaviours. ... Therefore, perturbation of systems that differentiate under endocrine control may result not only in the disruption of organ function, but also of an individual's social interactions. These effects on social behaviours may be dramatic. If animals within a population all show changes in social-sexual behaviours, marked disturbance in social structure can occur."
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