Thomas F Webster

Boston University, Boston, Massachusetts, United States

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Publications (95)334.44 Total impact

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    ABSTRACT: In this discussion paper, the transition from long-chain poly- and perfluorinated alkyl substances (PFASs) to fluorinated alternatives is addressed. Long-chain PFASs include perfluoroalkyl carboxylic acids (PFCAs) with 7 or more perfluorinated carbons, perfluoroalkyl sulfonic acids (PFSAs) with 6 or more perfluorinated carbons, and their precursors. Because long-chain PFASs have been found to be persistent, bioaccumulative and toxic, they are being replaced by a wide range of fluorinated alternatives. We summarize key concerns about the potential impacts of fluorinated alternatives on human health and the environment in order to provide concise information for different stakeholders and the public. These concerns include, amongst others, the likelihood of fluorinated alternatives or their transformation products becoming ubiquitously present in the global environment; the need for more information on uses, properties and effects of fluorinated alternatives; the formation of persistent terminal transformation products including PFCAs and PFSAs; increasing environmental and human exposure and potential of adverse effects as a consequence of the high ultimate persistence and increasing usage of fluorinated alternatives; the high societal costs that would be caused if the uses, environmental fate, and adverse effects of fluorinated alternatives had to be investigated by publicly funded research; and the lack of consideration of non-persistent alternatives to long-chain PFASs.
    Chemosphere 06/2014; · 3.14 Impact Factor
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    ABSTRACT: Concern has mounted over health effects caused by exposure to flame retardant additives used in consumer products. Significant research efforts have focused particularly on exposure to polybrominated diphenyl ethers (PBDEs) used in furniture and electronic applications. However, little attention has focused on applications in textiles, particularly textiles meeting a flammability standard known as CPAI-84. In this study, we investigated flame retardant applications in camping tents that met CPAI-84 standards by analyzing 11 samples of tent fabrics for chemical flame retardant additives. Furthermore, we investigated potential exposure by collecting paired samples of tent wipes and hand wipes from 27 individuals after tent setup. Of the 11 fabric samples analyzed, 10 contained flame retardant additives, which included tris(1,3-dichloroisopropyl) phosphate (TDCPP), decabromodiphenyl ether (BDE-209), triphenyl phosphate, and tetrabromobisphenol-A. Flame retardant concentrations were discovered to be as high as 37.5 mg/g (3.8% by weight) in the tent fabric samples, and TDCPP and BDE-209 were the most frequently detected in these samples. We also observed a significant association between TDCPP levels in tent wipes and those in paired hand wipes, suggesting that human contact with the tent fabric material leads to the transfer of the flame retardant to the skin surface and human exposure. These results suggest that direct contact with flame retardant-treated textiles may be a source of exposure. Future studies will be needed to better characterize exposure, including via inhalation and dermal sorption from air.
    Environmental science & technology letters. 02/2014; 1(2):152-155.
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    ABSTRACT: Polybrominated diphenyl ether (PBDE), flame retardants (FRs) have been ubiquitously detected at high concentrations in indoor environments; however, with their recent phase-out, more attention is being focused on measurements of exposure to alternative FRs such as organophosphate FRs (OPFRs). In our previous research, we found that PBDE residues measured on children's handwipes were a strong predictor of serum PBDE levels. Here we build upon this research to examine longitudinal changes in PBDEs in indoor dust and children's handwipes, and explore the associations between handwipes and dust for alternative FRs. Children from our previous study were re-contacted after approximately two years and new samples of indoor dust and handwipes were collected. PBDE dust-levels were significantly correlated between two different sampling rounds separated by two years; however, PBDE levels in handwipes were not correlated, perhaps suggesting that the sources of PBDEs remained relatively constant in the home, but that behavioral differences in children are changing with age and influencing handwipe levels. OPFRs [i.e. tris(1,3-dichloroisopropyl) phosphate (TDCPP), tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP)], 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB, also known as TBB), di(2-ethylhexyl) tetrabromophthalate (BEH-TEBP, also known as TBPH), and 1,2,5,6,9,10-hexabromocyclododecane (HBCD) were also ubiquitously detected in house dust samples and geometric mean levels were similar to PBDE levels, or higher in the case of the OPFRs. Significant associations between handwipes and house dust were observed for these alternative FRs, particularly for EH-TBB (rs=0.54; p<0.001). Increasing house dust levels and age were associated with higher levels of FRs in handwipes, and high hand washing frequency (>5timesd(-1)) was associated with lower FR levels in handwipes. Overall these data suggest that exposure to these alternative FRs will be similar to PBDE exposure, and the influence of hand-to-mouth behavior in children's exposure needs to be further examined to better estimate exposure potential.
