Isoproturon Reappearance after Photosensitized Degradation in the Presence of Triplet Ketones or Fulvic Acids

Targeted and Non-Targeted Identification of Dye and Chemical Contaminants in Loji River, Indonesia Using FT-ICR-MS

This study utilized liquid chromatography (LC) alongside Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to explore the dyes and chemical contaminants in Loji River, Indonesia. We tentatively identified a total of 655 contaminants at various confidence level, subsequently classifying them into 22 distinct categories. Of the 54 dyes we detected, 12 corresponded with entries in our specialized in-house database. These 12 dyes were further confirmed by reference standards, matching both retention time (RT) and MS/MS spectra. LC-FT-ICR MS data showed that dyes from printing batik and textile industries are key contributors to river pollution. Particularly noteworthy were two sample locations that displayed substantial contamination, predominantly from azoic and reactive dyes. Additionally, pharmaceuticals were identified as one of the most frequently occurring contaminants, underscoring the inadequacies in the area's sewage management. To corroborate these findings, we conducted physicochemical, phytotoxicity, and acute toxicity tests, all of which verified the harmful effects of the Loji River's water on both the local flora and human populations. Notably, water samples that tested positive for dye contamination exhibited elevated toxicity levels. To the best of our knowledge, this study is pioneering in its molecular-level investigation of dye contamination in Southeast Asian rivers. Our results accentuate the pressing need for both targeted and non-targeted screening methods to identify contaminants in the surface waters of developing nations.

Photo-transformation of isoproturon under UV-A irradiation: The synergy of nitrite and natural organic matter

Isoproturon (IPU), a widely utilized phenylurea herbicide, is recognized as an emerging contaminant. Previous studies have predominantly attributed the degradation of IPU in natural waters to indirect photolysis by natural organic matter (NOM). Here, we demonstrate that nitrite (NO2-) also serves as an important photosensitizer that induces the photo-degradation of IPU. Through radical quenching tests, we identify hydroxyl radicals (•OH) and nitrogen dioxide radicals (NO2•) originating from NO2- photolysis as key players in IPU degradation, resulting in the generation of a series of hydroxylated and nitrated byproducts. Moreover, we demonstrate a synergistic effect on the photo-transformation of IPU when both NOM and NO2- are present in the reaction mixture. The observed rate constant (kobs) for IPU removal increases to 0.0179 ± 0.0002 min-1 in the co-presence of NO2- (50 μM) and NOM (2.5 mgC/L), surpassing the sum of those in the presence of each alone (0.0135 ± 0.0004 min-1). NOM exhibits multifaceted roles in the indirect photolysis of IPU. It can be excited by UV and transformed to excited triplet states (3NOM*) which oxidize IPU to IPU•+ that undergoes further degradation. Simultaneously, NOM can mitigate the reaction by reducing the IPU•+ intermediate back to the parent IPU. However, the presence of NO2- alters this dynamic, as IPU•+ rapidly couples with NO2•, accelerating IPU degradation and augmenting the formation of mono-nitrated IPU. These findings provide in-depth understandings on the photochemical transformation of environmental contaminants, especially phenylurea herbicides, in natural waters where NOM and NO2- coexist.

Large-scale fate profiling of butralin between cultivated and processed garlics for multi-risk estimations

Elaborating on the fate profiling and risk magnitude of butralin during large-scale applications was conducive to agroecosystems sustainability and dietary rationality. Occurrence, dissipation and concentration variation of butralin were elucidated from garlic cultivation to household processing by tracing UHPLC-MS/MS within 2 min, with regard to original depositions, half-lives, and terminal magnitude in typical origins of garlic. The processing factors (Pfs) of butralin were further clarified among washing, stir-frying and pickling of garlic crops, and pickling was the most effective way for butralin removal with a Pf of 0.092. A probabilistic model with Pfs was further introduced for the comprehensive risk estimations, by reduction factors of 3.1-10.9 from raw garlic crops to processed products. The short-term risks of butralin from green garlic were greater than those between garlic shoot and garlic, with the %ARfDs of 0.030 %-6.323 % from 50^th to 99.9^th percentiles. The long-term risks were inversely correlated to the age of the population, whose location in rural (%ADIs, 0.256 %-0.768 %) suffered more serious exposures than in urban (%ADIs, 0.231 %-0.699 %). High potential risk amplification should be continuously emphasized given the increasing applications and persistent fate of butralin, especially for vulnerable rural children.

