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,^1,* Ellen A. Eisen,^1,2 Nicholas P. Jewell,^1,3 Lesliam Quirós-Alcalá,¹ Rosemary Castorina,¹ Jonathan Chevrier,¹ Nina T. Holland,¹ Dana Boyd Barr,⁴ Geri Kavanagh-Baird,¹ and Brenda Eskenazi¹

¹Center for Environmental Research and Children’s Health, ²Division of Environmental Health Sciences, and ³Division of Biostatistics, School of Public Health, University of California, Berkeley, Berkeley, California, USA; ⁴Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA


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.


Key words: biomarkers, children, exposure, metabolites, organophosphorous, pesticides, urine, variability. 


Environ Health Perspect 121:118–124 (2013). http://dx.doi.org/10.1289/ehp.1104808 [Online 9 October 2012]


Address correspondence to A. Bradman, Center for Environmental Research and Children’s Health (CERCH); School of Public Health; University of California, Berkeley; 1995 University Ave., Suite 265; Berkeley, CA 94704 USA. Telephone: (510) 643-3023. Fax: (510) 642-9083. E-mail: abradman@berkeley.edu


Supplemental Material is available online (http://dx.doi.org/10.1289/ehp.1104808).


*These authors share lead authorship.


We thank S. Mehta and T. Whitehead for statistical assistance and also thank our staff, community partners, and study participants. We thank the anonymous reviewers for insightful comments and suggestions to improve the paper.


This research was supported by grant numbers RD 83171001 and RD 876709 from the U.S. Environmental Protection Agency (EPA), and PO1 ES009605 from the National Institute of Environmental Health Sciences (NIEHS). 


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.


Received 2 December 2011; Accepted 9 October 2012; Online 9 October 2012.