Influence of DOM components, salinity, pH, nitrate, and bicarbonate on the indirect photodegradation of acetaminophen in simulated coastal waters

Effects of dissolved organic matter and halogen ions on phototransformation of pharmaceuticals and personal care products in aquatic environments

Photochemical reactions contribute to the attenuation and transformation of pharmaceuticals and personal care products (PPCPs) in surface natural waters. Nevertheless, effects of DOM and halogen ions on phototransformation of PPCPs remain elusive. This work selected disparate PPCPs as target pollutants to investigate their aquatic phototransformation processes. Results show that PPCPs containing multiple electron-donating groups (-OH, -NH2, -OR, etc.) are more reactive with photochemically produced reactive intermediates (PPRIs) such as triplet DOM (3DOM*), singlet oxygen (1O2), and reactive halogen species (RHSs), relative to PPCPs containing electron-withdrawing groups (-NOR, -COOR, -OCR, etc.). The generation of RHSs as a result of the coexistance of DOM and halide ions changed the contribution of PPRIs to the photochemical conversion of PPCPs during their migration from fresh water to seawater. For PPCPs (AMP, SMZ, PN, NOR, CIP, etc) with highly reactive groups toward RHSs, the generation of RHSs facilitated their photolysis in halide ion-rich waters, where Cl- plays a critical role in the photochemical transformation of PPCPs. Density functional theory (DFT) calculations showed that single electron transfer and H-abstraction are main reaction pathways of RHSs with the PPCPs. These results demonstate the irreplaceable roles of PPRIs and revealing the underlying reaction mechanisms during the phototransformation of PPCPs, which contributes to a better understanding of the environmental behaviors of PPCPs in complex aquatic environments.

Effect of the molecular weight of DOM on the indirect photodegradation of fluoroquinolone antibiotics

Dissolved organic matter (DOM) is ubiquitous and widespread in natural water and influences the transformation and removal of antibiotics. Nevertheless, the influence of DOM molecular weight (MW) on the indirect photodegradation of antibiotics has rarely been reported. This study attempted to explore the influence of the molecular weight of DOM on the indirect photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and norfloxacin (NOR), by using UV-vis absorption and fluorescence spectroscopy. The results showed that indirect photodegradation was considered the main photodegradation pathway of FQs in DOM fractions. Triplet-state excited organic matter (3DOM*) and singlet oxygen (1O2) were the main reactive intermediates (RIs) that affected the indirect photodegradation of FQs. The indirect photodegradation rate of FQs was significantly promoted in DOM fractions, especially in the low molecular weight DOM fractions (L-MW DOM, MW < 10 kDa). The results of excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) showed that terrestrial humic-like substances had a higher humification degree and fluorophore content in L- MW DOM fractions, which could produce more 3DOM* and 1O2 to promote the indirect photodegradation of FQs. This study provided new insight into the effects of DOM at the molecular weight level on the indirect photodegradation of antibiotics in natural water.

Release of dissolved organic matter from wetland plants and its interaction with polycyclic aromatic hydrocarbons

Dissolved organic matter (DOM) derived from wetland plants played a critical role in CWs pollutant migration. This study investigated the character and release pattern of DOM derived from two wetland plants, Phragmites australis and Cladophora sp., and the interaction between DOM with phenanthrene (PHE), benzo(a)pyrene (Bap), and benzo [k]fluoranthene (BkF) under different physical conditions were also studied using spectroscopic techniques. DOM release was related to plant species and withering stage. Humic acid (HA)-like fractions (C3 and C5) were dominated in P. australis (52%) and completely withered Cladophora sp. groups (55%), while protein-like fractions (C1 and C2) dominated in early withered Cladophora sp. groups (52%). Due to the cell and tissue structure difference among plants and their withering stage, DOM derived from early withered P. australis revealed a two-stage slow-fast phase, while other groups were linearly released (R2 0.87207-0.97091). A strong correlation existed between HA-like fractions and water quality index, reflecting the critical influence of plant decay in CWs operation performance. The analysis with Stern-Volmer equation indicated that plant-based DOM interacted with PAHs to form ground state complexes with possible involvement of π-π interaction, hydrogen bonding and cation bridging effect. Aromatic, molecular weight, and hydrophilicity of both DOM and PAHs affected their binding with the interaction capability in the order of BKF > Bap > PHE and C3 > C5 > C2 > C1 > C4. Besides, alkaline environment and high DO condition was highly unsuitable for the combination. Scientific management and appropriate operating condition were important in optimizing operation performance and controlling pollutant migration in CWs.

