Direct and indirect photolysis of the phytoestrogens genistein and daidzein

Environmental fate and risk evolution of calcium channel blockers from chlorine-based disinfection to sunlit surface waters

Organic micropollutants present in disinfected wastewater and discharged to sunlit surface waters may be transformed by multiple processes, such as chlorination due to the presence of chlorine residuals, solar irradiation as well as solar-irradiated chlorine residues. This study reports, for the first time, the multi-scenario degradation kinetics, transformation products, and risk evolution of calcium channel blockers (CCBs), a class of emerging pharmaceutical contaminants with worldwide prevalence in natural waters and wastewater. It was found that the chlorination of the studied CCBs (amlodipine (AML) and verapamil (VER)) was dominated by the reaction of HOCl with their neutral species, with second-order rate constants of 6.15×104 M-1 s-1 (AML) and 7.93×103 M-1 s-1 (VER) at pH 5.0-11.0. Bromination is much faster than chlorination, with the measured kapp,HOBr values of 2.94×105 M-1 s-1 and 6.58×103 M-1 s-1 for AML and VER, respectively, at pH 7.0. Furthermore, both CCBs would undergo photolytic attenuations with hydroxyl and carbonate radicals as the dominant reactive species in water. Notably, free chlorine mainly contributed to their abatement during the solar/chlorine treatment. Additionally, the halogen addition on the aromatic ring was observed during chlorination and bromination of the two CCBs. Cyclization was observed under solar irradiation only, while the aromatic ring was opened in the solar/chlorine system. Some products generated by the three transformation processes exhibited non-negligible risks of high biodegradation recalcitrance and toxicity, potentially threatening the aquatic environment and public health. Overall, this study elucidated the environmental fate of typical CCBs under different transformation processes to better understand the resulting ecological risks in these environmental scenarios.

Photodegradation of anthelmintic drugs under natural sunlight and simulated irradiation: kinetics, mechanisms, transformation products, and toxicity

Albendazole (ALB) and bithionol (BIT) are two anthelmintic drugs (ADs) with high consumption from benzimidazole group and diphenylsulfide group, respectively. However, information on the transformation of the two anthelmintics under environmental condition is scare. Therefore, in the present study, we investigated the natural attenuation of the two ADs in the aquatic environment, including biodegradation, hydrolysis, and direct and indirect photodegradation. The direct photodegradation occupied a vast portion among other degradation pathways of the two ADs in natural water, with near-surface summer half-lives of 0.272-0.387 h and 0.110-0.520 h for ALB and BIT, respectively. Suspended particles in water were found to facilitate the photodegradation of the two ADs. Study on the indirect photodegradation demonstrated the positive roles of singlet oxygen (1O2) and excited triplet dissolved organic matter (3DOM*) in the photolysis of the two ADs, whereas the hydroxyl radical (•OH) affected little on the overall photodegradation procedures of ALB due to the scavenging effect of HCO3-. Dual effects of DO, DOM, HCO3-, NO3-, and NO2- on the photodegradation of ALB and BIT were perceived. Transformation intermediates (TIs) of the two ADs during photodegradation were analyzed by UHPLC-QTOF-MS. Six TIs of ALB were identified, including a broad-spectrum fungicide carbendazim and another common AD ricobendazole. Two TIs of BIT yielded from dechlorination were also detected. Probable transformation mechanism and predicted aquatic ecotoxicity based on the identified TIs were unveiled.

Direct and indirect photodegradation of bisphenol A in the presence of natural water components

The impacts and mechanisms of natural water constituents, such as humic acid (HA), nitrates, iron and chloride ions, to the photodegradation of bisphenol A (BPA) were investigated in aqueous media under UV light irradiation. Due to the contributions of ·OH, 1O2, O2- and BPA* to BPA photodegradation in pure water in 13.4, 7.7, 22.9 and 47.9%, respectively, BPA was attenuated through the reaction pathway of direct photodegradation more than self-sensitized photodegradation. About indirect photodegradation, BPA photolysis through inhibitory effect from HA was mainly by light screening effect and quenching effect was insignificant. NO- 3 and NO- 2 both showed inhibitory effect but due to different reactive oxidization species (ROS). The photodegradation of BPA was significantly enhanced by the addition of iron from the formation of ·OH and H2O2, due to iron-assisted indirect photolysis for the degradation process. A dual effect of chloride depending on the different concentration levels involved quenching and promotion effect on reactive photo-induced species (RPS). A simple linear model revealed that BPA photodegradation was significantly impacted by the interaction of the above factors. In natural water, the decreased photolytic rate of BPA was mainly attributed to triple-excited dissolved organic matter (3DOM*), indicating that indirect photolysis was the primary transformation pathway of BPA. The detected photolysis products, such as nitrate and chlorinated products, suggest that there might be potential ecological risk of BPA photodegradation.

Formation of halogenated chloroxylenols through chlorination and their photochemical activity

Trace organic contaminants usually go through multiple treatment units in a modern water treatment train. Structural modification triggered by pretreatment (e.g., prechlorination) may influence the further transformation and fate of contaminants in downstream units. However, knowledge on this aspect is still limited. In this contribution, we investigated the chlorination of chloroxylenol (PCMX), an antimicrobial agent extensively used during COVID-19 pandemic, and the photoreactivity of its halogenated derivatives. Results indicate that chlorination of PCMX mainly proceeded through electrophilic substitution to give chlorinated products, including Cl- and 2Cl-PCMX. The presence of bromide (Br-) resulted in brominated analogues. Owing to the bathochromic and "heavy atom" effects of halogen substituents, these products show increased light absorption and photoreactivity. Toxicity evaluation suggest that these halo-derivatives have higher persistence, bioaccumulation, and toxicity (PBT) than the parent PCMX. Results of this contribution advance our understanding of the transformation of PCMX during chlorination and the photochemical activity of its halogenated derivatives in subsequent UV disinfection process or sunlit surface waters.

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.

Photolysis of 3-Nitro-1,2,4-triazol-5-one: Mechanisms and Products

Insensitive munitions formulations that include 3-nitro-1,2,4-triazol-5-one (NTO) are replacing traditional explosive compounds. While these new formulations have superior safety characteristics, the compounds have greater environmental mobility, raising concern over potential contamination and cleanup of training and manufacturing facilities. Here, we examine the mechanisms and products of NTO photolysis in simulated sunlight to further inform NTO degradation in sunlit surface waters. We demonstrate that NTO produces singlet oxygen and that dissolved oxygen increases the NTO photolysis rate in deionized water. The rate of NTO photolysis is independent of concentration and decreases slightly in the presence of Suwannee River Natural Organic Matter. The apparent quantum yield of NTO generally decreases as pH increases, ranging from 2.0 × 10-5 at pH 12 to 1.3 × 10-3 at pH 2. Bimolecular reaction rate constants for NTO with singlet oxygen and hydroxyl radical were measured to be (1.95 ± 0.15) × 106 and (3.28 ± 0.23) × 1010 M-1 s-1, respectively. Major photolysis reaction products were ammonium, nitrite, and nitrate, with nitrite produced in nearly stoichiometric yield upon the reaction of NTO with singlet oxygen. Environmental half-lives are predicted to span from 1.1 to 5.7 days. Taken together, these data enhance our understanding of NTO photolysis under environmentally relevant conditions.

Dichlorine radicals (Cl2•-) promote the photodegradation of propranolol in estuarine and coastal waters

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 Cl₂^•- in the photolytic systems. Cl₂^•- 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 Cl₂^•- 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 Cl₂^•- and ³DOM* was proposed as the primary role for PRO degradation in the presence of Cl^- or DOM.

