Urinary tetrabromobenzoic acid (TBBA) as a biomarker of exposure to the flame retardant mixture Firemaster® 550

Urinary biomarkers of flame retardant exposure among collegiate U.S. gymnasts

Flame retardants are widely used in polyurethane foam materials including gymnastics safety equipment such as pit cubes and landing mats. We previously reported elevated concentrations of flame retardants in the air and dust of a U.S. gymnastics training facility and elevated PentaBDE in the serum of collegiate gymnasts. Our objective in this pilot study was to compare urinary biomarkers of exposure to other flame retardants and additives of polyurethane foam including tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), triphenyl phosphate (TPHP) and 2-ethylhexyl- 2,3,4,5-tetrabromobenzoate (EH-TBB) in samples collected from 11 collegiate gymnasts before and after a gymnastics practice (n=53 urine samples total). We identified a 50% increase in the TPHP biomarker (p=0.03) from before to after practice, a non-significant 22% increase in the TDCIPP biomarker (p=0.14) and no change for the EH-TBB biomarker. These preliminary results indicate that the gymnastics training environment can be a source of recreational exposure to flame retardants. Such exposures are likely widespread, as we identified flame retardants in 89% of foam samples collected from gyms across the U.S.

Regional comparison of organophosphate flame retardant (PFR) urinary metabolites and tetrabromobenzoic acid (TBBA) in mother-toddler pairs from California and New Jersey

The use of alternative chemical flame retardants in consumer products is increasing as the result of the phase-out of polybrominated diphenyl ethers. Today, the most commonly detected alternatives in residential furniture include the organophosphate flame retardants (PFRs) and the Firemaster (R) 550 mixture (FM550). Urinary levels of dialkyl and diaryl phosphate esters, and 2-ethylhexyl tetrabromobenzoate (EH-TBB) have been used as biomarkers of human exposure to PFRs and FM550, respectively. In a previous study, we demonstrated that toddlers had significantly higher levels of PFRs relative to their mothers in a cohort from New Jersey; however, it is unclear if there are regional differences in exposure. It is possible that exposure to PFRs may be higher in California relative to other US States due to the California flammability standard, as was seen previously observed for PBDEs. In the current study, we examined urinary levels of PFR metabolites and TBBA in 28 mother-child pairs from California, USA, collected in 2015, and compared them with levels measured in our previous study from New Jersey. Urine samples were extracted using solid-phase extraction and analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Diphenyl phosphate (DPHP), isopropyl-phenyl phenyl phosphate (ip-PPP), bis(1,3-dichloro-2propyl) phosphate (BDCIPP) and BCIPHIPP conjugates were detected in 100% of mother and child urine samples, while bis(1-chloro-2-propyl) phosphate (BCIPP), tert-butyl-phenyl phenyl phosphate (tb-PPP) and TBBA were detected in < 50% of samples. Interestingly, BCIPHIPP conjugates were detected in 100% of the urine samples, suggesting ubiquitous exposure to the parent compound, tris(1-chloro-2-propyl) phosphate (TCIPP). The current study found significantly higher BDCIPP levels in California toddlers and higher and ip-PPP levels in mothers as compared to the New Jersey cohort, which may be reflective of California's furniture flammability standard. For example, BDCIPP levels in California children were 2.4 times higher than those in New Jersey children. Consistent with our previous work, the current study showed higher PFR and EH-TBB exposure in children, likely due to increased hand-mouth behavior. Children's DPHP and BDCIPP levels, on average, were 5.9 times and 15 times those of their mothers. Positive correlations between paired mothers and their children were shown for DPHP and BCIPHIPP conjugates but not BDCIPP or ip-PPP. In the children, several predictors of hand-mouth behavior were associated with BDCIPP, DPHP and ip-PPP urine levels, but no associations were observed with BCIPHIPP conjugates.