DOM optical parameters as a tool to understand degradation of phenolic contaminants of emerging concern

Composition and source of dissolved organic matter (DOM) in water influence the rate of production of reactive intermediates (RIs), affecting the photodegradation of phenolic contaminants of emerging concern (PhCECs). However, this relationship has not been fully quantified. Here, for the first time, we propose a mechanism for photodegradation of a surrogate of PhCECs, p-cresol, in different DOM standard solutions under simulated sunlight irradiation. More importantly, the correlation of DOM optical parameters and p-cresol photodegradation kinetic parameters was determined by Pearson correlation. Results showed that indirect photodegradation was the only degradation pathway for p-cresol, mainly through reaction with excited triplet state of dissolved organic matter (3DOM*). Singlet oxygen (1O2) and hydroxyl radical (•OH) hindered degradation of p-cresol by decreasing the steady state concentration of 3DOM*. Moreover, less aromatic and smaller molecular size DOM showed higher steady-state concentration and quantum yield of 1O2, and 3DOM*, resulting in faster p-cresol photodegradation. Finally, 7 out of 8 optical parameters showed strong correlation with the p-cresol photodegradation rate constant. The mechanism and correlations found are a potential tool to predict PhCECs photodegradation in water using DOM optical parameters.

Simultaneous degradation of sulfadiazine and dissolved organic matter based on low-impact development facilities

Sulfadiazine (SD) is a common antibiotic administered to treat bacterial infections in livestock, and its fate and migration are greatly affected by dissolved organic matter (DOM). The soil infiltration system [a typical low-impact development (LID) facility] can significantly alter DOM properties during runoff pollution, thus affecting the complexation of SD with DOM. Here, the binding characteristics of different DOM components and SD in the soil infiltration system were explored using spectroscopic techniques (excitation-emission matrices, parallel factor analysis, and synchronous fluorescence spectroscopy). Combined with the weakening of DOM fluorescence intensity and 78.63% reduction in mean SD concentration following treatment, synchronous degradation may have occurred. The binding sequence of SD and DOM fluorophores was further explored using two-dimensional correlation spectroscopy. Effluent DOM showed greater sensitivity to SD and more binding sites than influent DOM. Moreover, hydrophobic protein-like substances exhibited higher log K_M values than other fluorescent components, indicating that protein-like components play significant roles in SD complexation. The soil percolation system improved the complexation stability and binding sequence of fulvic-like substances. Thus, SD-DOM can be intercepted and degraded using LID facilities to reduce the risk of SD in aquatic environments.

Indirect photodegradation of sulfadimidine and sulfapyridine: Influence of CDOM components and main seawater factors

This study investigated the indirect photodegradation of sulfadimidine (SM₂) and sulfapyridine (SP) in the presence of chromophoric dissolved organic matter (CDOM), and studied the influences of main marine factors (salinity, pH, NO₃^- and HCO₃^-). Reactive intermediate (RI) trapping experiments demonstrated that triplet CDOM (³CDOM*) played a major role in the photodegradation of SM₂ with a 58% photolysis contribution, and the contributions to the photolysis of SP were 32%, 34% and 34% for ³CDOM*, hydroxyl radical (HO·) and singlet oxygen (¹O₂), respectively. Among the four CDOMs, JKHA, with the highest fluorescence efficiency, exhibited the fastest rate of SM₂ and SP photolysis. The CDOMs were composed of one autochthonous humus (C1) and two allochthonous humus (C2 and C3). C3, with the strongest fluorescence intensity, had the strongest capacity to generate RIs and accounted for approximately 22%, 11%, 9% and 38% of the total fluorescence intensity of SRHA, SRFA, SRNOM and JKHA, respectively, indicating the predominance of CDOM fluorescent components in the indirect photodegradation of SM₂ and SP. These results demonstrated the photolysis mechanism: The photosensitization of CDOM occurred after its fluorescence intensity decreased, and a large number of RIs (³CDOM*, HO· and ¹O₂, etc.) were generated by energy and electron transfer, then these RIs reacted with SM₂ and SP to cause photolysis. The increase in salinity stimulated the photolysis of SM₂ and SP consecutively. The photodegradation rate of SM₂ first increased and then decreased with increasing pH, whereas the photolysis of SP was remarkably promoted by high pH but remained stable at low pH. NO₃^- and HCO₃^- had little effect on the indirect photodegradation of SM₂ and SP. This research may contribute to a better understanding of the fate of SM₂ and SP in the ocean and provide new insights into the transformation of other sulfonamides (SAs) in marine ecological environments.