Carbon fibers as green and sustainable sorbent for the extraction of isoflavones from environmental waters

Isoflavones are a group of phytoestrogens of important environmental concern due to their endocrine disrupting effects. This article presents a rapid, green, and sustainable method for determining four isoflavones (daidzein, genistein, formononetin, and biochanin A) in environmental waters complying with current trends in Analytical Chemistry. The method consists of in-syringe dispersive solid-phase extraction (DSPE) as the extraction approach, using carbon fibers as extraction material. The synthesis of carbon fibers is simple and sustainable, since it only requires a natural product such as raw cotton as precursor, which is thermally treated (600 °C for 30 min) in an inert (Ar) atmosphere to convert it into carbon fibers. After extraction, the final eluate is analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The proposed methodology allows the determination of the four isoflavones in water samples at the ng L^-1 range, with limits of detection in the range from 17 to 25 ng L^-1, relative standard deviations (RSD) from 2.8 to 10.1%, and good batch-to-batch repeatability (RSD < 13%). The method was finally applied to six environmental water samples from different sources and two swimming pool waters, and concentrations of all analytes up to 490 ng L^-1 were found. The highest concentrations were found in those samples close to crop fields. Relative recovery values (80-121%) showed that the aqueous matrices considered in this work did not significantly affect the extraction process. This method overcomes the drawbacks of the previous works with the same purpose, such as consuming large volumes of organic solvents or prolonged extraction times. Moreover, this procedure would allow the extraction stage to be carried out in situ, since only the sorbent material (previously synthesized in the laboratory) and disposable syringes are required.

Elevated Temperatures Decrease the Photodegradation Rate of Pyrethroid Insecticides on Spinach Leaves: Implications for the Effect of Climate Warming

Climate warming is seldom considered in the transformation of pesticides on a plant leaf. This study investigated the effects of photodegradation temperature and spinach growth temperature from 15 to 21 °C on the photodegradation of bifenthrin, cypermethrin, fenvalerate, and deltamethrin on spinach leaves under xenon lamp irradiation in climate incubators. The photodegradation temperature had minor effects on pyrethroid photodegradation. Interestingly, the photodegradation rates decreased with increasing spinach growth temperature. For example, the photodegradation rate constant of bifenthrin on a spinach cultivated at 15 °C (3.73 (±0.59, 95% confidence level) × 10^-2 h^-1) was 1.9 times higher than that at 21 °C (1.96 (±0.17) × 10^-2 h^-1). Hydroxyl radicals (·OH) played a dominant role in the photodegradation. We speculate that ·OH originated from the degradation of hydroperoxide that was formed by oxidation of phenolic CH═CH, aliphatic CH₃ and aromatic C-O-C, and subsequent hydrogen abstraction. The contents of these functional groups decreased with increasing growth temperature, which resulted in lower photodegradation rates at higher growth temperatures. A possible photodegradation pathway including ester bond cleavage, decyanation, and phenyl group removal was proposed. This work provides new insight into the effects of climate warming on the generation of reactive oxygen species and the transformation of pesticides on a plant leaf.

Opposite pH-dependent roles of hydroxyl radicals in ozonation and UV photolysis of genistein

Phytoestrogens were frequently detected in municipal or industrial wastewater, and raised great attentions due to potential risks to humans or organisms. Until now, transformation mechanisms of phytoestrogens in advanced wastewater treatments were largely unknown. Here, pH influence mechanisms on transformations of phytoestrogens during two typical advanced wastewater treatments (ozonation and photolysis) were investigated, employing genistein (Gs) as a case. Removal efficiencies of Gs decreased significantly with increases of pH during ozonation, while photolytic rates increased by 44 or 200 times from pH 4.9 to 11.6 under irradiations without or with UVC. pH increases caused both dissociation of Gs and formation of hydroxyl radicals (OH) in ozonation or photolysis, however, led to opposite changes to degradation rates. This was because that OH played negatively as a competitor for O₃ in ozonation, but acted as an accelerating species inducing self-sensitized photooxidation of Gs under UV light. Ozonation and photolytic products of Gs were similar at pH 4.9 or 8.6, but were totally different at pH 11.6. Most of the transformation products maintained isoflavone structures, and might possess phytoestrogenic effects. This study provided a deep insight into the pH influencing mechanism on typical advanced wastewater treatment processes of phytoestrogens. MAIN FINDING OF THE WORK: Opposite pH-dependent degradation mechanisms caused by hydroxyl radicals (OH) were elucidated for ozonation and UV photolysis of phytoestrogens, taking genistein as a case.

Photodegradation of 2-(2-hydroxy-5-methylphenyl)benzotriazole (UV-P) in coastal seawaters: Important role of DOM

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.

A streamlined workflow to study direct photodegradation kinetic and transformation products for persistence assessment of a fragrance ingredient in natural waters

Photodegradation can be an important abiotic degradation process to consider for the fate and persistence assessment of chemical substances in the environment. In this work, using a fragrance ingredient (FI, (E)-4-(2,2,3,6-tetramethylcyclohexyl)but-3-en-2-one) as an example, we developed a streamlined workflow to investigate direct photodegradation of chemicals in the aquatic environment, including laboratory investigation of kinetics and transformation products and estimation of its aquatic environmental half-lives. Direct photodegradation was determined to be the dominant photodegradation process for FI with a quantum yield of 0.25, which was supported by photodegradation experiments conducted in natural sunlight. Accounting for light attenuation by dissolved organic matter in natural waters of different depths resulted in aquatic half-lives of <31 days even at polar latitudes. Photoisomerization was shown to be a major photodegradation pathway along with the formation and subsequent degradation of constitutional isomers and photooxidation products. These results contributed to FI being assessed as non-persistent in the environment.

Phytoestrogen coumestrol: Antioxidant capacity and its loading in albumin nanoparticles

Coumestrol is a polyphenol with promising therapeutic applications as phytoestrogen, antioxidant and potential cancer chemoprevention agent. The presence of two hydroxyl groups on its chemical structure, with orientation analogous to estradiol, is responsible of both, its antioxidant capacity and its estrogenic activity. However, several studies show that the interaction of polyphenols with food and plasma proteins reduces their antioxidant efficacy. We studied the interaction of coumestrol with bovine serum albumin protein (BSA) by fluorescence spectroscopy and circular dichroism techniques, and the effect of this interaction on its antioxidant activity as a hydroxyl radical scavenger. In addition, coumestrol antioxidant capacity profile using different assays (DPPH, ORAC-FL and ORAC-EPR) was studied. To explain its reactivity we used several methodologies, including DFT calculations, to define its antioxidant mechanism. Coumestrol antioxidant activity unveiled interesting antioxidant properties. BSA interaction with coumestrol reduces significantly photolytic degradation in several media thus preserving its antioxidant properties. Results suggest no significant changes in BSA structure and activity when interacting with coumestrol. Furthermore, this interaction is stronger than for other phytoestrogens such as daidzein and genistein. Considering our promising results, we reported for the first time the fabrication and characterization of coumestrol-loaded albumin nanoparticles. The resulting spherical and homogeneous nanoparticles showed a diameter close to 96 nm. The coumestrol incorporation efficiency in BSA NPs was 22.4%, which is equivalent to 3 molecules of coumestrol for every 10 molecules of BSA.

Photochemical degradation of halogenated estrogens under natural solar irradiance

Halogenated estrogens are thought to be moderately potent endocrine-disrupting compounds that are formed during chlorine-based wastewater disinfection processes and may represent a significant fraction of the total amount of estrogen delivered from wastewater treatment plants to receiving waters. Yet we lack key information about the photochemical degradation of halogenated estrogens, a process that has important implications for UV-based wastewater treatment and environmental fate modeling. To better understand halogenated estrogen degradation in aquatic environments, we studied the direct photolysis of 17β-estradiol (E2), 2-bromo-17β-estradiol (monoBrE2), 2,4-dibromo-17β-estradiol (diBrE2), and 2,4-dichloro-17β-estradiol (diClE2) as well as the indirect photolysis of diBrE2 under natural solar irradiance. We found that direct photolysis rate constants increased with halogenation as pKa values decreased and molar absorptivity spectra shifted toward higher wavelengths. Compared to E2, quantum yields were threefold larger for monoBrE2, but 15-32% smaller for the dihalogenated forms. The rate of diBrE2 (pKa ∼ 7.5) photolysis was strongly influenced by pH. At pH 7, diBrE2 degraded on minute time scales due to the large red-shifted molar absorptivity values and greater quantum yields of the phenolate form. Degradation rates were only slightly different in the presence of Suwannee River Humic Acid (5 mg L-1), and quenching experiments pointed to excited triplet state dissolved organic matter (3DOM*) as the dominant reactive intermediate responsible for the indirect photolysis of diBrE2. Overall, our data suggest that halogenated estrogens are particularly susceptible to photochemical degradation at environmentally relevant pH values.

