Release and Transformation of BTBPE During the Thermal Treatment of Flame Retardant ABS Plastics

Effects of 1, 2-bis (2,4, 6-tribromophenoxy) ethane and bis (2-ethylhexyl) tetrabromophthalate on serum metabolic and lipid profiles in male rats

This study explored the effects of 1, 2-bis (2,4, 6-tribromophenoxy) ethane (BTBPE) and bis (2-ethylhexyl) tetrabromophthalate (TBPH) on serum metabolites and lipids in male Sprague-Dawley (SD) rats. Rats were orally gavaged 250 mg/kg bw of BTBPE and 500 mg/kg bw of TBPH for 28 consecutive days. Serum samples were collected for metabolomics and lipidomics analysis. Orthogonal partial least squares discriminant analysis (OPLS-DA) was used to explore changes in rat metabolic patterns. Least absolute shrinkage and selection operator (LASSO) regression models were established using serum levels of total thyroxine (TT4), free thyroxine (FT4), and rats' grouping information as variables to screen for robust differential substances. SuperPred was the database to obtain potential targets. The metabolomics and lipidomics results showed that BTBPE and TBPH had an impact on rat metabolic patterns, affecting pathways such as vitamin B6 synthesis. For BTBPE treatment, pyridoxal and ceramide (Cer) 24:0;4O were selected as differential substances related to thyroid hormones. For TBPH treatment, dehydroascorbic acid, acylcarnitine (CAR) 19:0, and diglyceride (DG) 38:4 were selected as differential substances related to thyroid hormones. Serotonin 2c receptor and cyclooxygenase-2 were chosen as potential targets of BTBPE and TBPH, respectively. In conclusion, this study found that BTBPE and TBPH impacted the metabolism of rats, and this effect may be related to changes in thyroid function.

Plastic breath: Quantification of microplastics and polymer additives in airborne particles

The widespread extensive use of synthetic polymers has led to a substantial environmental crisis caused by plastic pollution, with microplastics detected in various environments and posing risks to both human health and ecosystems. The possibility of plastic fragments to be dispersed in the air as particles and inhaled by humans may cause damage to the respiratory and other body systems. Therefore, there is a particular need to study microplastics as air pollutants. In this study, we tested a combination of analytical pyrolysis, gas chromatography-mass spectrometry, and gas and liquid chromatography-mass spectrometry to identify and quantify both microplastics and their additives in airborne particulate matter and settled dust within a workplace environment: a WEEE treatment plant. Using this combined approach, we were able to accurately quantify ten synthetic polymers and eight classes of polymer additives. The identified additives include phthalates, adipates, citrates, sebacates, trimellitates, benzoates, organophosphates, and newly developed brominated flame retardants.

Mechanistic Insights into 1,2-bis(2,4,6-tribromophenoxy)ethane-Induced Male Reproductive Toxicity in Zebrafish

The novel brominated flame retardant, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), has increasingly been detected in environmental and biota samples. However, limited information is available regarding its toxicity, especially at environmentally relevant concentrations. In the present study, adult male zebrafish were exposed to varying concentrations of BTBPE (0, 0.01, 0.1, 1, and 10 μg/L) for 28 days. The results demonstrated underperformance in mating behavior and reproductive success of male zebrafish when paired with unexposed females. Additionally, a decline in sperm quality was confirmed in BTBPE-exposed male zebrafish, characterized by decreased total motility, decreased progressive motility, and increased morphological malformations. To elucidate the underlying mechanism, an integrated proteomic and phosphoproteomic analysis was performed, revealing a predominant impact on mitochondrial functions at the protein level and a universal response across different cellular compartments at the phosphorylation level. Ultrastructural damage, increased expression of apoptosis-inducing factor, and disordered respiratory chain confirmed the involvement of mitochondrial impairment in zebrafish testes. These findings not only provide valuable insights for future evaluations of the potential risks posed by BTBPE and similar chemicals but also underscore the need for further research into the impact of mitochondrial dysfunction on reproductive health.

The effects and mechanisms of the new brominated flame retardant BTBPE on thyroid toxicity

As an alternative to octabromodiphenyl ether (octa-BDE), 1, 2-bis (2,4, 6-tribromophenoxy) ethane (BTBPE) has been widely used in a variety of combustible materials, such as plastics, textiles and furniture. Previous studies have demonstrated the thyroid toxicity of traditional brominated flame retardants for example octa-BDE clearly. Nevertheless, little is known about the thyroid toxicity of alternative novel brominated flame retardants BTBPE. In this study, it was demonstrated that BTBPE in vivo exposure induced FT4 reduction in 2.5, 25 and 250 mg/kg bw treated group and TT4 reduction in 25 mg/kg bw treated group. TG, TPO and NIS are key proteins of thyroid hormone synthesis. The results of Western blot and RT-PCR from thyroid tissue showed decreased protein levels and gene expression levels of TG, TPO and NIS as well as regulatory proteins PAX8 and TTF2. To investigate whether the effect also occurred in humans, anthropogenic Nthy-ori 3-1 cells were selected. Similar results were seen in vitro condition. 2.5 mg/L BTBPE reduced the protein levels of PAX8, TTF1 and TTF2, which in turn inhibited the protein levels of TG and NIS. The results in vitro experiment were consistent with that in vivo, suggesting possible thyrotoxic effects of BTBPE on humans. It was indicated that BTBPE had the potential interference of T4 generation and the study provided more evidence of the effects on endocrine disorders.

