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Scientific Investigations Report 2014–5135

National Water-Quality Assessment Program

Pesticide Trends in Major Rivers of the United States, 1992–2010

By Karen R. Ryberg, Aldo V. Vecchia, Robert J. Gilliom, and Jeffrey D. Martin

Thumbnail of and link to report PDF (4.08 MB)Abstract

This report is part of a series of pesticide trend assessments led by the National Water-Quality Assessment Program of the U.S. Geological Survey. This assessment focuses on major rivers of various sizes throughout the United States that have large watersheds with a range of land uses, changes in pesticide use, changes in management practices, and natural influences typical of the regions being drained.

Trends were assessed at 59 sites for 40 pesticides and pesticide degradates during each of three overlapping periods: 1992–2001, 1997–2006, and 2001–10. In addition to trends in concentration, trends in agricultural-use intensity (agricultural use) were also assessed at 57 of the sites for 35 parent compounds with agricultural uses during the same three periods. The SEAWAVE-Q model was used to analyze trends in concentration, and parametric survival regression for interval-censored data was used to assess trends in agricultural use. All trends are provided in downloadable electronic files.

A subset of 39 sites was chosen to represent non-nested, generally independent basins for a national analysis of pesticide and agricultural-use trends for the most prevalent pesticides (15 pesticides and 2 degradation products). Graphical and numerical results are presented to provide a national overview of concentration and use trends. As another perspective on understanding pesticide concentration trends in large rivers in relation to multiple tributary watersheds, this report also presents a detailed assessment of concentration and use trends for simazine, metolachlor, atrazine, deethylatrazine, and diazinon for a set of 17 nested sites in the Mississippi River Basin (including the Ohio and Missouri River Basins), for the second and third trend periods.

Pesticides strongly dominated by agricultural use—cyanazine, metolachlor, atrazine, and alachlor—had widespread agreement between concentration trends and agricultural-use trends. Pesticides with substantial use in agricultural and urban applications—simazine, tebuthiuron, Dacthal, pendimethalin, chlorpyrifos, malathion, diazinon, fipronil, carbofuran, and carbaryl—had concentration trends that were mostly explained by a combination of agricultural-use trends and concentration trends in urban streams that were evaluated in a separate companion study. The importance of the urban stream trends for explaining concentration trends in major rivers indicates the significance of nonagricultural uses of some pesticides to concentrations in major rivers despite the much smaller area of urban land use compared to agriculture. Deethylatrazine, a degradate of atrazine, was the only pesticide compound assessed that had frequent occurrences during 1997–2006 and 2001–10 of concentration trends in the opposite direction of use trends (atrazine use). The nested analysis for the Mississippi River indicates that most trends observed in the largest rivers—multiple Mississippi River sites, the Ohio River, and the Missouri River—are consistent with streamflow contributions and concentration trends observed at tributary sites.

Streamflow (incorporated into the trend model and shown in the nested basin analysis), trends in agricultural use of pesticides (quantified in this report), and urban use of pesticides (represented by concentration trends in a companion study of urban streams) are all important influences on pesticide concentrations in streams and rivers. Consideration of these influences is vital to understanding trends in pesticide concentrations.

First posted September 8, 2014

For additional information contact:
Director, North Dakota Water Science Center
U.S. Geological Survey
821 East Interstate Avenue
Bismarck, North Dakota 58503

Or visit the Pesticide National Synthesis Project:

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Suggested citation:

Ryberg, K.R., Vecchia, A.V., Gilliom, R.J., and Martin, J.D., 2014, Pesticide trends in major rivers of the United States, 1992–2010: U.S. Geological Survey Scientific Investigations Report 2014–5135, 63 p.,

ISSN 2328-0328 (online)


Conversion Factors



Study Design and Methods

Use and Properties of Pesticides

Trend Results

National Analysis of Independent Trend Sites

Nested Basin Analysis for the Mississippi River Basin


References Cited

Appendix 1. Preparation of Concentration Data for Trend Analysis

Appendix 2. Examples of Agricultural-Use Intensity Data and Interval Censored Trend Analysis

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