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Estimation of Background Serum 2,3,7,8-TCDD Concentrations By Using Quantile Regression in the UMDES and NHANES Populations

Chen, Qixuana,b; Garabrant, David H.c,d; Hedgeman, Elizabethc; Little, Roderick J. A.b; Elliott, Michael R.b,e; Gillespie, Brendab; Hong, Bilingc; Lee, Shih-Yuanb; Lepkowski, James M.e; Franzblau, Alfredc,d; Adriaens, Peterf; Demond, Avery H.f; Patterson, Donald G. Jrg

doi: 10.1097/EDE.0b013e3181ce9550
Methodologic Issues in Environmental Exposures: Mixtures and Limits of Detection: Original Article

Background: The goal of the present study was to quantify the population-based background serum concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by using data from the reference population of the 2005 University of Michigan Dioxin Exposure Study (UMDES) and the 2003-2004 National Health and Nutrition Examination Survey (NHANES).

Methods: Multiple imputation was used to impute the serum TCDD concentrations below the limit of detection by combining the 2 data sources. The background mean, quartiles, and 95th percentile serum TCDD concentrations were estimated by age and sex by using linear and quantile regressions for complex survey data.

Results: Any age- and sex-specific mean, quartiles, and 95th percentiles of background serum TCDD concentrations of study participants between ages 18 and 85 years can be estimated from the regressions for the UMDES reference population and the NHANES non-Hispanic white population. For example, for a 50-year-old man in the reference population of UMDES, the mean, quartiles, and 95th percentile serum TCDD concentrations are estimated to be 1.1, 0.6, 1.1, 1.8, and 3.3 parts per trillion, respectively. The study also shows that the UMDES reference population is a valid reference population for serum TCDD concentrations for other predominantly white populations in Michigan.

Conclusion: The serum TCDD concentrations increased with age and increased more over age in women than in men, and hence estimation of background concentrations must be adjusted for age and sex. The methods and results discussed in this article have wide application in studies of the concentrations of chemicals in human serum and in environmental samples.

From the aDepartment of Biostatistics, Mailman School of Public Health, Columbia University, New York, NY; Departments of bBiostatistics and cEnvironmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI; dRisk Science Center, University of Michigan School of Public Health, Ann Arbor, MI; eSurvey Research Center, Institute for Social Research, University of Michigan, Ann Arbor, MI; fDepartment of Civil and Environmental Engineering, University of Michigan College of Engineering, Ann Arbor, MI; and gEnviro Solutions Consulting, Inc., Jasper, GA.

Submitted 12 August 2008; accepted 23 February 2009; posted 11 March 2010.

Supported by the Dow Chemical Company.

Correspondence: Qixuan Chen, 722 West 168 St., R652, New York, NY 10032. E-mail: qc2138@columbia.edu.

© 2010 Lippincott Williams & Wilkins, Inc.