USGS Collects Baseline Data for Emerging Contaminants
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 groundwater 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.
Groundwater samples were collected from a network of 47 wells with common environmental conditions and that 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 groundwater sites (35 percent of the sites) than they were in the stream reconnaissance (86 percent of the sites).
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 groundwater 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 groundwater 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.
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 groundwater, 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.