Mechanistic characterization of anaerobic microbial degradation of BTBPE in coastal wetland soils: Implication by compound-specific stable isotope analysis

As a novel brominate flame retardants, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) has been extensively used in various consumer products, and frequently detected in various environmental matrices. However, the microbial degradation of BTBPE remains unclear in the environment. This study comprehensively investigated the anaerobic microbial degradation of BTBPE and therein stable carbon isotope effect in the wetland soils. BTBPE degradation followed the pseudo-first-order kinetic, with degradation rate of 0.0085 ± 0.0008 day^-1. Based on identification of degradation products, stepwise reductive debromination was the main transformation pathway of BTBPE, and tended to keep the stable of 2,4,6-tribromophenoxy group during the microbial degradation. The pronounced carbon isotope fractionation was observed for BTBPE microbial degradation, and carbon isotope enrichment factor (ε_C) was determined to be -4.81 ± 0.37‰, indicating cleavage of C-Br bond as the rate-limiting step. Compared to previously reported isotope effects, carbon apparent kinetic isotope effect (AKIE_C = 1.072 ± 0.004) suggested that the nucleophilic substitution (S_N2 reaction) was the potential reaction mechanism for reductive debromination of BTBPE in the anaerobic microbial degradation. These findings demonstrated that BTBPE could be degraded by the anaerobic microbes in wetland soils, and the compound-specific stable isotope analysis was a robust method to discover the underlying reaction mechanisms.

Health Risks Posed by Dermal and Inhalation Exposure to High Concentrations of Chlorinated Paraffins Found in Soft Poly(vinyl chloride) Curtains

Chlorinated paraffins (CPs) are used in many products, including soft poly(vinyl chloride) curtains, which are used in many indoor environments. Health hazards posed by CPs in curtains are poorly understood. Here, chamber tests and an indoor fugacity model were used to predict CP emissions from soft poly(vinyl chloride) curtains, and dermal uptake through direct contact was assessed using surface wipes. Short-chain and medium-chain CPs accounted for 30% by weight of the curtains. Evaporation drives CP migration, like for other semivolatile organic plasticizers, at room temperature. The CP emission rate to air was 7.09 ng/(cm² h), and the estimated short-chain and medium-chain CP concentrations were 583 and 95.3 ng/m³ in indoor air 21.2 and 172 μg/g in dust, respectively. Curtains could be important indoor sources of CPs to dust and air. The calculated total daily CP intakes from air and dust were 165 ng/(kg day) for an adult and 514 ng/(kg day) for a toddler, and an assessment of dermal intake through direct contact indicated that touching just once could increase intake by 274 μg. The results indicated that curtains, which are common in houses, could pose considerable health risks through inhalation of and dermal contact with CPs.

Mechanism and characterization of microplastic aging process: A review

With the increasing production of petroleum-based plastics, the problem of environmental pollution caused by plastics has aroused widespread concern. Microplastics, which are formed by the fragmentation of macro plastics, are bio-accumulate easily due to their small size and slow degradation under natural conditions. The aging of plastics is an inevitable process for their degradation and enhancement of adsorption performance toward pollutants due to a series of changes in their physiochemical properties, which significantly increase the toxicity and harm of plastics. Therefore, studies should focus on the aging process of microplastics through reasonable characterization methods to promote the aging process and prevent white pollution. This review summarizes the latest progress in natural aging process and characterization methods to determine the natural aging mechanism of microplastics. In addition, recent advances in the artificial aging of microplastic pollutants are reviewed. The degradation status and by-products of biodegradable plastics in the natural environment and whether they can truly solve the plastic pollution problem have been discussed. Findings from the literature pointed out that the aging process of microplastics lacks professional and exclusive characterization methods, which include qualitative and quantitative analyses. To lessen the toxicity of microplastics in the environment, future research directions have been suggested based on existing problems in the current research. This review could provide a systematic reference for in-depth exploration of the aging mechanism and behavior of microplastics in natural and artificial systems.

