Browsing by Author "Stapleton, Heather M"
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Item Open Access Analyzing Euthyroid & Hyperthyroid Indoor Cat Exposure to Flame Retardants(2020-04-23) Osteen, Mary-CatherineHyperthyroidism in cats has increased since its original description in the 1970s. Environmental exposures are suggested as a potential contributing factor. This research investigated pet cats’ exposure to flame retardant chemicals in the home environment and associations with hyperthyroidism. Silicone collar tags were used as indicators of exposure to two classes of flame retardants: polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs). Though previous studies have documented PBDE exposure among house cats, less is known about exposure to OPEs. Thus, we first evaluated silicone tags as measures of internal exposure to OPEs. Cats wore silicone collar tags for 7 days in their home environment, after which tags were analyzed for flame retardants. Urine samples were collected from 9 cats and analyzed for OPE metabolites. Tris(2-chloroisopropyl) phosphate (TCIPP), was significantly and positively correlated with its urinary metabolites (r≥0.73; p<0.05), and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) was significantly and positively correlated with its urinary metabolite (r=0.77; p<0.05). Several other OPEs from tags were correlated with their metabolites in urine, suggesting that tags capture information about cats’ internal exposure; however, correlations were not statistically significant. To evaluate exposure differences by thyroid status, 12 hyperthyroid and 12 euthyroid cats (matched by age and sex) wore tags for 7 days. Tags were analyzed for PBDEs and OPEs. Two PBDEs, BDE-47 and BDE-99, were higher on tags worn by hyperthyroid compared to euthyroid cats (p<0.05). Associations with thyroid status were not significant for OPEs; however, we caution against over-interpretation of these results given our limited sample size. Potential confounders, including diet and activity level, were evaluated; however, no significant differences were found between hyperthyroid and euthyroid cats (p>0.20), suggesting these factors are not likely to confound associations with flame retardant exposures. Cumulatively, results suggest that exposure to PBDE flame retardants is higher among hyperthyroid cats, which is in agreement with previous studies that have reported differences in serum PBDE levels of hyperthyroid and euthyroid cats.Item Open Access Antibody Responses to Vaccines and PFAS Exposure in Early Childhood(2021-04-22) Bao, NancyPer- and polyfluoroalkyl substances (PFAS), are human-made chemicals commonly incorporated into personal care products, cookware, food packaging, and other industrial uses. Previous studies have found that early life exposure to PFAS is associated with health effects in both animal and human studies. There are growing concerns over the potential health consequences such as immunological health associated with prenatal and early childhood PFAS exposure. Studies have found that exposure to environmental stressors during early periods of fetal growth and development may have implications for the development of later life adverse health effects. Few studies have assessed the association between PFAS exposure and waning immunity to vaccines during early childhood. Of these studies, PFAS exposure has been inversely associated with antibody responses to vaccines against infectious diseases such as diphtheria and tetanus. Antibody responses to vaccines are commonly used as biomarkers to assess immune function and development. The objective of this study was to evaluate the impacts of PFAS exposures on critical windows of immune function and maturation in early childhood. Early childhood immune function was evaluated using antibody responses to the Diphtheria-Tetanus-acellular Pertussis (DTaP) vaccine. Multiple linear regression analyses (adjusted for child’s age, biological sex of child, and maternal age) were conducted to evaluate the associations between maternal and child serum PFAS levels in a North Carolina birth cohort (n=47) and antibody responses to the DTaP vaccine in children (ages 3-6). Maternal serum PFAS were used to assess prenatal exposure. Child serum was analyzed for diphtheria and tetanus antibody titers as well as postnatal PFAS exposure. Prenatal PFAS exposure measured from maternal serum was not significantly associated with tetanus antibody titers; however, a positive and significant association (p<0.05) was observed between prenatal PFNA exposure and diphtheria antibody titers. Postnatal PFAS exposure was not significantly associated with diphtheria antibody titers. Postnatal PFOA exposure was positively associated with tetanus antibody responses (p<0.05). The results do not suggest that prenatal and early childhood exposure to PFAS is associated with declines in immune responses to vaccines. Other factors associated with environmental PFAS exposure and vaccine antibody responses should be explored to expand on these findings.Item Open Access Are Higher Exposures to Flame Retardant Chemicals Associated with Papillary Thyroid Cancer?(2019-04-26) Xia, QianyiPapillary thyroid cancer (PTC) occurrence has been significantly increasing throughout the world, and particularly in the US, for several decades. At the same time the use of flame retardants (FR) chemicals has increased, as reflected by increasing concentrations in human tissues. In this study we sought to determine whether flame retardants exposures are higher in individuals recently diagnosed with papillary thyroid cancer relative to a healthy population. The study group included people diagnosed with PTC at the Duke Cancer Center, and controls were matched by age and sex who are recruited from the Duke Health System. Flame retardants (FRs) exposure were estimated from silicone wristband worn for 7 days by participants, which have been validated against traditional biomarkers of exposure. Results indicated that both obesity, and higher levels of the FR Tris (1,3-dichloro-isopropyl) phosphate (TDCPP), were related to increased odds of being a papillary thyroid cancer patient relative to a control. In adjusted statistical models, each log unit increase in TDCPPs on the wristband was found to be associated with a 57% increase in being a case vs a control, while each log unit increase in BMI will result in a 7.1% increase. Therefore, these results indicated that some FRs exposure may be associated with increased PTC incidence.Item Open Access Assessing Children's Exposure to Organophosphate Flame Retardants in the Home Environment(2017-04-28) Frenchmeyer, Meredith; Flaherty, BridgetOrganophosphate flame retardants (OPFRs) are increasingly being used in the home environment as replacements for the phased out polybrominated diphenyl ethers (PBDEs). Several studies utilizing hand wipes and dust samples in concert with urine samples have illustrated that human exposure is occurring in the home environment. While exposure has been measured across age groups and locations, few epidemiological studies have investigated the potential health effects of these individual compounds and their mixtures. Preliminary animal research indicates their potential for endocrine disruption, with a particular emphasis on thyroid hormone dysregulation. Additionally, particular OPFRs may bind with the PPARγ, a nuclear receptor involved in adipogenesis, or the formation of fat cells. The present study uses passive air and urine samples collected from a central North Carolina toddler cohort to explore, for the first time, associations between air and biomarkers of OPFR exposure (i.e. urinary metabolites). This will help to assess inhalation as a potentially important exposure pathway for OPFRs. In addition, associations between levels of OPFR metabolites measured in urine and growth measures are assessed. Few epidemiological studies have explored OPFRs and health outcomes such as weight; therefore, this study provides relevant and new information about specific metabolites and their relationship with BMI percentile. Univariate analyses revealed statistically significant differences in urinary metabolite concentrations between children whose mothers had a college degree compared to those that did not. The urinary metabolites DPHP and tbutylDPHP were significantly correlated with OPFR compounds measured in indoor air. One urinary metabolite, ip-DPHP, was found to have a statistically significant relationship with BMI percentile, suggesting exposure might be affecting growth. Limitations of the present study include the measure of exposure being limited to one time point, and the cohort being limited to the central North Carolina area.Item Open Access ASSESSING POTENTIAL EXPOSURE TO PER- AND POLYFLUOROALKYL SUBSTANCES (PFAS) IN PRODUCE AND DRINKING WATER IN CHATHAM COUNTY, NC(2021-05-25) Li, Yang (Leon)Diet constitutes a major human exposure pathway for per- and polyfluoroalkyl substances (PFAS) due to the contamination of drinking water supplies, and their use in food packaging, and accumulation in the food web. Significant PFAS levels have recently been reported in groundwater (Haw River and Cape Fear River) in North Carolina. This has raised concerns for potential exposure for communities consuming drinking water sourced from these rivers and produce grown from lands irrigated with this water. This study sought to evaluate dietary exposure to PFAS from consumption of produce (lettuce, potato and tomato) and drinking water in Chatham County, North Carolina, a previously reported PFAS