Wherever possible, Tina Casale switches to compact fluorescent light bulbs; she also recycles daily, rides in carpools or walks when she can, and, as a third-grade teacher, has made it a priority to ensure that global warming is a frequent topic in her science discussions.

But in the eyes of some activists, Casale could be doing more to save the environment: Namely, tossing out her birth control pills.

Birth control pills, like batteries and baby bottles, have become the latest item in American homes to become a focus of environmental and health concerns. As scientists debate the effects of synthetic hormones that are flushed into waterways, the potential threat has sparked a clash between advocates and critics of the pill.

“I’ve heard a little bit about the bad things that birth control can do to the environment,” said Casale, 26, who lives in New York City. “If it’s causing major problems, I guess I would stop. But, to me, the health effects of the pill are a much greater concern than the fate of fish.”

In 2003, a group of scientists in Washington state made headlines when they discovered that traces of synthetic estrogen in the state’s rivers had reduced the fertility of male fish. Hormonal birth control pills and patches were blamed. Two years later, a team of scientists funded by the U.S. Environmental Protection Agency found trout with both female and male characteristics. The culprit, again, was synthetic estrogen.

Dr. David Norris, a physiology professor at the University of Colorado, said it is not just the possible negative effects that estrogen is having on aquatic environments that concerns him as much as the exposure of these hormones to humans, especially fetuses and newborns. According to Norris, numerous reports show that estrogenic chemicals in water can result in thyroid problems and an adrenaline imbalance. Thyroid inhibitors are of major concern because they affect the nervous system’s development and can cause permanent mental retardation.

Although Norris points out that certain foods, plastics, cosmetics, personal-care products and animal wastes are also causing water contamination, studies in Boulder Creek, Colo., have shown that fish are about 10 times more sensitive to the contribution of estrogen from birth control pills than they are to estradiol, the type of natural estrogen excreted by animals like cows.

The National Catholic Register and WorldNet Daily, a conservative Web publication, seized on the findings, the latter calling birth control pills “poison.” The discovery left some environmentally-conscious women shaking their heads, unsure of what to make of all this talk of genetically-mutated fish and unsafe drinking water.

“It gets me angry,” said Tracy Oetting, 47, an environmental and political activist from Washington State. “It appears that there is no concern for women or the environment if everyone is OK with the eco-damage that hormones can do to women, men, fish and animals.”