science on the impacts of
endocrine disruptors on intelligence and behavior.
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.
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
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.
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.
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.
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...
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...
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.
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...
SA, MM McCarthy and EK Silbergeld. 1999. Neurotoxic effects of
endocrine disruptors. Current Opinion in Neurology 12:745-751.
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."
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.
M and G Gillies. 1999. Developing hypothalamic dopaminergic neurones
as potential targets for environmental estrogens. Journal of
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...
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.
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...
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.
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."
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.
C. 1997. Terminus Brain: The environmental threats to human
intelligence. Cassell, London and Herndon VA. ISBN 0-304-33857-5.
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...
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.
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.
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.
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.
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
. . .
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.
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."
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.
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.
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."