impacted area. A total of 18 produce samples were collected in local farmer markets and grocery stores. Drinking water PFAS data (N = 40) were abstracted from an ongoing study in Pittsboro, NC collected and analyzed in 2019 and 2020. PFAS were generally not detected in the produce samples analyzed here, with the exception of perfluorodecanoic acid (PFDA). PFDA was detected in potatoes and tomatoes, ranging from 0.11 to 1.11 ng/g, or parts per billion (ppb). Total PFAS were measured at concentrations ranging from 26.4 ng/L up to 458.1 ng/L in the drinking water samples. Using the median values of PFDA measured in produce and estimates of produce consumption in the general population (using the 50th and 95th percentiles), exposure to PFDA was estimated. Estimated exposure was highest from potato consumption (median exposure intake varies between 0.42 and 1.40 ng/kg-day). In drinking water, short-chain (<8 carbon) perfluoroalkyl carboxylate acids (PFCA) contributed the most to ∑PFAS exposure. The median exposure intake was 1.40 ng/kg-day for PFHxA and 1.17 ng/kg-day for PFPeA. Higher exposure was generally observed via drinking water compared to produce, and exposures were the highest for young children and decreased with age. The estimated hazard index suggests that a small portion of the population (~5%) could be at increased risk for adverse effects via produce exposure (in young children) and for all age groups via drinking water exposure.Item Open Access Biodegradation of a Sulfur-Containing PAH, Dibenzothiophene, by a Mixed Bacterial Community(2009) Cooper, Ellen M.Dibenzothiophene (DBT) is a constituent of creosote and petroleum waste contamination, it is a model compound for more complex thiophenes, and its degradation by mixed microbial communities has received little attention. The chemical characteristics, environmental fate and ecotoxicology of DBT degradation products are not well understood. This research investigated DBT degradation in an enrichment culture derived from creosote-contaminated estuarian sediment using a suite of assays to monitor bacterial populations, bacterial growth, degradation products, DBT loss, and toxicity. Ultraviolet (UV) irradiation was evaluated as a sequential treatment following biodegradation. Additionally, to advance SYBR-Green qPCR methodology for characterizing mixed microbial communities, an alternative approach for evaluating qPCR data using a sigmoidal model to fit the amplification curve was compared to the conventional approach in artificial mixed communities. The overall objective of this research was to gain a comprehensive understanding of the degradation of a model heterocyclic PAH, DBT, by a mixed microbial community, particularly within the context of remediation goals.
DBT biodegradation was evaluated in laboratory scale cultures with and without pH control. The microbial community was monitored with 10 primer sets using SYBR-Green quantitative polymerase chain reaction (qPCR). Twenty-seven degradation products were identified by gas chromatography and mass spectrometry (GC/MS). The diversity of these products indicated that multiple pathways functioned in the community. DBT degradation appeared inhibited under acidic conditions. Toxicity to bioluminescent bacteria Vibrio fischeri more than doubled in the first few days of degradation, was never reduced below initial levels, and was attributed in part to one or more degradation products. UV treatment following biodegradation was explored using a monochromatic (254 nm) low-pressure UV lamp. While DBT was not extensively photooxidized, several biodegradation products were susceptible to UV treatment. At higher doses, UV treatment following DBT biodegradation exacerbated cardiac defects in Fundulus heteroclitus embryos, but slightly reduced toxicity to V. fischeri.
This research provides a uniquely comprehensive view of the DBT degradation process, identifying bacterial populations previously unassociated with PAH biodegradation, as well as potentially hazardous products that may form during biodegradation. Additionally, this research contributes to development of unconventional remediation strategies combining microbial degradation with subsequent UV treatment.
Item Open Access Characterizing Azobenzene Disperse Dyes in Commercial Mixtures and Children’s Polyester Clothing(Environmental Pollution, 2021-05) Overdahl, Kirsten E; Gooden, David; Bobay, Benjamin; Getzinger, Gordon J; Stapleton, Heather M; Ferguson, P LeeItem Open Access Characterizing Environmental Per- and Polyfluoroalkyl Substance (PFAS) Exposure and Effects in North Carolina Communities(2022) Hall, Samantha MariePer- and polyfluoroalkyl substances (PFAS) are synthetic chemicals used in a wide array of products and applications (e.g., nonstick cookware, waterproof and water-repellent textiles, firefighting foam). Following their decades of use, PFAS have garnered concern as “forever chemicals” due to their extreme persistence in the environment and in humans. PFAS have further elicited concern because they have been linked to adverse health effects in humans, and their huge number (over 12,000 different chemicals) and complex chemistry make them very challenging to analyze and study for exposure and toxicology. Two particular PFAS chemicals, perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS), are drinking water contaminants that can be found in the blood of the vast majority of people. PFOA and PFOS are also linked to toxic effects like kidney and testicular cancer, increased blood cholesterol, and reproductive outcomes. These two chemicals are being phased out of use and federal drinking water standards are likely upcoming. However, the replacements for these two chemicals are much less well-characterized, and many of these newer, replacement PFAS chemicals can be found in the environment of North Carolina due (at least in part) to industrial pollution.
The overarching goal of this dissertation was to characterize the potential exposure and health effects of PFAS in North Carolina communities. The surface water and drinking water in some areas of North Carolina have been found to be contaminated with PFAS; however, there are additional routes of PFAS exposure beyond drinking water, such as ingestion of house dust or placental transfer during pregnancy. This dissertation explores various routes of PFAS exposure and better characterizes the specific PFAS analytes that can be found in North Carolina and the concentrations in which they are present. Additionally, this dissertation evaluates this exposure and potential associations with some adverse health outcomes in a few North Carolina communities.
In Chapter 2, the relationships between PFAS exposure during pregnancy and birth outcomes are explored. This chapter includes data on PFAS concentrations in placenta samples from 120 participants in Durham, North Carolina and evaluates the subsequent associations between placental PFAS exposure and birth outcomes (e.g., infant birth weight, gestational age). A total of 11 PFAS were measured in placental tissues collected in 2010-2011, and the compounds PFOS, PFOA, PFNA, and PFDA were detected in all placenta samples. A few placental PFAS were associated with birth outcomes. The most striking result was that placental PFOS was associated with changes in birth weight, but the direction of change depended on the sex of the infant. For male infants, placental PFOS was associated with lower birthweight, and in female infants, placental PFOS was associated with higher birthweight.
In Chapter 3, the exposure to PFAS through drinking water is evaluated in a community with known PFAS water contamination. This chapter includes data on PFAS concentrations in blood serum and drinking water samples from 49 participants in Pittsboro, North Carolina. The community receives its drinking water from the Haw River, a part of the Cape Fear River watershed. Blood and water samples were collected at two different timepoints to explore temporal variability in contamination. This community was found to have blood levels of PFAS about two to four times higher than the U.S. average. This chapter also includes results on the associations between PFAS blood level and clinical chemistry measurements, such as serum lipids, as indicators of health. Negative associations were found between serum PFOS and PFHxA with decreased electrolytes and decreased liver enzymes. Positive associations were found between serum PFOA and PFHxS with increased total cholesterol and increased non-HDL cholesterol.
In Chapter 4, the effects and toxicokinetics of PFAS in a pregnant rabbit model are evaluated. This chapter includes data from an animal study of 21 pregnant rabbits provided with drinking water that is representative of the PFAS exposure observed in Pittsboro, North Carolina. Rabbits were exposed to this environmentally-relevant mixture of ten different PFAS during and before pregnancy. After exposure, the wastes and tissues were evaluated to measure the PFAS concentration that accumulated. This provided information on where PFAS are distributed in the body after exposure. The liver of the pregnant rabbit was also evaluated to determine if there was an increase in lipids in the liver, or any changes in liver lipid metabolism. For this study, few differences were noted between treated animals and control animals, indicating that the environmentally-relevant dose had little effect on pregnant rabbits. However, due to the lack of PFAS accumulation in blood, tissue, or in wastes, it is likely that the dose of PFAS given through drinking water was too low.
