BOSTON, Massachusetts, November 6, 2001 (ENS) - Hermaphrodite fish - fish with both male and female characteristics - are on the rise, due to the birth control pill and other natural and unnatural forms of estrogen that have made their way into the water.

Feminized male fish were first found downstream from sewage plants in the United Kingdom, said researchers at the Geological Society of America's (GSA) annual meeting in Boston.

"Closer to home, we have observed intersex white perch in various locations in the Great Lakes, " explained Chris Metcalfe, professor of Environmental and Resource Studies at Trent University in Ontario. "And in the Columbia River, there is a much higher proportion of female salmon than males, indicating that some feminization process may be going on."

Metcalfe conducted lab experiments on aquarium fish to try to find out which of the various forms of estrogen are the culprits in the sexual alteration of fish. He reported his research findings and shared new statistics on estrogen concentrations in water, generated by the Canadian Department of Environment in Burlington, Ontario, at the GSA meeting on Monday.

Metcalfe found that very low levels of several estrogen hormones - 17 alpha-ethinylestradiol, 17 beta-estradiol, estrone and estriol - caused intersex and altered sex ratios in the aquarium fish.

"Ethinylestradiol is the active ingredient in the birth control pill," said Metcalfe. "The other compounds are the natural female estrogen (beta estradiol) and metabolites of that compound excreted by women."

Metcalfe also found from his experiments that other estrogen mimicking compounds - such as alkylphenol ethoxylate surfactants (compounds used in such things as pesticides, detergents and cosmetics) and the plasticizer, Bisphenol A (used in lacquers for dental treatment and to coat food cans and other metal containers) - had little or no effects on the fish.

Metcalfe believes that it is the female estrogen hormones released from sewage treatment plants that are responsible for the feminization of wild fish.