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Emerging Contaminants Targeted in a Reconnaissance of Ground Water and Untreated Drinking-Water Sources

A - wellhead for ground water -- B - intake structure for surface water
USGS scientists collected water-quality samples from 121 locations as part of two national-scale reconnaissance studies on the occurrence of organic wastewater contaminants in ground water and untreated sources of drinking water across the United States. All of the samples were raw water, collected from sampling ports at wellheads for ground water (A) or at intake structures for surface water (B) before any treatment or processing.

Two national-scale reconnaissance studies recently conducted by the U.S. Geological Survey (USGS) were the first to collect baseline information on the environmental occurrence of pharmaceuticals, personal-care products, detergents, flame retardants, naturally occurring sterols, and other organic contaminants in ground water and untreated sources of drinking water in the United States. These contaminants are commonly associated with human- and animal-waste sources, though other natural and human-related sources are also possible. These studies follow a previous reconnaissance of U.S. streams (see side bar).

Ground Water

Ground-water samples were collected from a network of 47 wells with common environmental conditions and which typically were not used for drinking water. The wells, in 18 states, were analyzed for 65 chemicals. The most frequently detected chemicals include N,N-diethyltoluamide (insect repellant), bisphenol A (plastic- and epoxy-manufacturing ingredient), tri(2-chloroethyl) phosphate (fire retardant), sulfamethoxazole (veterinary and human antibiotic), and 4-octylphenol monoethoxylate (detergent metabolite).   The concentrations of chemicals detected were low. Eighty-seven percent of the 137 measured detections were less than 1 microgram per liter (µg/L). Mixtures of chemicals were common.  Although similar chemicals were detected in the previous national stream reconnaissance, the chemicals were detected less frequently in this study's ground-water sites (35 percent of the sites) than they were in the stream reconnaissance (86 percent of the sites).

Untreated Drinking-Water Sources

Water samples were collected from untreated sources of drinking water at 25 ground-water and 49 surface-water sites in 25 states and Puerto Rico.  The most frequently detected chemicals in surface water were cotinine (nicotine metabolite), and 1,7-dimethylxanthine (caffeine metabolite); and in ground water were carbamazepine (pharmaceutical), bisphenol-A (plastic- and epoxy-manufacturing ingredient), 1,7-dimethylxanthine (caffeine metabolite), and tri(2-chloroethyl) phosphate (fire retardant).  Overall, detections were more common in water collected from surface-water sites than from ground-water sites.  Sixty percent of the 36 pharmaceuticals (including prescription drugs and antibiotics) analyzed were not detected in any water sample. The maximum concentrations of the measured chemicals were only slightly above detection levels. Mixtures of chemicals were common.  Pharmaceuticals, including antibiotics and prescription and non-prescription drugs, generally were detected less frequently in sources of drinking water than they were in the national stream reconnaissance.

National Stream Reconnaissance for Emerging Contaminants
In 2002 the Toxic Substances Hydrology Program published the results of the "National Reconnaissance of Pharmaceuticals, Hormones, and Other Organic Wastewater Contaminants in Streams." The study documented the presence of low levels of many emerging contaminants, including prescription and non-prescription drugs, hormones, and other wastewater compounds, in a network of 139 targeted streams across the United States. This study was the first national-scale examination of emerging contaminants in streams and supported the USGS mission to assess the quantity and quality of the Nation's water resources.

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What Does All This Mean?

Recent advances in laboratory analytical methods have given scientists the tools to detect a wide range of contaminants in the environment at extremely low concentrations. The findings of these reconnaissance studies support other recent scientific studies using low-level detection technologies that document the environmental presence of chemicals not commonly monitored in water resources—chemicals often associated with human and animal wastewaters and biosolids. As detection technologies improve, scientists are likely to find more and a larger variety of these chemicals in ground water, streams, rivers, and drinking-water sources in the future. It is important to note that detection at a low concentration does not necessarily signal a health concern, and that some of the chemicals detected in these reconnaissance studies can occur naturally. Data from these surveys will help scientists, regulators, water-resource managers, and health professionals to determine if the concentrations and mixtures of chemicals measured in these waters pose a threat to human or environmental health, and will help with the development of mitigating strategies where needed.


Barnes, K.K., Kolpin, D.W., Furlong, E.T., Zaugg, S.D., Meyer, M.T., and Barber, L.B., 2008, A national reconnaissance of pharmaceuticals and other organic wastewater contaminants in the United States--I. Groundwater: Science of the Total Environment, doi:10.1016/j.scitotenv.2008.04.028.

Focazio, M.J., Kolpin, D.W., Barnes, K.K., Furlong, E.T., Meyer, M.T., Zaugg, S.D., Barber, L.B., and Thurman, E.M., 2008, A national reconnaissance for pharmaceuticals and other organic wastewater contaminants in the United States--II. Untreated drinking water sources: Science of the Total Environment, doi:10.1016/j.scitotenv.2008.02.021.

Barnes, K.K., Kolpin, D.W., Focazio, M.J., Furlong, E.T., Meyer, M.T., Zaugg, S.D., Haack, S.K., Barber, L.B., and Thurman, E.M., 2008, Water-quality data for pharmaceuticals and other organic wastewater contaminants in ground water and in untreated drinking water sources in the United States, 2000-01: U.S. Geological Survey Open-File Report 2008-1293, 6 p. plus tables.

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