Critical review on the mechanistic photolytic and photocatalytic degradation of triclosan

Tailoring CuOx loading on CoFe2O4 nanocubes photocatalyst for superior photocatalytic degradation of triclosan pollutants under VL irradiation and toxicological evaluation

In this study, we report the development of a novel CuOx(3 wt%)/CoFe2O4 nanocubes (NCs) photocatalyst through simple co-precipitation and wet impregnation methods for the efficient photocatalytic degradation of triclosan (TCS) pollutants. Initially, rod-shaped bare CoFe2O4 was synthesized using a simple co-precipitation technique. Subsequently, CuOx was loaded in various percentages (1, 2, and 3 wt%) onto the surface of bare CoFe2O4 nanorods (NRs) via the wet impregnation method. The synthesized materials were systematically characterized to evaluate their composition, structural and electrical characteristics. The CuOx(3 wt%)/CoFe2O4 NCs photocatalyst exhibited superior photocatalytic degradation efficiency of TCS (89.9%) compared to bare CoFe2O4 NRs (62.1 %), CuOx(1 wt%)/CoFe2O4 (80.1 %), CuOx(2 wt%)/CoFe2O4 (87.0 %) under visible light (VL) irradiation (λ ≥ 420 nm), respectively. This enhanced performance was attributed to the improved separation effectiveness of photogenerated electron (e-) and hole (h+) in CuOx(3 wt%)/CoFe2O4 NCs. Furthermore, the optimized CuOx(3 wt%)/CoFe2O4 NCs exhibited strong stability and reusability in TCS degradation, as demonstrated by three successive cycles. Genetic screening on Caenorhabditis elegans showed that CuOx(3 wt%)/CoFe2O4 NCs reduced ROS-induced oxidative stress during TCS photocatalytic degradation. ROS levels decreased at 30, 60, and 120-min intervals during TCS degradation, accompanied by improved egg hatching rates. Additionally, expression levels of stress-responsible antioxidant proteins like SOD-3GFP and HSP-16.2GFP were significantly normalized. This study demonstrates the efficiency of CuOx(3 wt%)/CoFe2O4 NCs in degrading TCS pollutants, offers insights into toxicity dynamics, and recommends its use for future environmental remediation.

Efficient removal of triclosan from water through activated carbon adsorption and photodegradation processes

This study investigated the application of adsorption with activated carbons (ACs) and photodegradation to reduce the concentration of triclosan (TCS) in aqueous solutions. Concerning adsorption, ACs (Darco, Norit, and F400) were characterised and batch experiments were performed to elucidate the effect of pH on equilibrium. The results showed that at pH = 7, the maximum adsorption capacity of TCS onto the ACs was 18.5 mg g-1 for Darco, 16.0 mg g-1 for Norit, and 15.5 mg g-1 for F400. The diffusional kinetic model allowed an adequate interpretation of the experimental data. The effective diffusivity varied and increased with the amount of TCS adsorbed, from 1.06 to 1.68 × 10-8 cm2 s-1. In the case of photodegradation, it was possible to ensure that the triclosan molecule was sensitive to UV light of 254 nm because the removal was over 80 % using UV light. The removal of TCS increased in the presence of sulfate radicals. It was possible to identify 2,4-dichlorophenol as one of the photolytic degradation products of triclosan, which does not represent an environmental hazard at low concentrations of triclosan in water. These results confirm that the use of AC Darco, Norit, and F400 and that photodegradation processes with UV light and persulfate radicals are effective in removing TCS from water, reaching concentration levels that do not constitute a risk to human health or environmental hazard. Both methods effectively eliminate pollutants with relatively easy techniques to implement.