Framework of the Integrated Approach to Formation Mechanisms of Typical Combustion Byproducts─Polyhalogenated Dibenzo-p-dioxins/Dibenzofurans (PXDD/Fs)

Understanding the mechanisms through which persistent organic pollutants (POPs) form during combustion processes is critical for controlling emissions of POPs, but the mechanisms through which most POPs form are poorly understood. Polyhalogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs) are typical toxic POPs, and the formation mechanisms of PXDD/Fs are better understood than the mechanisms through which other POPs form. In this study, a framework for identifying detailed PXDD/Fs formation mechanisms was developed and reviewed. The latest laboratory studies in which organic free radical intermediates of PXDD/Fs have been detected in situ and isotope labeling methods have been used to trace transformation pathways were reviewed. These studies provided direct evidence for PXDD/Fs formation pathways. Quantum chemical calculations were performed to determine the rationality of proposed PXDD/Fs formation pathways involving different elementary reactions. Many field studies have been performed, and the PXDD/Fs congener patterns found were compared with PXDD/Fs congener patterns obtained in laboratory simulation studies and theoretical studies to mutually verify the dominant PXDD/Fs formation mechanisms. The integrated method involving laboratory simulation studies, theoretical calculations, and field studies described and reviewed here can be used to clarify the mechanisms involved in PXDD/Fs formation. This review brings together information about PXDD/Fs formation mechanisms and provides a methodological framework for investigating PXDD/Fs and other POPs formation mechanisms during combustion processes, which will help in the development of strategies for controlling POPs emissions.

Mixed bromine/chlorine transformation products of tetrabromobisphenol A formed in the combustion of printed circuit boards: Emission characteristics and transformation pathways

Recently, mixed bromine/chlorine transformation products of tetrabromobisphenol A (Cl_yBr_xBPAs) were found to be possibly related to the thermal treatment processes of electronic wastes. To explore their emission characteristics and formation mechanism, printed circuit board scraps were combusted in a tube furnace, under the temperature from 25 °C to 600 °C. The emission factor of the debromination products of tetrabromobisphenol A (Br_xBPAs) was the highest, whereas that of Cl_yBr_xBPAs was the lowest. Among three phases, most of the target compounds were partitioned into the oil and particle phases, and only negligible gaseous 2-BrBPA and bisphenol A were detected. The emission rates of most compounds were fastest at 300 °C, although 2-BrBPA, 2,6-Br₂BPA, and 2-Cl-6-BrBPA peaked at 350 °C. Among the chemicals in total emission, 2-BrBPA was the dominant congener in Br_xBPAs, whereas 2-Cl-2',6,6'-Br₃BPA, 2-Cl-2',6^#-Br₂BPA, and Σ₂Cl₁Br₁BPAs shared similar proportions in Cl_yBr_xBPAs. Meanwhile, the composition profiles at 300 °C showed that 2,2',6-Br₃BPA and 2-Cl-2',6,6'-Br₃BPA occupied the largest proportions in Br_xBPAs and Cl_yBr_xBPAs, respectively. To reveal the possible transformation pathways, the Gibbs free energy was calculated based on a radical substitution reaction. After "•Br" removal from tetrabromobisphenol A or other Br_xBPAs, the intermediate was more easily combined with "•H" than with "•Cl." In addition, the Cl_yBr_xBPA formation via "-•H + •Cl" by Br_xBPAs is nonspontaneous, thus limiting the further generation of Cl_yBr_xBPAs. This study not only provides ideas for the study of other mixed halogenated products, but also provides constructive suggestions for environmental source analysis by combining previous research on the occurrence of Cl_yBr_xBPAs in various environmental matrices.

Nano/microplastics: Fragmentation, interaction with co-existing pollutants and their removal from wastewater using membrane processes

NANO: and microplastic (NP/MP) is one of the most challenging types of micropollutants, coming from either direct release or degradation of plastic items into ecosystems. NP/MP can adsorb hazardous pollutants (such as heavy metals and pharmaceutical compounds) and pathogens onto their surface that are consumed by humans, animals, and aquatic living organisms. This paper presents the interaction of NP/MP with other pollutants in the water environment and mechanisms involved to enable the ultimate fate of NP/MP as well as the effectiveness of metal-organic frame (MOF)-based membrane over conventional membrane processes for NP/MP removal. It is found that conventional membranes could remove MPs when their size is usually more than 1000 nm, but they are ineffective in removing NPs. These NPs have potentially greater health impacts due to their greater surface area. MOF-based membrane could effectively remove both NP and MP due to its large porous structure, high adsorption capacity, and low density. This paper also discusses some challenges associated with MOF-based membranes for NP/MP removal. Finally, we conclude a specific MOF-based ultrafiltration membrane (ED-MIL-101 (Cr)) that can potentially remove both negative and positive charged NP/MP from wastewater by electrostatic attraction and repulsion force with efficient water permeability.