In Chapter 5, the levels of PFAS in indoor house dust were evaluated. This chapter includes data on PFAS concentrations in indoor dust from 184 homes in Durham, North Carolina, as well as 49 fire stations across the U.S. and Canada. House dust and fire station dust PFAS concentrations were then evaluated for associations with characteristics of the building (e.g., square footage, amount of carpeting, age of building construction). Levels of precursor PFAS, such as fluorotelomer alcohols, were typically higher in dust than the perfluoroalkyl acids. This study, along with previous literature, shows that the legacy PFAS in dust has been decreasing, but the precursor PFAS has been increasing in U.S. house dust. Few associations were found between building characteristics and dust PFAS. However, one notable result was that higher 8:2 FTOH was found in dust from buildings with more carpeting, indicating that carpets may be an important source of exposure to fluorotelomer alcohols (possibly from stain-proofing treatment).
Collectively, this dissertation provides important information on the potential exposure and health effects of PFAS in North Carolina communities.
Item Open Access Characterizing Exposure and In Vitro Effects of Azobenzene Disperse Dyes in the Indoor Environment(2021) Overdahl, Kirsten EliseAzobenzene disperse dyes are the fastest-growing category of commercial dyestuffs, accounting for 70% of the 9.9 million tons of industrial dye colorants used annually. Azobenzene disperse dyes are intended to be applied to synthetic fabrics such as polyester, nylon, and acrylic; however, azo dyes may also be used in cosmetic products such as hair dyes, and in fashion accessories such as leather goods. Recently, our group and others have detected azobenzene disperse dyes in dust particles collected from the indoor environment, and raising concerns about the release of these chemicals from products and human exposure. Although extensive literature characterizes these chemicals as toxic contaminants in aquatic environments, to date there exists little data on levels, exposures, and hazards associated wit exposures to azobenzene disperse dyes in the indoor environment. The presence of these dyes in the indoor environment is concerning. House dust is a sink for many contaminants that leach out or off-gas from products in the home. Due to children’s unique behaviors (e.g. crawling and hand to mouth activity) they have higher exposure to chemicals associated with dust. Azobenzene disperse dyes are implicated in literature as potentially allergenic: they are known to be present in clothing that elicits allergic reactions such as skin sensitization. Therefore, it is of crucial importance to support research that seeks to characterize children’s exposure in the home environment, and evaluate the in vitro effects of azobenzene disperse dyes. The hypothesis of this research dissertation is that azobenzene disperse dyes are prevalent in dust collected from the indoor environment at concentrations of concern for human health. In the first aim of this thesis research, azobenzene disperse dyes were characterized in commercial mixtures and in children’s polyester clothing. Azo dyes were first purified from dyestuffs by Soxhlet extraction and flash chromatography and then analyzed using ultra-high-performance liquid chromatography (UHPLC) coupled with high resolution mass spectrometry (HRMS), as well as by 1H and 13C NMR for structural elucidations. Nineteen total azobenzene dyes were detected in dyestuffs via a non-targeted analysis approach, including Disperse Blue 79:1, Disperse Blue 183:1, Disperse Orange 44, Disperse Orange 73, Disperse Red 50, Disperse Red 73, and Disperse Red 354. Samples of children's polyester clothing (n=X) were then analyzed via UHPLC-HRMS. In clothing, 21 azobenzene disperse dyes were detected, 12 of which were confirmed and quantified via reference standards. Individual dyes in apparel were quantified at concentrations up to 9230 μg dye/g shirt, with geometric means ranging 7.91–300 μg dye/g shirt. Total dye load in apparel was quantified at up to 11,430 μg dye/g shirt. This research supported the development of reference standards and library mass spectra for azobenzene disperse dyes previously absent from standard and spectral libraries. This study was the first to confirm and quantify these azo compounds in children’s products, facilitating a more robust understanding of sources of azobenzene disperse dyes in the indoor environment. The second aim of this thesis research investigated the presences and quantities of azobenzene disperse dyes and related compounds in indoor house dust (n=188) collected from homes in Durham, NC. Using a targeted approach, we quantified 12 azo disperse dyes and quantified at least one dye in every house dust sample. Detection frequencies ranged from 11% to 89%; of the dyes that were detected in at least 50% of the samples, geometric mean levels ranged from 32.4 to 360 ng/g. HRMS suspect screening analysis identified an additional eight azobenzene compounds in dust that are present at high relative abundances. This study indicates that azo disperse dyes and related compounds are ubiquitous in the indoor environment. To support quality assurance and control during the analysis, a house dust Standard Reference Material (NIST SRM 2585) was extracted and analyzed with the samples. Based on the detection and abundance of azo dyes in SRM 2585, which was prepared from hundreds of dust samples collected in the mid 1990s, azo dye levels in the indoor environment may be increasing over time. To our knowledge, this is the most comprehensive quantitative study of azo disperse dyes in house dust to date. Future studies are needed to quantify additional dyes in dust, particularly those identified here via suspect screening, and to examine exposure pathways of dyes in the indoor environment where children are concerned. The third aim of this thesis research examined the binding reactivity of azobenzene disperse dyes to nucleophilic peptide residues in order to understand their potential reactivity as electrophilic allergenic sensitizers. The Direct Peptide Reactivity Assay (DPRA) was utilized via both a spectrophotometric method and a high-performance liquid chromatography (HPLC) method. Dyes isolated from the commercial dyestuffs, and several potential transformation products, were tested. All dyes were found to react with nucleophilic peptides in a dose-dependent manner with pseudo-first order (kobserved) activity, but overall to react more potently with cysteine than with lysine: EC10 values for cysteine binding were determined as low as 0.005mM and pseudo-first order rate constants as high as 0.04 hr-1 (as observed for Disperse Blue 79:1). Observed rate constants were correlated to metrics of structural features such as Hammett constants and electrophilicity indices, indicating that binding reactivity may be related to structural properties of azobenzene disperse dyes. In addition to examining dyes, the reactivity of extracts of polyester shirts were also examined; shirt extracts with high relative abundances of azobenzene disperse dyes were observed to induce greater peptide reactivity. Results suggest that azobenzene disperse dyes may function as immune sensitizers, and that clothing containing azobenzene disperse dyes may pose risks for skin sensitization. Collectively, this thesis research suggests that azobenzene disperse dyes are common in clothing, and appear to be near ubiquitous in house dust. Given their reactivity in vitro, this may present health consequences, particularly for young children.
Item Open Access Characterizing the Binding Potential, Activity, and Bioaccessibility of Peroxisome Proliferator Activated Receptor Gamma (PPARγ) Ligands in Indoor Dust(2015) FANG, MINGLIANGAccumulating evidence is suggesting that exposure to some environmental contaminants may alter adipogenesis, resulting in accumulation of adipocytes, and often significant weight gain. Thus these types of contaminants are often referred to as obesogens. Many of these contaminants act via the activation (i.e. agonism) of the peroxisome proliferator activated receptor γ (PPARγ) nuclear receptor. To date, very few chemicals have been identified as possible PPAR ligands. In the thesis, our goal was to determine the PPARγ ligand binding potency and activation of several groups of major semi-volatile organic compounds (SVOCs) that are ubiquitously detected in indoor environments, including flame retardants such as polybrominated diphenyl ethers (PBDEs) and Firemaster 550 (FM550), and other SVOCs such as phthalates, organotins, halogenated phenols and bisphenols. Additional attention was also given to the potential activity of the major metabolites of several of these compounds. Since the primary sink for many of these SVOCs is dust, and dust ingestion has been confirmed as an important pathway for SVOCs accumulation in humans, the potential PPAR binding and activation in extracts from environmentally relevant dust samples was also investigated.
