Identified Transformation Products Research Articles

Reaction mechanisms for methyl isocyanate (CH3NCO) gas-phase degradation

Methyl isocyanate (MIC) is a toxic chemical found in many commercial, industrial, and agricultural processes, and was the primary chemical involved in the Bhopal, India disaster of 1984. The atmospheric environmental chemical reactivity of MIC is relatively unknown with only proposed reaction channels, mainly involving OH-initiated reactions. The gas-phase degradation reaction pathways of MIC and its primary product, formyl isocyanate (FIC), were investigated with quantum mechanical (QM) calculations to assess the fate of the toxic chemical and its primary transformation products. Transition state energy barriers and reaction energetics were evaluated for thermolysis/pyrolysis-like reactions and bimolecular reactions initiated by relevant radicals (•OH and Cl•) to evaluate the potential energy surfaces and identify the primary reaction pathways and products. Thermolysis/pyrolysis of MIC requires high energy to initiate N-CH3 and C-H bond dissociation and is unlikely to dissociate except under extreme conditions. Bimolecular radical addition and H-abstraction reaction pathways are deemed the most kinetically and thermodynamically favorable mechanisms. The primary transformation products of MIC were identified as FIC, methylcarbamic acid, isocyanic acid (isocyanate radical), and carbon dioxide. The results of this work inform the gas-phase reaction channels of MIC and FIC reactivity and identify transformation products under various reaction conditions.

Anthropogenic-induced ecological risks on marine ecosystems indicated by characterizing emerging pollutants in Pearl River Estuary, China

Anthropogenic Contaminants of Emerging Concern (CECs) in marine environments have raised significant concerns. Yet, analyses detailing their origins, fate, and environmental effects are limited. This study employs an integrated non-target screening methodology to elucidate CECs existence across 46 sampling sites in the Pearl River Estuary (PRE) of the South China Sea. Assisted by advanced liquid chromatography-high resolution mass spectrometry, we discovered 208 chemicals in six usage categories, with pesticides (33 %) and pharmaceuticals (29 %) predominating. Several CECs drew attention for their consistent detections, profound abundance, and significant ecotoxicities. The wide detection of them at offshore sites further implies that anthropogenic activities may contribute to large-scale contamination. Meanwhile, distinct distribution patterns of CECs across PRE are evident in semi-quantitative results, indicating regional anthropogenic influences. Identified transformation products may establish a novel and non-negligible negative contribution to ecology through elevated environmental toxicities, exemplified by HMMM and atrazine. Based on the ecological risks, we compiled a prioritized list of 21 CECs warranting intensified scrutiny. Our findings indicate the introduction of various CECs into the South China Sea via PRE, emphasizing the urgent necessity for ongoing surveillance of discharged CECs at estuary areas and assessment of their marine ecological consequences.

Biotransformation of HBCDs by the microbial communities enriched from mangrove sediments

1,2,5,6,9,10-Hexabromocyclododecanes (HBCDs) are a sort of persistent organic pollutants (POPs). This research investigated 12 microbial communities enriched from sediments of four mangroves in China to transform HBCDs. Six microbial communities gained high transformation rates (27.5–97.7%) after 12 generations of serial transfer. Bacteria were the main contributors to transform HBCDs rather than fungi. Analyses on the bacterial compositions and binning genomes showed that Alcanivorax (55.246–84.942%) harboring haloalkane dehalogenase genes dadAH and dadBH dominated the microbial communities with high transformation rates. Moreover, expressions of dadAH and dadBH in the microbial communities and Alcanivorax isolate could be induced by HBCDs. Further, it was found that purified proteins DadAH and DadBH showed high conversion rates on HBCDs in 36 h (91.9 ± 7.4 and 101.0 ± 1.8%, respectively). The engineered Escherichia coli BL21 strains harbored two genes could convert 5.7 ± 0.4 and 35.1 ± 0.1% HBCDs, respectively, lower than their cell-free crude extracts (61.2 ± 5.2 and 56.5 ± 8.7%, respectively). The diastereoisomer-specific transforming trend by both microbial communities and enzymes were γ- > α- > β-HBCD, differed from α- > β- > γ-HBCD by the Alcanivorax isolate. The identified transformation products indicated that HBCDs were dehalogenated via HBr elimination (dehydrobromination), hydrolytic and reductive debromination pathways in the enriched cultures. Two enzymes converted HBCDs via hydrolytic debromination. The present research provided theoretical bases for the biotransformation of HBCDs by microbial community and the bioremediation of HBCDs contamination in the environment.