    Chemosphere 01/2014; · 3.14 Impact Factor
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    ABSTRACT: Gymnastics training facilities contain large volumes of polyurethane foam, a material that often contains additive flame retardants such as PentaBDE. While investigations of human exposure to flame retardants have focused on the general population, potentially higher than background exposures may occur in gymnasts and certain occupational groups. Our objectives were to compare PentaBDE body burden among gymnasts to the general U.S. population and characterize flame retardants levels in gym equipment, air and dust. We recruited 11 collegiate female gymnasts (ages 18-22) from one gym in the Eastern U.S. The geometric mean (GM) concentration of BDE-153 in gymnast sera (32.5 ng/g lipid) was 4-6.5 times higher than general U.S. population groups. Median concentrations of PentaBDE, TBB and TBPH in paired handwipe samples were 2-3 times higher after practice compared to before, indicating the gymnasts contacted these flame retardants during practice. GM concentrations of PentaBDE, TBB and TBPH were 1-3 orders of magnitude higher in gym air and dust than in residences. Our findings suggest that these collegiate gymnasts experienced higher exposures to PentaBDE flame retardants compared to the general U.S. population and that gymnasts may also have increased exposure to other additive flame retardants used in polyurethane foam such as TBB and TBPH.
    Environmental Science & Technology 11/2013; · 5.26 Impact Factor
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    ABSTRACT: We aimed to characterize levels of polyfluorinated compounds (PFCs) in indoor dust from offices, homes, and vehicles; to investigate factors that may affect PFC levels in dust; and to examine the associations between PFCs in dust and office workers' serum. Dust samples were collected in 2009 from offices, homes, and vehicles of 31 individuals in Boston, MA and analyzed for nineteen PFCs, including perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS), fluorotelomer alcohols (FTOHs), and sulfonamidoethanols (FOSEs). Serum was collected from each participant and analyzed for eight PFCs including PFOA and PFOS. Perfluorononanoate, PFOA, perfluoroheptanoate, perfluorohexanoate, PFOS and 8:2 FTOH had detection frequencies >50% in dust from all three microenvironments. The highest geometric mean concentration in office dust was for 8:2 FTOH (309ng/g), while PFOS was highest in homes (26.9ng/g) and vehicles (15.8ng/g). Overall, offices had the highest PFC concentrations, particularly for longer-chain carboxylic acids and FTOHs. Perfluorobutyrate was prevalent in homes and vehicles, but not offices. PFOA serum concentrations were not associated with PFC dust levels after adjusting for PFC concentrations in office air. Dust concentrations of most PFCs are higher in offices than in homes and vehicles. However, indoor dust may not be a significant source of exposure to PFCs for office workers. This finding suggests that our previously published observation of an association between FTOH concentrations in office air and PFOA concentrations in office workers was not due to confounding by PFCs in dust.
    Environment international 09/2013; 60C:128-136. · 6.25 Impact Factor
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    ABSTRACT: Increased use of flame-retardants in office furniture may increase exposure to PBDEs in the office environment. However, partitioning of PBDEs within the office environment is not well understood. Our objectives were to examine relationships between concurrent measures of PBDEs in office air, floor dust, and surface wipes. We collected air, dust, and surface wipe samples from 31 offices in Boston, MA. Correlation and linear regression were used to evaluate associations between variables. Geometric mean (GM) concentrations of individual BDE congeners in air and congener specific octanol-air partition coefficients (Koa) were used to predict GM concentrations in dust and surface wipes and compared to the measured concentrations. GM concentrations of PentaBDEs in office air, dust, and surface wipes were 472pg/m(3), 2411ng/g, and 77pg/cm(2), respectively. BDE209 was detected in 100% of dust samples (GM=4202ng/g), 93% of surface wipes (GM=125pg/cm(2)), and 39% of air samples. PentaBDEs in dust and air were moderately correlated with each other (r=0.60, p=0.0003), as well as with PentaBDEs in surface wipes (r=0.51, p=0.003 for both dust and air). BDE209 in dust was correlated with BDE209 in surface wipes (r=0.69, p=0.007). Building (three categories) and PentaBDEs in dust were independent predictors of PentaBDEs in both air and surface wipes, together explaining 50% (p=0.0009) and 48% (p=0.001) of the variation respectively. Predicted and measured concentrations of individual BDE congeners were highly correlated in dust (r=0.98, p<0.0001) and surface wipes (r=0.94, p=002). BDE209 provided an interesting test of this equilibrium partitioning model as it is a low volatility compound. Associations between PentaBDEs in multiple sampling media suggest that collecting dust or surface wipes may be a convenient method of characterizing exposure in the indoor environment. The volatility of individual congeners, as well as physical characteristics of the indoor environment, influence relationships between PBDEs in air, dust, and surface wipes.
