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Benzotriazole UV stabilizers (BT-UVs) have attracted concerns due to their ubiquitous occurrence in the aquatic environment, and their bioaccumulative and toxic properties. However, little is known about their aquatic environmental degradation behavior. In this study, photodegradation of a representative of BT-UVs, 2-(2-hydroxy-5-methylphenyl)benzotriazole (UV-P), was investigated under simulated sunlight irradiation. Results show that UV-P photodegrades slower under neutral conditions (neutral form) than under acidic or alkaline conditions (cationic and anionic forms). Indirect photodegradation is a dominant elimination pathway of UV-P in coastal seawaters. Dissolved organic matter (DOM) from seawaters accelerate the photodegradation rates mainly through excited triplet DOM (3DOM⁎), and the roles of singlet oxygen and hydroxyl radical are negligible in the matrixes. DOM from seawaters impacted by mariculture exhibits higher steady-state concentration of 3DOM⁎ ([3DOM⁎]) relative to those from pristine seawaters, leading to higher photosensitizing effects on the photodegradation. Halide ions inhibit the DOM-sensitized photodegradation of UV-P by decreasing [3DOM⁎]. Photodegradation half-lives of UV-P are estimated to range from 24.38 to 49.66 hr in field water bodies of the Yellow River estuary. These results are of importance for assessing environmental fate and risk UV-P in coastal water bodies. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Dissolved organic matter (DOM) plays an important role in degradation of organic pollutants by photochemically-produced reactive intermediates (RIs), such as excited triplet-states of DOM (3DOM*), singlet oxygen (1O 2) and hydroxyl radical (·OH). However, it is not clear whether DOM extracted from coastal seawaters (CS-DOM) and DOM derived from freshwaters (FW-DOM) exhibit similar effects on photodegradation of organic micropollutants. Herein, 2,4-dihydroxybenzophenone (BP-1) was adopted as a model compound to probe the effects of different DOM on photodegradation kinetics of organic micropollutants. Results show that the CS-DOM promotes the photodegradation of BP-1 mainly via the pathway involving 3DOM*; while 3DOM*, 1O 2 and ·OH are responsible for BP-1 photodegradation in the presence of the FW-DOM. Compared with the FW-DOM, the CS-DOM undergoes more photobleaching, and contains less aromatic C=C and C=O functional groups. Although 3DOM* formation quantum yields for the CS-DOM are relatively higher than those for the FW-DOM, the CS-DOM has lower rates of light absorption, leading to lower steady-state RI concentrations for the CS-DOM. BP-1 photodegradation in the presence of the CS-DOM is faster than in the presence of the FW-DOM, due to higher second-order reaction rate constants between BP-1 and CS-3DOM* and fewer antioxidants contained in the CS-DOM. Graphical abstract Image 1 Highlights • Coastal seawater DOM is mainly from autochthonous sources with low aromaticity. • Coastal seawater DOM produces low steady-state concentrations of 3DOM*, 1O 2 and ·OH. • Coastal seawater DOM and freshwater DOM can enhance photodegradation of BP-1. • Coastal seawater DOM promotes photodegradation of BP-1 via 3DOM*. • Freshwater DOM promotes phototransformation of BP-1 via 3DOM*, ·OH and 1O 2. [ABSTRACT FROM AUTHOR]

Abstract Mariculture activities and river inputs lead to coastal seawaters with DOM levels that are comparable to or even higher than those in terrestrial water bodies. However, effects of seawater DOM, and especially of DOM occurring in areas impacted by mariculture, on photodegradation of organic micropollutants, are largely unknown. In this study, simulated sunlight irradiation experiments were performed to probe the effects of DOM extracted from mariculture impacted seawaters and from offshore areas, on photodegradation of three sulfonamide antibiotics (SAs). Results show that the SAs are transformed mainly by indirect photodegradation induced by triplet excited DOM (3DOM*). Compared with DOM from the more pristine coastal waters, the DOM from mariculture impacted areas undergoes less photobleaching, contains higher percentage of humic-like materials and higher proportions of aromatic and carbonyl structures. Thus, the DOM from mariculture areas exhibits higher rates of light absorption, higher formation quantum yields of 3DOM*, higher 3DOM* steady-state concentrations and higher reactivity on photodegradation of the SAs. Photochemistry of the seawater DOM is different from that reported for freshwater lake DOM. This study highlights the importance of probing the effects of DOM from coastal seawaters on photodegradation of organic micropollutants since coastal seawaters are sinks of many aquatic pollutants. Graphical abstract Image 1 Highlights • DOM were isolated from mariculture ponds, tidal creek waters and offshore waters. • Effects of DOM in coastal waters on photodegradation of pollutants were unveiled. • DOM from mariculture areas has higher aromaticity than those from offshore waters. • DOM from mariculture areas exhibits high reactivity on degradation of sulfonamides. [ABSTRACT FROM AUTHOR]

