A national reconnaissance of pharmaceuticals and other organic wastewater contaminants in the United States — I) Groundwater Kimberlee K. Barnes a, ⁎ , Dana W. Kolpin a , Edward T. Furlong b , Steven D. Zaugg b , Michael T. Meyer c , Larry B. Barber d a U.S. Geological Survey, 400 South Clinton Street, Room 269, Iowa City, Iowa 52244, United States b U.S. Geological Survey, National Water Quality Laboratory, P.O. Box 25046, MS 407, Denver Federal Center, Lakewood, Colorado 80225, United States c U.S. Geological Survey, 4821 Quail Crest Place, Lawrence, Kansas 66049, United States d U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303, United States ARTICLE INFO ABSTRACT Article history: Received 2 November 2007 Received in revised form 17 April 2008 Accepted 22 April 2008 As part of the continuing effort to collect baseline information on the environmental occurrence of pharmaceuticals, and other organic wastewater contaminants (OWCs) in the Nation's water resources, water samples were collected from a network of 47 groundwater sites across 18 states in 2000. All samples collected were analyzed for 65 OWCs representing a wide variety of uses and origins. Site selection focused on areas suspected to be susceptible to contamination from either animal or human wastewaters (i.e. down gradient of a landfill, unsewered residential development, or animal feedlot). Thus, sites sampled were not necessarily used as a source of drinking water but provide a variety of geohydrologic environments with potential sources of OWCs. OWCs were detected in 81% of the sites sampled, with 35 of the 65 OWCs being found at least once. The most frequently detected compounds include N,N-diethyltoluamide (35%, insect repellant), bisphenol A (30%, plasticizer), tri(2-chloroethyl) phosphate (30%, fire retardant), sulfamethoxazole (23%, veterinary and human antibiotic), and 4-octylphenol monoethoxylate (19%, detergent metabolite). Although sampling procedures were intended to ensure that all groundwater samples analyzed were indicative of aquifer conditions it is possible that detections of some OWCs could have resulted from leaching of well-construction materials and/or other site- specific conditions related to well construction and materials. Future research will be needed to identify those factors that are most important in determining the occurrence and concentrations of OWCs in groundwater. Published by Elsevier B.V. Keywords: Groundwater Pharmaceuticals Contaminants 1. Introduction Increasing standards of living and the continual growth of the human population has led to a growing demand for fresh- water. Thus, the protection of this natural resource is an important environmental issue. In the United States in 1995, groundwater withdrawals were estimated at more than 291 million liters per day (Solley et al., 1998). Groundwater not only provides about 40% of the Nation's public water supply, but it also is used by more than 40 million people, including most of SCIENCE OF THE TOTAL ENVIRONMENT 402 (2008) 192 – 200 ⁎ Corresponding author. Tel.: +1 319 358 3618; fax: +1 319 358 3606. E-mail address: kkbarnes@usgs.gov (K.K. Barnes). 0048-9697/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.scitotenv.2008.04.028 available at www.sciencedirect.com www.elsevier.com/locate/scitotenv