Toxic Transformation Products Research Articles

Determination of the efficiency of electrolyzed water devices for the removal of pesticides in aqueous solutions and the characteristics of the pesticide residues and their transformation products

The effect of electrolyzed water treatment on the degradation of pesticide residues (malathion, fenitrothion, p,p′-DDT, and 2-hydroxybiphenyl) in tap water was investigated. Electrolyzed water was generated by electrolysis in commercially available kitchen devices. Three devices with different parameters were tested. The transformation products of pesticides, which are formed after the electrolysis process, were also investigated. Results show that the reduction percentage for electrolyzed water was from 6.2 to 99.7 % for 2-hydroxyphenyl, from 75.5 to approx. 100 % for fenitrothion, from 79.7 to approx. 100 % for malathion, and from 52.1 to 78 % for p,p′-DDT. It was also shown that the obtained transformation products of selected pesticides are more toxic than the parent compounds. Extending the electrolysis time in water electrolysis devices results in more effective degradation of pesticides and transformation products. Our research has shown that electrolyzed water devices can effectively remove pesticide residues, but they can also be a source of other toxic transformation products that may have a synergistic effect.

Effects of Chemicals in Reporter Gene Bioassays with Different Metabolic Activities Compared to Baseline Toxicity.

High-throughput cell-based bioassays are used for chemical screening and risk assessment. Chemical transformation processes caused by abiotic degradation or metabolization can reduce the chemical concentration or, in some cases, lead to the formation of more toxic transformation products. Unaccounted loss processes may falsify the bioassay results. Capturing the formation and effects of transformation products is important for relating the in vitro effects to in vivo. Reporter gene cell lines are believed to have low metabolic activity, but inducibility of cytochrome P450 (CYP) enzymes has been reported. Baseline toxicity is the minimal toxicity a chemical can have and is caused by the incorporation of the chemical into cell membranes. In the present study, we improved an existing baseline toxicity model based on a newly defined critical membrane burden derived from freely dissolved effect concentrations, which are directly related to the membrane concentration. Experimental effect concentrations of 94 chemicals in three bioassays (AREc32, ARE-bla and GR-bla) were compared with baseline toxicity by calculating the toxic ratio (TR). CYP activities of all cell lines were determined by using fluorescence-based assays. Only ARE-bla showed a low basal CYP activity and inducibility and AREc32 showed a low inducibility. Overall cytotoxicity was similar in all three assays despite the different metabolic activities indicating that chemical metabolism is not relevant for the cytotoxicity of the tested chemicals in these assays. Up to 28 chemicals showed specific cytotoxicity with TR > 10 in the bioassays, but baseline toxicity could explain the effects of the majority of the remaining chemicals. Seven chemicals showed TR < 0.1 indicating inaccurate physicochemical properties or experimental artifacts like chemical precipitation, volatilization, degradation, or other loss processes during the in vitro bioassay. The new baseline model can be used not only to identify specific cytotoxicity mechanisms but also to identify potential problems in the experimental performance or evaluation of the bioassay and thus improve the quality of the bioassay data.

Optimisation of treatment efficiency and effluent toxicity during carbamazepine degradation via electrochemical oxidation

The commercialisation of electrochemical advanced oxidation processes (eAOPs) as a method for removing recalcitrant pollutants from wastewater is currently limited due to the potential for the formation of toxic by-products. In this regard, this research comprised a comprehensive optimisation study aimed at finding a balance between minimising the toxicity effects observed via phytotoxicity assays and maximising the eAOP degradation efficiency under low energy requirements. To this end, carbamazepine (CBZ) was selected as the target pollutant in synthetic wastewater, and the operating conditions considered for optimisation were the nature of the anolyte (i.e., sulfate- or chloride-based), its concentration, and the current density applied. Together with the identification of the CBZ transformation products and their estimated toxicity based on the ECOSAR model, the optimum treatment was found to correspond to the degradation in 500mgL−1 of a sulfate-based anolyte at a current density of 10Am−2. These conditions led to the fewest and least toxic transformation products and favoured plant growth indices in phytotoxicity tests. Even if additional process improvements are required to reduce effluent toxicity, continuing such a multi-target optimisation approach can lead to innocuous electrochemical wastewater treatment.

