Photodegradation of the novel brominated flame retardant 2,4,6-Tris-(2,4,6-tribromophenoxy)-1,3,5-triazine in solvent system: Kinetics, photolysis products and pathway

Degradation processes of brominated flame retardants dispersed in high impact polystyrene under UV-visible radiation

In order to protect human health and the environment, several regulations have been introduced in recent years to reduce or even eliminate the use of some brominated flame retardants (BFRs) due to their toxicity, persistence and bioaccumulation. Dispersions of these BFRs in polymers are widely used for various applications. In this report, four different brominated molecules, decabromodiphenyl ether (DBDE), hexabromocyclododecane (HBCDD), decabromodiphenyl ethane (DBDPE) and tris(tribromophenoxy)triazine (TTBPT), were dispersed in the solid matrix of an industrial polymer, high impact polystyrene (HIPS). The possibility of degradation of these BFRs within HIPS under UV-visible irradiation in ambient air was investigated. The degradation kinetics of DBDE and HBCDD were followed by Fourier transform infrared spectroscopy (FTIR) and high-resolution two-step laser mass spectrometry (L2MS). The thermal properties of the pristine and irradiated polymer matrix were monitored by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which showed that these properties were globally preserved. Volatile photoproducts from the degradation of DBDE, DBDPE and TTBPT were identified by headspace gas chromatography/mass spectrometry analysis. Under the chosen experimental conditions, BFRs underwent rapid degradation after a few seconds of irradiation, with conversions exceeding 50% for HIPS/DBDE and HIPS/HBCDD systems.

Investigating the debrominations of a subset of brominated flame retardants by biogenic reactive sulfur species

Brominated flame retardants (BFRs) are persistent organic pollutants. Many bacteria are able to debrominate BFRs, but the underlying mechanism is unclear. Herein, we discovered that reactive sulfur species (RSS), which have strong reductive activity and are commonly present in bacteria, might be one of the reasons leading to such ability. Experiments performed with RSS (H₂S and HSSH) and BFRs indicated that RSS can debrominate BFRs via two different mechanisms simultaneously: the substitutive debromination that generates thiol-BFRs and the reductive debromination that generates hydrogenated BFRs. Debromination reactions rapidly happened under neutral pH and ambient temperature, and the debromination degree was around 30% - 55% in one hour. Two Pseudomonas strains, Pseudomonas sp. C27 and Pseudomonas putida B6-2 both produced extracellular RSS and showed debromination activity. C27 debrominated HBCD, TBECH, and TBP by 5.4%, 17.7%, and 15.9% in two days. Whereas, B6-2 debrominated the three BFRs by 0.4%, 0.6%, and 0.3% in two days. The two bacteria produced different amounts and species of RSS, which were likely responsible for the contrasted degrees of the debromination. Our finding unveiled a novel, non-enzymatic debromination mechanism that many bacteria may possess. RSS producing bacteria have potentials to contribute to bioremediation of BFRs-polluted environments.

Biotransformation of 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ) can contribute to high levels of 2,4,6-tribromophenol (2,4,6-TBP) in humans

2,4,6-Tribromophenol (2,4,6-TBP) is a brominated flame retardant that accumulates in human tissues and is a potential toxicant. Previous studies found 2,4,6-TBP levels in human tissues were significantly higher than those of brominated flame retardants measured in the same samples. In contrast, the levels of 2,4,6-TBP in the environment and foodstuff are not elevated, suggesting a low potential for direct intake through environmental exposure or diet. Here, we hypothesized that high levels of 2,4,6-TBP in human tissues are partially from the indirect exposure sources, such as biotransformation of highly brominated substances. We conducted in vitro assays utilizing human and rat liver microsomes to compare the biotransformation rates of four highly brominated flame retardants, which could potentially transform to 2,4,6-TBP, including decabromodiphenyl ethane (DBDPE), 2,4,6-tris-(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), and tetrabromobisphenol A (TBBPA). Our results show that TTBP-TAZ rapidly metabolizes in both human and rat liver microsomes with a half-life of 1.1 and 2.2 h, respectively, suggesting that TTBP-TAZ is a potential precursor of 2,4,6-TBP. In contrast, 2,4,6-TBP was not formed as a result of biotransformation of TBBPA, BTBPE, and DBDPE in both human and rat liver microsomes. We applied suspect and target screening to explore the metabolic pathways of TTBP-TAZ and identified 2,4,6-TBP as a major metabolite of TTBP-TAZ accounting for 87% of all formed metabolites. These in vitro results were further tested by an in vivo experiment in which 2,4,6-TBP was detected in the rat blood and liver at concentrations of 270 ± 110 and 50 ± 14 μg/g lipid weight, respectively, after being exposed to 250 mg/kg body weight/day of TTBP-TAZ for a week. The hepatic mRNA expression demonstrated that TTBP-TAZ significantly activates the aryl hydrocarbon receptor (AhR) and promotes fatty degeneration (18 and 28-fold change compared to control, respectively) in rats.

