抗生素在水环境中的光化学行为

抗生素是在水环境中广泛存在的一类新兴污染物, 近年来, 由于其“假”持久性并能引起环境菌群的抗药性而备受关注. 光化学降解是水环境中抗生素类污染物的重要消减方式. 本文总结了水环境中抗生素光化学行为研究的最新进展, 介绍了抗生素的直接、间接和自敏化光解动力学, 评述了pH和水中溶解性物质对抗生素光解的影响及典型抗生素的光降解路径与机理, 讨论了抗生素的光致毒性, 最后对抗生素在水环境中光化学行为的研究进行了展望.     

Photodegradation study of the antifouling booster biocide dichlofluanid in aqueous media by gas chromatographic techniques

The aquatic photochemical behavior of the biocide dichlofluanid has been studied under natural sunlight conditions as well as under artificial solar irradiation in different types of natural waters (sea, river and lake water) as well as in distilled water. In order to examine the effect of dissolved organic matter (DOM), the photodegradation of the tested biocide was investigated also in the presence of various concentrations of humic and fulvic acids. It was found that the photodegradation proceeds via first-order reaction in all cases and that the presence of various concentrations of DOM inhibits the photolysis reaction. Kinetic experiments are monitored with GC–ECD with half-lives varied between 8 and 83 h. The major photodecomposition products identified by GC–MS were dichlorofluoromethane, aniline, and DMSA. Based on this byproduct identification a possible degradation pathway is proposed for the photolysis of dichlofluanid in aqueous media.     

Aqueous phototransformation of zinc pyrithione Degradation kinetics and byproduct identification by liquid chromatography--atmospheric pressure chemical ionisation mass spectrometry

The photochemical behavior of the antifouling agent zinc pyrithione (ZnPT) was studied in aqueous media of different composition under simulated solar irradiation using a xenon light source. The influence of important constituents of natural water (dissolved organic matter and nitrate) was also examined using a multivariate kinetic model. It was found that photodegradation proceeds via a pseudo first-order reaction. Kinetic experiments were monitored by LC-MS and photolytic half-lives ranging between 9.2 and 15.1 min have been observed. The increasing concentration of dissolved organic matter (DOM) accelerates the photolysis reaction, while the effect of nitrate ions was also positive since it increased the degradation rate, but to a lesser extent. Irradiation of the aqueous ZnPT solutions gave rise to several transformation products that were isolated by means of solid-phase extraction using poly(styrene-divinylbenzene) extraction disks. These byproducts were identified using liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry. Besides 2-pyridinesulfonic-acid, other degradation products formed included pyridine-N-oxide, 2-mercaptopyridine, 2,2'-dithiobis(pyridine-N-oxide), 2,2-dipyridyl disulfide and the pyridine/pyrithione mixed disulfide, 2,2'-dithiobispyridine mono-N-oxide (PPMD).     

Reaction pathways and mechanisms of photodegradation of pesticides

The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products. Potential use of photochemical processes in advanced oxidation methods for water treatment is also discussed. Processes considered include direct photolysis leading to homolysis or heterolysis of the pesticide, photosensitized photodegradation by singlet oxygen and a variety of metal complexes, photolysis in heterogeneous media and degradation by reaction with intermediates generated by photolytic or radiolytic means.     

Ice photolysis of 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100): Laboratory investigations using solid phase microextraction

Here, we report for the first time a laboratory investigation into the photochemical degradation of 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100) in ice solid samples using an artificial UV light source. Solid phase microextraction (SPME) was used as a sensitive extraction technique for monitoring trace amounts of the hydrophobic pollutant and its photoproducts. The results showed that ice photolysis kinetics for BDE-100 is similar to the one observed in the aqueous counterpart. The eight photoproducts identified consisted of brominated diphenyl ethers with lower bromine content and polybrominated dibenzofurans, suggesting two important photodegradation pathways for BDE-100 in ice solid samples: (i) stepwise reductive debromination and (ii) intramolecular elimination of HBr. Similarities in photochemical product arrays observed in the ice and water photolysis of BDE-100 were attributed to a similar mechanism for photochemical decomposition for both phases. Possible involvement of the water molecules in the reactions has been excluded by performing photolysis in D₂O ice solid and water samples. Taking advantage of the high preconcentration factor obtained with SPME at low temperatures, a SPME fiber cooled with liquid carbon dioxide down to 0 °C was used as a photoreaction support for BDE-100 allowing the identification of a greater number of photoproducts.     