Editor's Highlight: Comparative Toxicity of Organophosphate Flame Retardants and Polybrominated Diphenyl Ethers to Caenorhabditis elegans

With the phasing-out of the polybrominated diphenyl ether (PBDE) flame retardants due to concerns regarding their potential developmental toxicity, the use of replacement compounds such as organophosphate flame retardants (OPFRs) has increased. Limited toxicity data are currently available to estimate the potential adverse health effects of the OPFRs. The toxicological effects of 4 brominated flame retardants, including 3 PBDEs and 3,3',5,5'-tetrabromobisphenol A, were compared with 6 aromatic OPFRs and 2 aliphatic OPFRs. The effects of these chemicals were determined using 3 biological endpoints in the nematode Caenorhabditis elegans (feeding, larval development, and reproduction). Because C. elegans development was previously reported to be sensitive to mitochondrial function, results were compared with those from an in vitro mitochondrial membrane permeabilization (MMP) assay. Overall 11 of the 12 flame retardants were active in 1 or more C. elegans biological endpoints, with only tris(2-chloroethyl) phosphate inactive across all endpoints including the in vitro MMP assay. For 2 of the C. elegans endpoints, at least 1 OPFR had similar toxicity to the PBDEs: triphenyl phosphate (TPHP) inhibited larval development at levels comparable to the 3 PBDEs; whereas TPHP and isopropylated phenol phosphate (IPP) affected C. elegans reproduction at levels similar to the PBDE commercial mixture, DE-71. The PBDEs reduced C. elegans feeding at lower concentrations than any OPFR. In addition, 9 of the 11 chemicals that inhibited C. elegans larval development also caused significant mitochondrial toxicity. These results suggest that some of the replacement aromatic OPFRs may have levels of toxicity comparable to PBDEs.

Editor's Highlight: Transplacental and Lactational Transfer of Firemaster® 550 Components in Dosed Wistar Rats

Firemaster® 550 (FM 550) is a commercial mixture of organophosphate and brominated flame retardants currently in use as a replacement for pentaBDE. Its organophosphate components include triphenyl phosphate (TPHP) and a suite of isopropylated triarylphosphate isomers (ITPs); its brominated components include 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) and bis (2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP). Taken together, these chemicals have been shown to be endocrine disrupting and potentially toxic, and human exposure to them is widespread. In this study, maternal transfer of FM 550 components, and in some cases their metabolites, 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 fetus and whole pup tissue homogenates, and in dam and pup serum, and several metabolites were measured in dam and pup urine. EH-TBB body burdens resulting from lactational transfer were approximately 200- to 300-fold higher than those resulting from placental transfer, whereas low levels of BEH-TEBP were transferred during both lactation and gestation. 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 is the first to confirm ip-PPP as a urinary metabolite of ITPs and establish a pharmacokinetic profile of FM 550 in a mammalian model.

KEY WORDS

Firemaster 550 ;: lactational transfer ;: gestational transfer; metabolites; rodent.

Flame retardants: Dust - And not food - Might be the risk

Flame retardants (FRs) are used to delay ignition of materials such as furniture and electric and electronic instruments. Many FRs are persistent and end up in the environment. Environmental studies on flame retardants (FRs) took off in the late 1990s. Polybrominated diphenylethers (PBDEs) appeared to be bioaccumulative and were found in many organisms all over the world. When PBDEs were banned or their production voluntarily terminated, alternatives appeared on the market that often had similar properties or were of more concern due to their toxicity such as halogenated phosphorus-based FRs. Here we show that in spite of the ban on PBDEs more brominated FRs are being produced, an increasing number of other FRs is being applied and FR levels in our homes are much higher than in the outdoor environment. While nowadays we live in better isolated houses and sit in front of the computer or television, on flame retarded upholstery, we are at risk due to the toxic effects of a suite of FRs. The high exposure to these substances indoors calls for better risk assessments that include mixture effects.