On-line spectroscopic study of brominated flame retardant extraction in supercritical CO2

Removal of brominated flame retardants (BFRs) from polymers before disposal or recycling will alleviate negative environmental effects and ensure safe usage of recycled products. Extraction of BFRs in supercritical CO₂ is appealing but also presents challenges to industries due to limited solubility and lack of kinetic studies. For a more comprehensive evaluation of supercritical extraction potentialities, we (i) developed an on-line pressure apparatus that is compatible with both the FTIR and UV-vis spectrometers to enable kinetic and thermodynamic studies; (ii) studied kinetic extraction involving three conventional and two novel BFRs as well as three typical polymeric matrix. Solubilities were determined using the gravimetric method or X-ray fluorescence. FTIR exhibited a superior applicability compared to UV-vis in the following BFR extraction's time-dependency binary and ternary systems. We observed that faster stirring speed, higher temperature, and finer particle size can accelerate the overall extraction kinetics. In binary systems, it took less than 2 h to achieve equilibrium for each BFR at 60 °C, 25 MPa and 1000 rpm. In the presence of polymeric matrix, slower extraction kinetics were observed due to the occurrence of competitive dissolution and molecular diffusion within the matrix. Mathematical models derived from irreversible desorption and Fick's diffusion laws fitted well with the observed extraction kinetics of BFRs, thus enabling us to identify the rate-determining step. The high solubilization rate coefficients that we measured for BFRs revealed that the dynamic extraction process in up-scaling design could compensate for the low solubility with flowing supercritical CO₂.

Effects of natural organic matter on the photolysis of tetracycline in aquatic environment: Kinetics and mechanism

The residues of tetracycline in environment have raised increasing concern for the deleterious impact on ecological and human health. Natural organic matter (NOM), ubiquitous in natural waters, is unavoidable to encounter tetracycline, which might affect the fate of tetracycline in aquatic environment. In this study, we investigated the effect of natural organic matter (NOM) on the photolytic fate of tetracycline (TC). The photolysis kinetics of TC were evaluated with two representative NOM, tannic acid (TA) and gallic acid (GA). The presence of TA and GA obviously inhibited the removal of TC under UV irradiation with photolysis rate constant at 0.067 h^-1 and 0.071 h^-1, respectively, which were 32.3% and 28.3% less than that without TA and GA (0.099 h^-1). Furthermore, NOM exhibited different impacts on both indirect photolysis and direct photolysis. NOM promoted the formation of hydroxyl radical, induced the generation of triplet-excited state NOM and thus greatly enhanced the indirect photolysis of TC. However, direct photolysis was almost completely inhibited by NOM via inner filter effect and interacting with TC to form ground-state complex with low photoreactive. Moreover, similar intermediates were detected in the presence and absence of NOM, indicating that NOM exhibited limited influence on the degradation pathways of TC. This study reveals the multiple roles of NOM on tetracycline photolysis, contributing to better understand the photolytic fate of antibiotics in natural waters.

Development and validation of a liquid chromatography-mass spectrometry method for simultaneous analysis of triazine-based brominated flame retardants in environmental samples

In the present study, a novel and reliable analytical method was developed and validated for the simultaneous determination of 1,3,5-tris(2,3-dibromopropyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TDBP-TAZTO) and 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ) in environmental samples using high-performance liquid chromatography coupled to a tandem mass spectrometer. Firstly, for optimization of the liquid chromatography separation, mobile phases, oven temperatures, modifiers, and buffers were varied. Afterwards, the extraction efficiency of sediment and fish samples was tested with different techniques (pressurized liquid, solid-liquid, ultrasound-assisted, and Soxhlet extraction). Additionally, cleanup using modified multilayer silica gel (sediment) and gel permeation chromatography as well as Florisil® columns (fish) with several solvent mixtures were performed. The best results were obtained with the pressurized liquid extraction (optimal conditions: extraction solvent 100% toluene, extraction time 20 min, cycles two, extraction temperature 100 °C, and flushing volume 60%) compared to other solvent extraction methods. On the basis of this optimized analytical procedure, the method was validated with satisfactory values of correlation coefficient (R²) between 0.998 and 0.999 for both matrices in the calibration range of 2.0-502.0 μg kg^-1 for TDBP-TAZTO and 16.6-770.6 μg kg^-1 for TTBP-TAZ in sediment samples as well as 4.8-303.5 μg kg^-1 and 47.4-742.5 μg kg^-1 in fish samples (bream), respectively. Mean recoveries (n = 5) were calculated for both analytes with spiked matrices at one concentration level (100 μg kg^-1) between 98 and 114% with intra-day relative standard deviations less than 11%. The inter-day precision (n = 15) was also acceptable for both compounds < 11%. It was found that the limit of detection and limit of quantification were in the range of 0.4-1.3 μg kg^-1 for TDBP-TAZTO and 10-28 μg kg^-1 for TTBP-TAZ in surface sediment samples and 7-25 μg kg^-1 and 22-80 μg kg^-1 in fish samples (bream), respectively. The results indicated that these analytical methods could provide reliable and efficient approaches for quantification of TDBP-TAZTO and TTBP-TAZ in sediment and fish samples. Graphical abstract.