Introduction | Omens
The DES Paradigm: Crossing the tolerance threshold
Here, There, Everywhere: Chasing the plastic
Part VI. Altered
Destinies: Up against evolution
Carson Redux: Theo Colborn creates her
In July 1991, a group of scientists-including
Theo Colborn, then a fellow at the W. Alton Jones Foundation, and John
Peterson (Pete) Myers, the foundation's director, gathered at the Wingspread
conference center near Racine, Wisconsin, to discuss their concerns about
hormone-disrupting chemicals in the environment. They were disturbed by
mounting evidence that synthetic compounds found in pesticides and industrial
chemicals were wreaking havoc with endocrine systems.
The scientists shared
information on a broad range of species with problems that ranged from
thyroid dysfunction, decreased fertility, and gross birth deformities
to feminization of males, masculinization of females, and compromised
immune systems. Many of the chemical compounds under discussion had an
affinity for estrogen receptors in particular and their effects on wildlife
paralleled those seen in humans exposed to the synthetic estrogen DES
(diethylstilbestrol). Although environmental hormone disrupters were known
mainly for their effects on wildlife, the scientists at the Wingspread
meeting concluded that the substances had the potential to cause large-scale
dysfunction in humans as well.
In Our Stolen Future,
a new book excerpted here, Theo Colborn and Pete Myers have joined forces
with environmental science writer Dianne Dumanoski to survey the problem.
They have found that hormone-disrupting chemicals are ubiquitous and that
the pathologies they cause may result even from extremely low levels of
exposure. Although many synthetic chemicals have been tested for carcinogenic
effects, few have been scrutinized for their impact on the human endocrine
system. As the authors of Our Stolen Future observe, if such substances
are causing wide-scale disruption of the hormones that enable us to grow
and reproduce, we may be witnessing an evolutionary tragedy in the making.
-Bruce Stutz, Editor in Chief, Natural History
The late 1940s:
Gulf Coast, Florida
Charles Broley began his study of Florida's bald eagles in 1939 at
the suggestion of the National Audubon Society. In the early 1940s, Broley
followed 125 active nests along the peninsula's west coast from Tampa
to Fort Myers and banded some 150 young eaglets each year. In 1947 the
picture suddenly changed. The number of eaglets began dropping sharply
and in the succeeding years, Broley witnessed bizarre behavior in many
of the eagle pairs. At nesting sites he had visited for thirteen years,
two-thirds of the adult birds appeared indifferent to nesting, courtship,
and mating. As Broley continued his work through the mid-1950s, he became
convinced that 80 percent of Florida's bald eagles were sterile.
Although otters were no longer
as plentiful as in earlier times, the traditional sport of otter hunting
continued relatively unchanged into the mid-twentieth century. To the
sounds of horns and baying hounds, hunters still pursued their prey; by
the end of the 1950s, however, they began to have trouble finding otters
to hunt. When conservationists finally took note of the problem, some
suspected the pesticide dieldrin, but later work pointed to another synthetic
The mink industry that had grown
up around the Great Lakes because of the ready supply of cheap fish had
begun to falter because of the animals' mystifying reproductive problems.
Females weren't producing pups. Michigan State University researchers
eventually linked the reproductive failure to PCBs (polychlorinated biphenyls),
a family of synthetic chemicals used to insulate electrical equipment.
Curiously, a decade earlier, other mink herds in the Midwest had crashed
after the animals were fed scraps from chickens that had been given the
growth-promoting drug DES. Although the symptoms were strikingly similar
to those of the Michigan incident, the second crash of fish-fed mink could
not be linked to DES.
1970s: Channel Islands, Southern California
Working on San Nicolas Island
in 1968, Ralph Schreiber, of the Los Angeles County Natural History Museum,
spotted some gull nests with unusually large numbers of eggs. Since gulls
rarely incubate more than three eggs at a time, Schreiber immediately
suspected that more than one female was laying in these nests. Four years
later, George and Molly Hunt, of the University of California at Irvine,
noticed the same phenomenon on Santa Barbara Island. They also saw thinning
eggshells in the gull colony, leading them to expect the birds were suffering
from DDT exposure. Over the next two decades, nesting female pairs would
be found among the herring gulls in the Great Lakes, glaucous gulls in
Puget Sound, and roseate terns off the coast of Massachusetts. Were the
females sharing nests because of a shortage of males?
Lake Apopka, Florida
Surveys showed that in some Florida
lakes, 90 percent of alligator eggs hatched, but at Lake Apopka the hatching
rate barely reached 18 percent. Even worse, half of those that hatched
died within ten days. Louis Guillette, a University of Florida reptile
biologist, felt there was little question that the problems were linked
to a 1980 chemical spill, after which more than 90 percent of the alligators
disappeared. But why, after the waters were again clear, were researchers
still finding hatching problems, and why did at least 60 percent of the
males have abnormally tiny penises?
Over the years, Niels Skakkebaek,
a reproductive researcher at the University of Copenhagen, had seen more
and more human sperm abnormalities, as well as a drop in the typical sperm
count. At the same time, Denmark's rate of testicular cancer had tripled.
Skakkebaek also noticed low sperm counts and unusual cells in the testes
of men who developed this type of cancer. Were the findings connected?
He and his colleagues eventually reviewed sixty-one studies, most from
the a United States and Europe, but also from Asia, South America, and
Africa. They were stunned to find that average human male sperm counts
had dropped by almost 50 percent between 1938 and 1990.
Colborn, T., D.
Dumanoski, J. P. Myers. 1996. Hormonal Sabotage. This article and the
ones linked to it was originally published in Natural History, March 1996,
Excerpted from the book
Our Stolen Future.