The photoactivity of complexation of DOM and copper in aquatic system: Implication on the photodegradation of TBBPA

The photoactivity of dissolved organic matter (DOM) has a great impact on the photodegradation of organic pollutants in natural waters. In this study, the photodegradation of TBBPA was investigated under simulated sunlight irradiation in the presence of copper ion (Cu²⁺), dissolved organic matter (DOM) and Cu-DOM complexation (Cu-DOM) to illustrate the effect of Cu²⁺ on photoactivity of DOM. The rate of photodegradation of TBBPA in the presence of Cu-DOM complex was 3.2 times higher than that in pure water. The effects of Cu²⁺, DOM and Cu-DOM on the photodegradation of TBBPA were highly pH dependent and hydroxyl radical(·OH) responded for the acceleration effect. Spectral and radical experiments indicated that Cu²⁺ had high affinity to fluorescence components of DOM, and acted as both the cation bridge and electron shuttle, resulting the aggregation of DOM and increasing of steady-state concentration of ·OH (·OH_ss). Simultaneously, Cu²⁺ also inhibited intramolecular energy transfer leading to the decrease of steady-state concentration singlet oxygen (¹O_2ss) and triplet of DOM (³DOM^⁎_ss). The interaction between Cu²⁺ and DOM followed the order of conjugated carbonyl CO, COO^- or CO stretching in phenolic groups and carbohydrate or alcoholic CO groups. With these results, a comprehensive investigation on the photodegradation of TBBPA in the presence of Cu-DOM was conducted, and the effect of Cu²⁺ on the photoactivity of DOM was illustrated. These findings helped to understanding the potential mechanism of interaction among metal cation, DOM and organic pollutants in sunlit surface water, especially for the DOM-induced photodegradation of organic pollutants.

Occurrence and fate characteristics of isoproturon from garlic cultivation to household processing: Implication for human exposure

The fate characteristics of isoproturon (IPU) from garlic cultivation to household processing was elucidated by a tracing UHPLC-MS/MS based on the favorable storage stability. The occurrence, pharmacokinetics dissipation and terminal magnitude of IPU were reflected by parameters including original deposition of 31-170 μg kg^-1, half-lives of 11.5-19.4 d, and final concentrations of <1.0-250.6 μg kg^-1. The processing factors of IPU were further clarified in terms of washing, stir-frying and pickling, with processing factors of 0.008-0.828. The chronic dietary risks (%ADI) were assessed as 1.516-5.242 %, whereas the short-term exposures from green garlic should be continuously emphasized over 99th percentile with unacceptable %ARfD of 147.144-5074.018 %. The acute and chronic risk magnitude significantly decreased by a factor 2.0-125.0 and 2.2-3.3 from raw garlic crops to processed products, respectively. What was noteworthy was the unacceptable acute risks of IPU from green garlic at 99.9th percentile even after a series of processing procedures.

Insights into the characteristics, adsorption and desorption behaviors of microplastics aged with or without fulvic acid

Many aging experiments on microplastics (MPs) have been carried out using UV radiation or strong oxidants. Little attention has been paid to the role of water environmental factors such as dissolved organic matter (DOM). In this study, the role of fulvic acid (FA), the main component of DOM, in the UV-aging process of MPs was explored. MPs aged under UV, and UV along with 0.5 mg/L and 2 mg/L FA, were selected as subjects. The results showed that (1) FA accelerated the aging process of polyethylene (PE). PE aged with FA had a larger specific area (S_BET), with more holes and cracks on the surface. (2) FA enhanced the adsorption capacity of PE. The TC adsorption quantities of 0, 0.5, and 2 mg/L FA-aged PE were 1.100, 1.447, and 1.812 mg/L, respectively. (3) The quantity of TC desorbed by PE increased, whereas the desorption rate decreased as the FA concentration increased. The desorption rates of TC at 0, 0.5, and 2 mg/L FA-aged PE were 25.16%, 22.05%, and 19.52% in water, and 72.10%, 70.36%, and 59.51% in simulated intestinal fluid. This study explored the role of FA in the aging process of MPs. Moreover, research on the aging mechanism of MPs is enriched.

