Different Biodegradation methods of 4-bromophenol

Introduction

4-Bromophenol(p-Bromophenol; Figure 1) is an organic compound that is part of the brominated phenols family. 4-Bromophenol structure consists of a benzene ring attached to a hydroxyl group and a bromine atom. The substance is represented by the molecular formula C₆H₄BrOH and is recognized under CAS 106-41-2. This compound has widespread applications in the pharmaceutical, chemical, and agricultural industries, due to its distinct properties. Due to its constant use,these brominated phenolic compounds are common pollutants of soil and freshwater. Bromophenol levels up to 3690, 1140 and 187 mg/L have been reported in estuarine sediments, river water and photographic industrial wastewater respectively.Thus, the accumulation of bromophenol in the environment raises concerns because these compounds are suspected of having multiple adverse effects on living organisms. Moreover,bromophenol is also listed as a priority pollutant by the U.S. EPA. All of these factors warrant the development of an efficient system for the treatment of wastewater that contains 4-bromophenol (4-BP) prior to its discharge into the environment. Several physical and chemical methods such as volatilization, photodegradation, photo-catalysis and advanced oxidation have been investigated to treat wastewater containing phenolic compounds. Biodegradation has been proven promising over these techniques due to its several advantages such as lower treatment cost, no secondary pollution and eco-friendly treatment method.[1] Accordingly, extensive research interest has been aroused regarding the degradation of 4-bromophenol, and this paper briefly summarizes a number of related investigations.

Biodegradation of 4-bromophenol by Arthrobacter chlorophenolicus A6

Naresh Kumar Sahoo et al. have investigated growth and biodegradation of 4-bromophenol (4-BP) by Arthrobacter chlorophenolicus A6 in batch shake flasks as well as in a continuously operated packed bed reactor (PBR). Batch growth kinetics of A. chlorophenolicus A6 in presence of 4-bromophenol followed substrate inhibition kinetics with the estimated biokinetic parameters value of μ max=0.246 h^-1, K_i=111 mg/L, K_s=30.77mg/L and K=100mg/L. In addition, variations in the observed and theoretical biomass yield coefficient and maintenance energy of the culture were investigated at different initial 4-bromophenol concentration. Results indicates that the toxicity tolerance and the biomass yield of A. chlorophenolicus A6 towards 4-bromophenol was found to be poor as the organism utilized the substrate mainly for its metabolic maintenance energy. Further, 4-bromophenol biodegradation performance by the microorganism was evaluated in a continuously operated PBR by varying the influent concentration and hydraulic retention time in the ranges 400-1,200 mg/L and 24-7.5 h, respectively. Complete removal of 4-bromophenol was achieved in the PBR up to a loading rate of 2,276 mg/L/day.[1]

Degradation of 4-bromophenol by Ochrobactrum sp. HI1

Degradation pathways for brominated phenols differ for different microbial strains and geochemical conditions. As in the case of other halogenated organic compounds, reductive debromination may be an obvious route of degradation. Oxidative biodegradation of brominated phenols is less well documented, with fewer studies available to date. Tentatively, for 4-bromophenol an oxidative pathway proceeding through aromatic ring hydroxylation may be proposed using the analogy of other substituted phenols that were studied more extensively. Golan t al. presented the results from a study ofOchrobactrum sp. HI1, a new aerobic strain capable of 4-bromophenol (4-BP) degradation, isolated from acontaminated site in Israel. Degradation mechanismemployed by strain HI1 was characterized using theanalysis of degradation intermediates and multielement (C, Br, H) CSIA. Golan et al. Have investigated Ochrobactrum sp. HI1, a novel aerobic strain capable of degrading 4-bromophenol (4-BP), which was isolated from a contaminated site in Israel. The degradation mechanism of strain HI1 was elucidated by analyzing its degradation intermediates and conducting multi-element (C, Br, H) compound-specific stable isotope analysis (CSIA). A ring hydroxylation pathway of degradation was proposed, using the evidence from degradation intermediates analysis and multi-element (C, Br, H) compound-specific isotope analysis. Benzenetriol and 4-bromocatechol were detected during degradation of 4-bromophenol. Degradation resulted in a normal carbon isotope effect (ε_C=-1.11±0.09‰), and in insignificant bromine and hydrogen isotope fractionation. The dual C-Br isotope trend for ring hydroxylation obtained in the present study differs from the trends expected for reductive debromination or photolysis. Thus, the isotope data reported herein can be applied in future field studies to delineate aerobic biodegradation processes and differentiate them from other natural attenuation processes.[2]

