Anaerobic treatment removing tetrabromobisphenol A and biota safety: How do tropical aquatic species respond to effluent toxicity over short- and long-term exposures?

Wastewater containing tetrabromobisphenol A (TBBPA), a commonly used flame retardant found in wastewater, can present significant toxic effects on biota, yet its impact on tropical freshwater environments is not well understood. This study explores the effectiveness of two independent anaerobic treatment systems, the acidogenic reactor (AR) and the methanogenic reactor (MR), for the ecotoxicity reduction of TBBPA-rich wastewater in four tropical freshwater species. Despite presenting good physicochemical performance and reduced toxicity of the influent for most species, AR and MR treatments remain acute and chronic toxicity. Overall, MR exhibited greater efficacy in reducing influent toxicity compared with AR. TBBPA bioaccumulation was observed in Chironomus sancticaroli after short-term exposure to 100% MR effluent. Multigenerational exposures highlighted changes in the wing length of C. sancticaroli, showing decreases after influent and AR exposures and increases after MR exposures. These findings underscore the need for ecotoxicological tools in studies of new treatment technologies, combining the removal of emerging contaminants with safeguarding aquatic biota. PRACTITIONER POINTS: Acidogenic and methanogenic reactors reduced the acute and chronic toxicity of wastewater containing tetrabromobisphenol A. Both treatments still exhibit toxicity, inducing short- and long-term toxic effects on four native tropical species. The aquatic species Pristina longiseta was most sensitive to effluents from acidogenic and methanogenic reactors. TBBPA concentrations recovered from Chironomus sancticaroli bioaccumulation analysis ranged from 1.07 to 1.35 µg g-1. Evaluating new treatment technologies with multiple species bioassays is essential for a comprehensive effluent toxicity assessment and ensuring aquatic safety.

Mechanism of synergistic DNA damage induced by the hydroquinone metabolite of brominated phenolic environmental pollutants and Cu(II): Formation of DNA-Cu complex and site-specific production of hydroxyl radicals.

2,6-Dibromohydroquinone (2,6-DBrHQ) has been identified as an reactive metabolite of many brominated phenolic environmental pollutants such as tetrabromobisphenol-A (TBBPA), bromoxynil and 2,4,6-tribromophenol, and was also found as one of disinfection byproducts in drinking water. In this study, we found that the combination of 2,6-DBrHQ and Cu(II) together could induce synergistic DNA damage as measured by double strand breakage in plasmid DNA and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation, while either of them alone has no effect. 2,6-DBrHQ/Cu(II)-induced DNA damage could be inhibited by the Cu(I)-specific chelating agent bathocuproine disulfonate and catalase, but not by superoxide dismutase, nor by the typical hydroxyl radical (•OH) scavengers such as DMSO and mannitol. Interestingly, we found that Cu(II)/Cu(I) could be combined with DNA to form DNA-Cu(II)/Cu(I) complex by complementary application of low temperature direct ESR, circular dichroism, cyclic voltammetry and oxygen consumption methods; and the highly reactive •OH were produced synergistically by DNA-bound-Cu(I) with H2O2 produced by the redox reactions between 2,6-DBrHQ and Cu(II), which then immediately attack DNA in a site-specific manner as demonstrated by both fluorescent method and by ESR spin-trapping studies. Further DNA sequencing investigations provided more direct evidence that 2,6-DBrHQ/Cu(II) caused preferential cleavage at guanine, thymine and cytosine residues. Based on these data, we proposed that the synergistic DNA damage induced by 2,6-DBrHQ/Cu(II) might be due to the synergistic and site-specific production of •OH near the binding site of copper and DNA. Our findings may have broad biological and environmental implications for future research on the carcinogenic polyhalogenated phenolic compounds.

Evaluation of Polybrominated Diphenyl Ether Toxicity on HepG2 Cells - Hexabrominated Congener (BDE-154) Is Less Toxic than Tetrabrominated Congener (BDE-47).