    Environment international 06/2013; 59C:124-132. · 6.25 Impact Factor
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    ABSTRACT: With the phase-out of polybrominated diphenyl ether (PBDE) flame retardants, the use of new and alternate flame retardants has been increasing. 2,2-bis(chloromethyl)propane-1,3-diyltetrakis(2-chloroethyl) bisphosphate, known as V6, is a flame retardant applied to polyurethane foam commonly found in furniture and automobile foam. However, to the authors' knowledge, no research has been conducted on V6 levels in the environment. The intention of this study was to measure the concentration of V6 in foam collected from baby products where it was recently detected and measure levels in dust samples collected from homes and automobiles in the Boston, MA area. To accomplish this, a pure V6 commercial standard was purchased from a Chinese manufacturer and purified (>98%). An analytical method to measure V6 in dust samples using liquid chromatography tandem mass spectrometry (LC/MS-MS) was developed. Extraction was conducted using accelerated solvent extraction (ASE) and extracts were purified using an ENVI-Florisil SPE column (500 mg, 3 mL). V6 was measured in foam samples collected from baby products with a concentration ranging from 24 500 000 to 59 500 000 ng/g of foam (n = 12, average ± sd: 46 500 000 ± 12 000 000 ng/g; i.e., on average, 4.6% of the foam mass was V6). V6 was also detected in 19 of 20 car dust samples and 14 of 20 house dust samples analyzed. The concentration of V6 in the house dust ranged from <5 ng/g to 1110 ng/g with a median of 12.5 ng/g, and <5 ng/g to 6160 ng/g in the car dust with a median of 103.0 ng/g. Concentrations in car dust were significantly higher than in the house dust potentially indicating higher use of V6 in automobiles compared to products found in the home. Furthermore, tris (2-chloroethyl) phosphate (TCEP), a known carcinogen, was found in the V6 commercial mixture (14% by weight) as an impurity and was consistently detected with V6 in the foam samples analyzed. A significant correlation was also observed between V6 and TCEP in the dust samples suggesting that the use of V6 is a significant source of TCEP in the indoor environment.
    Environmental Science & Technology 04/2013; · 5.26 Impact Factor
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    Thomas F Webster, Heather M Stapleton
    Environmental Health Perspectives 04/2013; 121(4):a110-1. · 7.26 Impact Factor
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    ABSTRACT: Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is a flame retardant widely used in furniture containing polyurethane foam. It is a carcinogen, endocrine disruptor, and potentially neurotoxic. Our objectives were to characterize exposure of adult office workers (n=29) to TDCPP by measuring its primary metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCPP), in their urine; measuring TDCPP in dust from their homes; offices and vehicles; and assessing possible predictors of exposure. We identified TDCPP in 99% of dust (GM=4.43μg/g) and BDCPP in 100% of urine samples (GM=408pg/mL). Concentrations of TDCPP were significantly higher in dust from vehicles (GM=12.5μg/g) and offices (GM=6.06μg/g) than in dust from the main living area (GM=4.21μg/g) or bedrooms (GM=1.40μg/g) of worker homes. Urinary BDCPP concentrations among participants who worked in a new office building were 26% of those who worked in older buildings (p=0.01). We found some evidence of a positive trend between urinary BDCPP and TDCPP in office dust that was not observed in the other microenvironments and may be related to the timing of urine sample collection during the afternoon of a workday. Overall our findings suggest that exposure to TDCPP in the work environment is one of the contributors to the personal exposure for office workers. Further research is needed to confirm specific exposure sources (e.g., polyurethane foam), determine the importance of exposure in other microenvironments such as homes and vehicles, and address the inhalation and dermal exposure pathways.
