Photolytic Transformation Products of Decabromodiphenyl Ethane (DBDPE)

Hydroxylated transformation products obtained after UV irradiation of the current-use brominated flame retardants hexabromobenzene, pentabromotoluene, and pentabromoethylbenzene

Hexabromobenzene (HBB), pentabromotoluene (PBT), and pentabromoethylbenzene (PBEB) are current-use brominated flame retardants (cuBFRs) which have been repeatedly detected in environmental samples. Since information on hydroxylated transformation products (OH-TPs) was scarcely available, the three polybrominated compounds were UV irradiated for 10 min in benzotrifluoride. Fractionation on silica gel enabled the separate collection and identification of OH-TPs. For more insights, aliquots of the separated OH-TPs were UV irradiated for another 50 min (60 min total UV irradiation time). The present investigation of polar UV irradiation products of HBB, PBT, and PBEB was successful in each case. Altogether, eight bromophenols were detected in the case of HBB (three Br3-, four Br4-, and one Br5-isomer), and nine OH-TPs were observed in the case of PBT/PBEB (six Br3- and three Br4-congeners). In either case, Br➔OH exchange was more relevant than H➔OH exchange. Also, such exchange was most relevant in meta- and ortho-positions. As a further point, and in agreement with other studies, the transformation rate decreased with decreasing degree of bromination. UV irradiation of HBB additionally resulted in the formation of tri- and tetrabrominated dihydroxylated compounds (brominated diphenols) that were subsequently identified. These dihydroxylated transformation products were found to be more stable than OH-TPs.

Effect of adsorption on ferrihydrite on the photoreactivity of dissolved black carbon for photodegradation of sulfadiazine

The selective adsorption of dissolved black carbon (DBC) on inorganic minerals is a widespread geochemical process in the natural environment, which could change the chemical and optical properties of DBC. However, it remains unclear how selective adsorption affects the photoreactivity of DBC for photodegradation of organic pollutants. This paper was the first to investigate the effect of DBC adsorption on ferrihydrite at different Fe/C molar ratios (Fe/C molar ratios of 0, 7.50 and 11.25, and marked as DBC₀, DBC_7.50 and DBC_11.25) on the photoproduction of reactive intermediates generated from DBC and their interaction with sulfadiazine (SD). Results showed that UV absorbance, aromaticity, molecular weight and contents of phenolic antioxidants of DBC were significantly decreased after adsorption on ferrihydrite, and higher decrease was observed at higher Fe/C ratio. Photodegradation kinetics experiments showed that observed photodegradation rate constant of SD (k_obs) increased from 3.99 × 10^-5 s^-1 in DBC₀ to 5.69 × 10^-5 s^-1 in DBC_7.50 while decreased to 3.44 × 10^-5 s^-1 in DBC_11.25, in which ³DBC* played important roles and ¹O₂ played a minor role, while ·OH was not involved in the reaction. Meanwhile, the second-order reaction rate constant between ³DBC* and SD (k_{SD, 3DBC*}) increased from 0.84 × 10⁸ M^-1 s^-1 for DBC₀ to 2.53 × 10⁸ M^-1 s^-1 for DBC_7.50 while decreased to 0.90 × 10⁸ M^-1 s^-1 for DBC_11.25. The above results might be mainly attributed to the fact that the decrease of phenolic antioxidants in DBC weakened the back-reduction of ³DBC* and reactive intermediates of SD as the Fe/C ratio increased, while the decrease of quinones and ketones reduced the photoproduction of ³DBC*. The research revealed adsorption on ferrihydrite affected the photodegradation of SD by changing the reactivity of ³DBC*, which was helpful to understand the dynamic roles of DBC in the photodegradation of organic pollutants.

Assessing the environmental impact due to photolytic degradation of ethane-bis(pentabromophenyl) in plastics

Photolytic degradation of brominated flame retardants is one of the potential decomposition pathways in the environment, and for some flame retardants such as ethane-bis(pentabromophenyl) (EBP), also called decabromodiphenyl ethane, there are concerns that degradation products may be harmful. In this paper, we present photolytic studies of EBP in high-impact polystyrene (HIPS) and polypropylene impact copolymer (PP) using accelerated weatherometry. The half-life of photolytic debromination of EBP in HIPS was estimated to be more than 200 years, which can be contrasted with half-lives of minutes for photolysis conducted on dilute EBP solutions. Perhaps more importantly, there was no subsequent debromination to the octabrominated congeners or lower. No evidence of debromination was seen in PP, which confirms the importance of matrix effects. We also saw no evidence of accelerated resin photooxidation caused by EBP. These studies demonstrate that EBP is much more photolytically stable in resins than structurally-similar decabromodiphenyl ether, and a read-across comparison between the two flame retardant molecules for this degradation pathway is misleading.

