|1923||First estrogen bioassay is developed. The test detects estrogenic activity
in biological extracts and determines relative potencies of compounds and mixed
|1929||Commercial production of PCBs begins in the United States in response to
the electrical industry's need for a safer cooling and insulating fluid for
industrial transformers and capacitors.|
|1938||British scientist and physician Edward Charles Dodds announces the
synthesis of a chemical that acted in the body like a natural estrogen. Called
DES, it is hailed by leading researchers and gynecologists as a wonder drug
with a host of potential uses. (Dodds was later knighted for his scientific
achievement.) Soon after Dodds invents DES, researchers in the United States
begin giving the synthetic hormone to women with problem pregnancies. The
massive experiment would eventually involve an estimated 4.8 million pregnant
|1948||Paul Muller is awarded a Nobel Prize in medicine for discovering the
insect-killing properties of DDT.|
|1950||DDT is shown to disrupt sexual development in roosters -- possibly by
acting as a hormone. Scientists V.F. Lindeman and Howard Burlington find that
young roosters treated with DDT fail to develop normal male sex
characteristics, such as combs and wattles. The pesticide also stunted the
growth of the animals' testes. These scientists noted a similarity between DDT
and DES, a synthetic estrogen given to women for problem pregnancies. DDT,
they observe, "may exert an estrogen-like action" on the animal in question.|
|1952||By this date, four separate scientific studies show women treated with DES
to prevent miscarriage did no better than those treated with alternatives such
as bed rest or sedatives. Further analysis will show that DES actually
increases the number of miscarriages, premature births, and deaths among
|1962||"Silent Spring" is published. Rachel Carson's book describes health
problems observed in wildlife such as egg shell thinning, deformities and
population declines. Carson links these adverse effects to exposure to
pesticides and other synthetic chemicals.|
|1963||Study shows that newborn mice receiving estrogen injections developed
tissue pathologies such as cysts, cancers, and lesions. Results indicate that
exposure to naturally occurring hormones early in life can produce harmful
health effects and point to possible early life causes of cancer in adult human
|1968||DDT is shown to be estrogenic in mammals and birds.|
|1971||DES is linked to vaginal cancer in daughters whose mothers had taken the
drug during the first three months of pregnancy. By this date, millions of
pregnant women had received prescriptions from physicians for DES.|
U.S. Food and Drug Administration directs doctors not to prescribe DES to
pregnant women and bans the drug for animal use.
|1972||DDT use is restricted in agriculture by the U.S. Environmental Protection
|1973||International Joint Commission (IJC) for the U.S. and Canada singles out
first "Areas of Concern" in the Great Lakes region, noting extensive pollution
and threats to wildlife.|
|1975 & 1976||DES is shown to cause developmental abnormalities in male mice and
reproductive problems in humans.|
|1977||Use and manufacture of PCBs restricted by the U.S. Environmental
Protection Agency. PCBs continue to be manufactured and sold overseas|
|1978||Great Lakes Water Quality Agreement between U.S. and Canada calls for
virtual elimination of persistent toxic substances from Great Lakes basin.|
|1979||National Institute of Environmental Health Sciences holds conference
entitled: Estrogens in the Environment I. Presented papers identify and
evaluate both advertent and inadvertent hormone mimics.|
Manufacture of PCB's banned in the U.S., but not their use or storage.
|1982||DES is shown to cause developmental abnormalities and vaginal cancer in
|1983||Responding to public concern over dioxin contamination at Times Beach,
Love Canal, Jacksonville and other sites, the U.S. Congress directs the EPA to
conduct a National Dioxin Study to determine the extent of contamination
|1985||National Institute of Environmental Health Sciences holds a conference
called Estrogens in the Environment II: Influences on Development.
