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Data Series 630

National Water-Quality Assessment Program

Adjustment of Pesticide Concentrations for Temporal Changes in Analytical Recovery, 1992–2010

By Jeffrey D. Martin and Michael Eberle

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Abstract

Recovery is the proportion of a target analyte that is quantified by an analytical method and is a primary indicator of the analytical bias of a measurement. Recovery is measured by analysis of quality-control (QC) water samples that have known amounts of target analytes added (“spiked” QC samples). For pesticides, recovery is the measured amount of pesticide in the spiked QC sample expressed as a percentage of the amount spiked, ideally 100 percent. Temporal changes in recovery have the potential to adversely affect time-trend analysis of pesticide concentrations by introducing trends in apparent environmental concentrations that are caused by trends in performance of the analytical method rather than by trends in pesticide use or other environmental conditions.

This report presents data and models related to the recovery of 44 pesticides and 8 pesticide degradates (hereafter referred to as “pesticides”) that were selected for a national analysis of time trends in pesticide concentrations in streams. Water samples were analyzed for these pesticides from 1992 through 2010 by gas chromatography/mass spectrometry. Recovery was measured by analysis of pesticide-spiked QC water samples.

Models of recovery, based on robust, locally weighted scatterplot smooths (lowess smooths) of matrix spikes, were developed separately for groundwater and stream-water samples. The models of recovery can be used to adjust concentrations of pesticides measured in groundwater or stream-water samples to 100 percent recovery to compensate for temporal changes in the performance (bias) of the analytical method.

First posted October 2011

For additional information contact:
Jeff Martin, Pesticide National Synthesis Project
National Water-Quality Assessment Program
U.S. Geological Survey

See also the Pesticide National Synthesis Web page at
http://water.usgs.gov/nawqa/pnsp/

This report supplements USGS Scientific Investigations report 2009–5189:
http://pubs.usgs.gov/sir/2009/5189/

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.


Suggested citation:

Martin, J.D., and Eberle, Michael, 2011, Adjustment of pesticide concentrations for temporal changes in analytical recovery, 1992–2010: U.S. Geological Survey Data Series 630, 11 p., 5 app.



Contents

Abstract

Introduction

Analytical Method for Pesticides

Measurement of Recovery

Sources, Preparation, and Review of Recovery Data

Temporal Changes in Recovery

Summary

Acknowledgments

References Cited


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