Enhanced degradation of para-nitrophenol during the UV/chlorine process with the addition of Fe(III): Performance, reaction mechanisms, and DBPs formation

Para-nitrophenol (PNP) enters aquatic environments through wastewater discharge, potentially threatening ecological security and public health. This work investigated the enhanced degradation of PNP in wastewater during the UV/chlorine process with the addition of Fe(III) (UV/chlorine/Fe(III)). The UV/chlorine/Fe(III) process (61.85 %) exhibited higher performance in PNP degradation in 10 min compared to the UV/chlorine process (40.00 %) because the synergistic effect of Fe(III) and free chlorine enhanced hydroxyl radicals (OH) and reactive chlorine species (RCSs) production. Furthermore, OH and RCSs were identified as the primary contributors to degrade PNP during the UV/chlorine/Fe(III) process, and their corresponding contributions accounted for 40.09 % and 37.10 %, respectively. Besides, the degradation efficiencies of PNP were promoted by increasing the dosages of Fe(III) and free chlorine and declined by increasing pH and PNP concentration. Also, Cl− could promote PNP degradation, while SO42− and HCO3− inhibited it. Then, the reaction mechanisms of PNP degradation during the UV/chlorine/Fe(III) process were proposed based on the identified transformation products (TPs) and the density functional theory (DFT) calculation. Meanwhile, PNP, TPs, and other possible intermediate products presented different ecotoxicity. Finally, the formation and toxicity of disinfection by-products (DBPs) with different Fe(III) concentrations, chlorine dosages, initial pHs, and PNP concentrations were explored. Overall, the obtained findings can provide deep insights into the mechanisms of PNP degradation and a new approach to enhancing PNP degradation in wastewater.

Waste tire upcycling for the efficient electrogeneration of H2O2 in advanced degradation of the antibiotic tinidazole by electro-Fenton process

The electrochemical production of H2O2 using small- and medium-size modular devices has emerged as an interesting approach for water treatment. In this work, waste tire-derived carbon (WTC) has been innovatively employed as a cheap and recycled electroactive material to manufacture a gas-diffusion cathode. It was found that acidification with HNO3 significantly enhanced the H2O2 production, attaining a concentration of up to 1161 mg/L with a current efficiency around 40 %–60 %. These results were superior to those obtained by treating the WTC with H2SO4 or KOH, being also better than the values reached with reported carbons. Liner and cyclic voltammetries informed about the oxygen reduction reaction profiles; transmission electron microscopy revealed the morphological features of the synthesized carbons, whereas other properties were obtained by Brunauer−Emmett−Teller analysis, Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. The cathode was further employed to degrade tinidazole (TNZ), a typical nitroimidazole antibiotic, in water by electro-Fenton at pH 3.0, producing more than 10 mM H2O2. The effect of solution pH, Fe2+ dosage and initial TNZ concentration was investigated. Under optimal conditions (0.5 mM Fe2+ and 20 mA/cm2), the treatment of solutions containing 20 mg/L TNZ at pH 3.0 yielded a pseudo-first-order constant (k1) of 0.449 min−1. Besides, the degradation pathways were proposed according to the 7 identified transformation products. This study demonstrates that waste tires can become a source of inexpensive carbon able to catalyze the in-situ H2O2 synthesis for water decontamination, in excellent agreement with new policies on circular economy.