Propranolol (PRO) is frequently detected in estuarine and coastal waters, which has adverse effects on estuarine and coastal ecosystems. In this study, the effects of halide ions and DOM from estuarine and coastal waters on the photochemical transformation of PRO were investigated. The results demonstrated that the presence of Br- alone exhibited slight effect on photochemical transformation of PRO, while photodegradation rates of PRO increased with the addition of 0.1–0.54 M Cl-. The quenching experiments and the laser flash photolysis experiments together demonstrated the generation of Cl 2 •— in the photolytic systems. Cl 2 •— is possibly produced through the charge separation of exciplex of 3PRO* and Cl- rather than via direct oxidation of Cl-. Additional experiments indicated that addition of seawater DOM inhibited the halide ions-sensitized photodegradation rates of PRO, which may be due to the quenching of Cl 2 •— by phenolic substances in DOM molecules. Compared with pure water, three new photochemical intermediates were identified in the presence of DOM or Cl-. The direct photolysis of PRO mainly reacted by hydroxyl additions, hydroxyl elimination and de-propylation, whereas electron transfer coupled with H-abstraction by Cl 2 •— and 3DOM* was proposed as the primary role for PRO degradation in the presence of Cl- or DOM. [Display omitted] • Cl- significantly promotes PRO photodegradation under simulated sunlight. • The presence of Br- alone has negligible effects on the photodegradation of PRO. • Cl 2 •— contributes to the enhancement of PRO degradation in Cl- solutions. • Addition of DOM inhibits the photosensitized degradation of PRO by halide ions. • Electron transfer and H-abstraction products are identified in Cl-/DOM solutions. [ABSTRACT FROM AUTHOR]

• HCO 3 − significantly promotes SOT photodegradation under simulated sunlight. • Addition of HCO 3 − has negligible effects on the degradation of CAR and ARO. • Seawater DOM enhances HCO 3 −-induced photodegradation of SOT. • Freshwater DOM decreases HCO 3 −-induced photodegradation rate of SOT. • CO 3 •− contributes to the enhancement of SOT degradation in HCO 3 − solutions. The impact of HCO 3 − on the photodegradation of β-blockers was investigated under simulated sunlight irradiation. The results show that in the presence of HCO 3 −, 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 (CO 3 •−) is formed by direct oxidation of HCO 3 − 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 CO 3 •−. However, only 3SOT* has a higher reduction potential that can oxidize HCO 3 − to produce CO 3 •−. Thus, enhanced SOT removal rates in the presence of HCO 3 − were observed. In addition, the results show that seawater DOM could increase HCO 3 −-induced photodegradation of SOT, whereas SRNOM mainly behaves as a CO 3 •− quencher and decreases the removal rate of SOT. The results underscore the role of HCO 3 − in limiting the persistence of organic pollutants like SOT in sunlit natural waters, and especially in marine and coastal waters. [Display omitted] [ABSTRACT FROM AUTHOR]

• Seawater DOM facilitates but freshwater DOM slightly retards SCP photodegradation. • 3DOM* photogenerated by S-DOM is low in concentration but high in quantum yields. • High sensitization reactivity of 3S-DOM* to SCP is owed to less phenolic antioxidant. • Mariculture activity enhances formation of Hi-3DOM* from seawater DOM. • Predicted photolytic rates of SCP are within big error using DOM analogs instead of real DOM. Coastal seawater constitutes an important ecosystem receiving inputs of organic micropollutants (OMPs) such as sulfa antibiotics from land-based sources or mariculture activities. It is necessary to investigate photodegradation of OMPs in coastal seawaters for assessing their environmental fate and risks. However, effects of coastal seawater dissolved organic matter (S-DOM) on OMPs photodegradation are largely unknown, given that chemical compositions