Modeling photodegradation kinetics of organic micropollutants in water bodies: A case of the Yellow River estuary

Predicting photodegradation rate constants (k) of pollutants in water bodies is important for assessing their persistence and fate. This prediction used to be based on the k values determined under laboratory conditions that seldom consider underwater downward sunlight attenuation in the field. We studied a procedure to predict k taking the Yellow River estuary and two model chemicals (sulfamethoxazole and acyclovir) as a case. Models were developed for predicting underwater sunlight intensities from optically-active substances. Based on the predicted underwater sunlight intensities, hourly variation of k for the model compounds was predicted as a function of water depth, for a fresh water, an estuarine water and a seawater body in the estuary. Results show that photodegradation half-lives (t_1/2) of the two compounds will be underestimated by dozens of times if underwater downward sunlight attenuation and intensity variation are not considered. Outdoor validation experiments show the maximum deviation between the predicted and measured k values is a factor of 2. The developed models can be employed to predict k of environmental chemicals in coastal water bodies once they are locally calibrated.

Combination of experimental and in silico methods for the assessment of the phototransformation products of the antipsychotic drug/metabolite Mesoridazine

The lack of studies on the fate and effects of drug metabolites in the environment is of concern. As their parent compounds, metabolites enter the aquatic environment and are subject to biotic and abiotic process. In this regard, photolysis plays an important role. This study combined experimental and in silico quantitative structure-activity relationship (QSAR) methods to assess the fate and effects of Mesoridazine (MESO), a pharmacologically active human drug and metabolite of the antipsychotic agent Thioridazine, and its transformation products (TPs) formed through a Xenon lamp irradiation. After 256min, the photodegradation of MESO⋅besylate (50mgL^-1) achieved 90.4% and 6.9% of primary elimination and mineralization, respectively. The photon flux emitted by the lamp (200-600nm) was 169.55Jcm^-2. Sixteen TPs were detected by means of liquid chromatography-high resolution mass spectrometry (LC-HRMS), and the structures were proposed based on MSⁿ fragmentation patterns. The main transformation reactions were sulfoxidation, hydroxylation, dehydrogenation, and sulfoxide elimination. A back-transformation of MESO to Thioridazine was evidenced. Aerobic biodegradation tests (OECD 301 D and 301F) were applied to MESO and the mixture of TPs present after 256min of photolysis. Most of TPs were not biodegraded, demonstrating their tendency to persist in aquatic environments. The ecotoxicity towards Vibrio fischeri showed a decrease in toxicity during the photolysis process. The in silico QSAR tools QSARINS and US-EPA PBT profiler were applied for the screening of TPs with character of persistence, bioaccumulation, and toxicity (PBT). They have revealed the carbazole derivatives TP 355 and TP 337 as PBT/vPvB (very persistent and very bioaccumulative) compounds. In silico QSAR predictions for mutagenicity and genotoxicity provided by CASE Ultra and Leadscope® indicated positive alerts for mutagenicity on TP 355 and TP 337. Further studies regarding the carbazole derivative TPs should be considered to confirm their hazardous character.

Aquatic photochemistry of sulfamethazine: multivariate effects of main water constituents and mechanisms

The ubiquity of sulfonamides (SAs) in natural waters requires insight into their environmental fate for ecological risk assessment. Extensive studies focused on the effect of univariate water constituents on the photochemical fate of SAs, yet the multivariate effects of water constituents in environmentally relevant concentrations on SA photodegradation are poorly understood. Here, response surface methodology was employed to explore the integrative effects of main water constituents (dissolved organic matter (DOM), NO₃^-, HCO₃^-, Cu²⁺) on the photodegradation of a representative SA (sulfamethazine). Results showed that besides single factors, interaction of factors also significantly impacted the photodegradation. Radical scavenging experiments indicated that triplet-excited DOM (³DOM*) was responsible for the enhancing effect of DOM on the photodegradation. Additionally, DOM may also quench the ³DOM*-mediated oxidation intermediate of sulfamethazine causing the inhibiting effect of DOM-DOM interaction. We also found that HCO₃^- was oxidized by triplet-excited sulfamethazine producing CO₃˙^-, and the high reactivity of CO₃˙^- with sulfamethazine (second-order rate constant 2.2 × 10⁸ M^-1 s^-1) determined by laser flash photolysis revealed the enhancing photodegradation mechanism of HCO₃^-. This study is among the first attempts to probe the photodegradation of SAs considering the integrative effects of water constituents, which is important in accurate ecological risk assessment of organic pollutants in the aquatic environment.

Removal of emerging contaminants daidzein and coumestrol from water by nanozeolite beta modified with tetrasubstituted ammonium cation

In present research, a simplistic hydrothermal method was adopted for one-step synthesis of nanozeolite beta (NZB) having an average particle size of 18nm with Si/Al ratio 46.67, surface area 328m²/g, pore volume 0.287cm³/g, and pore diameter 3.5nm. The surface of the synthesized NZB was modified with 0.5wt% hexadecyltrimethylammonium bromide (HDTMA-Br) and used as an adsorbent for the removal of two phytoestrogens daidzein and coumestrol from aqueous solutions. The surface properties and surface charge of NZB considerably changed after modification with HDTMA-Br, which resulted in enhanced removal of daidzein (92-98% from 7 to 27%) and coumestrol (93.5-99% from 5 to 9.2%). The surface modified zeolite beta (SMZB) has similar physical characteristics as of NZB with an average particle size of 20nm, surface area 299.8m²/g, pore volume 0.263cm³/g, and pore diameter 3.51nm. The influence of various parameters was examined by conducting a sequence of batch experiments. The adsorption equilibrium was achieved in less than 3h with saturation capacity of 40.74mg/g and 42.87mg/g for daidzein and coumestrol, respectively. The Freundlich isotherm and fractional order kinetic models represented the adsorption data very closely. The thermodynamic parameters indicated that sorption of both phytoestrogens onto SMZB is spontaneous and exothermic.

Photolysis of sulfamethazine using UV irradiation in an aqueous medium

Although many studies have been focused on the photochemistry of antibiotics, the roles of reactive species in photolysis and the effects of dissolved substances on antibiotic photochemical behavior have been poorly examined. The photolytic behaviors of sulfamethazine (SMN) in pure water were investigated via adding different scavengers to quench the active species. Results showed that decomposition of the triplet-excited state of SMN (³SMN*) by direct photolysis was the main path of SMN photolysis in water. Moreover, self-sensitized SMN cannot be ignored during SMN photodegradation. The main photoproducts of SMN were identified by LC-MS/MS, which indicated that SMN could not be mineralized although the photolysis under UV was effective. The effects of Cl⁻, NO₃⁻, and fulvic acid (FA) (common substances in natural water) on SMN photolytic behaviors were also studied. The triplet-induced halogenation of SMN increases the ionic strength and reduces the ground state SMN; these are the primary causes of promotion of SMN photolysis by Cl⁻. More ˙OH produced in the presence of NO₃⁻ could promote SMN photolysis. Competitive absorption of photons of FA with SMN and ROS scavenged by FA were the main reasons for the inhibition of SMN photolysis. The research findings are helpful for further studies on the environmental risks of ACs in natural waters and promoting the development of AC pollution treatment technology.

The role of reactive species in SMN photolysis and the effects of dissolved substances on SMN photochemical behavior.

