Hexabromocyclododecane: concentrations and isomer profiles from sources to environmental sinks

Hexabromocyclododecane in sediments from riverine, port, and coastal areas of Kaohsiung, Taiwan: levels, spatial distribution, and potential ecological risk

The widespread use of hexabromocyclododecane (HBCD), a brominated flame retardant, is a major public health concern because of the toxic, persistent, and bioaccumulative nature of HBCD. However, there is limited information available regarding the distribution and transportation of HBCD in sediments across various environmental settings, spanning from riverine to marine environments in the Kaohsiung area of Taiwan. In this study, we comprehensively investigated the level and distribution of and potential ecological risk posed by HBCD in surface sediments in the Kaohsiung area of Taiwan. In sediment samples from stations on the Love River and Kaohsiung Port area, the concentrations of HBCD ranged from 10.6 to 320.1 μg/kg dry weight (dw) and nondetectable (n.d.) to 58.4 μg/kg dw, respectively. The concentrations of HBCD in sediment collected from the M1, M2, and M3 sites, located in the Cijin coastal area, were 896.2 μg/kg dw, 3.2 μg/kg dw ( 1. The M1 site had the highest risk level (RQ = 5.27). These data suggest that domestic sewage and industrial wastewater discharge pose a potential risk to marine environments. Consequently, timely measures to control HBCD-related risks are required. Our study offers insight into the environmental effects of HBCD contamination of sediment and provides valuable information that can be used to guide environmental policy and safety measures.

A comprehensive evaluation of factors affecting the reactivity of FeS towards hexabromocyclododecane diastereoisomers

Reactivity of iron sulfide (FeS) towards hexabromocyclododecane (HBCD) was explored under conditions of varying temperature, pH, inorganic ion and dissolved organic matter (DOM) in this study. Results show that the reduction of HBCD by FeS has an activation energy of 29.2 kJ mol^-1, suggesting that the rate-limiting step in the reduction was a surface-mediated reaction. The reduction of HBCD by FeS was a highly pH-dependent process. The optimal rate for HBCD reduction by FeS was observed at a pH of 6.2. All the tested inorganic ions suppressed the reduction of HBCD by FeS. XPS analysis confirmed that both Fe(II)-S and bulk S(-II) on FeS surface could be impacted by solution pH and inorganic ions and were responsible for the regulation of HBCD reduction. Some DOMs (i.e., fulvic acid, humic acid, salicylic acid, catechol and sodium dodecyl sulfate) were found to hinder the reduction via competing with HBCD for active sites on FeS surface. However, the presence of 2,2'-bipyridine, triton X-100 and cetyltrimethyl ammonium bromide was able to significantly enhance the rate of HBCD reduction by 5.8, 9.0 and 20 times, respectively. Different factors could influence the reduction efficiency of HBCD diastereoisomers to different extent, but not the reaction orders of HBCD diastereoisomers (α-HBCD < γ-HBCD < β-HBCD). Moreover, FeS could completely remove HBCD diastereoisomers in sediments with multiple factors within 9 d reaction. Our results contribute to give a better understanding on the performance of FeS towards HBCD under real and complex conditions and facilitate the application of FeS in remediation sites.

A low-volume air sampling method for legacy and novel brominated flame retardants in indoor environment using a newly developed sorbent mixture

