Fate and metabolism of the brominated flame retardant tetrabromobisphenol A (TBBPA) in rice cell suspension culture

Unraveling phytoremediation mechanisms of the common reed (Phragmites australis) suspension cells towards ciprofloxacin: Xenobiotic transformation and metabolic reprogramming

Phytoremediation is an effective solution to treat pollution with antibiotic compounds in aquatic environments; however, the underlying mechanisms for plants to cope with antibiotic pollutants are obscure. Here we used cell suspension culture to investigate the distribution and transformation of ciprofloxacin (CIP) in common reed (Phragmites australis) plants, as well as the accompanying phenotypic and metabolic responses of plants. By means of radioactive isotope labelling, we found that in total 68 % of CIP was transformed via intracellular Phase I transformation (reduction and methylation), Phase Ⅱ conjugation (glycosylation), and Phase Ⅲ compartmentalization (cell-bound residue formation mainly in cell walls, 23 %). The reduction and glycosylation products were secreted by the cells. To mitigate stress induced by CIP and its transformation products, the cells activated the defense system by up-regulating both intra- and extra-cellular antioxidant metabolites (e.g., catechin, l-cystine, and dehydroascorbic acid), anti-C/N metabolism disorder metabolites (e.g., succinic acid), secreting signaling (e.g., nicotinic acid), and anti-stress (e.g., allantoin) metabolites. Notably, the metabolic reprogramming could be involved in the CIP transformation process (e.g., glycosylation). Our findings reveal the strategy of wetland plants to cope with the stress from CIP by transforming the xenobiotic compound and reprogramming metabolism, and provide novel insights into the fate of antibiotics and plant defense mechanisms during phytoremediation.

Toxicity and tolerance mechanism of binary zinc oxide nanoparticles and tetrabromobisphenol A regulated by humic acid in Chlorella vulgaris

Recent studies have reported that nanoparticles (NPs) released into the aquatic environment may interact with persistent organic pollutants such as brominated flame retardants, whereas the environmental processes and toxicological impacts induced by such binary NPs require further specification. This study investigated the ultrastructural damage of Chlorella vulgaris triggered by exposure to zinc oxide (ZnO) NPs, tetrabromobisphenol A (TBBPA), ZnO-TBBPA, and ZnO-TBBPA-humic acid (HA), clarified the uptake and distribution of ZnO NPs in cells, and explored the physiological toxicity and tolerance mechanism. The results demonstrated that ZnO NPs induced irregular morphology in algal cells, and the disruption of the cellular ultrastructure by binary ZnO-TBBPA was also extremely severe due to the excessive uptake of ZnO NPs, which resulted in strong oxidative stress responses. In particular, the accumulation of reactive oxygen species further exacerbated the reduction of total chlorophyll content and algal density. Moreover, the cluster heat map and correlation analysis revealed that superoxide dismutase activity played a critical role in alleviating lipid peroxidation damage and enhancing the tolerance of algal cells to the stress of binary ZnO NPs. More notably, the existence of HA intensified the dispersion stability of NP suspensions and significantly mitigated the synergistic toxicity of binary ZnO-TBBPA. This study provides new insights into the environmental behavior and biological impacts of binary NPs in the natural environment.

Two halogenated flame retardants and cadmium in the soil-rice system: sorption, root uptake, and translocation

The migration and transformation of Tetrabromobisphenol A (TBBPA), DechloranePlus (DP), and cadmium in soil-rice system was investigated, and the influence on the quality of two varieties of rice was studied. The degradation half-lives of TBBPA, BBPAs, syn-DP, and anti-DP were 23.18 ~ 26.36 days, 30.14 ~ 36.10 days, 72.96-81.55 days, and 169.06-198.04 days in the soil. TBBPA was gradually degraded to tri-BBPA, di-BBPA, mono-BBPA, and bisphenol A by the debromination. TBBPA and its bromide metabolites could be bioaccumulated in different tissues of rice; mono-BBPA and bisphenol A was easy to accumulate in the stems, and bisphenol A was easy to bioaccumulate in the grain. Comparing with single and compound pollution, there was no significant difference in bioaccumulation factors of two rice species. The grain of NO7 had stronger bioaccumulation ability to mono-BBPA and BPA than NO1, and there is no significant difference in TBBPA. Residual level of DP in the rice: roots > stems > grain; there was no significant difference in bioaccumulation of two varieties of rice. Cadmium was easily bioaccumulated in the roots of rice and translocated to the rice stems and grains. NO7 rice had stronger bioaccumulation and transport capacity than NO1. The effects of the three pollutants on the quality of two varieties of rice varied significantly; cadmium had the greatest effect on the iodine blue value (BV) and amylase activity of the grain. This study proved that selecting rice varieties with low bioaccumulation to polluters can effectively reduce the risk of the food chain harming human health.