Impacts of properties of dissolved organic matters on indirect photodegradation of genistein

Excited triplet states of dissolved organic matters (³DOM*) are one of the most important photochemically-produced reactive intermediates leading to transformation of organic contaminants. However, relationships of photodegradation kinetics of different dissociation states of phenolic organic contaminants with chemical components or properties of ³DOM* are largely unknown. In this study, roles of ³DOM* in photodegradation of polyhydroxy phenolic genistein (Gs) at pH 5, 8 and 12 were investigated taking five kinds of DOM from different sources as examples. Relationships between photodegradation kinetics constants and DOM properties were built. Results showed that the contributions of direct ³DOM*-induced reactions to the total indirect photodegradation of Gs and second-order reaction rate constants (k_DOM,Gs) of Gs with ³DOM* increased with pH increases. This was mainly attributed to decreases in vertical ionization energy of Gs at higher pH, endowing Gs with stronger electron donating capacities. k_DOM,Gs was found to positively correlate with the specific ultraviolet absorbance at 254 nm, reflecting aromaticity of DOM, and negatively correlate with the absorbance ratio at 254 and 365 nm and contents of dissociated acidic functional groups of DOM, representing molecular weights of DOM, antioxidants and the repulsive forces between ³DOM* and Gs. This study provided a new insight into relationship between DOM properties and indirect photodegradation kinetics of phenolic contaminants in aquatic environments.

Elevated nitrate promoted photodegradation of PAHs in aqueous phase: Implications for the increased nutrient discharge

Polycyclic aromatic hydrocarbons (PAHs) are frequently released in aqueous phase by oil spill or from other sources, and photochemical oxidation is one of their major weathering processes. In this study, the photochemical behavior of phenanthrene (PHE, as a representative PAH) were studied and the effects of nitrogenous compounds were evaluated. The results showed that nitrate was an effective photosensitizer for improving the photodegradation of PHE, but the promoting effect was less effective in seawater due to the presence of halogen ions; the ammonia played a negligible role on PHE degradation. The photochemical ionization was a key process for PHE degradation, it can be retarded due to the quenching of triplet excited state by dissolved oxygen, and the inhibition was most prominent in fresh water. The presence of nitrate increased the steady state concentration of •OH from 2.08 × 10^-15 M to 1.04 × 10^-14 M in fresh water, and from 1.5 × 10^-16 M to 2.08 × 10^-15 M in seawater. The secondary-order reaction rate constant between PHE and •OH (k_•OH,PHE) was determined as 5.70 × 10⁹ M^-1 s^-1. Similar trend was observed for ¹O₂. The contribution of •OH to PHE removal was more prominent in fresh water than in seawater due to the quenching effects of halogen, and the increasing of nitrate enlarged the contribution of •OH. Two possible PHE degradation pathways were proposed based on GC-MS analysis and DFT calculation. The Quantitative Structure-activity Relationship (QSAR) evaluation showed that some degradation intermediates were more toxic than PHE, but the total environmental risk was still diminished due to the low percentage of toxic intermediates. This study provided theoretical and experimental insights into the influence of nitrogenous compounds on the photodegradation of PHAs in water environment.

