SUMMARY

A primary goal of the National Water-Quality Assessment (NAWQA) Program is to assess and understand long-term trends in the quality of the Nation’s streams and rivers, herein collectively referred to as streams. A key aspect of water quality that presents unique data-analysis problems for trend assessment is pesticide concentrations in stream water. Selective analyses to date (2009) have included assessment of trends in diazinon and other insecticides in urban streams of the northeastern and midwestern United States and of trends in major herbicides in agricultural streams of the Corn Belt. Data from NAWQA pesticide monitoring, supplemented by data from the National Stream Quality Accounting Network (NASQAN) Program, are now sufficiently extensive for a national assessment of trends in pesticide concentrations in streams. These data, however, require a number of specific preparation steps to address potential biases from differences in sampling strategies among sites, including different sampling periods and intensities, and changes over time in performance of the analytical method and changes in data-reporting practices. This report describes the steps taken to prepare data for trend analysis and provides the resulting trend data set.

This report describes the procedures and criteria used to compile, review, select, and prepare pesticide-concentration data for trend analysis. The data are from water samples collected from January 1992 through August 2006 at stream-water sites of the NAWQA and NASQAN Programs. Water samples were analyzed at the U.S. Geological Survey (USGS) National Water Quality Laboratory (NWQL) by a gas chromatography/mass spectrometry (GCMS) method for as many as 44 commonly used pesticides and 8 pesticide degradates. Stream-water sites with three or more years of data, each with six or more samples per year, were selected for pesticide trend analysis. These and other selection criteria described in the report yielded a data set of 16,869 pesticide samples at 201 sites that is suitable for a national assessment of trends in pesticide concentrations in streams of the United States.

---

Suggested citation:

Martin, J.D., 2009, Sources and preparation of data for assessing trends in concentrations of pesticides in streams of the United States, 1992–2006: U.S. Geological Survey Scientific Investigations Report 2009–5062, 41 p.

---

Contents

Foreword

Abstract

Introduction

Purpose and Scope

Monitoring Programs for Pesticides

National Water-Quality Assessment Program

National Stream Quality Accounting Network Program

Methods of Sample Collection and Analysis

Sample Collection, Processing, and Field Quality-Control Program

Pesticides, Analytical Method, Reporting Levels, and Laboratory Quality-Control Programs

Sources of Water-Quality Data

Review, Selection, and Preparation of Water-Quality Data

Data Review

Data Selection and Preparation for Trend Analysis

Selection of Stream-Water Sites for Trend Analysis

Determination of Reporting Levels

Reassigning the Concentration Value for Routine Nondetections

Precision and Rounding

Adjustment of Concentrations for Temporal Changes in Recovery

Identification of Samples Considered Inappropriate for Trend Analysis

Data Set for Trend Assessment

Summary

Acknowledgments

References Cited

Appendixes

Revised November 16, 2009

First posted June 5, 2009