Apoptotic cell death is one of the main consequences of exposure to brominated flame retardants, including polybrominated diphenyl ethers. However, few of these compounds have had their potential toxicity investigated. BDE-154 is one of the most poorly studied polybrominated diphenyl ether (PBDE) congeners, but its level in the environment and in biological fluids is rising. In addition, its chemical structure differs from the other congeners with well-documented toxicity, so BDE-154 may display a distinct toxicity pattern. This study has evaluated how BDE-154 affects the human hepatoblastoma cell line (HepG2) and has looked into the impact of this congener on human health. In addition, this study has related the effects of BDE-154 with the effects of BDE-47 to clarify the mechanism of PBDE toxicity. The HepG2 cell line was exposed to BDEs for 24 and 48 hr and submitted to assays to examine proliferation, viability, mitochondrial membrane potential, reactive oxygen species accumulation, phosphatidylserine exposure, nuclear fragmentation and evaluation of pro-caspase 3, pro-caspase 9, cytochrome c release, and apoptosis inductor factor release by Western blot analysis. BDE-154 induced mitochondrial damage and led to apoptotic death of HepG2 cells, but these effects were less intense than the effects promoted by BDE-47. Unlike other extensively reported congeners, BDE-154 was only toxic at the higher tested concentrations, whereas BDE-47 cytotoxicity was evident even at lower concentrations. Hence, like the toxicity pattern of other classes of substances such as polychlorinated biphenyls, the toxicity pattern of BDEs also depends on their chemical structure and aromatic substituent.

Comparative Study of Genotoxicity Induced by Six Different PBDEs.

Indiscriminate use of synthetic substances has led to environmental contamination and increasing human and animal exposure to harmful chemicals. Polybrominated flame retardants (PBDEs), which serve as non-covalent additives that enhance the safety of a variety of commercial and consumer goods, are an important class among potentially damaging synthetic substances. Its use is very common in developing countries, including Brazil. In theory, 209 different PBDE congeners exist, and many are currently being used during the manufacture of several products. Unfortunately, PBDEs are easily released from the original products, promptly reaching the environment. Knowledge about the toxicological power of these substances is still limited, which has prevented environmental and regulatory authorities from conducting adequate risk assessments. This research addresses the genotoxic and mutagenic potential of PBDEs. The effects of HepG2 cells and Salmonella typhimurium exposure to six main representatives of PBDEs, namely tetrabromodiphenyl ether (BDE-47), pentabromodiphenyl ether (BDE-99 and BDE-100), hexabromodiphenyl ether (BDE-153 and BDE-154) and decabromodiphenyl ether (BDE-209), were evaluated. The comet assay revealed that all the assessed BDEs exerted genotoxic effects but induced no micronuclei formation in HepG2 cells. These BDEs had no significant mutagenic effects on the Salmonella typhimurium strains TA98 and TA100. Taken together, the results of the genomic instability assays showed that PBDEs can represent a risk to the health of directly and indirectly exposed population, because the assessed BDEs induce genotoxic effects in the HepG2 cell line.

BDE-154 induces mitochondrial permeability transition and impairs mitochondrial bioenergetics.

Brominated flame retardants are used in various consumer goods to make these materials difficult to burn. Polybrominated diphenyl ethers (PBDE), which are representative of this class of retardants, consist of two benzene rings linked by an oxygen atom, and contain between 1 and 10 bromine atoms in their chemical structure, with the possibility of up to 209 different congeners. Among these congeners, BDE-154 (hexa-BDE) is persistent in the environment and easy to detect in the biota, but no apparent information regarding the mechanism underlying action and toxicity is available. Mitochondria, as the main energy-producing organelles, play an important role in the maintenance of various cellular functions. Therefore, mitochondria were used in the present study as an experimental model to determine the effects of BDE-154 congener at concentrations ranging from 0.1 µM to 50 µM. Our results demonstrated that BDE-154 interacts with the mitochondrial membrane, preferably by inserting into the hydrophobic core of the mitochondrial membrane, which partially inhibits respiration, dissipates Δψ, and permeabilizes the inner mitochondrial membrane to deplete ATP. These effects are more pronounced at concentrations equal to or higher than 10 µM. Results also showed that BDE-154 did not induce reactive oxygen species (ROS) accumulation within the mitochondria, indicating the absence of oxidative stress. Therefore, BDE-154 impairs mitochondrial bioenergetics and permeabilizes the mitochondrial membrane, potentially leading to cell death but not via mechanisms involving oxidative stress.

