National Water-Quality Assessment (NAWQA) Project
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Most concern about pesticides in ground water stems from their potential impact on drinking water. The U.S. Environmental Protection Agency establishes Maximum Contaminant Limits (MCLs) for pesticides in drinking water. Nationally, fewer than two percent of the wells sampled by multistate studies, which mostly focused on agricultural areas, had concentrations that exceeded MCLs. Although this suggests that the problem is small at the national scale, our current ability to assess the significance of pesticides in ground water is limited by several factors. First, MCLs or other water-quality criteria have not been established for many pesticides and for most transformation products, and existing criteria may be revised as more is learned about the toxicity of these compounds. Second, MCLs and other criteria are currently based on individual pesticides and do not account for possible cumulative effects if several different pesticides are present in the same well. Finally, many pesticides and most transformation products have not been widely sampled for in ground water and very little sampling has been done in urban and suburban areas, where pesticide use is often high.
The widespread detection of pesticides in ground water at levels below current MCLs -- particularly high-use compounds in vulnerable areas -- indicates that exceedances of water-quality criteria are likely to increase if existing criteria are lowered; as criteria are established for more compounds; as a wider range of pesticides and their transformation products are analyzed for; and as sampling expands to include more non-agricultural areas. Together, these factors create uncertainty in our present ability to make strong conclusions about the national significance of pesticide contamination of ground water, and suggest that major data gaps will need to be filled in order to reduce this uncertainty. Differences in scale or approach among existing studies, and the shortage of data on many compounds and on temporal trends, indicate that long-term investigations are required that have consistent study designs and that involve more comprehensive chemical analyses.
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Gianessi, L.P. and Puffer, C., 1990, Herbicide use in the United States, Resources for the Future, Inc.
Kolpin, D.W., Goolsby, D.A., and Thurman, E.M., (1995). Pesticides in near-surface aquifers: An assessment using highly sensitive analytical methods and tritium. Journal of Environmental Quality, v. 24, no. 6, pp. 1125-1132.
Majewski, M.S. and Capel, P.D., 1995, Pesticides in the Atmosphere: Distribution, Trends, and Governing Factors, Ann Arbor Press, Inc., Chelsea, MI.
Risch, M.R., 1994, A summary of pesticides in ground-water data collected by government agencies in Indiana, December 1985 to April 1991: U.S. Geological Survey Open-File Report 93-133, 30 p.
U.S. Environmental Protection Agency, 1990, National survey of pesticides in drinking water wells: Phase I report (EPA 570/9-90-015).
_____, 1992, Pesticides in ground water database: A compilation of monitoring studies, 1971-1991, National summary (EPA 734/12-92-001).
_____, 1994, Pesticides Industry Sales and Usage: 1992 and 1993 Market Estimates (EPA 733-K-94-001).
Chief, Pesticide National Synthesis
U.S. Geological Survey
Placer Hall
6000 J Street
Sacramento, CA 95819-6129
Additional information on NAWQA and other U.S. Geological Survey programs can be found by accessing the NAWQA "home page" on the World Wide Web at: " http://water.usgs.gov/nawqa/."
U.S Geological Survey Fact Sheet FS-244-95
U.S. Department of the Interior | U.S. Geological Survey
URL: http://water.usgs.gov/nawqa/pnsp/pubs/fs244-95/gw_10.html
Page Contact Information: gs-w_nawqa_whq@usgs.gov
Page Last Modified: Tuesday, 04-Mar-2014 14:44:26 EST