Interactions between lead(II) ions and dissolved organic matter derived from organic fertilizers incubated in the field

This work was to study composition characteristics and the subsequent effect on the lead (Pb) binding properties of dissolved organic matter (DOM) derived from seaweed-based (SWOF) and chicken manure organic fertilizers (CMOF) during a one-year field incubation experiment using the excitation-emission matrix-parallel factor (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2DCOS) analysis. Results showed that high aromatic and hydrophobic fluorescent substances were enriched in CMOF-derived DOM and SWOF-derived DOM and enhanced over time. And phenolic groups in the fulvic-like substances for SWOF-derived DOM and carboxyl groups in the humic-like substances for CMOF-derived DOM had the fastest responses over time, respectively. Moreover, both non-fluorescent polysaccharides and fluorescent humic-like substances or fulvic-like substances with aromatic (C=C) groups first participated in the binding process of Pb to SWOF-derived DOM on day 0 and 180 during the lead binding process. In contrast, humic-like substances associated with aromatic (C=C) and phenolic groups gave a faster response to Pb binding on day 360. Regarding CMOF-derived DOM, the fulvic-like substances associated with aromatic (C=C) and carboxylic groups displayed a faster response to Pb ions on day 0. Nonetheless, polysaccharides and humic-like associated with phenolic groups had a faster response on days 180 and 360. It is noteworthy that the polysaccharides, which participated in Pb binding to CMOF-derived DOM, posed a higher risk of Pb in the environment after 360 days. Therefore, these findings gave new insights into the long-term applications of commercial organic fertilizers for the amendment of soil.

Effect of fulvic acid concentration levels on the cleavage of piperazinyl and defluorination of ciprofloxacin photodegradation in ice

Ice is an important physical and chemical sink for various pollutants in cold regions. The photodegradation of emerging fluoroquinolone (FQ) antibiotic contaminants with dissolved organic matter (DOM) in ice remains poorly understood. Here, the photodegradation of ciprofloxacin (CIP) and fulvic acid (FA) in different proportions as representative FQ and DOM in ice were investigated. Results suggested that the photodegradation rate constant of CIP in ice was 1.9 times higher than that in water. When C_FA/C_CIP ≤ 60, promotion was caused by FA sensitization. FA increased the formation rate of cleavage in the piperazine ring and defluorination products. When 60 < C_FA/C_CIP < 650, the effect of FA on CIP changed from promoting to inhibiting. When 650 ≤ C_FA/C_CIP ≤ 2600, inhibition was caused by both quenching effects of 143.9%-51.3% and light screening effects of 0%-48.7%. FA inhibited cleavage in the piperazine ring for CIP by the scavenging reaction intermediate of aniline radical cation in ice. When C_FA/C_CIP > 2600, the light screening effect was greater than the quenching effect. This work provides new insights into how DOM affects the FQ photodegradation with different concentration proportions, which is beneficial for understanding the environmental behaviors of fluorinated pharmaceuticals in cold regions.

Phototransformation of tetrabromobisphenol A in saline water under simulated sunlight irradiation

The widespread use of halogenated flame retardants in recent years has led to the accumulation of TBBPA in water, which may cause potential harm to living organisms. The phototransformation of the flame retardant TBBPA in alkaline saline water under simulated sunlight irradiation was investigated. The effects of abiotic factors such as the initial concentration of TBBPA, chloride ion concentration, solution pH, inorganic anions and cations, dissolved organic matter (DOM) were studied. The results showed that the phototransformation rate of TBBPA accelerated with the decrease of the initial concentration of TBBPA, the increase of chloride ion concentration and solution pH. The scavenging experiments showed that •OH, ¹O₂, O₂•^- and ³TBBPA* all participated in the phototransformation of TBBPA. The presence of NO₃^-, CO₃^2-, SO₄^2-, Mg²⁺, Ca²⁺, Fe³⁺ and fulvic acid (FA) all inhibited the phototransformation of TBBPA in the present study. The phototransformation products of TBBPA were detected by liquid chromatography-mass spectrometry (LC-MS), and the phototransformation pathways were proposed. This is the first report on the photo-induced generation of halogen exchange products from TBBPA in saline solutions, which will contribute to a better understanding of the environmental behavior and risks of BFRs in water.

