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Domoic acid (DA) is a neurotoxin generated by several diatom species in harmful algae blooms (HABs). We report the photo-induced transformation products (TPs) and degradation mechanisms of DA in dissolved organic matter (DOM)-rich freshwater and brackish water. High-resolution quadrupole time-of-flight mass spectrometry (QTOF-MS) and the multivariate statistical strategy orthogonal partial least-squares discriminant analysis (OPLS-DA) identified 36 and 23 potential TPs in DOM-rich freshwater and brackish water, respectively. The main reactive sites of DA are the conjugated double bond and proline ring. Isomerization is the predominant transformation pathway induced by excited-state triplet DOM ( 3 DOM ∗ ). The second-order rate constant of the isomerization reaction was measured as (3.8 ± 0.2) × 10 8  M −1  s −1 . The inverse correlation between the dissolved oxygen (DO) concentration and the rate of photo-induced DA isomerization was revealed. Furthermore, under halide-present conditions, halide radicals are mainly responsible for the differentiation of products by quenching hydroxyl radicals and generating unique organic peroxide products. Our results indicated that halide radicals could be important in the photochemical transformation of organic contaminants in high saline environments. [ABSTRACT FROM AUTHOR]

Pharmaceutically active compounds (PhACs) are excreted by humans and animals and released into the aquatic environment through wastewater, which can have potential negative impacts on ecological systems. To conduct a nationwide investigation of the occurrence of PhACs in water resources in China, an analytical procedure based on solid-phase extraction (SPE) and LC-MS/MS was used to measure 45 PhACs in surface water samples from a network of 29 rivers across 31 provinces in China in 2014 and 2015. PhACs were prevalent in all sampled streams. The concentrations of commonly detected PhACs were comparable to those detected in other countries. High total concentrations (mean > 1 μg L −1 ) of all tested PhACs were primarily detected in areas under extreme water stress, specifically northern and eastern coastal areas. Source apportionment based on the profiles of the target compounds found that 54% of the PhACs in China originated from freshly discharged untreated sewage. Metformin (MET) and its biodegradation product, guanylurea (GUL), were used as a pair of indicators to predict PhAC contamination levels and differentiate between biotreated and unbiotreated wastewater. High MET/GUL can be used to indicate untreated wastewater, whereas low MET/GUL values are a strong indicator of treated wastewater. Furthermore, wastewater biotreatment ratios were calculated. We estimated that the biotreatment ratios of most of the provinces in China were less than 50%. We conclude that more attention should be paid to untreated sewage water, especially water in rural areas rather than the existing concentration on urban sewage treatment-oriented management. [ABSTRACT FROM AUTHOR]

Advanced oxidation processes (AOPs), such as hydroxyl radical (HO•)- and sulfate radical (SO4•-)-mediated oxidation, are alternatives for the attenuation of pharmaceuticals and personal care products (PPCPs) in wastewater effluents. However, the kinetics of these reactions needs to be investigated. In this study, kinetic models for 15 PPCPs were built to predict the degradation of PPCPs in both HO•- and SO4•--mediated oxidation. In the UV/H2O2 process, a simplified kinetic model involving only steady state concentrations of HO• and its biomolecular reaction rate constants is suitable for predicting the removal of PPCPs, indicating the dominant role of HO• in the removal of PPCPs. In the UV/K2S2O8 process, the calculated steady state concentrations of CO3•- and bromine radicals (Br•, Br2•- and BrCl•-) were 600-fold and 1-. orders of magnitude higher than the concentrations of SO4•-, respectively. The kinetic model, involving both SO4•- and CO3•- as reactive species, was more accurate for predicting the removal of the 9 PPCPs, except for salbutamol and nitroimidazoles. The steric and ionic effects of organic matter toward SO4•- could lead to overestimations of the removal efficiencies of the SO4•--mediated oxidation of nitroimidazoles in wastewater effluents. [ABSTRACT FROM AUTHOR]