Unravelling hidden threats of water disinfection: Toxicity evaluation and toxic products identification during diclofenac degradation

Diclofenac (DCF) is a widely-used nonsteroidal anti-inflammatory drug that is routinely found in surface water bodies. While ozonation and ultraviolet (UV) radiation are commonly employed as disinfection methods in water treatment processes, the degradation of DCF in these processes occurs due to the strong oxidizing activity of the reactive oxygen species produced during both ozonation and UV radiation. Despite extensive studies reporting the removal and transformation of DCF through ozone and UV treatments, the potential hidden hazards of toxicity arising from these processes as well as the identification of the toxic transformation products have often been overlooked. In this study, various toxicities including microtoxicity, genotoxicity and antiestrogenicity were evaluated using multiple in-vitro bioassays. The transformation products were identified via ultra-performance liquid chromatography equipped with mass spectrometry (UPLC-MS). Correlation analysis was employed to gain deeper insight into the contributions of degradation products to overall toxicity. The results revealed that DCF possessed significant genotoxic and antiestrogenic effects, but displayed minimal microtoxicity. Microtoxic products such as those containing carbazole were generated during DCF degradation with ozone, UVA and UVC. Antiestrogenic products with dichloroaniline structures were observed in DCF ozonation but not in photodegradation by UVA and UVC. These findings highlighted the hidden risks associated with the disinfection of water containing micropollutants such as DCF.

Comparison of photoinduced and electrochemically induced degradation of venlafaxine.

The European Union requires environmental monitoring of the antidepressant drug venlafaxine. Advanced oxidation processes provide a remedy against the spread of micropollutants. In this study, the photoinduced and electrochemical decompositions of venlafaxine were investigated in terms of mechanism and efficacy using high-performance liquid chromatography coupled to high-resolution multifragmentation mass spectrometry. Kinetic analysis, structure elucidation, matrix variation, and radical scavenging indicated the dominance of a hydroxyl-mediated indirect mechanism during photodegradation and hydroxyl and direct electrochemical oxidation for electrochemical degradation. Oxidants, sulfate, and chloride ions acted as accelerants, which reduced venlafaxine half-lives from 62 to 25 min. Humic acid decelerated degradation during ultra-violet irradiation up to 50%, but accelerated during electrochemical oxidation up to 56%. In silico quantitative structure activity relationship analysis predicted decreased environmental hazard after advanced oxidation process treatment. In general, photoirradiation proved more efficient due to faster decomposition and slightly less toxic transformation products. Yet, matrix effects would have to be carefully evaluated when potential applications as a fourth purification stage were to be considered.

Reactive Oxygen Species and Chromophoric Dissolved Organic Matter Drive the Aquatic Photochemical Pathways and Photoproducts of 6PPD-quinone under Simulated High-Latitude Conditions.

The photochemical degradation pathways of 6PPD-quinone (6PPDQ, 6PPD-Q), a toxic transformation product of the tire antiozonant 6PPD, were determined under simulated sunlight conditions typical of high-latitude surface waters. Direct photochemical degradation resulted in 6PPDQ half-lives ranging from 17.5 h at 20 °C to no observable degradation over 48 h at 4 °C. Sensitization of excited triplet-state pathways using Cs+ and Ar purging demonstrated that 6PPDQ does not decompose significantly from a triplet state relative to a singlet state. However, assessment of processes involving reactive oxygen species (ROS) quenchers and sensitizers indicated that singlet oxygen and hydroxyl radical do significantly contribute to the degradation of 6PPDQ. Investigation of these processes in natural lake waters indicated no difference in attenuation rates for direct photochemical processes at 20 °C. This suggests that direct photochemical degradation will dominate in warm waters, while indirect photochemical pathways will dominate in cold waters, involving ROS mediated by chromophoric dissolved organic matter (CDOM). Overall, the aquatic photodegradation rate of 6PPDQ will be strongly influenced by the compounding effects of environmental factors such as light screening and temperature on both direct and indirect photochemical processes. Transformation products were identified via UHPLC-Orbitrap mass spectrometry, revealing four major processes: (1) oxidation and cleavage of the quinone ring in the presence of ROS, (2) dealkylation, (3) rearrangement, and (4) deamination. These data indicate that 6PPDQ can photodegrade in cool, sunlit waters under the appropriate conditions: t1/2 = 17.4 h tono observable decrease (direct); t1/2 = 5.2-11.2 h (indirect, CDOM).