Inhibitory effects of natural organic matter on methyltriclosan photolysis kinetics

This study evaluated the effects and related mechanisms of natural organic matter (NOM) on the photolysis of methyltriclosan (MTCS), a metabolite of triclosan. Addition of two representative NOM isolates, Pony Lake fulvic acid (PLFA-microbial origin) and Suwannee River fulvic acid (SRFA-terrestrial origin), significantly inhibited the direct photolytic rate of MTCS by ∼70%. The MTCS photolytic rate in the presence of PLFA was greater than for SRFA. NOM not only suppressed photolysis by light-shielding, but also produced ROS to oxidatively degrade MTCS and/or triplet NOM (³NOM*) to sensitize degradation. The dual effects of light-screening and photo-sensitization led to an overall decrease in photolysis of MTCS with a positive concentration-dependence. Upon addition of NOM, EPR documented the occurrence of ¹O₂ and ˙OH in the photolytic process, and the bimolecular k value for the reaction of ¹O₂ with MTCS was 1.86 × 10⁶ M⁻¹ s⁻¹. ROS-quenching experiments indicated that the contribution of ˙OH (19.1–29.5%) to indirect photolysis of MTCS was lower than for ¹O₂ (38.3–58.7%). Experiments with D₂O further demonstrated that ¹O₂ participated in MTCS photodegradation. Moreover, the addition of sorbic acid and O₂ gas to the reaction confirmed the participation of ³NOM* as a key reactant in the photochemical transformation of MTCS. This is the first comprehensive analysis of NOM effects on the indirect photolysis of MTCS, which provides new insights for understanding the environmental fate of MTCS in natural environments.

We demonstrate that PLFA and SRFA inhibit the MTCS photolysis by synergistic effects of light-shielding and photo-sensitization.

Photophysical and photochemical insights into the photodegradation of sulfapyridine in water: A joint experimental and theoretical study

For organic pollutants, photodegradation, as a major abiotic elimination process and of great importance to the environmental fate and risk, involves rather complicated physical and chemical processes of excited molecules. Herein, we systematically studied the photophysical and photochemical processes of a widely used antibiotic, namely sulfapyridine. By means of density functional theory (DFT) computations, we examined the rate constants and the competition of both photophysical and photochemical processes, elucidated the photochemical reaction mechanism, calculated reaction quantum yield (Φ) based on both photophysical and photochemical processes, and subsequently estimated the photodegradation rate constant. We further conducted photolysis experiments to measure the photodegradation rate constant of sulfapyridine. Our computations showed that sulfapyridine at the lowest excited singlet state (S₁) mainly undergoes internal conversion to its ground state, and is difficult to transfer to the lowest excited triplet states (T₁) via intersystem crossing (ISC) and emit fluorescence. In T₁ state, compared with phosphorescence emission and ISC, chemical reaction is much easier to initiate. Encouragingly, the theoretically predicted photodegradation rate constant is close to the experimentally observed value, indicating that quantum chemistry computation is powerful enough to study photodegradation involving ultra-fast photophysical and photochemical processes.

Activation of peroxymonosulfate by phenols: Important role of quinone intermediates and involvement of singlet oxygen

In this study, the kinetics of reactions of peroxymonosulfate (PMS) with ten model phenols (including phenol, methylphenols, methoxyphenols, and dihydroxybenzenes) were examined. The oxidation kinetics of these phenols by PMS except for catechol and resorcinol showed autocatalysis in alkaline conditions (pH 8.5 and 10), due to the contribution of singlet oxygen (¹O₂) produced from PMS activation by quinone intermediates formed from their phenolic parents. The oxidation rates of ortho- and meta-substituted methylphenols and methoxyphenols by PMS were much higher than their para-substituted counterparts under similar conditions. This was attributed to the relatively low yields of quinone intermediates from para-substituted phenols. SMX could be efficiently degraded by PMS in the presence of phenols which showed great autocatalysis when they individually reacted with PMS, and the addition of methanol in excess had negligible influence suggesting that ¹O₂ rather than hydroxyl radical and sulfate radical played an important role. Transformation of SMX by ¹O₂ underwent three pathways including hydroxylation of aniline ring, oxidation of aromatic amine group to generate nitro-SMX, and oxidative coupling to generate azo-SMX and hydroxylated azo-SMX. These results obtained in this work improve the understanding of in situ chemical oxidation using PMS for remediation of subsurface, where phenolic and quinonoid moieties are ubiquitous.

Reactivity of Triplet Excited States of Dissolved Natural Organic Matter in Stormflow from Mixed-Use Watersheds

Dissolved organic matter (DOM) quantity and composition control the rate of formation (R_f,T) of triplet excited states of dissolved natural organic matter (³DOM*) and the efficiency of ³DOM* formation (the apparent quantum yield, AQY_T). Here, the reactivity of ³DOM* in stormflow samples collected from watersheds with variable land covers is examined. Stormflow DOM reflects variability in DOM quantity and composition as a function of land cover and may be important in controlling the fate of cotransported pollutants. R_f,T and AQY_T were measured using 2,4,6-trimethylphenol in stormflow samples under simulated sunlight. The DOM source and composition was characterized using absorbance and fluorescence spectroscopies and high-resolution mass spectrometry. R_f,T and the total rate of light absorption by the water samples (R_a) increased with the dissolved organic carbon (DOC) concentration. AQY_T was independent of DOC concentration, but varied with DOM source: developed land cover (4-6%) ≈ open water > vegetated land cover (3%). AQY_T was positively related to an index for microbial/algal DOM content and negatively related to DOM molecular weight, DOM aromaticity, and the content of polyphenols. This work demonstrates that TMP is an effective probe for the determination of R_f,T and AQY_T in whole water samples after accounting for the inhibition of TMP photodegradation by DOM.

Indirect photodegradation of the lampricides TFM and niclosamide

3-Trifluromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide) are lampricides used in tributaries of the Great Lakes to kill the invasive parasitic sea lamprey (Petromyzon marinus). Although the lampricides have been applied since the late 1950s, their photochemical behavior in natural environments is still not well understood. This study examines the indirect photodegradation of these two compounds and the resulting yields of organic and inorganic photoproducts in water samples collected from five tributaries of Lake Michigan. The tributaries were selected to span the length of Lake Michigan and its natural carbonate geologic gradient. In the presence of dissolved organic matter (DOM), the niclosamide photodegradation rate triples, while the rate of TFM photodegradation is unchanged. Additionally, the yield of lampricide organic products is influenced by DOM because many of the organic photoproducts themselves are prone to DOM-mediated indirect photodegradation. The indirect photodegradation of niclosamide is primarily mediated by reaction with singlet oxygen, which accounts for more than 50% of the increased photodegradation rate. Additionally, hydroxyl radicals and carbonate radicals (CO₃^-˙) influence niclosamide indirect photolysis, and their contribution is dependent on the specific river water chemistry. For example, CO₃^-˙ contribution to niclosamide photodegradation, while small, is greater in southern tributaries where there is higher carbonate alkalinity.

Photo-induced oxidative damage to dissolved free amino acids by the photosensitizer polycyclic musk tonalide: Transformation kinetics and mechanisms

Residue from the polycyclic musks (PCMs) in household and personal care products may harm human beings through skin exposure. To understand the health effects of PCMs when exposed to sunlight at molecular level, both experimental and computational methods were employed to investigate the photosensitized oxidation performance of 19 natural amino acids, the most basic unit of life. Results showed that a typical PCM, tonalide, acts as a photosensitizer to significantly increase photo-induced oxidative damage to amino acids. Both common and exceptional transformation pathways occurred during the photosensitization damage of amino acids. Experimental tests further identified the different mechanisms involved. The common transformation pathway occurred through the electron transfer from α amino-group of amino acids, accompanying with the formation of O₂^•-. This pathway was controlled by the electronic density of N atom in α amino-group. The exceptional transformation pathway was identified only for five amino acids, mainly due to the reactions with reactive oxygen species, e.g. ¹O₂ and excited triplet state molecules. Additionally, tonalide photo-induced transformation products could further accelerate the photosensitization of all amino acids with the common pathway. This study may support the protection of human health, and suggests the possible need to further restrict polycyclic musks use.

