Understanding Endocrine Disruption: Impacts and Consequences


OUR STOLEN FUTURE: Are We Threatening Our Fertility, Intelligence, and Survival?—A Scientific Detective Story by Theo Colborn, Diane Dumanoski, and Pete Myers(1996)


In 1988, Theo Colborn first recognized that the problems field biologists were discovering in Great Lakes wildlife were not, as Rachel Carson expected, tumors but rather reproductive failures leading to population crashes, developmental abnormalities such as crossed beaks in birds, and sexual abnormalities. She hypothesized that persistent toxic chemicals present in the Great Lakes ecosystem were to blame. In 1991, the biologists, endocrinologists, and biomedical specialists she invited to attend the First Wingspread Conference examined the evidence and agreed, issuing the Wingspread Consensus Statement, which stated that “a large number of man-made chemicals that have been released into the environment . . . have the potential to disrupt the endocrine system of animals, including humans.”

This was the first clear characterization of the concept of endocrine disruption, and it stressed the urgency of pursuing further research to determine the extent of, and mechanisms behind, such phenomena. While scientists and government officials took note and began to look at endocrine disruption more closely, Theo Colborn believed the public should also know about this important issue, leading to the publication of Our Stolen Future in 1996.

Our Stolen Future: Are We Threatening Our Fertility, Intelligence, and Survival?—A Scientific Detective Story by Theo Colborn, Diane Dumanoski, and Pete Myers was first published in 1996. It was the first popular book to explore the topic of endocrine disruption– the interference of environmental chemicals with the body’s hormone systems—and the impact endocrine disruption can have on the health of humans and wildlife. In a Foreword, Vice President Al Gore explained its importance: “Our Stolen Future is a critically important book that forces us to ask new questions about the synthetic chemicals that we have spread across this Earth. For the sake of our children and grandchildren, we must urgently seek the answers. All of us have the right to know and an obligation to learn.”

The authors delve into the concept of endocrine disruption and provide a comprehensive analysis of the scientific research available at the time. They discuss how certain synthetic chemicals—such as pesticides, industrial pollutants, and many common household products—can mimic or interfere with the function of the body’s natural hormones. This disruption can have far-reaching effects on various aspects of health and development, including reproductive function, neurological development, and immune system function.

Our Stolen Future emphasizes the potential long-term consequences of endocrine disruption on wildlife populations, particularly reproductive disturbances and developmental abnormalities. It also explores the potential links between endocrine disruption and human health issues, such as declining sperm counts and reduced fertility, certain cancers, and metabolic and developmental disorders.

Theo Colborn, an environmental health analyst and former director of the World Wildlife Fund’s Wildlife and Contaminants Program, provided her expertise in the field of endocrine disruption and environmental health. Dianne Dumanoski, an award-winning environmental journalist, and John Peterson (Pete) Myers, an environmental scientist and administrator, contributed their extensive research and writing expertise to the book.

Translated into several languages, Our Stolen Future was the first book to educate the public and raise awareness about the potential risks endocrine disruption poses. It played a crucial role in stimulating further scientific research, policy discussions, and regulatory actions related to endocrine disruptors. Today scientists continue to deepen our understanding of how chemicals harm human health, while concerned environmentalists work to convince governments to regulate the most dangerous and environmentally persistent toxic chemicals.

The book presented the evidence in 14 chapters, explaining the role of hormones in regulating the normal development and functioning of the body, and how certain chemicals could interfere with this process. The following description and quotations capture the leading argument presented in the book, with graphics drawn from the original illustrations by Kathryn Born. While reading the entire book is highly recommended—it is a tour de force in probing the fundamental meaning of important scientific findings about endocrine disruption—the following summary presents an overview of the authors’ basic points and concerns to serve as a précis of Our Stolen Future.

Foreword, Vice President Al Gore, January 22, 1996

Last year I wrote a foreword to the thirtieth anniversary edition of Rachel Carson’s classic work, Silent Spring. Little did I realize that I would so soon be writing a foreword to a book that is in many respects its sequel.

Thanks to Rachel Carson’s clarion call, we developed new and vital protections for the American public. Now Our Stolen Future raises questions just as profound as those Carson raised thirty years ago—questions for which we must seek answers.

Silent Spring was an eloquent and urgent warning about the dangers posed by manmade pesticides. Carson not only described how persistent chemicals were contaminating the natural world, she documented how those chemicals were accumulating in our bodies. Since then, studies of human breast milk and body fat have confirmed the extent of our exposure. Human beings in such remote locations as Canada’s far northern Baffin Island now carry traces of persistent synthetic chemicals in their bodies, including such notorious compounds as PCBs, DDT, and dioxin. Even worse, in the womb and through breast milk, mothers pass this chemical legacy on to the next generation.

As Carson warned in one of her last speeches, this contamination has been an unprecedented experiment: “We are subjecting whole populations to exposure to chemicals which animal experiments have proved to be extremely poisonous and in many cases cumulative in their effects. These exposures now begin at or before birth and—unless we change our methods—will continue through the lifetime of those now living. No one knows what the results will be because we have no previous experience to guide us.”

We are only now beginning to understand the consequences of this contamination. Our Stolen Future takes up where Carson left off and reviews a large and growing body of scientific evidence linking synthetic chemicals to aberrant sexual development and behavioral and reproductive problems. Although much of the evidence these scientific studies review is for animal populations and ecological effects, there are important implications for human health as well.…

We can never construct a society that is completely free of risk. At a minimum, however, the American people have a right to know the substances to which they and their children are being exposed and to know everything that science can tell us about the hazards. …

Our Stolen Future is a critically important book that forces us to ask new questions about the synthetic chemicals that we have spread across this Earth. For the sake of our children and grandchildren, we must urgently seek the answers. All of us have the right to know and an obligation to learn.\


[Stories of unusual problems experienced by wildlife around the world beginning in 1952.]

Beginning in the 1950s, these bizarre and puzzling problems began to surface in different parts of the world—in Florida, the Great Lakes, and California; in England, Denmark, the Mediterranean, and elsewhere. Many of the disturbing wildlife reports involved defective sexual organs and behavioral abnormalities, impaired fertility, the loss of young, or the sudden disappearance of entire animal populations. In time, the alarming reproductive problems first seen in wildlife touched humans, too.

Each incident was a clear sign that something was seriously wrong, but for years no one recognized that these disparate phenomena were all connected. While most incidents seemed linked somehow to chemical pollution, no one saw the common thread.

Then in the late ’80s, one scientist began to put the pieces together. (10)


[Theo Colborn sat in her office in the fall of 1987 surrounded by hundreds of reports and papers reviewing descriptions of the health of wildlife and humans in the Great Lakes region.]

Seeking to learn all she could, she had gathered hundreds of papers, in addition to the ones that kept arriving. … What she had seemed like a hodgepodge of disconnected information, yet at the same time, she sensed that something important was lurking beneath the confusing surface. The most promising material seemed to be new data linking toxic chemicals to cancer in fish. That made sense. That is what one would expect to find in lakes reputed to be full of cancer-causing chemicals.

But how did the hundreds of other studies reporting all manner of strangeness fit into the picture? Why were the terns in polluted areas neglecting their nests? And what about the bizarre wasting syndrome observed in tern chicks, which seemed normal at first but then suddenly began losing weight until they withered away and died? Then there were the reports of female herring gulls nesting together instead of with males. (12)

By the time the research deadline approached, Colborn had plowed through more than two thousand scientific papers and five hundred government documents. She felt like a beagle following its nose. She wasn’t sure where she was headed, but propelled by her curiosity and intuition, she was hot on the trail. She had found so many tantalizing parallels, so many echoes among the studies. Somehow, she was certain, it all fit together, because she kept finding unexpected links. Her latest discovery had come while she reexplored the literature on the eerie wasting syndrome seen in young birds. The chicks could look normal and healthy for days, but then suddenly and unpredictably they would begin to languish, waste away, and finally die. The wasting problem, scientists were learning, was a symptom of disordered metabolism. The young birds could not produce sufficient energy to survive. Though one would not at first suspect that this problem had anything in common with the gay gull phenomenon, it also stemmed from the disruption of the endocrine system and hormones.

But the elation of discovery passed quickly. The deadline was looming. What did this all mean? She had pieces and patterns but no picture. (25) …

Of course! Each and every one of these animals was a top predator that fed on Great Lakes fish. Although the concentrations of contaminants such as PCBs are so low in the water in the Great Lakes that they cannot be measured using standard water testing procedures, such persistent chemicals concentrate in the tissue and accumulate exponentially as they move from animal to animal up the food chain. Through this process of magnification, the concentrations of a persistent chemical that resists breakdown and accumulates in body fat can be 25 million times greater in a top predator such as a herring gull than in the surrounding water.

One other startling fact emerged from the spreadsheet. According to the scientific literature, the adult animals appeared to be doing fine. The health problems were found primarily in their offspring. Although

she had been thinking about offspring effects, Colborn had not recognized this stark, across-the-board contrast between adults and young.

Now the pieces were beginning to fall together. If the chemicals found in the parents’ bodies were to blame, they were acting as hand-me-down poisons, passed down from one generation to the next, that victimized the unborn and the very young. The conclusion was chilling.

But the host of disparate symptoms in everything from adult herring gulls to baby snapping turtles did not seem to add up. Some animals, like the gulls, exhibited strange behavior such as same-sex nests, while other species, including the double-crested cormorant, had visible gross birth defects such as club feet, missing eyes, crooked spines, and crossed bills. Again a pattern emerged from the confusing pieces of the puzzle as Colborn reflected on what she had learned by following her nose.

These were all cases of derailed development, a process guided to a significant extent by hormones. Most could be linked to disruption of the endocrine system.

This insight pointed Colborn’s investigation in another direction. She began reading everything she could find about the chemicals that showed up again and again in the tissue analyses of animals having trouble producing viable young. She quickly learned that the testing and reviews done by manufacturers and government regulatory agencies had focused largely on whether a chemical might cause cancer, but she found enough in the peer-reviewed scientific literature to prove that her hunch had been correct.

