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Chemicals have improved our quality of life, but the resulting environmental pollution has the potential to cause detrimental effects on humans and the environment. People and biota are chronically exposed to thousands of chemicals from various environmental sources through multiple pathways. Environmental chemists and toxicologists have moved beyond detecting and quantifying single chemicals to characterizing complex mixtures of chemicals in indoor and outdoor environments and biological matrices. We highlight analytical and bioanalytical approaches to isolating, characterizing, and tracking groups of chemicals of concern in complex matrices. Techniques that combine chemical analysis and bioassays have the potential to facilitate the identification of mixtures of chemicals that pose a combined risk.

Use of halogenated flame retardants continues despite health and environmental concerns Halogenated flame retardants are used widely in consumer products such as carpets, textiles, and electronics to reduce the risk of fire. It has been known for more than 20 years that these compounds can leach into the environment, with particularly high concentrations recorded in fish and marine mammals. Concerns have also been raised about carcinogenic and endocrine-disrupting effects in humans. Some brominated flame retardants—in particular, polybrominated diphenyl ether (PBDE) commercial mixtures and hexabromocyclododecane (HBCD)—have been banned or phased out in some jurisdictions, and the possible use of alternative flame retardants has been investigated. Yet, over the past 20 years, global production of flame retardants has continued to rise without a decrease in halogenated flame retardant production. It is time for a critical evaluation of flame retardant use.

Organophosphate flame retardants (PFRs) are becoming popular replacements for the phased-out polybrominated diphenyl ether (PBDE) mixtures, and they are now commonly detected in indoor environments. However, little is known about human exposure to PFRs because they cannot be easily measured in blood or serum. To investigate relationships between the home environment and internal exposure, we assessed associations between two PFRs, tris(1,3-dichloropropyl) phosphate (TDCIPP) and triphenyl phosphate (TPHP), in paired hand wipe and dust samples and concentrations of their metabolites in urine samples (n = 53). We also assessed short-term variation in urinary metabolite concentrations (n = 11 participants; n = 49 samples). Adult volunteers in North Carolina, USA, completed questionnaires and provided urine, hand wipe, and household dust samples. PFRs and PBDEs were measured in hand wipes and dust, and bis(1,3-dichloropropyl) phosphate (BDCIPP) and diphenyl phosphate (DPHP), metabolites of TDCIPP and TPHP, were measured in urine. TDCIPP and TPHP were detected frequently in hand wipes and dust (> 86.8%), with geometric mean concentrations exceeding those of PBDEs. Unlike PBDEs, dust TDCIPP and TPHP levels were not associated with hand wipes. However, hand wipe levels were associated with urinary metabolites. Participants with the highest hand wipe TPHP mass, for instance, had DPHP levels 2.42 times those of participants with the lowest levels (95% CI: 1.23, 4.77). Women had higher levels of DPHP, but not BDCIPP. BDCIPP and DPHP concentrations were moderately to strongly reliable over 5 consecutive days (intraclass correlation coefficients of 0.81 and 0.51, respectively). PFR exposures are widespread, and hand-to-mouth contact or dermal absorption may be important pathways of exposure.

Background: Organophosphate (OP) compounds, such as tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and triphenyl phosphate (TPP), are commonly used as additive flame retardants and plasticizers in a wide range of materials. Although widespread human exposure to OP flame retardants is likely, there is a lack of human and animal data on potential health effects. Objective: We explored relationships of TDCPP and TPP concentrations in house dust with hormone levels and semen quality parameters. Methods: We analyzed house dust from 50 men recruited through a U.S. infertility clinic for TDCPP and TPP. Relationships with reproductive and thyroid hormone levels, as well as semen quality parameters, were assessed using crude and multivariable linear regression. Results: TDCPP and TPP were detected in 96% and 98% of samples, respectively, with widely varying concentrations up to 1.8 mg/g. In models adjusted for age and body mass index, an inter-quartile range (IQR) increase in TDCPP was associated with a 3% [95% confidence interval (CI), -5% to -1%) decline in free thyroxine and a 17% (95% CI, 4-32%) increase in prolactin. There was a suggestive inverse association between TDCPP and free androgen index that became less evident in adjusted models. In the adjusted models, an IQR increase in TPP was associated with a 10% (95% CI, 2-19%) increase in prolactin and a 19% (95% CI, -30% to -5%) decrease in sperm concentration. Conclusion: OP flame retardants may be associated with altered hormone levels and decreased semen quality in men. More research on sources and levels of human exposure to OP flame retardants and associated health outcomes are needed.