Previous studies have also shown that SVOCs sorbed to organic matrices (e.g., soil and sediment), were only partially bioaccessible (bioavailable), but it was unclear how bioaccessible these compounds are from indoor dust matrices. In addition, bioactivation of SVOCs (via metabolism) could exacerbate their PPAR potency. Therefore, to adequately assess the potential risk of PPARγ activation from exposure to SVOC mixtures in house dust, it is essential that one also investigates the bioaccessibility and bioactivation of these chemicals following ingestion.
In the first research aim of this thesis, the bioaccessibility and bioactivation of several important SVOCs in house dust was investigated. To accomplish this, Tenax beads (TA) encapsulated within a stainless steel insert were used as an infinite adsorption sink to estimate the dynamic absorption of a suite of flame retardants (FRs) commonly detected in indoor dust samples, and from a few polyurethane foam samples for comparison. Experimental results demonstrate that the bioaccessibility and stability of FRs following ingestion varies both by chemical and by matrix. Organophosphate flame retardants (OPFRs) had the highest estimated bioaccessibility (~80%) compared to brominated compounds (e.g. PBDEs), and values generally decreased with increasing Log Kow, with <30% bioaccessibility measured for the most hydrophobic compound tested, BDE209. In addition, the stability of the more labile SVOCs that contained ester groups (e.g. OPFRs and 2-ethylhexyl-tetrabromo-benzoate (TBB)) were examined in a simulated digestive fluid matrix. No significant changes in the OPFR concentrations were observed in this fluid; however, TBB was found to readily hydrolyze to tetrabromobenzoic acid (TBBA) in the intestinal fluid in the presence of lipases.
In research aims 2 and 3, two commercially available high-throughput bioassays, a fluorescence polarization PPAR ligand binding assay (PolarScreenTM PPARγ-competitor assay kit, Invitrogen, Aim 2) and a PPAR reporter gene assay (GeneBLAzer PPARγ non-DA Assay, Invitrogen, Aim 3) were used to investigate the binding potency and activation of several groups of SVOCs and dust extracts with human PPARγ LBD; respectively. In the PPAR binding assay (Aim 2), most of the tested compounds exhibited dose-dependent binding to PPARγ. Mono(2-ethylhexyl) tetrabromophthalate (TB-MEHP), halogenated bisphenol/phenols, triphenyl phosphate and hydroxylated PBDEs were found to be potent or moderate PPARγ ligands, based on the measured ligand binding dissociation constant (Kd). The most potent compound was 3-OH-BDE47, with an IC50 of 0.24 μM. The extent of halogenation and the position of the hydroxyl group strongly affected binding. Of the dust samples tested, 21 of 24 samples showed significant PPAR binding potency at a concentration of 3 mg dust equivalents (DEQ)/mL. In the PPAR reporter assay (Aim 3), many SVOCs or their metabolites were either confirmed (based on previous reports) or for the first time were found to be potential PPARγ agonists with various potency and efficacy. We also observed that 15 of 25 dust extracts examined showed an activation percentage more than 8% (calculated activation threshold) of the maximal activation induced by rosiglitazone (positive control). In some cases, activation was as high as 50% of the rosiglitazone activation for the dust extracts with the highest efficacy. Furthermore, the correlation between the reporter assay and the ligand binding assay among the house dust extracts was significant and positive (r = 0.7, p < 0.003), suggesting the binding potency was predicting activation. In research aim 2, the effect of bioactivation on the PPARγ binding potency was also investigated. In vitro bioactivation of house dust extracts incubated with rat and human hepatic S9 fractions was used to investigate the role of in vivo biotransformation on PPAR gamma activity. The result showed that metabolism may lead to an increased binding affinity, as a 3-16% increase in PPARγ binding activity was observed following bioactivation of the dust extracts.
In research aim 4, an effect-directed analysis (EDA) was used to identify compounds likely contributing to the observed PPAR activity among the dust extract. Three dust extracts which showed significant PPAR activity with approximately 25, 30, and 50% of the maximal response induced by rosiglitazone at the highest efficacy were fractionated using normal phase high-performance liquid chromatography (NP-HPLC) and each fraction was individually tested for PPAR activity. Active fractions were then analyzed using gas-chromatography mass spectrometry (GC-MS) and possible compounds identified. Three dust extracts showed a similar PPAR activity distribution among the NP-HPLC fractions. In the most active fractions, fatty acids (FAs) were identified as the most active chemicals. The concentrations of four FAs were measured in the house dust extracts, and the concentrations were found to be highly correlated with the observed PPAR activity. These four FAs were also tested for PPAR activity and found to be partial PPAR agonists, particularly oleic and myristic acid. To tentatively identify sources of FAs, FAs in human/animal hair, dead skin cells, and two brands of cooking oil were analyzed. We found the same FAs in those samples and there concentrations were relatively abundant, ranging from 186 to 14,868 µg/g. Therefore, these results suggest that FAs are likely responsible for the observed PPAR activity in indoor dust. Also, this is the first study reporting on the level of FAs in dust samples. The source of these FAs in dust may be either from the cooking or accumulation of human/animal cells in indoor dust.
In conclusion, this research demonstrates that many SVOCs ubiqutiously detected in house dust, and/or their metabolites, can be weak or moderate PPAR ligands. In addition, chemical mixtures in house dust can effectively bind to and activate PPAR. However, our results suggest FAs are probably responsible for these observations, and likely outcompeting the synthetic environmental contaminants present in the dust extract. Furthermore, bioactivation of contaminants present in house dust can potentially increase their affinity for PPAR. And lastly, the bioaccessibility and stability of SVOCs in house dust after ingestion are likely to modulate the PPAR activity in the environmental mixtures and should be considered in future risk assessments.
Item Open Access Children's Exposure to the Flame Retardant TDCPP in Indoor Environments: A Risk Assessment(2013-04) Misenheimer, JohnTris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate additive flame retardant used in consumer products. Due to the phase out of the persistent and endocrine disrupting polybrominated diphenyl ether (PBDE) flame retardant commercial mixtures in 2005, the use of TDCPP has increased. However TDCPP is considered a suspected human carcinogen by the Consumer Product Safety Commission (CPSC, 2006), and it has recently been detected in both infant products, residential furniture, and in indoor air and dust particles at levels that are equivalent to, and in some cases higher than, levels of PBDEs (Kolpin et al, 2002 and Stapleton et al, 2009). Levels of TDCPP in indoor dust are particularly worrisome as children are known to have greater exposure to dust relative to adults, and therefore greater exposure to chemicals found in dust, including flame retardants, lead and pesticides (Xue et al, 2007). Due to these facts, more research is necessary to understand the magnitude of exposure that children are receiving to TDCPP in indoor environments and from contact with consumer products. With this in mind, the goal of this research study was to investigate children' exposure to TDCPP in indoor environments, and quantify exposure from both hand to mouth contact and exposure to house dust to compare with exposure limits set by the CPSC and the state of California. In the spring of 2012, a cohort of toddlers and young children residing in and around Durham, North Carolina were recruited into this research study. In every home, a research team collected house dust samples (n=30) and handwipe samples from toddlers. Handwipes and house dust samples were analyzed in the laboratory for several organophosphate flame retardants (OPFRs), including TDCPP, tris (2-chloroethyl) phosphate (TCEP), and tris (1-chloro-isopropyl) phosphate (TCPP), using gas chromatography mass spectrometry (GC/MS). Detection frequencies for TCEP, TCPP and TDCPP were 48.8%, 70.5% and 95.3% in handwipes, and 97.0%, 97.0% and 100% in house dust. Based on levels of TDCPP in house dust, the estimated daily dose for children' median exposure to TDCPP was 273 ng/day, and 1242 ng/day for children residing in homes with very high TDCPP dust levels (i.e. 99th percentile). Using levels of TDCPP measured in the handwipes, the estimated daily dose for children' median exposure to TDCPP was 833 ng/day, and 5242 ng/day for children with high levels of TDCPP on their hands (e.g. 99th percentile). California' acceptable daily dose of TDCPP is listed as 5.4 micrograms/day. Therefore, based on our estimates of children' exposure to TDCPP from hand to mouth contact measured here, a small percentage of children may be at an increased risk for cancer.Item Open Access Endocrine and Neurobehavioral Effects from Flame Retardant Exposure in Early and Juvenile Life Stages of Zebrafish(2015) Macaulay, Laura JeanPolybrominated diphenyl ethers (PBDEs) are a class of flame retardant chemicals that were added to furniture foam, electronics, plastics, and some textiles to reduce their flammability. While PBDEs have been phased out from use in current products, huge reservoirs of products containing PBDEs still exist. It is likely exposure to PBDEs will continue as older products are discarded and recycled. PBDEs are ubiquitous contaminants in indoor and outdoor environments due to their widespread use in many products and their ability to migrate out of treated materials.
