DETROIT -- Chemicals from caffeine to powerful cancer-fighting drugs are flowing from Americans' bladders almost directly into waterways, where they have become the target of a groundbreaking federal study.

The study surveys 94 drugs and household chemicals at 200 sites nationwide. It will be published March 15 in the journal Environmental Science and Technology.

The study is a starting point to determine whether infinitesimal amounts of substances as common as Advil and antibacterial soap affect ecosystems or human health, researchers say.

"For 40 or 50 years, scientists have focused on a small group of pollutants, ignoring the vast majority of pollutants that do exist,'' said Dr. Christian Daughton, chief of environmental chemistry in the Environmental Protection Agency's National Exposure Research Laboratory in Las Vegas.

Daughton is at the forefront of an emerging field of study about how tiny amounts of everyday products affect aquatic organisms.

The U.S. Geological Survey study is the most comprehensive one of such contaminants ever done in North America.

Scientists say they hope the results will kick-start fledgling efforts to get a handle on what's in the water and what it means.

Up to 90 percent of ingested drugs are excreted from the body in a still-potent form. Others, like stale coffee or unused prescriptions, are flushed directly down toilets or poured down drains.

Wastewater treatment plants don't screen for them, state and federal regulations generally don't address their disposal, and no significant studies have documented their effect on aquatic organisms, researchers say.

"We're seeing a whole lot more, and more powerful, medicines than we used to. If we keep on dumping stuff, somewhere there's going to be a critical juncture,'' said Dr. Michael Harbut, an environmental medicine physician based in Royal Oak. "There are a whole lot of health effects that these drugs have. The question is: at what concentrations?''

When Erin Lee Martin's stepmother died from cancer in late 2000, she was appalled at what happened to the leftover chemotherapy drugs.

A hospice worker inventoried about a dozen bottles of drugs, then poured them down the drain.

"I was flabbergasted,'' said Martin, 31, of Ann Arbor, Mich. "She said, 'They just go right into the sewers,' and I said, 'But the sewers go into the river and the river is our drinking water,' and she told me that's what they tell her to do. I mean, these were powerful medicines.''

Inevitably, Harbut said, minute amounts of such substances end up in tap water drawn from the watersheds where treatment plants discharge wastewater.

Additionally, significant amounts of antibiotics and hormones fed to livestock leach into the environment from farms -- especially concentrated factory farms with dense populations of cows or chickens.

Water suppliers are not required to test or screen for any of the drugs or household chemicals, focusing instead on traditional pollutants like heavy metals and indicators of sewage, Daughton said.

Medications such as codeine, antacids, cholesterol-lowering drugs, estrogen compounds, antibiotics and chemotherapy drugs have been found in streams across the United States.

The amounts are so minute that some are measured in parts per trillion.

"Someone would have to drink the equivalent of five Olympic-size swimming pools to get one pill's worth'' of many of the targeted drugs, said Mark Grayson, a spokesman for the Pharmaceutical Research and Manufacturers of America.

But how the drugs interact with one another is unknown. So is their effect on microscopic plankton, insect larvae and other organisms at the bottom of the food chain.

"When you have concentrations so extraordinarily low, it's difficult to measure effects,'' Daughton said. And it's even harder to determine the effects of dozens or hundreds of different compounds interacting with each other, he conceded. "It will be a long ordeal, teasing apart these issues we should be looking at,'' he said.