Fathead minnows have forced me to reevaluate my relationship with the natural world. Not that I've been remiss in my regard for nature before this. I've always cared about clean water and air. I reduce, reuse, and recycle. I feed my family locally grown organic produce, ride my bike when I can, and vote for Barbara Boxer. It's just that fathead minnows have added new meaning--a whole new dimension, really--to my relationship with the world around me.

It's the male fish that precipitated my environmental epiphany. They're the ones being used by scientists to monitor the concentrations of certain chemicals in the watersheds of the Central Valley and North Coast regions of California, as well as in lakes, streams, estuaries, and effluents from sewage treatment plants throughout the rest of the United States.

Male fathead minnows are like canaries in coal mines, but they don't have to drop dead to signal danger. What happens to them in the presence of estrogen-mimicking compounds can be likened to a sex change. Scientists are checking whether a gene normally turned "on" only in female fathead minnows has, because of exposure to certain compounds classified as endocrine-disrupting chemicals (EDCs), become unnaturally activated in males.

The EPA has found that exposure of a male fathead to an estrogen-mimicking EDC for only 24 hours can activate an egg-yolk gene that under normal conditions would never become activated in the wild. The more of these chemicals there are present in a waterway, the more strongly the egg-yolk gene is activated, scientists at EPA and elsewhere have found. Given enough of an estrogenic EDC, a male fathead can become "feminized," exhibiting the easily distinguishable physical and behavioral characteristics of the female of its species.

This phenomenon caused me to wonder how EDCs might affect my own species, and me personally. Reading an EPA report I found on the agency's website (www.epa.gov/eerd/VGQPCR.htm), as well as other reports of research on endocrine disruptors, made me rethink my relationship with--well, my drinking water, for one thing.

According to an article in the Los Angeles Times ("Traces of Prescription Drugs Found in Southland Aquifers"), for example, estrogens and a plethora of other pharmaceuticals are present in southern California's drinking water, which contains some purified wastewater. Water reclamation plants purify sewage to a standard considered pure enough to drink, but they do not remove all prescription drugs. The article quoted Shane Snyder, head toxicologist at the Southern Nevada Water Authority, as saying that "There is no place on Earth exempted from having pharmaceuticals and steroids in its wastewater. This is clearly an issue that is global, and we're going to see more and more of these chemicals in the environment; no doubt about it."

Although pharmaceuticals occur at very low levels in most water sources, scientists acknowledge that next to nothing is currently known about the effects of ingesting tiny doses of them continuously over a lifetime. Snyder thinks pharmaceuticals in drinking water are "highly unlikely" to cause human health problems, though he acknowledges that they may affect individual fish and potentially even fish populations.

More than a hundred synthetic chemical compounds are known to be capable of interfering with the normal processes of the endocrine systems in fish, birds, reptiles, and mammals. Released into the environment, some of them--the lipophilic EDCs that grip onto fat tissues--bioaccumulate, appearing in higher concentrations as they move up the food chain. Drinking a cool, clear glass of water after learning all this, I could not help but wonder what havoc EDCs might be wreaking with my genes. (Now seems a good time to admit that I'm a geneticist--a molecular geneticist trained to study gene expression.) I felt compelled to take a closer look at EDCs and what is known about them.

This article is greatly abridged. For the full text, see the print edition of Coast & Ocean.