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Determinants of Temporal Variability in NHEXAS-Maryland Environmental Concentrations, Exposures, and Biomarkers

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Abstract: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.
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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, (12):1-10, (2004).
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Contact: Liz Hope - (919) 541-2785 or hope.elizabeth@epa.gov
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Division: Human Exposure & Atmospheric Sciences Division
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Branch: Exposure Measurements & Analysis Branch
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Product Type: Journal
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Published: 12/15/2004
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Bullet Item Determinants of Temporal Variability in NHEXAS-Maryland Environmental Concentrations, Exposures, and Biomarkers
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Related Entries:
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Bullet Item Implement NHEXAS Analysis Strategy
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