Disposition of the emerging brominated flame retardant, bis(2-ethylhexyl) tetrabromophthalate, in female Sprague Dawley rats: effects of dose, route and repeated administration

1. Bis(2-ethylhexyl)-tetrabromophthalate (BEH-TEBP; CAS No. 26040-51-7; PubChem CID: 117291; MW 706.15 g/mol, elsewhere: TeBrDEPH, TBPH, or BEHTBP) is used as an additive brominated flame retardant in consumer products. 2. Female Sprague Dawley rats eliminated 92-98% of [¹⁴C]-BEH-TEBP unchanged in feces after oral administration (0.1 or 10 μmol/kg). A minor amount of each dose (0.8-1%) was found in urine after 72 h. Disposition of orally administered BEH-TEBP in male B6C3F1/Tac mice was similar to female rats. 3. Bioaccumulation of [¹⁴C]-radioactivity was observed in liver and adrenals following 10 daily oral administrations (0.1 μmol/kg/day). These tissues contained 5- and 10-fold higher concentrations of [¹⁴C]-radioactivity, respectively, versus a single dose. 4. IV-administered [¹⁴C]-BEH-TEBP (0.1 μmol/kg) was slowly eliminated in feces, with >15% retained in tissues after 72 h. Bile and fecal extracts from these rats contained the metabolite mono-ethylhexyl tetrabromophthalate (TBMEHP). 5. BEH-TEBP was poorly absorbed, minimally metabolized and eliminated mostly by the fecal route after oral administration. Repeated exposure to BEH-TEBP led to accumulation in some tissues. The toxicological significance of this effect remains to be determined. This work was supported by the Intramural Research Program of the National Cancer Institute at the National Institutes of Health (Project ZIA BC 011476).

Hair and Nails as Noninvasive Biomarkers of Human Exposure to Brominated and Organophosphate Flame Retardants

After the phase-out of polybrominated diphenyl ethers (PBDEs), the use of alternative flame retardants (AFRs), such as FireMaster 550, and of organophosphate esters (OPEs) has increased. However, little is known about human exposure to these chemicals. This lack of biomonitoring studies is partially due to the absence of reliable noninvasive biomarkers of exposure. Human hair and nails can provide integrated exposure measurements, and as such, these matrices can potentially be used as noninvasive biomarkers of exposure to these flame retardants. Paired human hair, fingernail, toenail, and serum samples obtained from 50 adult participants recruited at Indiana University Bloomington campus were analyzed by gas chromatographic mass spectrometry for 36 PBDEs, 9 AFRs, and 12 OPEs. BDE-47, BDE-99, 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), di(2-ethylhexyl) tetrabromophthalate (TBPH), tris(1,3-dichloro-2-propyl)phosphate (TDCIPP), and triphenyl phosphate (TPHP) were the most abundant compounds detected in almost all hair, fingernail, and toenail samples. The concentrations followed the order OPEs > TBB+TBPH > Σpenta-BDE. PBDE levels in the hair and nail samples were significantly correlated with their levels in serum (P < 0.05), suggesting that human hair and nails can be used as biomarkers to assess human exposure to PBDEs.

Phthalate metabolites in urine samples from Beijing children and correlations with phthalate levels in their handwipes

Little attention has been paid to dermal absorption of phthalates even though modeling suggests that this pathway may contribute meaningfully to total uptake. We have concurrently collected handwipe and urine samples from 39 Beijing children (5-9 years) for the purpose of measuring levels of five phthalates in handwipes, corresponding concentrations of eight of their metabolites in urine, and to subsequently assess the contribution of dermal absorption to total uptake. In summer sampling, DEHP was the most abundant phthalate in handwipes (median: 1130 μg/m(2) ), while MnBP was the most abundant metabolite in urine (median: 232 ng/ml). We found significant associations between the parent phthalate in handwipes and its monoester metabolite in urine for DiBP (r = 0.41, P = 0.01), DnBP (r = 0.50, P = 0.002), BBzP (r = 0.48, P = 0.003), and DEHP (r = 0.36, P = 0.03). Assuming that no dermal uptake occurred under clothing-covered skin, we estimate that dermal absorption of DiBP, DnBP, BBzP, and DEHP contributed 6.9%, 4.6%, 6.9%, and 3.3%, respectively, to total uptake. Assuming that somewhat attenuated dermal uptake occurred under clothing-covered skin, these estimates increase to 19%, 14%, 17%, and 10%. The results indicate that absorption from skin surfaces makes a meaningful contribution to total phthalate uptake for children and should be considered in future risk assessments.