    Environment international 03/2013; 55C:56-61. · 6.25 Impact Factor
  • Thomas F Webster
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    ABSTRACT: Must molecular mechanisms be the same for concentration addition to predict the effect of a mixture or is it sufficient for compounds to affect similar pathways or common outcomes? Does concentration addition provide a closer approximation to observations than alternative models such as independent action? Suppose effects are mediated by hormone A through receptor R, synthesis of A is reduced by compound B, and that C is a competitive antagonist to A. Both B and C reduce levels of the receptor-ligand complex AR but via different specific mechanisms. Are combinations of B and C concentration additive? We used simple pharmacodynamic models, deriving mathematical models using equilibrium binding and mass balance. Assume A binds the receptor at one site of R with effects proportional to the concentration of AR. Let C act as a competitive antagonist via the Gaddum equation. Let B affect synthesis of A via a function g(B). We derive a model describing the joint response surface of B and C, and a function describing its isoboles. Under concentration addition, the isoboles must be negatively sloped straight lines. We show that linearity of the isoboles depends crucially on g(B). The mixture is concentration additive if g"(B), the second derivative of g(B) with respect to B, is always zero. Responses are greater than concentration additive if g"(B) is always positive and less than concentration additive if g"(B) is always negative. We describe functions g(B) that lead to all three cases as well as one that is greater than concentration additive in some regions and less than concentration additive in others. At least in this simple model, concentration addition cannot be assumed: mixtures of competitive antagonists and compounds that alter hormone synthesis can lead to results that are concentration additive, greater than concentration additive or less than concentration additive. Nevertheless, concentration addition appears to provide a closer approximation to the pharmacodynamic model examined here than independent action. Care needs to be taken in extrapolating to other situations, but analysis of simple pharmacodynamic models appears to be a useful strategy.
    Toxicology 01/2013; · 4.02 Impact Factor
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    ABSTRACT: BACKGROUND: Perfluorooctanoic acid (PFOA) has been linked to cancer in occupational mortality studies and animal toxicological research. OBJECTIVE: We investigated the relationship between PFOA exposure and cancer among residents living near the DuPont plant in Parkersburg, West Virginia (WV). METHODS: Our analyses included incident cases of 18 cancers diagnosed from 1996-2005 in five Ohio (OH) counties and eight WV counties. For analyses of each cancer outcome, controls comprised all other cancers in the study dataset except kidney, pancreatic, testicular, and liver cancers, which have been associated with PFOA in animal or human studies. We applied logistic regression models to individual-level data to calculate odds ratios (OR) and confidence intervals (CI). For the combined analysis of WV and OH data, the exposure of interest was resident water district. Within OH, geocoded addresses were integrated with a PFOA exposure model to examine the relationship between cancer odds and categories of estimated PFOA serum. RESULTS: Our final dataset included 7,869 OH cases and 17,238 WV cases. There was a positive association between kidney cancer and the very high and high serum exposure categories (OR: 2.0, 95% CI: 1.0, 3.9; n=9 and OR: 2.0, 95% CI: 1.3, 3.2; n=22, respectively) and a null association with the other exposure categories compared to the unexposed. The largest OR was for testicular cancer with the very high exposure category (OR: 2.8, 95% CI: 0.8, 9.2; n=6) but there was an inverse association with the lower exposure groups, and all estimates are imprecise because of small case numbers. CONCLUSIONS: This study suggests that higher PFOA serum levels may be associated with testicular, kidney, prostate, and ovarian cancers and non-Hodgkin's lymphoma. Strengths of this study include near-complete case ascertainment for state residents, and well characterized contrasts in predicted PFOA serum levels from 6 contaminated water supplies.  