Photolytic Degradation of the Insecticide Clothianidin in Hydrochar Aquatic Suspensions and Extracts

In this study, the aqueous photolytic degradation of the neonicotinoid pesticide clothianidin was studied in suspensions and aqueous extracts of hydrochar produced from olive kernels. A slight and nonsignificant decrease in the photodegradation rate of clothianidin in aqueous extracts of hydrochar (HCw) with an initial concentration of hydrochar ranged from 50 to 400 mg L−1 (rate constants ranged between k = 0.0034 and 0.0039 min−1) was observed in comparison to the respective rate in the bi-distilled water (k = 0.0040 min−1). On the contrary, in the presence of hydrochar suspensions (HCp), a significant decrease was observed for 50 mg L−1 hydrochar particle concentration (k = 0.020 min−1), while for higher concentrations (100 to 400 mg L−1), rate constants increased but with nonsignificant differences compared with the kinetics followed in the absence of them. Generally, the photodegradation rate of clothianidin, in the presence of HCw and HCp, is reduced compared to the photodegradation rate in bi-distilled aqueous solutions, except in the case of the aqueous suspension with an HCp concentration of 200 mg L−1. The transformation products (TPs) of clothianidin formed in the photolytic degradation processes were identified using ultrahigh-performance liquid chromatography coupled with accurate high-resolution mass spectrometry technique (UHPLC-LTQ-ORBITRAP). The formation profiles of TPs varied according to the matrix showing different degrees of participation of direct and indirect (photosensitized) phototransformation pathways. Photolytic degradation of clothianidin takes place mainly through denitration, hydroxylation and dechlorination pathways. Finally, the toxicity of the identified TPs was studied using the Vibrio fischeri bioassay. Toxicity was slightly reduced after 300 min of irradiation while maximum value was observed after 180–240 min of irradiation showing the formation of more toxic TPs along the photochemical degradation.

Urine Excretion, Organ Distribution, and Placental Transfer of 6PPD and 6PPD-Quinone in Mice and Potential Developmental Toxicity through Nuclear Receptor Pathways.

The rubber antioxidant 6PPD has gained significant attention due to its highly toxic transformation product, 6PPD-quinone (6PPDQ). Despite their detection in urines of pregnant women, the placental transfer and developmental toxicity of 6PPD and 6PPDQ are unknown. Here, we treated C57Bl/6 mice with 4 mg/kg 6PPD or 6PPDQ to investigate their urine excretion and placental transfer. Female and male mice exhibited sex difference in excretion profiles of 6PPD and 6PPDQ. Urine concentrations of 6PPDQ were one order of magnitude lower than those of 6PPD, suggesting lower excretion and higher bioaccumulation of 6PPDQ. In pregnant mice treated with 6PPD or 6PPDQ from embryonic day 11.5 to 15.5, 6PPDQ showed ∼1.5-8 times higher concentrations than 6PPD in placenta, embryo body, and embryo brain, suggesting higher placental transfer of 6PPDQ. Using in vitro dual-luciferase reporter assays, we revealed that 6PPDQ activated the human retinoic acid receptor α (RARα) and retinoid X receptor α (RXRα) at concentrations as low as 0.3 μM, which was ∼10-fold higher than the concentrations detected in human urines. 6PPD activated the RXRα at concentrations as low as 1.2 μM. These results demonstrate the exposure risks of 6PPD and 6PPDQ during pregnancy and emphasize the need for further toxicological and epidemiological investigations.