Transcriptomic and metabolomic insights into the defense response to HFRs in Arabidopsis

Tetrabromobisphenol A (TBBPA), Tetrachlorobisphenol A (TCBPA), Tetrabromobisphenol S (TBBPS) and their derivatives as the most widely used halogenated flame retardants (HFR), had been employed in the manufacturing industry to raise fire safety. HFRs have been shown to be developmentally toxic to animals and also affect plant growth. However, little was known about the molecular mechanism responded by when plants were treated with these compounds. In this study, when Arabidopsis was exposed to four HFRs (TBBPA, TCBPA, TBBPS-MDHP, TBBPS), the stress of these compounds had different inhibitory effects on seed germination and plant growth. Transcriptome and metabolome analysis showed that all four HFRs could influence the expression of transmembrane transporters to affect ion transport, Phenylpropanoid biosynthesis, Plant-pathogen interaction, MAPK signalling pathway and other pathways. In addition, the effects of different kinds of HFR on plants also have variant characteristics. It is very fascinating that Arabidopsis shows the response of biotic stress after exposure to these kinds of compounds, including the immune mechanism. Overall, the findings of the mechanism recovered by methods of transcriptome and metabolome analysis supplied a vital insight into the molecular perspective for Arabidopsis response to HFRs stress.

Uptake, phytovolatilization, and interconversion of 2,4-dibromophenol and 2,4-dibromoanisole in rice plants

The structural analogs, 2,4-dibromophenol (2,4-DBP) and 2,4-dibromoanisole (2,4-DBA), have both natural and artificial sources and are frequently detected in environmental matrices. Their environmental fates, especially volatilization, including both direct volatilization from cultivation solution and phytovolatilization through rice plants were evaluated using hydroponic exposure experiments. Results showed that 2,4-DBA displayed stronger volatilization tendency and more bioaccumulation in aboveground rice tissues. Total volatilized 2,4-DBA accounted for 4.74% of its initial mass and was 3.43 times greater than 2,4-DBP. Phytovolatilization of 2,4-DBA and 2,4-DBP contributed to 6.78% and 41.7% of their total volatilization, enhancing the emission of these two contaminants from hydroponic solution into atmosphere. In this study, the interconversion processes between 2,4-DBP and 2,4-DBA were first characterized in rice plants. The demethylation ratio of 2,4-DBA was 12.0%, 32.0 times higher than methylation of 2,4-DBP. Formation of corresponding metabolites through methylation and demethylation processes also contributed to the volatilization of 2,4-DBP and 2,4-DBA from hydroponic solution into the air phase. Methylation and demethylation processes increased phytovolatilization by 12.1% and 36.9% for 2,4-DBP and 2,4-DBA. Results indicate that phytovolatilization and interconversion processes in rice plants serve as important pathways for the global cycles of bromophenols and bromoanisoles.

Assessment of tetrabromobisphenol-A (TBBPA) content in plastic waste recovered from WEEE

Due to the variability of additives and polymer types used in electrical and electronic equipment (EEE), and in accordance with the European Directive 2012/19/EU, an implementation of sound management practices is necessary. This work focuses on assessing the content of tetrabromobisphenol-A (TBBPA) in acrylonitrile-butadiene-styrene (ABS), polypropylene (PP), polycarbonate (PC) and their polymer blends (i.e. PC/ABS). A total of 36 plastic housing samples originating from microwave ovens, electric irons, vacuum cleaners and DVD/CD players were subjected to microwave-assisted-extraction (MAE) and/or ultrasound-assisted-extraction (UAE). Maximum mean concentration values of TBBPA measured in DVD/CD players and vacuum cleaners ranged between 754-1146 μg/kg, and varied per polymer type, as follows: 510-2515 μg/kg in ABS and 55-3109 μg/kg in PP. The results indicated that MAE was more sufficient than UAE in the extraction of TBBPA from ABS. To optimize the UAE procedure, various solvents were tested. Higher amounts of TBBPA were obtained from ABS and PP using a binary mixture of a polar-non-polar solvent, isopropanol:n-hexane (1:1), whereas the sole use of isopropanol exhibited incomplete extraction.