The hand-me-down poisons found in the fat of the wildlife had one thing in common: one way or another, they all acted on the endocrine system, which regulates the body’s vital internal processes and guides critical phases of prenatal development. The hand-me-down poisons disrupted hormones. (25-28)


[Description of Frederick vom Saal’s research on mice. His wombmate studies indicate how small shifts in hormone levels before birth can have consequences that last a lifetime. His work helped highlight the hazard posed by synthetic chemicals that can disrupt hormonal systems.” (29)]

[Discovery of male aggression. “Males with male wombmates and the highest testosterone exposure before birth were indeed the most aggressive toward other adult males, and males with female wombmates were the least aggressive.” (38-39)]

Scientists working in this field are still debating how estrogen shapes the development of males and females, particularly the development of the brain and behavior, but vom Saal believes that estrogen is helping to masculinize males by acting to enhance some effects of the male hormone testosterone. Together the two hormones influence the organization of the developing brain to increase the level of sexual activity the male mouse will exhibit as an adult. …

But variability is just one of the larger lessons emerging from vom Saal’s work. It has also opened a window on the powerful role of hormones in the development of both sexes and the extreme sensitivity of developing mammals to slight shifts in hormone levels in the womb. The wombmate studies have also underscored that hormones permanently “organize” or program cells, organs, the brain, and behavior before birth, in many ways setting the individual’s course for an entire lifetime. (39-40) …

What is astonishing about vom Saal’s wombmate studies is how little it takes to dramatically change the tune. Hormones are exceptionally potent chemicals that operate at concentrations so low that they can be measured only by the most sensitive analytical methods. When considering hormones such as estradiol, the most potent estrogen, forget parts per million or parts per billion. The concentrations are typically parts per trillion, one thousand times lower than parts per billion. One can begin to imagine a quantity so infinitesimally small by thinking of a drop of gin in a train of tank cars full of tonic. One drop in 660 tank cars would be one part in a trillion; such a train would be six miles long. (40) …

This is a degree of sensitivity that approaches the unfathomable, a sensitivity, vom Saal says, “beyond people’s wildest imagination.” If such exquisite sensitivity provides rich opportunities for varied offspring from the same genetic stock, this same characteristic also makes the system vulnerable to serious disruption if something interferes with normal hormone levels—a frightening possibility that first dawned on vom Saal when Theo Colborn called him to talk about synthetic chemicals that could act like hormones. (41) …

[What determines whether a fertilized egg becomes a male or female is not simply whether it has two X chromosomes or an XY configuration.]

In animals such as birds and humans, one sex is the basic model and the other is what might be described as a custom job, since the latter requires a sequence of additional changes directed by hormones to develop properly into the opposite sex. In birds, this basic model happens to be male. In mammals, including humans, the opposite is the case, and an embryo will develop into a female unless male hormones override the program and set it off on the alternative course.

Although the sperm delivers the genetic trigger for a male when it penetrates the egg, the developing baby does not commit itself to one course or another for some time. Instead, it retains the potential to be either male or female for more than six weeks, developing a pair of unisex gonads that can become either testicles or ovaries and two separate sets of primitive plumbing—one the precursor to the male reproductive tract and the other the making of the fallopian tubes and uterus. These two duct systems, known as the Wolffian and Mullerian ducts, are the only part of the male and female reproductive systems that originate from different tissues. All the other essential equipment—which might seem dramatically different between the two sexes—develop from common tissue found in both boy and girl fetuses. Whether this tissue becomes the penis or the clitoris, the scrotal sack that carried the testicles or the folds of labial flesh around a woman’s vagina, or something in between depends on the hormonal cues received during a baby’s development.

The big moment for the Y chromosome comes around the seventh week of life, when a single gene on the chromosome directs the unisex sex glands to develop into male testicles. In doing this, the Y chromosome throws the switch initiating the very first step in male development, the development of the testes, and that is the beginning and end of its role in shaping a male. From this point on, the remainder of the process of masculinization is driven by hormone signals originating from the baby’s brand-new testicles. In adult life, the testicles produce sperm to fertilize a woman’s eggs, the male’s contribution to reproduction and posterity. But the testicles play an even more important role in a male’s life before birth. Without the right hormone cues at the right time—cues emanating from the testicles—the baby will not develop the male body and brain that go along with the testicles. It might not even develop the penis required to deliver the sperm the testicles produce.

In girls, the changes that turn the unisex glands into ovaries, the part of the female anatomy that produces eggs, begin somewhat later, in the third to fourth month of fetal life. During this same period, one set of ducts—the Wolffian ducts that provide the option for a male reproductive tract-wither and disappear without any special hormone instructions. While the development of the female body isn’t as dependent on hormone cues as the development of males, animal research suggests estrogen is essential for proper development and normal functioning of the ovaries.

The process of laying the groundwork for the reproductive tract is more complicated in males and is marked by critical stages where hormones direct now-or-never decisions. Shortly after they are formed, the testicles produce a special hormone whose function is to trigger the disappearance of the female option—the Mullerian ducts. To accomplish this milestone, the hormone message must arrive at the right time, because there is only a short period when the female ducts respond to the signal to disappear. Then the testicles have to send another message to the Wolffian ducts, because they are programmed to disappear automatically by the fourteenth week unless they receive orders to the contrary.

The messenger is the predominantly male hormone testosterone, which insures the preservation and growth of the male Wolffian ducts. Under the influence of testosterone, these ducts form the epididymis, vas deferens, and seminal vesicles—the sperm delivery system that leads from the testicles to the penis.

A potent form of testosterone guides the development of the prostate gland and external genitals, directing the genital skin to form a penis and a scrotum that holds the testicles when they finally descend from the abdomen late in a baby’s development. A naturally occurring defect dramatically illustrates what can happen if these messages do not get through.

From time to time, a young patient will show up in a gynecologist’s office because the teenager still hasn’t had her first period although all the other girls in her class have passed this milestone. Usually nothing serious is wrong. But once in a rare while, the physician will deliver an utterly shocking diagnosis. The patient isn’t menstruating because despite all appearances, she is not female. Although such individuals have grown up as normal-looking girls, they have the XY chromosomes of males and testicles in their abdomen instead of ovaries. But because a defect makes them insensitive to testosterone, they never responded to the hormone cues that trigger masculinization. They never developed the body and brain of a male.

The pictures in medical textbooks of these unrealized males are fascinating, for there is nothing about their unclothed bodies that looks the least bit odd or unusual. As hard as one searches for a hint that a genetic male lurks inside these bodies, there is no sign of development derailed. These genetic males look like perfectly ordinary women with normally developed breasts, narrow shoulders, and broader hips.

These completely feminized males are the most extreme example of what happens when something blocks the chemical messages that guide development. If anything interferes with the testosterone or the enzyme that amplifies its effect, the common tissue found in boy and girl fetuses will develop instead into a clitoris and other external female genitals. In less extreme cases of disruption, males may have ambiguous genitals or abnormally small penises and undescended testicles.

But sex is more than a purely physical matter. According to physicians who treat them, these feminized males not only look like women, they act and think of themselves as women. There is nothing the least bit telling in their behavior to suggest that they are really male. In most animals, the development of a properly functioning male or female involves the brain as much as the genitals, and research such as vom Saal’s shows that hormones permanently shape some aspects of behavior before birth as much as they sculpt the penis. If an individual is going to act like a male as well as look like one, the brain must receive testosterone messages from the testicles during a critical period when brain cells are making some of their now-or-never decisions.

An individual who gets the wrong hormone messages during this critical period of brain development may show abnormal behavior and fail to mate even though it has the right physical equipment. In an influential 1959 study, Charles Phoenix of the University of Kansas found that female guinea pigs exposed to high levels of testosterone in the womb acted like males. They would not show the classic female mating posture, a raised posterior, known as “lordosis,” adults or respond normally to the female hormones that stimulate sexual behavior and reproduction.

No one debates that hormones act to give males and females different bodies and that their role in the development of animals and humans is pretty much the same. But how hormones influence the development of the human brain is hotly debated. Do they shape the brain and behavior in humans as dramatically as they do in mice or rats or guinea pigs? Are there structural differences between the brains of men and women, and is there any evidence that the differences stem from hormone influences before birth?

These questions are difficult to answer. Not only is human behavior more complex than that of vom Saal’s mice, but we aren’t free to give pregnant women various doses of hormones to see the effect on the brain development of their babies.

Those who have probed the question of whether the behavioral differences between men and women have a biological basis or are purely cultural have found evidence of some structural differences linked to hormones, but so far these sex-linked areas are fewer and less pronounced than those seen in rats. Psychologists have also reported certain general differences in the way men and women think, reporting that women have greater verbal skills as a rule and men tend to be better at solving spatial problems. Many also believe that the rough-and-tumble play and fighting seen to a much greater degree in young boys than in girls stems from biology rather than from culture or child-rearing methods.

At the same time that hormones are guiding at least some aspects of sexual development of the unborn child, these chemical messengers are also orchestrating the growth of the baby’s nervous and immune systems, and programming organs and tissues such as the liver, blood, kidneys, and muscles, which function differently in men and women. Normal brain development, for example, depends on thyroid hormones that cue and guide the development of nerves and their migration to the right area in this immensely complex organ.

For all these systems, normal development depends on getting the right hormone messages in the right amount to the right place at the right time. As this elaborate chemical ballet rushes forward at a dizzying pace, everything hinges on timing and proper cues. If something disrupts the cues during a critical period of development, it can have serious lifelong consequences for the offspring. (39-46)


As we pursue the mystery of hand-me-down poisons, two tragic episodes in medical history contain important lessons and immediate relevance to our quest. They leave no doubt that humans are vulnerable to hormone-disrupting synthetic chemicals and demonstrate that animal studies had repeatedly provided an early warning about the hazards for humans.

[(1) Thalidomide, prescribed to treat morning sickness in pregnant women, that resulted in babies born with severe deformities and malformations.

(2) DES (diethylstilbestrol), given to women experiencing problems during pregnancy in the belief that insufficient estrogen levels caused miscarriages and premature births, resulting in female babies with increased risks of cervical and vaginal cancer, congenital anomalies of the female and male genitourinary tracts, and adverse effects on fertility and reproductive function.]

Both effects “appeared to depend on the timing of drug use, not the dose. … A small dose of a drug or hormone that might have no effect at one point in a baby’s development, for example, might be devastating just a few weeks earlier.” (50-51)

The DES experience is rich in lessons. … It dramatized the dangers of interfering with the delicate balance of hormones during development. It showed how fragile the fetus is and how it passes through critical stages when it is particularly vulnerable. It underscored that an unborn baby is not just a small adult. Drugs and chemicals that have little effect on adults can cause serious and permanent damage to a baby during its rapid prenatal development.