Fat mass and obesity-associated gene (FTO) hypermethylation induced by decabromodiphenyl ethane causing cardiac dysfunction via glucolipid metabolism disorder

Decabromodiphenyl ethane (DBDPE) is a major alternative to BDE-209 owing to its lower toxicity. However, the mass production and increased consumption of DBDPE in recent years have raised concerns related to its adverse health effects. However, the effect and mechanism of DBDPE on cardiotoxicity have rarely been studied. In the present study, we investigated the impacts of DBDPE on the cardiovascular system in male SD rats and then explored the underlying mechanisms to explain the cardiotoxicity of DBDPE using AC16 cells. Under in vivo conditions, male rats were administered with an oral dosage of DBDPE at 0, 5, 50, and 500 mg/kg/day for 28 days, respectively. Histopathological analysis demonstrated that DBDPE induced cardiomyocyte injury and fibrosis, and ultrastructural observation revealed that DBDPE could induce mitochondria damage and dissolution. DBDPE could thus decrease the level of MYH6 and increase the level of SERCA2, which are the two key proteins involved in the maintenance of homeostasis during myocardial contractile and diastolic processes. Furthermore, DBDPE could increase the serum levels of glucose and low-density lipoprotein but decrease the content of high-density lipoprotein. In addition, DBDPE could activate the PI3K/AKT/GLUT2 and PPARγ/RXRα signaling pathways in AC16 cells. In addition, DBDPE decreased the UCP2 level and ATP synthesis in mitochondria both under in vitro and in vivo conditions, consequently leading to apoptosis via the Cytochrome C/Caspase-9/Caspase-3 pathway. Bisulfite sequencing PCR (BSP) identified the hypermethylation status of fat mass and obesity-associated gene (FTO). 5-aza exerted the opposite effects on the PI3K/AKT/GLUT2, PPARγ/RXRα, and Cytochrome C/Caspase-9/Caspase-3 signaling pathways induced by DBDPE in AC16 cells. In addition, the DBDPE-treated altered levels of UCP2, ATP, and apoptosis were also found to be significantly reversed by 5-aza in AC16 cells. These results suggested that FTO hypermethylation played a regulative role in the pathological process of DBDPE-induced glycolipid metabolism disorder, thereby contributing to the dysfunction of myocardial contraction and relaxation through cardiomyocytes fibrosis and apoptosis via the mitochondrial-mediated apoptotic pathway resulting from mitochondrial dysfunction.

Full Characterization of the UV Hydrodebromination Products of the Current-Use Brominated Flame Retardants Hexabromobenzene, Pentabromotoluene, and Pentabromoethylbenzene

UV transformation was studied with three structurally closely related current-use brominated flame retardants (cuBFRs), i.e., hexabromobenzene (HBB), pentabromotoluene (PBT), and pentabromoethylbenzene (PBEB). Irradiation in toluene and benzotrifluoride (BTF) showed pseudo-first-order kinetics. Repeated high-performance liquid chromatographic (HPLC) fractionation, available reference standards, dedicated syntheses, gas chromatography with mass spectrometry (GC/MS), GC separation on two different phases including retention time rules based on dipole interactions, and proton magnetic resonance spectroscopy (¹H NMR) evaluation enabled a full structural characterization of all 22 transformation products formed by hydrodebromination. In addition to pentabromobenzene (only transformation product with five bromine), tetra- and tribrominated transformation products were predominantly formed in the case of all three cuBFRs. Hydrodebromination was favored by bromine removal from positions with a high Br density. Br → H exchange was about 3 times faster in positions flanked by two vicinal Br atoms. This favored pathway explained why hydrodebromination sharply dropped at the level of tribrominated cuBFRs because readily degradable precursors were no more available at this point. Hence, a full degradation of tribrominated and lower-brominated transformation products may only be achieved in combination with a different process such as microbial transformation.

Naturally occurring organobromine compounds (OBCs) including polybrominated dibenzo-p-dioxins in the marine sponge Hyrtios proteus from The Bahamas

Halogenated natural products (HNPs) were identified from organic extracts of the marine sponge Hyrtios proteus from The Bahamas using gas chromatography with electron capture negative ion mass spectrometry and non-targeted gas chromatography with electron ionization mass spectrometry. The HNPs found have similar properties to anthropogenic persistent organic pollutants (POPs). Two ortho-methoxy brominated diphenyl ethers (MeO-BDEs) 2'-MeO-BDE 68 and 6-MeO-BDE 47 were the most abundant compounds. Fourteen other MeO-BDEs were detected along with several polybrominated dibenzo-p-dioxins (PBDDs) (1,3,7-triBDD, 1,3,6,8-tetraBDD and 1,3,7,9-tetraBDD) and MeO-PBDDs. Further analysis of a higher trophic level octopus (Octopus maya) from the same FAO fishing area showed that the major HNPs detected in Hyrtios proteus were also predominant. Moreover, HNPs were more than 30-fold higher in abundance than the major POPs in the octopus, i.e., polychlorinated biphenyls. Hence, Caribbean marine organisms, including those potentially used for food, harbor relatively high concentrations of HNPs.