Perfluorooctanoic acid (PFOA) is a poly- and perfluoroalkyl substance (PFAS) associated with adverse pregnancy outcomes in mice and humans, but little is known regarding one of its replacements, hexafluoropropylene oxide dimer acid (HFPO-DA, referred to here as GenX), both of which have been reported as contaminants in drinking water. We compared the toxicity of PFOA and GenX in pregnant mice and their developing embryo-placenta units, with a specific focus on the placenta as a hypothesized target. Pregnant CD-1 mice were exposed daily to PFOA (0, 1, or ) or GenX (0, 2, or ) via oral gavage from embryonic day (E) 1.5 to 11.5 or 17.5 to evaluate exposure effects on the dam and embryo-placenta unit. Gestational weight gain (GWG), maternal clinical chemistry, maternal liver histopathology, placental histopathology, embryo weight, placental weight, internal chemical dosimetry, and placental thyroid hormone levels were determined. Exposure to GenX or PFOA resulted in increased GWG, with increase in weight most prominent and of shortest latency with GenX exposure. Embryo weight was significantly lower after exposure to PFOA (9.4% decrease relative to controls). Effect sizes were similar for higher doses ( PFOA and GenX) and lower doses ( PFOA and GenX), including higher maternal liver weights, changes in liver histopathology, higher placental weights and embryo-placenta weight ratios, and greater incidence of placental abnormalities relative to controls. Histopathological features in placentas suggested that PFOA and GenX may exhibit divergent mechanisms of toxicity in the embryo-placenta unit, whereas PFOA- and GenX-exposed livers shared a similar constellation of adverse pathological features. Gestational exposure to GenX recapitulated many documented effects of PFOA in CD-1 mice, regardless of its much shorter reported half-life; however, adverse effects toward the placenta appear to have compound-specific signatures. https://doi.org/10.1289/EHP6233.

Background: Polybrominated diphenyl ethers (PBDEs) are chemical additives used as flame retardants in commercial products. PBDEs are bioaccumulative and persistent and have been linked to several adverse health outcomes. Objectives: This study leverages an ongoing pregnancy cohort to measure PBDEs and PBDE metabolites in serum collected from an understudied population of pregnant women late in their third trimester. A secondary objective was to determine whether the PBDEs or their metabolites were associated with maternal thyroid hormones. Methods: One hundred forty pregnant women > 34 weeks into their pregnancy were recruited into this study between 2008 and 2010. Blood samples were collected during a routine prenatal clinic visit. Serum was analyzed for a suite of PBDEs, three phenolic metabolites (i.e., containing an -OH moiety), and five thyroid hormones. Results: PBDEs were detected in all samples and ranged from 3.6 to 694 ng/g lipid. Two hydroxylated BDE congeners (4'-OH-BDE 49 and 6-OH-BDE 47) were detected in > 67% of the samples. BDEs 47, 99, and 100 were significantly and positively associated with free and total thyroxine (T₄) levels and with total triiodothyronine levels above the normal range. Associations between T₄ and PBDEs remained after controlling for smoking status, maternal age, race, gestational age, and parity. Conclusions: PBDEs and OH-BDEs are prevalent in this cohort, and levels are similar to those in the general population. Given their long half-lives, PBDEs may be affecting thyroid regulation throughout pregnancy. Further research is warranted to determine mechanisms through which PBDEs affect thyroid hormone levels in developing fetuses and newborn babies.

Firemaster® 550 (FM 550) is a commercial flame retardant mixture of brominated and organophosphate compounds applied to polyurethane foam used in furniture and baby products. Due to widespread human exposure, and structural similarities with known endocrine disruptors, concerns have been raised regarding possible toxicity. We previously reported evidence of sex specific behavioral effects in rats resulting from developmental exposure. The present study expands upon this prior finding by testing for a greater range of behavioral effects, and measuring the accumulation of FM 550 compounds in placental tissue. Wistar rat dams were orally exposed to FM 550 during gestation (0, 300 or 1000 µg/day; GD 9 – 18) for placental measurements or perinatally (0, 100, 300 or 1000 µg/day; GD 9 – PND 21) to assess activity and anxiety-like behaviors. Placental accumulation was dose dependent, and in some cases sex specific, with the brominated components reaching the highest levels. Behavioral changes were predominantly associated with a loss or reversal of sex differences in activity and anxiety-like behaviors. These findings demonstrate that environmental chemicals may sex-dependently accumulate in the placenta. That sex-biased exposure might translate to sex-specific adverse outcomes such as behavioral deficits is a possibility that merits further investigation.

