Study: Trace amounts of chemicals in streams

WASHINGTON (CNN) -- A government survey of 139 streams in 30 states turned up small quantities of a host of manmade chemicals, including antibiotics, other prescription drugs, veterinary drugs, hormones, steroids and fire retardants.

The U.S. Geological Survey, which conducted the study, stresses that the chemical concentrations in most samples were very, very low.

As an example, one sample found acetominophone -- the active ingredient in Tylenol -- at concentrations so low you'd have to drink 300,000 gallons of the water to get a one-tablet dose.

It's not known whether these small concentrations might, over time, cause problems for plants, animals or people.

"It is unknown at this point what, if any, environmental or human effect these compounds may have," a USGS statement said.

"It raises more questions than it answers," USGS spokesman Bruce Kinerney said.

The study says chemicals used in households, agriculture and industry enter the environment -- albeit in small quantities -- not just through runoff, but also through treated wastewater.

Caffeine, prescription drugs and other chemicals are not targeted by wastewater-treatment plants, which are designed to remove bacteria and other pathogens from sewage. So residues of drugs taken upstream can end up in water downstream.

"Little is known about the environmental occurrence of many chemicals we use to maintain and improve the quality of our daily lives," said Dr. Robert Hirsch, USGS associate director for water. "This study begins a process of exploring the occurrence of these chemicals in our nation's streams."

List of chemicals

The most frequently detected compounds included:

"Overall, steroids, nonprescription drugs and a chemical found in insect repellents were the chemical groups most frequently detected," said Dana Kolpin, a USGS research hydrologist who headed up the study.

"Detergent metabolites, steroids and plasticizers were generally measured at higher concentrations than the other chemical groups, but concentrations measured in this study generally were very low (less than 1 part per billion)."

The samples were gathered during 1999 and 2000 from sites selected based on where the chemicals are most likely to occur. Most sites were located downstream of areas of intense urbanization and livestock activity, where wastewater is known or suspected to enter the streams.

The paper "Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999-2000: A national reconnaissance" can be found in the March 15 issue of Environmental Science & Technology, or on the Internet at: http://toxics.usgs.gov/regional/emc.