Redox-directed identification of toxic transformation products during ozonation of aromatics

The toxicity assessment of transformation products (TPs) formed in oxidative water treatment is crucial but challenging because of their low concentration, structural diversity, and mixture complexity. Here, this study developed a novel redox-directed approach for identification of toxic TPs without the individual toxicity and concentration information. This approach based on sodium borohydride reduction comprised an integrated process of toxicological evaluation, fluorescence excitation-emission matrix characterization, high-resolution mass spectrometry detection, followed by ecological toxicity assessment of identified TPs. The redox-directed identification of primary causative toxicants was experimentally tested for the increased nonspecific toxicity observations in the ozonated effluents of model aromatics. Reduction reaction caused a remarkable decrease in toxicity and increase in fluorescence intensity, obtaining a good linear relation between them. More than ten monomeric or dimeric p-benzoquinone (p-BQ) TPs were identified in the ozonated effluents. The occurrence of the p-BQ TPs was further verified through parallel sodium sulfite reduction and actual wastewater ozonation experiments. In vitro bioassays of luminescent bacteria, as well as in silico genotoxicity and cytotoxicity predictions, indicate that the toxicity of p-BQ TPs is significantly higher than that of their precursors and other TPs. These together demonstrated that the identified p-BQ TPs are primary toxicity contributors. The redox-directed approach facilitated the revelation of primary toxicity contribution, illustrating emerging p-BQs are a concern for aquatic ecosystem safety in the oxidative treatment of aromatics-contaminated wastewater.

Removal of micropollutants and ecotoxicity during combined biological activated carbon and ozone (BO3) treatment

Ozonation is a viable option to improve the removal of micropollutants (MPs) in wastewater treatment plants (WWTPs). Nevertheless, the application of ozonation is hindered by its high energy requirements and by the uncertainties regarding the formation of toxic transformation products in the process. Energy requirements of ozonation can be reduced with a pre-ozone treatment, such as a biological activated carbon (BAC) filter, that removes part of the effluent organic matter before ozonation. This study investigated a combination of BAC filtration followed by ozonation (the BO3 process) to remove MPs at low ozone doses and low energy input, and focused on the formation of toxic organic and inorganic products during ozonation. Effluent from a WWTP was collected, spiked with MPs (approximately 1 µg/L) and treated with the BO3 process. Different flowrates (0.25–4 L/h) and specific ozone doses (0.2–0.6 g O3/g TOC) were tested and MPs, ecotoxicity and bromate were analyzed. For ecotoxicity assessment, three in vivo (daphnia, algae and bacteria) and six in vitro CALUX assays (Era, GR, PAH, P53, PR, andNrf2 CALUX) were used.Results show that the combination of BAC filtration and ozonation has higher MP removal and higher ecotoxicity removal than only BAC filtration and only ozonation. The in vivo assays show a low ecotoxicity in the initial WWTP effluent samples and no clear trend with increasing ozone doses, while most of the in vitro assays show a decrease in ecotoxicity with increasing ozone dose. This suggests that for the tested bioassays, feed water and ozone doses, the overall ecotoxicity of the formed transformation products during ozonation was lower than the overall ecotoxicity of the parent compounds. In the experiments with bromide spiking, relevant formation of bromate was observed above specific ozone doses of approximately 0.4 O3/g TOC and more bromate was formed for the samples with BAC pre-treatment. This indirectly indicates the effectivity of the pre-treatment in removing organic matter and making ozone more available to react with other compounds (such as MPs, but also bromide), but also underlines the importance of controlling the ozone dose to be below the threshold to avoid formation of bromate. It was concluded that treatment of the tested WWTP effluent in the BO3 process at a specific ozone dose of 0.2 g O3/g TOC, results in high MP removal at limited energy input while no increase in ecotoxicity, nor formation of bromate was observed under this condition. This indicates that the hybrid BO3 process can be implemented to remove MPs and improve the ecological quality of this WWTP effluent with a lower energy demand than conventional MP removal processes such as standalone ozonation.