Brominated flame retardants (BFRs) are a series of stable and outstanding flame retardants bringing human exposure risks in indoor environment. However, sampling methods now available for BFRs are solvent-consuming and relatively complicated. This study provides a new option of low-volume air sampling device using cartridges with a sorbent mixture for different types of legacy and novel BFRs. In this study, we found that HC-C₁₈ sorbent is most suitable for polybrominated diphenyl ethers (PBDEs) and novel BFRs (NBFRs) enrichment, and that NH₂ for hexabromocyclododecanes (HBCDs). The sorbent mixture was optimized using a complex of HC-C₁₈ and NH₂ sorbents with elution recovery of 69.4% ± 7.9-117% ± 10%, pumping-through recovery of 84.5% ± 7.9-127% ± 36%, and breakthrough recovery of 70.8% ± 3.4-118% ± 6% for PBDEs, NBFRs, and HBCDs in indoor air. A sequential elution was also achieved using hexane for PBDEs and NBFRs and ethyl acetate for HBCDs. The method was validated with field sampling at nine student dormitory rooms. For legacy BFRs, all the isomers of HBCDs were detected in the air of nine rooms with the median concentrations of 91, 33, and 25 pg/m³ for (±)α-HBCD, (±)β-HBCD, (±)γ-HBCD, respectively, while PBDEs were hardly detected. In contrast, NBFRs were detected at total concentrations of 15-811 pg/m³. Pentabromotoluene (PBT) was the most frequently detected NBFRs with a median concentration of 4 pg/m³, followed by EHTBB at 56 pg/m³ and HBBZ at 21 pg/m³. For the risk assessment, the total hazard index value for air inhalation of BFRs was estimated at 6.1⎓10^-4-0.35, which are consistently lower than 1, indicating no immediate health risk, while their long-term effects remain worth concerns.

Transfer of POP-BFRs within e-waste plastics in recycling streams in China

Due to the rapid increase of e-waste plastics and the national policy's strong preference for mechanical recycling, a substantial amount of POP-BFRs is flowing into recycling streams in China. Therefore, confronting with the worldwide prohibition in manufacturing and consumption, identifying the transfer and inventory of POP-BFRs in recycling stage has become the key to their effective management and elimination. In this study, the level of PBDEs in e-waste housings, recycled plastics and daily-use products from recycling facilities and the commodity market was determined, and a gradual decrease of PBDEs was observed along with the downstream life cycle, indicating that recycling is a crucial medium of POP-BFRs transferred from their original use to an expansive reutilization market. Based on that, an extrusion experiment was conducted to imitate the mechanical recycling of e-waste plastics. It was found that, about 77% of PBDEs and 39% of HBCD were retained in recycled materials, with levels comparable to those in the products from recycling manufacturers and the consumer market. Mechanical recycling had no effect on the predominance of highly brominated BDE congeners, and no obvious transformation from higher to lower brominated diphenyl ethers was observed in recycled materials under thermal conditions; however, the isomerization of γ-HBCD brought about a noticeable increase in the relative abundance of α-HBCD. According to a Monte Carlo method estimation by using the transfer rate, approximately 235-687.8 tons of PBDEs have entered into recycling streams annually in the most recent five years. The field survey, laboratory findings and model evaluation results obtained in this study would not only contribute to a broader understanding of POP-BFRs sources and impact scopes posed on human health and the environment, but also provide a basis for developing effective strategies to manage POP-BFRs from the recycling perspective.

Distribution and diastereoisomeric profiles of hexabromocyclododecanes in air, water, soil, and sediment samples in South Korea: Application of an optimized analytical method

In this study, the levels and distribution patterns of HBCD diastereoisomers in air, water, soil, and sediment samples in South Korea were investigated after optimizing the UPLC-MS/MS analytical process. Extraction and cleanup efficiencies were tested using several different extraction solvents and adsorbents. Dichloromethane was selected as the base extraction solvent, and multi-layer silica gel (MSG) and MSG-alumina columns were selected for the removal of HBCDs from complex environmental matrices. The concentration of Ʃ₃ HBCDs was 22-133 pg/m³, 10-128 ng/g, 0.2-151 ng/L, and 0.5-552 ng/g dw for air, soil, water, and sediment samples, respectively. Relatively higher concentrations of Ʃ₃ HBCDs were observed at stations adjacent to industrial facilities (e.g., rubber and plastic, textile, chemical, fabricated metal, and wholesale trade factories) associated with the use of commercial HBCDs. The proportion of γ-HBCD in the soil (48.3-86.2%) and sediment (54.2-78.1%, except for one station) samples was similar to that found in technical and commercial HBCDs. In contrast, α-HBCD (52.3-71.2%) was dominant in all air samples, while the water samples displayed no clear trend in their diastereoisomer profiles. As the first nationwide report on HBCD diastereoisomers in the environment, this study demonstrates that most environmental compartments in South Korea are moderately contaminated with HBCDs.