An updated review on environmental occurrence, scientific assessment and removal of brominated flame retardants by engineered nanomaterials

Due to the extensive manufacturing and use of brominated flame retardants (BFRs), they are known to be hazardous, bioaccumulative, and recalcitrant pollutants in various environmental matrices. BFRs make flame-resistant items for industrial purposes (textiles, electronics, and plastics equipment) that are disposed of in massive amounts and leak off in various environmental matrices. The consumption of plastic items has expanded tremendously during the COVID-19 pandemic which has resulted into the increasing load of solid waste on land and water. Some BFRs, such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDs), are no longer utilized or manufactured owing to their negative impacts, which promotes the utilization of new BFRs as alternatives. BFRs have been discovered worldwide in soil, sludge, water, and other contamination sources. Various approaches such as photocatalysis-based oxidation/reduction, adsorption, and heat treatment have been found to eradicate BFRs from the environment. Nanomaterials with unique properties are one of the most successful methodologies for removing BFRs via photocatalysis. These methods have been praised for being low-cost, quick, and highly efficient. Engineered nanoparticles degraded BFRs when exposed to light and either convert them into safer metabolites or completely mineralize. Scientific assessment of research taking place in this area during the past five years has been discussed. This review offers comprehensive details on environmental occurrence, toxicity, and removal of BFRs from various sources. Degradation pathways and different removal strategies related to data have also been presented. An attempt has also been made to highlight the research gaps prevailing in the current research area.

Bromination mechanisms of aromatic pollutants: formation of Br2 and bromine transfer from metallic oxybromides

Bromination mechanisms of aromatic pollutants assume a chief contribution in the observed yields and pattern's distribution of a wide array of dioxin-like toxicants. However, salient features of the governing pathways remain largely speculative. This study presents detail mechanistic insights into two commonly discussed routes; namely: surface-assisted conversion of HBr into Br₂ and direct bromine transfer from oxybromides into a benzene ring. Utilizing iron surfaces, as structural representative of the metallic content in electronic wastes, results from density functional theory calculations portray accessible reactions into the successive dissociative adsorption of HBr over the Fe(100) surface and the subsequent evolution of gas phase bromine molecules. Activation energies for HBr uptake by the plain iron surface reside in the range of 129-182 kJ/mol. Over an oxygen pre-covered surface, dissociative adsorption of HBr leading to bromine molecules requires significantly lower activation energies (45-78 kJ/mol). Likewise, bromination of a benzene ring into a monobromobenzene molecule over Fe(100)_O*Br* (i.e., an oxybromide) configuration ensues with an opening activation energy of ~ 165 kJ/mol. Adsorption of a phenyl radical over an iron-oxybromide forms a phenolate moiety that subsequently desorbs from the surface into a phenoxy radical. Reaction pathways presented herein shall be useful in the ongoing efforts to comprehend the formation and bromination routes of the notorious bromine-bearing pollutants in real scenarios, such as, these encountered in the open burning and primitive thermal recycling of electronic wastes.

Mixed bromine/chlorine transformation products of tetrabromobisphenol A: Potential specific molecular markers in e-waste dismantling areas

Mixed bromine/chlorine transformation products (Cl_yBr_xBPAs) of tetrabromobisphenol A (TBBPA) were recently identified for the first time in an electronic waste (e-waste) dismantling site. To determine whether these compounds can be used as specific molecular markers of e-waste dismantling activities, the environmental occurrences and distributions of TBBPA and its transformation products including debromination products (Br_xBPAs) and Cl_yBr_xBPAs were analyzed in soil samples from three sites in China: Guiyu (an e-waste site), Qingyuan (a former e-waste site now mainly used for old wire and cable recycling), and Shouguang (a flame retardant production base). Levels of the target analytes in Guiyu were significantly higher than in Qingyuan and Shouguang. Br_xBPAs and Cl_yBr_xBPAs were widely detected in Guiyu at concentrations between 1 and 4 orders of magnitude lower than their parent compound TBBPA. The highest concentration was found in an e-waste dismantling park, with lower concentrations in surrounding area. The levels of Cl_yBr_xBPAs in Qingyuan were much lower, indicating that the Cl_yBr_xBPAs may come from the processing of wires and cables, but not rule out the incubation on their own in soils. None of Cl_yBr_xBPAs were detected in Shouguang. Cl_yBr_xBPAs may thus be useful as specific molecular markers for determining the intensity of e-waste dismantling activities.

Environmental behaviors of microplastics in aquatic systems: A systematic review on degradation, adsorption, toxicity and biofilm under aging conditions

Microplastics (MPs, < 5 mm) in the environment have attracted worldwide attention due to their wide distribution and difficulty in handling. Aging processes such as UV irradiation, biodegradation, physical abrasion and chemical oxidation can affect the environmental behavior of MPs. This review article summarizes different aging processes of MPs and subsequent effects on the adsorption of pollutants, the leaching of additives, and the toxicity of MPs. In addition, the formation process of biofilm on the surface of MPs and the interactions between biofilm and aged MPs are revealed. MPs can accumulate different environmental pollutants (organic pollutants, heavy metals, microorganisms, etc.) through surface adsorption, pore filling and distribution. Moreover, the aging of MPs affects their adsorption performance toward these pollutants due to a series of changes in their specific surface area and oxygen-containing functional groups. The release of some toxic additives such as phthalates after aging can enhance the toxic effects of MPs. Aging also changes the shape and size of MPs, which can affect the eating habits of the organisms and further increase the potential toxicity of MPs. This article conducts a systematical analysis and summary of the environmental behavior and physicochemical properties of MPs as well as the changes due to MPs aging, which helps to better understand the impact of aging on MPs in the environment. Future research on MPs aging should reduce the knowledge gap between laboratory simulation and actual conditions and increase the environmental relevance.