Aqueous photolysis of the sunscreen agent octyl-dimethyl-p-aminobenzoic acid. Formation of disinfection byproducts in chlorinated swimming pool water

The photochemical behavior of the sunscreen agent octyl-dimethyl-p-aminobenzoic acid (ODPABA) was studied in different aqueous solutions and under different conditions. ODPABA photolysis was performed under laboratory conditions using a xenon light source and under natural sunlight conditions in sea, swimming pool as well as in distilled water. The influence of dissolved organic matter (DOM) on the degradation kinetics was also studied in the presence of various concentrations of humic acids (HA). The phototransformation was shown to proceed via pseudo-first-order reaction in all cases and the reaction rates followed the order: distilled water > swimming pool water > seawater, depending mainly on the presence of dissolved organic matter that retarded the photolysis reaction. Kinetic experiments were monitored with HPLC/UV-DAD and the half-lives (t 1/2) varied between 1.6 and 39 h in simulated solar irradiation and between 27 and 39 h in natural sunlight conditions. The product distribution during illumination was strongly dependent on the constitution of the irradiated media. Irradiation of the aqueous ODPABA solutions gave rise to several transformation products that were isolated by means of solid-phase extraction (SPE) and identified using GC-MS techniques. These were formed mainly through dealkylation and hydroxylation reactions and were detected in all aqueous solutions investigated. In the case of swimming pool water some additional byproducts were isolated and were tentatively identified as chlorinated intermediates, formed by the subsequent chlorination of the parent molecule as well as other intermediates.     

Study of alloxydim photodegradation in the presence of natural substances: Elucidation of transformation products

A photodegradation study of alloxydim was performed under simulate solar irradiation (Suntest apparatus) at different irradiation intensities. Moreover, indirect photolysis of the tested herbicide was investigated under the presence of various concentrations of humic acids (HA), nitrate and Fe (III) ions. The photodegradation of alloxydim follows a first-order reaction kinetics in all cases. HA inhibited the photolysis kinetic whereas rate constants measured in the presence of nitrate ions indicated no effect on degradation. On the contrary, Fe (III) ions enhanced the photodegradation rate of alloxydim. Kinetics experiments were monitored by HPLC–DAD and the half-lives ranged from 165.78 to 4.63 min for different intensities in direct photolysis and from 104.81 to 1.14 min for indirect photolysis. The study of transformation products have been investigated by HPLC coupled to quadrupole time-of-flight mass spectrometry (QTOF-MS) employing the electrospray technique.The most important transformation process was found to be the cleavage of the O–N bond of the oxime moiety. Minor photo-isomerization to Z-isomer was also observed. The appearance of these degradation products is reported in aqueous media for the first time.     

Polycyclic aromatic hydrocarbons in the atmosphere: monitoring, sources, sinks and fate. II: Sinks and fate

This paper reviews the transformation processes that polycyclic aromatic hydrocarbons (PAHs) undergo in the atmosphere. These processes can take place both in the gas phase and in the particulate/aerosol one. Among the gas-phase processes, the most important ones are the daytime reaction with *OH and the nighttime reaction with *NO3. The relative importance of the two processes depends on the particular PAH molecule. For instance, gaseous naphthalene is mainly removed from the atmosphere upon reaction with *OH, while gaseous phenanthrene is mainly removed by reaction with *NO3. Oxy-, hydroxy-, and nitro-PAHs are the main transformation intermediates. Reaction with ozone and photolysis play a secondary role in the transformation of gaseous PAHs. The particle-associated processes are usually slower than the gas-phase ones, thus the gas-phase PAHs usually have shorter atmospheric lifetimes than those found on particulate. Due to the higher residence time on particulate when compared with the gas phase, direct or assisted photolysis plays a relevant role in the transformation of particle-associated PAHs. Among the other processes taking place in the condensed phase, nitration plays a very important role due to the health impact of nitro-PAHs, some of them being the most powerful mutagens found so far in atmospheric particulate extracts.     