    Environmental Health Perspectives 01/2013; · 7.26 Impact Factor
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    ABSTRACT: California's furniture flammability standard Technical Bulletin 117 (TB 117) is believed to be a major driver of chemical flame retardant (FR) use in residential furniture in the United States. With the phase-out of the polybrominated diphenyl ether (PBDE) FR mixture PentaBDE in 2005, alternative FRs are increasingly being used to meet TB 117; however, it was unclear which chemicals were being used and how frequently. To address this data gap, we collected and analyzed 102 samples of polyurethane foam from residential couches purchased in the United States from 1985 to 2010. Overall, we detected chemical flame retardants in 85% of the couches. In samples purchased prior to 2005 (n = 41) PBDEs associated with the PentaBDE mixture including BDEs 47, 99, and 100 (PentaBDE) were the most common FR detected (39%), followed by tris(1,3-dichloroisopropyl) phosphate (TDCPP; 24%), which is a suspected human carcinogen. In samples purchased in 2005 or later (n = 61) the most common FRs detected were TDCPP (52%) and components associated with the Firemaster550 (FM 550) mixture (18%). Since the 2005 phase-out of PentaBDE, the use of TDCPP increased significantly. In addition, a mixture of nonhalogenated organophosphate FRs that included triphenyl phosphate (TPP), tris(4-butylphenyl) phosphate (TBPP), and a mix of butylphenyl phosphate isomers were observed in 13% of the couch samples purchased in 2005 or later. Overall the prevalence of flame retardants (and PentaBDE) was higher in couches bought in California compared to elsewhere, although the difference was not quite significant (p = 0.054 for PentaBDE). The difference was greater before 2005 than after, suggesting that TB 117 is becoming a de facto standard across the U.S. We determined that the presence of a TB 117 label did predict the presence of a FR; however, lack of a label did not predict the absence of a flame retardant. Following the PentaBDE phase out, we also found an increased number of flame retardants on the market. Given these results, and the potential for human exposure to FRs, health studies should be conducted on the types of FRs identified here.
    Environmental Science & Technology 11/2012; · 5.26 Impact Factor
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    ABSTRACT: Background/Aims: Our limited understanding of how polyfluoroalkyl chemicals (PFCs) may impact on human health suggests the potential for a protective impact on brain health. This study was designed to explore the association between PFCs and cognitive ability in older adults. Methods: We assessed the association between four PFCs, perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA) and perfluorohexane sulfonic acid (PFHxS), and self-reported limitation due to difficulty remembering or periods of confusion using data from participants aged 60-85 years from the 1999-2000 and 2003-2008 National Health and Nutrition Examination Surveys. We also considered whether diabetic status or diabetic medication use modifies this association in light of in vitro evidence that PFCs may act on the same receptors as some diabetic medications. Results: In multivariable adjusted models, point estimates suggest a protective association between PFCs and self-reported cognitive limitation (odds ratio, OR; 95% confidence interval, CI) for a doubling in PFC concentration: PFOS (OR, 0.90; 95% CI, 0.78, 1.03), PFOA (OR, 0.92; 95% CI, 0.78, 1.09), PFNA (OR, 0.91; 95% CI, 0.79, 1.04) and PFHxS (OR, 0.93; 95% CI, 0.82, 1.06). The protective association was concentrated in diabetics, with strong, significant protective associations in nonmedicated diabetics. Conclusions: This cross-sectional study suggests that there may be a protective association between exposure to PFCs and cognition in older adults, particularly diabetics.
    Neuroepidemiology 10/2012; 40(2):125-132. · 2.37 Impact Factor
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    Gregory J Howard, Thomas F Webster
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    ABSTRACT: Background: Epidemiologists and toxicologists face similar problems when assessing interactions between exposures, yet they approach the question very differently. The epidemiologic definition of interaction leads to the additivity of risk differences (RDA) as the fundamental criterion for causal inference about biological interactions. Toxicologists define interaction as departure from a model based on mode of action: Concentration addition (CA, for similarly-acting compounds) or independent action (IA, for compounds that act differently). Objectives: We compare and contrast theoretical frameworks for interaction in the two fields. Methods: The same simple thought experiment has been used in both fields to develop the definition of non-interaction, with nearly opposite interpretations. In epidemiology, the "sham combination" leads to a requirement that non-interactive dose-response curves be linear. In toxicology, it results in the model of concentration addition. We apply epidemiologic tools to mathematical models of concentration-additive combinations to evaluate their utility. Results: RDA is equivalent to CA only for linear dose-response curves. Simple models demonstrate that concentration-additive combinations can result in strong synergy or antagonism in the epidemiologic framework at even the lowest exposure levels. For combinations acting through non-similar pathways, RDA approximates independent action at low effect levels. Conclusions: While epidemiologists have argued for a single logically consistent definition of interaction, the toxicologic perspective would consider this approach less biologically informative than a comparison with CA or IA. We suggest methods for analysis of concentration-additive epidemiologic data. The two fields can learn a great deal about interaction from each other.