Presentations address the effects of environmental estrogens on puberty in
young children. Also noted is the ubiquitous nature of the contaminants, their
potency and their potential impact on public and environmental health.|
EPA's Dioxin Risk Assessment classifies dioxin as a known animal and
probable human carcinogen, setting the lowest "safe exposure level" on
Eight Great Lakes states develop remedial action plans to address
environmental damage seen in IJC-targeted "Areas of Concern."
|1986||Documents are leaked to Greenpeace showing EPA agreed to demands from the
paper industry to keep results of National Dioxin Survey secret.|
Under threat of lawsuit, EPA releases National Dioxin Survey. The study
finds dioxin is present in discharge from paper mills and in finished paper
products (due to chlorine bleaching of white paper).
Paper industry pressures EPA to reconsider its 1985 Dioxin Risk Assessment
in hopes of obtaining a less damaging judgment on dioxin's health effects.
|1988||EPA begins its first reassessment of dioxin.|
|1990||The EPA and the Chlorine Institute (an industry group) co-sponsor the
Banbury Conference on Dioxin, which takes place on Long Island, New York.
Conference attendees reach a consensus on dioxin's probable mechanism of
Theo Colborn co-authors "Great Lakes, Great Legacy?," detailing
developmental, reproductive, metabolic and behavioral damage to wildlife from
persistent chemical pollutants.
Fifth Biennial report of IJC puts threat in plain language, saying that the
principle danger of persistent organochlorine chemicals is to the fetus.
Environmental groups around the Great Lakes form the Zero Discharge
Alliance to oppose production of bioaccumulative toxic substances.
|1991||Theo Colborn helps organize a conference called "Chemically Induced
Alterations in Sexual Development: The Wildlife-Human Connection" and held at
Wingspread in Racine, Wisconsin. For the first time, scientists from many
disciplines are brought together to discuss concerns about endocrine-disrupting
chemicals in the environment. Participants present evidence that compounds may
have deleterious effects on sexual development in a variety of wildlife
species. Possible impacts include reproductive system abnormalities, reduced
fertility, behavioral abnormalities, and population declines -- particularly in
Researchers Ana Soto and Carlos Sonnenschein report that some plastic
compounds widely used in a variety of consumer products are estrogenic in
The Chlorine Institute (an industry group) prematurely issues a press
release stating that below a certain threshold of exposure, dioxin has no
adverse effects. Group makes false claim that this was the consensus of the
EPA administrator Bill Reilly states publicly that dioxin seems less
dangerous than previously thought. He initiates a second EPA reassessment of
Greenpeace tours 40 Great Lakes cities by boat in preparation for upcoming
IJC meeting in Traverse City, Michigan. The publicity campaign focuses on the
goal of zero dioxin discharge by the paper industry. Greenpeace distributes a
report entitled: "The Product is the Poison: The Case for a Chlorine
|1992||Sixth Biennial Report of the IJC calls for a phase-out of chlorine as an
industrial feedstock. Drinking water and pharmaceutical uses are exempted.
Environmental groups and industry are surprised by this wide-reaching
Physician Niels Skakkebaek publishes a paper demonstrating that human sperm
counts may have declined 50 percent over the last 50 years.
|1993||Referring to the perceived decrease in human sperm counts, scientist Lou
Guillette tells the U.S. Congress, "Every man sitting in this room today is
half the man his grandfather was, and the question is, are our children going
to be half the men we are?"|
A link between environmental estrogens and male reproductive problems is
hypothesized in scientific papers.
Chemical Manufacturer's Association forms the Chlorine Chemistry Council
(CCC) to promote the industry's agenda in the debate over chlorine chemistry.
CCC launches a public relations campaign, including television advertisements
asserting the need for chlorine.
|1994||EPA releases a Public Review Draft of its Dioxin Reassessment. It covers
dioxin, dioxin-like PCBs and furans. The report concludes that these chemicals
cause harm at levels similar to those seen in the general public. In addition
to cancer, potential damage is seen to the immune, nervous and reproductive
|1995||The National Academy of Sciences and National Research Council sponsor a
panel study called "Hormone Related Toxicants in the Environment."|
The EPA's Science Advisory Board reviews draft of Dioxin Reassessment.
|1996||The topic of endocrine disrupters is popularized with the publication of
"Our Stolen Future," which is co-authored by Theo Colborn and
includes an introduction by U. S. Vice President Al Gore.|
*President Clinton signs the Food Quality Protection Act and amendments to
the Safe Drinking Water Act, establishing the EPA's Endocrine Disruptor
Screening and Testing Advisory Committee (EDSTAC). EDSTAC is a unique advisory
committee of 40 members from industry, academia, government and environmental
groups. It is charged by Congress to develop a chemical screening program for
endocrine disruptors by 1998, and to implement the program by August, 1999.
