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Sex-Changing Chemicals Can Wipe Out Fish, Study Shows

John Roach
for National Geographic News
May 21, 2007
 
Tiny amounts of the estrogen used in birth control pills can cause wild fish populations to collapse, according to a new study.

The finding raises concern about even low levels of estrogen in municipal wastewater, said study leader Karen Kidd, a biologist with the Canadian Rivers Institute at the University of New Brunswick.

"Women excrete estrogen naturally, and women on birth control pills also secrete the synthetic estrogen in those pills," she explained.

"And these estrogens, depending on the level of wastewater treatment, may not be completely broken down during sewage treatment, so they get discharged into rivers and streams."

Male fish exposed to the hormone become feminized—they produce the same proteins that female fish do to develop eggs. Some males even develop eggs in their testes.

"It doesn't take a lot of estrogen to feminize male fish and, based on the results of our experiment, to impact fish populations," Kidd said. (Learn more about freshwater pollution.)

Experimental Lake

Several studies have shown that exposure to estrogen and related compounds feminizes male fish, but until now the impact on wild fish populations was unknown.

(Read related story: "Animals' Sexual Changes Linked to Waste, Chemicals" [March 1, 2004].)

Kidd and colleagues from Canada's federal fisheries agency added the synthetic estrogen found in birth control pills to a remote, isolated lake set aside for such experiments in northwestern Ontario, Canada.

For three summers the researchers added estrogen at levels found in untreated municipal wastewaters.

Several fish species live in the lake, including the short-lived fathead minnow.

After the first summer, male minnows were producing egg proteins. By the second year their sperm cells were undeveloped. Shortly after that they produced eggs as well.

In addition, females were producing more egg protein than normal, and their sexual development was also delayed, Kidd said.

The result was an impaired ability of the minnows to reproduce, which caused the population to collapse in the second year of the study, the researchers found.

The population even failed to recover in the two years after the researchers stopped adding estrogen, indicating the effects were quite persistent, according to Kidd.

"Low … concentrations of an estrogen can have very dramatic, very severe effects on fish reproduction and fish population," she said.

Kidd and colleagues report the findings this week in the journal Proceedings of the National Academy of Sciences. The Canadian government and the American Chemical Council funded the research.

Sharp Drop

Douglas Chambers is a biologist with the U.S. Geological Survey's West Virginia Water Science Center who has studied possible causes of feminized fish in the Potomac River Basin.

(Read related story: "Sex-Changing Chemical Found in Potomac River" [January 22, 2007].)

He said the finding of a sharp drop in the minnow population attributed only to synthetic estrogen was surprising.

He had suspected that feminization in addition to other environmental stresses could lead to population collapse. The new study shows feminization alone causes the decline.

Study leader Kidd and colleagues believe that if they had continued to add estrogen to the experimental lake for more than three years, the estrogen would also have had an impact on the populations of longer-lived fish in the lake—trout, white suckers, and pearl dace.

"It's critical that our municipal wastewaters are treated at least with secondary treatment to reduce the input of these estrogens into surface waters," Kidd said.

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