Environmental characteristics and formations of polybrominated dibenzo-p-dioxins and dibenzofurans

Polybrominated dibenzo-p-dioxins and furans (PBDD/Fs) are emerging persistent organic pollutants (POPs) that have similar or higher toxicities than the notorious dioxins. Toxicities, formation mechanisms, and environmental fates of PBDD/Fs are lacking because accurate quantification, especially of higher brominated congeners, is challenging. PBDD/F analysis is difficult because of photolysis and thermal degradation and interference from polybrominated diphenyl ethers. Here, literatures on PBDD/F analysis and environmental occurrences are reviewed to improve our understanding of PBDD/F environmental pollution and human exposure levels. Although PBDD/Fs behave similarly to dioxins, different congener profiles between PBDD/Fs and dioxins in the environment indicates their different sources and formation mechanisms. Herein, potential sources and formation mechanisms of PBDD/Fs were critically discussed, and current knowledge gaps and future directions for PBDD/F research are highlighted. An understanding of PBDD/F formation pathways will allow for development of synergistic control strategies for PBDD/Fs, dioxins, and other dioxin-like POPs.

PAH and POP Presence in Plastic Waste and Recyclates: State of the Art

The presence of different pollutants in recycled plastics is reviewed in this article. The desirable circular economy of plastics should be linked to the availability of clean recycled plastics with a non-significant and small to nil amount of substances of concern. Different researchers found polycyclic aromatic hydrocarbons (PAHs) and Persistent Organic Pollutants (POPs), such as brominated flame retardants (BFRs), pesticides, dioxins and furans (PCDD/Fs and PBDD/Fs) in plastic recyclates. This represents an added difficulty to the effective recycling process of plastics that reduces the demand for energy and materials, in addition to posing a great environmental danger since they represent a vector of accumulation of the contaminants that will finally appear in the most unexpected products. Life Cycle Analysis of the plastic wastes recycling process indicates a great saving of energy, water and CO2 emissions.

Review of the artificially-accelerated aging technology and ecological risk of microplastics

After being discarded into the environment, the microplastics (MPs) will undergo weathering effects. However, the low degradation rate of MPs in natural processes greatly limits the understanding of long-term aging behavior. By critically reviewing 82 articles in Web of Science from 2015 to 2020, the paper summarized different laboratory technologies including light irradiation, chemical oxidation, heat treatment and γ-ray irradiation to simulate and accelerate the aging of MPs, and evaluated the feasibility by comparison with natural processes. The advantages of laboratory technologies are that aging conditions can be artificially controlled and that the labor and time costs can be saved, whereas the laboratory system is too simple to simulate complex aging processes in the environment. We further reviewed the potential impacts of aging process on the risks of MPs (i.e. physical injury, combined toxicity with external pollutants and chemical risk of additives and low-molecular products). The overall risks are seemingly enhanced by aging process due to the high ingestion by organisms, the strong interaction with pollutants and the release of MP-derived organic compounds. Further studies on the aging behavior of MPs should be focused on the laboratory techniques that can simulate multiple processes of natural aging, the long-term fragmentation behavior of MPs, the effect of aging on growth rate of biofilm in MPs and ingestion property by organisms, and the relationship between aging property of MPs and release rate of chemicals in leachates.

Insights into the Occurrence, Fate, and Impacts of Halogenated Flame Retardants in Municipal Wastewater Treatment Plants

Halogenated flame retardants (HFRs) have been extensively used in various consumer products and many are classified as persistent organic pollutants due to their resistance to degradation, bioaccumulation potential and toxicity. HFRs have been widely detected in the municipal wastewater and wastewater treatment solids in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental HFRs contamination. This review seeks to provide a current overview on the occurrence, fate, and impacts of HFRs in WWTPs around the globe. We first summarize studies recording the occurrence of representative HFRs in wastewater and wastewater treatment solids, revealing temporal and geographical trends in HFRs distribution. Then, the efficiency and mechanism of HFRs removal by biosorption, which is known to be the primary process for HFRs removal from wastewater, during biological wastewater treatment processes, are discussed. Transformation of HFRs via abiotic and biotic processes in laboratory tests and full-scale WWTPs is reviewed with particular emphasis on the transformation pathways and functional microorganisms responsible for HFRs biotransformation. Finally, the potential impacts of HFRs on reactor performance (i.e., nitrogen removal and methanogenesis) and microbiome in bioreactors are discussed. This review aims to advance our understanding of the fate and impacts of HFRs in WWTPs and shed light on important questions warranting further investigation.

