| Backward Estimation of Exposure to Organochlorines Using Repeated Measurements Wilfried Karmaus, Christopher Fussman, Jyotsna Muttineni, and Xiaobei Zhu Michigan State University, College of Human Medicine, Department of Epidemiology, East Lansing, Michigan, USA Abstract
Great Lakes sport-caught fish are contaminated with various organochlorines (OCs) such as polychlorinated biphenyls (PCBs) . Through consumption of these fish, humans are subject to continuing levels of OC contamination. To assess potential adverse effects of past exposure, we compared three different backward extrapolation models. The data originated from OC determinations in a cohort of anglers and their families. Repeated PCB measurements collected in the 1970s, 1980s, and 1990s were used when testing the backward extrapolations. We applied a simple and a complex decay model based on assumptions used in previous studies ; a third was a regression model incorporating markers of OC intake and loss. These techniques provided past exposure estimates. Intraclass correlation coefficients (ICCs) were calculated comparing measured and estimated PCB values. ICC values for the regression model equations were 0.77 and 0.89 ; ICC values for the simple and complex decay models were significantly lower, with ranges of 0.07-0.45 and -0.14-0.69, respectively. Plots showing trends of OC concentrations in fish and humans indicate comparable increases and decreases of PCB in fish and humans, with fish concentrations peaking approximately 10 years before that in humans. Our findings suggest that one should be cautious when using simple backward extrapolation techniques to estimate OC exposure in situations involving changing environmental exposures. Whenever repeated measurements are available, regression analyses seem to produce more accurate backward estimations of exposure. Key words: backward extrapolation, epidemiology, exposure assessment, fish consumption, Great Lakes, organochlorines. Environ Health Perspect 112:710-716 (2004) . doi:10.1289/ehp.6761 available via http://dx.doi.org/ [Online 4 February 2004]
Address correspondence to W. Karmaus, Michigan State University, College of Human Medicine, Department of Epidemiology, 4660 South Hagadorn, Suite 600, East Lansing, MI 48823 USA. Telephone: (517) 353-8623, ext. 115. Fax: (517) 432-1130. E-mail: karmaus@msu.edu We thank all the participants of the Great Lakes Fish Eaters Studies. We also thank W. Fu and P.K. Pathak for their statistical advice. This work was supported by grant H75-ATH82536-06 from the Agency for Toxic Substances and Disease Registry. The authors declare they have no competing financial interests. Received 25 September 2003 ; accepted 4 February 2004. An erratum was published in Environ Health Perspec 112: A543 (2004) .
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