Delineating the global plastic marine litter challenge: clarifying the misconceptions

Plastics, owing to their various beneficial properties (durability, flexibility and lightweight nature), are widely regarded as the workhorse material of our modern society. Being ubiquitously and increasingly present over the past 60 years, they provide various benefits to the global economy. However, inappropriate and/or uncontrolled disposal practices, poor waste management infrastructure, and application of insufficient recycling technologies, coupled with a lack of public awareness and incentives, have rendered plastic waste (PW) omnipresent, littering both the marine and the terrestrial environment with multifaceted impacts. The plastic marine litter issue has received much attention, especially in the past decade. There is a plethora of articles and reports released on an annual basis, as well as a lot of ongoing research, which render the issue either to be overexposured or misconstrued. In addition, there are several misinterpretations that surround the presence and environmental impact of plastics in the oceans and, consequently, human health, that require much more critical and scientific thinking. This short communication aims at unveiling any existing misconceptions and attempts to place this global challenge within its real magnitude, based either on scientific facts or nuances. Graphical abstract.

Uptake, biotransformation and physiological response of TBBPA in mangrove plants after hydroponics exposure

To better understand the uptake, biotransformation and physiological response to tetrabromobisphenol A (TBBPA) in mangrove plants, a short term 14-day hydroponic assay with two mangrove species, Avicennia marina (A. marina) and Kandelia obovata (K. obovata), was conducted. Results showed that two mangrove species could uptake, translocate and accumulate TBBPA from solution. The hydroxylation and debromination metabolites of TBBPA, including OH-TBBPA, TriBBPA, MonoBBPA, and BPA, were found in both mangroves for the first time. The high-level TBBPA suppressed the growth and increased malondialdehyde (MDA) content of K. obovata, did not pose any negative affect on A. marina. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of K. obovata significantly increased in the 7th day, whereas, SOD and POD activities at high-levels of TBBPA became comparable to the control in the 14th day. Contrastingly, the antioxidant enzymes activities of A. marina were positively stimulated by TBBPA during the 14-day of observation, indicating that A. marina was more tolerant of TBBPA.

Glycosylation of Tetrabromobisphenol A in Pumpkin

Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant (BFR), and it bioaccumulates throughout the food chains. Its fate in the first trophic level, plants, is of special interest. In this study, a four-day hydroponic exposure of TBBPA at a concentration of 1 μmol L^-1 to pumpkin seedlings was conducted. A nontarget screening method for hydrophilic bromine-containing metabolites was modified, based on both typical isotope patterns of bromine and mass defect, and used to process mass spectra data. A total of 20 glycosylation and malonyl glycosylation metabolites were found for TBBPA in the pumpkin plants. Representative glycosyl TBBPA reference standards were synthesized to evaluate the contribution of this glycosylation process. Approximately 86% of parent TBBPA was metabolized to form those 20 glycosyl TBBPAs, showing that glycosylation was the most dominant metabolism pathway for TBBPA in pumpkin at the tested exposure concentration.