Again and again, the DES experience brought home the common fate of mice and men. Rodents and humans exposed to DES in the womb suffer identical damage to the genitals and the reproductive tract, a parallel that also holds true not just for mammals but for many other animal types as well. To an astonishing degree, evolution has conserved through hundreds of millions of years a basic strategy in vertebrates for embryonic development that is dependent on hormones. Regardless of whether the offspring is a human or a deer mouse, a whale or a bat, hormones regulate its development in fundamentally the same way.

The DES experience offered another critical lesson as well that is relevant not just to those exposed to DES but to all of us. The developmental effects of DES made it clear that the human body could mistake a man-made chemical for a hormone. (68-69)


Despite the problems it would later cause, DES lived up to the promise in one regard-it mimicked natural estrogen. This fact alone is an intriguing puzzle, for this man-made chemical bears surprisingly little structural resemblance to natural estrogen. How could it act like a hormone?

This question lies at the heart of the deepening mystery of how foreign chemicals trick the body and disrupt its own chemical messengers. In the past half century since DES appeared, scientists have learned that DES is not unique in its hormone effects. One by one, they have stumbled upon many other chemicals-both man-made and natural compounds-that act like hormones, and gradually the realization has dawned that the world is full of hormone disruptors. Unlike DES, however, most don’t come in little pills.

By an interesting coincidence, in the very same year that Edward Dodds announced the synthesis of DES, a Swiss chemist, Paul Muller, discovered a powerful new pesticide, and both synthetic chemicals made their debut amid great acclaim in 1938. Just as DES was heralded as a “wonder drug,” DDT was hailed as a “miraculous pesticide.” Dodds received a knighthood for his efforts in synthesizing sex hormones, and Müller won the Nobel Prize in 1948.

Twelve years after the advent of these compounds, researchers at Syracuse University learned the two chemicals shared a deeper kinship. Although DDT had been developed to kill insects and not for use as a drug or synthetic hormone, it, too, seemed to have the effect of estrogen when it was given to young roosters: it feminized them. The males treated with DDT had severely underdeveloped testes and failed to grow the ample combs and wattles that roosters display. In considering these results, Verlus Frank Lindeman and his graduate student Howard Burlington noted that the chemical structure of DDT bears a similarity to that of DES.

However much these two synthetic chemicals resemble each other, these impostors do not look much like estrogen or the other steroid hormones made by the body itself. The steroid hormone family is one of three hormone groups, which are generally classified according to their chemical structure or function. The steroid hormones that help carry on the body’s never-ending internal conversation all share a common architecture based on four rings. The male and female hormones, testosterone and estrogen, may have powerfully different effects, but in diagrams of their chemical structure, they are remarkable similar. The divergent destinies of male and female hinge on an atom here and there. By contrast, DDT and DES have a two-ringed configuration. The difference between this arrangement and that of estrogen is immediately apparent even to someone who has never taken chemistry. Based on their structure, it would be impossible to mistake these synthetic chemicals for members of the steroid hormone family.

Yet for reasons that still aren’t fully understood, the body does mistake them for the real thing. (68-70)

The body has hundreds of different kinds of receptors, each one designed for a particular kind of chemical signal. Some receive messages from the thyroid gland, which may cue cells to consume more oxygen and generate more heat. Others are tuned to the adrenal glands, which send messages that regulate blood pressure and the body’s response to stress. The hypothalamus in the brain has all kinds of receptors to monitor hormone levels in the blood so the brain can signal the hormone-producing glands when adjustments are needed. And there is a whole class of mystery receptors, known as “orphan” receptors, that are tuned to messages that scientists have not yet identified.

Each hormone and its particular receptor have a “made for each other” attraction, which scientists describe as a “high affinity.” When they encounter one another, they grab hold, engaging in a molecular embrace known as “binding.” … They fit together … like a lock and key, and once joined, they move into the cell’s nucleus to “turn on” the biological activity associated with the hormone. This union of hormone and receptor targets genes that trigger the production of particular proteins. In the case of estrogen, these proteins accelerate cell division. So when estrogen joins with receptors in the uterus, it will cause the lining of that organ to thicken. Estrogen produces such a response in the first half of the menstrual cycle to prepare the uterus in the event an egg is fertilized when ovulation occurs at midcycle.

This lock-and-key notion has dominated the theory of how the body communicates through hormones. In endocrinology textbooks, one still finds flat assertions that receptors are highly discriminating about chemical structure and will bind only to their intended hormone or a very closely related compound. Although theory holds true in a general way, reality is proving considerably messier and unpredictable, not only in the case of the estrogen receptor but with other hormone receptors as well. (71-72)

How many man-made chemicals scramble the body’s chemical e ages? No one knows and no one has systematically screened the tens of thousands of synthetic chemicals created since World War II for such effects. As with kepone, which is now banned, many of those that are known have been discovered by accident.

To date, researchers have identified at least fifty-one synthetic chemicals—many of them ubiquitous in the environment—that disrupt the endocrine system in one way or another. Some mimic estrogen like DES, but others interfere with other parts of the system, such as testosterone and thyroid metabolism. This tally of hormone disruptors includes large chemical families such as the 209 compounds classified as PCBs, the 75 dioxins, and the 135 furans, which have a myriad of documented disruptive effects.

Most discussions of hormone-disrupting chemicals inevitably focus on DDT, the PCBs, and dioxin, but not because they necessarily pose the only or the gravest threat. These get the lion’s share of attention because they happen to be the only hormone-disrupting chemicals that scientists have studied in any depth. While admittedly far from the whole story, these well-known cases do, however, serve to illustrate a much broader problem, so they will also receive considerable attention in this book. The magnitude of this problem is still unclear, but those who have watched the list of hormone disruptors grow think the age of discovery is far from over. “There are probably a lot more,” says John McLachlan. (80-81)

However important, estrogen and the receptor mechanism are far from the whole story on endocrine disruption. Man-made chemicals scramble all sorts of hormone messages, and they can disrupt this communication system without ever binding with a receptor. If cellular phone messages aren’t getting through, the problem isn’t necessarily with your phone. There may be trouble somewhere else in the system, such as in the satellite that relays the message from continent to continent or the transmitter that sends the message into space. The same holds true with the endocrine system. …

And even within the group of compounds known to disrupt estrogen levels, other mechanisms can be at work. Although DDT is regarded as a classic estrogen mimic that elevates hormone levels, this is only one of its effects in the body. According to Gray, DDE, the form of DDT that persists the longest in the body fat of humans and animals, has the opposite effect. It depletes hormones by accelerating their breakdown and elimination, leaving the body short not just of estrogen but of testosterone and the other steroid hormones as well. This can lead to abnormally low hormone levels. Since a developing fetus is extremely sensitive to hormone levels, too little can be as devastating as too much. …

In Earl Gray’s view, animal studies of hormone-disrupting chemicals have clear and immediate relevance to humans. In the broader environmental debate, some have challenged the predictive value of rat studies to assess possible cancer risks posed by synthetic chemicals to humans on the grounds that animals and humans sometime react differently to a chemical. The use of animals to study hormone-disrupting chemicals is, however, fraught with less uncertainty, Gray explains, because scientists understand far more about the role of hormones in development than they do about the biological events that give rise to cancer. Moreover, the evidence show that humans and animals respond in generally the same way to hormone-disrupting chemicals. The available human data and the effect seen in lab animals show “a perfect correlation.” Earl Gray spells out the bottom line with intensity and directness.

“We know a lot about the process. We know it can be altered by chemicals. It is important to take the effects you see in animal studies seriously.”  (85-86)


[How is it that chemicals can be found in animals living far from where they are manufactured?]

The story of PCBs and how they have spread throughout the planet and into the body fat of almost every living creature is one the most fascinating and instructive chapters in the history of the of synthetic chemicals. Of the fifty-one synthetic chemicals that have now been identified as hormone disruptors, at least half, including PCBs, are “persistent” products in that they resist natural processes of decay that render them harmless. These long-lived chemicals will be a legacy and a continuing hazard to the unborn for year, decades, or in the case of some PCBs, several centuries.

Introduced in 1929, PCBs became the first big commercial success for a new elite of chemical engineers who would eventually synthesize tens of thousands of novel chemicals that exist nowhere in nature. The engineers created PCBs by adding chlorine atoms to a molecule with two joined hexagonal benzene rings known as a biphenyl. The result of their tinkering was a family of 209 chemicals known collectively as polychlorinated biphenyls, or PCBs, which soon proved to be immensely useful compounds.

In early assessments, PCBs seemed to have many virtues and no obvious faults. They are nonflammable and extremely stable. Toxicity tests at the time did not identify any hazardous effects. Confident of their safety as well as their utility, the Swann Chemical Company, which would soon become a part of Monsanto Chemical Company in 1935, quickly moved them into production and onto the market.

With the issuance of federal regulations requiring the use of nonflammable cooling compounds in transformers used inside buildings, PCBs quickly found a steady major market in the electrical industry. Other industries put PCBs to use as lubricants, hydraulic fluids, cutting oils, and liquid seals. In time, these chemicals also found their way into a host of consumer products and thus into the home. They made wood and plastics nonflammable. They preserved and protected rubber. They made stucco weatherproof. They became ingredients in paints, varnishes, inks, and pesticides. In retrospect, it is clear that the very characteristics that made them a runaway commercial success also made them one of our most serious environmental pollutants. (89-90)

Ten years later, in 1976, the United States banned the manufacture of PCBs, and other industrial countries eventually followed. In half a century of production, however, the synthetic chemical industry worldwide (excluding the USSR) had produced an estimated 3.4 billion pounds of PCBs, and much of it was already loose in the environment and beyond recall. Moreover, the ban did not address existing PCBs, allowing their use to continue in closed applications—such as transistors, electric ballasts, and small appliances—even today.

There is no way todiscover exactly how the PCBs in the polar bars made their way to the Svalbard archipelago or where they came from. But research over the past two decades has given scientists a good understanding of how PCBs travel through ecosystems and migrate over long distances. Based on this knowledge, it is possible to imagine the journey of an individual PCB molecule. Though the specific route and events in the journey we are about todescribe are hypothetical, the plot is a plausible scenario built from historical accounts and a myriad of scientific studies. (91) …

It has been three decades since health researchers discovered that DDT, PCBs, and other persistent chemicals were accumulating in human body fat and breast milk, as well as in every other part of the environment. The measurements have been the easy part. Since then, concerned scientists have been trying to understand their meaning. If we all carry around an alphabet soup of novel chemicals in our body fat, how is it affecting us? How is it affecting our children?