Photodegradation of chloramphenicol in micro-polluted water using a circulatory thin-layer inclined plate reactor

This study describes the photodegradation of chloramphenicol (CAP) in micro-polluted water with a thin-layer inclined plate reactor. Under simulated sunlight irradiation, the effect of reaction parameters including solution pH, initial CAP concentration, and co-existed humic acid (HA) or chloride was evaluated. The photodegradation of CAP was independent of initial pH in the range of 6.0-9.0, but sharply decreased by 25.5% with the increase of initial CAP concentration from 0.4 to 1.0 mg/L. The presence of HA exhibited a significant inhibitory effect, while Cl^- promoted the photoreaction. In this study, CAP was degraded through both direct and indirect photolysis, in which ¹O₂ was the main reactive species responsible for the indirect route. Its steady-state concentration in the micro-polluted water was determined to be 1.40 × 10^-13 mol/L. Transformation intermediates were identified to propose the degradation pathway of CAP, which substantially met the density functional theory (DFT) calculation results. Moreover, four other pharmaceuticals including tetracycline, doxycycline, oxytetracycline, and minocycline were also successfully photodegraded during 5 h irradiation. Therefore, the designed circulatory thin-layer inclined plate reactor is suggested to be effectively applied to the decontamination of organic micro-polluted water.

Effects of natural colloidal particles derived from a shallow lake on the photodegradation of ofloxacin and ciprofloxacin

Natural colloidal particles (NCPs), which are ubiquitous and abundant in surface waters, may play a crucial role in the sunlight-driven transformation of organic contaminants. This research focused on the effects of NCPs on the photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and ciprofloxacin (CIP), and assessed the photosensitivity of colloidal organic matter (COM). Results showed that the photodegradation rate constants (k_obs) of OFL and CIP in NCP solutions ranged from 9.28 × 10^-2 h^-1 to 15.98 × 10^-2 h^-1 and 63.88 × 10^-2 h^-1 to 196.59 × 10^-2 h^-1, respectively, and NCPs can significantly accelerate the photodegradation rate of OFL and CIP. Indirect photodegradation (IP) accounted for >50% of the overall observed degradation in most treatments and was the dominant degradation pathway for the two FQs, especially for CIP, for which IP reached 82%-94%. In the IP process, the contributions of triplet states of colloidal organic matter (³COM^⁎) to the photolysis of OFL and CIP were close to 42% and 46%, respectively. The compositions of COM played an important role in the IP of the FQs, among which terrestrial sources of COM tended to have higher photoreactivity than biological sources. This study is essential in predicting the photochemical effect of FQs and also allows for a better understanding of the real environmental fate of antibiotic contaminants.

Mechanism of bicarbonate enhancing the photodegradation of β-blockers in natural waters

The impact of HCO₃^- on the photodegradation of β-blockers was investigated under simulated sunlight irradiation. The results show that in the presence of HCO₃^-, the photodegradation rates increase significantly for sotalol (SOT), whereas no effects on the degradation of carvedilol and arotinolol are observed. Using quenching experiments, electron paramagnetic resonance spectra and degradation product determination, we demonstrate that carbonate radical (CO₃^•-) is formed by direct oxidation of HCO₃^- by triplet-excited SOT (³SOT*) and plays a significant role in SOT photodegradation. Competition kinetics experiments show that the three β-blockers all have high second-order rate constants (10⁷-10⁸ M^-1 s^-1) for the reaction with CO₃^•-. However, only ³SOT* has a higher reduction potential that can oxidize HCO₃^- to produce CO₃^•-. Thus, enhanced SOT removal rates in the presence of HCO₃^- were observed. In addition, the results show that seawater DOM could increase HCO₃^--induced photodegradation of SOT, whereas SRNOM mainly behaves as a CO₃^•- quencher and decreases the removal rate of SOT. The results underscore the role of HCO₃^- in limiting the persistence of organic pollutants like SOT in sunlit natural waters, and especially in marine and coastal waters.

Intracellular organic matter from Chlorella vulgaris enhances the photodegradation of acetaminophen