QSARs for phenols and phenolates: oxidation potential as a predictor of reaction rate constants with photochemically produced oxidants

Quantitative structure-activity relationships (QSARs) for prediction of the reaction rate constants of phenols and phenolates with three photochemically produced oxidants, singlet oxygen, carbonate radical, and triplet excited state sensitizers/organic matter, are developed. The predictive variable is the one-electron oxidation potential (E₁), which is calculated for each species using density functional theory. The reaction rate constants are obtained from the literature, and for singlet oxygen, are augmented with new experimental data. Calculated E₁ values have a mean unsigned error compared to literature values of 0.04-0.06 V. For singlet oxygen, a single linear QSAR that includes both phenols and phenolates is developed that predicts experimental rate constants, on average, to within a factor of three. Predictions for only 6 out of 87 compounds are off by more than a factor of 10. A more limited data set for carbonate radical reactions with phenols and phenolates also gives a single linear QSAR with prediction of rate constant being accurate to within a factor of three. The data for the reactions of phenols with triplet state sensitizers demonstrate that two sensitizers, 2-acetonaphthone and methylene blue, most closely predict the reactivity trend of triplet excited state organic matter with phenols. Using sensitizers with stronger reduction potentials could lead to overestimation of rate constants and thus underestimation of phenolic pollutant persistence.

Studies on the formation of formaldehyde during 2-ethylhexyl 4-(dimethylamino)benzoate demethylation in the presence of reactive oxygen and chlorine species

In order to protect the skin from UV radiation, personal care products (PCPS) often contain chemical UV-filters. These compounds can enter the environment causing serious consequences on the water ecosystems. The aim of this study was to examine, the effect of different factors, such as UV light, the presence of NaOCl and H₂O₂ on the formaldehyde formation during popular UV filter, 2-ethylhexyl 4-(dimethylamino)benzoate (ODPABA) demethylation. The concentration of formaldehyde was determined by VIS spectrophotometry after derivatization. The reaction mixtures were qualitatively analyzed using GC/MS chromatography. The highest concentration of formaldehyde was observed in the case of ODPABA/H₂O₂/UV reaction mixture. In order to describe two types of demethylation mechanisms, namely, radical and ionic, the experimental results were enriched with Fukui function analysis and thermodynamic calculations. In the case of non-irradiated system containing ODPABA and NaOCl, demethylation reaction probably proceeds via ionic mechanism. As it was established, amino nitrogen atom in the ODPABA molecule is the most susceptible site for the HOCl electrophilic attack, which is the first step of ionic demethylation mechanism. In the case of irradiated mixtures, the reaction is probably radical in nature. The results of thermodynamic calculations showed that abstraction of the hydrogen from N(CH₃)₂ group is more probable than from 2-ethylhexyl moiety, which indicates higher susceptibility of N(CH₃)₂ to the oxidation.

Probe Compounds to Assess the Photochemical Activity of Dissolved Organic Matter

The photochemical properties of dissolved organic matter (DOM) have been of interest to scientists and engineers since the 1970s. Upon light absorption, chromophoric DOM (CDOM) can sensitize the formation of different short-lived reactive intermediates (RIs), including hydroxyl radical (^•OH), singlet oxygen (¹O₂) and superoxide radical anion (O₂^•-). In addition, a fraction of the excited singlet states in CDOM decays into excited triplet states (³CDOM*), which are also important photochemical transients in environmental systems. These RIs have a significant impact on different processes in sunlit waters, including degradation of organic contaminants and the inactivation of pathogens. Due to their transient nature and low steady-state concentrations, the use of common analytical techniques for the direct measurement of these species is impractical. Therefore, specific probe compounds (PCs) are used. PCs include furfuryl alcohol for ¹O₂, and terephthalic acid for ^•OH. In this publication, we present a critical review of the use of PCs for the assessment of the formation of photochemically generated RIs. We first introduce the concept of a PC, including the kinetic treatment and necessary assumptions needed to conduct a specific measurement. Afterward, we present short overviews of the most studied RIs and review relevant issues regarding the use of specific PCs for their measurement. We finalize by offering recommendations regarding the use of PCs in environmental photochemistry.

Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties

Excited triplet states of chromophoric dissolved organic matter (³CDOM*) play a major role among the reactive intermediates produced upon absorption of sunlight by surface waters. After more than two decades of research on the aquatic photochemistry of ³CDOM*, the need for improving the knowledge about the photophysical and photochemical properties of these elusive reactive species remains considerable. This critical review examines the efforts to date to characterize ³CDOM*. Information on ³CDOM* relies mainly on the use of probe compounds because of the difficulties associated with directly observing ³CDOM* using transient spectroscopic methods. Singlet molecular oxygen (¹O₂), which is a product of the reaction between ³CDOM* and dissolved oxygen, is probably the simplest indicator that can be used to estimate steady-state concentrations of ³CDOM*. There are two major modes of reaction of ³CDOM* with substrates, namely triplet energy transfer or oxidation (via electron transfer, proton-coupled electron transfer or related mechanisms). Organic molecules, including several environmental contaminants, that are susceptible to degradation by these two different reaction modes are reviewed. It is proposed that through the use of appropriate sets of probe compounds and model photosensitizers an improved estimation of the distribution of triplet energies and one-electron reduction potentials of ³CDOM* can be achieved.

Probing the Photosensitizing and Inhibitory Effects of Dissolved Organic Matter by Using N,N-dimethyl-4-cyanoaniline (DMABN)

Dissolved organic matter (DOM) can act as a photosensitizer and an inhibitor in the phototransformation of several nitrogen-containing organic contaminants in surface waters. The present study was performed to select a probe molecule that is suitable to measure these antagonistic properties of DOM. Out of nine studied nitrogen-containing aromatic compounds, 4-cyanoaniline, N,N-dimethyl-4-cyanoaniline (DMABN), sotalol (a β-blocker) and sulfadiazine (a sulfonamide antibiotic) exhibited a marked photosensitized transformation that could be substantially inhibited by addition of phenol as a model antioxidant. The photosensitized transformation of DMABN, the selected probe compound, was characterized in detail under UV-A and visible irradiation (λ > 320 nm) to avoid direct phototransformation. Low reactivity of DMABN with singlet oxygen was found (second-order rate constant <2 × 10⁷ M^-1 s^-1). Typically at least 85% of the reactivity of DMABN could be inhibited by DOM or the model antioxidant phenol. The photosensitized transformation of DMABN mainly proceeded (>72%) through demethylation yielding N-methyl-4-cyanoaniline and formaldehyde as primary products. In solutions of standard DOM extracts and their mixtures the phototransformation rate constant of DMABN was shown to vary nonlinearly with the DOM concentration. Model equations describing the dependence of such rate constants on DOM and model antioxidant concentrations were successfully used to fit experimental data.

Aqueous photochemical degradation of BDE-153 in solutions with natural dissolved organic matter

The compound 2,2',4,4',5,5'-hexabrominated diphenyl ether (BDE-153) is an intermediate photolytic product in the degradation of highly brominated diphenyl ethers to lower brominated forms. Herein, we report the effects of two natural organic matter (NOM) sources, Suwannee River fulvic acid (SRFA) and Pony Lake fulvic acid (PLFA), on BDE-153 photolysis in water. The rate constant (k) and half-life of BDE-153 was 2.26 × 10(-2) min(-1) and 30.72 min under UV-Vis irradiation (direct photolysis at λ > 290 nm). The k value for BDE-153 decreased markedly in the presence of NOM with a larger decrease in the presence of PLFA than SRFA. Electron spin resonance (ESR) demonstrated generation of free radicals in the photolytic process that mainly involved (1)O2 and OH. The biomolecular k values for reaction of (1)O2 and OH with BDE-153 were 3.65 × 10(6) and 7.70 × 10(8) M(-1) s(-1), respectively. The contribution of OH (28.7-31.0%) to the indirect photolysis of BDE-153 was higher than for (1)O2 (12.9-14.9%). The photolytic rate of BDE-153 in oxygen-rich (aerated) solution was much slower than in oxygen-poor (nitrogen-sparged) conditions, demonstrating that (3)NOM* is a more effective reagent for degradation of BDE-153 than (1)O2. Addition of sorbic acid (a (3)NOM* quencher) significantly reduced the photolytic rate of BDE-153 confirming the important role of (3)NOM* in indirect photolysis. In the presence of NOM, BDE-153 indirect photolysis was facilitated mainly by reaction with (3)NOM* and OH. To the best of our knowledge, this is the first comprehensive investigation of indirect photolysis of BDE-153 in water containing NOM.