    Environmental Health Perspectives 09/2012; · 7.26 Impact Factor
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    ABSTRACT: Background: Bis-(2-ethylhexyl) tetrabromophthalate (TBPH) is widely used as a replacement for polybrominated diphenyl ethers (PBDEs) in commercial flame retardant mixtures such as Firemaster 550. It is also used in a commercial mixture called DP 45. Mono-(2-ethyhexyl) tetrabromophthalate (TBMEHP) is a potentially toxic metabolite. Objectives: To evaluate human exposure, and potential metabolism and toxicity of TBPH using rodent in vivo and in vitro models. Methods: Dust collected from homes, offices and cars was measured for TBPH using gas chromatography followed by mass spectrometry. Pregnant rats were gavaged with 200 or 500 mg/kg TBMEHP, or corn oil, on gestational days 18 and 19, and dams and fetuses were evaluated histologically for toxicity. TBMEHP was assessed for deiodinase inhibition using rat liver microsomes, and for peroxisome proliferator-activated receptor (PPAR) α and γ activation in murine FAO and NIH 3T3 L1 cells. Results: TBPH concentrations in dust from office buildings (median=410 ng/g) were higher than in home main living areas (median=150 ng/g). TBPH was metabolized by purified porcine esterases to TBMEHP. Two days of TBMEHP exposure in the rat produced maternal hypothyroidism with markedly decreased serum T3, hepatotoxicity, and increased multinucleated germ cells (MNGs) in fetal testes without anti-androgenic effects. In vitro, TBMEHP inhibited deiodinase activity, induced adipocyte differentiation in NIH 3T3 L1 cells, and activated PPARα and γ-mediated gene transcription in NIH 3T3 L1 cells and FAO cells, respectively. Conclusions: TBPH is present in dust from indoor environments, implying human exposure, can be metabolized to TBMEHP by porcine esterases, elicited maternal thyrotoxic and hepatotoxic effects, and induced MNGs in the fetal testes in a rat model. TBMEHP inhibited rat hepatic microsome deiodinase activity and was a PPARα and γ agonist in mouse NIH 3T3 L1 preadipocyte cells.
    Environmental Health Perspectives 09/2012; · 7.26 Impact Factor
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    ABSTRACT: Tetrabromobisphenol-A (TBBP-A) and hexab-romocyclododecanes (HBCDs) are brominated flame retard-ants that have been found in human milk and serum throughout the world, but have received comparatively little attention in the United States. The objective of this study is to determine concentrations of these analytes in samples of breast milk collected from first-time mothers in the Greater Boston, Massachusetts area and to explore predictors of exposure. Human milk samples were analyzed by LC-ESI-MS/MS for TBBP-A, HBCDs (the α, β, and γ diastereomers), and HBCD degradation products: pentabromocyclododecanes (PBCDs) and tetrabromocyclododecadienes (TBCDs). HBCD diaster-eomers were detected in all samples with α-HBCD present in the highest proportion. TBBP-A, PBCDs, and TBCDs were detected in 35%, 42%, and 56% of the analyzed samples, respectively. Self-reported demographic, dietary and behavioral data were examined as predictors of HBCD levels. Levels of HBCD were significantly, positively associated with the number of stereo and video electronics in the home (17% increase/item; 95% Confidence Interval (CI) = 4−31%) and reduced in participants who regularly chose organic foods compared to those who did not (0.51, 95% CI = 0.32−0.82). These results suggest that lifestyle factors are related to body burdens of HBCD and that domestic electronics may be an important source of HBCD exposure in the indoor environment. ■ INTRODUCTION Tetrabromobisphenol-A (TBBP-A) and hexabromocyclodode-canes (HBCDs) are widely used brominated flame retardants (BFRs). 1 Over the past decade global production and environmental concentrations of these BFRs has increased. 2,3 Both are stable, lipophilic/hydrophobic compounds that persist in the environment. 4,5 HBCD is on the U.S. Environmental Protection Agency's list of Chemicals of Concern and a global phase-out will be reviewed by the Stockholm Convention in 2013. 6,7 The main use of TBBP-A is as a reactive flame retardant in epoxy resins for printed circuit boards in computers, tele-communications equipment, industrial controls, and automo-tive electronics. 8 In reactive applications, flame retardants are not expected to migrate from the product. However, TBBP-A is also used as an additive to circuit boards for low energy applications such as remote controls and video recorders as well as the plastic housing for electrical and electronic equipment, mainly computer monitors and printers. 2 In additive applications, there is potential for the flame retardant to escape from the product and enter the air and dust of the indoor environment. The major use of HBCDs is as an additive to expanded and extruded polystyrene foam used to thermally insulate buildings. It is also added to the back-coating of textiles of upholstered furniture as well as the high impact polystyrene housing of electrical and electronic equipment and appliances. 9 TBBP-A has an estimated biological half-life of 2−6 days based on measurements in human serum. 10 It structurally resembles the thyroid hormone thyroxine, and is characterized as a suspected endocrine disruptor due to its activity in multiple in vitro assays. 11,12 These include competitive binding of transthyretin, activation of peroxisome proliferator-activated receptors α, β, and γ, and activation of estrogen receptors α and
