CHEMICALS AND THE BRAIN, PART 1
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Environmental Research Foundation
P.O. Box 5036, Annapolis, MD 21403
Fax (410) 263-8944; Internet: erf@rachel.clark.net
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CHEMICALS AND THE BRAIN, PART 1
An international group of scientists and physicians --including
U.S. government scientists --issued a consensus statement May 30,
1996, expressing great concern about the effects of
hormone-disrupting chemicals on the brain and central nervous
system. The new statement resulted from a workshop Nov. 5-10,
1995 at Erice, Italy. Therefore, we will refer to this as the
Erice Statement.[1]
Hormones are chemical messengers that travel in the blood stream,
turning on and off critical bodily functions to maintain health
and well being. Hormones control growth, development, and
behavior in birds, fish, reptiles, amphibians, and mammals,
including humans. In humans, 100 different hormones have been
identified. Taken together, the tissues and organs that produce,
and respond to, hormones are called the endocrine system. In
1991, an international group of 23 scientists issued a consensus
statement, expressing great concern that many synthetic
(human-created) industrial chemicals can interfere with hormones
in wildlife and humans. (See REHW #263, #264). The 1991
statement focused on the ability of industrial chemicals to
interfere with sexual development and behavior in wildlife and
humans. The Erice Statement issued last month focuses attention
on industrial chemicals that can interfere with the development
of the brain and other parts of the central nervous system. The
statement is not easy reading, but it is important, so we present
it verbatim.
The Erice Statement begins with a paragraph labeled "background,"
which says, in part:
Research since 1991 has reinforced concerns over the scope of the
problems posed to human health and ecological systems by
endocrine-disrupting [hormone-disrupting] chemicals. New
evidence is especially worrisome because it underscores the
exquisite sensitivity of the developing nervous system to
chemical perturbations [disturbances] that result in functional
abnormalities. Moreover, the consequences of these perturbations
depend upon the stage of development during which exposure occurs
and are expressed in different ways at different times in life,
from birth through to advanced age. This work session was
convened because of the growing concern that failure to confront
the problem could have major economic and societal implications.
CONSENSUS STATEMENT
The following consensus was reached by participants at the
[Erice] workshop.
1. We are certain of the following:
** Endocrine-disrupting chemicals can undermine neurological and
behavioral development and subsequent potential of individuals
exposed in the womb or, in fish, amphibians, reptiles, and birds,
the egg. This loss of potential in humans and wildlife is
expressed as behavioral and physical abnormalities. It may be
expressed as reduced intellectual capacity and social
adaptability, as impaired responsiveness to environmental
demands, or in a variety of other functional guises. Widespread
loss of this in nature can change the character of human
societies or destabilize wildlife populations. Because profound
economic and social consequences emerge from small shifts in
functional potential at the population level, it is imperative to
monitor levels of contaminants in humans, animals, and the
environment that are associated with disruption of the nervous
and endocrine systems and reduce their production and release.
** Because the endocrine system is sensitive to perturbation, it
is a likely target for disturbance. In contrast to natural
hormones found in animals and plants, some of the components and
by-products of many manufactured organic compounds that interfere
with the endocrine system are persistent and undergo
biomagnification in the food web, which makes them of greater
concern as endocrine disruptors.
** Man-made endocrine-disrupting chemicals range across all
continents and oceans. They are found in native populations from
the Arctic to the tropics, and, because of their persistence in
the body, can be passed from generation to generation. The
seriousness of the problems is exacerbated by the extremely low
levels of hormones produced naturally by the endocrine system
which are needed to modulate [change] and induce [cause]
appropriate responses. In contrast, many endocrine disrupting
contaminants, even if less potent than the natural products, are
presented in living tissue at concentrations millions of times
higher than the natural hormones. Wildlife, laboratory animals,
and humans exhibit adverse health effects at contemporary
environmental concentrations of man-made chemicals that act as
endocrine disruptors. New technology has revealed that some
man-made chemicals are present in tissue at concentrations
previously not possible to measure with conventional analytical
methods, but at concentrations which are biologically active.
** Gestational exposure to persistent man-made chemicals reflects
the lifetime of exposure of females before they become pregnant.
[Gestation is the period of development, from conception through
birth; in the case of eggs, it is the incubation period.] Hence,
the transfer of contaminants to the developing embryo and fetus
during pregnancy and to the newborn during lactation is not
simply a function of recent maternal exposure. For some
egg-laying species, the body-burden of the females just prior to
ovulation [egg production] is the most critical period. For
mammals, exposure to endocrine disruptors occurs during all of
prenatal and early postnatal development because they are stored
in the mother.
** The developing brain exhibits specific and often narrow
windows during which exposure to endocrine disruptors can produce
permanent changes in its structure and function. The timing of
exposure is crucial during early developmental stages,
particularly during fetal development when a fixed sequence of
structural change is occurring and before protective mechanisms
have developed. A variety of chemical challenges [exposures] in
humans and animals early in life can lead to profound and
irreversible abnormalities in brain development at exposure
levels that do not produce permanent effects in adults.