Sources and transport of contaminants of emerging concern: A two-year study of occurrence and spatiotemporal variation in a mixed land use watershed

The occurrence and spatiotemporal variation of 26 contaminants of emerging concern (CECs) were evaluated in 68 water samples in 2011-2012 in the Zumbro River watershed, Minnesota, U.S.A. Samples were collected across a range of seasonal/hydrological conditions from four stream sites that varied in associated land use and presence of an upstream wastewater treatment plant (WWTP). Selected CECs included human/veterinary pharmaceuticals, personal care products, pesticides, phytoestrogens, and commercial/industrial compounds. Detection frequencies and concentrations varied, with atrazine, metolachlor, acetaminophen, caffeine, DEET, and trimethoprim detected in more than 70% of samples, acetochlor, mecoprop, carbamazepine, and daidzein detected in 30%-50% of samples, and 4-nonylphenol, cotinine, sulfamethoxazole, erythromycin, tylosin, and carbaryl detected in 10%-30% of samples. The remaining target CECs were not detected in water samples. Three land use-associated trends were observed for the detected CECs. Carbamazepine, 4-nonylphenol, erythromycin, sulfamethoxazole, tylosin, and carbaryl profiles were WWTP-dominated, as demonstrated by more consistent loading and significantly greater concentrations downstream of the WWTP and during low-flow seasons. In contrast, acetaminophen, trimethoprim, DEET, caffeine, cotinine, and mecoprop patterns demonstrated both seasonally-variable non-WWTP-associated and continual WWTP-associated influences. Surface water studies of CECs often target areas near WWTPs. This study suggests that several CECs often characterized as effluent-associated have additional important sources such as septic systems or land-applied biosolids. Finally, agricultural herbicide (atrazine, acetochlor, and metolachlor) profiles were strongly influenced by agricultural land use and seasonal application-runoff, evident by significantly greater concentrations and loadings at upstream sites and in early summer when application and precipitation rates are greatest. Our results indicate that CEC monitoring studies should consider a range of land uses, seasonality, and transport pathways in relation to concentrations and loadings. This knowledge can augment CEC monitoring programs to result in more accurate source, occurrence, and ecological risk characterizations, more precisely targeted mitigation initiatives, and ultimately, enhanced environmental decision-making.

Organic Contaminant Abatement in Reclaimed Water by UV/H2O2 and a Combined Process Consisting of O3/H2O2 Followed by UV/H2O2: Prediction of Abatement Efficiency, Energy Consumption, and Byproduct Formation

UV/H2O2 processes can be applied to improve the quality of effluents from municipal wastewater treatment plants by attenuating trace organic contaminants (micropollutants). This study presents a kinetic model based on UV photolysis parameters, including UV absorption rate and quantum yield, and hydroxyl radical (·OH) oxidation parameters, including second-order rate constants for ·OH reactions and steady-state ·OH concentrations, that can be used to predict micropollutant abatement in wastewater. The UV/H2O2 kinetic model successfully predicted the abatement efficiencies of 16 target micropollutants in bench-scale UV and UV/H2O2 experiments in 10 secondary wastewater effluents. The model was then used to calculate the electric energies required to achieve specific levels of micropollutant abatement in several advanced wastewater treatment scenarios using various combinations of ozone, UV, and H2O2. UV/H2O2 is more energy-intensive than ozonation for abatement of most micropollutants. Nevertheless, UV/H2O2 is not limited by the formation of N-nitrosodimethylamine (NDMA) and bromate whereas ozonation may produce significant concentrations of these oxidation byproducts, as observed in some of the tested wastewater effluents. The combined process of O3/H2O2 followed by UV/H2O2, which may be warranted in some potable reuse applications, can achieve superior micropollutant abatement with reduced energy consumption compared to UV/H2O2 and reduced oxidation byproduct formation (i.e., NDMA and/or bromate) compared to conventional ozonation.

Pollution by oestrogenic endocrine disruptors and β-sitosterol in a south-western European river (Mira, Portugal)

The Mira River is a Portuguese water body widely known for its wilderness and is advertised as one of the less polluted European rivers. On this presumption, the levels of endocrine-disrupting compounds (EDCs) in Mira waters were never measured. However, because environmentalists have claimed that the Mira could be moderately polluted, a range of 17 EDCs were measured not only at the estuary but also along the river. The targeted EDCs included natural and pharmaceutical oestrogens (17β-oestradiol, oestrone and 17α-ethynylestradiol), industrial/household pollutants (octylphenols, nonylphenols and their monoethoxylates and diethoxylates and bisphenol A), phytoestrogens (formononetin, biochanin A, daidzein, genistein) and the phytosterol sitosterol (SITO). For this propose, waters from six sampling sites were taken every 2 months, over a 1-year period (2011), and analysed by gas chromatography-mass spectrometry. Unexpectedly high levels of oestrogens and of industrial/household pollutants were measured at all sampling sites, including those located inside natural protected areas. Indeed, the annual average sum of EDCs was ≈57 ng/L for oestrogens and ≈1.3 μg/L for industrial/household chemicals. In contrast, the global average levels of phytoestrogens (≈140 ng/L) and of SITO (≈295 ng/L) were lower than those reported worldwide. The EDC concentrations were normalised for ethynylestradiol equivalents (EE2eq). In view of these, the oestrogenic load of the Mira River attained ≈47 ng/L EE2eq. In addition, phosphates were above legal limits at both spring and summer (>1 mg/L). Overall, data show EDCs at toxicant relevant levels in the Mira and stress the need to monitor rivers that are allegedly less polluted.

Indirect photochemical transformations of acyclovir and penciclovir in aquatic environments increase ecological risk

Acyclovir and penciclovir, 2 antiviral drugs, are increasingly detected in aquatic environments. The present study explores the natural photochemical transformation mechanisms and fate of these drugs, examining direct and indirect photochemical transformation under simulated sunlight irradiation. The 2 antiviral drugs are photostable under certain conditions but significantly degrade in the presence of chromophoric dissolved organic matter (DOM). The degradation rate associated with the drugs' indirect photochemical transformation scaled with chromophoric DOM concentration. Quenchers and sensitizers were used to identify indirect photochemical transformation mechanism. Results suggested that both pharmaceuticals could be transformed by reacting with (1)O2, (•)OH, and excited chromophoric DOM. The (1)O2 played an important role in indirect photochemical transformation. Furthermore, the reaction kinetics between their substructural molecules, guanine, isocytosine, and imidazole, with different reactive oxygen species were evaluated to determine which substrate functionalities were most susceptible to singlet oxygenation. Imidazole was identified as the reaction site for (1)O2, and preliminary (1)O2 oxidation mechanisms were further evaluated based on liquid chromatographic-tandem mass spectrometric results. Finally, aquatic ecotoxicity assessment of phototransformed solutions revealed that the degradation of acyclovir and penciclovir may not ultimately diminish environmental risk because of either formation of more toxic intermediates than parent pharmaceuticals or some synergistic effects existing between the intermediates.

The Role of Singlet Oxygen in Surface Water Photochemistry

Singlet oxygen, (1O2, 1Δg), is a selective oxidant produced in sunlit surface waters. It is an electrophile produced from the quenching of excited state triplet natural organic matter (3NOM) by dissolved oxygen and it reacts with electron-rich alkenes, sulfides, and phenols. The concentration of 1O2 is high near the NOM molecules that sensitize its production and significantly decreases moving away from the NOM source. This chapter discusses the formation, quenching, reactivity, and detection of 1O2 and includes examples of surface water contaminants that react with 1O2.