Scientist Lou Guillette publishes his finding that male alligators in Florida's Lake Apopka have strikingly low levels of testosterone and
abnormally small phallus size. Pesticide residues in this contaminated lake
appear to have "feminized" the alligators there.
Psychologists Sandra and Joe Jacobson report that children exposed to high
levels of PCBs before birth have as much as a 6.2 point IQ deficit later in
Dr. Harry Fisch publishes a study refuting any decline in U.S. sperm
counts. He found, instead, striking geographical variation in sperm counts
across the U.S. While sperm counts remained constant in a given region between
1970 and 1994, New York had higher counts than Minnesota, which had higher
counts than California. Fisch thinks that the geographical variation may have
confused other research that, in 1992, showed a worldwide decline in human
|1997||Work by researcher Fred vom Saal shows that bisphenol-A, a component
of polycarbonate plastic, can alter the reproductive development of lab mice at
extremely low doses. Bisphenol-A mimics the natural sex hormone estrogen. Male
mice exposed to this plastic during fetal development have premanently enlarged
prostates and lower sperm counts. The effects occur at doses near those that
humans are exposed to each day from sources like food packaging and dental
A study by the Centers for Disease Control and Prevention shows that
hypospadias, a hormone-dependent genital defect, is on the rise in baby
The National Institute of Environmental Health Sciences (HHS) holds its
fourth major conference on estrogens in the environment in Arlington VA.
Numerous scientific papers and reports are presented on toxicology, risk
assessment and research for this emerging health concern.
Tulane University scientists retract an environmental estrogen study
published in a June 1996 issue of Science. The report had claimed that
combinations of pesticides were as much as 1,600 times more potent as
environmental estrogens than the individual pesticides. The research results
couldn't be replicated and the study was retracted.
|1998||The National Academy of Sciences Institute of Medicine is expected to issue
its report on hormone-related toxicants in the environment. The NAS panel will
critically review the literature, identify known and suspected impacts on fish,
wildlife and humans, and recommend research, monitoring and testing priorities,
among other activities.|
By August, the EPA committee EDSTAC is mandated to develop recommendations
on how to screen and test chemicals for their potential to disrupt hormone
function in humans and wildlife. EDSTAC's final plenary session is set for June
17-18 in Washington, D.C.
A research paper published in the Journal of the American Medical
Association reports that the proportion of males to females born has been
declining in the U.S. and Canada since the 1970s and in Denmark and the
Netherlands between 1950 and 1994. The study's authors suggest that endocrine
disruptors may play a role, pointing to increased numbers of male reproductive
disorders. When the study is reported in the popular press, some scientists
downplay the significance of the reported trend.
Vice-president Al Gore urges the chemical industry to voluntarily release
vital health information about thousands of commonly used chemicals. He says
such a move would "empower citizens with new knowledge" to safeguard their
neighborhoods against potential chemical hazards.
The United Nations Environment Programme plans to hold a meeting in late
June in Montreal to expand throughout the world an agreement to ban, phase out
or limit the production of Persistent Organic Pollutants (POPs). POPs are
chemical substances that persist in the environment, bioaccumulate through the
food web, and pose a risk of causing adverse effects to human health and the
environment. Persistent Organic Pollutants include: aldrin, dieldrin, endrin,
chlordane, DDT, heptachlor, hexachlorobenzene, mirex, toxaphene, PCBs, dioxins,
On Earth Day, the Chemical Manufacturers Association announces it will
urge its members to voluntarily increase their health effects testing program
of industrial chemicals to 100 chemicals a year by 2003.