River pollution study finds hormonal defects in fish: Discovery in Britain suggests sewage plants worldwide may
cause similar reproductive-tract damage
By Marla Cone, Times environmental writer
Copyright 1998 Los Angeles Times
September 22, 1998
In a surprising scientific discovery that suggests pollution is feminizing
animals throughout the wild, everyday concentrations of sewage effluent in
rivers appear to contain estrogen-like chemicals potent enough to
cause fish to be born half-male, half-female.
The finding by British scientists
provides strong new evidence that hormone-altering pollution--one of the most
troubling and controversial environmental issues of modern times--could be a
global ecological threat.
Other recent studies had found scattered populations of animals with bizarre
sexual defects living in highly polluted waters, but the
new research suggests that the problems are more widespread than previously
detected.
The British researchers said they uncovered very compelling evidence that
sewage treatment plants routinely release hormone-like compounds into rivers
that are feminizing
"a surprisingly large proportion" of wild fish. The fish were found in eight rivers
throughout Great Britain that are considered typical in terms of pollution, so
scientists suspect damage to sex hormones is so pervasive that it could be
happening in many rivers around the world.
"The incidence and severity of intersexuality . . . is both alarming and
intriguing," researchers from Brunel University and the British government reported in the
September issue of the journal Environmental Science and Technology.
Some male fish have such mixed-up hormones that they are born with ovaries and
eggs instead of sperm ducts. In two of the eight rivers
downstream of sewage treatment plants, 100% of the male fish sampled had
feminized reproductive tracts, ranging from severe to slight. The other six
rivers had rates of 20% to 80%.
Hundreds of widely used manufactured chemicals--including pesticides,
industrial compounds, dioxins and ingredients of plastics and detergents--are
believed to mimic
estrogen or block testosterone, disrupting the endocrine system that is
critical to sexual development.
A Growing Suspicion
In their report, the scientists called their findings
"the first documented example of a widespread sexual disruption in wild
populations of any vertebrate." Hormonal havoc, however, has previously been reported in alligators,
birds, river otters, carp and other U.S. wildlife in isolated locations from
the Channel Islands to Lake Mead to the Great Lakes.
The phenomenon of
"intersex" animals was first discovered in the 1970s, but it was dismissed as a fluke
until the early 1990s, when biologists found feminized alligators
in a highly polluted Florida lake and began to suspect that manufactured
chemicals were altering sex hormones.
The British work
"is an extremely important study for many reasons," said Theo Colborn, a World Wildlife Fund scientist and activist who was one
of
the first to notice
a pattern of hormonal problems in animals. The sexual damage the researchers
found
"is pervasive, it's widespread," Colborn said.
"That's what's disturbing about this."
Judith Weis, a Rutgers University marine biologist who studies the effects of
pollution, said the British research
"lends more support to endocrine
disruption as being a very serious issue."
Adult animals are unharmed by hormone-imitating pollutants; instead, the damage
is inflicted on the next generation. Mothers pass the excessive amounts of
estrogen to their embryos or fetuses, which cannot distinguish between fake
estrogens and real ones. When this estrogen boost comes
during a critical phase of sexual development, genetic signals go haywire and
males are born with feminized genitalia or other reproductive problems.
No one knows what threat, if any, these artificial estrogens pose to human
health and fertility. Some scientists suspect that men exposed in their
mothers'
wombs might have depleted sperm counts that lower their fertility; it also
might explain a recent surge in testicular
cancer.
Hormones play the same vital sexual role in humans as they do in fish and other
animals. Although people are exposed through food and water to the same
pollutants as water-inhabiting animals, they encounter much lower doses, so any
human effects may be subtle.
One of the most surprising aspects of the British findings is that fish are
suffering so many sexual defects in a part of the world with sophisticated
environmental laws and technologies. Scientists
wonder how minute concentrations of fake hormones in the environment--which are
hundreds of times less potent than natural estrogen--could have such a severe
impact.
"Perhaps the most disturbing fact is that discharges from sewage treatment works
are an inevitable consequence of human existence, and hence estrogenic
contaminants could have a global impact
on all populations of riverine fish exposed to sewage discharges," the research team wrote.
The scientists do not know which chemicals are to blame, because sewage is a
mix of wastes from homes and industries--everything that is washed down drains.
The culprits could be anything from the urine of women excreting artificial
hormones from birth control
pills, to pesticides or plastics.
"It's really anybody's guess as to what is causing this," said Weis, who serves on a U.S. Environmental Protection
Agency task force
developing a national plan to screen chemicals for hormonal effects.
"That's the hard part--it's a lot easier to look
at effects on the fish than to look at this witches' brew of chemicals in
sewage . It's also possible it's not a single thing, but a mixture effect."
Of 87,000 chemicals currently in commercial use today, there is evidence that
about 1,000 can act like
hormones; about 61,000 have not been tested, the EPA estimates.
Shrugging Off Evidence
Pesticide manufacturers and other industry groups are skeptical that hormone
problems occur at the low amounts of pollution that animals and people
routinely encounter today. Industry representatives have contended that if
hormone disruption is happening, it
occurs only in animals living in
"hot spots," such as Great Lakes harbors, created several decades ago, before compounds
such as DDT were banned and industrial practices were improved.
Now, though, as research spreads, evidence is emerging that wildlife is being
feminized in waters where modern environmental
practices and laws are followed and the ecosystem appears outwardly healthy.
"The rivers we studied are typical rivers in Great Britain and are not
particularly known for contamination or industrial dumping," said Brunel biologist Susan Jobling, one of the authors of the fish study.
The prevalence and severity of feminized fish was highest
in spots where the effluent was the most concentrated. On the average, the
scientists reported, fish collected from rivers several miles downstream of
sewage treatment plants had five times more sexual defects than fish in
waterways that receive no sewage effluent.
The relevance to waters in the United States is
unknown, but sewage treatment processes here are similar to Great Britain's.
Feminized carp had previously been reported in the Mississippi River,
downstream from a sewage treatment plant serving St. Paul, Minn.
Most raw sewage is filtered and disinfected to kill germs, but many toxic
chemicals
remain in the huge volumes of effluent discharged into thousands of rivers,
lakes, bays and ocean waters in the United States.
The conditions in the British rivers
"are far from unusual," the scientists said.
"Water quality in the U.K. is generally thought to be good and improving,
particularly when compared with many other
European countries where sewage is often discharged into rivers and canals
after little or no treatment."
Tim Kubiak, a contaminant expert at the U.S. Fish and Wildlife Service, said he
suspects
"there is a lot more hormone damage to be found" in the wild, but the sex defects are uncovered
only when scientists take the time to look.
The reproductive damage might have dire consequences for an ecosystem, because
if males are sterile, an entire animal population might gradually be depleted.
Fish, in particular, are an important link in the world's food chain.
So far, the fish
in the British study--a species called
"roaches"--remain abundant, even in the Aire and Nene rivers, where 100% of tested males
were feminized. Apparently some of the males still have enough of their systems
intact to reproduce.
"What we still don't know is if these intersex fish are reproductive or not.
That's the bottom line,"
Weis said.
"Some of them have no sperm ducts, so obviously they can't reproduce."
Because females are more critical to reproduction than males, populations can
regenerate themselves even if only a few males are fertile. Over the
generations, though, if feminization remains unchecked, fisheries could
collapse.
Colborn said the
study
"really shows that population effects are possible. It's such an insidious
problem."
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