You are here:
DETERMINANTS OF TEMPORAL VARIABILITY IN NHEXAS-MARYLAND ENVIRONMENTAL CONCENTRATIONS, EXPOSURES, AND BIOMARKERS
Citation:
Egeghy, P P., J J. Quackenboss, S. N. Catlin, AND B. Ryan. DETERMINANTS OF TEMPORAL VARIABILITY IN NHEXAS-MARYLAND ENVIRONMENTAL CONCENTRATIONS, EXPOSURES, AND BIOMARKERS. JOURNAL OF EXPOSURE ANALYSIS AND ENVIRONMENTAL EPIDEMIOLOGY. Nature Publishing Group, London, Uk, (12):1-10, (2004).
Impact/Purpose:
The NHEXAS analysis projects being conducted by NERL address the following scientific issues/questions:
- Do exposure distributions vary by demographic group?
- What is the impact of censoring (BDL) on multimedia distributions and associations?
- Which questionnaire/diary items are most useful in explaining variability or identifying "high exposure" groups?
- How do exposure classifications and measurements compare in their ability to explain variability in exposures and biomarkers?
- Can changes in exposures over time be explained by dietary and questionnaire/activity information?
- How well do NHEXAS findings compare with existing models/assessments (e.g., NATA)?
Description:
The longitudinal NHEXAS-Maryland study measured metals, PAHs, and pesticides in several media to capture temporal variability. Questionnaires were concurrently administered to identify factors that influenced changes in contaminant levels over time. We constructed mixed-effects regression models for lead, phenanthrene, and chlorpyrifos (including metabolites) in indoor air, dust, dermal wipes, and biological fluids. Significant predictors represented time-varying activities as well as unchanging housing and demographic factors. There was little overlap among the models, with predictors generally reflecting the diverse characteristics of the target compounds. We estimated between- and within-person variance components to evaluate the reliability of the measurements. While only one measurement of lead in blood or chlopyrifos in dust was needed for a dependable estimate of an individual's average level, three to eight measurements were needed for most other compound/exposure medium combinations because of considerable temporal variability. Measurements in biological fluids and dust were generally more consistent than those in indoor air. The significant covariates in the full models preferentially reduced the between-person variance component. Since the regression models explained only 1 to 37% of the within-person variance, the questionnaires in this study provided only modest insight into the factors responsible for the temporal variability in the contaminant levels.
The U.S. Environmental Protection Agency through its Office of Research and Development funded, managed, and collaborated in the research described here under NHEXAS Cooperative Agreement no. CR822038-1 to Harvard University, Johns Hopkins University, Emory University, Southwest Research Institute, and Westat. It has been subjected to Agency review and approved for publication.