    Environmental Science and Technology 09/2012; · 5.26 Impact Factor
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    Veronica M Vieira, Janice Weinberg, Thomas F Webster
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    ABSTRACT: BACKGROUND: Although daily emergency department (ED) data is a source of information that often includes residence, its potential for space-time analyses at the individual level has not been fully explored. We propose that ED data collected for surveillance purposes can also be used to inform spatial and temporal patterns of disease using generalized additive models (GAMs). This paper describes the methods for adapting GAMs so they can be applied to ED data. METHODS: GAMs are an effective approach for modeling spatial and temporal distributions of point-wise data, producing smoothed surfaces of continuous risk while adjusting for confounders. In addition to disease mapping, the method allows for global and pointwise hypothesis testing and selection of statistically optimum degree of smoothing using standard statistical software. We applied a two-dimensional GAM for location to ED data of overlapping calendar time using a locally-weighted regression smoother. To illustrate our methods, we investigated the association between participants' address and the risk of gastrointestinal illness in Cape Cod, Massachusetts over time. RESULTS: The GAM space-time analyses simultaneously smooth in units of distance and time by using the optimum degree of smoothing to create data frames of overlapping time periods and then spatially analyzing each data frame. When resulting maps are viewed in series, each data frame contributes a movie frame, allowing us to visualize changes in magnitude, geographic size, and location of elevated risk smoothed over space and time. In our example data, we observed an underlying geographic pattern of gastrointestinal illness with risks consistently higher in the eastern part of our study area over time and intermittent variations of increased risk during brief periods. CONCLUSIONS: Spatial-temporal analysis of emergency department data with GAMs can be used to map underlying disease risk at the individual-level and view changes in geographic patterns of disease over time while accounting for multiple confounders. Despite the advantages of GAMs, analyses should be considered exploratory in nature. It is possible that even with a conservative cutoff for statistical significance, results of hypothesis testing may be due to chance. This paper illustrates that GAMs can be adapted to measure geographic trends in public health over time using ED data.
    BMC Public Health 08/2012; 12(1):687. · 2.08 Impact Factor
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    ABSTRACT: Polybrominated diphenyl ethers (PBDEs) are persistent, bioaccumulative, and endocrine-disrupting chemicals. We used handwipes to estimate exposure to PBDEs in house dust among toddlers and examined sex, age, breast-feeding, race, and parents' education as predictors of serum PBDEs. Eighty-three children from 12 to 36 months of age were enrolled in North Carolina between May 2009 and November 2010. Blood, handwipe, and house dust samples were collected and analyzed for PBDEs. A questionnaire was administered to collect demographic data. PBDEs were detected in all serum samples (geometric mean for ΣpentaBDE in serum was 43.3 ng/g lipid), 98% of the handwipe samples, and 100% of the dust samples. Serum ΣpentaBDEs were significantly correlated with both handwipe and house dust ΣpentaBDE levels, but were more strongly associated with handwipe levels (r = 0.57; p < 0.001 vs. r = 0.35; p < 0.01). Multivariate model estimates revealed that handwipe levels, child's sex, child's age, and father's education accounted for 39% of the variation in serum ΣBDE3 levels (sum of BDEs 47, 99, and 100). In contrast, age, handwipe levels, and breast-feeding duration explained 39% of the variation in serum BDE 153. Our study suggests that hand-to-mouth activity may be a significant source of exposure to PBDEs. Furthermore, age, socioeconomic status, and breast-feeding were significant predictors of exposure, but associations varied by congener. Specifically, serum ΣBDE3 was inversely associated with socioeconomic status, whereas serum BDE-153 was positively associated with duration of breast-feeding and mother's education.