While researchers do not have all the answers to these questions, they are convinced that humans carry high enough levels of synthetic chemicals to endanger their children. Without knowing exactly how all these chemicals act, separately or together, the researchers have linked them not only to damage in wildlife offspring but in humans as well. We explore these links in later chapters.

While prenatal exposure seems to pose the greatest hazard, health specialists also worry about the chemicals passed on in breast milk because some sensitive developmental processes continue in the weeks immediately after birth. During breast feeding, human infants are exposed to higher concentrations of these chemicals than in any subsequent time in their lives. In just six months of breast feeding, a baby in the United States and Europe gets the maximum recommended lifetime dose of dioxin, which rides through the food web like PCBs and DDT. The same breast feeding baby gets five times the allowable daily level of PCBs set by international health standards for a 150-pound adult.

The contamination of breast milk has been particularly severe among indigenous people in the high Arctic, where many people still eat the wild food the land and sea provide. There, researchers have found that babies take in seven times more PCBs than the typical infant in southern Canada or the United States. The PCBs and other chemicals that contaminate the infants have almost all arrived by wind and water currents. (106-107)

… No matter where we live, we share their fate to some degree. Many chemicals that threaten the next generation have found their way into our bodies. There is not safe, uncontaminated place. (109)


Out in the wild, Theo Colborn quickly learned, persistent chemicals were showing up in the most unexpected places. By early 1990, she knew that the problem extended far beyond the Great

Lakes. Her file cabinets contained dozens of papers showing that scientists had found the same persistent chemicals everywhere they had bothered to look. The contamination was truly global and well documented. …

Toxicologists are fond of the axiom that it is the dose that makes the poison. The mere presence of a substance doesn’t necessarily product damage. Even though our body fat and blood testify to our exposure to PCBs, DDT, dioxin, chlordane, and a litany of other persistent chemicals, the amounts we carry are counted in parts per billion or even parts per trillion. Unimaginably small amounts.

Nevertheless, Colborn knew that Fred vom Saal’s work showed that even tiny shifts in hormone levels before birth had major consequences for mouse pups. Based on his experiments, ten or twenty parts per trillion of natural estrogen are not inconsequential.

But estrogen is a natural hormone and an extremely potent one at that. How much of a synthetic chemical does it take to disrupt hormone levels and do lifelong harm? How much? The question haunted Colborn. She kept searching through the scientific literature, moving from one paper to another, looking for clues. With the passion of a pack rat, she collected every sort of relevant evidence and filed even the smallest tidbit in an ever expanding database on hormone disruption. She had been at it for three years, already, trying to synthesize the far-flung studies from hundreds of researchers in dozens of disciplines into a coherent picture. It was the kind of work that almost never gets done by either the government or the universities because there is no support and no reward for doing it; nobody ever got tenure for analyzing and assessing other people’s work. Yet how absurd to spend billions on individual scientific studies but virtually nothing to figure out what they collectively say about the state of the Earth. …

As she tried to keep abreast of the latest science on half a dozen fronts, she usually had little time to reflect on the implications of what she was doing. But once in a rare while, alone late at night, she would sit by her apartment window overlooking the illuminated dome of the capitol in Washington and think about what all of the pieces might add up to. The prospects were frightening. What were the long-term effects of these hormone-disrupting chemicals? Were we sabotaging our own fertility as well as that of wildlife? Was it possible that we were unknowingly and invisibly undermining the reproductive future of our children? The thought seemed on the face of it preposterous. How could human fertility be in jeopardy when world population was soaring from five billion toward ten? Maybe she was chasing phantoms.

A few months later, any lingering doubts vanished. (110-112) … In the world of synthetic chemicals, dioxin has enjoyed the reputation of being the worst of the troublemakers—the most deadly, the most feared, and the most elusive to scientists seeking to unravel the secrets of its toxicity. Lab tests had shown dioxin to be thousands of times more deadly than arsenic to guinea pigs, who died after swallowing only one-millionth of a gram per kilogram of body weight, and the most potent carcinogen ever tested in a number of animal species.

Unlike most other hormone-disrupting synthetic chemicals, however, dioxin was not created intentionally. Although some dioxin is released by volcanoes and forest fires, the chemical—known to scientists as 2,3,7,8-TCDD and to the public as “the most toxic chemical on earth”—is for the most part an inadvertent by-product of twentieth-century life, a contaminant created during the manufacture of certain chlorine-containing chemicals such as pesticides and wood preservatives, as well as by bleaching paper with chlorine, incinerating trash containing plastics and paper, and burning fossil fuels. Like DDT and PCBs, dioxin is a fat-loving persistent compound that accumulates in the body. And like other persistent chemicals, it has been detected virtually everywhere—in air, water, soil, sediment, and food.

[The dioxin family also contains many other members, including the synthetic herbicide Agent Orange, dumped in Vietnam from 1962 to 1971. A 1993 National Academy of Sciences report “found sufficient evidence to link exposure to dioxin-contaminated herbicides to three cancers: soft-tissue sarcoma, non-Hodgkin’s lymphoma, and Hodgkin’s disease.” (114)]

Scientists understand less about dioxin than they do about the more straightforward hormone mimics or blockers, such as methoxychlor and vinclozolin, which cause disruption by binding with estrogen or androgen receptors. For this reason, Gray explains, he would be less confident predicting what might happen to humans based on animal experiments. Recent discoveries are, however, giving scientists increasing confidence that the responses in humans and animals are likely to be roughly similar. Researchers have found that dioxin acts almost exclusively through a receptor-one of the “orphan” receptors whose normal chemical messenger remains unknown. Although this receptor was first identified in animals, studies have shown that humans also have a fully functional aryl hydrocarbon, or Ah, receptor that binds to dioxin. Once dioxin occupies the receptor in a human cell, researchers have found it binds to DNA in the cell nucleus, prompting many of the same changes in gene expression seen in animal experiments. Humans seem no less sensitive to this effect. But what happens afterward to produce all of dioxin’s disparate biological effects, including developmental disruption, remains a mystery.

However it happens, dioxin acts like a powerful and persistent hormone that is capable of producing lasting effects at very low doses—doses similar to levels found in the human population. (120)


[The accidental discovery by Drs. Ana Soto and Carlos Sonnenschein at Tufts Medical School that a new resin used in the plastic test tubes they were using to conduct tests in human breast cancer cells about whether certain “growth factors” cause cells to multiply was a “phantom estrogen.”]

… For years, the ongoing discussion about possible human health risks from synthetic chemicals had been based on the assumption that most human exposure comes from chemical residues, primarily pesticides, in food and water. Now Soto and Sonnenschein had discovered hormone-disrupting chemicals where you would least expect them—in ubiquitous products considered benign and inert. Here was glaring evidence of our vast ignorance about hormone-disrupting chemicals in the environment and how we might be exposed to them. … The plastic, which they had always regarded as a benign, inert substance must contain chemicals that can cause significant, worrisome changes in human cells. Far from inert, the plastic appeared biologically active. (125, 127)

… It took months to purify the compound in the plastic that caused the estrogenlike effect in their experiments and do a preliminary identification using mass spectrometry analysis. … At the end of 1989—two years after their detective work had started—they had a definitive answer: p-nonylphenol.

Through further investigation, Soto and Sonnenschein learned that p-nonylphenol is one of a family of synthetic chemicals known as alkylphenols. Manufacturers add nonylphenols to polystyrene and polyvinyl chloride, known commonly as PVC, as an antioxidant to make these plastics more stable and less breakable. The plastic centrifuge tubes in which they stored blood serum had been of polystyrene—

a plastic that, depending on the manufacturer, may or may not include nonylphenols.

In a search of the scientific literature, they found bits and pieces of information that only heightened their concern. One study had found that the food processing and packaging industry used PVCs that contained alkylphenols. Another reported finding nonylphenol contamination in water that had passed through PVC tubing. Soto and Sonnenschein even discovered that nonylphenol is used to synthesize a compound found in contraceptive creams-nonoxynol-9. In studies with rats, researchers had found that the nonoxynol-9 breaks down once inside the animal’s body, creating nonylphenol.

They also learned that the breakdown of chemicals found in industrial detergents, pesticides, and personal care products can likewise give rise to nonylphenol. The United States and other countries use vast quantities of these chemicals called alkylphenol polyethoxylates—450 million pounds in 1990 in the United States alone and more than 600 million pounds globally. Although the products purchased by the consumer, such as detergents, are not themselves estrogenic, studies have found that bacteria in animals’ bodies, in the environment, or in sewage treatment plants degrade these alkylphenol polyethoxylates, creating nonylphenol and other chemicals that do mimic estrogens. (128-129)

The brother and sister team of Fatima Olea, a food toxicologist, and Nicolas Olea, a physician specializing in endocrine cancers, had visited the United States and worked at the Tufts Medical School lab with Soto and Sonnenschein. Their time in Boston had alerted them to the potential hazards from plastics.

Their suspicions proved well-founded. In a study analyzing twenty brands of canned foods purchased in the United States and in Spain, they not only discovered bisphenol-A, the same chemical that Stanford researchers had found leaching from polycarbonate lab flasks, they also found stunningly high concentrations in such products as corn, artichokes, and peas. Bisphenol-A contamination was detected in about half the canned foods they analyzed. In some instances, the cans contained as much as eighty parts per billion—twenty-seven times more than the amount that the Stanford team reported was enough to make breast cancer cells proliferate. At such levels, a synthetic estrogen mimic might contribute significantly to a person’s exposure regardless of whether it is a “weak” estrogen or not.

Biologically active plastics were leaching from cans, containers where one would not expect to find plastic at all.

All the incidents discussed in this chapter involve synthetic chemicals that mimic estrogen, but the synthetic chemicals that disrupt hormones do not all act like estrogens. Other hormones in the body are vulnerable as well. Recall, for example, that some fungicides interfere with the action of male hormones. Moreover, in ongoing studies at the U.S. Environmental Protection Agency lab in Research Triangle Park, North Carolina, Earl Gray has discovered that even the classic estrogen mimics have far broader effects than scientists in this field had hitherto recognized. Some of these “estrogenic” synthetic chemicals, it turns out, also take a direct toll on males by blocking the androgen receptors that respond to male hormones.