Degradation of triclosan by peroxydisulfate/peroxomonosulfate binary oxidants activation under thermal conditions: Efficiency and mechanism

Peroxydisulfate (PDS) and peroxymonosulfate (PMS) could be efficiently activated by heat to generate reactive oxygen species (ROS) for the degradation of organic contaminants. However, defects including the inefficiency treatment and pH dependence of monooxidant process are prominent. In this study, synergy of heat and the PDS-PMS binary oxidant was studied for efficient triclosan (TCS) degradation and apply in rubber wastewater. Under different pH values, the degradation of TCS followed pseudo-first-order kinetics, the reaction rate constant (kobs) value of TCS in heat/PDS/PMS system increased from 1.8 to 4.4 fold and 6.8-49.1 fold when compared to heat/PDS system and heat/PMS system, respectively. Hydroxyl radicals (·OH), sulfate radicals (SO4·-) and singlet oxygen (1O2) were the major ROS for the degradation of TCS in heat/PDS/PMS system. In addition, the steady-state concentrations of ·OH/1O2 and SO4·-/·OH/1O2 increased under acidic conditions and alkaline conditions, respectively. It was concluded that the pH regulated the ROS for degradation of TCS in heat/PDS/PMS system significantly. Based on the analysis of degradation byproducts, it was inferred that the dechlorination, hydroxylation and ether bond breaking reactions occurred during the degradation of TCS. Moreover, the biological toxicity of the ten byproducts was lower than that of TCS was determined. Furthermore, the heat/PDS/PMS system is resistant to the influence of water substrates and can effectively improve the water quality of rubber wastewater. This study provides a novel perspective for efficient degradation of TCS independent of pH in the heat/PDS/PMS system and its application of rubber wastewater.

Biological treatment of triclosan using a novel strain of Enterobacter cloacae and introducing naphthalene dioxygenase as an effective enzyme

In recent years, triclosan (TCS) has been widely used as an antibacterial agent in personal care products due to the spread of the Coronavirus. TSC is an emerging contaminant, and due to its stability and toxicity, it cannot be completely degraded through traditional wastewater treatment methods. In this study, a novel strain of Enterobacter cloacae was isolated and identified that can grow in high TCS concentrations. Also, we introduced naphthalene dioxygenase as an effective enzyme in TCS biodegradation, and its role during the removal process was investigated along with the laccase enzyme. The change of cell surface hydrophobicity during TCS removal revealed that a glycolipid biosurfactant called rhamnolipid was involved in TCS removal, leading to enhanced biodegradation of TCS. The independent variables, such as initial TCS concentration, pH, removal duration, and temperature, were optimized using the response surface method (RSM). As a result, the maximum TCS removal (97%) was detected at a pH value of 7 and a temperature of 32 °C after 9 days and 12 h of treatment. Gas chromatography-mass spectrometry (GC/MS) analysis showed five intermediate products and a newly proposed pathway for TCS degradation. Finally, the phytotoxicity experiment conducted on Cucumis sativus and Lens culinaris seeds demonstrated an increase in germination power and growth of stems and roots in comparison to untreated water. These results indicate that the final treated water was less toxic.

Dissolved black carbon incorporating with ferric minerals promoted photo-Fenton-like degradation of triclosan in acidic conditions

Dissolved black carbon (DBC) has been recognized as an important organic matter that influences the photochemical processes of organic pollutants. The excited triplet state (3DBC*) of DBC usually exhibits activity in neutral and basic aqueous conditions, rather than in acidic conditions. In this study, we found the crop (wheat, rice, maize) straw sourced DBC can substantially enhance the photodegradation of triclosan in relatively acidic conditions, and in the presence of ferric minerals (ferrihydrite and lepidocrocite), when exposed to simulated sunlight irradiation. This should be ascribed to the rapid non-reductive dissolution of ferric minerals by DBC, which leads to the generation of abundant hydrogen peroxides (H2O2) and hydroxyl radicals (•OH) through photo Fenton-like reactions. •OH is the dominant reactive species that leads to triclosan degradation in acidic conditions. Otherwise, triclosan itself is resistant to direct photolysis at pH < 5.0. The triplet state (3DBC*) plays a critical role in accelerating the Fe3+/Fe2+ cycling, which further promotes •OH generation. This study provides a new perspective on the role of DBC in surface water or mineral-water interfaces with acidic conditions and adds a more comprehensive understanding about the environmental implications of the DBC-ferric mineral system in sunlit surface water.

