Nitrate-induced photodegradation of atenolol in aqueous solution: kinetics, toxicity and degradation pathways

The extensive utilization of β-blockers worldwide led to frequent detection in natural water. In this study the photolysis behavior of atenolol (ATL) and toxicity of its photodegradation products were investigated in the presence of nitrate ions. The results showed that ATL photodegradation followed pseudo-first-order kinetics upon simulated solar irradiation. The photodegradation was found to be dependent on nitrate concentration and increasing the nitrate from 0.5 mM L⁻¹ to 10 mM L⁻¹ led to the enhancement of rate constant from 0.00101 min⁻¹ to 0.00716 min⁻¹. Hydroxyl radical was determined to play a key role in the photolysis process by using isopropanol as molecular probe. Increasing the solution pH from 4.8 to 10.4, the photodegradation rate slightly decreased from 0.00246 min⁻¹ to 0.00195 min⁻¹, probably due to pH-dependent effect of nitrate-induced OH formation. Bicarbonate decreased the photodegradation of ATL in the presence of nitrate ions mainly through pH effect, while humic substance inhibited the photodegradation via both attenuating light and competing radicals. Upon irradiation for 240 min, only 10% reduction of total organic carbon (TOC) can be achieved in spite of 72% transformation rate of ATL, implying a majority of ATL transformed into intermediate products rather than complete mineralization. The main photoproducts of ATL were identified by using solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) techniques and possible nitrate-induced photodegradation pathways were proposed. The toxicity of the phototransformation products was evaluated using aquatic species Daphnia magna, and the results revealed that photodegradation was an effective mechanism for ATL toxicity reduction in natural waters.     

Photolysis of nonylphenol ethoxylates: the determination of the degradation kinetics and the intermediate products

The photolysis of nonylphenol ethoxylates with an average oligomers length of ten ethoxylate units (NPEO(10)) in aqueous solution under UV, as well as the influence of humic acid (HA) on the photolysis was studied. A 125W high-pressure mercury lamp was employed as the light source. The intermediate products from the photolysis were determined by LC-MS. The results indicated that NPEO(10) underwent direct photolysis upon exposed to UV. The degradation pathway was complex. Besides the generally proposed degradation pathway of ethylene oxide (EO) side chains shortening, the oxidation of alkyl chain and EO chain led to intermediates having both a carboxylated (as well as carbonylated) ethoxylate and alkyl chain of varying lengths. The hydrogenation of benzene ring was also detected. The kinetics data showed that the first order reaction kinetics could be well used to describe the kinetics of NPEO(10) degradation. In the presence of dissolved organic matter by HA addition, the performance of NPEO(10) photodegradation was reduced. The photolysis rate decreased with increased HA concentration.     

Evaluation of photolysis and hydrolysis of atrazine and its first degradation products in the presence of humic acids

Relative importance of hydrolysis and photolysis of atrazine and its degradation products in aqueous solutions with dissolved humic acids (HA) has been assessed under exposure to sunlight and under UV irradiation. Quantum yield for direct photolysis of atrazine at 254 nm was 0.037 mol photon(-1), the reaction order was 0.8. Atrazine, desethylatrazine and desisopropylatrazine converted to their 2-hydroxy analogs with rate constants 0.02-0.08 min(-1) in clear solutions, while addition of HA (300 mg L(-1)) caused a 10-fold increase in rate constants. Hydroxyatrazine was not degraded. No evidence of photo-Fenton reaction was found. Under exposure to solar light, atrazine, desethylatrazine and desisopropylatrazine were converted to 2-hydroxy analogs only at pH 2 because of acid hydrolysis and possible contribution of photolysis. At lower HA concentration, only their light-shielding effect was noticed, while at higher concentrations, HA-catalysed hydrolysis prevailed. Hydroxyatrazine concentration diminished at all pH values in solutions without HA exposed to sunlight.     