The question of exposure lies at the heart of the debate about whether hormone-disrupting chemicals pose a hazard or not. (135)

Although synthetic chemicals now seem an inextricable part of the fabric of modern life, they have come into common use relatively recently. The synthetic chemical industry first developed in the second half of the nineteenth century, after chemists learned to synthesize textile dyes in the laboratory and manufacturing of these man-made dyes began on a large scale. But the “chemical age” that has transformed daily life did not dawn until around World War II, when new discoveries and new techniques revolutionized the industry and led to an era of explosive expansion in the production of synthetic chemicals. Between 1940 and 1982, production of synthetic materials increased roughly 350 times, and billions of pounds of man-made chemicals poured into the environment, exposing humans, wildlife, and the planetary system to countless compounds never before encountered. (137)

The discovery that hormone-disrupting chemicals may lurk in unexpected places, including products considered biologically inert such as plastics, has challenged traditional notions about exposure and suggests that humans may be exposed to far more than previously believed. (139)

Each and every discovery discussed in this chapter has added to scientific knowledge about endocrine-disrupting chemicals, but ironically, these discoveries have also underscored our astonishing ignorance about the man-made chemicals that we have spread liberally across the face of the Earth and incorporated into every part of our daily lives.

In truth, no one yet knows how much it takes of these synthetic hormone-disrupting chemicals to pose a hazard to humans. All evidence suggests that it may take very little if the exposure occurs before birth. In the case of dioxin at least, the recent studies have shown that human exposure is sufficient to be of concern.

Despite our vast ignorance, we should not lose sight of some important things we do know.

Most of us carry several hundred persistent chemicals in our body, including many that have been identified as hormone disruptors. Moreover, we carry them at concentrations several thousand times higher than the natural levels of free estrogen-the estrogen that is not bound up by blood proteins and is therefore biologically active.

As Fred vom Saal has discovered, vanishingly small amounts of free estrogen are capable of altering the course of development in the womb—as little as one-tenth of a part per trillion. Given this exquisite sensitivity, even small amounts of a weak estrogen mimic—a chemical that is one thousand times less potent than the estradiol made by the body itself-may nevertheless spell big trouble.


[Description of findings of mass die-off of animal species around the world, such as beluga whales.]

… There is growing evidence in the scientific literature that both prenatal exposure to hormone-disrupting chemicals and direct adult exposure to toxic compounds can weaken immunity. …

In light of the growing evidence that many synthetic chemicals disrupt hormones, impair reproduction, interfere with development, and undermine the immune system, we must now ask to what degree contaminants are responsible for dwindling animal populatition. Could hormone disruptors account wholly or in part for some losses that have been blamed on classically invoked factors such as habitat loss or overexploitation? Have overexploited species failed to rebound after protection because synthetic chemicals are impairing reproduction? (147)

[Descriptions of various species—the Florida panther, Florida alligators, bald eagles, mink, otters, Great Lakes lake trout and salmon, whales, dolphins, seals, and polar bears— that seem to indicate that hormone-disrupting synthetic chemicals may be behind reproductive problems.]

With the growing amount of evidence and theories that link wildlife problems to hormone disruption, there is now good reason to regard endocrine-disrupting chemicals as a major long-term threat to the world’s biodiversity and perhaps an immediate threat to certain endangered species, such as the St. Lawrence belugas and the Florida panthers. In searching for the causes of loss, scientists must look for functional changes, such as impaired reproduction and altered behavior, along with more evident disruptions, such as vanishing habitat and changing climate. As many of the cases discussed in this chapter demonstrate, it is important to look beyond appearances. Animals that appear normal and healthy may, in fact, show skewed hormone ratios, scrambled sex organs, or physical changes in their brains when one takes a closer look. Diminished and impaired by invisible damage, such animals lose the edge honed by millions of years of natural selection. They may lose their ability to withstand otherwise tolerable stresses or to rebound after natural disasters. For no apparent reason, they may suddenly disappear or slowly, imperceptibly slip into extinction. (166)


“Our fate is connected with the animals,” Rachel Carson wrote more than three decades ago in Silent Spring, a now classic indictment of synthetic pesticides and human hubris that helped launch the modem environmental movement. This has long been a guiding belief among environmentalists, wildlife biologists, and others who recognize two fundamental realities—our shared evolutionary inheritance and our shared environment. What is happening to the animals in Florida, English rivers, the Baltic, the high Arctic, the Great Lakes, and Lake Baikal in Siberia has immediate relevance to humans. The damage seen in lab animals and in wildlife has ominously foreshadowed symptoms that appear to be increasing in the human population.

As noted in earlier chapters, basic physiological processes such as those governed by the endocrine system have persisted relatively unchanged through hundreds of millions of years of evolution. Evolutionary narratives tend to highlight the innovations of natural selection, ignoring the stubborn conservative streak that has marked the history of life on Earth. At the same time that evolution experimented greatly with form, shaping the vessels in various and wondrous ways, it has strayed surprisingly little from an ancient recipe for life’s biochemical brew. In examining our place in the evolutionary lineage, humans tend to focus inordinately on those characteristics that make us unique. But these differences are small, indeed, when compared to how much we share not only with other primates such as chimpanzees and gorillas, but with mice, alligators, turtles, and other vertebrates. Though turtles and humans bear little physical similarity, our kinship is unmistakable. The estrogen circulating in the painted turtle seen basking on logs during lazy summer afternoons is exactly the same as the estrogen rushing through the human bloodstream.

Humans and animals share a common environment as well as a common evolutionary legacy. Living in a man-made landscape, we easily forget that our well-being is rooted in natural systems. Yet all human enterprise rests on the foundation of natural systems that provide a myriad of invisible life-support services. Our connection to these natural systems may be less direct and obvious than those of an eagle or an otter, but we are no less deeply implicated in life’s web. No one has stated this fundamental ecological principle more simply than the early twentieth-century American environmental philosopher, John Muir. “When we try to pick out anything by itself, we find that it is bound by a thousand invisible cords … to everything in the universe.”

Our regrettable experience with persistent chemicals over the past half century has demonstrated the reality of this deep and complex interconnection. Whether we live in Tokyo, New York, or a remote

Inuit village in the Arctic thousands of miles from farm field or sources of industrial pollution, all of us have accumulated a store of persistent synthetic chemicals in our body fat. Through this web of inescapable connection, these chemicals have found their way to each and every one of us just as they have found their way to the birds, seals, alligators, panthers, whales, and polar bears. With this shared biology and shared contamination, there is little reason to expect that humans will in the long term have a separate fate. (167-168)

Because the endocrine disruption question has surfaced so recently, the scientific case on the extent of the threat is still far from complete. Nevertheless, if one looks broadly at a wide array of existing studies from various branches of science and medicine, the weight of the evidence indicates that humans are in jeopardy and are perhaps already affected in major ways. Taken together, the pieces of this scientific patchwork quilt have, despite admitted gaps, a cumulative power that is compelling and urgent.

This was the lesson from the historic meeting on endocrine disruption that took place in July 1991 at the Wingspread Conference Center in Racine, Wisconsin. Over the years, dozens of scientists have explored isolated pieces of the puzzle of hormone disruption, but the larger picture did not emerge until Theo Colborn and Pete Myers finally brought twenty-one of the key researchers together. At this unique gathering, specialists from diverse disciplines ranging from anthropology to zoology shared what they knew about the role of hormones in normal development and about the devastating impacts of hormone-disrupting chemicals on wildlife, laboratory animals, and humans. For the first time, Ana Soto, Frederick vom Saal, Michael Fry,

Howard Bern, John McLachlan, Earl Gray, Richard Peterson, Peter Reijnders, Pat Whitten, Melissa Hines, and others explored the exciting connections between their work and the ominous implications that arose from this exercise. As the evidence was laid out, the parallels proved remarkable and deeply disturbing. The conclusion seemed inescapable: the hormone disruptors threatening the survival of animal populations are also jeopardizing the human future.

At the end of the session, the scientists issued the Wingspread Statement, an urgent warning that humans in many parts of the world are being exposed to chemicals that have disrupted development in wildlife and laboratory animals, and that unless these chemicals are controlled, we face the danger of widespread disruption in human embryonic development and the prospect of damage that will last a lifetime.

The pressing question is whether humans are already suffering damage from half a century of exposure to endocrine-disrupting synthetic chemicals. Have these man-made chemicals already altered individual destinies by scrambling the chemical messages that guide development?

Many of those familiar with the scientific case believe the answer is yes. Given human exposure to dioxinlike chemicals, for example, it is probable that some humans, especially the most sensitive individuals, are suffering some effects. But whether hormone-disrupting chemicals are now having a broad impact across the human population is difficult to assess and even harder to prove. This is inescapable in light of the nature of the contamination, the transgenerational effects, the often long lag time before damage becomes evident, and the invisible nature of much of this damage. Those trying to document whether perceived increases in specific problems reflect genuine trends in human health find themselves thwarted by a dearth of reliable medical data. Few disease registries exist for anything except cancers. A number of pediatricians from various parts of the United States have expressed their concern about an increasing frequency of genital abnormalities in children such as undescended testicles, extremely small penises, and hypospadias, a defect in which the urethra that carries urine does not extend to the end of the penis, but it is virtually impossible to document these anecdotal reports. Unfortunately, the problems caused by endocrine disruption may have to reach crisis proportion before we have a clear sign that something serious is happening. … (170-171)

Laboratory experiments, wildlife studies, and the human DES experience link hormone disruption with a variety of male and female reproductive problems that appear to be on the rise in the general human population—problems ranging from testicular cancer to endometriosis, a condition in which tissue that normally lines the uterus mysteriously migrates to the abdomen, ovaries, bladder, or bowel, resulting in growths that cause pain, severe bleeding, infertility, and other problems. (172)

[Evidence for the reduction in male sperm counts and the increase of prostate cancer and in hormone-responsive breast cancer.]

Our fears about toxic chemicals have typically centered around cancer and other physical illnesses. But as one surveys the scientific literature, it becomes quickly apparent that physical disease or visible birth defects may not be the most immediate danger. Long before concentrations of synthetic chemicals reach sufficient levels to cause obvious physical illness or abnormalities, they can impair learning ability and cause dramatic, permanent changes in behavior, such as hyperactivity. Save for a few compounds such as PCBs, we know virtually nothing about the hazards posed to thinking and behavior by the thousands of synthetic chemicals in commerce.