Nanomaterials for Removal of Phenolic Derivatives from Water Systems: Progress and Future Outlooks

Environmental pollution remains one of the most challenging problems facing society worldwide. Much of the problem has been caused by human activities and increased usage of various useful chemical agents that inadvertently find their way into the environment. Triclosan (TCS) and related phenolic compounds and derivatives belong to one class of such chemical agents. In this work, we provide a mini review of these emerging pollutants and an outlook on the state-of-the-art in nanostructured adsorbents and photocatalysts, especially nanostructured materials, that are being developed to address the problems associated with these environmental pollutants worldwide. Of note, the unique properties, structures, and compositions of mesoporous nanomaterials for the removal and decontamination of phenolic compounds and derivatives are discussed. These materials have a great ability to scavenge, adsorb, and even photocatalyze the decomposition of these compounds to mitigate/prevent their possible harmful effects on the environment. By designing and synthesizing them using silica and titania, which are easier to produce, effective adsorbents and photocatalysts that can mitigate the problems caused by TCS and its related phenolic derivatives in the environment could be fabricated. These topics, along with the authors' remarks, are also discussed in this review.

Mechanistic exploration on neurodevelopmental toxicity induced by upregulation of alkbh5 targeted by triclosan exposure to larval zebrafish

Because triclosan (TCS) has been confirmed to cause severe neurotoxicity, it is urgent to disclose the underlying toxicity mechanisms at varying levels. TCS exposure resulted in a series of malformations in larval zebrafish, including reduced neurons, blood-vessel ablation and abnormal neurobehavior. Apoptosis staining and the upregulated expression of proapoptotic genes demonstrated that TCS induced neuronal apoptosis and neurotransmitter disorders. By integrating RT-qPCR analysis with the effects of pathway inhibitors and agonists, we found that TCS triggered abnormal regulation of neuron development-related functional genes, and suppressed the BDNF/TrkB signaling pathway. TCS inhibited total m⁶A-RNA modification level by activating the demethylase ALKBH5, and induced neurodevelopmental toxicity based on the knockdown experiments of alkbh5 and molecular docking. The main novelties of this study lies in: (1) based on specific staining and transgenic lines, the differential neurotoxicity effects of TCS were unravelled at individual, physiological, biochemical and molecular levels in vivo; (2) from a epigenetics viewpoint, the decreasing m⁶A methylation level was confirmed to be mediated by alkbh5 upregulation; and (3) both homology modeling and molecular docking evidenced the targeting action of TCS on ALKBH5 enzyme. These findings open a novel avene for TCS's risk assessment and early intervention of the contaminant-sourcing diseases.

Cobalt-molybdenum-selenide nanoflowers for bifunctional visible light photocatalysis

The renewability and zero carbon emissions of hydrogen make it a promising clean energy resource to meet future energy demands. Owing to its benefits, photocatalytic water-splitting has been extensively investigated for hydrogen production. However, the low efficiency poses a serious challenge to its implementation. Herein, we attempted to synthesize bimetallic transition metal selenides, namely Co/Mo/Se (CMS) photocatalysts, with varying atomic compositions (CMSa, CMSb, and CMSc) and investigated their photocatalytic water splitting efficiencies. The observed hydrogen evolution rates were as follows: 134.88 μmol g^-1 min^-1 for CoSe₂, 145.11 μmol g^-1 min^-1 for MoSe₂, 167.31 μmol g^-1 min^-1 for CMSa, 195.11 μmol g^-1 min^-1 for CMSb, and 203.68 μmol g^-1 min^-1 for CMSc. Hence, we deemed CMSc to be the most potent photocatalytic alternative among the compounds. CMSc was also tested for its efficiency towards degradation of triclosan (TCN), and results substantiated that CMSc succeeded degrading 98% TCN while CMSa and b were able to degrade 80 and 90% TCN respectively-the attained efficiency being exponentially higher than CoSe₂ and MoSe₂ taken for comparative analysis in addition to complete degradation of the pollutants leaving no harmful intermediaries during the process. Thus, CMSc shall be identified as a highly potential photocatalyst with respect to both environmental and energy applications.

