T. Towey

The university of Michigan dioxin exposure study: Predictors of human serum dioxin concentrations in Midland and Saginaw, Michigan

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.

The University of Michigan Dioxin Exposure Study: Methods for an Environmental Exposure Study of Polychlorinated Dioxins, Furans, and Biphenyls

Background The University of Michigan Dioxin Exposure Study (UMDES) was undertaken in response to concerns that the discharge of dioxin-like compounds from the Dow Chemical Company facilities in Midland, Michigan, resulted in contamination of soils in the Tittabawassee River floodplain and areas of the city of Midland, leading to an increase in residents’ body burdens of polychlorinated dibenzodioxins and polychlorinated dibenzofurans. Objectives The UMDES is a hypothesis-driven study designed to answer important questions about human exposure to dioxins in the environment of Midland, where the Dow Chemical Company has operated for > 100 years, and in neighboring Saginaw, Michigan. In addition, the UMDES includes a referent population from an area of Michigan in which there are no unusual sources of dioxin exposure and from which inferences regarding the general Michigan population can be derived. A central goal of the study is to determine which factors explain variation in serum dioxin levels and to quantify how much variation each factor explains. Conclusions In this article we describe the study design and methods for a large population-based study of dioxin contamination and its relationship to blood dioxin levels. The study collected questionnaire, blood, dust, and soil samples on 731 people. This study provides a foundation for understanding the exposure pathways by which dioxins in soils, sediments, fish and game, and homegrown produce lead to increased body burdens of these compounds.

Impact of WHO 2005 revised toxic equivalency factors for dioxins on the TEQs in serum, household dust and soil

BACKGROUND In 2005, the World Health Organization (WHO) - International Programme on Chemical Safety reevaluated the toxic equivalency factors (TEFs) for dioxin-like compounds and made changes that affect the calculation of the total toxic equivalent (TEQ). The impact of these changes on the TEQs for human blood and abiotic matrices such as soil and household dust has not been widely assessed or reported. METHODS AND RESULTS Using a major exposure study which examined blood, household dust, and soil levels of dioxin-like compounds in several regions of Michigan, we found the mean total TEQ was significantly reduced by 26%, 12% and 14% for serum, household dust, and soil, respectively, when the TEQ was based on the 2005 TEFs compared to the 1998 TEFs. The decrease in the serum total TEQ was largely due to the down-weighting of the TEFs for the majority of mono-ortho PCBs. In contrast, the decrease in the soil total TEQ was mostly due to the down-weighting of the TEF for 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (1998 TEF=0.5, 2005 TEF=0.3). For household dust, the decrease in total TEQ was not due to any single TEF but was due to small changes in a number of compounds. There was a dramatic decrease (-88%) in the mean and 95th percentile for mono-ortho PCB TEQ due to the 2005 TEFs. DISCUSSION These findings suggest that comparisons between studies based on the TEQ-WHO(98) and TEQ-WHO(05) may need to consider an appropriate conversion factor to assure comparability. Furthermore, the changes in TEFs may have impact in locations where regulations of soil contamination are triggered by specific TEQ levels.

HIERARCHICAL CLUSTER ANALYSIS OF POLYCHLORINATED DIOXINS AND FURANS IN MICHIGAN, USA, SOILS: EVALUATION OF INDUSTRIAL AND BACKGROUND CONGENER PROFILES

As part of the University of Michigan Dioxin Exposure Study, soil samples were collected from 766 residential properties near the Tittabawassee River between Midland and Saginaw; near the Dow Chemical Facility in Midland; and, for comparison, in the other areas of Midland and Saginaw Counties and in Jackson and Calhoun Counties, all located in the state of Michigan, USA. A total of 2,081 soil samples were analyzed for 17 polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). In order to better understand the distribution and sources of the PCDD/F congeners in the study area, hierarchical cluster analysis (HCA) was used to statistically group samples with similar congener patterns. The analysis yielded a total of 13 clusters, including: 3 clusters among the soils impacted by contamination present in the Tittabawassee River sediments, a cluster comprised mainly of samples collected within the depositional area of the Dow incinerator complex, a small cluster of samples with elevated 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TCDD), and several clusters exhibiting background patterns. The clusters related to the Tittabawassee River floodplain contamination all contained elevated PCDF levels and were differentiated from one another primarily by their relative concentrations of higher-chlorinated PCDDs, a difference likely related to both extent and timing of impacts from Tittabawassee sediments. The background clusters appear to be related to combustion processes and are differentiated, in part, by their relative fractions of TCDD. Thus, HCA was useful for identifying congener profile characteristics in both contaminated and background soil samples.

