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Decadal-Scale Changes of Pesticides in Ground Water of the United States, 1993–2003

U.S. Geological Survey, New Mexico Water Science Center, 5338 Montgomery Blvd., N.E., Suite 400, Albuquerque, New Mexico 87109. Chemical names of all pesticide compounds mentioned in this paper are listed in Table 2 of the article by Rosen and Lapham (2008)

^* Corresponding author (bexfield{at}usgs.gov).

Received for publication January 30, 2007. Pesticide data for ground water sampled across the United States between 1993–1995 and 2001–2003 by the U.S. Geological Survey National Water-Quality Assessment Program were evaluated for trends in detection frequency and concentration. The data analysis evaluated samples collected from a total of 362 wells located in 12 local well networks characterizing shallow ground water in agricultural areas and six local well networks characterizing the drinking water resource in areas of variable land use. Each well network was sampled once during 1993–1995 and once during 2001–2003. The networks provide an overview of conditions across a wide range of hydrogeologic settings and in major agricultural areas that vary in dominant crop type and pesticide use. Of about 80 pesticide compounds analyzed, only six compounds were detected in ground water from at least 10 wells during both sampling events. These compounds were the triazine herbicides atrazine, simazine, and prometon; the acetanilide herbicide metolachlor; the urea herbicide tebuthiuron; and an atrazine degradate, deethylatrazine (DEA). Observed concentrations of these compounds generally were <0.12 µg L^–1. At individual wells, changes in concentrations typically were <0.02 µg L^–1. Data analysis incorporated adjustments for changes in laboratory recovery as assessed through laboratory spikes. In wells yielding detectable concentrations of atrazine, DEA, and prometon, concentrations were significantly lower ( = 0.1) in 2001–2003 than in 1993–1995, whereas detection frequency of these compounds did not change significantly. Trends in atrazine concentrations at shallow wells in agricultural areas were found to be consistent overall with recent atrazine use data.

Abbreviations: ACFB, Apalachicola–Chattahoochee–Flint Basin • AgLUS, agricultural land-use study • AI, active ingredient • CCPT, Central Columbia Plateau • DDT, dichloro-diphenyl-trichloroethane • DEA, deethylatrazine • GAFL, Georgia–Florida Coastal Plain • LRL, laboratory reporting level • LT-MDL, long-term method detection level • MAS, major aquifer study • MRL, method reporting level • NAWQA, National Water-Quality Assessment • NVBR, Nevada Basin and Range • NWQL, National Water-Quality Laboratory of the USGS • POTO, Potomac River Basin • SANJ, San Joaquin–Tulare Basins • SPLT, South Platte River Basin • USGS, United States Geological Survey • WHIT, White River Basin • WILL, Willamette Basin • WMIC, Western Lake Michigan Drainage