Molecular Toxicity Mechanism Induced by the Antibacterial Agent Triclosan in Freshwater Euglena gracilis Based on the Transcriptome

Triclosan (TCS), a commonly used antibacterial preservative, has been demonstrated to have high toxicological potential and adversely affects the water bodies. Since algae are one of the most significant primary producers on the planet, understanding the toxicological processes of TCS is critical for determining its risk in aquatic ecosystems and managing the water environment. The physiological and transcriptome changes in Euglena gracilis were studied in this study after 7 days of TCS treatment. A distinct inhibition ratio for the photosynthetic pigment content in E. gracilis was observed from 2.64% to 37.42% at 0.3-1.2 mg/L, with TCS inhibiting photosynthesis and growth of the algae by up to 38.62%. Superoxide dismutase and glutathione reductase significantly changed after exposure to TCS, compared to the control, indicating that the cellular antioxidant defense responses were induced. Based on transcriptomics, the differentially expressed genes were mainly enriched in biological processes involved in metabolism pathways and microbial metabolism in diverse environments. Integrating transcriptomics and biochemical indicators found that changed reactive oxygen species and antioxidant enzyme activities stimulating algal cell damage and the inhibition of metabolic pathways controlled by the down-regulation of differentially expressed genes were the main toxic mechanisms of TCS exposure to E. gracilis. These findings establish the groundwork for future research into the molecular toxicity to microalgae induced by aquatic pollutants, as well as provide fundamental data and recommendations for TCS ecological risk assessment.

Triclosan and related compounds in the environment: Recent updates on sources, fates, distribution, analytical extraction, analysis, and removal techniques

Triclosan (TCS) has been widely used in daily life because of its broad-spectrum antibacterial activities. The residue of TCS and related compounds in the environment is one of the critical environmental safety problems, and the pandemic of COVID-19 aggravates the accumulation of TCS and related compounds in the environment. Therefore, detecting TCS and related compound residues in the environment is of great significance to human health and environmental safety. The distribution of TCS and related compounds are slightly different worldwide, and the removal methods also have advantages and disadvantages. This paper summarized the research progress on the source, distribution, degradation, analytical extraction, detection, and removal techniques of TCS and related compounds in different environmental samples. The commonly used analytical extraction methods for TCS and related compounds include solid-phase extraction, liquid-liquid extraction, solid-phase microextraction, liquid-phase microextraction, and so on. The determination methods include liquid chromatography coupled with different detectors, gas chromatography and related methods, sensors, electrochemical method, capillary electrophoresis. The removal techniques in various environmental samples mainly include biodegradation, advanced oxidation, and adsorption methods. Besides, both the pros and cons of different techniques have been compared and summarized, and the development and prospect of each technique have been given.

Biopolymer templated strategized greener protocols for fabrication of ZnO nanostructures and their application in photocatalytic technology for phasing out priority pollutants

Zinc oxide (ZnO) nanostructures have been successfully synthesized via template-assisted and template-free route using three different synthetic methods, i.e., sonochemical, mechanochemical, and hydrothermal. Biopolymer xanthan gum (XG) served as sacrificial template for ZnO synthesis as provided the surface for the growth of nanostructures in a controlled manner. The employment of multifarious synthetic techniques resulted in fabrication of ZnO nanoparticles with diverse morphologies such as needle shaped, hexagonal, and spherical particles. Further, the template-assisted protocols generated thermally stable highly crystalline nanostructures along with high surface area, larger pore size, and low band gap energies in contrast to template-free protocol. The structural and other physicochemical studies were manifested by XRD, N₂ adsorption desorption, FESEM, TGA, and UV-Vis spectral analysis. The template-assisted ZnO nanostructures were explored as a potential photocatalyst for the catalytic degradation of emerging pollutants, i.e., triclosan (TCS) and imidacloprid (IMD) under the exposure of UV light. The products formed during the photocatalytic reaction were monitored by UV-Vis spectroscopy and HPLC. The results obtained revealed the high catalytic efficiency of ZnO synthesized via template-assisted sonochemical method for TCS (99.60%) and IMD (96.09%) which is attributed to the high surface area and lower band gap energy of the catalyst. The high catalytic potential of the sonochemically synthesized ZnO also substantiated from the kinetic data as high-rate constant was obtained. Thus, the template-assisted protocols developed led to preparation of nanostructures having tailored properties for efficient photocatalysis and can rapidly degrade selected emerging contaminants such as personal care products and organophosphate pesticides. Hence, environment-friendly synthesized photocatalyst can be appropriately employed to wastewater treatment contaminated with emerging pollutants.