Major health effect concerns from PBDE exposure identified in laboratory studies include neurotoxicity, reproductive/developmental toxicity, and thyroid disruption. Importantly, mammals metabolize PBDEs into the hydroxylated polybrominated diphenyl ethers (OH-BDEs), which are structurally similar to endogenous thyroid hormones. Thyroid hormones are essential for metabolic processes, growth, and development, particularly brain development. Multiple studies have demonstrated enhanced potency of OH-BDEs relative to the parent PBDE chemicals, particularly for neurodevelopmental processes. Additionally, in fish species, thyroid hormones are essential for transitioning between larval, juvenile, and adult life stages. Therefore, studying the effects of both PBDEs and OH-BDEs during sensitive developmental life stages (i.e. larval and juvenile development) is warranted. The hypothesis of this thesis research is that PBDE metabolites interfere with thyroid hormone signaling (through interacting with thyroid receptor and deiodinase enzymes) which may result in decreased growth, morphological deficits, and altered neurodevelopment. The objectives of this research project were to evaluate the toxicity of PBDE metabolites and mixtures of PBDEs/OH-BDEs on larval and juvenile zebrafish development, examining both potential modes of action as well as functional consequences of exposure in developing animals.
In the first aim of this thesis research, structural relationships were examined between eleven different halogenated phenolic compounds (OH-BDEs, OH-PCBs, halogenated phenols, and TBBPA) to test developmental toxicity in zebrafish from 0-6 days post fertilization (dpf). In addition, follow up studies were performed with the most toxic compound, 6-hydroxy- 2,2’,4,4’-tetrabromodiphenyl ether (6-OH-BDE-47), to examine effects on TH-mediated morphological development and to better understand its mechanism of action in zebrafish. Thyroid disrupting agents including propylthiouracil, iopanoic acid, and native thyroid hormones were also used as positive controls for morphologic studies. Exposures to 6-OH-BDE-47 (10 nM to 100 nM) during development resulted in severe delays, similar to exposures from the T3 and thyroid disrupting agents. Lower jaw deformities and craniofacial cartilage malformations were also observed following exposure to 6-OH-BDE-47 at doses greater than 50 nM. Of interest, these developmental delays were rescued by overexpression of TRβ mRNA during the exposure period. These data indicate that OH-BDEs can adversely affect early life development of zebrafish and suggest they may be impacting thyroid hormone regulation in vivo through downregulation of the thyroid hormone receptor.
In the second aim of this dissertation research, neurobehavioral performance was monitored in larval and juvenile fish following a developmental exposure to 6-OH-BDE-47. 6-OH-BDE-47 has been identified as a neurotoxicant in previous cell based assays, and was identified as overtly toxic to zebrafish larvae in Aim 1 of this research. Developmental exposures (0-6 dpf) to 6-OH-BDE-47 resulted in decreased larval swimming activity at 6 dpf, with persisting impacts on behavior at 45 dpf. Young adult fish, when tested at 45 dpf, exhibited increased fear/anxiety response in the novel tank diving task and hyperactivity in a test of sensorimotor habituation. These data indicate that exposures to PBDE flame retardants and their metabolites during critical developmental windows can alter long term cognitive responses more than a month after the exposure has ceased.
Finally, for the third aim of this dissertation research, zebrafish undergoing larval-juvenile metamorphosis were exposed to a mixture of PBDEs (30-600 µg/L DE-71) and OH-BDEs (1-300 nM) from 9-23 dpf. Metamorphosis is a unique developmental period in fishes which is partially mediated by thyroid hormones. Juvenile animals, like larval animals, represent a sensitive and unique subpopulation of animals. At the end of the exposure period (23 dpf), a subset of fish were reared in clean water until 45 dpf for neurobehavioral testing. Fish samples were collected at 3 time points throughout the experiments, Days 12, 23, and 45. Tissue accumulation of test chemicals was monitored, and juvenile fish treated with the High Mixture were found to accumulate over 100 µg/g ww ∑PentaBDEs. The highest mixture treatment was found to be acutely toxic to zebrafish juveniles, resulting in >85% mortality within 14 days of exposure. Fish treated with 30 nM 6-OH-BDE-47 or the lower mixture exhibited reduced morphology scores relating to fin, pigmentation, and swim bladder maturation. In addition, reduced skeletal ossification and caudal area was observed at earlier time points with treatment to 6-OH-BDE-47. These alterations were accompanied by increases in chondrogenic gene expression, declines in osteogenic gene expression, and increases in thyroid receptor expression. Approximately 3.5 weeks after the exposure period, juvenile fish were tested on neurobehavioral tasks of novel tank exploration and sensorimotor habituation, however, no significant treatment related effects on task performance were observed. Collectively, these data suggested that the larval/juvenile development stage is a sensitive developmental window which can be adversely impacted by PBDE/OH-BDE exposure.
Item Open Access Evaluating Exposures to Semi-Volatile Organic Compounds in Indoor Environments(2019) Hammel, Stephanie CSemi-volatile organic compounds (SVOCs) are used in consumer products in a wide variety of applications such as flame retardants, plasticizers, pesticides, preservatives, and fragrances. Due to their extensive use in everyday products, SVOCs are widely detected in indoor environments, and human exposure is common and often chronic. As the wealth of toxicological data examining the negative health impacts of these compounds grows, the need for reliable tools to accurately measure human exposure becomes increasingly more crucial. In the past few decades, external exposure to these compounds have been evaluated through measurements in indoor air, house dust, and hand wipes, all of which have been shown to be associated with internal dose (e.g., concentrations in urine or blood). However, there are significant limitations to using each of these approaches to characterizing exposure. In recent years, silicone wristbands have been used as personal passive samplers for evaluating ambient exposure to a wide array of consumer product and industrial compounds. While over a thousand chemicals have been reported to be detected on the wristbands, very few studies have measured the concentrations on wristbands and determined how well they correlate to established biomarkers of exposure. This dissertation research sought to evaluate the use of silicone wristbands for measuring personal exposure to three classes of SVOCs- organophosphate esters (OPEs), brominated flame retardants (BFRs), and phthalates. The central hypothesis is that wristbands are an effective tool for evaluating personal exposure to SVOCs and provide more accurate measures of exposure compared to tools currently in use.
Within the first aim of this dissertation research, paired samples of polyurethane foam (collected from sofas), house dust, and serum were analyzed for flame retardants (FRs) chemicals and associations were evaluated. The detection of two FR mixtures, PentaBDE and FM 550, in foam was significantly associated with 4 to 6.5 times as high concentrations of their primary components in house dust (p<0.01). These relationships were modified by the size of the sofa footprint within the room and dust-loading rates. PentaBDE in foam was also associated with higher levels of individual PBDE congeners in serum, particularly two of the primary congeners BDE-47 and -153. Participants who lived in a home with a sofa containing PentaBDE had serum BDE-47 levels that were 2.5 times as high as participants whose sofa did not contain PentaBDE (p<0.01). This study was the first to relate a specific FR application in a consumer product with house dust and a known biomarker of exposure.