of S-DOM are different from those of freshwater DOM. Herein, photochemical characteristics of S-DOM extracted from Dalian coastal seawaters were investigated by simulating photochemical experiment adopting sulfachloropyridazine as a case. Results show that S-DOM accelerates the photodegradation mainly through excited triplet-state DOM (3DOM*) with an apparent rate constant (4.43 × 108 M−1 s−1) ten folds of that of freshwater DOM, which is mainly due to much lower phenol contents detected in the S-DOM (0.022 mg-Gallic acid mg-C−1). The S-DOM impacted by mariculture can photogenerate more high-energy 3DOM* than those less impacted by mariculture, further contributing to the high 3DOM* reactivity. The study shows that to accurately predict photolytic persistence of OMPs in field water bodies, it is of significance to determine the second-order reaction rate constants between 3DOM* and target OMPs using DOM extracted from relevant water bodies. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Nebivolol (NEB) is widely used for the treatment of hypertension and chronic heart failure and has become an ubiquitous emerging organic pollutant. It has been shown to undergo direct photolysis, but the role of DOM in its degradation kinetics and mechanism is not well understood. In this study, we studied the photochemical behavior of NEB in the presence of seawater DOM (SW-DOM) and freshwater DOM (SRNOM) under simulated sunlight irradiation. SW-DOM had a promotion effect on NEB photodegradation, whereas SRNOM retarded its photolytic transformation. After eliminating the influence of light screening, we found that the indirect photodegradation rate of NEB in the presence of SRNOM was lower than that in the presence of SW-DOM. Results show that the indirect photodegradation pathway occurred by reaction with triplet-excited DOM (3DOM*). The second-order rate constants for 3SW-DOM* and 3SRNOM* reaction with NEB are 3.7 × 109 M−1 s−1 and 3.7 × 108 M−1 s−1, respectively. The electron donating capacity of SRNOM is higher than that of SW-DOM, indicating that SRNOM may contain more activated phenolic moieties. SRNOM may thus have higher antioxidant activity, leading a higher inhibitory effect on NEB photodegradation. A total of six degradation products were identified in the absence and presence of DOM by HPLC-ESI-MS/MS. The substitution of F by OH-groups and further oxidation a OH-group in the lateral chain to a ketone, and cleavage of N–C bond by the attack of 3DOM* are here proposed as the main degradation pathways. Image 1 • Seawater DOM promotes NEB photodegradation under simulated sunlight irradiation. • Freshwater DOM retards the photodegradation of NEB. • 3DOM* contributes to the indirect photodegradation of NEB. • Photoreactivity of seawater 3DOM* to NEB is higher than that of freshwater 3DOM*. • Three new photoproducts are identified in DOM solutions compared to pure water. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) is the most important light absorber that may induce indirect photolytic transformation of organic pollutants in natural waters. In this study, effects of DOM derived from freshwater and seawater on the photodegradation of three antiviral drugs acyclovir, lamivudine and zidovudine were investigated. Results show that the photodegradation of acyclovir is promoted mainly by excited triplet states DOM (3DOM*), and the photodegradation of lamivudine is accelerated by 3DOM*, •OH and 1O 2 together; however, the photodegradation of zidovudine is inhibited by DOM mainly via light screening. Compared with DOM from freshwater, promotion effect of DOM extracted from seawater (SDOM) on the photodegradation of acyclovir and lamivudine is weaker, which is attributed to lower productivity of reactive intermediates. On the other hand, inhibitory effect of SDOM on the photodegradation of zidovudine is also weaker, which is due to weaker light screening caused by lower light absorption. Photodegradation half-lives of the three antiviral drugs are predicted to be all more than 20 days in freshwater and seawater bodies of the Yellow River estuarine region. These findings are significant for understanding the phototransformation processes of antiviral drugs and other organic pollutants in estuarine and coastal regions. Image 1 • Seawater DOM has low rate of light absorption compared with freshwater DOM. • Triplet-excited DOM is largely responsible for photodegradation of acyclovir. • Seawater DOM shows weak inhibitory effect on photodegradation of zidovudine. • Photodegradation half-lives of antiviral drugs are more than 20 days. [ABSTRACT FROM AUTHOR]