In this study, a fully automated analytical method, based on online solid phase extraction coupled to liquid chromatography-triple quadrupole tandem mass spectrometry (online SPE-LC-MS/MS), has been developed and optimized for the quantification of 10 illicit drugs and metabolites in environmentally aqueous samples collected from China. The particular attention was devoted to minimize the matrix effects through a washing step, which washed out the interferences effectively and helped to reduce the matrix effect significantly. The key advantages of the method are high sensitivity, selectivity and reliability of results, smaller sample manipulation, full automation, and fairly high throughput. The whole procedure was then successfully applied in the analysis of various surface water and wastewater effluents samples. Pseudoephedrine have been detected at trace levels (several tens ng L −1 or less), while MDA, MDMA, benzoylecgonine and methadone were below the LOQ in all samples. Caffeine, cotinine and paraxanthine, which may be derived from medicines and foods, were detected with the highest frequencies and concentrations. [ABSTRACT FROM AUTHOR]

Simultaneous quantification of short-, medium-, and long-chain chlorinated paraffins (CPs) in environmental matrices is challenging and has received much attention from environmental chemists. In this study, ammonium-chloride-enhanced liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) was developed for the first time to quantify CPs in sediments and aqueous samples. Three ionization sources, including atmospheric pressure chemical ionization (APCI), electrospray ionization (ESI), and thermal-assisted-ESI, were employed to examine the performance of ammonium chloride as the chloride ion supply reagent in comparison with traditional chloride ion supply reagent, dichloromethane. Ammonium chloride can be easily used with reversed-phase liquid chromatography (LC), whereas dichloromethane is not compatible with aqueous LC mobile phase. Furthermore, other anion-supply reagents, such as ammonium formate, ammonium acetate, and ammonium bromide, were also tested. It was concluded that the adducts of the CPs with the anions were reversible and could partially dissociate into deprotonated CP ions. The yield of deprotonated CP ions was associated with the gas-phase basicity of the deprotonated CP ions and the corresponding anions. Furthermore, collision-induced dissociation curves were drawn to quantify the stability of anionic CP adducts. The ammonium-chloride-enhanced LC-HRMS was further employed for identifying CPs in sediment samples and coupled with an online SPE method for detecting CPs in aqueous samples. This study may significantly contribute to the qualification and quantification of CPs in environmental matrices. Image 1 • The NH 4 Cl enhanced QTOF MS method has been developed for identification of CPs. • The stability of the CP adducts follows: Br− < CH 3 COO− < HCOO− < Cl− adducts. • The yield of [CP−H]− follows: Br − < Cl − < HCOO− < CH 3 COO − adducts. • The method has been employed to examine CPs in sediments and aqueous samples. An ammonium-chloride-enhanced LC-HRMS method has been developed for the first time to quantify CPs in sediments and aqueous samples. [ABSTRACT FROM AUTHOR]

Abstract: Pt/TiO2 derived from complete decomposition of the surface-anchored Pt(dcbpy)Cl2 (dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) precursor (denoted as C-Pt/TiO2) was prepared to serve as photocatalyst in visible light region. For dye-sensitized hydrogen production experiments, the photocatalyst was sensitized by Ru(2,2′-bipyridine-4,4′-dicarboxylic)2(NCS)2 (the N3 dye) and Ru(2,2′bipyridyl-4,4′-dicarboxylic) (4,4′- dinonyl-2,2′bipyridine) (NCS)2 (the Z907 dye) to induce hydrogen evolution in the presence of sacrificial electron donor, triethanolamine (TEA). The hydrogen generation results showed that C-Pt/TiO2 was found to be a much more active photocatalyst when compared to P-Pt/TiO2, prepared by conventional method of photochemical deposition of H2PtCl6 (denoted as P-Pt/TiO2). For further investigation, the photodegradation experiments in visible region were also confirmed the better photocatalytic activity of C-Pt/TiO2. The enhanced catalytic activity is due to efficient interparticle electron transfer with the small-size and high-disperse platinum particles generated from photodeposition of Pt(dcbpy)Cl2, which was verified by the transmission electron microscopy (TEM) measurement. [Copyright &y& Elsevier]

