Variability of organophosphorous pesticide metabolite levels in spot and 24-hr urine samples collected from young children during 1 week.
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.
Center for Environmental Research and Children’s Health, School of Public Health, University of California, Berkeley, Berkeley, California 94704, USA. abradman@berkeley.edu
Asa
A
Bradman
Katherine
K
Kogut
Ellen A
EA
Eisen
Nicholas P
NP
Jewell
Lesliam
L
Quirós-Alcalá
Rosemary
R
Castorina
Jonathan
J
Chevrier
Nina T
NT
Holland
Dana Boyd
DB
Barr
Geri
G
Kavanagh-Baird
Brenda
B
Eskenazi
D002648:Child; D002675:Child, Preschool; D004781:Environmental Exposure / Q000032:analysis; D006801:Humans; D009943:Organophosphorus Compounds / Q000652:urine*; D010575:Pesticides / Q000652:urine*; D015203:Reproducibility of Results
D009943:Organophosphorus Compounds; D010575:Pesticides