Algae is able to accelerate the photodegradation rate of contaminants under sunlight irradiation, and this process can be attributed to algal substances, namely, intracellular organic matter (IOM) and extracellular organic matter (EOM). This study aimed to investigate the efficiencies and mechanisms of the photodegradation of three pharmaceuticals - acetaminophen (ACE), codeine (COD) and cephradine (CFD) - in the presence of Chlorella vulgaris and its algal substances. The result shows that a much higher photodegradation rate of acetaminophen was obtained in the presence of IOM (k_obs = 0.250 hr^-1) than in the presence of EOM (k_obs = 0.060 hr^-1). The photodegradation mechanisms of acetaminophen were demonstrated and verified by scavenger experiments and probe tests. The major reactive species for acetaminophen photodegradation was triplet-state IOM (³IOM∗), which contributed 93.52% of the photodegradation, while ⋅OH was the secondary contributor (5.60%), with ¹O₂ contributing the least (0.88%). Chlorella vulgaris also effectively enhanced the photodegradation of codeine and cephradine. However, the photodegradation behaviors of codeine and cephradine in the presence of algal substances were different from those of acetaminophen, indicating that the photodegradation mechanisms might depend on the type of compound. This study not only demonstrates the effectiveness of algal substances in the photodegradation of acetaminophen, codeine and cephradine under sunlight irradiation but also provides a comprehensive study on the photodegradation mechanisms of acetaminophen in the presence of algal substances.

Indirect photodegradation of sulfadiazine in the presence of DOM: Effects of DOM components and main seawater constituents

The presence of pharmaceuticals and personal care products in coastal waters has caused concern over the past decade. Sulfadiazine (SD) is a very common antibiotic widely used as human and fishery medicine, and dissolved organic matter (DOM) plays a significant role in the indirect photodegradation of SD; however, the influence of DOM compositions on SD indirect photodegradation is poorly understood. The roles of reactive intermediates (RIs) in the indirect photolysis of SD were assessed in this study. The reactive triplet states of DOM (³DOM∗) played a major role, whereas HO· and ¹O₂ played insignificant roles. DOM was divided into four components using excitation-emission matrix spectroscopy combined with parallel factor analysis. The components included three allochthonous humic-like components and one autochthonous humic-like component. The allochthonous humic-like components contributed more to RIs generation and SD indirect photolysis than the autochthonous humic-like component. A significant relationship between the indirect photodegradation of SD and the decay of DOM fluorescent components was found (correlation coefficient, 0.99), and the different indirect photodegradation of SD in various DOM solutions might be ascribed to the different components of DOM. The indirect photolysis rate of SD first increased and then decreased with increasing pH. SD photolysis was enhanced by low salinity but remained stable at high salinity. The increased carbonate concentration inhibited SD photolysis, whereas nitrate showed almost no effect in this study.

Photo-catalytic degradation of polyphenolic tannins in continuous-flow reactor using titanium dioxide immobilized on a cellulosic material

Tannins are recalcitrant polyphenolic molecules that resist microbial attack. Their main environmental damage is due to their low biodegradability. This work aims to investigate the photo-catalytic degradation of two commercial tannin extracts, chestnut (hydrolysable tannin) and mimosa (condensed tannin). The experiments were carried out under UV-light irradiation in a continuous-flow reactor using titanium dioxide (TiO₂) immobilized on cellulosic fibers. It was highlighted that photo-catalytic degradation is unfavourable in acidic medium and when the pH is too high (pH above 12); it reaches its maximum efficiency at pH 7.5 (99 and 97% for chestnut and mimosa, respectively). Nearly complete degradation of tannins requires an irradiation period of 6 h. The process efficiency is inversely affected by the concentration of tannins essentially above 75 mg/L for chestnut and 60 mg/L for mimosa. Above 240 mL/min, any increase in feed flow negatively affects the performance of the process. Furthermore, a significant decrease of treatment efficiency was seen when increasing the concentration of ethanol and salts in the medium. Obtained results suggest that UV-light irradiation in a continuous-flow photo-reactor using immobilized TiO₂ may be considered as an adequate process for the treatment of water containing recalcitrant tannin molecules.

Phototransformation of biochar-derived dissolved organic matter and the effects on photodegradation of imidacloprid in aqueous solution under ultraviolet light