Enhanced removal of phenolic compounds by ferrate(VI): Unveiling the Bi(III)-Bi(V) valence cycle with in situ formed bismuth hydroxide as catalyst

The use of 2-hydroxybenzophenone (2-HBP) in personal care products is of great concern due to its potential negative effects on the ecosystem and public health. This paper presents the degradation of 2-HBP by bismuth(III) (Bi3+)-ferrate(VI) (FeVIO42−, Fe(VI)) (Bi3+-Fe(VI) system). Experimental studies at different pH and dosages of Bi3+ and Fe(VI) showed that the Bi3+-Fe(VI) system increased the degradation rate and removal efficiency of 2-HBP compared to Fe(VI) alone. The in situ formed flake-like white flocculent precipitate of Bi(OH)3 showed catalytic performance through the Bi(III)-Bi(V)-Bi(III) valence cycle which was demonstrated through spectroscopic measurements. The hydrogen transfer-mediated reactions between Fe(VI) and Bi(OH)3 as well as subsequent formation of Bi(V) were supported by performing density functional theoretical (DFT) calculations. Seventeen identified transformation products of 2-HBP by Fe(VI) with and without Bi3+ revealed hydroxylation, bond breaking, carboxylation, and polymerization reaction pathways. Significantly, Bi3+ facilitated the polymerization reaction and the dioxygen transfer-mediated hydroxylation reaction pathways. The ions (anions and cations) and humic acids (HA) present in the Bi3+-Fe(VI) system had minimal influence on the removal efficiency of 2-HBP. Reusability tests and use of real water samples as well as toxicity assessments of transformation products unveiled the practical application aspect of the Bi3+-Fe(VI) system. Finally, the results showed that the system exhibits good removal efficiency for all 12 phenolic compounds, indicating theuniversality. The Bi3+-Fe(VI) system may be an easy-to-implement cost-effective method for the catalytic degradation of benzophenones by Fe(VI).

Comparison of the photocatalytic degradability of PFOA, PFOS and GenX using Fe-zeolite in water

Knowledge on the photocatalytic degradability of the emerging poly- and perfluorinated alkyl substances (PFAS) in water, specifically GenX, is limited. GenX has been detected globally in river water and is considered potentially more toxic than legacy PFAS. In this study, we compared the photocatalytic degradability of GenX with the legacy compounds perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) using Fe-zeolite photocatalysts. After 7 h of irradiation, GenX showed lower removal (79%) and defluorination (33%) as compared to PFOA (100% removal and 69% defluorination) and PFOS (100% removal and 51% defluorination). The quasi-first-order degradation rate of GenX (1.5 h1) was 12 and 1.2 times lower than PFOA (18.4 h−1) and PFOS (1.8 h−1), respectively. Additionally, PFOA's defluorination rate (0.9 h−1) was approximately 2.6 and 9 times higher than GenX (0.35 h−1) and PFOS (0.1 h−1), respectively. These outcomes correlate with GenX's lower hydrophobicity, leading to reduced adsorption (40%) compared to PFOA (99%) and PFOS (87%). Based on identified transformation products, we proposed a GenX degradation pathway, resulting in ultra-short-chain PFASs with a chain length of 2 and 3 carbon atoms, while PFOA and PFOS degraded stepwise, losing 1 carbon-fluorine bond at a time, leading to gradually shorter chain lengths (from 7 to 2 carbon atoms). In conclusion, GenX is more challenging to remove and degrade due to its lower adsorption on the photocatalyst, potential steric hindrance, and higher production of persistent ultra-short-chain transformation products through photocatalysis.

Status quo on identified transformation products of organic ultraviolet filters and their persistence.

Organic micropollutants of concern - including organic UV filters (UVF) - are getting increasing attention. Personal care products such as sun screens or cosmetic articles often contain large quantities of UVF. These substances enter the environment either directly (during outdoor activities) or indirectly (via sewages from households). Therefore, the removal or degradation of UVF by natural or technical treatment processes is important to understand. UVF are often incompletely removed and transformed to side products of incomplete mineralization by abiotic and biotic processes. An extensive overview on transformation products (TPs) is essential to systematically identify knowledge gaps and to derive research needs. Whilst there are many reviews on the UVF themselves, the number of reviews which focus on their TPs is limited. Consequently, this review gives an overview on the latest findings regarding TPs of UVF. In this publication, known TPs of UVF, which were formed during abiotic and biotic processes, are reviewed. Target substances were defined and a literature database was reviewed for studies on TPs of the target substances. The first list of studies was shortened stepwise, thus generating a final list of studies which contained only the relevant studies. Since biodegradation is one of the most important pathways for removal of organic compounds from the environment, this review presents an overview on known TPs of organic UVF and their biodegradability, which determines their environmental fate. In this way, all identified TPs of UVF were listed and checked for information on their biodegradability. 2,731 records of studies were assessed. 42 studies, which assessed 46 processes that lead to the formation of identified TPs, were included in this review. 177 different TPs resulting from eleven different UVF were identified. Little to no data on the biodegradability was found for TPs. This indicates a severe lack of data on the biodegradability of TPs of organic UVF substances. Since most TPs lack information on biodegradability, further research should provide information on both - identity and biodegradability - of formed TPs to be able to assess their hazardousness for the environment.