Identification of novel pathways for biotransformation of tetrabromobisphenol A by Phanerochaete chrysosporium, combined with mechanism analysis at proteome level

The investigation of tetrabromobisphenol A (TBBPA) removal by Phanerochaete chrysosporium (P. chrysosporium) was conducted. Under optimal conditions (pH 5, inoculum size of 5% (v/v), initial glucose concentration of 5 g/L, TBBPA concentration of 5 mg/L), >97% of initial TBBPA was removed after 3 days. The TBBPA metabolites, tetrabromobisphenol A glycoside, tribromobisphenol A glycoside and monohydroxylated tetrabromobisphenol A, were identified for the first time by fungi transformation as being produced by glycosylation and oxidative hydroxylation, respectively. Proteome analysis showed that P. chrysosporium significantly upregulated cytochrome P450 monooxygenase, glutathione S-transferases, UDP-glucosyltransferase, O‑methyltransferase and other oxidoreductases for TBBPA oxidative hydroxylation, reductive debromination, glycosylation, O‑methylation and oxidative cleavage for detoxification. Data from cytotoxicity tests with human hepatocellular liver carcinoma (HepG2) confirmed that TBBPA toxicity was effectively decreased by P. chrysosporium treatment. Bioaugmentation with P. chrysosporium significantly improved the removal efficiency of TBBPA in water microcosms to 63.1% within 12 h. This study suggests that P. chrysosporium might be suitable for the removal of TBBPA from contaminated water.

Transformation/degradation of tetrabromobisphenol A and its derivatives: A review of the metabolism and metabolites

Although the abiotic and biotic transformation/degradation (T/D) processes of tetrabromobisphenol A (TBBPA) have been widely investigated in model experiments, few reviews have focused on these processes along with their metabolites or degradation products. In this paper, we summarize the current knowledge on the T/D of TBBPA and its derivatives, including abiotic and biotic T/D strategies/conditions, mechanisms, metabolites and environmental occurrences. Various treatments, such as pyrolysis, photolysis, chemical reactions and biotransformation, have been employed to study the metabolic mechanism of TBBPA and its derivatives and to remediate associated contaminated environments. To date, more than 100 degradation products and metabolites have been identified, dominated by less brominated compounds such as bisphenol A, 2,6-dibromo-4-isopropylphenol, 2,6-dibromo-4-hydroxyl-phenol, 2,6-dibromophenol, isopropylene-2,6-dibromophenol, 4-(2-hydroxyisopropyl)-2,6-dibromophenol, etc. It can be concluded that the T/D of TBBPA mainly takes place through debromination and β-scission. In some environmental media and human and animal tissues, brominated metabolites, glucoside and sulfate derivatives are also important T/D products. Here, the T/D products of TBBPA and its derivatives have been most comprehensively presented from the literature in recent 20 years. This review will enhance the understanding of the environmental behaviors of TBBPA-associated brominated flame retardants along with their ecological and health risks.

Biotransformation of tetrabromobisphenol A dimethyl ether back to tetrabromobisphenol A in whole pumpkin plants

As the metabolites of tetrabromobisphenol A (TBBPA), tetrabromobisphenol A mono- and di-methyl ethers (TBBPA MME and TBBPA DME) have been detected in various environmental media. However, knowledge of the contribution of plants to their environmental fates, especially to the interactions between TBBPA DME and TBBPA, is quite limited. In this study, the metabolism and behaviors of TBBPA DME was studied with pumpkin plants through 15-day hydroponic exposure. The TBBPA were also studied separately using in-lab hydroponic exposure for comparison. The results showed that more TBBPA DME accumulated in pumpkin roots and translocated up to stems and leaves compared with TBBPA. Transformation of TBBPA DME occurred later and more slowly than that of TBBPA. Interconversion between TBBPA DME and TBBPA was verified in intact plants for the first time. Namely, TBBPA DME can be biotransformed to TBBPA MME (transformation ratio in mole mass, TRMM 0.50%) and to TBBPA (TRMM 0.53%) within pumpkin; and TBBPA can be biotransformed to TBBPA MME (TRMM 0.58%) and to TBBPA DME (TRMM 0.62%). In addition, two single benzene-ring metabolites, 2,6-dibromo-4-(2-(2-hydroxyl)-propyl)-anisole (DBHPA, TRMM 3.4%) with an O-methyl group and 2,6-dibromo-4-(2-(2-hydroxyl)-propyl)-phenetole (DBHPP, TRMM 0.57%) with an O-ethyl group, were identified as the transformation products in the TBBPA exposure experiments. The transformation and interconversion from TBBPA DME back to TBBPA is reported as a new pathway and potential source for TBBPA in the environment.