Acebutolol (ACE) has been widely used for the treatment of cardiovascular disorders, and its photochemical fate in natural waters is a matter of concern due to its ubiquitous occurrence and its toxicity to aquatic organisms. In this study, the photodegradation of ACE in river water and synthetic waters were investigated under simulated sunlight irradiation. The results demonstrated that ACE photodegradation rate in river water was 3.2 times higher than that in pure water. Then the influences of HCO 3 −, NO 3 − and DOM on ACE photolysis were investigated under their concentrations similar with the ones in river water. ACE photodegradation was significantly enhanced in the presence of HCO 3 − alone, and the scavenging experiments and the electron paramagnetic resonance experiments together proved that HCO 3 − could be oxidized by triplet-excited state of ACE to generate CO 3 •-, which subsequently played a key role in ACE degradation. The presence of both NO 3 − and DOM also increased the ACE photodegradation rates, and •OH and 3DOM* were found to be involved in the degradation. In addition, when DOM was added to a solution with HCO 3 −, the enhancement effect of HCO 3 − on ACE photodegradation was weakened due to the scavenging of CO 3 •- by DOM combined with the light screening effect of DOM. [Display omitted] • Both direct and indirect photodegradation of ACE can occur in river water. • The presence of HCO 3 − alone greatly enhances the photodegradation of ACE. • HCO 3 − can be photosensitized by triplet excited state of ACE to generate CO 3.•-. • The presence of NO 3 − and DOM both can promote the photodegradation of ACE. • Addition of DOM inhibits the photosensitized degradation of ACE by HCO 3 −. [ABSTRACT FROM AUTHOR]

• Degradation of INDO was studied under natural and simulated irradiation. • Local DOM increases the photolysis of INDO by 30% than commercial DOM. • The contribution of 3DOM* in INDO photodegradation exceeds 70% in DOM solution. • DFT calculation further confirms the degradation pathway of INDO. • Indirect photolysis products in DOM are more toxic to aquatic organisms. Indomethacin (INDO) is an antipyretic and analgesic pharmaceutical that has been widely detected in the aquatic environment. Photodegradation is an essential pathway for removal of INDO in sunlit surface water, however the effect of dissolved organic matter (DOM) on its photodegradation and the ecotoxicity of photodegradation products are largely unknown. In this study, the effect of DOM on the photodegradation of INDO under both natural and simulated light irradiation was studied. The results showed that indirect photolysis is the main photodegradation pathway of INDO in presence of DOM where 3DOM* plays the most important promoting role. Compared to commercial DOM (SRNOM and SRFA), DOM extracted from local-lake water (SLDOM) promoted the photodegradation to the highest extent. Although the steady-state concentrations of 3DOM* of SRNOM and SRFA were higher than SLDOM, their inhibition effect surpassed SLDOM namely higher light screening effect and phenolic antioxidant concentrations. The photodegradation pathway in pure water is different from that in DOM system where the decarboxylation of acetic acid chain and the oxidative fracture of indole ring are the main degradation pathways. Density Functional Theory (DFT) calculation further supports the proposed degradation pathways of INDO. ECOSAR calculation showed that the toxicity of INDO photodegradation products to aquatic organisms may maintain or even exceed its parent compound. Therefore, comprehensive understanding of the impact of DOM on the photodegradation of INDO is of crucial significance for evaluating its ecological risk in the natural environment. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The photodegradation of PRO can be enhanced in river water under natural sunlight. • 3DOM* is the main reactive species responsible for the photodegradation of PRO. • DOM with higher steady-state concentration of 3DOM* has higher reactivity. • The main degradation pathways of PRO are hydroxylation and dehydration. • The degradation product of PRO is more toxic to aquatic organisms than PRO itself. The widespread use of propranolol (PRO) has led to its detection in all types of natural water bodies, and it is hazardous to both aquatic organisms and humans. In this study, the photochemical transformation of PRO in the natural environment was investigated using both simulated and outdoor light experiments. The