Overlap of colloid chemistry and photochemistry in surfactant systems

Interactions of organic photochemistry and colloid chemistry in surfactant systems can be divided in two distinct sections: (i) influences of the colloids on photochemical reactions and (ii) influences of photochemical reactions on macroscopic properties of colloidal surfactant systems. As to (i), the (generally poor) selectivity of photochemical reactions can be improved by performing the reactions in systems containing surfactant aggregates. Regioselectivity, stereoselectivity and multiplicity selectivity can be directed. As to (ii), in lyotropic liquid crystalline systems the solubilization of certain aromatic compounds specifically changes phase transition temperatures. Upon photochemically transforming such solubilizates in situ isothermal phase transitions can be brought about, provided that photoeducts and photoproducts induce distinct transition temperatures. Similarly in dilute surfactant systems solubilizates specifically affect size and shape of micellar aggregates, so that changes in flow behaviour take place, which can be switched via photochemical transformation of solubilizates. Possible exploitations of the effects are discussed and compared with the application of similar effects in related non-surfactant systems, with emphasis on photochemical information storage.     

Mechanistic Aspects of the Effects of Stress on the Rates of Photochemical Degradation Reactions in Polymers

Abstract

This review examines the mechanistic origins of the effects of stress on the photochemical degradation rates of polymers. Recent studies have shown that tensile and shear stresses accelerate the rate of the photochemical degradation of polymers. Conversely, compressive stress generally retards the rate of photochemical degradation. After an initial discussion of the photochemical auto‐oxidation mechanism, the three primary hypotheses that purport to explain how stress affects photochemical degradation are examined. The first hypothesis is attributed to Plotnikov, who proposed that stress changes the quantum yields of the reactions that lead to bond photolysis. The second hypothesis, attributed to a number of researchers, says that stress affects the ability of the geminate radical pairs, formed in the photochemical bond cleavage reactions, to recombine. The third hypothesis proposes that stress changes the rates of radical reactions subsequent to radical formation. A further attempt to account for the effects of stress on degradation rates is a modification of the so‐called Zhurkov equation that has been used rather successfully to predict the effects of stress on degradation rates in thermal reactions. This empirical equation relates the quantum yield of degradation to a composite activation barrier for the overall photochemical reaction. Following the discussion of these hypotheses, experimental mechanistic studies of stress effects are summarized, and what little data there is is shown to be consistent with the hypothesis that proposes that stress primarily affects the ability of photochemically generated radical pairs to recombine. By decreasing the efficiency of radical–radical recombination, the effect is to increase the relative efficiencies of the radicals' other reactions and hence the rate of degradation. In addition to stress, other factors can affect the rates of polymer photodegradation. These factors include the absorbed light intensity, the polymer morphology, the rate of oxygen diffusion in the polymer, and the chromophore concentration. Each of these parameters must be carefully controlled in mechanistic studies that probe the effects of stress on degradation rates.     

Characterization of transient species in laser photolysis of aromatic amino acids using acetone as photosensitizer

The photochemical processes of aromatic amino acids were investigated in aqueous solution using acetone as photosensitizer by KrF (248 nm) laser flash photolysis. Laser-induced transient species were characterized according to kinetic analysis and quenching experiments. The intermediates recorded were assigned to the excited triplet state of tryptophan, the radicals of tryptophan and tyrosine. The excited triplet state of tryptophan produced via a triplet-triplet excitation transfer and the radicals arising from electron transfer reaction has been identified. Neither electron transfer nor energy transfer between triplet acetone and phenylalanine can occur in photolysis of phenylalanine aqueous solution which contains acetone. Furthermore, triplet acetone-induced radical transformation: Trp/N-Tyr→Trp-Tyr/O was observed directly in photolysis of dipeptide (Trp-Tyr) aqueous solution containing acetone, and the transformation resulting from intramolecular electron transfer was suggested.     

Photochemical degradation of polycyclic aromatic hydrocarbons (PAH) in real and laboratory conditions

Studies were carried out on the effects induced by the main components of airborne particulate matter (APM) as soot, inorganic and cyclohexane soluble substances and by glass fiber filters on photodegradation of pyrene, benz(a)anthracene and benzo(a)pyrene exposed to UV and solar radiation. In both experimental models tested hydrocarbons showed a higher photochemical stability when absorbed on APM. Inorganic components of APM slightly enhance UV photodegradation. In real condition (outdoor exposure to solar radiation) PAH half lives generally showed a good linear correlation with mean solar radiation intensity; only degradation rate of benzo(a)pyrene on APM, exposed to sunlight was practically constant. Pyrene, in particular, showed a higher degradation rate when high ozone concentrations (0.2 ppm) occurred.     