Intelligent Workflow and Software for Non-Target Analysis of Complex Samples Using a Mixture of Toxic Transformation Products of Unsymmetrical Dimethylhydrazine as an Example.

Unsymmetrical dimethylhydrazine (UDMH) is a widely used rocket propellant. Entering the environment or being stored in uncontrolled conditions, UDMH easily forms an enormous variety (at least many dozens) of transformation products. Environmental pollution by UDMH and its transformation products is a major problem in many countries and across the Arctic region. Unfortunately, previous works often use only electron ionization mass spectrometry with a library search, or they consider only the molecular formula to propose the structures of new products. This is quite an unreliable approach. It was demonstrated that a newly proposed artificial intelligence-based workflow allows for the proposal of structures of UDMH transformation products with a greater degree of certainty. The presented free and open-source software with a convenient graphical user interface facilitates the non-target analysis of industrial samples. It has bundled machine learning models for the prediction of retention indices and mass spectra. A critical analysis of whether a combination of several methods of chromatography and mass spectrometry allows us to elucidate the structure of an unknown UDMH transformation product was provided. It was demonstrated that the use of gas chromatographic retention indices for two stationary phases (polar and non-polar) allows for the rejection of false candidates in many cases when only one retention index is not enough. The structures of five previously unknown UDMH transformation products were proposed, and four previously proposed structures were refined.

Fluorescent spectroscopy paired with parallel factor analysis for quantitative monitoring of phenanthrene biodegradation and metabolite formation

Polycyclic aromatic hydrocarbons (PAHs) are a class of environmental contaminants released into the environment from both natural and anthropogenic sources that are associated with carcinogenic, mutagenic, and teratogenic health effects. Many remediation strategies for the treatment of PAH contaminated material, including bioremediation, can lead to the formation of toxic transformation products. Analytical techniques for PAHs and PAH transformation products often require extensive sample preparation including solvent extraction and concentration, chromatographic separation, and mass spectrometry to identify and quantify compounds of interest. Excitation-emission matrix (EEM) fluorescent spectroscopy paired with parallel factor analysis (PARAFAC) is an approach for analyzing PAHs that eliminates the need for extensive sample preparation and separation techniques before analysis. However, this technique has rarely been applied to monitoring PAH biotransformation and formation of PAH metabolites. The objectives of this research were to compare an established targeted analytical method to two-dimensional fluorescent spectroscopy and combined EEM-PARAFAC methods to monitor phenanthrene degradation by a bacterial pure culture, Mycobacterium Strain ELW1, identify and quantify phenanthrene transformation products, and derive kinetic constants for phenanthrene degradation and metabolite formation. Both phenanthrene and its primary transformation product, trans-9,10-dihydroxy-9,10-dihydrophenanthrene, were identified and quantified with the EEM-PARAFAC method. The value of the EEM-PARAFAC method was demonstrated in the superiority of sensitivity and accuracy of quantification to two-dimensional fluorescent spectroscopy. Quantification of targets and derivation of kinetic constants using the EEM-PARAFAC method were validated with an established gas chromatography-mass spectrometry (GC-MS) method. To the authors’ knowledge, this is the first study to use an EEM-PARAFAC method to monitor, identify, and quantify both PAH biodegradation and PAH metabolite formation by a bacterial pure culture.

Evaluation of the Environmental Fate of a Semivolatile Transformation Product of Ibuprofen Based on a Simple Two-Media Fate Model.