Degradation mechanism and the toxicity assessment in TiO2 photocatalysis and photolysis of parathion

The photocatalytic degradation of methyl parathion was carried out using a circulating TiO2/UV reactor. The experimental results showed that parathion was more effectively degraded in the photocatalytic condition than the photolysis and TiO2-only condition. With photocatalysis, 10mg/l parathion was completely degraded within 60 min with a TOC decrease exceeding 90% after 150 min. The main ionic byproducts during photocatalysis were measured. The nitrogen from parathion was recovered mainly as NO3-, NO2- and NH4+, 80% of the sulfur as SO4(2-), and less than 5% of the phosphorus as PO4(3-). The organic intermediates 4-nitrophenol and paraoxon were also identified, and these were further degraded. Two different bioassays (Vibrio fischeri and Daphnia magna) were used to test the acute toxicity of solutions treated by photocatalysis and photolysis. A Microtox test using V. fischeri showed that the toxicity, expressed as the relative toxicity (%), was reduced almost completely after 90 min under photocatalysis, whereas only an 83% reduction was achieved with photolysis alone. Another toxicity test using D. magna also showed that the relative toxicity disappeared after 90 min under photocatalysis, whereas there was a 65% reduction in relative toxicity with photolysis alone. The pattern of toxicity reduction parallels the decrease in parathion and TOC concentrations.     

Semiconductor-mediated photocatalysed degradation of two selected priority organic pollutants,benzidine and 1,2-diphenylhydrazine,in aqueous suspension

The photocatalysed degradation of two selected priority organic pollutants, namely benzidine (1) and 1,2-diphenylhydrazine (DPH, 2) has been investigated in aqueous suspensions of titanium dioxide (TiO2) under a variety of conditions employing a pH-stat technique. The degradation was studied by monitoring the change in substrate concentration of the model compound employing HPLC analysis and the decrease in total organic carbon content, respectively, as a function of irradiation time. The degradation kinetics were studied under different conditions such as reaction pH, substrate and photocatalyst concentration, type of TiO2 photocatalyst and the presence of alternative additives such as H2O2, KBrO3 and (NH4)2S2O8 besides molecular oxygen. The degradation rates and the photonic efficiencies were found to be strongly influenced by the above parameters. Toxicity tests for the irradiated samples of benzidine measuring the luminescence of bacteria Vibrio fischeri after 30 min of incubation were also performed. 4-amino-biphenyl (7) and hydroquinone (13) were identified as intermediate products by GC/MS technique and probable pathways for the formation of the products are proposed.     

Influence of humic substances on the photolysis of aqueous pesticide residues

The present work investigated the direct and indirect photolysis of pesticide residues (atrazine, imazaquin, iprodione), in aqueous solutions and under UV-visible radiation (280-480nm). Different kinds of humic substances (HS) were added to samples in order to evaluate their behaviour as possible photocatalysts and their effect on the photolysis of pesticides. The fulvic acids were purchased from the International Humic Substances Society, and they were added to samples in concentrations ranging from 1 to 150 mgl(-1). Titanium dioxide was used as the photocatalyst, in concentration ranging from 10 to 150 mgl(-1). Pesticides photolysis were measured by UV-visible absorption spectroscopy and differential pulse polarography with all used pesticides, reaching total degradation after 2h of irradiation, thus indicating a fast direct photolysis. Photocatalysis by TiO(2) could increase the pesticides photolysis rate up to 40%. This effect, however, was not observed for imazaquin photolysis. Again, except for imazaquin, HS presence showed a positive effect in increasing pesticide degradation, but only within specific concentration ranges (below 10mg l(-1) for iprodione and about 30mgl(-1) for atrazine). Above these ranges HS induce a decrease in the pesticides photolysis rate. Spin-trapping measurements by electronic paramagnetic resonance spectroscopy, using the spin-trap DMPO, showed that HS are able to photogenerate hydroxyl radicals, increasing the pesticides molecule degradation. However, the HS also react with the photogenerated hydroxyl radical, influencing the pesticide photolysis, leading to a decrease in the photolysis rate and causing it to be strongly dependent on the nature and concentration of residues in the water to be treated.     