Pharmaceutical and personal care products (PPCPs) are a group of emerging contaminants that have frequently been detected in aqueous environments. Phototransformation driven by solar irradiation is one of the most important natural processes for the elimination of PPCPs. In this study, primidone (PMD) was chosen as a model "photorefractory" compound. A series of experiments were conducted to assess if reactive intermediates (RIs), such as hydroxyl radical (HO), singlet oxygen (1O 2), and triplet states of dissolved organic matter (3DOM⁎), inhibited or enhanced the photochemical transformation of PMD under simulated solar irradiation. The results indicate that HO plays a key role in the photodegradation of PMD and that dissolved oxygen can affect the degradation rate of PMD by promoting HO formation. Our results demonstrated that PMD can not only react with free HO (HO -free) but also react with lower-energy hydroxylation agents (HO -like). The contributions of HO -free and HO -like to PMD degradation in various dissolved organic matter (DOM) solutions were estimated by a methane-quenching experiment. The results indicated that the HO -like species were important in the photodegradation of "photorefractory" compounds. The bimolecular reaction rate constant of the reaction of free HO with PMD was measured as (5.21 ± 0.02) × 109 M−1 s−1 by using electron pulse radiolysis. Furthermore, PMD was used as a probe to estimate the steady-state concentration of HO -free in various DOM solutions. Using the multivariate statistical strategies of orthogonal projection to latent structures discriminant analysis (OPLS-DA) and hierarchical clustering, 28 photochemical transformation products (TPs) of PMD were successfully identified from the DOM matrix. Unlabelled Image • Photochemical transformation of Primidone was investigated. • The contributions of free hydroxyl radical and lower-energy hydroxylation species were examined. • A method was proposed for the first time to estimate the steady state concentration of free hydroxyl radical. • 28 photochemical products of PMD were identified from the water matrix. • The photochemical degradation mechanisms of PMD were proposed. [ABSTRACT FROM AUTHOR]

The iron(II)-activated peroxymonosulfate [Fe(II)/PMS] process is effective in degrading organic contaminants with a rapid oxidation stage followed by a slow one. Nevertheless, prior studies have greatly underestimated the degradation rates of organic contaminants in the rapid oxidation stage and ignored the differences in the kinetics and mechanism of organic contaminants degradation in these two oxidation stages. In this work, we investigated the kinetics and mechanisms of organic contaminants in this process under acidic conditions by combining the stopped-flow spectrophotometric method and batch experiments. The organic contaminants were rapidly oxidized with rate constants of 0.18-2.9 s -1 in the rapid oxidation stage. Meanwhile, both Fe(IV) and SO 4 •- were active oxidants and contributed differently to the degradation of different organic contaminants in this stage. Additionally, the presence of Cl - promoted the degradation of both phenol and estradiol but the effects of Br - and humic acid on phenol degradation differed from those on estradiol degradation in the rapid oxidation stage. In contrast, the degradation of phenol and estradiol was slow and the amounts of Fe(IV) and SO 4 •- generated were small in the slow oxidation stage. This work updates the fundamental understanding of the degradation of organic contaminants in this process.

The photochemical formation and decay rates of superoxide radical ions (O 2 •- ) in irradiated dissolved organic matter (DOM) solutions were directly determined by the chemiluminescent method. Under irradiation, uncatalyzed and catalyzed O 2 •- dismutation account for ∼25% of the total O 2 •- degradation in air-saturated DOM solutions. Light-induced O 2 •- loss, which does not produce H 2 O 2 , was observed. Both the O 2 •- photochemical formation and light-induced loss rates are positively correlated with the electron-donating capacities of the DOM, suggesting that phenolic moieties play a dual role in the photochemical behavior of O 2 •- . In air-saturated conditions, the O 2 •- quantum yields of 12 DOM solutions varied in a narrow range, from 1.8 to 3.3‰, and the average was (2.4 ± 0.5)‰. The quantum yield of O 2 •- nonlinearly increased with increasing dissolved oxygen concentration. Therefore, the quantum yield of one-electron reducing intermediates, the precursor of O 2 •- , was calculated as (5.0 ± 0.4)‰. High-energy triplets ( 3 DOM*, E T > 200 kJ mol -1 ) and 1 O 2 quenching experiments indicate that 3 DOM* and 1 O 2 play minor roles in O 2 •- production. These results are useful for predicting the photochemical formation and decay of O 2 •- in sunlit surface waters.