Compartmentalization and Excretion of 2,4,6-Tribromophenol Sulfation and Glycosylation Conjugates in Rice Plants

The most environmentally abundant bromophenol congener, 2,4,6-tribromophenol (2,4,6-TBP, 6.06 μmol/L), was exposed to rice for 5 d both in vivo (intact seedling) and in vitro (suspension cell) to systematically characterize the fate of its sulfation and glycosylation conjugates in rice. The 2,4,6-TBP was rapidly transformed to produce 6 [rice cells (3 h)] and 8 [rice seedlings (24 h)] sulfated and glycosylated conjugates. The predominant sulfation conjugate (TP₄₀₈, 93.0-96.7%) and glycosylation conjugate (TP₄₉₀, 77.1-90.2%) were excreted into the hydroponic solution after their formation in rice roots. However, the sulfation and glycosylation conjugates presented different translocation and compartmentalization behaviors during the subsequent Phase III metabolism. Specifically, the sulfated conjugate could be vertically transported into the leaf sheath and leaf, while the glycosylation conjugates were sequestered in cell vacuoles and walls, which resulted in exclusive compartmentalization within the rice roots. These results showed the micromechanisms of the different compartmentalization behaviors of 2,4,6-TBP conjugates in Phase III metabolism. Glycosylation and sulfation of the phenolic hydroxyl groups orchestrated by plant excretion and Phase III metabolism may reduce the accumulation of 2,4,6-TBP and its conjugates in rice plants.

Occurrence and spatial distribution of legacy and novel brominated flame retardants in seawater and sediment of the South China sea

The occurrence and spatial distribution of polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (NBFRs) in seawater and surficial sediment samples (N = 19 and 45, respectively) from the South China Sea (SCS) in 2018 were investigated, and the correlation between BFRs and site parameters (total organic carbon, depth, etc.) were assessed by principal component analysis. The concentration ranges of ΣPBDEs in seawater and sediments were 0.90-4.40 ng/L and 0.52-22.67 ng/g dry weight (dw), respectively, while those of ΣNBFRs were 0.49-37.42 ng/L and 0.78-82.29 ng/g dw, respectively. BDE-209 and decabromodiphenyl ethane were the predominant BFRs, accounting for 38.65% and 36.94% in seawater and 26.71% and 68.42% in sediments, respectively. Notably, tris(2,3-dibromopropyl)isocyanurate and 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, seldomly detected in aquatic matrices worldwide, were detected for the first time in the study area, and their relatively high levels and detection frequencies indicate the ubiquitous application of these NBFRs in the Pearl River Delta. Zhuhai and Jiangmen are the main sources of NBFRs in the SCS. Preliminary risk assessment on NBFRs using hazard quotient indicates low to medium risks to marine organisms at some sites. The occurrence of NBFRs in the SCS highlights the prioritization of more toxicological information on these compounds.

Critical effect of iron red pigment on photoaging behavior of polypropylene microplastics in artificial seawater

Microplastics (MPs) containing chemical additives undergo extensive aging in the environment, but the effect of additives on aging behavior of MPs is not fully understood. This study evaluated the effects of iron red pigment on the photoaging behavior of polypropylene (PP) MPs and the release kinetics of Fe(II) and Fe(III) under simulated sunlight. Based on analyses in surface property and aging products of leachate, the incorporated iron red pigment significantly decreased the photoaging rate of PP MPs. The critical effect mainly depended on the light shielding and the competition of pigment for electrons and reactive oxygen species generated from irradiated MPs. Light irradiation also caused the production of homologous series of organic products containing dicarboxylic acid end groups. Moreover, aging of pigmented MPs enhanced the release of Fe ions in leachates, and the types of released iron ions were different between dark and light conditions, where the iron ion in dark system was mainly as Fe(III), while Fe(II) was the dominant form in light irradiation, since the released Fe(III) reacted with MP-derived organic acids and reactive oxygen species in light condition. The findings highlight the critical role of inorganic pigments in the environmental fate and risk of MPs.

Microplastics physicochemical properties, specific adsorption modeling and their interaction with pharmaceuticals and other emerging contaminants

This review discusses the imminent threat that microplastics (MPs) associated with pharmaceuticals represent to the aquatic environment and public health. We initially focused upon recognizing and stressing that MPs are ubiquitous pollutants. The influence of environmental factors, such as pH, mechanical stress, and photodegradation, are examined, aiming to elucidate how both substances might associate, what are their simultaneous degradation pathways and, to understand the interactions between MPs and pharmaceuticals. Mathematical tools, such as modeling and simulations, are presented in detail, aiming to improve how information is interpreted. Furthermore, it is exhibited that MPs sorption and interaction behavior towards organic contaminants play an important role in understanding its dynamics in the environment, as well as their possible interactions with pharmaceuticals that are summarized. At last, MPs and pharmaceuticals toxicity and bioaccumulation are presented.