Application of solid-phase microextraction to the study of the photochemical behaviour of five priority pesticides: "on-fiber" and aqueous photodegradation

Solid-phase microextraction (SPME) is applied to study the photochemical degradation of five priority pesticides: atrazine, alachlor, aldrin, dieldrin, endrin. Analyses were carried out by gas chromatography-mass spectrometry. The possibility of studying the photochemical degradation of the target compounds in solid-phase microextraction fibers, "photo-SPME", is evaluated employing different SPME coatings. The target analytes were extracted from aqueous solutions using different commercial coatings and then, the fibers were exposed to UV light. Results indicated that on-fiber photodegradation takes place in a considerably major extent using PDMS coating for an irradiation time of 30min. On-fiber photodegradation kinetics of each analyte were determined by UV irradiation of the PDMS for different times. A large number of photoproducts were generated and they were tentatively identified by means of their mass spectra and with the aid of literature. In this way, main photodegradation mechanisms could be postulated. Aqueous photodegradation studies followed by SPME were performed and compared with photo-SPME. All the photoproducts detected in the aqueous experiments were previously found in the photo-SPME experiments. This study shows the potential of photo-SPME to evaluate the photo-transformation of organic pollutants.     

Photodegradation study of decabromodiphenyl ether by UV spectrophotometry and a hybrid hard- and soft-modelling approach

This work presents an exploratory study of the photochemical degradation process of decabromodiphenyl ether (decaBDE) and gives an interpretation of the kinetic pathway, species and effects of the key factors involved in the degradation process. Use of lowly brominated diphenyl ethers (PBDE) has been banned by the EU and there seems to be evidence of the photolytic degradation of highly brominated PBDEs into lowly brominated congeners. Hence, the importance of knowing the photodegradation process of decaBDE.The photodegradation was investigated under UV light by UV-spectrophotometric monitoring. A novel hybrid data analysis approach, based on the combination of hard- and soft-spectrophotometric multivariate curve resolution, was applied to elucidate the mechanism of the degradation process, to resolve kinetic profiles and pure spectra of the photodegradation products and to evaluate the rate constants. The photodegradation process could be described with a kinetic model based on three consecutive first-order reactions and a decrease of the degradation process was observed as solvent polarity increased. Complementary identification of photodegradation products by gas chromatography coupled to mass spectrometry using negative chemical ionization (GC-NCI-MS) is attempted.This work presents a novel attempt of describing in a comprehensive way the photochemical degradation process of decaBDE, with all successive steps and related rate constants. This study proves also the potential of the proposed hybrid data analysis methodology as a general strategy to interpret the evolution of these photochemical reactions.     

Two-Photon Photochemical Reactions of Aromatic Compounds in the Gas Phase

Studies on the gas-phase two-photon photochemistry of aromatic compounds performed in the past 25 years were summarized. Photophysical and photochemical unimolecular and bimolecular reactions occurring in the gas phase on the exposure of molecular systems (aliphatic aldehydes, ketones, and alcohols; aromatic hydrocarbons and their halogen derivatives; and heteroaromatic compounds with a conjugated -electron system) to pulsed laser UV radiation were considered. Data on the kinetics and mechanisms of primary two-photon photoexcitation, photodissociation, and photoionization of aromatic molecules were systematized, and the nature of electronically excited states responsible for these processes was determined. Data on the reactivity of transient species and on the kinetics of elementary steps of laser UV photolysis (bimolecular charge transfer and heavy particle transfer reactions and termolecular association and cluster ion formation reactions) were presented. General prerequisites to the stability of aromatic compounds under non-steady-state conditions of UV photolysis were found in accordance with the electronic structure of reactants and with the donor–acceptor properties of mixture components.     