Detoxification of 4-Bromophenol by Pseudomonas sp. EN-4 in Simulated Microcosm

An indigenous bacterium Pseudomonas sp. EN-4 had been reported earlier for its ability to co-metabolise 4-bromophenol (4-BP), in presence of phenol (100 mg/L) as co-substrate. The present study was undertaken to validate the efficacy of biotransformation by comparing the toxicity profiles of untreated and EN-4 transformed samples of 4-bromophenol, using both plant and animal model. The toxicity studies in Allium cepa (A. cepa) indicated to lowering of mitotic index (MI) from 12.77% (water) to 3.33% in A. cepa bulbs exposed to 4-BP + phenol, which reflects the cytotoxic nature of these compounds. However, the MI value significantly improves to 11.36% in its biologically treated counterpart, indicating normal cell growth. This was further supported by significant reduction in chromosomal aberrations in A. cepa root cells exposed to biologically treated samples of 4-bromophenol as compared to untreated controls. The oxidative stress assessed by comparing the activity profiles of different marker enzymes showed that the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) were reduced by 56%, 72%, and 37% respectively, in EN-4 transformed samples of 4-BP + phenol compared to its untreated counterpart. Similar trends were evident in the comet assay of fish (Channa punctatus) blood cells exposed to untreated and biologically treated samples of 4-bromophenol. The comparative studies showed significant reduction in tail length (72.70%) and % tail intensity (56.15%) in fish blood cells exposed to EN-4 treated 4-BP + phenol, compared to its untreated counterpart. The soil microcosm studies validated the competency of the EN-4 cells to establish and transform 4-bromophenol in soil polluted with 4-bromophenol (20 mg/kg) and 4-BP + phenol (20 + 100 mg/kg). The isolate EN-4 achieved 98.08% transformation of 4-BP in non-sterile microcosm supplemented with phenol, indicating to potential of EN-4 cells to establish along with indigenous microflora.[3]

Photodegradation of 4-Bromophenol by TiO₂/g-C₃N₄ Visible-Light-Driven Photocatalyst

The utilization of photocatalysts for the degradation of organic pollutants has been considered an effective strategy to address environmental pollution issues. TiO₂, as atypical photocatalyst, has been considered a promising photocatalyst due to its high oxidation efficiency, chemical stability, and cost-affordable synthesis method. CN has been modified with TiO₂ to expand visible light harvesting through photocatalytic reactions, due to improved charge carrier separation and its low recombination rate. Miri et al. synthesized TiO₂/CN heterostructure through a facile solvothermal method in acidic condition to degrade 4-bromophenol (4-BP) as an emergent pollutant through photocatalytic reactions under visible light irradiation (λ = 420 nm). In this study, the various ratios of TiO₂ on g-C₃N₄ (CN) to form nano photocatalysts were synthesized by the solvothermal method. The 30% TiO₂/CN showed the best performance to degradation and debromination of 4-bromophenol (4-BP) solution completely (kobs=6.6×10^-2 min^-1) under visible light emitted by LED (420 nm) in 30 min. Remarkably, the photocatalyst showed superior stability and reusability, maintaining its efficiency after four cycles of 4-bromophenol degradation. The dominant ROS participating in 4-BP degradation were ●O^-₂ and photogenerated holes (h⁺), as investigated by free radical scavenging tests. The optical properties analysis revealed that the introduction of TiO₂ to the bulk CN decreases electron-hole recombination and improve photocatalytic performance by facilitating electrons transfer through the TiO₂ nanoparticles in a chain. The findings of this study showed that the TiO₂/CN photocatalyst is a promising catalyst for the degradation of 4-bromophenol. It exhibits a higher rate constant and photocatalytic efficiency compared with previous studies conducted under visible light irradiation.[4]

References

[1] Sahoo NK, Pakshirajan K, Ghosh PK. Biodegradation of 4-bromophenol by Arthrobacter chlorophenolicus A6 in batch shake flasks and in a continuously operated packed bed reactor. Biodegradation. 2014;25(2):265-276. doi:10.1007/s10532-013-9658-x

[2] Golan R, Gelman F, Kuder T, Taylor AA, Ronen Z, Bernstein A. Degradation of 4-bromophenol by Ochrobactrum sp. HI1 isolated from desert soil: pathway and isotope effects. Biodegradation. 2019;30(1):37-46. doi:10.1007/s10532-018-9860-y

[3] Mahajan R, Sharma G, Chadha P, Saini HS. Evaluating efficacy of Pseudomonas sp. EN-4 to lower the toxic potential of 4-bromophenol and assessing its competency in simulated microcosm. Environ Pollut. 2024;349:123990. doi:10.1016/j.envpol.2024.123990

[4] Miri A, Shih YH, Chen WL. The highly efficient photodegradation of 4-bromophenol by TiO₂/g-C₃N₄ nano photocatalyst with LED visible light. Chemosphere. 2024;362:142658. doi:10.1016/j.chemosphere.2024.142658