Partitioning between surface waters and the atmosphere is an important process, influencing the fate and transport of semi-volatile contaminants. In this work, a simple methodology that combines experimental data and modeling was used to investigate the degradation of a semi-volatile pollutant in a two-phase system (surface water + atmosphere). 4-Isobutylacetophenone (IBAP) was chosen as a model contaminant; IBAP is a toxic transformation product of the non-steroidal, anti-inflammatory drug ibuprofen. Here, we show that the atmospheric behavior of IBAP would mainly be characterized by reaction with •OH radicals, while degradation initiated by •NO3 or direct photolysis would be negligible. The present study underlines that the gas-phase reactivity of IBAP with •OH is faster, compared to the likely kinetics of volatilization from aqueous systems. Therefore, it might prove very difficult to detect gas-phase IBAP. Nevertheless, up to 60% of IBAP occurring in a deep and dissolved organic carbon-rich water body might be eliminated via volatilization and subsequent reaction with gas-phase •OH. The present study suggests that the gas-phase chemistry of semi-volatile organic compounds which, like IBAP, initially occur in natural water bodies in contact with the atmosphere is potentially very important in some environmental conditions.

Hydroxyl radicals can significantly influence the toxicity of ofloxacin transformation products during ozonation

Ozonation is often applied to eliminate the recalcitrant contaminants in water. During the process, toxic transformation products (TPs) can be generated mainly via the reactions with ozone and hydroxyl radicals (•OH). However, the toxicity difference between the TPs generated from O3 and •OH has not been well elucidated. In this study, we designed ozonation scenarios with different Rct values (the exposure ratio of •OH to O3) via varying pH values, adding a catalyst or a radical scavenger, and investigated the degradation of a popularly used antibiotic ofloxacin (OFX). The microbial oxygen uptake, the development of zebrafish embryos, and the calculation with the Toxicity Estimation Software Tool (T.E.S.T) were applied to evaluate the toxicity of TPs generated from the above reaction scenarios. The toxicity tests demonstrated that TPs formed at high-Rct conditions were less toxic than those at low-Rct conditions. Ten and eleven TPs were identified during ozonation of OFX at pH 3 and 9, respectively, based on which the different pathways were proposed. The piperazine ring's demethylation and opening occurred at both pH values, while the hydroxylation of quinolone and oxazine mainly occurred at pH 9. The study suggests that •OH might be more efficient in eliminating the toxicity of OFX than O3.

Evaluation of a full-scale wastewater treatment plant with ozonation and different post-treatments using a broad range of in vitro and in vivo bioassays

Micropollutants present in the effluent of wastewater treatment plants (WWTPs) after biological treatment are largely eliminated by effective advanced technologies such as ozonation. Discharge of contaminants into freshwater ecosystems can thus be minimized, while simultaneously protecting drinking water resources. However, ozonation can lead to reactive and potentially toxic transformation products. To remove these, the Swiss Federal Office for the Environment recommends additional "post-treatment" of ozonated WWTP effluent using sand filtration, but other treatments may be similarly effective. In this study, 48 h composite wastewater samples were collected before and after full-scale ozonation, and after post-treatments (full-scale sand filtration, pilot-scale fresh and pre-loaded granular activated carbon, and fixed and moving beds). Ecotoxicological tests were performed to quantify the changes in water quality following different treatment steps. These included standard in vitro bioassays for the detection of endocrine, genotoxic and mutagenic effects, as well as toxicity to green algae and bacteria, and flow-through in vivo bioassays using oligochaetes and early life stages of rainbow trout.Results show that ozonation reduced a number of ecotoxicological effects of biologically treated wastewater by 66 - 93%: It improved growth and photosynthesis of green algae, decreased toxicity to luminescent bacteria, reduced concentrations of hormonally active contaminants and significantly changed expression of biomarker genes in rainbow trout liver. Bioassay results showed that ozonation did not produce problematic levels of reaction products overall. Small increases in toxicity observed in a few samples were reduced or eliminated by post-treatments. However, only relatively fresh granular activated carbon (analyzed at 13,000 - 20,000 bed volumes) significantly reduced effects additionally (by up to 66%) compared to ozonation alone. Inhibition of algal photosynthesis, rainbow trout liver histopathology and biomarker gene expression proved to be sufficiently sensitive endpoints to detect the change in water quality achieved by post-treatment.

