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Jung-Wan Koo,¹ Frederick Parham,¹ Michael C. Kohn,¹ Scott A. Masten,¹ John W. Brock,² Larry L. Needham,² and Christopher J. Portier¹

¹Environmental Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA; ²National Center for Environmental Health, Center for Disease Control and Prevention, Atlanta, Georgia, USA

Abstract

Population-based estimates of environmental exposures using biomarkers can be difficult to obtain for a variety of reasons, including problems with limits of detection, undersampling of key strata, time between exposure and sampling, variation across individuals, variation within individuals, and the ability to find and interpret a given biomarker. In this article, we apply statistical likelihoods, weighted sampling, and regression methods for censored data to the analysis of biomarker data. Urinary metabolites for seven phthalates, reported by Blount et al., are analyzed using these methods. In the case of the phthalates data, we assumed the underlying model to be a log-normal distribution with the mean of the distribution defined as a function of a number of demographic variables that might affect phthalate levels in individuals. Included as demographic variables were age, sex, ethnicity, residency, family income, and education level. We conducted two analyses: an unweighted analysis where phthalate distributions were estimated with changes in the means of these distributions as a function of demographic variables, and a weighted prediction for the general population in which weights were assigned for a subset of the population depending on the frequency of their demographic variables in the general U.S. population. We used statistical tests to determine whether any of the demographic variables affected mean phthalate levels. Individuals with only a high school education had higher levels of di-n-butyl phthalate than individuals with education beyond high school. Subjects who had family income less than $1,500 in the month before sampling and/or only high school education had higher levels of n-butyl benzyl phthalate levels than other groupings. Di(2-ethylhexyl) phthalate was higher in males and/or in urban populations and/or in people who had family income less than $1,500 per month. Our findings suggest that there may be significant demographic variations in exposure and/or metabolism of phthalates and that health-risk assessments for phthalate exposure in humans should consider different potential risk groups. Key words: demographic factors, phthalates, risk assessment. Environ Health Perspect 110:405-410 (2002) . [Online 11 March 2002]

http://ehpnet1.niehs.nih.gov/docs/2002/110p405-410koo/ abstract.html

Address correspondence to C.J. Portier, National Institute of Environmental Health Sciences, 111 T.W. Alexander Drive, MD A3-02, Research Triangle Park, NC 27709, USA. Telephone: (919) 541-3802. Fax: (919) 541-3647. E-mail: portier@niehs.nih.gov

Received 24 August 2001 ; accepted 7 November 2001.