Insight into wavelength-dependent UVA-LED/chlorine process for micropollutant degradation: Performance, mechanism, and effects of water matrix

Ultraviolet A light-emitting diode (UVA-LED)-activated chlorine effectively degraded micropollutants at different irradiation wavelengths. Quenching experiments indicated that OH, reactive chlorine species (RCS), and O3 were the main reactive species for degradation of atenolol (ATL). Bezafibrate and ibuprofen, were used for the first time to jointly quantify the concentrations of Cl2− and ClO. Notably, O3 contributed most to the degradation of ATL (38.9%), following by OH (30.2%) and RCS (27.6%) at pH 7.0 by the UVA-LED/chlorine at 385 nm. ATL degradation increased with the decrease of wavelengths, due to the higher quantum yields of chlorine. The kobs of ATL was positively correlated to the quantum yield of chlorine at the UVA wavelength band. Higher light intensity could enhance the photolysis of chlorine, leading to enhanced ATL degradation. The protonated chlorine is more conducive to the degradation of ATL. Specifically, the contributions of OH, O3, and RCS to ATL degradation changed from 40.9%, 6.53%, and 41.0% at pH 4.0 to 11.6%, 59.9%, and 26.6% at pH 9.0, respectively. Cl− had no significant influence on ATL degradation, mainly due to the synergistic effect of different reactive species. HCO3− and HA inhibited ATL degradation owing to the quenching effect for reactive species and/or UV filtering effect. The primary transformation pathway of ATL included hydroxylation, chlorination, and bond-cleavage pathways based on the structures of the eight identified transformation products. Seven chlorinated disinfection by-products decreased as wavelengths and pH increased. The above results show that UVA-LED/chlorine might be an efficient process for water treatment.

Sonochemical degradation of the artificial sweetener acesulfame in aqueous medium and identification of transformation products

The sonochemical degradation of acesulfame (ACE), a widely used artificial sweetener, was investigated. The impact of power density (40 and 71 W/L), initial ACE concentration (1.5–30.6 μΜ), and initial solution pH (3–9) for the elimination of the target pollutant from water was studied. It was found that nearly complete degradation of ACE was achieved within 120 min of treatment under conditions suitable for high production of free radicals. Degradation follows a pseudo-first order kinetic model. Coupling sonochemical degradation at optimal conditions with sodium persulfate (0.2–1.0 mM) enhanced the rate of ACE oxidation by six times. The influence of water complexity was also examined; the natural occurrence of humic acid in the water matrix reduced the degradation rate, despite the fact that at least 42 % of ACE removal was achieved. Finally, LC-QToF-MS was used to evaluate the generated transformation products (TPs). Using HRMS suspect and non-target screening, seven ACE TPs were identified, and their time-trend formation profiles showed a rising trend throughout the experiment. According to the ECOSAR model, most of the identified transformation products exhibited lower toxicity than acesulfame, with one notable exception that was classified as harmful due to its acute toxicity on fish and green algae.

