1. ^aEnvironmental Health Sciences Division, School of Public Health, University of Minnesota, Minneapolis, MN, USA
2. ^bBiostatistics Division, School of Public Health, University of Minnesota, Minneapolis, MN, USA
3. ^cDepartment of Epidemiology, Rollins School of Public Health, Emory University, USA
4. ^dMonsanto Company, St Louis, MO (Retired), USA
5. ^eDow Chemical Company, Midland, MI, USA

Correspondence: Ms. Deanna Scher, Environmental Health Sciences Division, University of Minnesota School of Public Health, MMC 807, 420 Delaware Street SE, Minneapolis, MN 55455, USA. Tel.: +1 612 247 4996. Fax: +1 612 626 4837. E-mail: sche0580@umn.edu

Received 23 January 2006; Accepted 1 May 2006; Published online 21 June 2006.

Abstract

In pesticide biomonitoring studies, researchers typically collect either single voids or daily (24-h) urine samples. Collection of 24-h urine samples is considered the "gold-standard", but this method places a high burden on study volunteers, requires greater resources, and may result in misclassification of exposure or underestimation of dose due to noncompliance with urine collection protocols. To evaluate the potential measurement error introduced by single void samples, we present an analysis of exposure and dose for two commonly used pesticides based on single morning void (MV) and 24-h urine collections in farmers and farm children. The agreement between the MV concentration and its corresponding 24-h concentration was analyzed using simple graphical and statistical techniques and risk assessment methodology. A consistent bias towards overprediction of pesticide concentration was found among the MVs, likely in large part due to the pharmacokinetic time course of the analytes in urine. These results suggest that the use of single voids can either over- or under-estimate daily exposure if recent pesticide applications have occurred. This held true for both farmers as well as farm children, who were not directly exposed to the applications. As a result, single void samples influenced the number of children exposed to chlorpyrifos whose daily dose estimates were above levels of toxicologic significance. In populations where fluctuations in pesticide exposure are expected (e.g., farm families), the pharmacokinetics of the pesticide and the timing of exposure events and urine collection must be understood when relying on single voids as a surrogate for longer time-frames of exposure.