    Environmental Health Perspectives 07/2012; 120(7):1049-54. · 7.26 Impact Factor
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    ABSTRACT: Human exposure to polycyclic aromatic hydrocarbons (PAHs) can be assessed by biomonitoring of their urinary monohydroxylated metabolites (OH-PAHs). Limited information exists on the human pharmacokinetics of OH-PAHs. This study aimed to investigate the excretion half-life of 1-hydroxypyrene (1-PYR), the most used biomarker for PAH exposure, and 9 other OH-PAHs following a dietary exposure in 9 nonsmoking volunteers with no occupational exposure to PAHs. Each person avoided food with known high PAH-content during the study period, except for a high PAH-containing lunch (barbecued chicken) on the first day. Individual urine samples (n = 217) were collected from 15 h before to 60 h following the dietary exposure. Levels of all OH-PAHs in all subjects increased rapidly by 9-141-fold after the exposure, followed by a decrease consistent with first-order kinetics, and returned to background levels 24-48 h after the exposure. The average time to reach maximal concentration ranged from 3.1 h (1-naphthol) to 5.5 h (1-PYR). Creatinine-adjusted urine concentrations for each metabolite were analyzed using a nonlinear mixed effects model including a term to estimate background exposure. The background-adjusted half-life estimate was 3.9 h for 1-PYR and ranged 2.5-6.1 h for the other 9 OH-PAHs, which in general, were shorter than those previously reported. The maximum concentrations after barbecued chicken consumption were comparable to the levels found in reported occupational settings with known high PAH exposures. It is essential to consider the relatively short half-life, the timing of samples relative to exposures, and the effect of diet when conducting PAH exposure biomonitoring studies.
    Chemical Research in Toxicology 06/2012; 25(7):1452-61. · 3.67 Impact Factor
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    ABSTRACT: BACKGROUND: In epidemiologic studies researchers are often interested in detecting confounding (when a third variable is both associated with and affects associations between the outcome and predictors). Confounder detection methods often compare regression coefficients obtained from "crude" models that exclude the possible confounder(s) and "adjusted" models that include the variable(s). One such method compares the relative difference in effect estimates to a cutoff of 10% with differences of at least 10% providing evidence of confounding. METHODS: In this study we derive the asymptotic distribution of the relative change in effect statistic applied to logistic regression and evaluate the sensitivity and false positive rate of the 10% cutoff method using the asymptotic distribution. We then verify the results using simulated data. RESULTS: When applied to a logistic regression models with a dichotomous outcome, exposure, and possible confounder, we found the 10% cutoff method to have an asymptotic lognormal distribution. For sample sizes of at least 300 the authors found that when confounding existed, over 80% of models had >10% changes in odds ratios. When the confounder was not associated with the outcome, the false positive rate increased as the strength of the association between the predictor and confounder increased. When the confounder and predictor were independent of one another, false positives were rare (most < 10%). CONCLUSIONS: Researchers must be aware of high false positive rates when applying change in estimate confounder detection methods to data where the exposure is associated with possible confounder variables.
    Journal of biometrics & biostatistics. 05/2012; 3(4):142.

Publication Stats

2k Citations
334.44 Total Impact Points

Institutions

  • 2002–2014
    • Boston University
      • • Department of Environmental Health
      • • Department of Biostatistics
      • • Department of Epidemiology
      Boston, Massachusetts, United States
  • 2009–2013
    • University of Massachusetts Boston
      Boston, Massachusetts, United States
  • 2008–2013
    • Duke University
      • Nicholas School of the Environment
      Durham, NC, United States
  • 2012
    • Dickinson College
      Carlisle, Pennsylvania, United States
  • 2011
    • Brown University
      Providence, Rhode Island, United States
  • 2010
    • University of Birmingham
      • School of Geography, Earth and Environmental Sciences
      Birmingham, ENG, United Kingdom
  • 2009–2010
    • Massachusetts Department of Public Health
      Boston, Massachusetts, United States