Case Report: The University of Michigan Dioxin Exposure Study: A Follow-up Investigation of a Case with High Serum Concentration of 2,3,4,7,8-Pentachlorodibenzofuran

Context Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls that have toxic equivalency factors (TEFs) were measured in serum of 946 subjects in five Michigan counties. The study was motivated by concerns about human exposure to dioxin-contaminated sediments in the Tittabawassee River (TR). Most of the toxic equivalency in TR sediments is from two furan congeners, 2,3,7,8-tetrachlorodibenzofuran and 2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-pentaCDF). Case presentation The individual with the highest adjusted (for age, age squared, and body mass index) serum level of 2,3,4,7,8-pentaCDF in the study (42.5 ppt) reported a unique history of raising cattle and vegetables in the floodplain of the TR. Interviews and serum samples were obtained from the index case and 15 other people who ate beef and vegetables raised by the index case. 2,3,4,7,8-pentaCDF in beef lipid was estimated to have been more than three orders of magnitude greater than background (1,780 vs. 1.1 ppt). The mean, median, and 95th percentile for serum 2,3,4,7,8-pentaCDF in the study control population were 6.0, 5.4, and 13.0 ppt, respectively, and were 9.9, 8.4, and 20.5 ppt among beef and vegetable consumers, respectively. Back extrapolation for the index case suggests that his increase in serum concentration of 2,3,4,7,8-pentaCDF above background may have been as high as 146 ppt. Discussion Consumption of beef and/or vegetables raised on dioxin-contaminated soil may be an important completed pathway of exposure. Relevance to public health practice Animals and crops should not be raised for human consumption in areas contaminated with dioxins.

Polytopic vector analysis of soil, dust, and serum samples to evaluate exposure sources of PCDD/Fs

As part of the University of Michigan Dioxin Exposure Study, soil, household dust, and serum samples were collected from more than 750 households in five populations around the city of Midland and in Jackson and Calhoun Counties, Michigan, USA. Polytopic vector analysis, a type of receptor model, was applied to better understand the potential sources of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans found in these samples and to quantify the contributions of the sources in each matrix across populations. The results indicated that source signatures found in soil are similar to those found in dust, reflecting various combustion profiles, pentachlorophenol, and graphite electrode sludge. The profiles associated with contamination in the Tittabawassee River, likely related to historical discharges from the Dow Chemical Company facility in Midland, exhibited the largest differences among the regional populations sampled. Differences in serum source contributions among the study populations were consistent with some of the regional differences observed in soil samples. However, the age trends of these differences suggested that they are related to past exposures, rather than ongoing sources.

Relationship between polychlorinated dibenzo‐p‐dioxin, polychlorinated dibenzofuran, and dioxin‐like polychlorinated biphenyl concentrations in vegetation and soil on residential properties

The University of Michigan Dioxin Exposure Study was undertaken to address concerns that the industrial discharge of dioxin-like compounds in the Midland, Michigan, USA area had resulted in the contamination of soil and vegetation in the Tittabawassee River floodplain and downwind of the incinerator in the City of Midland. The study included the analysis of 597 vegetation samples, predominantly grass and weeds, from residential properties selected through a multistage probabilistic sample design in the Midland area, and in Jackson and Calhoun Counties (Michigan), as a background comparison, for 29 polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). The mean toxic equivalent (TEQ) of the house perimeter vegetation samples ranged from 4.2 to 377 pg/g. The ratio of TEQs (vegetation to soil) was about 0.3, with a maximum of 3.5. Based on a calculation of the similarity of the congener patterns between the soil and the vegetation, it appeared that the source of the contamination on the vegetation was the surrounding soil. This conclusion was supported by linear regression analysis, which showed that the largest contributor to the R(2) for the outcome variable of log(10) of the vegetation concentration was log(10) of the surrounding soil concentration. Models of vegetation contamination usually focus on atmospheric deposition and partitioning. The results obtained here suggest that the deposition of soil particles onto vegetation is a significant route of contamination for residential herbage. Thus, the inclusion of deposition of soil particles onto vegetation is critical to the accurate modeling of contamination residential herbage in communities impacted by historic industrial discharges of persistent organic compounds.