Child Exposure Validation Study

This study examines the validity of estimating children’s organophosphate pesticide exposure using dialkyl phosphate metabolites in urine.  We measured metabolites in urine collected from 3-to-6-year-old children over a 7-day period to learn more about the utility of dialkyl phosphate metabolites as biomarkers of exposure.

The goals of the Child Exposure Validation Study are:

  • To quantify variability in children’s urinary pesticide metabolite levels over a 7-day period.
  • To compare within- and between-children variability.
  • To learn whether metabolite concentrations in spot samples are representative of concentrations over a 24-hour period.
  • To learn whether metabolites in spot samples are representative of chronic exposure.

Exposures Studied:

  • Organophosphate (OP) pesticides

Findings from the Child Exposure Validation Study: (Findings are forthcoming)
(Go to the Exposure Studies Findings page for related findings)

Why study the validity of dialkyl phosphate metabolite exposure assessment?

Metabolite measurements in urine samples collected over a 24-hour period are often considered the “gold standard” for exposure assessment, but it is difficult to collect 24-hour urine samples from children. Thus, exposure and epidemiologic studies have used measurements of metabolites in a single “spot” urine sample to assess exposure. However, it is not known how well metabolite levels in spot urine samples represent exposure over a 24-hour period.  It is also not known whether spot or 24-hour samples represent long-term exposure over days or longer time periods.

Study Location:

  • The Salinas Valley, CA

Study Participants:

  • In March – April 2004, a convenience sample of 25 study participants between ages 3 and 6 years old was enrolled.
  • Participants were recruited from clinics serving low-income families in the Salinas Valley.
  • Population characteristics: The 25 study participants consisted of 15 girls and 10 boys, ranging in age from 3 to 6½ years (mean age: 4.5 years).  All were of Mexican-American ethnicity. Eleven children (44%) had at least one parent employed in agriculture and 15 children (68%) lived in a home with at least one agricultural worker.

Data Collection:

  • We collected urine samples over 7 consecutive days from 25 children.
  • The sampling regimen included daily spot-sampling, two 24-hr urine samples, and two first morning urine samples.
  • Parents completed an initial questionnaire and home inspection, as well as a brief daily diet and exposure questionnaire.
  • Urinary metabolite measurements were assessed for within-child versus between-child variability, and were analyzed relative to daily diet and activity logs and nearby agricultural pesticide use.
  • Sampling Schedule:
Sample Type Collection Day
1 2 3 4 5 6 7
Spot Urine x x x x x x x
First Morning Void x x x x
24-Hour Sample x x


Community Partners:

  • Learn more about our community partners here.

Research Team:

  • Asa Bradman, PhD
  • Brenda Eskenazi, PhD
  • Ellen Eisen, ScD
  • Nicholas Jewell, PhD
  • Katie Kogut, MPH MSc
  • Rosemary Castorina, PhD
  • Jonathan Chevrier, PhD
  • Dana Barr, PhD, Centers for Disease Control and Prevention (currently at Emory University)


This study is in the data analysis phase (2011).
Check back for updates on our progress and findings.


Funded By: Duration: Study Contact:
  • The National Institute for Environmental Health Sciences (NIEHS)
  • U.S. Environmental Protection Agency (EPA)
  • National Institute for Occupational Safety and Health (NIOSH) 2001-2006
Asa Bradman, PhD
Associate Director, Exposure Assessment, CERCH
[email protected]

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