Mammalian toxicology and human exposures to the flame retardant 2,2',6,6'-tetrabromo-4,4'-isopropylidenediphenol (TBBPA): implications for risk assessment.

The compound 2,2',6,6'-Tetrabromo-4,4'-isopropylidenediphenol (tetrabromobisphenol A, TBBPA) is used as a reactive and additive flame retardant. This review evaluates the mammalian toxicology of TBBPA and summarizes recent human exposure and risk assessments. TBBPA has a low potential for systemic or reproductive toxicity, and no-observed-adverse-effect-levels were greater than 1,000 mg/kg body weight (bw)/day in a 90-day oral toxicity study, a developmental toxicity study and a two-generation reproductive and developmental toxicity study. Some interactions of TBBPA with hormone-mediated pathways were noted in vitro; however, when studied in vivo, TBBPA did not produce adverse effects that might be considered to be related to disturbances in the endocrine system. Therefore, in accordance with internationally accepted definitions, TBBPA should not be considered an "endocrine disruptor." Furthermore, TBBPA is rapidly excreted in mammals and therefore does not have a potential for bioaccumulation. Measured concentrations of TBBPA in house dust, human diet and human serum samples are very low. Daily intakes of TBBPA in humans were estimated to not exceed a few ng/kg bw/day. Due to the low exposures and the low potential for toxicity, margins of exposures for TBBPA in the human population were between 6 × 10(4) (infants) to 6 × 10(7) (adults). Exposures of the general population are also well below the derived-no-effect-levels derived for endpoints of potential concern in REACH.

Polybrominated diphenyl ether congener (BDE-100) induces mitochondrial impairment.

Brominated flame retardants are used in various consumer products to increase their resistance to fire and/or high temperatures. Polybrominated diphenyl ethers (PBDEs) are representatives of this class and among the most widely used congeners, and BDE-100 is produced on a large scale. There is a lack of toxicological data about these compounds, which has recently become a matter of concern to the scientific community. The mitochondria are recognized as the main energy-producing organelles, as well as playing a vital role in the maintenance of many cell functions. Therefore, mitochondria were used in the present work as an experimental model to evaluate the effects of the BDE-100 congeners at concentrations ranging from 0.1 µM to 50 µM. The results showed that high concentrations of BDE-100 were able to induce mitochondrial alterations. It was observed that the substance had an affinity for the hydrophilic portion of the mitochondrial membrane, as monitored by ANS, inhibiting the glutamate + malate-stimulated mitochondrial respiration and also inducing dissipation of the mitochondrial membrane potential, deregulation of calcium homoeostasis and mitochondrial swelling, the latter being insensitive to cyclosporin A (CsA) but partially inhibited by Ruthenium Red and N-ethyl maleimide. In addition, a significant reduction in mitochondrial ATP content was found, but on the other hand, no oxidative stress was observed after exposure of the mitochondria to BDE-100. These results show the key role of mitochondria in the cytotoxicity induced by BDE-100.

The effect of polybrominated biphenyl on infants and young children.

The effects of PBB on 33 children born between September 1, 1973, and December 31, 1975, were evaluated in September, 1977. These children, born to families who lived on quarantined farms, were compared to 20 children who were not exposed to PBB. The birthdate interval was selected to obtain children who were exposed in utero or in early infancy or both, the two time periods when damage to developing tissues and organ systems should have been maximal. The results of these studies failed to identify any effects on physical growth, physical examination, or neurologic assessment, although the parents indicated by historical review that the exposed children had had more illnesses, especially respiratory, than had the control children. There were some indications of an inverse relationship between PBB fast level and performance on selected developmental tests.