For the second aim of this research, adult exposure to OPEs and BFRs were evaluated using silicone wristbands. OPEs quantified on the wristbands were significantly associated with metabolites from pooled urine samples, and polybrominated diphenyl ethers (PBDEs) on the wristbands were similarly correlated to PBDE levels in serum (rs=0.4-0.6, p<0.05). Several novel BFR compounds which lack verified biomarkers of exposure were also measured on the wristbands and reported for the first time. These two studies were the first to evaluate FR concentrations on wristbands with known biomarkers and represent two of now four published manuscripts providing evidence that measurements on wristbands are predictive of internal dose.
In the third aim of this research, children’s exposure to OPEs, phthalates, and BFRs were examined using silicone wristbands. The ability of the wristband measurements to predict urinary metabolite levels of OPEs and phthalates was compared to that of hand wipes and house dust. Across the three classes, the children’s wristband concentrations were positively and significantly associated with a number of their corresponding biomarkers in both urine and serum, similar to observations in our adult cohort. For OPEs, phthalates, and PBDEs, the wristbands were found to have similar or an improved utility, compared to hand wipes and dust, for evaluating children’s exposures to these compounds. For instance, one of the OPEs, 4-tertbutylphenyl diphenyl phosphate (4tBPDPP), on wristbands was more strongly correlated to its urinary metabolite, tert-butyl phenyl phenyl phosphate (tb-PPP), compared to that on hand wipes and dust (rs=0.35, p<0.01, compared to rs=0.16 and 0.05 for hand wipes and dust, respectively). For the phthalate benzyl butyl phthalate (BBP), wristbands and hand wipes were similar associated with the urinary metabolite, mono benzyl phthalate (MBzP), but both were stronger than the dust correlation (rs=0.56 for wristbands and hand wipes, p<0.001; rs=0.23 for dust, p<0.05). Similar results were observed among the PBDEs on the three exposure mediums and their serum biomarkers, although the magnitudes of correlation with serum were more similar for wristbands and dust.
Taken together this dissertation research provides some of the first insights on the evaluation of personal exposures to SVOCs using silicone wristbands. It includes six distinct studies evaluating human exposure to sixty-five chemicals from three classes of compounds. Further, this research offers novel contributions to the field of exposure science, evaluating the relationship between wristbands and established biomarkers of exposure and comparing them to the existing tools used in standard exposure assessments. Wristbands have the potential to serve as an inexpensive and non-invasive medium for evaluating human exposure to chemical mixtures, and this work provides support for their use in large-scale research efforts to characterize SVOC exposures. Additional research should continue to assess wristbands for their ability to measure meaningful exposures for additional classes of chemicals, and importantly, identify the pathways of exposure (e.g., dermal absorption, inhalation, etc.) that are captured by the wristbands.
Item Open Access Examining Predictors of Exposure to Polybrominated Diphenyl Ethers (Pbdes) Among Chinese University Students(2013-04) Gloekler, LaurenPolybrominated diphenyl ethers (PBDEs) are flame-retardant compounds common in furniture, textiles, plastics, and electronic items. Throughout the use and disposal of products, PBDEs may enter the indoor or outdoor environment. Many studies have shown that PBDEs cause adverse human health effects, including but not limited to disruptions in thyroid and estrogen hormones, changes in fertility, and developmental effects. In order to decrease human exposure to PBDEs, it is important to understand the fate and behavior of these compounds in the environment. Globally, usage patterns differ between geographical regions. Although fate and distribution of PBDEs has been well studied in the U.S. and Europe, much less is known about exposure in Asia, specifically for China. The purpose of this study was to document the levels of major commercial PBDE mixtures, and common replacement compounds (Firemaster 550), in handwipes taken from a small population of Chinese students as an estimate of exposure potential. Additionally, PBDE levels were compared to differences in behavioral and lifestyle variables to see if any were significant predictors of exposure. It was hypothesized that time spent indoors, number of electronic items, hand washing frequency, and cleaning behaviors would influence the PBDE levels found on the hands. In each handwipe sample, at least one of the PBDE congeners or alternative compounds were detected, suggesting that the Chinese population is being exposed to these compounds. Several behavioral and product variables were significantly correlated to exposure levels and others were suggestive of a relationship. For PentaBDE, floor cleaning method was a significant predictor of exposure (p=0.02). For DecaBDE, floor cleaning method and number of computers in the room were significant predictors (p=0.02, p=0.05). Other variables showed large differences in the mean flame retardant levels between groups, such as time spent indoors, transportation behavior, and time spent watching TV, but were not statistically significant. Due to the small sample size and non-normal distribution of PBDE levels in the study population, it is recommended that these variables be examined again with a larger sample size. To date, this is the first study to measure levels of PBDEs and alternative compounds in handwipes from a population in China.Item Open Access Exploring Associations Between Prenatal PFAS Exposure and Childhood Asthma(2021-04-28) Bogar, LanePer- and polyfluoroalkyl substances (PFAS) are a large class of man-made chemicals used extensively in consumer and industrial products, making them ubiquitous in the built and natural environment. These chemicals pose a cause for concern, as there is increasing experimental and epidemiological evidence suggesting that exposure is associated with adverse health outcomes, especially prenatal PFAS exposure during critical periods of development. This study explored the associations between prenatal PFAS exposure, measured via maternal serum levels collected during pregnancy, and childhood asthma incidence in a cohort of 155 women, and 165 of their children from North Carolina. PFAS were detected in all serum samples and levels were similar to those in the general population. Statistical analyses incorporated potential predictors and covariates, including sex, age and race. After adjusting for these factors, statistically significant associations with asthma were found. Future efforts are needed to examine prenatal PFAS exposures and respiratory outcomes in later life.Item Embargo Exploring the Utility of Silicone Wristbands for Monitoring Exposure to Chemicals Present in Personal Care Products with a Focus on Parabens(2024) Levasseur, Jessica LesaParabens are environmental phenols that are most commonly found in personal care products (PCPs) worldwide. Though used widely, there is some contradictory information and data in the peer reviewed literature regarding their safety. To support informed risk assessment, more detailed information on exposure, exposure sources, and behaviors that contribute to exposure are needed. Current approaches for assessing exposure to parabens typically utilize urine samples that may not reflect average chronic exposure due to their short half-lives in the body. Wearable sensors, such as the silicone wristband (SWB), hold promise for improving exposure research in this area, particularly for chemicals that are quickly metabolized in the body. The overarching goal of this dissertation was to determine if SWBs could be an effective tool for measuring individual level exposure to parabens as a result of PCP use. Four parabens are examined herein: methylparaben, ethylparaben, propylparaben, and butylparaben. These compounds are often measured in exposure measurement matrices as a proxy for PCP exposure. Current research suggests that SWBs integrate both inhalation and dermal routes of exposure, the two major exposure routes for parabens. This dissertation therefore set out to determine if SWBs could provide more precise measures of exposure compared to more traditional approaches that utilize house dust samples, hand wipes, or spot urine samples. Aim 1 of this thesis sought to investigate the relationships between environmental and biological samples for phenols, including parabens and triclosan, in the home environment . This involved analysis of paired house dust, hand wipes, children’s urine, and SWBs collected from children in North Carolina. Guardians of these children (aged 3-6 years) completed questionnaires on habits and behaviors. All questionnaires and samples were collected between 2014 and 2016. Positive correlations for methyl-, ethyl-, and propylparaben were observed frequently in all matrices investigated. Exposure measurements from the sampled abiotic matrices were significantly correlated to associated urinary biomarkers for these parabens , although correlations with urine were higher for hand wipes and SWBs compared to dust. Everyday lotion use was also associated with significantly higher levels of urinary paraben biomarkers in children. These results demonstrated that lotion is a predictor of paraben exposure in children, and that SWBs may be a suitable tool for assessing children’s exposure to both parabens and triclosan. Aim 2 was designed to determine if SWBs could provide a quantitative estimate of total paraben internal dose by comparing their predictive ability compared to a spot urine sample. Uptake of parabens onto SWBs was assessed by asking 10 adults from central North Carolina to wear five SWBs, with one removed each day over five days. 24-hour urine samples and random spot urine samples were also collected daily to evaluate paraben biomarkers of exposure for methyl-, ethyl-, propyl-, and butylparaben. The concentrations of parabens and triclosan in SWB and spot urine samples were compared to measures of the total mass excreted over five days. Results demonstrated that butylparaben had a significant and positive linear uptake over five days, while methyl- and ethylparaben displayed an apparent steady state concentration over five days. SWBs and spot urine samples were similarly correlated to total mass excreted for parabens. Due to the advantages of SWBs over spot urine samples, such as higher sensitivity (i.e. greater detection rates), reduced participant burden, and less dependency on the timing of sample collection, SWBs may be a more suitable tool for assessing exposure to PCPs. Lastly, Aim 3 investigated the sensitivity of SWBs in their ability to detect paraben exposures resulting from the use of a specific PCP (lotion) and whether concentrations observed in SWBs correlate with the total mass of parabens excreted in urine. To support this aim, 20 adults from central North Carolina were asked to participate for two, three-day periods over two weeks. Participants were asked to keep PCP use identical between the two periods, but during one period (randomized as first or second period per participant) participants were asked to apply one pump of a body lotion (containing a known about of parabens) to the arm on which they wore the wristband. During both periods, participants wore a single SWB and collected three 24-hour urine samples. Results demonstrate that wristbands were able to differentiate paraben exposure between Lotion and No Lotion periods as well as urinary biomarkers of exposure. This study provides evidence that SWBs can detect chemical exposures originating from use of PCPs, and suggest that SWBs are a promising and sensitive tool to capture differences in PCP use in individuals. Collectively, this dissertation provides evidence that SWBs are a promising method to measure exposure to chemicals found within PCPs. Accurate exposure classification is critical for both epidemiological studies of health effects and risk assessments used for chemical regulation. This dissertation supplies the first evidence that SWBs can be used to measure common exposures, such as those from PCPs like lotions, and that these measurements realistically correlate to common measurements of internal dose.