Photocatalytic degradation of triclocarban in aqueous solution using a modified zeolite/TiO2 composite: kinetic, mechanism study and toxicity assessment

The current work aimed to investigate the degradation of the triclocarban (TCC) in aqueous solution using a modified zeolite/TiO₂ composite (MZTC) synthesized by applying the electrochemical anodization (ECA). The synthesis process was conducted at different voltages (10, 40, and 60) V in 1 h and using electrophoresis deposition (EPD) in doping zeolite. The MZTC was covered with the array ordered, smooth and optimum elongated nanotubes with 5.1 μm of the length, 120.3 nm of the inner diameter 14.5 nm of the wall thickness with pure titanium and crystalline titania as determined by FESEM/EDS, and XRD. The kinetic study by following Langmuir-Hinshelwood(L-H) model and pseudo first order, the significant constant rate was obtained at pH 11 which was 0.079 ppm/min, 0.75 cm² of MZTC catalyst loading size achieved 0.076 ppm/min and 5 ppm of TCC initial concentration reached 0.162 ppm/min. The high-performance liquid chromatography (HPLC) analysis for mechanism study of TCC photocatalytic degradation revealed eleven intermediate products after the whole process of photocatalysis. In regard of toxicology assessment by the bacteria which is Photobacterium phosphoreum, the obtained concentration of TCC at minute 60 was less satisfied with remained 0.36 ppm of TCC was detected indicates that the concentration was above allowable level. Where the allowable level of TCC in stream is 0.1 ppm.

Degradation of Triclosan in the Water Environment by Microorganisms: A Review

Triclosan (TCS), a kind of pharmaceuticals and personal care products (PPCPs), is widely used and has had a large production over years. It is an emerging pollutant in the water environment that has attracted global attention due to its toxic effects on organisms and aquatic ecosystems, and its concentrations in the water environment are expected to increase since the COVID-19 pandemic outbreak. Some researchers found that microbial degradation of TCS is an environmentally sustainable technique that results in the mineralization of large amounts of organic pollutants without toxic by-products. In this review, we focus on the fate of TCS in the water environment, the diversity of TCS-degrading microorganisms, biodegradation pathways and molecular mechanisms, in order to provide a reference for the efficient degradation of TCS and other PPCPs by microorganisms.

Novel assembly of BiVO4@N-Biochar nanocomposite for efficient detoxification of triclosan

The wide spread of antibacterial and antifungal agents demands in growing multifunctional materials to completely eliminate these organic contaminants in water. BiVO₄ (Bismuth vanadate) is a superior catalyst under visible light but suffers with high photoelectron-hole pair recombination rate and poor adsorption capacity which limits its efficiency. Addition of N-doped Biochar (N-Biochar) to BiVO₄ with large specific surface area and high conductivity are anticipated to overcome the problem and promote the catalytic performance. Thus, the present study developed a simple hydrothermal method to prepare BiVO₄@N-Biochar catalyst for efficient detoxification of Triclosan (TCS). The morphological analysis results suggested that BiVO₄ particles were evenly distributed on carbon surface amongst the N-Biochar matrix. Within 60 min of visible light irradiation, nearly 94.6% TCS degradation efficiency was attained by BiVO₄@N-Biochar (k = 0.02154 min^-1) while only 56.7% was attained with pure BiVO₄ (k = 0.00637 min^-1). In addition, LC-MS/MS technique was utilized to determine the TCS degradation products generation in the photodegradation process and pathway was proposed. Furthermore, the E. coli (Escherichia coli) colony forming unit assay was used to determine the biotoxicity of the degradation products in which 72.3 ± 2.6% of detoxification efficiency was achieved and suggested a substantial reduction in biotoxicity during the photodegradation.