PRACTICAL IMPLICATIONS

This study indicates that children’s hands acquire substantial amounts of various phthalates. The levels measured in handwipes, although higher, are somewhat representative of levels on other body locations. Via dermal absorption, as well as hand-to-mouth activity, phthalates on hands and other body locations contribute to the overall body burden of these compounds. Dermal absorption from air and contact transfer from surfaces is expected to occur for many SVOCs commonly found indoors (e.g. bisphenols, synthetic musks, organophosphates). However, the dermal pathway has often been neglected in exposure assessments of indoor pollutants. Knowledge regarding phthalates and other SVOCs in handwipes can facilitate our understanding of risks and aid in the mitigation of adverse health effects resulting from indoor exposures. To make progress toward these goals, further studies are necessary, including investigations of phthalate level variability in skinwipes collected at different locations on the body and the impact of clothing on dermal absorption from air.

My Winding Road: From Microbiology to Toxicology and Environmental Health

I would certainly never have predicted that I would become the director of the National Institute of Environmental Health Sciences (NIEHS) and the National Toxicology Program (NTP) when I was a Jewish girl growing up in Teaneck, New Jersey. My family stressed the importance of education. Yet for a girl there were many not-so-subtle suggestions that the appropriate careers were in teaching or nursing, and the most important thing was to be a wife and mother. Well, I can't disagree with the latter, although I would have to add grandmother to that list of achievements. My parents were both college graduates, but my mom only taught high school English for one year before leaving the field to start our family. My dad returned from World War II and joined his brother in accounting. After my first sister was born, my father joined my mother's family jewelry business and helped to open a second retail store. My mother helped my dad out during the busy times—Christmas and wedding season—but otherwise focused on our growing family of three girls and one boy. This became increasingly challenging when it became clear that my little brother was severely retarded and would require extra care.

Activation of Human Peroxisome Proliferator-Activated Nuclear Receptors (PPARγ1) by Semi-Volatile Compounds (SVOCs) and Chemical Mixtures in Indoor Dust

Recently, we reported that several semi-volatile compounds (SVOCs) were competitive ligands for human peroxisome proliferator-activated nuclear receptor gamma (PPARγ1). We also observed significant binding from chemicals extracted from house dust at a concentration of 3 mg dust/mL in the dosing medium. To follow up on this study, a commercially available reporter gene assay (GeneBLAzer PPARγ1 non-DA Assay, Invitrogen) was used to investigate the PPARγ1 activation by 30 common SVOCs (e.g., brominated flame retardants, organophosphates, and phthalates) and in house dust extracts. Twenty-eight SVOCs or their metabolites were either confirmed or for the first time were found to be weak or moderate PPARγ1 agonists. We also observed activation in 15 of 25 dust extracts examined. In some cases, activation was as high as 50% of the activation of the positive control (rosiglitazone). Furthermore, there was a significant and positive correlation (r = 0.7, p < 0.003) between data collected from this reporter assay and our previous ligand binding assay tested on the same dust extracts. Our results suggest that many SVOCs ubiquitous in house dust, or their metabolites, are possible PPARγ1 agonists. Also, chemical mixtures present in house dust at environmentally relevant levels can activate human PPARγ1 in a transfected cell culture system, and further research is needed to identify the primary chemical(s) driving this activity.

