Estrogen Makes Fish Too Feminine To Reproduce

May 22, 2007

Release from: Tom Spears
CanWest News Service

Estrogen that goes down Canadian toilets -- some naturally from women, some from birth-control pills -- is enough to make entire fish species too feminine to reproduce, a seven-year Canadian study shows.

Fish scientist Karen Kidd dripped small amounts of estrogen into a clean lake in northwestern Ontario over several years, just as if urine with the female hormone were running in via sewage from a nearby city.

This constant hormone bath made male minnows produce eggs in unnatural, part-female sex organs.And even after she stopped adding estrogen and the water turned clean again, the minnows almost completely disappeared for several years. Even small concentrations of estrogen can decimate wild fish populations, the University of New Brunswick biology professor concludes, even at levels found in some Canadian waters. She would not name individual rivers.

And while the minnows were prone to fast extinction because of their short lifespan (about two years), she says bigger fish such as trout or pike might also be hurt if they are exposed for long enough.

The first dramatic news of "feminized" fish came from British rivers in the 1990s where male fish near sewage plants were producing eggs and carrying reproductive organs that were partly female.

"A lot of follow-up studies showed it was the natural estrogens that women excrete and then the synthetic estrogens in birth control pills that were the main causes of feminization in male fish," Ms. Kidd said.

"The Pill is one of the most heavily prescribed pharmaceuticals in the world. There are over a million women on it in Canada."

She chose an unpolluted lake with healthy fish to learn what damage estrogen would cause.

Male minnows in water with estrogen just stopped looking male. Where they should have distinct colours and bumps at spawning time, they didn't have any visible sign of maleness.

"And then when you opened them up, their testes were much smaller than they should have been" -- about one-third the normal size. By the third year of adding estrogen to the lake, the testes had ovary-type tissue, and were producing eggs -- a condition called "intersex."

It's exactly what scientists had seen in the wild. The achievement is in reproducing this effect in a previously clean lake, proving that estrogen is the cause. Meanwhile, the female fish produced eggs too slowly. The Kidd team found these effects early, but continued the study for several years to see what would happen. And the whole minnow population crashed.

"That was the big question: What does it mean for the fish population? We've shown that it has profound effects on the fathead minnow."

If minnows don't sound very exciting, she notes that they are a staple source of food for bigger fish across North America, right up to lake trout and northern pike. Killing the minnows in a lake is like taking wheat or rice out of the human food supply.

The last estrogen went into the lake in 2003. Since then, bacteria and sunlight have broken down the estrogen and the water quickly returned to normal. The minnow population, however, took a further two years to recover.

And in the real world, no one stops adding estrogen after a couple of years of study. "That's the issue for our waterways. There's a constant input of these kinds of chemicals into our rivers and lakes," she said. "Certainly we're more concerned about the systems [rivers] that are still getting untreated sewage.

The seven-year study was funded by Fisheries and Oceans Canada, where Ms. Kidd worked during most of it, and the American Chemistry Council. It is published today in the Proceedings of the National Academy of Sciences.

"A lot of our [pollution] regulations tend to be centred around chemicals that are persistent in the environment, and that accumulate in fish," she said. These include pesticides such as DDT and industrial PCB oils, both of which last for years.

Estrogen does not last long, but it, too, needs control--mostly through decent sewage treatment, she said. The bacteria in a modern sewage plant chew up estrogen effectively.

"We don't know a whole lot about the concentration of these compounds in our waters." She noted that her own city of Saint John, N.B., still sends 40% of its sewage untreated into streams and ultimately the Bay of Fundy. The city recently obtained federal funds to treat all its sewage in a few years.