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Evaluating changes in matrix based, recovery-adjusted concentrations in paired data for pesticides in groundwater

Journal of Environmental Quality

By:
,
DOI: 10.2134/jeq2011.0271

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Abstract

Pesticide concentration data for waters from selected carbonate-rock aquifers in agricultural areas of Pennsylvania were collected in 1993–2009 for occurrence and distribution assessments. A set of 30 wells was visited once in 1993–1995 and again in 2008–2009 to assess concentration changes. The data include censored matched pairs (nondetections of a compound in one or both samples of a pair). A potentially improved approach for assessing concentration changes is presented where (i) concentrations are adjusted with models of matrix-spike recovery and (ii) area-wide temporal change is tested by use of the paired Prentice-Wilcoxon (PPW) statistical test. The PPW results for atrazine, simazine, metolachlor, prometon, and an atrazine degradate, deethylatrazine (DEA), are compared using recovery-adjusted and unadjusted concentrations. Results for adjusted compared with unadjusted concentrations in 2008–2009 compared with 1993–1995 were similar for atrazine and simazine (significant decrease; 95% confidence level) and metolachlor (no change) but differed for DEA (adjusted, decrease; unadjusted, increase) and prometon (adjusted, decrease; unadjusted, no change). The PPW results were different on recovery-adjusted compared with unadjusted concentrations. Not accounting for variability in recovery can mask a true change, misidentify a change when no true change exists, or assign a direction opposite of the true change in concentration that resulted from matrix influences on extraction and laboratory method performance. However, matrix-based models of recovery derived from a laboratory performance dataset from multiple studies for national assessment, as used herein, rather than time- and study-specific recoveries may introduce uncertainty in recovery adjustments for individual samples that should be considered in assessing change.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evaluating changes in matrix based, recovery-adjusted concentrations in paired data for pesticides in groundwater
Series title:
Journal of Environmental Quality
DOI:
10.2134/jeq2011.0271
Volume
41
Issue:
4
Year Published:
2012
Language:
English
Publisher:
ACSESS DL
Publisher location:
Madison, WI
Contributing office(s):
Pennsylvania Water Science Center
Description:
8 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
1238
Last page:
1245
Country:
United States
State:
Pennsylvania