Hexabromocyclododecanes promoted autophagy through the PI3K/Akt/mTOR pathway in L02 cells

As additive brominated flame retardants, hexabromocyclododecanes (HBCDs) are being widely used in diverse artificial materials and products, including thermal insulation building materials, housings of electronic equipment, and upholstery textiles. Toxicology studies have shown that HBCDs exposure are closely related to hepatotoxicity and liver diseases. The present study is designed to explore how HBCDs affect cell apoptosis and autophagy process in a human hepatocyte cell line (L02) and to reveal the underline molecular mechanisms. Firstly, HBCDs could elevate the apoptosis rate of L02 cells dose-dependently. Three apoptosis related proteins (apoptotic protease activating factor 1 (Apaf-1), cysteinyl aspartate specific proteinase 3 (caspase-3) and cysteinyl aspartate specific proteinase 9 (caspase-9)) were observed to be up-regulated using western blotting method. Autophagy process was also started by HBCDs in L02 cells as indicated by the increased expressions of LC3-phosphatidylethanolamine conjugate (LC3-II) and other autophagic protein markers (Beclin-1, autophagy related protein 3 (Atg3), autophagy related protein 5 (Atg5), autophagy related protein 7 (Atg7) and autophagy related protein 16L1(Atg16L1)). The results of the green fluorescent protein (GFP)-microtubule-associated protein 1 light chain 3 (LC3) intracellular localization and fluorescence intensity further evidenced the activation of autophagy in L02 cells after treated with HBCDs. In addition, phosphatidylinositide 3-kinases/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway was activated in L02 cells by HBCDs, suggested by the increased expressions of related proteins. The inhibitors of PI3K (LY294002), DNA-activated protein kinase catalytic subunit (DNA-PKcs) (NU7441), Akt (MK2206), and mTOR (KU0063794) could obviously reduce the autophagic proteins prompted by HBCDs. The fluorescence intensities of GFP-LC3 transfected L02 cells were also decreased significantly after the application of these inhibitors. These results indicated that PI3K/Akt/mTOR pathway was participated in regulating autophagy process promoted by HBCDs. In above, HBCDs could induce mitochondrial-dependent apoptosis and autophagy in L02 cells, which was modulated by PI3K/Akt/mTOR pathway.

Occurrence, levels and profiles of brominated flame retardants in daily-use consumer products on the Chinese market

With the global phasing-out of POP-BFRs (brominated flame retardants restricted under the Stockholm Convention on Persistent Organic Pollutants), the main challenge for their environmentally sound management has shifted from manufacturing and consumption to their recycling and disposal. For the end-of-life products containing POP-BFRs, material recycling and reuse in new articles is the favorite approach widely adopted by recyclers. This would result in POP-BFRs being transferred into daily-use consumer products. To identify the possible reservoirs of POP-BFRs in consumer products on the Chinese market, 120 samples were screened for Br by using a portable X-ray fluorescence (XRF) spectrometer, and the three traditional BFRs, i.e., polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA), were analyzed in 15 Br-positive samples. The results showed that 36.7% of products contained at least one test point positive for Br, and higher detection frequencies were found in electric appliances and toys. The concentrations of ∑BFRs ranged from 0.48 to 73.82 mg kg-1 with a general contribution in the order of ∑PBDEs > TBBPA > HBCD. BDE-209 was the dominant congener among PBDEs in most investigated samples, accounting for 48.18-99.36%. Relatively high proportions of the more bioaccumulative and toxic substances of lower brominated PBDE congeners and α-HBCD in products may increase the adverse impacts on the environment and human health. The obtained results will be helpful to understand the downstream flow of POP-BFRs with great significance to the control on their unintended contamination in daily life.