Mechanism of bicarbonate enhancing the photodegradation of β-blockers in natural waters

The impact of HCO₃^- on the photodegradation of β-blockers was investigated under simulated sunlight irradiation. The results show that in the presence of HCO₃^-, the photodegradation rates increase significantly for sotalol (SOT), whereas no effects on the degradation of carvedilol and arotinolol are observed. Using quenching experiments, electron paramagnetic resonance spectra and degradation product determination, we demonstrate that carbonate radical (CO₃^•-) is formed by direct oxidation of HCO₃^- by triplet-excited SOT (³SOT*) and plays a significant role in SOT photodegradation. Competition kinetics experiments show that the three β-blockers all have high second-order rate constants (10⁷-10⁸ M^-1 s^-1) for the reaction with CO₃^•-. However, only ³SOT* has a higher reduction potential that can oxidize HCO₃^- to produce CO₃^•-. Thus, enhanced SOT removal rates in the presence of HCO₃^- were observed. In addition, the results show that seawater DOM could increase HCO₃^--induced photodegradation of SOT, whereas SRNOM mainly behaves as a CO₃^•- quencher and decreases the removal rate of SOT. The results underscore the role of HCO₃^- in limiting the persistence of organic pollutants like SOT in sunlit natural waters, and especially in marine and coastal waters.

Advances in high resolution GC-MS technology: a focus on the application of GC-Orbitrap-MS in metabolomics and exposomics for FAIR practices

Gas chromatography-mass spectrometry (GC-MS) provides a complementary analytical platform for capturing volatiles, non-polar and (derivatized) polar metabolites and exposures from a diverse array of matrixes. High resolution (HR) GC-MS as a data generation platform can capture data on analytes that are usually not detectable/quantifiable in liquid chromatography mass-spectrometry-based solutions. With the rise of high-resolution accurate mass (HRAM) GC-MS systems such as GC-Orbitrap-MS in the last decade after the time-of-flight (ToF) renaissance, numerous applications have been found in the fields of metabolomics and exposomics. In a short span of time, a multitude of studies have used GC-Orbitrap-MS to generate exciting new high throughput data spanning from diverse basic to applied research areas. The GC-Orbitrap-MS has found application in both targeted and untargeted efforts for capturing metabolomes and exposomes across diverse studies. In this review, I capture and summarize all the reported studies to date, and provide a snapshot of the milieu of commercial and open-source software solutions, spectral libraries, and informatics solutions available to a GC-Orbitrap-MS system instrument user or a data analyst dealing with these datasets. Lastly, but importantly, I provide an account on data sharing and meta-data capturing solutions that are available to make HRAM GC-MS based metabolomics and exposomics studies findable, accessible, interoperable, and reproducible (FAIR). These FAIR practices would allow data generators and users of GC-HRMS instruments to help the community of GC-MS researchers to collaborate and co-develop exciting tools and algorithms in the future.

NLRP3 inflammasome-mediated endothelial cells pyroptosis is involved in decabromodiphenyl ethane-induced vascular endothelial injury

Decabromodiphenyl ethane (DBDPE) is a novel environmental pollutant that has attracted growing attention. Previous studies have indicated that DBDPE could induce vascular endothelial injury and cardiovascular damage, but the underlying mechanisms are not well understood. This study was designed to examine the mechanisms of DBDPE induces vascular endothelial injury. In vivo, Sprague-Dawley rats were administered with 0, 5, 50, 500 mg/kg bw/day of DBDPE via gavage for 28 days. Results showed that DBDPE could damage abdominal aortas morphological and ultrastructural structure and increase the protein levels of interleukin 1β (IL-1β) and interleukin 18 (IL-18) of the abdominal aortas. Moreover, DBDPE induced NLRP3 inflammasome activation and activated caspase-1 in abdominal aorta endothelium of rats. In vitro, human vascular endothelial cells (HAECs) were treated with different concentrations of DBDPE (0, 6.25, 12.5, 25, 50, and 100 μM). DBDPE not only induced cytotoxicity and reactive oxygen species (ROS) generation in HAECs but also caused HAECs pyroptosis, which was evidenced by the elevated expression of Nod-like receptor protein -3 (NLRP3), ASC, and caspase-1 in DBDPE-treated group. To further elucidate the effects of NLRP3 inflammasome on DBDPE-induced HAECs pyroptosis, we constructed NLRP3 knockdown HAECs by lentivirus-mediated short hairpin RNA (shRNA). And the results showed that NLRP3 knockdown downregulated DBDPE-induced increases of caspase-1 activity and caspase-1, ASC and NLRP3 mRNA and protein expression levels. Accordingly, our data suggested that DBDPE may damage vascular endothelium by NLRP3 inflammasome-mediated endothelial cells pyroptosis.