Influence of nitrate/nitrite on the degradation and transformation of triclosan in the UV based disinfection

This study investigated the influence of nitrate/nitrite on the degradation and transformation pathway of triclosan (TCS) in UV, UV/peracetic acid (PAA) and UV/HClO processes. The results indicated that the function of nitrate/nitrite significantly depended on the UV source and wavelength, especially nitrate. Generally, the presence of nitrate decreased the direct photo-degradation of TCS in the UV based disinfection. In the LED-UV and LED-UV/HClO processes, the presence of nitrate improved the radical oxidation, and transformation pathway of TCS was varied accordingly. However, nitrate more played a role of photo-competitor in the UV/PAA process, and the reactive nitrogen species (RNS) was difficult to participant in the degradation of TCS due to low redox potential. Compared to nitrate, the presence of nitrite decreased the degradation of TCS in three different UV based disinfection processes. Under UV irradiation, nitrite primarily acted as an irradiation competitor and radical scavenger. Thus, the indirect photo-degradation of TCS was reduced. Noticeably, nitrate/nitrite were the improtant precersors of nitrogenous products in the UV base disinfection. Many new nitrogenous products were identified. But RNS preferentially reacted with the intermediates by -NO₂ addition compared to directly reacted with TCS.

Triclosan: A Small Molecule with Controversial Roles

Triclosan (TCS), a broad-spectrum antimicrobial agent, has been widely used in personal care products, medical products, plastic cutting boards, and food storage containers. Colgate Total^® toothpaste, containing 10 mM TCS, is effective in controlling biofilm formation and maintaining gingival health. Given its broad usage, TCS is present ubiquitously in the environment. Given its strong lipophilicity and accumulation ability in organisms, it is potentially harmful to biohealth. Several reports suggest the toxicity of this compound, which is inserted in the class of endocrine disrupting chemicals (EDCs). In September 2016, TCS was banned by the U.S. Food and Drug Administration (FDA) and the European Union in soap products. Despite these problems, its application in personal care products within certain limits is still allowed. Today, it is still unclear whether TCS is truly toxic to mammals and the adverse effects of continuous, long-term, and low concentration exposure remain unknown. Indeed, some recent reports suggest the use of TCS as a repositioned drug for cancer treatment and cutaneous leishmaniasis. In this scenario it is necessary to investigate the advantages and disadvantages of TCS, to understand whether its use is advisable or not. This review intends to highlight the pros and cons that are associated with the use of TCS in humans.

Fabrication of Ag3PO4/polyaniline-activated biochar photocatalyst for efficient triclosan degradation process and toxicity assessment

Triclosan (TCS) is a typical environmental pollutant, which seriously threatens the health of humans and organisms. A novel strategy of biochar/Ag₃PO₄/polyaniline (PANI) composite photocatalyst was synthesized by a facile chemical precipitation method to efficiently degrade TCS. XRD, Raman, ESR, etc. were used to reveal the effective associations among physiochemistry, photochemistry and photocatalytic properties of the composite. It was proved the synergistic effects of biochar (T-Bio) and PANI resulted in the decrease of Ag₃PO₄ particle size, the enhancement of adsorption, the improvement of light utilization, the increase of photogenerated carrier separation and the promotion of reactive species. The photocatalytic mechanism showed h⁺ was the main active species, O₂^- and OH played minor roles. Under the irradiation of visible light, the optimal photocatalyst (1.0% T-Bio/AP/1.0% PANI) displayed excellent photocatalytic activity with the removal rate of 85.21% for TCS within 10 min, and the apparent rate constant K' was 2.38 times of Ag₃PO₄. 11 main intermediates for TCS degradation were identified, and their toxicity was significantly reduced. The possible degradation pathways were proposed. This work is the first systematic study on the degradation behavior of TCS by Ag₃PO₄-based photocatalyst, and it provides a new approach to fabricate photocatalysts with synergistic effects and amazing photocatalytic activity by biochar.