Investigation of transformation products of selected veterinary drugs generated by electrochemistry, microsomal assays, hydrolysis & photolysis

The knowledge of transformation pathways and transformation products of veterinary drugs is important for health, food and environmental matters. Residues (original veterinary drug and transformation products) are found in food products of animal origin and also in the environment (e.g., soil or surface water). Several transformation processes can alter the original veterinary drug, ranging from biotransformation in living organism to environmental degradation processes like photolysis, hydrolysis, or microbial processes. In this thesis, four veterinary drugs were investigated, three ionophore antibiotics Monensin, Salinomycin and Lasalocid and the macrocyclic lactone Moxidectin. Ionophore antibiotics are mainly used to cure and prevent coccidiosis in poultry especially prophylactic in broiler farming. Moxidectin is an antiparasitic drug and is used for the treatment of internal and external parasites in food‐ producing and companion animals. The main objective of this work was the usage of different laboratory approaches to generate and identify transformation products. The identification was conducted using high‐resolution mass spectrometry (HR‐MS). A major focus was put on the application of electrochemistry for simulation of transformation processes. The electrochemical reactor, equipped with a three‐electrode flow‐through cell, enabled the oxidation or reduction by applying a potential. Derived transformation products were analyzed by online coupling of the electrochemical reactor and a HR‐MS and offline by liquid chromatography (LC) combined with HR‐MS. The main modification reaction of the identified transformation products was different for each investigated veterinary drug. Monensin was showing decarboxylation and demethylation as main modification reactions, for Salinomycin mostly decarbonylation was occurring and for Lasalocid methylation was prevalent. For Moxidectin I observed oxidation (hydroxylation) reaction and adduct formation with solvent. In general, for salinomycin and Lasalocid more transient transformation products (online measurement) than stable transformation products (offline measurements) were detected. In contrast, the number of transformation products using online and offline measurements were identical for monensin and moxidectin. As a complementary approach, metabolism tests with rat or human liver microsomes were made for the ionophore antibiotics. Monensin was investigated by using rat liver microsomes and identified transformation products were based on decarboxylation and demethylation. Salinomycin and Lasalocid were converted by human and rat liver microsomes. For both substances were more transformation products found by using human liver microsomes. The transformation products of the rat liver microsome conversion were redundant, the transformation products were also found at the human liver microsome assay. Oxidation (hydroxylation) was found to be the main modification reaction for both. In addition, a frequent ion‐exchange between sodium and potassium was identified. The last two experiments were performed for one substance each, the hydrolysis of monensin and the photolysis of moxidectin was investigated. The transformation products of the pH‐ dependent hydrolysis were based on ring‐opening and dehydration. Moxidectin formed several transformation products by irradiation with UV‐C light and main modification reactions were isomeric changes, (de‐)hydration and changes of the methoxime moiety. In summary, transformation products of the four investigated veterinary drugs were generated by the different laboratory approaches. Most of the identified transformation products were identified for the first time. The resulting findings provide an understanding for clarifying the transformation behavior.

Uncovering the Dissipation of Chlorantraniliprole in Tomatoes: Identifying Transformation Products (TPs) and Coformulants in Greenhouse and Laboratory Studies by UHPLC-Q-Orbitrap-MS and GC-Q-Orbitrap-MS.

The present study addressed the dissipation of the insecticide chlorantraniliprole in tomatoes treated with Altacor 35 WG under laboratory and greenhouse conditions, as well as the identification of transformation products (TPs) and coformulants, performing suspect screening analysis. Analyses were performed by ultra-high-performance liquid and gas chromatography coupled to quadrupole-Orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap-MS and GC-Q-Orbitrap-MS). In all cases, chlorantraniliprole was fitted to a biphasic kinetic model, with R2 values greater than 0.99. Dissipation was noticeably faster in greenhouse studies, in which even 96% dissipation was achieved over 53 days. One TP, IN-F6L99, was tentatively identified in both greenhouse and laboratory studies and was semiquantified by using chlorantraniliprole as the analytical standard, yielding a top value of 354 μg/kg for laboratory studies, whereas values for greenhouse studies fell under the limit of quantitation (LOQ). Finally, a total of 15 volatile coformulants were identified by GC-Q-Orbitrap-MS.

