El Dorado Hills, CA, United States
El Dorado Hills, CA, United States

Time filter

Source Type

Jiang X.,University of Michigan | Broadwater K.,University of Michigan | Meeker J.,University of Michigan | Luksemburg W.,Vista Analytical Laboratory | And 3 more authors.
Chemosphere | Year: 2015

Polychlorinated dibenzo-. p-dioxins (PCDDs) occur naturally in ball clay at elevated concentrations. Thus, persons who habitually work with clay may be at risk for exposure to PCDDs. An earlier case report provided some evidence of elevated PCDD levels in serum for long-term hobby ceramicists; however, no previous study has measured serum dioxin concentrations among ceramicists. This study measured PCDD serum levels for 27 individuals involved in ceramics making. The average residual, defined as the average of the [log measured serum lipid concentration - log background serum lipid concentration], was calculated and then tested to determine whether it was significantly different from zero. The p-values for the average residuals indicated that the serum lipid concentrations for several PCDD congeners were elevated relative to background. The number of significant residuals increased dramatically if the background concentrations were adjusted to account for the fact that they were not contemporaneous with the measurements for the ceramicists. The ratio of the 1,2,3,6,7,8-HxCDD concentration to the 1,2,3,7,8,9-HxCDD concentration was greater than 1.0, unlike in ball clay, suggesting that although long-term working with ball clay elevates the PCDD levels in serum somewhat, it is not the predominant source of the PCDD body burden for ceramicists. © 2014 Elsevier Ltd.


Fillos D.,ChemRisk | Scott L.L.F.,ChemRisk | Scott L.L.F.,University of Minnesota | De Sylor M.A.,ChemRisk | And 3 more authors.
Environmental Toxicology and Chemistry | Year: 2012

Currently, environmental studies describing levels of polychlorinated biphenyls (PCBs) in imported shrimp are limited, particularly studies of aquaculture shrimp. In the present study, we measured concentrations of the 209 PCB congeners in 84 uncooked, warm-water shrimp samples from the United States and 14 other countries in three continents. Total PCB and dioxin-like PCB (DL-PCB) levels were not significantly different between wild-caught and farm-raised shrimp, and the distribution of total PCB levels did not vary considerably by country of origin although significant differences were observed in some cases. Regional trends in both total PCB and DL-PCB concentrations were observed, with the highest concentrations measured in shrimp from North America followed by Asia and then South America. The lower chlorinated homologues (i.e., mono-, di-, and tri-PCBs) generally comprised a greater fraction of the total levels measured in farm-raised shrimp and shrimp from Asia and South America whereas higher chlorinated homologues (i.e., hepta-, octa-, nona-, and deca-PCBs) contributed more to levels in wild-caught shrimp and shrimp from North America. Estimated daily intake of PCBs associated with shrimp consumption ranged from 2pg/kg/d (shrimp from South America) to 15pg/kg/d (shrimp from North America). Results from the present study were comparable to other studies conducted recently and demonstrate that exposure to PCBs from consumption of farm-raised and wild-caught shrimp imported from different regions are not likely to pose any health risks. © 2012 SETAC.


Towey T.P.,University of Michigan | Chang S.-C.,University of Michigan | Chang S.-C.,National Chung Hsing University | Demond A.,University of Michigan | And 8 more authors.
Environmental Toxicology and Chemistry | Year: 2010

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. © 2009 SETAC.


Gillespie B.W.,University of Michigan | Chen Q.,University of Michigan | Chen Q.,Columbia University | Reichert H.,University of Michigan | And 7 more authors.
Epidemiology | Year: 2010

Background: Data with some values below a limit of detection (LOD) can be analyzed using methods of survival analysis for left-censored data. The reverse Kaplan-Meier (KM) estimator provides an effective method for estimating the distribution function and thus population percentiles for such data. Although developed in the 1970s and strongly advocated since then, it remains rarely used, partly due to limited software availability. Methods: In this paper, the reverse KM estimator is described and is illustrated using serum dioxin data from the University of Michigan Dioxin Exposure Study (UMDES) and the National Health and Nutrition Examination Survey (NHANES). Percentile estimates for left-censored data using the reverse KM estimator are compared with replacing values below the LOD with the LOD/2 or LOD/2. Results: When some LODs are in the upper range of the complete values, and/or the percent censored is high, the different methods can yield quite different percentile estimates. The reverse KM estimator, which is the nonparametric maximum likelihood estimator, is the preferred method. Software options are discussed: The reverse KM can be calculated using software for the KM estimator. The JMP and SAS (SAS Institute, Cary, NC) and Minitab (Minitab, Inc, State College, PA), software packages calculate the reverse KM directly using their Turnbull estimator routines. Conclusion: The reverse KM estimator is recommended for estimation of the distribution function and population percentiles in preference to commonly used methods such as substituting LOD/2 or LOD/2 for values below the LOD, assuming a known parametric distribution, or using imputation to replace the left-censored values. Copyright © 2010 by Lippincott Williams & Wilkins.


Demond A.,University of Michigan | Towey T.,LimnoTech | Adriaens P.,University of Michigan | Zhong X.,University of Michigan | And 9 more authors.
Environmental Toxicology and Chemistry | Year: 2010

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 R2 for the outcome variable of log10 of the vegetation concentration was log10 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. © 2010 SETAC.


Broadwater K.,University of Michigan | Meeker J.D.,University of Michigan | Luksemburg W.,Vista Analytical Laboratory | Maier M.,Vista Analytical Laboratory | And 3 more authors.
Chemosphere | Year: 2014

Ball clay is known to be naturally contaminated with high levels of polychlorinated di-benzo-p-dioxins (PCDDs). This study evaluated the potential for PCDD, polychlorinated dibenzofuran (PCDF) and polychlorinated biphenyl (PCB) release during the kiln firing of ball clay in an art studio. Toxic equivalence (TEQ) were calculated using World Health Organization (WHO) 2005 toxic equivalence factors (TEF) and congener concentrations. Ten bags of commercial ball clay were found to have an average TEQ of 1370nanograms/kilogram (ngkg-1) dry weight (dw), almost exclusively due to PCDDs (99.98% of TEQ). After firing, none of the 29 dioxin-like analytes was measured above the limits of detection (LOD) in the clay samples. Air samples were taken during firings using both low-flow and high-flow air samplers. Few low-flow air samples contained measurable levels of dioxin congeners above the LOD. The mean TEQ in the high volume air samples ranged from 0.07pgm-3 to 0.21pgm-3 when firing ball clay, and was 0.11pgm-3 when no clay was fired. These concentrations are within the range measured in typical residences and well-controlled industrial settings. The congener profiles in the high-flow air samples differed from the unfired clay; the air samples had a considerable contribution to the TEQ from PCDFs and PCBs. Given that the TEQs of all air samples were very low and the profiles differed from the unfired clay, it is likely that the PCDDs in dry ball clay were destroyed during kiln firing. These results suggest that inhalation of volatilized dioxins during kiln firing of dry ball clay is an unlikely source of exposure for vocational and art ceramicists. © 2013 Elsevier Ltd.

Loading Vista Analytical Laboratory collaborators
Loading Vista Analytical Laboratory collaborators