Formation of environmentally persistent free radicals from photodegradation of triclosan by metal oxides/silica suspensions and particles

Metal oxides play an essential role in the photocatalysis of contaminants and substantially increase in the environment by the engineering production. However, whether emerging contaminants will be produced during photocatalysis of contaminants remains unclear. Here, triclosan (TCS) photodegradation in metal oxides/silica suspensions and particles, simulated as the states of metal oxides in water and soil environments, were studied. The photodegradation results confirmed that metal oxides exhibited a double-effect. They promoted TCS photodegradation by generating reactive oxidizing species (ROS) in metal oxides/silica suspensions and inhibited the photodegradation by competing with TCS for irradiation in metal oxides/silica particles. In this study, the critical discovery was the formation of emerging contaminants, environmentally persistent free radicals (EPFRs), and EPFRs yields were promoted by metal oxides (Al₂O₃, ZnO, TiO₂). They were more stable in metal oxides than silica, and the half-lives ranged from 6.7 h to 90.9 d. Although CuO did not increase EPFRs yields compared to silica, the half-lives of EPFRs were also longer. In addition, this study found that EPFRs yields were dependent on the metal oxides concentrations. Our results provided a new insight into the negative environmental impacts of metal oxides and improved our understanding of the formation and fate of EPFRs by metal oxides in soil and aquatic environments.

Transcriptional response of a green alga (Raphidocelis subcapitata) exposed to triclosan: photosynthetic systems and DNA repair

Recent studies show that triclosan (TCS) exposure causes reduction in pigments, suppression of photosynthesis, and induction of oxidative stress at the physiological level, resulting in morphological alteration and growth inhibition in algae including Raphidocelis subcapitata (R. subcapitata, a freshwater model green alga). However, the underlying molecular mechanisms remain to be elucidated, especially at environmentally relevant concentrations. The present study uncovered the transcriptional profiles and molecular mechanisms of TCS toxicity in R. subcapitata using next-generation sequencing. The algal growth was drastically inhibited following a 7-day exposure at both 75 and 100 μg/L TCS, but not at 5 μg/L (environmentally realistic level). The transcriptomic analysis shows that molecular signaling pathways including porphyrin and chlorophyll metabolism, photosynthesis - antenna proteins, and photosynthesis were suppressed in all three TCS treatments, and the perturbations of these signaling pathways were exacerbated with increased TCS exposure concentrations. Additionally, signaling of replication-coupled DNA repair was only activated in 100 μg/L TCS treatment. These results indicate that photosynthesis systems were sensitive targets of TCS toxicity in R. subcapitata, which is distinct from the inhibition of lipid synthesis by TCS in bacteria. This study provides novel knowledge on molecular mechanisms of TCS toxicity in R. subcapitata.

Environmental occurrence and remediation of emerging organohalides: A review

As replacements for "old" organohalides, such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), "new" organohalides have been developed, including decabromodiphenyl ethane (DBDPE), short-chain chlorinated paraffins (SCCPs), and perfluorobutyrate (PFBA). In the past decade, these emerging organohalides (EOHs) have been extensively produced as industrial and consumer products, resulting in their widespread environmental distribution. This review comprehensively summarizes the environmental occurrence and remediation methods for typical EOHs. Based on the data collected from 2015 to 2021, these EOHs are widespread in both abiotic (e.g., dust, air, soil, sediment, and water) and biotic (e.g., bird, fish, and human serum) matrices. A significant positive correlation was found between the estimated annual production amounts of EOHs and their environmental contamination levels, suggesting the prohibition of both production and usage of EOHs as a critical pollution-source control strategy. The strengths and weaknesses, as well as the future prospects of up-to-date remediation techniques, such as photodegradation, chemical oxidation, and biodegradation, are critically discussed. Of these remediation techniques, microbial reductive dehalogenation represents a promising in situ remediation method for removal of EOHs, such as perfluoroalkyl and polyfluoroalkyl substances (PFASs) and halogenated flame retardants (HFRs).