Photoassisted and photocatalytic degradation of sulfur mustard using TiO2 nanoparticles and polyoxometalates

The decomposition of highly toxic chemical warfare agent, sulfur mustard (bis(2-chloroethyl) sulfide or HD), has been studied by homogeneous photolysis and heterogeneous photocatalytic degradation on titania nanoparticles. Direct photolysis degradation of HD with irradiation system was investigated. The photocatalytic degradation of HD was investigated in the presence of TiO₂ nanoparticles and polyoxometalates embedded in titania nanoparticles in liquid phase at room temperature (33?±?2 °C). Degradation products during the treatment were identified by gas chromatography–mass spectrometry. Whereas apparent first-order kinetics of ultraviolet (UV) photolysis were slow (0.0091 min^?1), the highest degradation rate is obtained in the presence of TiO₂ nanoparticles as nanophotocatalyst. Simultaneous photolysis and photocatalysis under the full UV radiation leads to HD complete destruction in 3 h. No degradation products observed in the presence of nanophotocatalyst without irradiation in 3 h. It was found that up to 90 % of agent was decomposed under of UV irradiation without TiO₂, in 6 h. The decontamination mechanisms are often quite complex and multiple mechanisms can be operable such as hydrolysis, oxidation, and elimination. By simultaneously carrying out photolysis and photocatalysis in hexane, we have succeeded in achieving faster HD decontamination after 90 min with low catalyst loading. TiO₂ nanoparticles proved to be a superior photocatalyst under UV irradiation for HD decontamination.     

Photochemical degradation and mineralization of 4-chlorophenol

INTENTION, GOAL, SCOPE, BACKGROUND: Since the intermediate products of some compounds can be more toxic and/or refractory than the original compund itself, the development of innovative oxidation technologies which are capable of transforming such compounds into harmless end products, is gaining more importance every day. Advanced oxidation processes are one of these technologies. However, it is necessary to optimize the reaction conditions for these technologies in order to be cost-effective. OBJECTIVE: The main objectives of this study were to see if complete mineralization of 4-chlorophenol with AOPs was possible using low pressure mercury vapour lamps, to make a comparison of different AOPs, to observe the effect of the existence of other ions on degradation efficiency and to optimize reaction conditions. METHODS: In this study, photochemical advanced oxidation processes (AOPs) utilizing the combinations of UV, UV/H2O2 and UV/H2O2/Fe2+ (photo-Fenton process) were investigated in labscale experiments for the degradation and mineralization of 4-chlorophenol. Evaluations were based on the reduction of 4-chlorophenol and total organic carbon. The major parameters investigated were the initial 4-chlorophenol concentration, pH, hydrogen peroxide and iron doses and the effect of the presence of radical scavengers. RESULTS AND DISCUSSION: It was observed that the 4-chlorophenol degradation efficiency decreased with increasing concentration and was independent of the initial solution pH in the UV process. 4-chlorophenol oxidation efficiency for an initial concentration of 100 mgl(-1) was around 89% after 300 min of irradiation in the UV process and no mineralization was achieved. The efficiency increased to > 99% with the UV/H2O2 process in 60 min of irradiation, although mineralization efficiency was still around 75% after 300 min of reaction time. Although the H2O2/4-CP molar ratio was kept constant, increasing initial 4-chlorophenol concentration decreased the treatment efficiency. It was observed that basic pHs were favourable in the UV/H2O2 process. The results showed that the photo-Fenton process was the most effective treatment process under acidic conditions. Complete disappearance of 100 mgl(-1) of 4-chlorophenol was achieved in 2.5 min and almost complete mineralization (96%) was also possible after only 45 min of irradiation. The efficiency was negatively affected from H2O2 in the UV/H2O2 process and Fe2+ in the photo-Fenton process over a certain concentration. The highest negative effect was observed with solutions containing PO4 triple ions. Required reaction times for complete disappearance of 100 mgl(-1) 4-chlorophenol increased from 2.5 min for an ion-free solution to 30 min for solutions containing 100 mgl(-1) PO4 triple ion and from 45 min to more than 240 min for complete mineralization. The photodegradation of 4-chlorophenol was found to follow the first-order law. CONCLUSION: The results of this study showed that UV irradiation alone can degrade 4-CP, although at very slow rates, but cannot mineralize the compound. The addition of hydrogen peroxide to the system, the so-called UV/H2O2 process, significantly enhances the 4-CP degradation rate, but still requires relatively long reaction periods for complete mineralization. The photo-Fenton process, the combination of homogeneous systems of UV/H2O2/Fe2+ compounds, produces the highest photochemical elimination rate of 4-CP and complete mineralization is possible to achieve in quite shorter reaction periods when compared with the UV/H2O2 process. RECOMMENDATIONS AND OUTLOOK: It is more cost effective to use these processes for only purposes such as toxicity reduction, enhancement of biodegradability, decolorization and micropollutant removal. However the most important point is the optimization of the reaction conditions for the process of concern. In such a case, AOPs can be used in combination with a biological treatment systems as a pre- or post treatment unit providing the cheapest treatment option. The AOP applied, for instance, can be used for toxicity reduction and the biological unit for chemical oxygen demand (COD) removal.     