Item Open Access Exposure to flame retardant chemicals and occurrence and severity of papillary thyroid cancer: A case-control study.(Environ Int, 2017-10) Hoffman, Kate; Lorenzo, Amelia; Butt, Craig M; Hammel, Stephanie C; Henderson, Brittany Bohinc; Roman, Sanziana A; Scheri, Randall P; Stapleton, Heather M; Sosa, Julie AnnBACKGROUND: Thyroid cancer is the fastest increasing cancer in the U.S., and papillary thyroid cancer (PTC) accounts for >80% of incident cases. Increasing exposure to flame retardant chemicals (FRs) has raised concerns about their possible role in this 'epidemic'. The current study was designed to test the hypothesis that higher exposure to FRs is associated with increased odds of PTC. METHODS: PTC patients at the Duke Cancer Institute were approached and invited to participate. Age- and gender-matched controls were recruited from the Duke Health System and surrounding communities. Because suitable biomarkers of long-term exposure do not exist for many common FRs, and levels of FRs in dust are significantly correlated with exposure, relationships between FRs in household dust and PTC were evaluated in addition to available biomarkers. PTC status, measures of aggressiveness (e.g. tumor size) and BRAF V600E mutation were included as outcomes. RESULTS: Higher levels of some FRs, particularly decabromodiphenyl ether (BDE-209) and tris(2-chloroethyl) phosphate in dust, were associated with increased odds of PTC. Participants with dust BDE-209 concentrations above the median level were 2.29 times as likely to have PTC [95% confidence interval: 1.03, 5.08] compared to those with low BDE-209 concentrations. Associations varied based on tumor aggressiveness and mutation status; TCEP was more strongly associated with larger, more aggressive tumors and BDE-209 was associated with smaller, less aggressive tumors. CONCLUSIONS: Taken together, these results suggest exposure to FRs in the home, particularly BDE-209 and TCEP, may be associated with PTC occurrence and severity, and warrant further study.Item Open Access Exposure to Hazardous Flame Retardant Chemicals in Camping Tents and Assessment of Potential Alternatives(2015-04-24) Gomes, Genna; Ward, PeytonAre the chemicals applied to your camping tent to protect you from fire actually harming you and the environment? Commercially available camping tents are required to meet a flammability standard, which is most often done through application of flame retardant chemicals. Many flame retardant chemicals have been demonstrated to leach from products, accumulate in people, persist in the environment and, potentially, have toxic effects on humans and wildlife. In this study, we measured human exposure to flame retardants in camping tents through experimental simulations using five leading brands of backpacking tents. Data collected from this exposure study and from the published literature on toxicity and hazard were then used to formulate a guide for industry that can be used to help them make more informed decisions about the use of flame retardants in their products.Item Open Access Exposure, Metabolism, and in Vitro Effects of Isopropylated and Tert-butylated Triarylphosphate Ester (ITP & TBPP) Flame Retardants and Plasticizers(2019) Phillips, AllisonFollowing the phase-out of polybrominated diphenyl ethers (PBDEs) in the early 2000s, organophosphate esters (OPEs) emerged as PBDE substitutes and have been applied to furniture foam, electronics, building materials, and some plastics to reduce their flammability. Although they have been used for quite some time in hydraulic fluids, isopropylated and tert-butylated triaryl phosphate esters (ITPs & TBPPs) have been more recently introduced as flame retardant (FR) replacements for the pentaBDE mixture in polyurethane foam (PUF). In addition to their use as FRs, ITPs and TBPPs are also used as plasticizers.
ITPs and TBPPs comprise a family of aryl organophosphate esters with varying degrees of isopropylation and tert-butylation. Individual ITP and TBPP isomers have been widely detected in indoor house dust, and recent biomonitoring studies demonstrate that human exposure to these compounds is widespread. Due to concerns about their persistence, bioaccumulation, and potential toxicity (P, B, & T), the U.S. Environmental Protection Agency (EPA) listed ITPs as one of five high priority chemicals fast-tracked for expedited risk assessment under the 2016 Toxic Substances Control Act (TSCA) reform.
As such, studying the exposure, metabolism, and in vitro effects of these compounds is especially timely. The hypothesis of this research dissertation is that ITP and TBPP isomers may exhibit some of the same P, B, & T properties that motivated the phase out of PBDEs. The main objectives of this research project were to generate meaningful data to fill gaps in our knowledge of ITP and TBPP isomers, and to contribute to the ongoing risk assessment of these compounds.
In the first aim of this thesis research, the maternal transfer of Firemaster® 550 (FM 550), a commercial mixture containing ITP isomers and brominated FRs, was investigated in dosed Wistar rats. Gestational and lactational transfer were examined separately, with dams orally exposed to 300 or 1000 µg of FM 550 for 10 consecutive days during gestation (gestational day [GD] 9-18) or lactation (postnatal day [PND] 3-12). Levels of parent compounds were measured in dam and pup urine. The two brominated components of FM 500, 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) and bis (2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP), underwent both gestational and lactational transfer. Triphenyl phosphate (TPHP) and ITPs were rapidly metabolized by the dams and were not detected in whole tissue homogenates. However, diphenyl phosphate (DPHP) and mono-isopropylphenyl phenyl phosphate (ip-PPP) were detected in urine from the dosed animals. This study was the first to confirm ip-PPP as a urinary metabolite of ITPs and establish a pharmacokinetic profile of FM 550 in a mammalian model.