New transformation products from ozonation and photolysis of diclofenac in the aqueous phase

Ozone and UV photolysis can be effective for the treatment of pharmaceuticals in wastewater, however, these processes can result in the formation of potentially toxic transformation products (TPs). This study investigates the structural elucidation of the TPs formed during ozone and UV treatments of diclofenac (DCF), a ubiquitous pharmaceutical. Using liquid chromatography – electrospray ionisation - mass spectrometer (LC-ESI-MS) and a Waters Xevo™ Quadrupole Time-of-Flight (Qtof) mass spectrometer, the chemical structures of DCF TPs were identified, including the fragmentation ion patterns and exact mass of the detected molecular ions. TPs formed during ozonation showed an addition of one or more hydroxyl groups to the DCF molecule including changes to the double bond equivalent for some products. The other identified DCF ozonation products were formed by removal of the (-CH2COOH) group in two steps and resulted in the formation of a diverse range of TPs. By contrast, UV photolysis formed DCF TPs via removal of its chlorine atoms and ring closure followed by dimerization. In comparison, all ozonation TPs retained the two chlorine atoms of DCF whereas UV TPs did not possess any chlorine atom except for one compound that retained one chlorine atom. Possible reaction pathways for the identified DCF TPs are also proposed.

Diclofenac biotransformation in the enhanced biological phosphorus removal process

Diclofenac is a pharmaceutical active compound frequently detected in wastewater and water bodies, and often reported to be persistent and difficult to biodegrade. While many previous studies have focussed on assessing diclofenac biodegradation in nitrification and denitrification processes, this study focusses on diclofenac biodegradation in the enhanced biological phosphorus removal (EBPR) process, where the efficiency of this process for diclofenac biodegradation as well as the metabolites generated are not well understood. An enrichment of Accumulibacter polyphosphate accumulating organisms (PAOs) was operated in an SBR for over 300 d, and acclimatized to 20 μg/L of diclofenac, which is in a similar range to that observed in domestic wastewater influents. The diclofenac biotransformation was monitored in four periods of stable operation and linked to the microbial community and metabolic behaviour in each period. Nitrification was observed in two of the four periods despite the addition of a nitrification inhibitor, and these periods were positively correlated with increased diclofenac biodegradation. Interestingly, in two periods with excellent phosphorus removal (>99%) and no nitrification, different levels of diclofenac biotransformation were observed. Period 2, enriched in Accumulibacter Type II achieved more significant diclofenac biotransformation (3.4 μg/gX), while period 4, enriched in Accumulibacter Type I achieved lower diclofenac biotransformation (0.4 μg/gX). In total, 23 transformation products were identified, with lower toxicity than the parent compound, enabling the elucidation of multiple metabolic pathways for diclofenac biotransformation. This study showed that PAOs can contribute to diclofenac biotransformation, yielding less toxic transformation products, and can complement the biodegradation carried out by other organisms in activated sludge, particularly nitrifiers.

Degradation and toxicity of the antidepressant fluoxetine in an aqueous system by UV irradiation