Kinetic and chemical assessment of the UV/H2O2 treatment of antiepileptic drug carbamazepine

The UV/H2O2-induced degradation of carbamazepine, a worldwide used antiepileptic drug, recently found as contaminant in many municipal sewage treatment plant (STP) effluents and other aquatic environments, is investigated. The oxidation treatment caused an effective removal of the drug. At complete abatement of the substrate after 4 min treatment, a 35% value of removed total organic carbon (TOC) was obtained. A kinetic constant of (2.05+/-0.14) x 10(9) lmol(-1)s(-1) was determined for OH radical attack to carbamazepine in the UV/H2O2 process. Preparative TLC of the reaction mixture led to the isolation of acridine-9-carboxaldehyde as a reaction intermediate. HPLC and GC/MS analysis indicated formation of small amounts of acridine, salicylic acid, catechol and anthranilic acid among the reaction products. Under the same reaction conditions, synthetically prepared 10,11-epoxycarbamazepine was easily degraded to acridine as main product, suggesting that this epoxide is a likely intermediate in the oxidative conversion of carbamazepine to acridine. Under sunlight irradiation, carbamazepine in water underwent slow degradation to afford likewise acridine as main product. In view of the mutagenic properties of acridine, these results would raise important issues concerning the possible environmental impact of carbamazepine release through domestic wastewaters and support the importance of prolonged oxidation treatments to ensure complete degradation of aromatic intermediates.     

Photolytic degradation of quinalphos in natural waters and on soil matrices under simulated solar irradiation

The photochemical persistence of quinalphos, one of the most widely used organophosphorous insecticides, was investigated in a variety of environmental matrices such as natural waters and soils of different composition. Simulated solar irradiation was obtained using a xenon arc lamp (Suntest CPS+ apparatus) giving an irradiation intensity of 750 W m(-2) equivalent to a light dose per hour of irradiation of 2,700 kJ m(-2). The phototransformation rates were determined using solid-phase microextraction (SPME) and ultrasonic extraction (USE) coupled to GC-FTD, while the identification of photoproducts was carried out by GC-MS. In water samples, the degradation kinetics followed a pseudo-first-order reaction and photolysis half-lives ranged between 11.6 and 19.0 h depending on the constitution of the irradiated media. Dissolved organic matter (DOM) has a predominant retarding effect, while nitrate ions accelerated the photodegradation kinetics. In soil samples, the degradation kinetics was monitored on 1mm soil layer prepared on glass TLC plates. The kinetic behaviour of quinalphos was complex and characterized by a double step photoreaction, fast in the first 4h of irradiation followed by a slow degradation rate up to 64 h. The photolysis half-life of quinalphos was shorter in sandy soil compared to the rest of the soil samples, varying between 16.9 and 47.5 h, and showing a strong dependence on the composition of the irradiated media. Among the transformation products formed mainly through photohydrolysis and photoisomerization processes, some photoproduct structures were proposed according to their mass spectral information.     

