River Pollution Study Finds Hormonal Defects in Fish


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.”