Photodegradation mechanism of sulfonamides with excited triplet state dissolved organic matter: a case of sulfadiazine with 4-carboxybenzophenone as a proxy

Excited triplet states of dissolved organic matter ((3)DOM*) are important players for photodegradation sulfonamide antibiotics (SAs) in sunlit natural waters. However, the triplet-mediated reaction mechanism was poorly understood. In this study, we investigated the reaction adopting sulfadiazine as a representative SA and 4-carboxybenzophenone (CBBP)as a proxy of DOM. Results showed that the excited triplet state of CBBP ((3)CBBP*) is responsible for the photodegradation of sulfadiazine. The reaction of (3)CBBP* with substructure model compounds verified there are two reaction sites (amino-or sulfonyl-N atoms) of sulfadiazine. Density functional theory calculations were performed, which unveiled that electrons transfer from the N reaction sites to the carbonyl oxygen atom of (3)CBBP* moiety, followed by proton transfers, leading to the formation of sulfadiazine radicals. Laser flash photolysis experiments were performed to confirm the mechanism. Thus, this study identified that the photodegradation mechanism of SAs initiated by (3)DOM*, which is important for understanding the photochemical fate, predicting the photoproducts, and assessing the ecological risks of SAs in the aquatic environment.

Sediment-water distribution of contaminants of emerging concern in a mixed use watershed

This study evaluated the occurrence and distribution of 15 contaminants of emerging concern (CECs) in stream water and sediments in the Zumbro River watershed in Minnesota and compared these with sub-watershed land uses. Sixty pairs of sediment and water samples were collected across all seasons from four stream sites for over two years and analyzed for selected personal care products, pesticides, human and veterinary medications, and phytoestrogens. Spatial and temporal analyses indicate that pharmaceuticals and personal care products (urban/residential CECs) are significantly elevated in water and/or sediment at sites with greater population density (>100 people/km(2)) and percentage of developed land use (>8% of subwatershed area) than those with less population density and land area under development. Significant spatial variations of agricultural pesticides in water and sediment were detectable, even though all sites had a high percentage of agricultural land use. Seasonality in CEC concentration was observed in water but not in sediment, although sediment concentrations of three CECs did vary between years. Average measured non-equilibrium distribution coefficients exceeded equilibrium hydrophobic partitioning-based predictions for 5 of the 7 detected CECs by at least an order of magnitude. Agreement of measured and predicted distribution coefficients improved with increasing hydrophobicity and in-stream persistence. The more polar and degradable CECs showed greater variability in measured distributions across different sampling events. Our results confirm that CECs are present in urban and agricultural stream sediments, including those CECs that would typically be thought of as non-sorptive based on their log Kow values. These results and the observed patterns of sediment and water distributions augment existing information to improve prediction of CEC fate and transport, leading to more accurate assessments of exposure and risk to surface water ecosystems.

Sorption of isoflavones to river sediment and model sorbents and outcomes for larval fish exposed to contaminated sediment

Isoflavones are compounds whose presence in the aquatic environment is increasingly recognized and may be of concern due to their potential to act as endocrine disruptors. Sorption to particles may be a relevant removal mechanism for isoflavones. This work investigated the influence of pH, ionic strength, and sediment composition on sorption of genistein and daidzein, two key isoflavones, using sorption isotherms and edges. The effect of sorbed isoflavones on the survival, growth, and predator avoidance performance of larval fathead minnows (Pimephales promelas) was assessed. Sorption to goethite and kaolinite was pH-dependent, with a maximum near pH 7 for both compounds. Sorption to montmorillonite was ionic-strength dependent but largely pH-independent. Overall, sorption to sediments is likely to sequester less than 5% of isoflavones in a discharge. No statistically significant effects were observed for larvae exposed to sorbed isoflavones, suggesting that sorption to sediments reduces exposure to isoflavones.

Investigation of humic substance photosensitized reactions via carbon and hydrogen isotope fractionation

Humic substances (HS) acting as photosensitizers can generate a variety of reactive species, such as OH radicals and excited triplet states ((3)HS*), promoting the degradation of organic compounds. Here, we apply compound-specific stable isotope analysis (CSIA) to characterize photosensitized mechanisms employing fuel oxygenates, such as methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), as probes. In oxygenated aqueous media, Λ (Δδ(2)H/Δδ(13)C) values of 23 ± 3 and 21 ± 3 for ETBE obtained by photosensitization by Pahokee Peat Humic Acid (PPHA) and Suwannee River Fulvic Acid (SRFA), respectively, were in the range typical for H-abstraction by OH radicals generated by photolysis of H2O2 (Λ = 24 ± 2). However, (3)HS* may become a predominant reactive species upon the quenching of OH radicals (Λ = 14 ± 1), and this process can also play a key role in the degradation of ETBE by PPHA photosensitization in deoxygenated media (Λ = 11 ± 1). This is in agreement with a model photosensitization by rose bengal (RB(2-)) in deoxygenated aqueous solutions resulting in one-electron oxidation of ETBE (Λ = 14 ± 1). Our results demonstrate that the use of CSIA could open new avenues for the assessment of photosensitization pathways.

Flavonoids protecting food and beverages against light

Flavonoids, which are ubiquitously present in the plant kingdom, preserve food and beverages at the parts per million level with minor perturbation of sensory impressions. Additionally, they are safe and possibly contribute positive health effects. Flavonoids should be further exploited for the protection of food and beverages against light-induced quality deterioration through: (1) direct absorption of photons as inner filters protecting sensitive food components; (2) deactivation of (triplet-)excited states of sensitisers like chlorophyll and riboflavin; (3) quenching of singlet oxygen from type II photosensitisation; and (iv) scavenging of radicals formed as reaction intermediates in type I photosensitisation. For absorption of light, combinations of flavonoids, as found in natural co-pigmentation, facilitate dissipation of photon energy to heat thus averting photodegradation. For protection against singlet oxygen and triplet sensitisers, chemical quenching gradually decreases efficiency hence the pathway to physical quenching should be optimised through product formulation. The feasibility of these protection strategies is further supported by kinetic data that are becoming available, allowing for calculation of threshold levels of flavonoids to prevent beer and dairy products from going off. On the other hand, increasing understanding of the interplay between light and matrix physicochemistry, for example the effect of aprotic microenvironments on phototautomerisation of compounds like quercetin, opens up for engineering better light-to-heat converting channels in processed food to eventually prevent quality loss.

Transformation of acesulfame in water under natural sunlight: joint effect of photolysis and biodegradation

The transformation of acesulfame in water under environmentally relevant conditions, including direct and indirect photolysis, biodegradation, and hydrolysis, was systematically evaluated. Under natural sunlight, both direct and indirect photolysis of acesulfame were negligible in sterilized systems at neutral or alkaline pH, whereas direct photolysis occurred at pH of 4 with a rate constant of 0.0355 d(-1) in deionized water. No significant reduction in acesulfame contents was found in the dark controls or in the incubation experiments, indicating acesulfame was resistant to hydrolysis and biodegradation. In unsterilized systems, photolysis was substantially enhanced, implying that there was a joint effect of photolysis and biodegradation or that the sterilization process had the secondary effect of inactivating some photosensitizers. The near-surface summer half-life of acesulfame in the water from the Haihe River was 9 d. Specific experiments revealed the involvement of (1)O2/(3)DOM* in acesulfame photolysis, whereas OH exhibited only a slight contribution in the presence of DOM or bicarbonate. As indicated by the total organic carbon data, no significant mineralization occurred in both sterilized and unsterilized systems after acesulfame was irradiated under simulated sunlight for 7 d, suggesting the generation of persistent intermediates. Finally, major degradation intermediates were analyzed, and the degradation pathways of acesulfame under environmentally relevant conditions were proposed for the first time.

Photodegradation of 2,4-D induced by NO₂(-) in aqueous solutions: the role of NO₂

To elucidate the effect of nitrite ion (NO₂(-)) on the photodegradation of organic pollutants, a 300 W mercury lamp and Pyrex tubes restricting the transmission of wavelengths below 290 nm were used to simulate sunlight, and the photodegradation processes of 2,4-dichlorophenoxyacetic acid (2,4-D) with different concentrations of NO₂(-) in freshwater and seawater were studied. The effect of reactive oxygen species (ROS) on the photolysis of 2,4-D was also demonstrated using electron paramagnetic resonance (EPR). The results indicated that the 2,4-D photolysis reaction followed the first-order kinetics in freshwater and seawater under different concentrations of NO₂(-). Meanwhile, the photochemical reaction rate of 2,4-D increased with increasing concentration of NO₂(-). When the concentration of NO₂(-) was lower than 23 mg/L, the photodegradation rate of 2,4-D in seawater was higher than that in freshwater. However, when the concentration of NO₂(-) was reached 230 mg/L, 2,4-D degradation slowed down in seawater. It was important to note that EPR spectra showed NO₂ radical was generated in the NO₂(-) solution under simulated sunlight irradiation, indicating that 2,4-D photodegradation could be induced by NO₂. These results show the key role of NO₂(-) in photochemistry and are helpful for better understanding of the phototransformation of environmental contaminants in natural aquatic systems.