Microplastics generated under simulated fire scenarios: Characteristics, antimony leaching, and toxicity

Intentional or incidental thermal changes inevitably occur during the lifecycle of plastics. High temperatures accelerate the aging of plastics and promote their fragmentation to microplastics (MPs). However, there is little information available on the release of MPs after fires. In this study, an atomic force microscope combined with nanoscale infrared analysis was used to demonstrate the physicochemical properties of polypropylene (PP) plastics under simulated fire scenarios. Results showed that the chemical composition and relative stiffness of heat-treated plastic surfaces changed, significantly enhancing the generation of MPs under external forces; over (2.1 ± 0.2) × 10⁵ items/kg abundance of MPs released from PP which were burned at 250 °C in air and trampled by a person. The leaching of antimony (Sb) from MPs in different solutions first increased and then decreased with increasing temperature, reaching a maximum at 250 °C. Higher concentrations of humic acid (10 vs 1 mg/L) caused a greater release of Sb. Furthermore, the tap water leachates of PP burned at 250 °C had the greatest effect on the growth and photosynthetic activity of Microcystis aeruginosa. Our results suggest fires as a potential source of MPs and calls for increased focus on burning plastics in future research.

Formation of polybrominated dibenzofurans (PBDFs) and polybrominated diphenyl ethers (PBDEs) from oxidation of brominated flame retardants (BFRs)

Brominated aromatic rings constitute main structural entities in virtually all commercially deployed brominated flame retardants (BFRs). Oxidative decomposition of BFRs liberates appreciable quantities of bromobenzenes (BBzs). This contribution reports experimental measurements for the generation of notorious polybrominated dibenzofurans (PBDFs) and polybrominated diphenyl ethers (PBDEs) from oxidation of monobromobenzene (MBBz). In the light of developed product profiles, we map out reaction pathways and report kinetic parameters for PBDFs and PBDEs formation from coupling reactions of MBBz molecule and its derived ortho-bromophenoxy (o-BPhxy) radical using quantum chemical calculations. The identification and quantitation of product species involve the use of gas chromatograph - triple quadrupole mass spectrometer (GC-QQQMS) operating in the multiple reaction monitoring (MRM) mode. Bimolecular reactions of MBBz and o-BPhxy result in the generation of twelve pre-PBDF intermediates, of which four can also serve as building blocks for the synthesis of PBDEs. These four intermediates are denoted as pre-PBDE/pre-PBDF, with the remaining eight symbolised as pre-PBDF. The resonance-stabilised structure of the o-BPhxy radical accumulates more spin density character on its phenoxy O atom (30.9 %) in reference to ortho-C and para-C sites. Thus, the formation of the pre-PBDE/pre-PBDF structures via O/o-C couplings advances faster as it requires lower activation enthalpies (79.2 - 84.9 kJ mol^-1) than the pre-PBDF moieties, which arise via pairing reactions involving o-C(H or Br)/o-C(H or Br) sites (97.2 - 180.2 kJ mol^-1). Kinetic analysis indicates that, the O/o-C pre-PBDE/pre-PBDF adducts self-eject the out-of-plane H atoms to produce PBDEs, rather than undergo a three-step mechanism forming PBDFs. However, experimental measurements demonstrate PBDEs appearing in lower yields as compared to those of PBDFs; presumably due to H- and Br-induced conversion of the PBDEs into PBDFs following a simple ring-closure reaction. High reaction temperatures facilitate loss of ortho Br atom from PBDEs, followed by cyclisation step to generate PBDFs. PBDFs are observed in a narrow temperature range of 700-850 °C, whereas PBDEs form between 550-850 °C. Since formation mechanisms of PBDFs and polybrominated dibenzo-p-dioxins (PBDDs) are typically only sensitive to the bromination at ortho positions, the results reported herein apply also to higher brominated isomers of BBzs.

Insights into Mechanism of Hypochlorite-Induced Functionalization of Polymers toward Separating BFR-Containing Components from Microplastics