What little we do know about those few chemicals that have been studied has alarming implications. Both animal experiments and human studies report behavioral disorders and learning disabilities similar to those reported with increasing frequency among school children across the nation. In the United States, an estimated five to ten percent of school-age children suffer from a suite of symptoms related to hyperactivity and attention deficit that make it difficult for them to pay attention and learn. Countless others experience learning problems ranging from difficulties with memory to impaired fine motor skills that make it harder to hold a pen and learn how to write.

Scientists still do not have a complete understanding of how PCBs impair neurological development in the womb and early in life, but emerging evidence suggests that the ability of PCBs to cause brain damage stems in part from disruption to another component of the endocrine system, thyroid hormones.

Extensive research on the developing brain and nervous system has found that thyroid hormones help orchestrate the elaborate step-by-step process that is required for normal brain development. As touched on in Chapter 3, these hormones stimulate the proliferation of nerve cells and later guide the orderly migration of nerve cells to appropriate areas of the brain. The brain and nervous system, like other parts of the body, pass through critical periods during their development both in the womb and in the first two years of life. When thyroid levels are too high or too low, this development process will go awry and permanent damage will result, which can range from mental retardation to more subtle behavioral disorders and learning disabilities. The precise nature of the damage done by abnormal thyroid levels will depend on the timing and the extent of the disruption. (186-187)

Two studies done in the United States have attempted to discover whether children suffer neurological damage when exposed through their mothers to the normal range of contamination encountered in the environment. Both reported signs of impaired neurological development, which might not be evident to the parents but could be detected through specialized tests.

The first study, done in the early 1980s by psychologists Sandra and Joseph Jacobson of Wayne State University, enlisted new mothers in Michigan who had eaten Great Lakes fish, which contain significant levels of PCBs and numerous other chemical contaminants. Despite the contamination levels, state fish and game agencies in the Great Lakes region continue to stock salmon, lake trout, and other game fish, and sport fishing remains a 3- to 4-billion-dollar industry. Signs posted by state health officials at some fishing area warn that eating salmon and lake trout may be hazardous to health, but many fishermen and their families continue to eat what they catch. The women in the fish-eating group in this study had all eaten two or three fish meals a month in the six years before becoming pregnant, although some had eaten no fish during pregnancy. Since PCBs are persistent, these women accumulated them in their body fat and then passed the PCBs on to their babies through the placenta and through breast milk.

Differences between the children of fish-eaters and nonfish-eaters were evident immediately at birth. The higher the mother’s consumption of Lake Michigan fish, the lower the birth weight and the smaller the head circumference of her baby. A series of tests done at birth and at intervals afterward also found persistent evidence of neurological impairment. The Jacobsons cannot be certain, however, that PCBs are solely responsible for the effects seen in the children born to these women because their mothers were exposed to so many other chemicals as well.

Among the more than three hundred children tested in this study, those whose mothers had eaten greater quantities of fish showed subtle signs of damage, including weak reflexes and more jerky, unbalanced movements as newborns . In later testing at seven months of age, the Jacobsons found signs of impaired cognitive function based on a test in which a child is shown two identical pictures of human faces posted on a board. After a period of time, the researcher will remove the board, replace one of the pictures with a new face, and show the display to the child again. A child normally recognizes the new face and spends more time looking at it rather than the face the child had seen before. The higher the PCB levels in the mother, the less time an infant spent looking at the new picture. Children with lower scores on this test tend to perform more poorly on intelligence tests during childhood. When the children were tested again at four years of age, the children of women with the highest PCB levels had lower scores in verbal and memory tests. (190-191)

As we wrestle with the question of how much chemical contaminants are contributing to the trends and societal patterns we see—in breast cancer, prostate disease, infertility, and learning disabilities—it is important to keep one thing in mind. Scientists keep finding significant, often permanent effects at surprisingly low doses. The danger we face is not simply death and disease. By disrupting hormones and development, these synthetic chemicals may be changing who we become. They may be altering our destinies. (197)


Early in her detective work, Theo Colborn stumbled onto a long-forgotten study published in the Proceedings of the Society of Experimental Biology and Medicine in 1950—the first warning in the scientific literature that synthetic chemicals could have the inadvertent effect of disrupting hormones. The paper by two Syracuse University zoologists, Verlus Frank Lindeman and his graduate student Howard Burlington, described how doses of DDT prevented young roosters from developing into normal males and even suggested that the pesticide was acting as a hormone. So the first bizarre, frightening evidence of hormone havoc had surfaced soon after the chemical age swept into American life at the end of World War II like a tsunami. Colborn posted the Burlington and Lindeman paper above her desk—a reminder of the slow acceptance of new ideas.

How did we miss so many warning signs, and for so long?

Colborn’s own experience with the Great Lakes provides part of the answer. Our obsession with cancer blinds us to other dangers. There is a strong tendency, seen again and again in this story, to overlook or ignore important new evidence that does not fit into reigning concepts about how things work and what is important—a strong tendency to turn a deaf ear. (198-199)

With cancer as the ultimate measure of our fears, it was widely assumed that setting levels based on cancer risk would protect humans as well as fish and wildlife from all other hazards as well. So over the past two decades, pesticide manufacturers and federal regulators looked mainly for cancer and obvious hazards such as lethal toxicity and gross birth defects in screening chemicals for safety. Cancer has also dominated the scientific research program exploring possible human health effects from chemical contaminants in the environment. This preoccupation with cancer has blinded us to evidence signaling other dangers. It has thwarted investigation of other risks that may prove equally important not only to the health of individuals but also to the well-being of society.

If this book contains a single prescriptive message, it is this: we must move beyond the cancer paradigm. Until we do, it will be impossible to grapple with the challenges of hormone-disrupting chemicals and the threat they pose to the human prospect. This is not simply an argument for broadening our horizons to recognize additional risks. We need to bring new concepts to our consideration of toxic chemicals. The assumptions about toxicity and disease that have framed our thinking for the past three decades are inappropriate and act as obstacles to understanding a different kind of damage.

Hormone-disrupting chemicals are not classical poisons or typical carcinogens. They play by different rules. They defy the linear logic of current testing protocols built on the assumption that higher doses do more damage. For this reason, contrary to our long-held assumption, screening chemicals for cancer risk has not always protected us from other kinds of harm. Some hormonally active chemicals appear to pose little if any risk of cancer. And as Lindeman and Burlington discovered, such chemicals are typically not poisons in the normal sense. Until we recognize this, we will be looking in the wrong places, asking the wrong questions, and talking at cross-purposes.

Up to now, our concept of injury from toxic chemicals has focused primarily on two things: whether a chemical damages and kills cells as poisons do or whether it attacks the DNA, our genetic blueprint, and permanently alters it by causing a mutation as carcinogens do. With poisoning, the consequences can be illness or death for the affected human or animal. Mutations can eventually give rise to cancer.

At levels typically found in the environment, hormone-disrupting chemicals do not kill cells nor do they attack DNA. Their target is hormones, the chemical messengers that move about constantly within the body’s communications network. Hormonally active synthetic chemicals are thugs on the biological information highway that sabotage vital communication. They mug the messengers or impersonate them. They jam signals. They scramble messages. They sow disinformation. They wreak all manner of havoc. Because hormone messages orchestrate many critical aspects of development, from sexual differentiation to brain organization, hormone-disrupting chemicals pose a particular hazard before birth and early in life. As previous chapters have recounted, relatively low levels of contaminants that have no observable impact on adults can have devastating impacts on the unborn. The process that unfolds in the womb and creates a normal, healthy baby depends on getting the right hormone message to the fetus at the right time. The key concept in thinking about this kind of toxic assault is chemical messages. Not poisons, not carcinogens, but chemical messages. (202-204)

The cancer paradigm also hampers the recognition of the effects of endocrine disruption because it characterizes the threat as disease. Hormone-disrupting chemicals can diminish individuals without making them sick. For this reason, there is an urgent need to look for “impaired function” as well as for disorders that fit the classic notions of disease. For example, having a poor short-term memory or difficulty in paying attention because of exposure to PCBs is very different from having a brain tumor. The former are deficits,

Not diseases, but they can nevertheless have serious consequences over a lifetime and for a society. They erode human potential and undermine the quality of human life. They undermine the ways in which humans interact with one another and thereby threaten the social order of modern civilization. (206-207)

If we are to come to grips with this threat, we must also shift to a different way of making judgments about environmental contaminants. There is little chance of showing a simple cause-and-effect link between any one or selected groups of hormone-disrupting synthetic chemicals and problems such as the drop in human sperm count that we have already witnessed. Risk assessment in the real world must respond to real problems in real time.

To address this need, some in the environmental field have begun developing an assessment method known as eco-epidemiology. This method, which was pioneered by Glen Fox, Canadian Wildlife Service, and Michael Gilbertson at the International Joint Commission, the advisory body to the United States and Canadian governments on Great Lakes policy, draws together information from a variety of sources, including wildlife data, laboratory studies, and research on the mechanisms of hormone action or toxicity, and makes pragmatic judgments based on the entire body of evidence. In this approach, one assesses the totality of the information in the light of epidemiological criteria for causality, such as whether the exposure precedes the effect, whether there is a consistent association between a contaminant and damage, and whether the association is plausible in light of the current understanding of biological mechanisms. But this real-world environmental detective work comes to judgment based on “the weight of the evidence” rather than on scientific ideals of proof that are more appropriate to controlled laboratory experiments and the practice of science than to problem solving and protecting public health in the real world. As some have noted, it is akin to the decision-making process a physician uses to diagnose a case of appendicitis—where failing to act has grave consequences. In the same way that accumulating evidence and common-sense inferences led to the conclusion that smoking causes lung cancer, it may soon be possible to conclude, if not prove, based on the weight of the evidence, that hormone-disrupting chemicals are linked to testicular cancer, falling sperm counts, and learning disabilities and attention deficits inchildren.

Cancer is a dramatic disease with devastating effects on victims and their families. It poses little threat, however, to the survival of animal and human populations as a whole. While cancer is tragic on a personal level, healthy populations can quickly replace individuals lost to the disease.

Because hormone-disrupting chemicals act broadly and insidiously to sabotage fertility and development, they can jeopardize the survival of entire species—perhaps in the long run, even humans. This might be hard to imagine in a world facing soaring human numbers, but the sperm count studies suggest environmental contaminants are already having an impact on the human population as a whole, not just on individuals. In their assault on development, these chemicals have the power to erode human potential. In their assault on reproduction, they not only undermine the health and happiness of individuals suffering from infertility, they attack a fragile biological system that over billions of years of evolution has allowed life to miraculously recreate life. (208-209)


The threat explored in this book may seem overwhelming, especially to those confronting it for the first time. Feelings of fright and helplessness are, in our experience, not unusual. This is indeed a frightening problem. No one should underestimate its seriousness even though the magnitude of this threat to human health and wellbeing is as yet unclear. It would likewise be dangerous to retreat into denial, which can be a strong temptation in the face of large, insidious problems that leave individuals feeling helpless and hopeless.