Application of a KOH-activated biochar for the activation of persulfate and the degradation of sulfamethoxazole

In this work, valorized biomass was simultaneously pyrolyzed and activated with potassium hydroxide to produce a biochar with specific surface area of 1148 m2g−1, i.e. ten times greater than the pristine material, and significant amounts of surface oxygen species and carbonates, as evidenced by XRD and FTIR characterization. The activated biochar (50–250 mgL−1) was employed for a first time as sodium persulfate (100–750 mgL−1) activator to induce the adsorption/oxidation of sulfamethoxazole (SMX: 0.25–1.5 mgL−1), a representative emerging micropollutant, in various water matrices, including the detailed study of different parameters in wastewater. In general, the degradation follows pseudo-first order kinetic law and the apparent constant was found to increase with increasing biochar, persulfate concentration and acidity of the solution and decreasing with SMX concentration, matrix complexity (from surface water or ultrapure water to actual or simulated wastewater). The mechanism of oxidation is mainly through radical pathway and/or electron transfer, while singlet oxygen’s contribution is inconsiderable, as evidenced by scavenging experiments and the structure of the various identified transformation products.

Evolvement of carbamazepine under solar irradiation in the presence of chlorine: Efficiency, influences, degradation pathways and ecotoxicity

Carbamazepine (CBZ) and residual chlorine coexist in wastewater discharged from wastewater treatment plants (WWTPs), while the mechanism of their photochemical transformation in the natural aquatic environment is still unclear. In this study, an approach combining experiment and quantum chemical calculation was used to explore the degradation mechanism of CBZ under chlorine/solar irradiation. The degradation of CBZ was not evident during disinfection alone or sunlight irradiation. However, CBZ was rapidly degraded under chlorine/solar irradiation (kobs = 0.463 min−1 at pH = 8.0). Quenching and probe experiments showed that the efficient removal of CBZ under chlorine/solar irradiation was credited with the production of ·Cl, ·OH, and O3, in which ·Cl (61.95%) and ·OH (33.14%) contributed significantly. The reaction mechanism of CBZ degradation was postulated, in conjunction with the identification of degradation products by HPLC/MS analysis and density functional theory. Among them, the primary degradation way was acridine production under the action of ·Cl and ·OH, and the decarboxylation process was the rate-limiting step. In addition, bioassay results indicated that the luminescent bacteria toxicity and genotoxicity of CBZ after chlorine/solar irradiation increased. Based on the identified transformation products and the quantitative structure-activity relationship, the elevated ecotoxicity was attributed to the TP209 and TP179 generated by pathway 1, and then controlling the decarboxylation process by adjusting pH and temperature to reduce the high toxic degradation products were proposed for ecological safety.

Mechanistic investigation of phosphonate photolysis in aqueous solution by simultaneous LC-IRMS and HRMS analysis

The mechanism of photolytic degradation of aminotrimethylphosphonic acid (ATMP) in an aqueous solution is not completely elucidated with respect to the transformation products formed during technical photodegradation. For the first time, the degradation of ATMP was investigated with simultaneous analysis by isotope ratio and high-resolution mass spectrometry (LC-IRMS+HRMS). This instrumental coupling combines quantitative data on degradation with compound-specific stable carbon isotope analysis (CSIA) in terms of kinetic isotope effects while identifying transformation products. Additionally, in combination with wet chemical analysis of ortho-phosphate (o-PO4), phosphorus balances were established to elucidate and interpret the degradation mechanism of ATMP under photolysis. Various experimental conditions during photolysis (temperature, dissolved oxygen concentration, and wavelength range) were investigated.ATMP was transformed to iminodimethylphosphonic acid (IDMP), aminomethylphosphonic acid (AMPA), and o-PO4 as main products during photolysis with a medium pressure mercury lamp. UV radiation < 310 nm was found to be required for ATMP degradation. The degradation of ATMP and its transformation products is slightly affected by temperature and dissolved oxygen concentration. Considering possible reactive oxygen species, such as hydroxyl radicals, it is assumed that the degradation of ATMP occurs to a small extent via a parallel degradation pathway in addition to photolysis. Complementary CSIA revealed an inverse carbon isotopic effect of ATMP due to direct photolysis, unaffected by the experimental conditions considered, while no isotopic effect was associated with the hydroxyl radical (H2O2) oxidation of ATMP. In UV/H2O2 oxidation of ATMP, four of five additional unknown transformation products, which have not yet been described in literature, could be assigned to postulated structures based on HRMS data. The findings achieved in this study demonstrate the advantages of simultaneous analysis by LC-IRMS+HRMS as a tool to elucidate reaction mechanisms for the first time.

