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ANALYSIS OF CONCORDANCE OF PROBABILISTIC AGGREGATE EXPOSURE PREDICTIONS WITH OBSERVED BIOMONITORING RESULTS: AN EXAMPLE USING CTEPP DATA
Citation:
SMITH, J. A., J. C. KISSEL, J. H. SHIRAI, M. K. MORGAN, L. S. SHELDON, AND C. W. CROGHAN. ANALYSIS OF CONCORDANCE OF PROBABILISTIC AGGREGATE EXPOSURE PREDICTIONS WITH OBSERVED BIOMONITORING RESULTS: AN EXAMPLE USING CTEPP DATA. Presented at International Society of Exposure Analysis Conference, Tucson, AZ, October 30 - November 03, 2005.
Impact/Purpose:
The overall objectives of CTEPP were to measure the aggregate exposures of approximately 260 preschool children and their adult caregivers to low levels of a suite of pesticides and organic pollutants that the children may encounter in their everyday environments, and to apportion the routes of exposure and estimate the relative contributions of each route.
Description:
Three key areas of scientific inquiry in the study of human exposure to environmental contaminants are 1) assessment of aggregate (i.e., multi-pathway, multi-route) exposures, 2) application of probabilistic methods to exposure prediction, and 3) the interpretation of biomarker measurements. An EPA-funded study has begun at the University of Washington that attempts to integrate these three areas of inquiry by simultaneous application to selected case studies. The project entails prediction of aggregate pesticide exposures using second order probabilistic methods, and comparison of those predictions to observed levels of urinary biomarkers using previously collected datasets. Concordance of predicted and observed results is evaluated following the methods of Lin and van Belle, which permit apportionment of overall deviance among accuracy, bias and scale. It is anticipated that insights gained will lead to improved model evaluation and, ultimately, improved exposure prediction. Demonstration of the overall approach is shown using chlorpyrifos (CP) exposure-related data from the U.S. EPA's Children's Total Exposure to Persistent Pesticides and Other Persistent Organic Pollutants (CTEPP) pilot study. The CTEPP study investigated the sources and routes of children's exposure to over 50 pollutants at their homes and daycares in selected North Carolina and Ohio counties in 2000-2001. Spot urine samples were collected from 257 children under 6 years of age over a 48-hr period. Urine samples were analyzed by gas chromatography/mass spectrometry for multiple compounds including 3,5,6-trichloro-2-pyridinol (TCPy), which is the specific urinary biomarker of exposure to chlorpyrifos in humans. TCPy is also the signature degradation product of chlorpyrifos in exposure media. Prior deterministic analysis of the North Carolina CTEPP data has suggested a shortfall of predicted exposure to CP and TCPy relative to observed excretion of TCPy. This finding, the relatively rich dataset collected, and the critical population involved render CTEPP an excellent case for application of a second order probabilistic approach and for quantitative evaluation of the performance of that approach.
This project is supported in part by U.S. EPA via STAR Grant RD-83184401-0. Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy. JAS was also partially supported via CDC/NIOSH Training Grant T42/CCT010418-11.