Released into an Ontario lake as an experiment, tiny amounts of the hormone wreak havoc on male fish

MARTIN MITTELSTAEDT

ENVIRONMENT REPORTER

May 22, 2007

Back in the summer of 2001, a team of Canadian and U.S. researchers spiked a lake in Northwestern Ontario with traces of synthetic estrogen used in human birth control pills. They then repeated the unusual treatment for the next two years and sat back and watched what happened to minnows living in the lake.

The results were nothing short of frightening. Exposing fish to tiny doses of the active ingredient in the pill, amounts little more than a whiff of estrogen, started turning male fish into females. Instead of sperm, they started developing eggs. Instead of looking like males, they became indistinguishable from females. Within a year of exposure, the minnow population began to crash. Within a few years, the fish, which at one time teemed in the lake, had practically vanished.

After treatment, the lake water had estrogen concentrations of about 5 parts per trillion, the scientific equivalent of almost nothing. A part per trillion is the equivalent of a few grains of salt in an Olympic-size swimming pool. The amount of estrogen added was about a fifth of a gram a day, or about one-tenth the weight of a penny.

"What's sobering for me is that we've shown such a dramatic response in fish population at these low concentrations," Dr. Kidd said in an interview.

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Click here to read the study summary

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