Fluoxetine (FLU), a selective serotonin reuptake inhibitor, is commonly found in aquatic environments. Ultraviolet (UV) photolysis is widely used to remove certain pharmaceuticals from water and wastewater. The present study aimed to investigate the toxicity of FLU and its transformed products formed during UV photolysis by using zebrafish embryos (Danio rerio) as a model. The degradation rates of FLU for five days were approximately 63.6% ± 2.14%, 84.6% ± 0.99%, and 97.5% ± 0.25% after 15, 30, and 60 min of UV irradiation, respectively. Furthermore, the degradation mechanism was explored using LC-MS measurements and density flooding theory (DFT) theoretical calculations. Comprehensive toxicity preassessment of FLU and its degradation products was carried out using the T.E.S.T. software. The effects of physiological and biochemical parameters and neuron- and apoptosis-related gene expression were examined in zebrafish embryos exposed to non-irradiated (0-min) and irradiated (15, 30- and 60-min) solutions from 4 h post-fertilization (hpf) to 120 hpf. The hatching time of zebrafish embryos exposed to the non-irradiated solution (0-min) and irradiated solution (60-min) was delayed, their heart rate at 48 and 72 hpf increased, and their body length at 120 hpf decreased. Significant differences were found between the non-irradiated (0-min) and UV-irradiated (15- or 30-min) groups. A dynamic response involving acetylcholinesterase (AChE) and superoxide dismutase (SOD) activity was also observed in the non-irradiated and UV-irradiated groups. During the UV treatment experiments, the expression levels of neuron-related and apoptosis-related genes were significantly reduced over time alongside the formation of FLU degradation products. Overall, this study provides new concepts to remove and assess the toxicity of emerging contaminants in aquatic environments and highlights the need to consider the formation and persistence of toxic transformation products.

UV aged epoxy coatings ̶ Ecotoxicological effects and released compounds

Organic coatings can guarantee long-term protection of steel structures due to causing a physical barrier against water and oxygen. Because of their mechanical properties and resistances to heat and chemicals, epoxy resin-based coatings are widely used for corrosion protection. Despite of the aromatic backbone and the resulting susceptibility to UV degradation, epoxy resins are frequently used as binding agent in top layers of anti-corrosion coating systems. Consequently, these organic polymers are directly exposed to sunlight and thus UV radiation. The present study was designed to investigate if toxic effects of epoxy resin-based-coatings are changed by UV-A irradiation. For this purpose, two epoxide-based top coatings were examined with and without UV aging for their bacterial toxicity and estrogenicity. In addition, chemical analyses were performed to identify released compounds as well as photolytic degradation products and to assign toxic effects to individual substances. UV-A irradiation of epoxy resin based top coatings resulted in an overall decrease of acute and specific ecotoxicological effects but as well to the formation of toxic transformation products. Both, in leachates of untreated and UV-A irradiated coatings, 4tBP was identified as the main driver of estrogenicity and toxicity to luminescent bacteria. BPA and structural analogs contributing to estrogenic effects in leachates were formed by UV-A irradiation. The combination of HPTLC coupled bioassays and LC-MS analyses supported the identification of bioactive compounds in terms of an effect-directed analysis. The present findings indicate that epoxide-based coatings are less suitable for the application as top coatings and more UV stable coatings like aliphatic polyurethanes should be preferred.

Removal and fate of carbamazepine in the microbial fuel cell coupled constructed wetland system

Carbamazepine (CBZ), which is difficult to remove in the wastewater treatment system and easily forms toxic transformation products during the treatment process, is one of the priority pollutants of pharmaceuticals and personal care products (PPCPs). Increasing attention has been paid to explore their treatment technology without side effects from the treatment products. This study aims to reveal the removal and transformation of CBZ in the microbial fuel cell coupled constructed wetland (CW-MFC) system. The CW-MFC system was operated continuously at room temperature for nearly 80 days. The results show that CW-MFC system can effectively remove CBZ with an average removal rate of 97%. Three transformation products were identified by liquid chromatography−high-resolution mass spectrometry: 2-(2-oxoquinazolin-1(2H)-yl) benzoic acid (TP267), methyl 2-(2-oxoquinazolin-1(2H)-yl) benzoate (TP281), 2-(2,4-dioxo-3,4-dihydroquinazolin-1(2H)-yl) benzoic acid (TP283). Except TP281 in the influent, the other transformation products were formed in the system, which indicated that TP267 and TP283 were the main transformation products of CBZ. The formation pathway of transformation products could be explained by reactions including oxidation, hydrolysis, bond rupture and intramolecular reaction. The results also indicate that the CW-MFC system might be a promising technology for PPCPs treatment.