Dissolved organic matter (DOM) strongly influences the photodegradation of organic pollutants, varying depending on the structure of DOM. With the wide application of biochar, increasing amounts of DOM is released from biochar to the environment, which has different structural characteristics compared to natural DOM. In this study, DOM was derived from maize straw (MS) and pig manure (PM) and biochars by pyrolyzing MS and PM at 300 °C and 500 °C and the optical characteristics of DOM before and after phototransformation were explored via ultraviolet-visible spectroscopy and excitation-emission matrix fluorescence. Photodegradation of an insecticide, imidacloprid (IMI) in the presence of DOM was examined. The results showed that DOM derived from biochar obtained by pyrolyzing MS and PM mainly contained two identified fluorescent components and high pyrolysis temperature (500 °C) was associated with low molecular weight, small light-screening effects and great aromaticity of the DOM. After exposure to UV light, the aromaticity and molecular weight of the DOM declined due to phototransformation. Significant enhancement was observed in IMI photodegradation in the presence of biochar-derived DOM, and the enhancement was the greatest with DOM derived from pig manure biochar pyrolyzed at 500 °C. In addition to the light shielding effect, the ¹O₂ generated from DOM played an important role in the phototransformation of IMI and DOM. The loss of the nitro group and oxidation at the imidazolidine ring were the main photodegradation pathways for IMI. This study expands our understanding of the fate of biochar-derived DOM and its effects on the fate of coexisting organic pollutants.

Effects of fertilization on the triafamone photodegradation in aqueous solution: Kinetic, identification of photoproducts and degradation pathway

Triafamone is a highly effective, low toxicity sulfonamide herbicide widely used for weeding paddy fields. The triafamone photodegradation in water environment must be explored for its ecological risk assessment. In this work, the effects of chemical fertilizer (urea, diammonium phosphate, potassium chloride, and potassium sulfate), urea metabolites (CO₃^2- and HCO₃^-), and organic fertilizers (unfermented organic fertilizer [UOF] and fermented organic fertilizer [FOF]) on the triafamone photodegradation in aqueous solution under simulated sunlight were evaluated. Results showed that the triafamone photodegradation rate was unaffected by urea. The half-life of triafamone decreased from 106.8 h to 68.4 h with increasing diammonium phosphate concentration. Potassium chloride, potassium sulfate, CO₃^2-, and HCO₃^- could accelerate the triafamone photodegradation at all concentrations, whereas the degradation rate of triafamone decreased when the concentration of potassium sulfate or CO₃^2- was 2000 mg/L. Triafamone photodegradation was promoted by 20-200 mg/L UOF and FOF but decreased to 236.6 and 142.3 h when the concentration reached 2000 mg/L. Twenty-three transformation products were isolated and identified from triafamone by using ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry under simulated sunlight irradiation, and the kinetic evolution of these products was explored. Five possible degradation pathways were inferred, including the cleavage of C-N, C-C, and C-O bonds; CO bond hydrogenation; the cleavage of triazine ring; the cleavage of the sulfonamide bridge; hydroxylation; hydroxyl substitution; methylation; demethylation; amination; and rearrangement. In summary, these results are important for elucidating the environmental fate of triafamone in aquatic systems and further assessing environmental risks.

Photodegradation of tefuryltrione in water under UV irradiation: Identification of transformation products and elucidation of photodegradation pathway

Photodegradation is an important abiotic degradation process in the aquatic environment. In this study, the photodegradation of tefuryltrione in aqueous solution was investigated under UV-Visible irradiation. Effects of carbonate (CO₃^2-), bicarbonate (HCO₃^-), nitrate (NO₃^-), hydrogen phosphate (HPO₄^2-), potassium (K⁺), and ammonium (NH₄⁺) on the photodegradation kinetics of tefuryltrione were evaluated. Results showed that tefuryltrione photodegradation was increased by HCO₃^-, CO₃^2-, and NO₃^- in the range of 0.1-10 mmol L^-1; decreased by HPO₄^2-; and insignificantly affected by K⁺ and NH₄⁺. Twelve main transformation products (TPs) were separated and identified on the basis of mass spectrum data assigned by elemental-composition calculations, comparison of structural analogs, and available literature. A tentative photodegradation pathway was further proposed depending on the identified TPs and their kinetic evolutions. Results indicated that TP 1 was generated by the hydroxyl that substituted for chlorine, TP 2 was formed by the cleavage of the ether bond of tefuryltrione, and TPs 3-6 were formed by the breakage of the CC bond of the keto moiety of tefuryltrione. Further, TPs 9-12 were formed by the rearrangement of tefuryltrione-photodegradation products. These findings are highly important for elucidating the environmental fate of tefuryltrione in aquatic ecosystems.