紫外光协助高锰酸钾降解四环素的研究

高锰酸钾氧化法在实际水处理中得到了一定的应用,但对有机污染物的去除和降解能力相对有限,为此提出了以外加紫外光照射协助高锰酸钾氧化的方法。以四环素作为模型污染物,考察了四环素浓度、高锰酸钾浓度、反应时间、初始pH条件和不同紫外光照射等的影响。结果表明,高锰酸钾能够氧化并去除四环素,紫外光照射明显提高了高锰酸钾对四环素的降解效果,并且254 nm紫外光照射对降解的促进作用远大于365 nm紫外光。在所考察的pH范围内,无论紫外光照射与否,高锰酸钾在酸性条件下的降解效率最高,中性条件较高,碱性条件次之。     

Determination photostability of selected agrochemicals in water and soil.

The photolysis of selected pesticides in aqueous solutions has been investigated. The photolysis produced different intermediate substances, which were also found to be soil and microbial degradation products. The phototransformation in the presence of TiO2 and humic substances leads to a disappearance of these compounds. The reaction rate is dependent on the semiconductor oxide and concentration. Photoproducts were isolated and characterized by different spectroscopic methods. Results from this study indicate that degradation products of isoproturon are more toxic on Daphnia magna than on the parent compound.     

Photodegradation of naproxen in water under simulated solar radiation: mechanism,kinetics, and toxicity variation

The main objective of this study was to investigate the degradation mechanism, the reaction kinetics, and the evolution of toxicity of naproxen in waters under simulated solar radiation. These criteria were investigated by conducting quenching experiments with reactive oxygen species (ROS), oxygen concentration experiments, and toxicity evaluations with Vibrio fischeri bacteria. The results indicated that the degradation of naproxen proceeds via pseudo first-order kinetics in all cases and that photodegradation included degradation by direct photolysis and by self-sensitization via ROS; the contribution rates of self-sensitized photodegradation were 1.4 %, 65.8 %, and 31.7 % via ·OH, ¹O₂ and O₂ ^??, respectively. Furthermore, the oxygen concentration experiments indicated that dissolved oxygen inhibited the direct photodegradation of naproxen, and the higher the oxygen content, the more pronounced the inhibitory effect. The toxicity evaluation illustrated that some of the intermediate products formed were more toxic than naproxen.     

Radiation degradation of Congo Red in aqueous solution

Radiation-induced degradation of Congo Red (an azo dye) in aqueous solution was studied both with steady-state radiolysis and time-resolve techniques of pulse radiolysis and laser flash photolysis. Decomposition and mineralization of Congo Red by gamma-rays was investigated with the changes of absorption spectra, degradation efficiency, TOC removal and pH changes of the solutions in different irradiation systems. The main radiolytic products resulting from steady-state radiolysis of Congo Red were examined by HPLC and LC-MS. Complete degradation of Congo Red was observed at different absorbed doses under diverse irradiation condition. The TOC removal of the solutions saturated with O2 or N2O reached 76% and 86% at the absorbed dose of 11.9 kGy, respectively. Pulse radiolysis and laser flash photolysis experiments were carried out to study the reaction of Congo Red with e(aq)- and ()OH. The reaction rate constants were determined.     