Combining In Silico Tools with Multicriteria Analysis for Alternatives Assessment of Hazardous Chemicals: Accounting for the Transformation Products of decaBDE and Its Alternatives

Transformation products ought to be an important consideration in chemical alternatives assessment. In this study, a recently established hazard ranking tool for alternatives assessment based on in silico data and multicriteria decision analysis (MCDA) methods was further developed to include chemical transformation products. Decabromodiphenyl ether (decaBDE) and five proposed alternatives were selected as case chemicals; biotic and abiotic transformation reactions were considered using five in silico tools. A workflow was developed to select transformation products with the highest occurrence potential. The most probable transformation products of the alternative chemicals were often similarly persistent but more mobile in aquatic environments, which implies an increasing exposure potential. When persistence (P), bioaccumulation (B), mobility in the aquatic environment (M), and toxicity (T) are considered (via PBT, PMT, or PBMT composite scoring), all six flame retardants have at least one transformation product that can be considered more hazardous, across diverse MCDA. Even when considering transformation products, the considered alternatives remain less hazardous than decaBDE, though the range of hazard of the five alternatives was reduced. The least hazardous of the considered alternatives were melamine and bis(2-ethylhexyl)-tetrabromophthalate. This developed tool could be integrated within holistic alternatives assessments considering use and life cycle impacts or additionally prioritizing transformation products within (bio)monitoring screening studies.

Photodegradation of 1,3,5-Tris-(2,3-dibromopropyl)-1,3,5-triazine-2,4,6-trione and decabromodiphenyl ethane flame retardants: Kinetics, Main products, and environmental implications

Photodegradation has been demonstrated as one of the important environmental factors affecting the fate of contaminants such as brominated flame retardants (BFRs). However, a number of emerging BFRs, particularly those with high bromine substitution, have rarely been investigated for their photodegradation kinetics. Our study evaluated photodegradation of two highly brominated FRs, 1,3,5-tris-(2,3-dibromopropyl)-1,3,5-triazine-2,4,6-trione (TDBP-TAZTO) and decabromodiphenyl ethane (DBDPE), under various conditions. The results indicated that the degradation kinetics was affected by UV irradiation wavelength, intensity, solvent type, as well as the structural characteristics. TDBP-TAZTO exhibited degradation half-lives (t_1/2) of 23.5-6931 min under various UV irradiation conditions and 91.2 days under natural sunlight. Its degradation was much slower than that of DBDPE which exhibited t_1/2 of 0.8-101.9 min under UV and 41.3 min under natural sunlight. A variety of degradation products were detected as a result of different breakdown pathways. This indicated that photodegradation could substantially influence the fate of these highly brominated FRs, resulting in a cocktail of degradation products as environmentally occurring contaminants. This could also complicate the evaluation of the ecological risks of these target flame retardants, given that degradation products generally possess physicochemical properties and biological effects different from their parent chemicals.

Photochemical degradation of nebivolol in different natural organic matter solutions under simulated sunlight irradiation: Kinetics, mechanism and degradation pathway

Nebivolol (NEB) is widely used for the treatment of hypertension and chronic heart failure and has become an ubiquitous emerging organic pollutant. It has been shown to undergo direct photolysis, but the role of DOM in its degradation kinetics and mechanism is not well understood. In this study, we studied the photochemical behavior of NEB in the presence of seawater DOM (SW-DOM) and freshwater DOM (SRNOM) under simulated sunlight irradiation. SW-DOM had a promotion effect on NEB photodegradation, whereas SRNOM retarded its photolytic transformation. After eliminating the influence of light screening, we found that the indirect photodegradation rate of NEB in the presence of SRNOM was lower than that in the presence of SW-DOM. Results show that the indirect photodegradation pathway occurred by reaction with triplet-excited DOM (³DOM*). The second-order rate constants for ³SW-DOM* and ³SRNOM* reaction with NEB are 3.7 × 10⁹ M^-1 s^-1 and 3.7 × 10⁸ M^-1 s^-1, respectively. The electron donating capacity of SRNOM is higher than that of SW-DOM, indicating that SRNOM may contain more activated phenolic moieties. SRNOM may thus have higher antioxidant activity, leading a higher inhibitory effect on NEB photodegradation. A total of six degradation products were identified in the absence and presence of DOM by HPLC-ESI-MS/MS. The substitution of F by OH-groups and further oxidation a OH-group in the lateral chain to a ketone, and cleavage of N-C bond by the attack of ³DOM* are here proposed as the main degradation pathways.