What goes into millions of Americans who take prescription drugs each year very likely approximates what's being returned to the environment, researchers reported Wednesday during a scientific meeting.
Padma Venkatraman, a postdoctoral fellow in the Department of Geography and Environmental Engineering at Johns Hopkins University, described "probable environmental concentrations" of the 200 most commonly prescribed drugs in the United States to the American Chemical Society, meeting in Orlando, Fla., this week.
"We're trying to make an intelligent guess as to what's out there in the environment and what's probably toxic (to aquatic life)," said Venkatraman.
But concentrations of the drugs probably aren't high enough to post any immediate human health risk.
The first national survey of drugs in the nation's streams was released last month by the U.S. Geological Survey, which found antibiotics and other animal and human prescription drugs widespread in many of the 139 streams sampled across 30 states. It also found steroids, caffeine, nicotine, pesticides, detergents and plastic hardeners in a search that screened for 95 specific contaminants.
That survey was considered a scouting effort to set some benchmarks for future research.
The Hopkins study will serve a similar function, but it started at the source of drug contamination - the billions of bottles of prescription and over-the-counter medicines Americans take each year.
The drugs are designed to dissolve quickly in water, but are also supposed to do their job and move on so the active ingredients don't accumulate and damage the liver and other organs. So, perhaps 50 percent to 90 percent of every pill, capsule and capful a person takes passes on through the body. And many people flush unused drugs down the toilet.
The new analysis is based on pharmaceutical industry reports of sales and prescriptions and a search of medical literature. "Based on the existing data about the drug's biochemistry and existing data on metabolism, we came up with the estimates on what should be prevalent in waterways," said Venkatraman.
Although he didn't name individual drugs, Venkatraman said antimicrobials, antidepressants, anticonvulsants and anticancer drugs are likely to be found at the highest concentrations.
"This is an important new research area," said A. Lynn Roberts, who heads the Hopkins team. "Over the past few years, scientists in Europe have found pharmaceuticals in natural waterways, sewage treatment effluent and even drinking water. Yet until this year, there have been virtually no scientific studies examining this issue in this country."
There are many differences in drug prescribing patterns and in the treatment of sewage and drinking water between the United States and Europe that require researchers studying the issue to start with fresh assumptions, Robert said.
"There are many ways in which pharmaceuticals in the environment could produce undesirable effects on aquatic organisms or even humans," she said.
For instance, many popular antidepressants work by altering levels of a brain chemical called serotonin. But serotonin also causes many aquatic creatures to spawn, so pharmaceuticals in the wild could upset natural breeding cycles.
And there's concern about untested effects of even small amounts of some drugs on developing human fetuses and the potential cancer-inducing effects of other hormonal drugs, even at low concentrations.
Another member of the team, Hopkins undergraduate Michael Blumenfeld, presented a new method for detecting minute amounts of several drugs in water samples, using a technique called gas chromatography-mass spectrometry.
The researchers say the test is so sensitive it can detect less than a third of an ounce of a drug in 250 million gallons of water.