Statistical Comparison of Residential Soil Concentrations of PCDDs, PCDFs, and PCBs from Two Communities in Michigan

Abstract

The University of Michigan dioxin exposure study was undertaken to address concerns that the industrial discharge of dioxin-like compounds in the Midland, MI area had resulted in contamination of soils in the Tittabawassee River floodplain and downwind of the incinerator. The study was designed in a rigorously statistical manner comprising soil measurements of 29 polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) from 766 residential properties, selected probabilistically, in the Midland area and in Jackson and Calhoun Counties (Michigan) as a background comparison. A statistical comparison determined that the geometric mean toxic equivalent (TEQ) levels in samples from the target populations were statistically significantly above background. In addition, the probabilities of being above the 75th and 95th percentiles of background were also greater. Congener contributions to the TEQ were dominated by 2,3,4,7,3,7, in the floodplain and by 2,3,7,8-TCDD in the incinerator plume. However, PCB 126 was the top congener contributing to the background TEQ.On the basis of statistical inference to the total population, it was estimated that about 36% of the properties in the floodplain and incinerator plume have at least one soil sample over the Michigan Department of Environmental Quality's soil direct contact criterion of 90 pg/g TEQ. IntroductionThe University of Michigan dioxin exposure study (UMDES) was undertaken in response to concerns among residents in the Midland, MI area that the historic discharge of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from the Dow Chemical Company facilities had resulted in soil contamination in the Tittabawassee River floodplain and in the City of Midland leading to an increase in residents' body burdens of these compounds. Dow Chemical has operated in Midland, MI since 1897 manufacturing a wide range of chemical products such as chlorine through the electrolysis of brine (since its founding (1)) and chlorinated phenols by reacting chlorine gas and phenol (from 1937 to 1982 (2)). Historically, wastes from these manufacturing operations were incinerated, resulting in aerial deposition in the City of Midland, discharged directly to the Tittabawassee River or discharged to waste ponds that were periodically breached during flooding events. To analyze the relationship between soil contamination and area residents' body burdens, UMDES was a large multidisciplinary undertaking including measurements of dioxin-like compounds not only in soil but also in household dust and serum from populations in Midland, Saginaw, and Bay Counties (Michigan) as the target areas and from Jackson and Calhoun Counties (Michigan) as a background comparison. To account for additional factors that might impact levels of dioxin-like compounds in serum, the study also comprised the administration of a questionnaire covering age, weight, and smoking habits; residential, occupational, and dietary histories; an...

Hierarchical cluster analysis of polychlorinated dioxins and furans in Michigan, USA, soils: Evaluation of industrial and background congener profiles

“…Emissions from the incinerator located at the Dow Chemical plant in Midland have been shown to resemble those from other hazardous waste combustion facilities [5] with PCDDs as the primary contributor to TEQ. Summary statistical analysis of the congener distributions found in the soils collected as part of the UMDES shows agreement with these general conclusions [6], yet the analysis was based on looking at the means of the primary contributors to the TEQ. In order to better understand the patterns of PCDDs and PCDFs in the environment to which the study participants Environmental Toxicology and Chemistry, Vol.…”

“…The house perimeter 0 to 2.5 cm sample and, if collected, the garden 0 to 15 cm sample were analyzed from every residence. Additional samples from some residences were submitted based on the population from which the sample was collected and the results of the house perimeter 0 to 2.5 cm sample [6]. A total of 2,081 soil samples from 766 properties were analyzed for the World Health Organization (WHO) designated 29 PCDD, PCDF, and PCB Congeners by Vista Analytical Laboratory (El Dorado Hills, CA, USA) using internal modifications of U.S. Environmental Protection Agency (U.S. EPA) Method 1688A [17] and U.S. EPA Method 8290 [18].…”

“…Toxic equivalent values were calculated using the 2005 WHO toxic equivalency factors for PCDDs and PCDFs [20] and are denoted as TEQ DF2005 . Further details regarding soil sample collection and analysis, along with summary statistics of the soil results, are presented in Demond et al [6]. The WHO-29 includes only 2,3,7,8-substituted PCDD/F congeners.…”

Derivation of Soil Clean-Up Levels for 2,3,7,8-Tetrachloro-dibenzo-p-dioxin (TCDD) Toxicity Equivalence (TEQD/F) in Soil Through Deterministic and Probabilistic Risk Assessment of Exposure and Toxicity

“…As described earlier, the UMDES investigation, which was conducted independent of any hypothetical risk or exposure estimates, provided an unusually comprehensive analysis of environmental exposures and serum TEQ D/F for 1324 people representative of those residing for at least 5 years in the study area, including Midland and the Tittabawassee River and Saginaw River floodplains (Hedgeman et al 2008;Franzblau et al 2008aFranzblau et al ,b, 2009aGarabrant et al 2008a,b;Demond et al 2008). Evaluation of the relationship between a residential soil TEQ D/F and serum TEQ D/F did not identify any correlation.…”

“…In an independent investigation by the University of Michigan, individuals and properties in a larger area have been the subject of a comprehensive exposure-biomonitoring survey (the University of Michigan Dioxin Exposure Study (UMDES)) (www.sph.umich.edu/dioxin, Hedgeman et al 2008;Franzblau et al 2008aFranzblau et al ,b, 2009aGarabrant et al 2008a,b;Demond et al 2008), which included exposure survey data on 1324 adults (including 359 from the reference area and 326 from the Midland Saginaw Floodplain area) who had lived at their current address for 5 years or longer. It included a complete set of interview data, serum data, and soil and dust sample data for 731 persons.…”