Nontarget screening based on molecular networking strategy to identify transformation products of citalopram and sertraline in wastewater

Citalopram (CIT) and sertraline (SER) are highly consumed antidepressants worldwide and have been extensively detected in wastewater. Due to the incomplete mineralization, transformation products (TPs) of them can be detected in wastewater. Comparing with parent compounds, knowledge on TPs are limited. To fill these research gaps, lab-scale batch experiments, WWTPs sampling and in silico toxicity prediction were implemented to investigate the structure, occurrence and toxicity of TPs. Based on molecular networking nontarget strategy, 13 TPs of CIT and 12 TPs of SER were tentatively identified. Among them, 4 TPs from CIT and 5 TPs from SER were newly found in present study. TPs identification results compared with results obtained from previous nontarget strategies demonstrated that the excellent performances for molecular networking strategy on candidate TPs prioritizing and new TPs finding, especially for low abundance TPs. Further, transformation pathways for CIT and SER in wastewater were proposed. Newly identified TPs provided insights on defluorination, formylation and methylation for CIT and dehydrogenation, N-malonylation and N-acetoxylation for SER transformed in wastewater. Nitrile hydrolysis and N-succinylation were found to be the dominant transformation pathways for CIT and SER in wastewater, respectively. WWTPs sampling results shown the concentrations of SER and CIT ranged from 0.46 to 28.66 ng/L and 17.16 to 58.36 ng/L. In addition, 7 TPs of CIT and 2 TPs of SER found in lab-scale wastewater samples were found in WWTPs. In silico results suggested 2 TPs of CIT may be more toxic than CIT toward all three trophic levels organisms. Present study provides new insights into the transformation processes of CIT and SER in wastewater. In addition, the necessity of paying more attention on TPs was further highlighted from the aspects of toxicity for TPs of CIT and SER in effluent of WWTPs.

Solar photodegradation of irinotecan in water: optimization and robustness studies by experimental design.

Irinotecan, a widely prescribed anticancer drug, is an emerging contaminant of concern that has been detected in various aquatic environments due to ineffective removal by traditional wastewater treatment systems. Solar photodegradation is a viable approach that can effectively eradicate the drug from aqueous systems. In this study, we used the design of experiment (DOE) approach to explore the robustness of irinotecan photodegradation under simulated solar irradiation. A full factorial design, including a star design, was applied to study the effects of three parameters: initial concentration of irinotecan (1.0-9.0mg/L), pH (5.0-9.0), and irradiance (450-750W/m2). A high-performance liquid chromatography coupled with a high-resolution mass spectrometry (HPLC-HRMS) system was used to determine irinotecan and identify transformation products. The photodegradation of irinotecan followed a pseudo-first order kinetics. In the best-fitted linear model determined by the stepwise model fitting approach, pH was found to have about 100-fold greater effect than either irinotecan concentration or solar irradiance. Under optimal conditions (irradiance of 750W/m2, 1.0mg/L irinotecan concentration, and pH 9.0), more than 98% of irinotecan was degraded in 60min. With respect to irradiance and irinotecan concentration, the degradation process was robust in the studied range, implying that it may be effectively applied in locations and/or seasons with solar irradiance as low as 450W/m2. However, pH needs to be strictly controlled and kept between 7.0 and 9.0 to maintain the degradation process robust. Considerations about the behavior of degradation products were also drawn.

