5 November 2004
Concern Over Environmental Estrogen
by Kate Melville

Long-term exposure to a synthetic estrogen at levels below those currently found in the environment could have a major impact on fish populations, according to a study appearing in the journal Environmental Health Perspectives. The study, authored by Jon P. Nash, shows that ethynylestradiol, a potent synthetic form of estrogen used in oral contraceptives, can produce sexually compromised males.

The researchers exposed zebrafish to low concentrations of the hormone over three generations and measured the effects. After 210 days, or a full zebrafish lifetime of exposure to ethynylestradiol, second-generation fish showed reduced fertility. In addition, out of nearly 12,000 eggs spawned, none were viable. Upon examination, researchers found that none of the second-generation male fish had normal testes, and they did not produce expressible semen. However, the fish showed normal reproductive behavior patterns, including competing with healthy males.

The research suggests that the development of the testes is more sensitive to disruption by ethynylestradiol than is reproductive behavior. This could have significant population-level consequences, as infertile males still have the same ability to interfere with breeding behaviour and dynamics.

"Previous studies in fish have shown that endocrine disruptors can reduce sperm counts and induce female-specific proteins in males," said Jim Burkhart, an editor for Environmental Health Perspectives. "But until now little evidence existed to show that environmentally relevant concentrations of endocrine disruptors could induce such changes and actually reduce fertility."