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David H. Garabrant,¹ Alfred Franzblau,¹ James Lepkowski,² Brenda W. Gillespie,³ Peter Adriaens,⁴ Avery Demond,⁴ Elizabeth Hedgeman,¹ Kristine Knutson,¹ Lynn Zwica,¹ Kristen Olson,^2,5 Timothy Towey,⁴ Qixuan Chen,³ Biling Hong,¹ Chiung-Wen Chang,¹ Shih-Yuan Lee,³ Barbara Ward,² Kathy LaDronka,² William Luksemburg,⁶ and Martha Maier⁶

¹Department of Environmental Health Sciences and Risk Science Center, University of Michigan School of Public Health, Ann Arbor, Michigan, USA; ²Survey Research Center, Institute for Social Research, University of Michigan, Ann Arbor, Michigan, USA; ³Department of Biostatistics, University of Michigan School of Public Health, Ann Arbor, Michigan, USA; ⁴Department of Civil and Environmental Engineering, University of Michigan College of Engineering, Ann Arbor, Michigan, USA; ⁵Survey Research and Methodology Program, University of Nebraska–Lincoln, Gallup Research Center, Lincoln, Nebraska, USA; ⁶Vista Analytical Laboratory, El Dorado Hills, California, USA

Abstract
Background: We conducted a population-based human exposure study in response to concerns among the population of Midland and Saginaw counties, Michigan, that discharges by the Dow Chemical Company of dioxin-like compounds into the nearby river and air had led to an increase in residents’ body burdens of polychlorinated dibenzofurans (PCDDs) , polychlorinated dibenzofurans (PCDFs) , and dioxin-like polychlorinated biphenyls (PCBs) , here collectively referred to as “dioxins.”

Objectives: We sought to identify factors that explained variation in serum dioxin concentrations among the residents of Midland and Saginaw counties. Exposures to dioxins in soil, river sediments, household dust, historic emissions, and contaminated fish and game were of primary interest.

Methods: We studied 946 people in four populations in the contaminated area and in a referent population, by interview and by collection of serum, household dust, and residential soil. Linear regression was used to identify factors associated with serum dioxins.

Results: Demographic factors explained a large proportion of variation in serum dioxin concentrations. Historic exposures before 1980, including living in the Midland/Saginaw area, hunting and fishing in the contaminated areas, and working at Dow, contributed to serum dioxin levels. Exposures since 1980 in Midland and Saginaw counties contributed little to serum dioxins.

Conclusions: This study provides valuable insights into the relationships between serum dioxins and environmental factors, age, sex, body mass index, smoking, and breast-feeding. These factors together explain a substantial proportion of the variation in serum dioxin concentrations in the general population. Historic exposures to environmental contamination appeared to be of greater importance than recent exposures for dioxins.

Key words: epidemiology, exposure pathways, polychlorinated biphenyls, polychlorinated dioxins, polychlorinated furans, soil contamination. Environ Health Perspect 117:818–824 (2009) . doi:10.1289/ehp.11779 available via http://dx.doi.org/ [Online 22 December 2008]

Address correspondence to D.H. Garabrant, Department of Environmental Health Sciences, SPHII, Room 6529, 1420 Washington Heights, Ann Arbor, MI 48109-2029 USA. Telephone: (734) 936-0753. Fax: (734) 763-7170. E-mail: dhg@umich.edu

We thank S. Vantine for her assistance, and L. Birnbaum, R. Hites, P. Boffetta, and M.H. Sweeney for their guidance as members of our scientific advisory board.

Financial support came from the Dow Chemical Company through an unrestricted grant to the University of Michigan.

D.H.G. and A.F. have at times been retained as consultants and served as expert witnesses for the Dow Chemical Company. The remaining authors declare they have no competing financial interests.

Received 9 June 2008 ; accepted 22 December 2008.