Benzimidazole fungicide biotransformation by comammox Nitrospira bacteria: Transformation pathways and associated proteomic responses

Benzimidazole fungicides are frequently detected in aquatic environments and pose a serious health risk. Here, we investigated the metabolic capacity of the recently discovered complete ammonia-oxidizing (comammox) Nitrospira inopinata and kreftii to transform a representative set of benzimidazole fungicides (i.e., benzimidazole, albendazole, carbendazim, fuberidazole, and thiabendazole). Ammonia-oxidizing bacteria and archaea, as well as the canonical nitrite-oxidizing Nitrospira exhibited no or minor biotransformation activity towards all the five benzimidazole fungicides. In contrast, the investigated comammox bacteria actively transformed all the five benzimidazole fungicides, except for thiabendazole. The identified transformation products indicated hydroxylation, S-oxidation, and glycosylation as the major biotransformation pathways of benzimidazole fungicides. We speculated that these reactions were catalyzed by comammox-specific ammonia monooxygenase, cytochrome P450 monooxygenases, and glycosylases, respectively. Interestingly, the exposure to albendazole enhanced the expression of the antibiotic resistance gene acrB of Nitrospira inopinata, suggesting that some benzimidazole fungicides could act as environmental stressors that trigger cellular defense mechanisms. Altogether, this study demonstrated the distinct substrate specificity of comammox bacteria towards benzimidazole fungicides and implies their significant roles in the biotransformation of these fungicides in nitrifying environments.

Identification of Reactive Oxygen Species and Mechanism on Visible Light-Induced Photosensitized Degradation of Oxytetracycline

This study investigated the photolysis and TiO2-assisted photosensitized degradation of oxytetracycline (OTC) under visible light, the active reactive oxygen species (ROS), and the degradation mechanisms in these two reactions. The results show that the deprotonated OTC could be photolyzed more easily under visible light because of the redshift of its absorption spectrum at high pH values. Due to the TiO2-assisted self-photosensitized degradation of OTC, OTC removal in the visible light/TiO2 system was more efficient with the addition of TiO2, as demonstrated when TiO2 was replaced with insulator SiO2. The study's ROS scavenging experiments show that superoxide radical anion (O2•-) ROS was most responsible for the self-sensitized degradation of OTC in both reactions. OTC degradation under the visible light/TiO2 system was enhanced with increasing TiO2 load, while the elimination of total organic carbon (TOC) was very limited after 5 h of visible light irradiation. Based on the eight identified transformation products found, five potential reaction mechanisms, including hydroxylation, quinonization, decarbonylation, de-methylation, and dehydration, were proposed for the photolytic and TiO2-assisted photosensitized degradation mechanisms of OTC under visible light. This study indicates that OTC can degrade under visible light with or without a semiconductor when conditions are suitable.

Degradation of contaminants of PPCPs by photocatalysis for water purification: Kinetics, mechanisms, and cytotoxicity analysis

Pharmaceuticals and personal care products (PPCPs) have drawn increasing regulatory attention and research interest in recent years. Since it does not require any additional dissolved oxidants, heterogeneous photocatalytic technology has attracted much interest in the efficient degradation of PPCPs in recent years. The present study examined the degradation kinetics of PPCPs using Fe-ZnS@TiO2/nickel foam photocatalytic system (ZTN PS) in Milli-Q water and a solid surface water background, including estrone, diclofenac, cyclophosphamide, triclosan, and sulfamethoxazole. To evaluate ZTN PS, MF-treated water samples from the Songhua River (SR) were obtained and used as reaction matrices with spiked additions of PPCPs. The influence of single ion addition on degradation kinetics was investigated to determine the degradation rule under various water parameter conditions. Using high-resolution mass spectrometry to identify transformation products (TPs), potential degradation pathways of a few PPCPs were hypothesised. During photocatalysis, the oxidation properties of different oxidants (photogenic holes, OH, O2−) on different structural sites of PPCPs were analysed. To examine possible environmental impacts of PPCP degradation by ZTN PS, cytotoxicity and estrogen (ER) receptor-binding activity were evaluated. It was found that ZTN PS substantially reduced cytotoxicity and estrogenic activity while degrading PPCPs in Milli-Q water. Also, the presence of complex substances in water did not significantly affect the toxicity of mixed PPCP degradation TPs. However, comparing natural water to Milli-Q water, the toxicity and ER-binding activity of TPs under natural water background increased marginally (9%–13％). Thus, this study aimed to understand the effects of post-ZTN PS PPCPs and TPs on human and environmental health at the cellular level.