Neurotoxicity of FireMaster 550® in zebrafish (Danio rerio): Chronic developmental and acute adolescent exposures

BACKGROUND

FireMaster® 550 (FM 550) is the second most commonly used flame retardant (FR) product in consumer goods and has been detected in household dust samples. However, neurobehavioral effects associated with exposure have not been characterized in detail. We investigated the behavioral effects of FM 550 in zebrafish to facilitate the integration of the cellular and molecular effects of FM 550 with its behavioral consequences. The effects of developmental FM 550 exposure on zebrafish larvae swimming shortly after the end of exposure as well as the persisting effects of this exposure on adolescent behavior were studied. In addition, the acute effects of FM 550 on behavior with exposure during adolescence in zebrafish were studied.

METHODS

Developmental exposure to 0, 0.01, 0.1 or 1 mg/L of FM 550 via immersion spanned 0-5 days post fertilization, with larval testing on day 6 and adolescent testing on days 40-45. Acute adolescent (45 dpf) exposure was to 0, 1.0 or 3.0 mg/L of FM 550 via immersion, for 24 h, with testing 2 h or 1 week later. The vehicle condition was colony tank water with .0004% (developmental) or .0012% (adolescent) DMSO. Zebrafish behavior was characterized across several domains including learning, social affiliation, sensorimotor function, predator escape, and novel environment exploration.

RESULTS

Persisting effects of developmental FM 550 exposure included a significant (p<0.01) reduction in social behavior among all dose groups. Acute FM 550 exposure during adolescence caused hypoactivity and reduced social behavior (p's<0.05) when the fish were tested 2 h after exposure. These effects were attenuated at the 1 week post exposure testing point

DISCUSSION

Taken together, these data indicate that FM 550 may cause persisting neurobehavioral alterations to social behavior in the absence of perturbations along other behavioral domains and that developmental exposure is more costly to the organism than acute adolescent exposure.

Quantification of tetrabromo benzoic acid and tetrabromo phthalic acid in rats exposed to the flame retardant Uniplex FPR-45

The first withdrawal of certain polybrominated diphenyl ethers flame retardants from the US market occurred in 2004. Since then, use of brominated non-PBDE compounds such as bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) in commercial formulations has increased. Assessing human exposure to these chemicals requires identifying metabolites that can potentially serve as their biomarkers of exposure. We administered by gavage a dose of 500 mg/Kg bw of Uniplex FRP-45 (>95 % BEH-TEBP) to nine adult female Sprague-Dawley rats. Using authentic standards and mass spectrometry, we positively identified and quantified 2,3,4,5-tetrabromo benzoic acid (TBBA) and 2,3,4,5-tetrabromo phthalic acid (TBPA) in 24-h urine samples collected 1 day after dosing the rats and in serum at necropsy, 2 days post-exposure. Interestingly, TBBA and TBPA concentrations correlated well (R (2) = 0.92). The levels of TBBA, a known metabolite of EH-TBB, were much higher than the levels of TBPA both in urine and serum. Because Uniplex FRP-45 was technical grade and EH-TBB was present in the formulation, TBBA likely resulted from the metabolism of EH-TBB. Taken together, our data suggest that TBBA and TBPA may serve as biomarkers of exposure to non-PBDE brominated flame retardant mixtures. Additional research can provide useful information to better understand the composition and in vivo toxicokinetics of these commercial mixtures.

Characterizing the peroxisome proliferator-activated receptor (PPARγ) ligand binding potential of several major flame retardants, their metabolites, and chemical mixtures in house dust

BACKGROUND

Accumulating evidence has shown that some environmental contaminants can alter adipogenesis and act as obesogens. Many of these contaminants act via the activation of the peroxisome proliferator-activated receptor γ (PPARγ) nuclear receptor.

