Timeline of Endocrine Disruption and Man-Made Chemicals

The following timeline is based on a PBS feature aired in February of 1998 and featuring interviews with Theo Colborn, author of Our Stolen Future, Lois J. Guillette, PhD, and Fredrick Vom Saal.

1923 First estrogen bioassay is developed. The test detects estrogenic activity in biological extracts and determines relative potencies of compounds and mixed natural materials.

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 women worldwide.

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, 4 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 infants.

1962 Silent Spring is published. Rachel Carson’s book describes health problems observed in wildlife such as eggshell 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 populations.

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. The US 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 US Environmental Protection Agency.

1973 International Joint Commission (IJC) for the US and Canada singles out first “Areas of Concern” in the Great Lakes region, noting extensive pollution and threats to wildlife.

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 US 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 PCBs banned in the US, but not their use or storage.

1982 DES is shown to cause developmental abnormalities and vaginal cancer in female mice.

1983 Responding to public concern over dioxin contamination at Times Beach, Love Canal, Jacksonville and other sites, the US Congress directs the EPA to conduct a National Dioxin Study to determine the extent of contamination nationwide.

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 record.

1985 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).

1986 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 action. Theo Colborn co-authors “Great Lakes, Great Legacy?,” detailing developmental, reproductive, metabolic and behavioral damage to wildlife from persistent chemical pollutants.

1990 Fifth Biennial report of IJC puts threat in plain language, saying that the principal danger of persistent organochlorine chemicals is to the fetus.

1990 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 top predators. Researchers Ana Soto and Carlos Sonnenschein report that some plastic compounds widely used in a variety of consumer products are estrogenic in laboratory research.

1991 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 Banbury Conference.

1991 EPA administrator Bill Reilly states publicly that dioxin seems less dangerous than previously thought. He initiates a second EPA reassessment of dioxin.

1991 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 Phase-Out.”

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 recommendation.

1992 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 US 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.

1993 Chemical Manufacturers’ 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 systems.

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.

1996 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.

1996 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.

1996 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 life.

1996 Dr. Harry Fisch publishes a study refuting any decline in US 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 sperm counts.

1997 Work by researcher Dr. Fredrick 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 sealants.

1997 A study by the Centers for Disease Control and Prevention shows that hypospadias, a hormone-dependent genital defect, is on the rise in baby boys.

1997 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.

1997 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.

1998 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 US 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.

1998 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.

1998 The United Nations Environment Programme meets 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 on human health and the environment. Persistent Organic Pollutants include: aldrin, dieldrin, endrin, chlordane, DDT, heptachlor, hexachlorobenzene, mirex, toxaphene, PCBs, dioxins, and furans.

1998 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.


This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly magazine of the Weston A. Price Foundation, Fall 2002.

Jill Nienhiser has been a Weston A. Price Foundation member since 2001, and has provided web maintenance, editing, and proofreading support for westonaprice.org and realmilk.com for many years. She also helped launched the Farm-to-Consumer Legal Defense Fund in 2007.

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