Parsing the downstream effects of pharmaceutical compounds is an exceedingly complicated task. For one thing, more than 100 new drugs -- both prescription and over-the-counter -- are introduced each year. Researchers are confronted with long latency periods for some human diseases, making it difficult to connect an illness or disorder with long-ago exposures. Some of the drugs in our waterways act upon more than one hormonal pathway; some may end up in humans through multiple exposures (for example, antibiotics from both food and water); and exposure to mixtures of contaminants may lead to an adverse effect using one particular recipe, but produce a dif-ferent effect when the ratio of those same ingredients is changed. "For many of these drugs, the mechanism of action for humans is unknown," says Daughton. "So it's difficult to anticipate what's going to happen to them after they've entered the environment. There isn't even a database for all published work to show their presence, their location, and their concentration."

This fall, when water flows are at their lowest, Allison MacKay, accompanied by Raquel and another grad student, hopes to inch down the riverbanks once again to capture small pieces of the Pomperaug. MacKay knows her study is just the beginning of a very long process, but it is fundamental to an understanding of drugs in our waterways. "The power of knowing about the fate of these compounds is to use it in a predictive way," MacKay says. "Once we know what's happening, we can say, 'I'm going to release this, and this is when it will degrade.' I don't know about drugs, but pesticides have been reformulated to degrade faster and be less bioaccumulative in water-ways."

Could manufacturers reformulate pharmaceuticals in a similar way? "There's a trade-off in terms of having molecules break down readily versus having a stable molecule that does its work as a medicine and has a reasonable shelf life," says Thomas White, a technical consultant to the Pharmaceutical Research and Manufacturers of America (PhRMA), which represents brand-name drug manufacturers and accounts for 80 percent of all drug sales in the United States. "We've looked at studies of 26 compounds and there doesn't appear to be any human health risk." Because there is no accepted methodology for evaluating interactions among active pharmaceutical ingredients, the studies that PhRMA reviewed, which came from a variety of sources, considered drugs singly, not in combination. The PhRMA review included antibiotics, cardiovascular drugs, and antidepressants, but not estrogen or steroids. "Hormones," White concedes, "are a class of drug that would be a problem: They're designed to affect the human endocrine system. Their fate effects are under study now."

Marc Taylor, like many health-care professionals, thinks a good first step for getting drugs out of waterways is to persuade hospitals and nursing homes to abandon their policy of flushing unused drugs down the toilet. A handful of states and municipalities have launched pharmaceutical take-back programs, in which consumers bring unwanted or expired medications to an official collection site. Drugs are then either returned to manufacturers or disposed of by incineration. But creating a national return policy is more complex than it sounds. "You've got federal and state regulations, the governing boards of pharmacies, and the Drug Enforcement Agency," says Daughton. "Everyone has to get together."

Even if the federal government did devise such a policy, it would deal only with unused drugs, not with those actually swallowed and then flushed, which is the primary pathway to the environment. If redesigning drugs to break down sooner in the environment is a non-starter, then what about improving wastewater treatment? "We already have the tools and technology to take out everything," says Lynn Orphan, former president of the Water Environment Federation, which represents operators of municipal wastewater treatment plants. "We can use activated carbon or membrane filters, which have tiny pores. There's reverse-osmosis filtration [which removes organic contaminants] and exposure to ozone or to ultraviolet light. Sometimes it's just a matter of extra retention time in holding tanks."

But Hugh Kaufman, a senior policy analyst on waste issues at the EPA, says, "Some of those technologies have been demonstrated to work in a laboratory, but they haven't been scaled up for day-to-day use. The cost of putting them in place, plus their operation, is astronomical -- hundreds of millions over the lifetime of a plant."

Standing in his backyard, Marc Taylor can, with little effort, toss a stone into the riffles of the Pomperaug. The water is so clear that he could, if he wanted, easily retrieve it. He continues to swim in the river and to drink from it -- his well water comes from the Pomperaug aquifer.

As he awaits the results of MacKay's study, Taylor says, "I'll keep prescribing the medications that Patricia Reilly and my other patients need." In a philosophical mode, he continues, "The public will have to get used to the reality that the drugs and chemicals we use all go somewhere and have potential effects. The environmental fate of all consequential drugs and chemicals should be known. It's worth studying because this problem is only going to get worse as the population ages." For now, he says, "we'll have to rely on the health of the fauna in our rivers to get hints about the consequences to people. The fish and the amphibians are our canaries."