Photochemical transformation driven by sunlight is one of the most important natural processes for organic contaminant attenuation. In the current study, statistical analysis-assisted high-resolution mass spectrometry was employed to investigate the phototransformation of nontarget features in wastewater effluents under various radical quenching/enhancing conditions. A total of 9694 nontarget features were extracted from the effluents, including photoresistant features, photolabile features, and transformation products. 65% of the wastewater effluent features were photoresistant, and the photolabile features could be classified into five groups: direct photolysis group (group I), HO • -originated species-dominated group (group II), 3 OM*-dominated group (group III), photochemically produced reactive intermediates combination-dominated group (group IV), and non-first-order degradation group (group V). The direct photolyzed features were observed to degrade significantly faster than the indirect photolyzed features. Moreover, group II dominated by HO • -originated species contributed 34% to the photolabile features. The reaction types that occurred in the phototransformation process were analyzed by linkage analysis. The results suggested that oxygen addition and dealkyl group reactions were the most common reaction types identified in the phototransformation process. Overall, high-resolution mass spectrometry coupled with statistical analysis was applied here to understand the photochemical behavior of the unknown features in wastewater effluents.

Carbamate insecticides, which are common micropollutants in surface waters, were found to generate dichloromethlyamine (DCMA) during chlorination. DCMA formation from other precursors has been reported previously; it is part of the emerging class of nitrogen-based disinfection byproducts (N-DBPs) of health concern in chlorinated water. However, there is a limited understanding about its formation, stability, and toxicity. Four carbamate insecticides (methomyl, carbofuran, carbaryl, and thiodicarb) were examined as DCMA precursors over a range of reaction conditions, based on variables of chlorine/precursor (Cl/P) molar ratio, pH, time, and temperature. DCMA was found to be the dominant volatile DBP to result from chlorination of all four carbamate insecticides, with molar yields ranging from 12% to 150% at a Cl/P molar ratio of 20. Further experiments indicated CH 3 NCl 2 to be relatively stable, with a half-life of up to 35 h in water. The toxicity of CH 3 NCl 2 was investigated using a bacterial bioluminescence inhibition test and survival of human lung tumor cells. The results of these toxicity assays indicated that CH 3 NCl 2 is about 3 orders of magnitude more toxic than CHCl 3 . CH 3 NCl 2 concentrations in the ppb range were observed to result from chlorination of surface water or tap water samples collected from several different locations in China. The results suggest that precursors to CH 3 NCl 2 formation are ubiquitous and that CH 3 NCl 2 poses a hazard to public health and the environment and should be considered in disinfection chemistry and water treatment.

Nicotine is a highly toxic tobacco alkaloid that is ubiquitous in wastewater effluent. For the first time, we report the identification of the products and the pathways for the photodegradation of nicotine in an effluent matrix under simulated solar irradiation. Nicotine was found to be degraded by triplet-state organic matter ( 3 OM*), thus indicating that electron transfer is a preferred reaction mechanism. Using the multivariate statistical strategies orthogonal projection to latent structures discriminant analysis (OPLS-DA) and hierarchical clustering, 49 potential transformation products (TPs) of nicotine were successfully extracted from the water matrix via high-resolution ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS). Overall, 30 TPs, including 4 groups of nonseparated isomeric photo TPs, were identified with various levels of confidence based on the tandem mass spectrometry information on standard compounds and the isotope-labeling method (using rac-nicotine-2',3',3'-D 3 , rac-nicotine- 13 CD 3 , and rac-nicotine-D 4 ) under air-saturated conditions. The pyrrolidine ring of nicotine was found to be the reactive site under sunlight irradiation. Pseudooxynicotine was the main primary TP from nicotine, with a maximum transformation ratio of 64%. Nicotinic acid, cotinine, 3'-hydroxycotinine, and myosmine were the final stable TPs after 72 h of solar irradiation, with yields of 13%, 3%, 5%, and 5%, respectively.

