for National Geographic News
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.)
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.
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