photodegradation of PRO was found to be faster in Pearl river water and the dissolved organic matter (DOM) solutions than that in pure water under sunlight irradiation. Quenching experiments show that the excited triplet states DOM (3DOM*) played a major role while ·OH and 1O 2 played minor roles in PRO degradation. The secondary reaction rate constants of 3DOM* with PRO were determined to be (4.32 ∼ 6.38) × 108 M−1 s−1. DOM with high steady-state concentrations of the generated reactive species has higher photochemical reactivity for PRO photodegradation. Total of seven products were identified in in pure water, Pearl River water and three DOM solutions. The degradation of PRO can be mainly through hydroxyl addition, dehydration, naphthalene removal and isopropyl removal reactions. The reaction sites predicted by frontier electronic density calculations can further infer degradation pathways. The ecotoxicity of degradation products was found to be decreased relative to PRO through Ecological Structure Activity Relationship (ECOSAR) program. [ABSTRACT FROM AUTHOR]

• Importance of photodegradation in removal of OMPs in waters was discussed. • Processes of OMPs' photodegradation was compared to biodegradation. • Understanding on roles of DOM on photodegradation is concisely updated. • Major knowledge gaps in environmental photochemistry are identified. Photochemical reactions widely occur in the aquatic environment and play fundamental roles in aquatic ecosystems. In particular, solar-induced photodegradation is efficient for many organic micropollutants (OMPs), especially those that cannot undergo hydrolysis or biodegradation, and thus can mitigate chemical pollution. Recent reports indicate that photodegradation may play a more important role than biodegradation in many OMP transformations in the aquatic environment. Photodegradation can be influenced by the water matrix such as pH, inorganic ions, and dissolved organic matter (DOM). The effect of the water matrix such as DOM on photodegradation is complex, and new insights concerning the disparate effects of DOM have recently been reported. In addition, the photodegradation process is also influenced by physical factors such as latitude, water depth, and temporal variations in sunlight as these factors determine the light conditions. However, it remains challenging to gain an overview of the importance of photodegradation in the aquatic environment because the reactions involved are diverse and complex. Therefore, this review provides a concise summary of the importance of photodegradation and the major processes related to the photodegradation of OMPs, with particular attention given to recent progress on the major reactions of DOM. In addition, major knowledge gaps in this field of environmental photochemistry are highlighted. [Display omitted] [ABSTRACT FROM AUTHOR]

Antihypertensive propranolol (PRO) is frequently detected in surface waters and has adverse effects on aquatic organisms. In this study, its photochemical fate in surface water with the aspect of kinetics, products and toxicity were investigated employing steady-state photochemistry experiments and ecotoxicity tests. The results showed that photodegradation of PRO was enhanced in river water than that in phosphate buffer where dissolved organic matter (DOM), NO 3 −, and HCO 3 − played important roles. DOM accelerated the photodegradation mainly through generation of excited triplet-state DOM while NO 3 − played dual roles in the photodegradation. The reaction between excited triplet-state PRO and HCO 3 − can generate carbonate radical (CO 3 ·-) to promote the photodegradation. The second-order reaction rate constant between PRO and CO 3 ·- was determined to be (3.4 ± 0.8) × 108 M−1 s−1. Eight photodegradation products were identified in the studied river water sample. Finally, the toxicity evaluated by Vibrio fischeri increased after photodegradation and three photodegradation products were responsible for the increasing toxicity, which was concluded from the significant correlation between toxicity parameters and quantity of the photodegradation products. [Display omitted] • Photodegradation rate of PRO is faster in river water relative to pure water. • Both river water DOM and NO 3 − show enhancement effects on PRO photodegradation. • CO 3.•- is responsible for promoting the photodegradation of PRO in HCO 3 − solution. • Eight photodegradation products are identified in the river water. • The photodegradation of PRO enhances their toxicity against vibrio fischeri. [ABSTRACT FROM AUTHOR]