Characterization of brominated flame retardants from e-waste components in China

Many studies show that high levels of many toxic metals and persistent and bio-accumulative chemicals have been found in electronic waste (e-waste) dismantling sites and their surrounding environmental media. Both flame-retardant plastic housing materials and printed circuit boards (PCBs) could be the major contributors. However, relatively little work has focused on the use or content of toxic substances and their changing in scrap housing materials and PCBs from home appliances. This study evaluated the existence of brominated flame retardants (BFRs, including polybrominated diphenyl ethers (PBDEs) and Tetrabromobisphenol-A (TBBPA)) in housing plastics and PCBs from home appliances collected from various e-waste recyclers in China. These were then analyzed for the potential migration of BFRs from the e-waste components into their recycled products. The results show that both PBDEs and TBBPA were found with high level in most of e-waste samples, indicating that the widespread use of BFRs in home appliances are entering into the end-of-life stage. For the plastics samples, CRT TVs and LCD monitors should be given priority for the control of BFRs. Regarding PBDEs, the dominant congeners of BDE-209 in the plastics samples contributed 90.72-93.54% to the total concentrations of PBDEs, yet there are large variations for PCBs samples: BDE-28, -47, -99, and -153 were also important congeners compositions, except for BDE-209. Compared with previous studies, the BFRs concentrations in current Chinese e-waste are trending to decline. This study also found that BFRs in housing plastics and PCBs will be transferred into the recycled products with other purpose use, and the new products could have highly enriched capacities for BFRs. The obtained results could be helpful to manage e-waste and their components properly in order to minimize associated environmental and health risks of BFRs, particularly for their further reuse.

Bioaccumulation and elimination of bisphenol a (BPA) in the alga Chlorella pyrenoidosa and the potential for trophic transfer to the rotifer Brachionus calyciflorus

In this study, we investigated the bioaccumulation and elimination of ¹⁴C-labeled BPA by the green alga Chlorella pyrenoidosa and the subsequent transfer of ¹⁴C-BPA residues from the contaminated alga to the rotifer Brachionus calyciflorus. After 10 days of BPA exposure, the algal cells accumulated 15% of the initial radioactivity from the medium, with 71% of the accumulated radioactivity occurring in the form of non-extractable bound residues. An approximate steady state of the accumulation of the ¹⁴C-BPA residues in the algae was reached after about 4 days of exposure. The bioconcentration factor of total radioactivity in the algae was 106 mL (g dry weight)^-1 at steady state. During the elimination phase, only the extractable residues were released from the algae into the water whereas the bound residues, following their ingestion by the rotifers, were converted to extractable forms and then also released. Furthermore, our results demonstrated the biomagnification of BPA-related residues in the food chain between algae and rotifers. The trophic transfer of these BPA-derived residues from the algae to rotifers and thus the environmental hazard may posed by this pathway, because of subsequent effects on the food chain.

Direct Conjugation of Emerging Contaminants in Arabidopsis: Indication for an Overlooked Risk in Plants?

Agricultural use of treated wastewater, biosolids, and animal wastes introduces a multitude of contaminants of emerging concerns (CECs) into the soil-plant system. The potential for food crops to accumulate CECs depends largely on their metabolism in plants, which at present is poorly understood. Here, we evaluated the metabolism of naproxen and ibuprofen, two of the most-used human drugs from the Profen family, in Arabidopsis thaliana cells and the Arabidopsis plant. The complementary use of high-resolution mass spectrometry and ¹⁴C labeling allowed the characterization of both free and conjugated metabolites, as well as nonextractable residues. Naproxen and ibuprofen, in their parent form, were conjugated quickly and directly with glutamic acid and glutamine, and further with peptides, in A. thaliana cells. For example, after 120 h, the metabolites of naproxen accounted for >90% of the extractable chemical mass, while the intact parent itself was negligible. The structures of glutamate and glutamine conjugates were confirmed using synthesized standards and further verified in whole plants. Amino acid conjugates may easily deconjugate, releasing the parent molecule. This finding highlights the possibility that the bioactivity of such CECs may be effectively preserved through direct conjugation, a previously overlooked risk. Many other CECs are also carboxylic acids, such as the profens. Therefore, direct conjugation may be a common route for plant metabolism of these CECs, making it imperative to consider conjugates when assessing their risks.