The University of Michigan Dioxin Exposure Study: Population Survey Results and Serum Concentrations for Polychlorinated Dioxins, Furans, and Biphenyls

The University of Michigan Dioxin Exposure Study (UMDES) was undertaken in response to concerns from residents that the discharge of dioxin-like compounds (DLCs) from the Dow Chemical Company facilities in Midland, Michigan, resulted in contamination of soils in the Tittabawassee River floodplain and in the city of Midland, leading to an increase in residents’ body burdens of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). PCDDs, PCDFs, and polychlorinated biphenyls (PCBs) are ubiquitous in soils, sediments, air, and animal tissues in industrialized nations [Alcock and Jones 1996; U.S. Environmental Protection Agency (EPA) 2003]. They are often the unintentional byproducts of burning and waste incineration, primary and secondary metal smelting, and chlorine-based chemical processes (U.S. EPA 2006). Within the lower peninsula of Michigan, background soil concentrations of the 17 PCDDs and PCDFs recognized by the World Health Organization (WHO) as having dioxin-like activity (Van den Berg et al. 1998) range from 0.4 to 34.7 ppt toxic equivalency (TEQDF-1998, where D is PCDDs, F is PCDFs, and 1998 indicates the WHO 1998 toxic equivalency factors, respectively), with a median level of 4.6 ppt TEQDF-1998 [Michigan Department of Environmental Quality (MDEQ) 1999]. In contrast, soils and sediments sampled from along the Tittabawassee River, downstream of the Dow Chemical Company, ranged from 4 to 1,980 ppt TEQDF-1998 (Hilscherova et al. 2003). Previous sampling of the top 1 in. of soils from along the Tittabawassee River (Demond et al. 2008) ranged from 1.1 to 9,351 ppt TEQDFP-1998 (or from 1.1 to 7,258 ppt TEQDFP-2005; where D is PCDDs, F is PCDFs, P is PCBs, and 1998 or 2005 indicates the WHO 1998 or 2005 toxic equivalency factors, respectively). These elevated soil concentrations are the result of a century of chlorine and chlorine-based chemical manufacture. With the increased awareness of the elevated concentrations of PCDDs and PCDFs in the Tittabawassee River floodplain soils, there has been increasing pressure to monitor the concentrations of PCDDs and PCDFs in the local biota. Fish caught from the rivers downstream of the Dow Chemical Company have concentrations of PCDDs and PCDFs ranging from 1.5 to 40 ppt wet weight TEQDF-2005 (MDEQ 2003). In the Family Fish Consumption Guide, the Michigan Department of Community Health (MDCH) cautioned fishers to limit or avoid consumption of fish from these waters (MDCH 2004a). White-tailed deer, wild turkeys, and squirrels harvested from areas downstream of the Dow Chemical Company were reported to have a statistically elevated mean TEQDF-1998 in their tissues compared with animals harvested from a reference area (Entrix, Inc. 2004). With respect to humans, a pilot study of 20 residents living on contaminated Tittabawassee River floodplain soils showed elevated mean serum levels of TEQDFP-1998 and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), although the range of the serum samples fell within the age-specific range of the comparison population (MDCH 2007). Although various soils, fish, and animals from the Tittabawassee River floodplain and surrounding areas have increased levels of DLCs, it is unclear whether these contribute to human serum levels and by what pathways. The UMDES is the first population-based exposure study of residents living in and around the Tittabawassee River floodplain. It was designed to determine whether residents living on contaminated soils, participating in activities in the contaminated region, and eating fish, game, and other foods from the contaminated region have higher serum levels of dioxins than residents in areas with no unusual source of DLCs. This study included a multi stage, random sample of the population who were interviewed in person, gave an 80-mL blood sample, and allowed collection of household dust and residential soil samples. We analyzed the blood serum, household dust, and soil samples for the 29 PCDD, PCDF, and PCB congeners recognized by WHO as having dioxin-like activity (Van den Berg et al. 1998, 2006). In this article, we describe the characteristics of the populations interviewed and the serum, household dust, and house perimeter soil concentrations determined by high-resolution gas chromatography/high-resolution mass spectrometry analyses for PCDDs, PCDFs, and PCBs. With detailed serum concentration data from 946 individuals, the UMDES is one of the largest population studies of human exposure to PCDDs, PCDFs, and PCBs in the United States.