But however grim and unsettling the facts appear in this instance, facts are not fate. Trends are not destiny. Three decades ago, Rachel Carson’s predictions about the impacts of synthetic pesticides led to major changes in their use and thus prevented much of the apocalyptic “silent spring” she envisioned. Today, the growing scientific knowledge about endocrine-disrupting chemicals gives us similar power to avert the hazards outlined in previous chapters. This should be reason for hope rather than despair.

Unfortunately, however, solutions to this problem will be neither quick nor easy. Much of the concern about hormonally active synthetic chemicals arises from the persistence that many of them have in the environment. Many don’t readily degrade into benign components. A generation after industrial countries stopped the production of the most notorious of these persistent chemicals, their legacy endures in food and in human and animal bodies. Some will be in the environment for decades, and in a few cases even centuries. At the same time, other hormonally active chemicals remain in production, and unexpected new sources of exposure continue to come to light. Most disturbing of all, many of us already carry contamination levels that may put us and our children at risk.

Defending ourselves from this hazard requires action on several fronts aimed at eliminating new sources of hormone disruption and minimizing exposure to hormonally active contaminants already abroad in the environment. This will entail scientific research; redesign of chemicals, manufacturing processes, and products by companies; new government policies; and efforts by individuals to protect themselves and their families. Tragically, there is no way to repair the damage done to individuals who now suffer impairments stemming from chemically caused disruption during their early development. Such damage cannot be undone. But with diligent work by government bodies, scientists, corporations, and individuals, we can reduce the threat to the next generation. Over time, the ill effects now evident in wildlife and humans could diminish and gradually disappear.

That is the good news in this troubling picture. Although hormone-disrupting chemicals can cause grievous, permanent damage to those exposed in the womb, they do not attack genes or cause mutations that persist across generations. They have not altered the basic genetic blueprint that underlies our humanity. Remove the disruptors from the mother and the womb, and the chemical messages that guide development can once again arrive unimpeded. (210-211)

[Things individuals can do: (1) Know your water, (2) Choose your food intelligently, (3) Avoid unnecessary uses and exposure.]

Improving Protection

While individuals can do a great deal to protect themselves, these efforts must be matched by broad government action to eliminate synthetic chemicals that disrupt hormones.

It is beyond the scope of this book to provide a detailed critique of the laws and regulations relevant to this problem: Nonetheless, it is possible to identify several basic principles that can inform future efforts to improve the laws protecting people and ecosystems.

Following the model of the 1987 Montreal Protocol, an international treaty that mandates the phase-out of chlorofluorocarbons and other ozone-depleting chemicals, the United States and other nations should move quickly to implement comprehensive international treaties to halt the use and ecological dispersal of biologically active persistent compounds such as PCBs, DDT, and lindane. While negotiating such international environmental agreements is admittedly challenging, past experience has shown that governments can come together and act in the face of a genuine threat to human welfare. These protocols on persistent hormone-disrupting chemicals should phase out the production and use of these compounds worldwide and provide institutional and financial support for their containment, retrieval, and cleanup.

As a first step, these protocols should require the prior informed consent of countries that are importing chemicals that become persistent contaminants. The exporting business or agency should be required to notify an international monitoring body of each trade and to notify the importing country of the nature of the compounds and the associated risk.

At the same time, individual nations should move to revise domestic laws governing environmental health standards to ensure that they provide protection from chemicals that interfere with hormones. Such revisions should include the following key points:

Shift the burden of proof to chemical manufacturers. Chemical materials continue to be regulated with very inadequate and incomplete information. To a disturbing degree, the current system assumes that chemicals are innocent until proven guilty. This is wrong. The burden of proof should work the opposite way, because the current approach, a presumption of innocence, has time and again made people sick and damaged ecosystems. We are convinced that emerging evidence about hormonally active chemicals should be used to identify those posing the greatest risk and to force them off the market and out of our food and water until studies can prove their impact to be trivial. Every new compound should be subjected to this test before it is allowed to enter into commerce. The tool of risk assessment is now used to keep questionable compounds on the market until they are proven guilty. It should be redefined as a means of keeping untested chemicals off the market and eliminating the most worrisome compounds in an orderly, timely fashion.

Emphasize prevention of exposure. Many hormone disrupting chemicals alter normal developmental processes, causing permanent consequences that cannot be reversed or even mitigated through later treatment. Because these effects are usually irreversible, treatment after the fact is an unsatisfactory solution. The goal must be to prevent exposure to such chemicals in the first place by eliminating the use and release of hazardous compounds.

Set standards that protect the most vulnerable, namely children and the unborn. Today’s standards have been developed based on the risk of cancer and gross birth defects and calculate these risks for a 150-pound adult male. They do not take into consideration the special vulnerability of children before birth and early in life.

Consider the interactions among compounds, not just the effect of each chemical individually. Government regulations and toxicity testing methods currently assess each chemical by itself. In the real world, we encounter complex mixtures of chemicals. There is never just one alone. Scientific studies make it clear that chemicals can interact or can act together to produce an effect that none could produce individually. Current laws ignore these additive or interactive effects. Regulating as if chemicals act only individually is as unrealistic as assuming that a batter in a baseball game can only score a run for his team if he hits a home run. In real life and in baseball the bases may already be loaded and a single could well be enough.

Take account of cumulative exposure from air, water, food, and other sources. The current legal structure, which includes a number of laws addressing pesticides, food safety, water safety, and air pollution, encourages regulators to focus on one avenue of exposure at a time, such as the contaminant levels in drinking water or pesticide residues on food. This type of approach often fails to consider how the exposure from all the different sources—air, water, food, dust, etc.—adds up. Although exposure from any single source may be tolerable, the total from all sources may be unsafe. For this reason, contaminant levels from any single source must be assessed within the context of total cumulative exposure.

Amend trade secrets laws to make it possible for people to protect themselves against undesired exposure while preserving any real need for confidentiality. Trade secrets laws have been enacted to prevent business competitors from gaining an unfair economic advantage by adopting a company’s methods without having borne the cost of product research and development. In practice, these laws are routinely used by manufacturers to deny the public access to information about the composition of their products. Since a skilled chemist can discover what a product contains, we are skeptical that trade secrets laws are keeping such information from business competitors determined to find out. One has to ask who is being kept in the dark by trade secrets provisions, save for consumers, who do not have the money to do the chemical analysis. Until manufacturers provide honest and complete labels for their products, consumers will not have the information they need to protect themselves and their families from hormonally active compounds.

Require companies selling products, especially food but also consumer goods and other potential sources of exposure, to monitor their products for contamination. This should begin in the grocery store. Grocers should be able to tell you, when you want to know, whether your food is contaminant-free. The current testing system, implemented by the Food and Drug Administration, is simply inadequate. It doesn’t have the money or the manpower to do the job responsibly. The burden for testing should be shifted to the manufacturer and distributor, with the FDA charged with monitoring to ensure compliance.

Broaden the concept of the Toxic Release Inventory. This powerful right-to-know law, enacted in 1986, now requires companies in the United States to disclose the amount of toxic contaminants that escape from their facilities into the environment in the course of normal operations. As the hazards explored in this book make clear, many hormone-disrupting chemicals enter the environment through “purposeful” release in agricultural pesticides, through detergents, and in plastics. The reporting under the Toxic Release Inventory should include this deliberate release through products as well as inadvertent releases during manufacturing. Companies should, therefore, be required to report the quantity of known endocrine-disrupting compounds incorporated into products sold or transferred from each facility.

Require notice and full disclosure when pesticides are used in settings where the public might encounter them. This would include multifamily dwellings; lawns; places of worship; motel and hotels; places where food is stored, sold, or prepared; and day-care centers, schools, colleges, and other places of learning.

Reform health data systems so they provide the information needed to make sound and protective policies. A lack of crucial data on the national and international level cripples our ability to make timely, intelligent decisions. Our ignorance about trends in many areas of human health is truly appalling. We must undertake a concerted effort to build better records of birth defects and symptoms of impaired function with particular attention to reproductive and neurological disorders. This can be done in ways that protect patient confidentiality while satisfying the health research community’s need for better, more comprehensive data. Until this kind of scientific data are available, it will be impossible to determine whether important changes are occurring and to respond appropriately to new hazards.

Research Directions

Changes to laws and regulations must go hand in hand with an ongoing scientific research effort to discover more about the impact of hormone-disrupting chemicals, how they do their damage, and how damage can be avoided. The research should be driven by the need to answer a small number of crucial questions:

■ How much are we exposed?

■ How is the human body really responding to these chemicals?

■ What is the impact on ecosystems?

■ When and how should the government act? (222)

Redesigning Manufacture and Use of Chemicals

Hormone-disrupting synthetic chemicals are today an inescapable fact of life. They are inour food and water. They reach us through the air and through consumer goods we bring into our homes. They have spread across the face of the Earth and insinuated themselves into virtually every nook and cranny of the food web. There is no way to recall them. That is the dilemma we face. We can, though, as suggested above, reduce the risks of exposure by personal choice and through government action, but such after-the-fact remedies are inevitably disruptive, difficult, and incapable of eliminating the problem. Once problematic chemicals are at large, there is only one option-to manage and cope.

Ultimately, one arrives at the question of how to prevent such hazards in the first place. How can we enjoy the benefits of synthetic chemicals without putting ourselves and our children at risk? What can we do to make sure we don’t repeat this kind of mistake in the future? Traditional regulations and pollution prevention practices provided are only partial solutions.

To answer the question—how to achieve protection—we must rethink how we make and use synthetic chemicals. We must redesign the practices, processes, and products that create the problem. Here and there, efforts that move in this direction are already under way. Two advocates for fundamental rethinking and redesign—Dr. Michael Braungart, a German chemist, and William McDonough, an American architect—have also been working on a set of overall criteria to guide such efforts, criteria for the synthetic chemicals themselves as well as for the processes and products that contain them. While this movement is still in its infancy, it signals the direction for changes that will diminish hazards by reducing waste and the contaminants reaching the environment.