Background Organophosphate esters (OPEs) are synthetic chemicals used as flame retardants and plasticizers in a variety of goods. Despite ubiquitous human exposures and laboratory evidence that prenatal OPE exposures may disrupt offspring metabolism, perinatal studies of OPE health effects are limited. The objectives of this study were to: 1) Determine predictors and reproducibility of urinary OPE biomarker concentrations during pregnancy, and 2) Estimate the relation of prenatal OPE exposures with birth outcomes and cord blood adipokine and insulin concentrations. Methods We analyzed five OPE metabolites in urine samples collected at up to three visits during pregnancy from 90 women enrolled in the ORigins of Child Health And Resilience in Development (ORCHARD) pregnancy cohort in Baltimore, MD from 2017 to 2019. To quantify the variability of metabolite concentrations during pregnancy, we calculated intraclass correlation coefficients (ICCs) for each metabolite using mixed effects regression models. Using self-reported questionnaire data collected during gestation, we assessed possible sociodemographic and environmental/behavioral predictors of each OPE metabolite using generalized estimating equations to account for repeated exposure measures. We ascertained birth outcomes of 76 offspring from medical records, including weight-for-gestational age, length, ponderal index, and gestational age. In a subset of 37 infants, we measured cord blood concentrations of leptin, adiponectin, and insulin. To account for repeated exposure measures, we used linear structural equation models to assess the relations of standard deviation (SD) increases in prenatal OPE metabolite factor scores with continuous birth outcomes and cord blood biomarker concentrations. Results ICCs ranged from 0.09 for isopropylphenyl-phenyl phosphate (ip-PPP) to 0.59 for bis(1,3-dichloro-2-propyl) phosphate (BDCIPP). We observed little consistency in environmental or behavioral predictors of OPE exposures, although concentrations were generally lower for samples collected in the afternoon compared to morning and winter compared to other seasons. In adjusted analyses, a SD increase in BDCIPP concentration was associated with a 0.06 g/cm 3 (95% CI: 0.00, 0.12) greater ponderal index. A SD increase in BDCIPP was associated with a 0.37 (95% CI: − 0.62, − 0.13) SD lower insulin concentration and 0.24 (95% CI: − 0.39, − 0.08) SD lower leptin concentration. Other OPEs were not associated with infant outcomes. Conclusions These findings suggest some OPEs may be metabolic disruptors warranting investigation in larger studies.

Photolytic degradation of decabromodiphenyl ether (BDE 209) has been observed in several matrices such as solvent/water mixtures, sediments, and soil; however, no studies have investigated the degradation potential of BDE 209 in house dust. In the present study, both a natural and a BDE 209–spiked dust material were exposed to sunlight for 200 cumulative h. Degradation of BDE 209 was observed in both matrices but was 35% greater in the spiked dust relative to the natural dust material. The pseudo‐first‐order degradation rates were 2.3 × 10−3 and 1.7 × 10−3 per hour for the spiked and natural dust, respectively. During the 200‐h exposure, as much as 38% of the original BDE 209 mass was degraded in the spiked dust, 25% of which could not be accounted for and was lost to unknown pathways and/or products. The remaining 13% was accounted for by the formation of lower brominated congeners. Debrominated products detected in the spiked dust included all three nonabrominated congeners (BDE 206, BDE 207, and BDE 208) and several octabrominated congeners (BDE 196, BDE 197, BDE 201, BDE 202, and BDE 203/200). In technical commercial octa‐BDE mixtures, BDE 201 is a very small component (below detection limit to 0.8%), and BDE 202 is not detected. Therefore, the presence of these congeners in house dust may provide a marker of environmental debromination of BDE 209. The ratio of BDE 197 to BDE 201 may also be indicative of BDE 209 degradation. as the ratio of these two congeners appeared to reach a steady‐state value (∼1) in both exposure scenarios in the present study.

Thyroid hormones are essential hormones for regulating growth and development in humans and wildlife. Methods to monitor precise and low levels of these hormones in serum and tissues are needed to assess overall health, whether from disease considerations or possibly from environmental contaminant exposures. Common and routine methods typically rely upon radioimmunoassays, which can be expensive, and typically only measure thyroxine and 3,3′,5-triidothyronine, which can be a limitation in fully evaluating impacts on thyroid regulation. In this study we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous analysis of five thyroid hormones—thyroxine, 3,3′,5-triidothyronine, 3,3′,5′-triiodothyronine, 3,3′-diiodothyronine, and 3,5-diiodothyronine—in serum samples. The LC-MS/MS parameters were optimized and calibrated over a wide concentration range (1.0-500 ng/mL) with on-column detection limits of 1.5-7.0 pg. With use of spiked bovine serum samples, the mean method recoveries were calculated to be 81.3-111.9% with relative standard deviations of 1.2-9.6% at spiking levels ranging from 10 to 100 ng/mL. This method was compared with measurements made by standard radioimmunoassays and with measurements made in a serum Standard Reference Material (SRM 1951b). Development of this method expands the capacity to measure thyroid hormones by including a larger suite of thyroid hormones, and has promising applications for measuring catabolism of thyroid hormones in vitro.