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. 2013 Jan;121(1):118-24.
doi: 10.1289/ehp.1104808. Epub 2012 Oct 9.

Variability of organophosphorous pesticide metabolite levels in spot and 24-hr urine samples collected from young children during 1 week

Asa Bradman  1 , Katherine Kogut, Ellen A Eisen, Nicholas P Jewell, Lesliam Quirós-Alcalá, Rosemary Castorina, Jonathan Chevrier, Nina T Holland, Dana Boyd Barr, Geri Kavanagh-Baird, Brenda Eskenazi
Affiliations

Variability of organophosphorous pesticide metabolite levels in spot and 24-hr urine samples collected from young children during 1 week

Asa Bradman et al. Environ Health Perspect. 2013 Jan.

Abstract

Background: Dialkyl phosphate (DAP) metabolites in spot urine samples are frequently used to characterize children's exposures to organophosphorous (OP) pesticides. However, variable exposure and short biological half-lives of OP pesticides could result in highly variable measurements, leading to exposure misclassification.

Objective: We examined within- and between-child variability in DAP metabolites in urine samples collected during 1 week.

Methods: We collected spot urine samples over 7 consecutive days from 25 children (3-6 years of age). On two of the days, we collected 24-hr voids. We assessed the reproducibility of urinary DAP metabolite concentrations and evaluated the sensitivity and specificity of spot urine samples as predictors of high (top 20%) or elevated (top 40%) weekly average DAP metabolite concentrations.

Results: Within-child variance exceeded between-child variance by a factor of two to eight, depending on metabolite grouping. Although total DAP concentrations in single spot urine samples were moderately to strongly associated with concentrations in same-day 24-hr samples (r ≈ 0.6-0.8, p < 0.01), concentrations in spot samples collected > 1 day apart and in 24-hr samples collected 3 days apart were weakly correlated (r ≈ -0.21 to 0.38). Single spot samples predicted high (top 20%) and elevated (top 40%) full-week average total DAP excretion with only moderate sensitivity (≈ 0.52 and ≈ 0.67, respectively) but relatively high specificity (≈ 0.88 and ≈ 0.78, respectively).

Conclusions: The high variability we observed in children's DAP metabolite concentrations suggests that single-day urine samples provide only a brief snapshot of exposure. Sensitivity analyses suggest that classification of cumulative OP exposure based on spot samples is prone to type 2 classification errors.

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Conflict of interest statement

The contents are solely the responsibility of the authors and do not necessarily represent the views of the EPA or the NIEHS.

B.E. recently consulted on a pesticide exposure case. The other authors declare they have no actual or potential competing financial interests.

Figures

Figure 1
Figure 1
Concentration of total DAP metabolites (nmol/ gram creatinine) in log10 scale for all spot samples and 24-hr samples collected over 1 week. Each panel represents an individual participant (n = 25; P1–P25.) The dots in each panel represent the total DAP metabolite concentration in the 24-hr samples from sampling days 2 and 5, respectively. The panels are ranked in order of ascending arithmetic mean of all spot samples collected for each child. Thus, the bottom row (P21–P25) contains the children rated as having “true” high (top 20%) weekly exposure in the sensitivity and specificity analysis, and the bottom two rows exposure.
See this image and copyright information in PMC

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