Biomarkers-based assessment of triclosan toxicity in aquatic environment: A mechanistic review

Triclosan (TCS), an emergent pollutant, is raising a global concern due to its toxic effects on organisms and aquatic ecosystems. The non-availability of proven treatment technologies for TCS remediation is the central issue stressing thorough research on understanding the underlying mechanisms of toxicity and assessing vital biomarkers in the aquatic organism for practical monitoring purposes. Given the unprecedented circumstances during COVID 19 pandemic, a several-fold higher discharge of TCS in the aquatic ecosystems cannot be considered a remote possibility. Therefore, identifying potential biomarkers for assessing chronic effects of TCS are prerequisites for addressing the issues related to its ecological impact and its monitoring in the future. It is the first holistic review on highlighting the biomarkers of TCS toxicity based on a comprehensive review of available literature about the biomarkers related to cytotoxicity, genotoxicity, hematological, alterations of gene expression, and metabolic profiling. This review establishes that biomarkers at the subcellular level such as oxidative stress, lipid peroxidation, neurotoxicity, and metabolic enzymes can be used to evaluate the cytotoxic effect of TCS in future investigations. Micronuclei frequency and % DNA damage proved to be reliable biomarkers for genotoxic effects of TCS in fishes and other aquatic organisms. Alteration of gene expression and metabolic profiling in different organs provides a better insight into mechanisms underlying the biocide's toxicity. In the concluding part of the review, the present status of knowledge about mechanisms of antimicrobial resistance of TCS and its relevance in understanding the toxicity is also discussed referring to the relevant reports on microorganisms.

Dioxins and furans toxicity during the photocatalytic remediation of emerging pollutants. Triclosan as case study

The benefits of wastewater remediation technologies are offset in those cases where, as a result of operating conditions, harmful compounds are formed in the degradation routes of the original organic pollutants. This may be the case for the application of some advanced oxidation processes to wastewater containing precursors of dioxins and furans, as previously reported in the application of electrochemical and Fenton oxidation to degrade Triclosan and 2-chlorophenol. This work reports for the first time a detailed kinetic analysis of the formation of dioxins and furans during the photocatalytic treatment of aqueous samples containing 5-Chloro-2-[2,4-dichlorophenoxy] phenol, commercially known as Triclosan. After analysis of the PCDD/Fs concentration, the toxicity of the samples has been determined in terms of toxic equivalents (TEQ). TEQ values have been calculated, first with the group of 17 congeners with higher toxicity. Finally, a multivariable analysis and linear regression have been applied to reduce the significant number of congeners and optimize the analytical effort.

Photocatalytic Transformation of Triclosan. Reaction Products and Kinetics

5-Chloro-2-[2,4-dichlorophenoxy]-phenol, or triclosan (TCS), is an antimicrobial and antifungal agent with high resistance to conventional wastewater treatments, thus, more effective remediation technologies are necessary, where photocatalytic processes deserve special attention due to the high degradation rates of TCS, and the use of a renewable source of energy. However, different by-products may be formed during the treatment, sometimes more harmful than the parent compounds. Efforts to detail reaction pathways continually feed into related literature; however, knowing the transformation kinetics and the dependence on the operating variables is essential for the correct design of the abovementioned remediation technologies. This work contributes to increasing the knowledge necessary for the application of photocatalytic processes for the degradation of emerging pollutants, with TCS as a case study. First, an experimental plan to analyze the influence of the operating variables was carried out, determining time courses of the parent and intermediate compounds. Next, the kinetic model and parameters that are capable of predicting TCS concentration and its derivatives as a function of the operating conditions are provided. This constitutes a very useful tool to predict the performance of wastewater remediation treatment both in the degradation of the original pollutant and in the reduction of the toxicity in the treated water.