In the second aim of this thesis research, the contribution of individual ITP and TBPP isomers was quantified in four commercial flame retardant mixtures: FM 550, Firemaster® 600 (FM 600), an ITP mixture, and a TBPP mixture. Findings suggested similarities between FM 550 and the ITP mixture, with 2-isopropylphenyl diphenyl phosphate (2IPPDPP), 2,4-diisopropylphenyl diphenyl phosphate (24DIPPDPP), and bis(2-isopropylphenyl) phenyl phosphate (B2IPPPP) being the most prevalent ITP isomer in both mixtures. FM 600 differed from FM 550 in that it contained TBPP isomers rather than ITP isomers. ITP and TBPP isomers were also detected and quantified in house dust standard reference material, SRM 2585, demonstrating their environmental relevance.
The third aim of this thesis research investigated phase I and II in vitro metabolism of TPHP, 4-tert-butylphenyl diphenyl phosphate (4tBPDPP), 2-isopropylphenyl diphenyl phosphate (2IPPDPP), and 4-isopropylphenyl diphenyl phosphate (4IPPDPP) at 1 and 10 µM doses using human liver subcellular fractions. Parent depletion and the formation of known metabolites, including DPHP, hydroxyl-triphenyl phosphate (OH-TPHP), ip-PPP, and tert-butylphenyl phenyl phosphate (tb-PPP), were monitored via gas chromatography/mass spectrometry (GC/MS) and liquid chromatography tandem mass spectrometry (LC/MS/MS). Tb-PPP and its conjugates were identified as the major in vitro metabolites of 4tBPDPP, accounting for up to 33% of the initial parent dose. While the mass balance between parents and metabolites was conserved for TPHP and 4tBPDPP, approximately 20% of the initial parent mass was unaccounted for after quantifying metabolites of 2IPPDPP and 4IPPDPP that had authentic standards available. Two novel ITP metabolites, mono-isopropenylphenyl diphenyl phosphate and hydroxy-isopropylphenyl diphenyl phosphate, were tentatively identified by high-resolution mass spectrometry (HRMS) and screened for in recently collected human urine. This study provided insight into recent human biomonitoring and epidemiological studies and contributed to our understanding of the biological fate of ITP and TBPP isomers.
Finally, the fourth aim of this thesis research evaluated ITPs, TBPPs, and related commercial mixtures for their effect on the activity of purified human liver carboxylesterase (hCE1). Four of the 15 OPEs tested had IC50 values lower than 100 nM, including TPHP, 2-ethylhexyl diphenyl phosphate (EHDPP), 4-isopropylphenyl diphenyl phosphate (4IPPDPP), and 4-tert-butylphenyl diphenyl phosphate (4tBPDPP), as did four commercial flame retardant mixtures tested. Because hCE1 is critical for the activation of imidapril, an ACE-inhibitor prodrug prescribed to treat hypertension, the most potent inhibitors, TPHP and 4tBPDPP, and an environmentally relevant mixture (house dust) were further evaluated for their effect on imidapril bioactivation in vitro. TPHP and 4tBPDPP were potent inhibitors of hCE1-mediated imidapril activation (Ki = 49.0 and 17.9 nM, respectively), as were extracts of house dust (100 µg/ml), which caused significant reductions in imidapril activation. Combined, these data suggest that exposure to OPEs can affect pharmacotherapy.
Collectively and in context of other recently published findings, this thesis research suggests that ITPs and TBPPs may be regrettable substitutes for PBDEs.
Item Open Access Halogenated Organophosphate Flame Retardants: Developmental Toxicity and Endocrine Disruptive Effects(2015) Dishaw, Laura VictoriaFollowing the phase out of polybrominated diphenyl ethers (PBDEs), manufacturers turned to several alternative flame retardants (FRs) to meet flammability standards. Organophosphate FRs (OPFRs), and in particular tris (1,3-dichloropropyl) phosphate (TDCPP), have been increasingly detected in textiles and foam padding used in a variety of consumer products including camping equipment, upholstered furniture, and baby products. Like PBDEs, OPFRs are additive, meaning that they are not chemically bound to the treated material and can more readily leach out into the surrounding environment. Indeed, OPFRs have been detected in numerous environmental and biological matrices, often at concentrations similar to or exceeding that of PBDEs.
Although OPFRs have been in use for several decades, relatively little is known regarding their potential for adverse human and environmental health consequences. However, based on their structural similarity to OP pesticides, they may have analogous mechanisms of toxicity. OP pesticide toxicity is classically associated with cholinesterase inhibition, resulting in cholinergic intoxication syndrome. OPFRs have been shown to be ineffective cholinesterase inhibitors, however chlorpyrifos (CPF) and other OP pesticides have been shown to elicit adverse effects on developing organisms through other mechanisms.
The main objective of this research project was to evaluate the toxicity of four structurally similar OPFRs (TDCPP; tris (2,3-dibromopropyl) phosphate, (TDBPP); tris (1-chloropropyl) phosphate (TCPP) and tris (2-chloroethyl) phosphate (TCEP)) in comparison to chlorpyrifos (CPF), a well-studied OP pesticide. A combination of in vitro and in vivo models was used to elucidate potential mechanisms as well as functional consequences of exposure in developing organisms.
In the first research aim, a series of in vitro experiments with neurotypic PC12 cells was used to evaluate the effects of four structurally similar OPFRs (TDCPP, TDBPP, TCEP, or TCPP) and CPF on neurodevelopment. The effects of TDCPP were also compared to that of BDE-47, a major component of the commercial PentaBDE mixture. In general, TDCPP elicited similar or greater effects when compared to an equimolar concentration of CPF. All OPFRs tested produced similar decrements in cell number and altered phenotypic differentiation, while BDE-47 had no effect on cell number, cell growth, or neurite growth.
For the second research aim, zebrafish (Danio rerio) were used to evaluate the effects of the same suite of chemicals on early development. TDCPP, TDBPP, and CPF elicited overt toxicity (e.g., malformations or death) within the concentration range tested (0.033-100 µM). TDBPP was the most potent with 100% mortality by 6 days post fertilization (dpf) at ≥3.3 µM. CPF and TDCPP showed equivalent toxicity with malformations observed in at 10 µM and significant mortality (≥75%) at ≥33 µM. There was no overt toxicity among TCEP- and TCPP-exposed fish. All test chemicals affected larval swimming behavior on 6 dpf at concentrations below the overt toxicity threshold. Parent chemical was detected in all in embryonic (1 dpf) and larval (5 dpf) tissues. TDCPP and TDBPP showed rapid and extensive metabolism.
Finally, for the third aim, juvenile (45-55 dpf) zebrafish were exposed to CPF (1 µg/g food) or TDCPP (Low TDCPP = 1 µg/g food; High TDCPP = 40 µg/g food) via diet for 28 days followed by a 7 day depuration period where all treatments received clean food. A dietary exposure was chosen to more closely recapitulate exposure in humans. Samples were collected at seven time points throughout the experiment: days 0, 7, 14, 21, 28, 30, 35. Whole tissues were collected for tissue accumulation and histopathology endpoints. Viscera and brain were dissected and flash frozen separately for DNA damage analyses.
Tissue measurements of CPF, TDCPP, and the metabolite bis (1,3-dichloropropyl) phosphate (BDCPP) were often below the method detection limit, however when present there was a trend towards increased accumulation with treatment and time. On Day 7 Low TDCPP caused a dramatic but transient increase in DNA damage in both viscera and brain that returned to control levels by Day 14. Similar results have been seen previously with other genotoxicants and may be due to CPF and High TDCPP inducing an adaptive response prior to the 7 day sampling point. All treatments shifted the neurohypophysis to adenohypophysis ratio (NH/AH; Day 7 only) and significantly increased thyroid follicle activation (Day 14). Finally High TDCPP affected gonad maturation, causing a significant increase in ovary follicle development (Day 14) and a transient but marked decrease in testes maturity (Day 7). Taken together these data suggest that dietary exposure to TDCPP and CPF elicits DNA damage in brain and viscera and alters endocrine function in juvenile zebrafish. Importantly, analyses were restricted to the first three time points (Days 0, 7, and 14) due to the emergence a disease among the experimental colony. Although these samples were collected prior to the disease becoming apparent, it remains a potential confounder of the current results.