Photocatalytic degradation of an organophosphorus pesticide phosalone in aqueous suspensions of titanium dioxide

The present work deals with photocatalytic degradation of an organophosphorus pesticide, phosalone, in water in the presence of TiO2 particles under UV light illumination (1000 W). The influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time, stirring rate, and distance from UV source, on the photodegradation efficiency of phosalone was investigated. The degradation rate of phosalone was not high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. The half-life (DT50) of a 20 ppm aqueous solution of phosalone was 15 min in optimized conditions. The plot of lnC (phosalone) vs. time was linear, suggesting first order reaction (K=0.0532 min(-1)). The half-life time of photomineralization in the concentration range of 7.5-20 ppm was 13.02 min. The efficiency of the method was also determined by measuring the reduction of Chemical Oxygen Demand (COD). During the mineralization under optimized conditions, COD decreased by more than 45% at irradiation time of 15 min. The photodegradation of phosalone was enhanced by addition of proper amount of hydrogen peroxide (150 ppm).     

Comparisons of polychromatic and monochromatic UV-based treatments of bisphenol-A in water via toxicity assessments

Polychromatic ultraviolet irradiation, such as from medium pressure (MP) Hg lamps may enhance the UV degradation of environmental pollutants as compared to low pressure (LP) Hg UV sources emitting monochromatic irradiation. Typically, studies involving destruction of environmental pollutants such as endocrine disrupting compounds (EDCs) are based on measurement of the parent compound decay using analytical chemistry, but such information is insufficient to determine an effective treatment endpoint because the identity and biological activity of many transformation products remain unknown. Bioanalytical methods to assess residual biological activity of a treated water offers one means to compare removal efficiency of EDC activity between MP- and LP-UV lamps under photolysis and UV/H2O2 oxidation. In this study, changes in estrogenic activity of bisphenol-A (BPA) as a function of UV treatment were evaluated using both an in vitro yeast estrogen screen and in vivo vitellogenin assay with Japanese medaka (Oryzias latipes) fish. Decay of BPA parent compound and formation of degradation products were followed using HPLC analysis. Results demonstrated that MP-UV direct photolysis more effectively removed BPA and associated estrogenic activity compared to LP-UV lamps. UV in combination with H2O2 significantly removed estrogenic activity in vitro and in vivo compared to direct photolysis; however, no significant difference in removal rates was found between the two lamps under UV/H2O2 oxidation. Furthermore, the UV/H2O2 process was effective for reducing embryo toxicity of BPA, but resulted in the production of acidic intermediates, causing acute toxicity and delayed hatching in some medaka embryos.     

Photolytic and photocatalytic degradation of 6-chloronicotinic acid

This work describes for the first time the photolytic and photocatalytic degradation of 6-chloronicotinic acid (6CNA) in double deionised water, which is a degradation product of neonicotinoid insecticides imidacloprid and acetamiprid, and it is known to appear in different environmental matrices. Photolytic experiments were performed with three UVA (ultraviolet A) polychromatic fluorescent lamps with broad maximum at 355 nm, while photocatalytic experiments were performed using immobilised titanium dioxide (TiO₂) on six glass slides in the spinning basket inside a photocatalytic quartz cell under similar irradiation conditions. Photolytic degradation revealed no change in concentration of 6CNA within 120 min of irradiation, while the photocatalytic degradation within 120 min, obeyed first-order kinetics. The observed disappearance rate constant was k = 0.011 ± 0.001 min⁻¹ and t_1/2 was 63.1 ± 5.5 min. Mineralisation rate was estimated through total organic carbon (TOC) and measurements revealed no carbon removal in case of photolysis after 120 min of exposure. However in photocatalytic experiments 46 ± 7% mineralisation was achieved within 120 min of irradiation. Nevertheless, the removal of total nitrogen (TN) was not observed across all experiments. Ion chromatographic analyses indicated transformation of chlorine atoms to chloride and increase of nitrate(V) ions only via photocatalytic experiments. Efficiency of selected advanced oxidation process (AOP) was investigated through toxicity assessment with Vibrio fischeri luminescent bacteria and revealed higher adverse effects of treated samples on bacteria following photocatalytic degradation in spite of the fact that higher mineralisation was achieved. New hydroxylated product generated in photocatalytic experiments with TiO₂, was confirmed with liquid chromatography-electro spray ionisation mass spectrometry (LC-ESI-MS/MS) analyses, gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (¹H NMR).     