Braungart identifies several guidelines for the production of chemicals that will make them easier to track and recycle:

Greatly reduce the number of chemicals on the market. With one hundred thousand synthetic chemicals in commerce globally and one thousand additional new substances coming onto the

market each year, there is little hope of discovering their fate in ecosystems or their harm to humans and other living creatures until the damage is done.

Reduce the number of chemicals used in a given product; make them simpler.

Make and market only chemicals that can be readily detected at relevant levels in the real world with current technology. Some compounds currently in broad use are very hard to measure in the world at large, making it difficult, economically and practically, to study human exposure or their fate in the environment.

Restrict production to only products that have a completely defined chemical makeup and stop production of products containing unpredictable mixtures of chemicals. Such mixtures-for example the 209 PCBs-are difficult to test for safety and to track once released in the environment.

Do not produce a chemical unless its degradation in the environment is well understood. In some instances, chemicals released into the environment can break down into substances that pose a greater hazard than the original chemical. (225-227)


Any reader who has come with us this far, who has followed the path from the gull colonies on Lake Ontario and the swamps of Florida to university laboratories and then to the doctor’s office, must have paused at some point to wonder whether these symptoms have anything to do with the ills of modern human society. Such questions inevitably leap to mind when one learns that gulls in contaminated colonies neglect their nests, or that male mice born to mothers fed with pesticides are much more territorial and potentially aggressive as adults than those who did not have this prenatal exposure. At the moment, there are many provocative questions and few definitive answers, but the potential disruption to individuals and society is so serious that these questions bear exploration.

Declining sperm counts loom ominously over this discussion, for these reports harbor implications that extend beyond the question of male fertility. Animal experiments indicate that contamination levels sufficient to impair sperm production may affect brain development and behavior as well. Thus, it is likely that sperm counts are just one concrete, measurable signal of much broader effects on aspects of human health and well-being that are not so easily quantified. What is at stake is not simply a matter of some individual destinies or impacts on the most sensitive among us but a widespread erosion of human potential over the past half century. The evidence taken as a whole makes it difficult to avoid questions about the significance of this chemical assault for society at large.

Wildlife data, laboratory experiments, the DES experience, and a handful of human studies support the possibility of physical, mental, and behavioral disruption in humans that could affect fertility, learning ability, aggression, and conceivably even parenting and mating behavior. To what extent have scrambled messages contributed to what we see happening around us—the reproductive problems seen among family and friends, the rash of learning problems showing up in our schools, the disintegration of the family and the neglect and abuse of children, and the increasing violence in our society? If hormone-disrupting chemicals undermine the immune system, could they be increasing our vulnerability to disease and, thus, contributing to rising health-care costs? Most fundamentally, what does this mean for the human prospect?

If these effects are occurring broadly, hormone disruption may well be contributing to aberrant and unhealthy tendencies in our society. On the other hand, it is doubtful these chemicals are causing all the social dysfunction we see around us. Those seeking a single, simple explanation for such complicated phenomena are bound to be frustrated and disappointed. … (231-232)

What we fear most immediately is not extinction, but the insidious erosion of the human species. We worry about an invisible loss of human potential. We worry about the power of hormone-disrupting chemicals to undermine and alter the characteristics that make us uniquely human—our behavior, intelligence, and capacity for social organization. The scientific evidence about the impact of hormone disruptors on brain development and behavior may shed new light on some of the troubling trends we are witnessing. (234-235) …

Nevertheless, at the moment it is impossible to know whether hormone-disrupting chemicals are contributing to any of the disturbing social and behavioral problems besetting our society and, if so, how much. Each of these problems is immensely complex and the result of a variety of forces acting together. At the same time, studies with animals are clearly showing that disrupting chemical messages during development can have a lifelong impact on learning ability and behavior. Hormone disruption can increase the tendency toward a certain kind of behavior, such as territoriality, or attenuate normal social behaviors, such as parental vigilance and protectiveness. Given this provocative evidence, we should consider chemical contamination as a factor contributing to the increasing prevalence of dysfunctional behavior in human society as well.

Some might find irony in the prospect that humans in their restless quest for dominance over nature may be inadvertently undermining their own ability to reproduce or to learn and think. They may see poetic justice in the possibility that we have become unwitting guinea pigs in our own vast experiment with synthetic chemicals. But in the end, it is hard to regard such a chemical assault on our children and their potential for a full life as anything but profoundly sad. Chemicals that disrupt hormone messages have the power to rob us of rich possibilities that have been the legacy of our species and, indeed, the essence of our humanity. There may be fates worse than extinction. (238)


Every creature inevitably alters its surroundings as it scrambles to make a living. This is a part of life and has been so since microorganisms first began changing the chemical makeup of the Earth’s atmosphere some two billion years ago.

Humans have been no different. We have hunted game, gathered fruit, cleared forests, drained wetlands, planted fields, dammed rivers, built cities, soiled streams, constructed factories, and thrust railroads across desolate plains. But for most of the few million years that humans have trod upon the planet, our impact has been discrete. We have transformed one valley but not the next; one watershed but not its neighbor; one county but not a continent. The scale of human changes has always seemed slight when compared with that of the natural forces shaping the planet.

Today this has all changed. The twentieth century marks a true watershed in the relationship between humans and the Earth. The unprecedented and awesome power of science and technology, combined with the sheer number of people living on the planet, have transformed the scale of our impact from local and regional to global. With that transformation, we have been altering the fundamental systems that support life. These alterations amount to a great global experiment-with humanity and all life on Earth as the unwitting subjects.

Synthetic chemicals have been a major force in these alterations. Through the creation and release of billions of pounds of man-made chemicals over the past half century, we have been making broadscale changes to the Earth’s atmosphere and even in the chemistry of our own bodies. Now, for example, with the stunning hole in the Earth’s protective ozone layer and, it appears, the dramatic decline in human sperm counts, the results of this experiment are hitting home. From any perspective, these are two huge signals of trouble. The systems undermined are among those that make life possible. The magnitude of the damage that has already occurred should leave any thoughtful person profoundly shaken.

It is equally disturbing that the global scale of the experiment makes it extremely difficult to assess the effects. Over the past fifty years, synthetic chemicals have become so pervasive in the environment and in our bodies that it is no longer possible to define a normal, unaltered human physiology. There is no clean, uncontaminated place, nor any human being who hasn’t acquired a considerable load of persistent hormone-disrupting chemicals. In this experiment, we are all guinea pigs and, to make matters worse, we have no controls to help us understand what these chemicals are doing. Faced with the question of whether synthetic chemicals are contributing, for example, to learning disabilities, researchers have typically set up studies comparing contaminated children with an uncontaminated control group. Tragically, no children today are born chemical-free. In the search for relatively uncontaminated control populations, researchers have ironically discovered the appalling universality of this contamination. Even Inuits living a traditional lifestyle in remote regions of the Arctic have not escaped. The pollution has come to them.

The early results from this unintended experiment raise thorny and profound questions that reach far beyond the immediate challenge of managing and eliminating the chemicals that have caused these problems. It is no longer sufficient to look for the next round of substitutes for existing chemicals, for a new generation of supposedly less damaging synthetic compounds. The time has come to shift the discussion to the global experiment itself. … Is there any way to stop the experiment with our children and the environment, an experiment that has been an accepted way of life in the twentieth century? Or is the prospect of such hair-raising surprises a part of the Faustian bargain we have made in exchange for health, comfort, and convenience? (239-241)

The situation confronting us is not one that lends itself to easy prescriptions or simple answers. Our current economy and civilization are built on a foundation of fossil fuels and synthetic chemicals.

According to one chemical industry estimate, chlorinated synthetic chemicals and the products made from them constitute forty-five percent of the world’s GNP. If it has taken fifty years to work our way into this dilemma, it will almost certainly take just as long or longer to find our way out of it. (245)

Phasing out hormone-disrupting chemicals should be just the first step, in our view. We must then move to slow down the larger experiment with synthetic chemicals. This means first curtailing the introduction of thousands of new synthetic chemicals each year. It also means reducing the use of pesticides as much as possible, for these compounds are biologically active by design, and billions of pounds are deliberately released into the environment each year.

But these steps merely deal with the problems of which we have some inkling, however crude. They help not at all with the next generation of surprises, the next unexpected results from our massive alterations of the planetary system. In this light, eroding ozone and falling sperm counts cast dark shadows across the human future. They confront us with the unavoidable question of whether to stop manufacturing and releasing synthetic chemicals altogether. There is no glib answer, no pat recommendation to offer. The time has come, however, to pause and finally ask the ethical questions that have been overlooked in the headlong rush of the twentieth century. Is it right to change Earth’s atmosphere? Is it right to alter the chemical environment in the womb for every unborn child?

It is imperative that humans as a global community give serious consideration to this question and begin a broad discussion that reaches far beyond the usual participants-the chemical companies, government regulators, farmers, economists, scientists, and environmental groups. This discussion must engage teachers and parents, physicians and philosophers, artists and historians, spiritual leaders such as the Pope and the Dalai Lama, and others who reflect the richness and diversity of human experience and wisdom. (247)

… The chemical age has created products, institutions, and cultural attitudes that require synthetic chemicals to sustain them.

 The journey to a different future must begin by defining the problem differently than we have until now. As a general rule, the framing of a problem limits solutions more than a lack of ingenuity or technology. The task is not to find substitutes for chemicals that disrupt hormones, attack the ozone layer, or cause still undiscovered problems, though it may be necessary to use replacements as a temporary measure. The task that confronts us over the next half century is one of redesign. When forced by the phaseout of CFCs to reconsider the use of solvents when manufacturing electronic circuitry, one research effort in the United States found a way to eliminate the need for CFCs or any other solvent by redesigning the soldering process. Following such examples, we need to redesign not only lawns, food packaging, and detergents, but also agriculture, industry, and other institutional arrangements spawned by the chemical age. We have to find better, safer, more clever ways to meet basic human needs and, where possible, human desires. This is the only way to opt out of the experiment.

As we work to create a future where children can be born free of chemical contamination, our scientific knowledge and technological expertise will be crucial. Nothing, however, will be more important to human well-being and survival than the wisdom to appreciate that however great our knowledge, our ignorance is also vast. In this ignorance we have taken huge risks and inadvertently gambled with survival. Now that we know better, we must have the courage to be cautious, for the stakes are very high. We owe that much, and more, to our children. (248-249)


© 2023 Theo Colborn and Endocrine Disruption