Surface functionalization of polymers is significant for an emerging flotation technique for separation of microplastics toward the recycling of plastic wastes. In this study, the hypochlorite-induced functionalization of polymers, including ABS, PMMA, PS, and PVC polymers, was intensively investigated. Afterward, its emerging application in flotation separation of microplastic mixtures was assessed based on a Box-Behnken design of the response surface methodology. The functionalization favorably induced decreases in the contact angle and zeta potential of polymers, suggesting hydrophilic and negatively charged surfaces. Particularly, the functionalization of ABS polymers was the most effective, leading to the obviously decreased contact angle (from 92.5° to 67.8°) and zeta potential (from -26.4 mV to -41.7 mV) at neutral condition. The major mechanism for these variations was the oxidation of the sp³-C and butenyl group by hydroxyl radical and the hydrolysis of cyano group, which introduced the hydroxyl, carboxyl, and amide groups and rough topographies on the surface of ABS polymers. Oxygen functionalities introduced on the surfaces of other polymers were far less than those of ABS polymers. This selectivity inspired us to apply the functionalization in flotation separation of ABS microplastics from microplastic mixtures. After functionalization, ABS microplastics showed a significantly decreased floatability in flotation tests since the hydrophilic surface was repulsive to the adhesion of air bubbles. An empirical model was built to optimize the separation efficiency using the overall desirability function. Under optimum conditions, ABS microplastics were efficiently separated, and their removal rate, recovery, and purity were 99.8%, 99.8%, and >99.9%, respectively. These findings provide significant insights into the mechanism of the functionalization of polymers and show a promising prospect for pollution control of plastic wastes.

Detection of high PBDD/Fs levels and dioxin-like activity in toys using a combination of GC-HRMS, rat-based and human-based DR CALUX® reporter gene assays

Brominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) are increasingly reported at significant levels in various matrices, including consumer goods that are manufactured from plastics containing certain brominated flame retardants. PBDD/Fs are known ligands for the aryl hydrocarbon receptor (AhR) but are not yet considered in the hazard assessment of dioxin mixtures. The aim of the present study was to determine if PBDD/Fs levels present in plastic constituents of toys could pose a threat to children's health. PBDD/Fs, unlike their chlorinated counterparts (PCDD/Fs), have not been officially assigned toxic equivalence factors (TEFs) by the WHO therefore, we determined their relative potency towards AhR activation in both human and rodent cell-based DR CALUX® bioassays. This allowed us to compare GC-HRMS PBDD/F congener levels, converted to total Toxic Equivalents (TEQ) by using the PCDD/F TEFs, to CALUX Bioanalytical Equivalents (BEQ) levels present in contaminated plastic constituents from children's toys. Finally, an estimate was made of the daily ingestion of TEQs from PBDD/Fs-contaminated plastic toys by child mouthing habits. It is observed that the daily ingestion of PBDD/Fs from contaminated plastic toys may significantly contribute to the total dioxin daily intake of young children.

Leaching behavior of Sb and Br from E-waste flame retardant plastics

The improper disposal of E-waste flame retardant plastics laden with antimony (Sb) and bromine (Br) has brought enormous environmental hazards, however, rare information on the effective removal of Sb and Br is available. In this study, through building an alkaline sulfide system under hydrothermal conditions, Sb and Br were simultaneously extracted from flame retardant plastic with high efficiency of 85.60% and 90.13%, respectively. Sulfur ion through mass transfer reacted with encapsulated Sb₂O₃ to form safe and non-toxic SbS₃^3-. Alkaline solution trapped the Br through substitution or neutralization reaction to inhibit the formation of brominated organic compounds. The results showed that the optimum temperature, residence time, Na₂S and NaOH concentration for hydrothermal removal of Sb and Br were 220 °C, 2 h, 50 g/L and 20 g/L. The results also revealed that both Na₂S and NaOH played an interrelated role in the process of Sb removal. However, NaOH was the only factor controlling the process of debromination. Moreover, the FTIR structure of plastic after alkaline sulfide hydrothermal treatment remained unchanged, which implies that the treated plastic can be reused, and is an added advantage of this technology. The TG-DTG analysis proved the effectiveness of alkaline sulfide hydrothermal treatment in removing Sb and Br.

Effect of weathering on environmental behavior of microplastics: Properties, sorption and potential risks

Microplastic (MP) pollution is a raising global concern in recent years due to its wide distribution. Additionally, most of the MPs have undergone extensive weathering in the environment, and weathered MPs may exhibit different physicochemical properties from pristine ones. The review reveals the change in physicochemical properties (e.g. size, color, crystallinity, mechanical property and oxygen-containing groups) and the release of additives and MP-derived intermediates (i.e. oligomers and oxygenated compounds) during weathering processes. Weathering further affects the sorption behavior of MPs for environmental pollutants because of the changed crystallinity, specific surface area and oxygen functional groups. The interaction mechanisms of pristine and weathered MPs with pollutants are summarized, and how weathering processes affect sorption behavior is critically revealed. Because of the changed size, color and surface charges, weathered MPs might be ingested by aquatic organisms in different ways from the pristine ones. The detailed effects of weathering on the ingestion of MPs are discussed, and the potential toxicity of leachates from weathering processes is evaluated. In addition, the environmental components (e.g. natural organic matter and salinity) and biofilm correlated to the sorption behavior of MPs are reviewed. As for the knowledge gap, further studies should focus on the long-term weathering of MPs and the relationships between weathering properties and sorption capacities toward pollutants. The potential risks of weathered MPs and leachates on organisms should be explored.