Degradation of polychlorinated dibenzo-p-dioxins in aqueous solution by Fe(II)/H2O2/UV system

The photodegradation of polychlorinated dibenzo-p-dioxins (PCDDs), which include tetra- to octa-CDDs (TeCDD, PeCDD, HxCDD, HpCDD and OCDD), was carried out in the presence of Fe(II) and H2O2 mixed reagent. The degradation efficiency was strongly influenced by UV irradiation, and the initial concentrations of H2O2 and Fe(II). An initial TeCDD concentration of 10 ng l(-1) was completely degraded within 20 min under the optimum conditions. All PCDDs tested were successfully degraded by Fe(II)/H2O2/UV treatment and complete degradation of TeCDD, PeCDD and HxCDD was achieved within 120 min. PCDD photodegradation rates decreased with the number of chlorine atoms. The degradation process of TeCDD by this system seems to be initiated by an oxidative reaction (OH* radical attack) because less chlorinated DDs as intermediate products were not detected. From the Frontier electron density calculation, the first OH* radical attack positions on TeCDD were found to be four C atoms neighboring two O atoms. The decomposition of TeCDD gave 4,5-dichlorocatechol as an intermediate product. A TeCDD degradation scheme was proposed based on the identified intermediate and the values of Frontier electron density. Based on these results, Fe(II)/H2O2/UV system could be useful technology for the treatment of wastewater containing persistent pollutants such as dioxins and polychlorinated biphenyls.     

Photolysis of atrazine in aqueous solution: role of process variables and reactive oxygen species

Photochemical advanced oxidation processes have been considered for the treatment of water and wastewater containing the herbicide atrazine (ATZ), a possible human carcinogen and endocrine disruptor. In this study, we investigated the effects of the photon emission rate and initial concentration on ATZ photolysis at 254 nm, an issue not usually detailed in literature. Moreover, the role of reactive oxygen species (ROS) is discussed. Photon emission rates in the range 0.87?×?10¹⁸–3.6?×?10¹⁸ photons L^?1 s^?1 and [ATZ]₀?=?5 and 20 mg L^?1 were used. The results showed more than 65 % of ATZ removal after 30 min. ATZ photolysis followed apparent first-order kinetics with k values and percent removals decreasing with increasing herbicide initial concentration. A fivefold linear increase in specific degradation rate constants with photon emission rate was observed. Also, regardless the presence of persistent degradation products, toxicity was efficiently removed after 60-min exposure to UV radiation. Experiments confirmed a noticeable contribution of singlet oxygen and radical species to atrazine degradation during photolysis. These results may help understand the behavior of atrazine in different UV-driven photochemical degradation treatment processes.     

Photodegradation of the antimicrobial triclocarban in aqueous systems under ultraviolet radiation

This work aimed to investigate the effectiveness of ultraviolet (UV) radiation on the degradation of the antimicrobial triclocarban (TCC). We investigated the effects of several operational parameters, including solution pH, initial TCC concentration, photocatalyst TiO₂ loading, presence of natural organic matter, and most common anions in surface waters (e.g., bicarbonate, nitrate, and sulfate). The results showed that UV radiation was very effective for TCC photodegradation and that the photolysis followed pseudo-first-order kinetics. The TCC photolysis rate was pH dependent and favored at high pH. A higher TCC photolysis rate was observed by direct photolysis than TiO₂ photocatalysis. The presence of the inorganic ions bicarbonate, nitrate, and sulfate hindered TCC photolysis. Negative effects on TCC photolysis were also observed by the addition of humic acid due to competitive UV absorbance. The main degradation products of TCC were tentatively identified by gas chromatograph with mass spectrometer, and a possible degradation pathway of TCC was also proposed.