β-Cyclodextrin as a photostabilizer of the plant growth regulator 2-(1-naphthyl) acetamide in aqueous solution

The plant growth regulator 2-(1-naphthyl) acetamide (NAAm) is susceptible to degradation by sunlight and UV light in aqueous solution. Its inclusion complex with β-cyclodextrin (β-CD) was characterized by absorption and fluorescence spectroscopy and its photodegradation was compared with that of aqueous solutions of NAAm. The complex was formed with a stoichiometric ratio of 1:1 with a binding constant of 651 M^?1. The photodegradation behavior of NAAm in the inclusion complex NAAm:β-CD was investigated using both UV (λ = 254 nm) and simulated solar light (Suntest) irradiation. It was found that the NAAm:β-CD complex increases NAAm photostability towards photochemical degradation markedly. In addition, an influence of β-CD concentration was also observed on NAAm degradation rate: higher β-CD concentrations lead to a slower photoinduced transformation. Moreover, some differences were found in the photoproducts in the presence and absence of the cyclodextrin, indicating inhibition of some of the mechanistic pathways. β-CD stabilizes NAAm photodegradation towards sunlight and UV irradiation, enhancing its efficient application on formulations for the treatment of fruits and vegetables.     

Photoreactivity of the nonsteroidal anti-inflammatory 2-arylpropionic acids with photosensitizing side effects.

The photoreactivity of the nonsteroidal anti-inflammatory 2-arylpropionic acids benoxaprofen, carprofen, naproxen, ketoprofen, tiaprofenic acid, and suprofen is reviewed with special emphasis on fundamental photophysical and photochemical properties. The absorption and emission properties of the excited states of these drugs as well as their main photodegradation routes are summarized. The photochemical mechanisms are discussed on the basis of product studies and detection of short-lived intermediates by means of laser flash photolysis. After dealing with the unimolecular processes, attention is focused on the photosensitized reactions of key biomolecules, such as lipids, proteins or nucleic acids. Finally, a short section on the photobiological effects on simple biological models is also included. Although some earlier citations are included, the literature coverage is in general limited to the last decade.     

Photolysis and photocatalysis of ibuprofen in aqueous medium: characterization of by‐products via liquid chromatography coupled to high‐resolution mass spectrometry and assessment of their toxicities against Artemia Salina

The degradation of the pharmaceutical compound ibuprofen (IBP) in aqueous solution induced by direct photolysis (UV‐A and UV‐C radiation) and photocatalysis (TiO₂/UV‐A and TiO₂/UV‐C systems) was evaluated. Initially, we observed that whereas photocatalysis (both systems) and direct photolysis with UV‐C radiation were able to cause an almost complete removal of IBP, the mineralization rates achieved for all the photodegradation processes were much smaller (the highest value being obtained for the TiO₂/UV‐C system: 37.7%), even after an exposure time as long as 120 min. Chemical structures for the by‐products formed under these oxidative conditions (11 of them were detected) were proposed based on the data from liquid chromatography coupled to high‐resolution mass spectrometry (LC‐HRMS) analyses. Taking into account these results, an unprecedented route for the photodegradation of IBP could thus be proposed. Moreover, a fortunate result was achieved herein: tests against Artemia salina showed that the degradation products had no higher ecotoxicities than IBP, which possibly indicates that the photocatalytic (TiO₂/UV‐A and TiO₂/UV‐C systems) and photolytic (UV‐C radiation) processes can be conveniently employed to deplete IBP in aqueous media. Copyright © 2014 John Wiley & Sons, Ltd.     

Oxidation of atrazine by photoactivated potassium persulfate in aqueous solutions

General laws of the photochemical oxidation of atrazine by inorganic peroxo compounds under the impact of solar radiation are studied. It is found that almost complete conversion of atrazine can be achieved via photochemical oxidation with persulfate after 120 min, but no deep mineralization is observed. The effect an aqueous matrix has on the processes of atrazine degradation in combined oxidation systems is considered.     

Chemical reactions in clouds

Summary In contrast to a fairly extensive knowledge of gas phase chemical reactions in the atmosphere, our current understanding of the chemistry in the aqueous phase of clouds is still inadequate. Particularly for continental clouds the difficulties arise primarily from uncertainties in reaction mechanisms for the oxidation of various sulfur(IV) species originating from the dissolution of sulfur dioxide in cloud water and the role of the ions of transition metals in this oxidation process. The importance of OH and other radicals in gas-phase reactions has led to models, in which radical reactions are held responsible for much of the chemical change also in the liquid phase. This viewpoint has gained support specifically from the identification of iron(III)-hydroxo complexes as a photochemical source of OH radicals in continental clouds. Their reactions with sulfur(IV) compounds in the aqueous phase initiate chain processes, which are currently being examined by laboratory studies.