Phytoestrogens in the environment, II: microbiological degradation of phytoestrogens and the response of fathead minnows to degradate exposure

Phytoestrogens are endocrine active compounds derived from plants, including the isoflavones genistein and daidzein, and their methylated derivatives biochanin A and formononetin. These compounds have been detected at the µg/L level in the effluents of plant-processing industries and municipal treatment plants and at the ng/L level in surface waters worldwide. The present study assessed the persistence of genistein and daidzein in natural aquatic systems, specifically riverine samples. Initial concentration, temperature, sample location, and time of sample collection varied. Genistein and daidzein were found to be readily biodegradable at all tested concentrations, at both 10 °C and 20 °C, in samples collected during different seasons, and in samples from 3 different rivers. In addition, organismal responses in larval and sexually mature fathead minnows (Pimephales promelas) were quantified following exposure to microbiologically degraded phytoestrogens (genistein, daidzein, and formononetin). Products of the microbiological degradation of parent phytoestrogens did not affect larval survival, growth, or predator avoidance. Female adult fathead minnows exposed to these degradation products produced significantly fewer eggs than those exposed to a control, but no other morphological, physiological, or behavioral changes were observed with male or female minnows. The present research suggests that although phytoestrogens are not likely to persist in aquatic systems, they may pseudo-persist if discharges are continuous; in addition, caution should be exercised with respect to high-concentration effluents because of the potentially antiestrogenic effects of phytoestrogen degradates.

Antioxidant activity of selected natural polyphenolic compounds from soybean via peroxyl radical scavenging

Excellent antioxidantsviaSPLET in aqueous solution, moderate antioxidantsviaHAT in lipid medium.

Identifying sources of emerging organic contaminants in a mixed use watershed using principal components analysis

Principal components analysis (PCA) was used to identify sources of emerging organic contaminants in the Zumbro River watershed in Southeastern Minnesota. Two main principal components (PCs) were identified, which together explained more than 50% of the variance in the data. Principal Component 1 (PC1) was attributed to urban wastewater-derived sources, including municipal wastewater and residential septic tank effluents, while Principal Component 2 (PC2) was attributed to agricultural sources. The variances of the concentrations of cotinine, DEET and the prescription drugs carbamazepine, erythromycin and sulfamethoxazole were best explained by PC1, while the variances of the concentrations of the agricultural pesticides atrazine, metolachlor and acetochlor were best explained by PC2. Mixed use compounds carbaryl, iprodione and daidzein did not specifically group with either PC1 or PC2. Furthermore, despite the fact that caffeine and acetaminophen have been historically associated with human use, they could not be attributed to a single dominant land use category (e.g., urban/residential or agricultural). Contributions from septic systems did not clarify the source for these two compounds, suggesting that additional sources, such as runoff from biosolid-amended soils, may exist. Based on these results, PCA may be a useful way to broadly categorize the sources of new and previously uncharacterized emerging contaminants or may help to clarify transport pathways in a given area. Acetaminophen and caffeine were not ideal markers for urban/residential contamination sources in the study area and may need to be reconsidered as such in other areas as well.

Quenching of excited triplet states by dissolved natural organic matter

Excited triplet states of aromatic ketones and quinones are used as proxies to assess the reactivity of excited triplet states of the dissolved organic matter ((3)DOM*) in natural waters. (3)DOM* are crucial transients in environmental photochemistry responsible for contaminant transformation, production of reactive oxygen species, and potentially photobleaching of DOM. In recent photochemical studies aimed at clarifying the role of DOM as an inhibitor of triplet-induced oxidations of organic contaminants, aromatic ketones have been used in the presence of DOM, and the question of a possible interaction between their excited triplet states and DOM has emerged. To clarify this issue, time-resolved laser spectroscopy was applied to measure the excited triplet state quenching of four different model triplet photosensitizers induced by a suite of DOM from various aquatic and terrestrial sources. While no quenching for the anionic triplet sensitizers 4-carboxybenzophenone (CBBP) and 9,10-anthraquinone-2,6-disulfonic acid (2,6-AQDS) was detected, second-order quenching rate constants with DOM for the triplets of 2-acetonaphthone (2AN) and 3-methoxyacetophenone (3MAP) in the range of 1.30-3.85 × 10(7) L mol(C)(-1) s(-1) were determined. On the basis of the average molecular weight of DOM molecules, the quenching for these uncharged excited triplet molecules is nearly diffusion-controlled, but significant quenching (>10%) in aerated water is not expected to occur below DOM concentrations of 22-72 mg(C) L(-1).

Photochemical formation of hydroxyl radical from effluent organic matter: role of composition

The photochemical formation of hydroxyl radical (HO(•)) from effluent organic matter (EfOM) depends upon the chemical properties of this heterogeneous mixture. In this study, two EfOM samples collected from wastewater treatment plants (WWTP A and B) were fractionated by both hydrophobicity (bulk and non-humic) and apparent molecular weight (AMW). The apparent quantum yield for HO(•) formation (ΦHO(•)) and the maximum fluorescence quantum yield (ΦF) were subsequently measured for each subfraction. The formation rates of HO(•) (considering only the hydrogen-peroxide-independent pathways) for the bulk waters were 4.8 × 10(-10) and 9.6 × 10(-11) M s(-1) for WWTP A and B, respectively. For the AMW fractions, the values of ΦHO(•) increased as the AMW of the material decreased. For the WWTP A sample, the ΦHO(•) increased from 2.54 × 10(-4) (bulk water) to 6.29 × 10(-4) for the <1 kDa fraction, and for the WWTP B sample, the value of ΦHO(•) increased from 6.50 × 10(-5) for bulk water to 3.45 × 10(-4) for the <1 kDa fraction. In the case of fluorescence, the values of ΦF ranged from 2.37 × 10(-4) (bulk water) to 3.48 × 10(-4) (<1 kDa fraction) for WWTP A and 3.19 × 10(-4) (bulk water) to 5.75 × 10(-4) (<1 kDa fraction) for WWTP B. There was a linear correlation between ΦHO(•) and ΦF, suggesting that different photophysical processes occur in the chemical components of the fractions. Understanding the formation of HO(•) from EfOM is essential for understanding wastewater-impacted aquatic systems because these results influence the photochemical degradation and mineralization of trace organic contaminants.

Modelling lake-water photochemistry: three-decade assessment of the steady-state concentration of photoreactive transients (·OH, CO3(-·) and (3)CDOM(∗)) in the surface water of polymictic Lake Peipsi (Estonia/Russia)

Over the last 3-4 decades, Lake Peipsi water (sampling site A, middle part of the lake, and site B, northern part) has experienced a statistically significant increase of bicarbonate, pH, chemical oxygen demand, nitrate (and nitrite in site B), due to combination of climate change and eutrophication. By photochemical modelling, we predicted a statistically significant decrease of radicals ·OH and CO3(-·) (site A, by 45% and 35%, respectively) and an increase of triplet states of chromophoric dissolved organic matter ((3)CDOM(∗); site B, by ∼25%). These species are involved in pollutant degradation, but formation of harmful by-products is more likely with (3)CDOM(∗) than with ·OH. Therefore, the photochemical self-cleansing ability of Lake Peipsi probably decreased with time, due to combined effects of climate change and eutrophication. In different environments (e.g. Lake Maggiore, NW Italy), ecosystem restoration policies had the additional advantage of enhancing sunlight-driven detoxification, suggesting that photochemical self-cleansing would be positively correlated with lake water quality.