From its headwaters at Echo Lake in Hopkinton, Mass., the Charles River glides past yards, saturates wetlands, and slips under highways before emptying into Boston Harbor.
Over the years, this 80-mile odyssey through 23 cities and towns has left what seemed to be a faint imprint on the Charles's tea-colored water. But advances in the ability to detect pollutants are giving scientists a clearer idea of the nature of that imprint and is also triggering interest in research on whether these pose a threat to the environment and to humans.
The chemicals range from fire retardants and detergent byproducts to prescription drugs, antibiotics, and hormones.
Known as organic-waste contaminants, these compounds pass through sewage-treatment plants virtually untreated. They represent the vanguard of what researchers have dubbed emerging contaminants: chemicals whose presence in US rivers, streams, and lakes has gone undetected for years and whose effects singly and in combination on fish, aquatic plants, and humans often are poorly understood.
Last week, the United States Geological Survey (USGS) released its first survey of organic-waste contaminants in US surface waters, and the Charles River has plenty of company. Researchers found organic-waste contaminants in 80 percent of the 139 streams and rivers that were tested in 30 states.
During the course of the survey, which ran from 1999 through 2000, the researchers found 82 compounds out of the 95 they sought.
The researchers acknowledge that the sites were selected because they presented a high likelihood that the contaminants would be found. The survey was as much a test of new sampling technologies as it was an exercise in environmental monitoring. But the target compounds also were selected because several are beginning to appear in scientific journals as potential ecological villains.
According to Herbert Buxton, a USGS scientist who took part in the survey, "Thirty-three compounds are known or suspected to be hormonally active." These chemicals, which include steroids, can affect the growth and development of aquatic life.
Dr. Buxton and his colleagues note that the compounds they found appeared in concentrations that rarely violated drinking-water or aquatic-life standards.
But, he adds, many of the compounds have no such guidelines. Moreover, samples exhibited chemical stews of up to 38 contaminants, and little is known about how these interact, he says.
"We shouldn't confuse the ability to measure these concentrations with whether or not they're harmful," Buxton cautions, noting that these are two separate issues.
However, he adds, the ability to measure organic waste contaminants in ever weaker concentrations allows researchers to focus on questions of risk early.
Compared with other parts of the world, the United States is a late bloomer on the issue of these emerging organic wastewater contaminants, particularly pharmaceuticals and antibiotics, according to Christian Daughton, who heads the environmental chemistry branch at the Environmental Protection Agency's National Exposures Research Laboratory in Las Vegas, Nev.
The sources for these compounds vary. Hormones and antibiotics in animal feed appear in waste and can leach into local streams and rivers. Drugs and antibiotics designed for humans move through sewage systems.
Tossed into the trash, such leftovers also are often carted off to landfills, where seeping rainwater can dissolve the capsules and carry away the compounds they contain.
EPA chemist Wayne Garrison was the first to identify drugs in sewage, in the mid-1970s. His chemo-sleuthing turned up evidence of caffeine, aspirin, and nicotine. "It was noted, then people shrugged and moved on," Dr. Daughton says.
The issue lay dormant until the 1990s, when the Europeans tested samples from their waterways and found evidence for a range of human and agricultural pharmaceuticals.
"The Europeans have a higher density of urban life around surface waters" than does the US, Daughton says in explaining why European researchers were quicker to focus environmental research on human and animal drugs in their waterways.
Moreover, European farming practices, antiquated and ill-maintained sewer systems, (particularly in the former East bloc), and the flow characteristics of many European rivers raised the likelihood that drugs were finding their way back into drinking water.
Daughton notes, for example, that following the fall of the East bloc in the early 1990s, scientists found evidence of drugs in the former East Berlin's tap water.
The research in Europe and rising concerns among public-health researchers and officials in the US triggered the USGS study, says Buxton, who coordinates the toxic-substances hydrology program at the USGS office in Trenton, N.J.
To ecologist Rebecca Goldburg, the most troubling set of ingredients is antibiotics, particularly down on the farm.
"The use of antibiotics in agriculture is growing," notes Dr. Goldburg, senior scientist with Environmental Defense, a New York-based group. Of particular concern, she says, are those fed each year to hogs, chickens, and cattle to promote growth.
By some estimates, these "subtherapeutic" doses constitute 8,000 tons of antibiotics a year.
The concerns arise over the prospect that over time, the bacteria these antibiotics are designed to destroy will grow increasingly resistant to the compounds and at a faster pace than would be the case if the antibiotics were used only to treat animals diagnosed with disease.
In addition, over the years antibacterial agents have become common in soaps and other personal-care products, which wind up being rinsed down the sink and into the sewer system.
For his part, the EPA's Daughton is focusing his research on the effects pharmaceuticals may have on aquatic environments.
"Drugs are designed for people, so not much has been done to test them on aquatic organisms," he says.
Thus, he continues, the presence of drugs in rivers, lakes, and streams may have a more serious effect on fish, shellfish, and other organisms they rely on for food than on humans. The problem is that little is known about the impact of drugs on aquatic ecosystems.
Research in this area could become more important as drug companies develop new, more potent compounds. Daughton notes that the drug companies are intensely interested in results coming out of the federal Human Genome Project.
That project aims by the end of next year to complete its goals of identifying all of the estimated 30,000 genes in human DNA, and determining the sequence of four basic chemical building blocks that DNA is built upon.
Drug companies, he says, hope to use data from the project to develop new, more potent compounds for battling a range of diseases -- compounds that, if history is any indication, also could wind up in waterways.
Already, he notes, studies have shown that antidepressants can trigger premature spawning in shellfish, while other compounds used to treat heart conditions have blocked the ability of fish to repair damaged fins.
Even less well-known are the effects these and other compounds might have in combination, he says.
Some pharmaceuticals include compounds also found in pesticides, according to Marsha Black, an aquatic toxicologist at the University of Georgia at Athens.
Armed with a $500,000 grant from the EPA, she is heading a team that will be looking for five commonly prescribed antidepressants in samples taken from wastewater treatment plants.
Already, Dr. Black has documented one antidepressant's lethal effects on sand fleas. While most people might not mind fewer of these tiny crustaceans nipping at them, these creatures, like canaries in a coal mine, provide researchers with valuable clues about the quality of surface waters, she says.
Using new technology, scientists are finding chemicals in US rivers, streams, and lakes that have gone undetected for years.
These "emerging contaminants" include:
Other prescription drugs.