OBJECTIVES

Our goal was to determine the PPARγ ligand binding potency of several major flame retardants, including polybrominated diphenyl ethers (PBDEs), halogenated phenols and bisphenols, and their metabolites. Ligand binding activity of indoor dust and its bioactivated extracts were also investigated.

METHODS

We used a commercially available fluorescence polarization ligand binding assay to investigate the binding potency of flame retardants and dust extracts to human PPARγ ligand-binding domain. Rosiglitazone was used as a positive control.

RESULTS

Most of the tested compounds exhibited dose-dependent binding to PPARγ. Mono(2-ethylhexyl) tetrabromophthalate, halogenated bisphenols and phenols, and hydroxylated PBDEs were found to be potent PPARγ ligands. The most potent compound was 3-OH-BDE-47, with an IC50 (concentration required to reduce effect by 50%) of 0.24 μM. The extent of halogenation and the position of the hydroxyl group strongly affected binding. In the dust samples, 21 of the 24 samples tested showed significant binding potency at a concentration of 3 mg dust equivalent (DEQ)/mL. A 3-16% increase in PPARγ binding potency was observed following bioactivation of the dust using rat hepatic S9 fractions.

CONCLUSION

Our results suggest that several flame retardants are potential PPARγ ligands and that metabolism may lead to increased binding affinity. The PPARγ binding activity of house dust extracts at levels comparable to human exposure warrants further studies into agonistic or antagonistic activities and their potential health effects.

Evaluating the bioaccessibility of flame retardants in house dust using an in vitro Tenax bead-assisted sorptive physiologically based method

Exposure to house dust is a significant source of exposure to flame retardant chemicals (FRs), particularly in the US. Given the high exposure there is a need to understand the bioaccessibility of FRs from dust. In this study, Tenax beads (TA) encapsulated within a stainless steel insert were used as an adsorption sink to estimate the dynamic absorption of a suite of FRs commonly detected in indoor dust samples (n = 17), and from a few polyurethane foam samples for comparison. Organophosphate flame retardants (OPFRs) had the highest estimated bioaccessibility (∼ 80%) compared to brominated compounds (e.g., PBDEs), and values generally decreased with increasing Log K(ow), with <30% bioaccessibility measured for BDE209. These measurements were in very close agreement with reported PBDE bioavailability measures from an in vivo rat exposure study using indoor dust. The bioaccessibility of very hydrophobic FRs (Log K(ow) > 6) in foam was much less than that in house dust, and increasing bioaccessibility was observed with decreasing particle size. In addition, we examined the stability of more labile FRs containing ester groups (e.g., OPFRs and 2-ethylhexyl-tetrabromo-benzoate (EH-TBB)) in a mock-digestive fluid matrix. No significant changes in the OPFR concentrations were observed in this fluid; however, EH-TBB was found to readily hydrolyze to tetrabromobenzoic acid (TBBA) in the intestinal fluid in the presence of lipases. In conclusion, our study demonstrates that the bioaccessibility and stability of FRs following ingestion varies by chemical and sample matrix and thus should be considered in exposure assessments.

Exposures, mechanisms, and impacts of endocrine-active flame retardants

This review summarizes the endocrine and neurodevelopmental effects of two current-use additive flame retardants (FRs), tris (1,3-dichloro-isopropyl) phosphate (TDCPP) and Firemaster(®) 550 (FM 550), and the recently phased-out polybrominated diphenyl ethers (PBDEs), all of which were historically or are currently used in polyurethane foam applications. Use of these chemicals in consumer products has led to widespread exposure in indoor environments. PBDEs and their hydroxylated metabolites appear to primarily target the thyroid system, likely due to their structural similarity to endogenous thyroid hormones. In contrast, much less is known about the toxicity of TDCPP and FM 550. However, recent in vitro and in vivo studies suggest that both should be considered endocrine disruptors as studies have linked TDCPP exposure with changes in circulating hormone levels, and FM 550 exposure with changes in adipogenic and osteogenic pathways.