** Thyroid hormones are essential for normal brain functions throughout
life. Interference with thyroid hormone function during development leads
to abnormalities in brain and behavioral development. The eventual results
of moderate to severe alterations of thyroid hormone concentrations,
particularly during fetal life, are motor dysfunction of varying severity
including cerebral palsy, mental retardation, learning disability, attention
deficit hyperactivity disorder, hydrocephalus, seizures and other permanent
neurological abnormalities. Similarly, exposure to man-made chemicals during
early development can impair motor function [ability to move], spatial
perception, learning, memory, auditory development, fine motor coordination
[for example, coordinating movement of the hands and eyes], balance, and
attentional processes; in severe cases, mental retardation may result.
** Sexual development of the brain is under the influence of
estrogenic (female) and androgenic (male) hormones. Not all
endocrine disruptors are estrogenic or anti-estrogenic. For
example, new data reveal that DDE, a breakdown product of DDT,
found in almost all living tissue, is an anti-androgen in
mammals. Man-made chemicals that interfere with sex hormones
have the potential to disturb normal brain sexual development.
Wildlife studies of gulls, terns, fishes, whales, porpoises,
alligators and turtles link environmental contaminants with
disturbances in sex hormone production and/or action. These
effects have been associated with exposure to sewage and
industrial effluents, pesticides, ambient ocean and freshwater
contamination, and the aquatic food web.
** Commonalties across species in the hormonal mechanisms
controlling brain development and function mean that adverse
effects observed in wildlife and in laboratory animals may also
occur in humans, although specific effects may differ from
species to species. Most important, the same man-made chemicals
that have shown these effects in mechanistic studies in
laboratory animals also have a high exposure potential for humans.
** The full range of substances interfering with natural
endocrine modulation of neural and behavioral development cannot
be entirely defined at present. However, compounds shown to have
endocrine effects include dioxins, PCBs, phenolics, phthalates,
and many pesticides. Any compounds mimicking or antagonizing
actions of, or altering levels of, neurotransmitters, hormones,
and growth factors in the developing brain are potentially in
this group.
[The Erice Statement continues; we will present the remainder in
a future issue of REHW.]
--Peter Montague
(National Writers Union, UAW Local 1981/AFL-CIO)
[1] The Erice Statement was signed by: Dr. Enrico Alleva (Head,
Section of Behavioral Pathophysiology; Institute of Neurobiology;
Rome, Italy); Dr. John Brock (Chief -PCBs and Pesticides
Laboratory; Center for Environmental Health; Centers for Disease
Control; Atlanta, Georgia); Dr. Abraham Brouwer (Associate
Professor and Toxicology and Research Coordinator; Department of
Toxicology; Agricultural University; Wageningen, The
Netherlands); Dr. Theo Colborn (Senior Program Scientist;
Wildlife and Contaminants Project; World Wildlife Fund;
Washington, D.C.;) Dr. M. Cristina Fossi (Professor, Department
of Environmental Biology; University of Siena; Siena, Italy); Dr.
Earl Gray (Section Chief; Developmental and Reproductive
Toxicology Section; U.S. Environmental Protection Agency [EPA]
Research Triangle Park, North Carolina); Dr. Louis Guillette
(Professor; Department of Zoology; University of Florida;
Gainesville, Florida); Peter Hauser, M.D. (Chief of Psychiatry
Service [116A]; Baltimore Veterans Administration Medical Center;
10 North Greene Street; Baltimore, Maryland); Dr. John
Leatherland (Professor, Chair; Department of Biomedical Sciences;
Ontario Veterinary College; University of Guelph; Guelph,
Ontario, Canada); Dr. Neil MacLusky (Professor; Director of Basic
Research; Division of Reproductive Science; Toronto Hospital;
Toronto, Ontario, Canada); Dr. Antonio Mutti (Professor;
Laboratory of Industrial Toxicology; University of Parma Medical
School; Parma, Italy); Dr. Paola Palanza (Researcher; Department
of Biology and Physiology; University of Parma; Parma, Italy);
Dr. Susan Porterfield (Associate Professor and Associate Dean of
Curriculum; Medical College of Georgia; Augusta, Georgia); Dr.
Risto Santti (Associate Professor; Department of Anatomy;
Institute of Biomedicine; University of Turku; Turku, Finland);
Dr. Stuart A. Stein (Associate Professor of Neurology, Medicine,
Pediatrics, OB-GYN, and Molecular and Cellular Pharmacology;
University of Miami School of Medicine; Miami, Florida; and Chief
of Neurology Children's Hospital of Orange County, Orange,
California); Dr. Frederick vom Saal (Professor; Division of
Biological Sciences, University of Missouri; Columbia, Missouri);
Dr. Bernard Weiss (Professor, Department of Environmental
Medicine; University of Rochester School of Medicine and
Dentistry; Rochester, New York).
Descriptor terms: hormones; endocrine disrupters; brain; central
nervous system; erice statement; wildlife; human health; thyroid;
cerebral palsy; mental retardation; learning disability;
attention deficit hyperactivity disorder; hydrocephalus;
seizures; sexual development; estrogen; androgen; sewage;
pesticides; pcbs; phenolics; phthalates;
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--Peter Montague, Editor
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