Excited triplet states of chromophoric dissolved organic matter ( 3 CDOM*) are critical transient species in environmental photochemistry. In the present study, sorbic amine (2,4-hexadien-1-amine) and sorbic alcohol were employed as new probe molecules for triplet measurements and compared to the results measured from sorbic acid under identical conditions. Unlike sorbic acid, sorbic amine and sorbic alcohol were not directly photolyzed under solar irradiation. Photosensitized isomerization of the probes with the conjugated diene structure could yield four geometrical isomers. The separation and quantitative determination of the geometrical isomers were accomplished using HPLC and high-resolution NMR analyses. When photoirradiated Suwannee River natural organic matter (SRNOM) was employed as a source of 3 CDOM*, significantly different photosensitized isomerization rates were observed for the diverse charged probes. The bimolecular reaction rate constants between 3 SRNOM* and the probes were calculated as (0.42 ± 0.1) × 10 9 M -1 s -1 for sorbic acid, (1.1 ± 0.1) × 10 9 M -1 s -1 for sorbic alcohol, and (5.2 ± 0.4) × 10 9 M -1 s -1 for sorbic amine, respectively. The average apparent Φ triplet was (0.96 ± 0.03)% based on an irradiation range of 290 to 400 nm. We developed highly selective and efficient probes for triplet determination and elucidated the different reaction behaviors of these conjugated dienes containing different charged substituents within the photochemical energy transfer process.

Buckminsterfullerenes (C 60 ) are widely used nanomaterials that are present in surface water. The combination of C 60 and humic acid (HA) generates reactive oxygen species (ROS) under solar irradiation, but this process is not well understood. Thus, the present study focused on the photochemical formation of singlet oxygen ( 1 O 2 ), hydroxyl radical (HO • )-like species, superoxide radicals (O 2 •- ), hydrogen peroxide (H 2 O 2 ), and triplet excited states ( 3 C 60 */ 3 HA*) in solutions containing both C 60 and HA. The quantum yield coefficients of excited triplet states (f TMP ) and apparent quantum yields of ROS were measured and compared to the calculated values, which were based on the conservative mixing model. Although C 60 proved to have only a slight impact on the 1 O 2 formation from HA, C 60 played a key role in the inhibition of O 2 •- . The photochemical formation of H 2 O 2 followed the conservative mixing model due to the reaction of C 60 •- with HO 2 • /O 2 •- , and the biomolecular reaction rate constant has been measured as (7.4 ± 0.6) × 10 6 M -1 s -1 . The apparent f TMP was significantly lower than the calculated value, indicating that the steric effect of HA was significant in the reaction of 3 C 60 * with the TMP probe. In contrast, C 60 did not have an effect on the photochemical formation of HO • from HA, suggesting that HO • is elevated from the hydrophilic surface of HA. The aforementioned results may be useful for predicting the photochemical influence of C 60 on aqueous environments.

Cyanogen chloride (CNCl) and trichloramine (NCl3) are important disinfection byproducts in chlorinated swimming pools. However, some unknowns exist regarding the precursors of their formation. In this study, uric acid is shown to be an efficient precursor to formation of CNCl and NCl3. The molar yields of CNCl and NCl3 were observed to be as high as 44% (pH = 6.0, chlorine/precursor molar ratio [Cl/P] = 6.4) and 108% (pH = 7.0, Cl/P = 30), respectively, both being strong functions of Cl/P, pH, and temperature. Analysis of swimming pool water samples, combined with the results of experiments involving chlorination of uric acid, and chlorination of body fluid analog mixtures, indicated that uric acid chlorination may account for a large fraction of CNCl formation in swimming pools. Moreover, given that uric acid introduction to pools is attributable to urination, a voluntary action for most swimmers, these findings indicate important benefits to pool water and air chemistry that could result from improved hygiene habits on the part of swimmers.