Effect of Solution pH on the Dual Role of Dissolved Organic Matter in Sensitized Pollutant Photooxidation

Dissolved organic matter (DOM) has a dual role in indirect phototransformations of aquatic contaminants by acting both as a photosensitizer and an inhibitor. Herein, the pH dependence of the inhibitory effect of DOM and the underlying mechanisms were studied in more than 400 kinetic irradiation experiments over the pH range of 6-11. Experiments employed various combinations of one of three DOM isolates, one of two model photosensitizers, the model antioxidant phenol, and one of nine target compounds (TCs), comprising several aromatic amines, in particular anilines and sulfonamides, and 4-cyanophenol. Using model photosensitizers without antioxidants, the phototransformation of most TCs increased with increasing pH, even for TCs for which pH did not affect speciation. This trend was attributed to pH-dependent formation yields of TC-derived radicals and their re-formation to the parent TC. Analogous trends were observed with DOM as a photosensitizer. Comparison of model and DOM photosensitizer data sets showed increasing inhibitory effects of DOM on TC phototransformation kinetics with increasing pH. In systems with anilines as a TC and phenol as a model antioxidant, pH trends of the inhibitory effect could be rationalized based on the reduction potential difference (ΔE_red) of phenoxyl/phenol and anilinyl/aniline couples. Our results indicate that the light-induced transformation of aromatic amines in the aquatic environment is governed by the pH-dependent inhibitory effects of antioxidant phenolic moieties of DOM and pH-dependent processes related to the formation of amine oxidation intermediates.

Fluoroquinolone antibiotics sensitized photodegradation of isoproturon

Fluoroquinolone (FQ) antibiotics are a group of contaminants of emerging environmental concern. In the present study, we demonstrated that norfloxacin (NORF) and ofloxacin (OFLO), two typical FQs, have photochemical reactivity analogous to chromophoric dissolved natural organic matter (DOM) in surface waters and can sensitize the photodegradation of isoproturon (IPU), a phenylurea herbicide. Such photochemical reactivity is ascribed to the quinolone chromophore that is excited to a triplet state (³FQ*) upon UV-A irradiation. ³FQ* further reacts with dissolved oxygen to give rise to singlet oxygen. ³FQ* steady-state concentrations of 6.72 × 10^-15 and 1.27 × 10^-15 M were measured in 10 μM NORF and OFLO solutions, respectively, under UV_365nm irradiation. The degradation of IPU was due to the reaction with ³FQ*, with bimolecular rate constants of 6.07 × 10⁹ and 1.51 × 10¹⁰ for ³NORF* and ³OFLO*, respectively. Intriguingly, NORF and OFLO per se were unstable and photolyzed during UV-A irradiation, but the photochemical reactivities of the solutions were not lost accordingly. High-resolution mass spectrometry analysis revealed that defluorination and piperazine moiety oxidation were the main photolysis pathways, while the core quinolone structure remained intact. Thus, the photolysis products largely inherited the photochemical reactivity of the parent compounds. Since all FQs share the same quinolone structure, similar photochemical reactivity is expected. The presence of FQs in surface water would affect the transformation and fate of coexisting compounds. To the best of our knowledge, this is the first study examining the environmental behavior of FQs as photosensitizers. The findings greatly advance the understandings of the influence of FQs in aquatic environment.

Mechanistic Insight into the Reactivities of Aqueous-Phase Singlet Oxygen with Organic Compounds

Singlet oxygen (¹O₂) is a selective reactive oxygen species that plays a key role for the fate of various organic compounds in the aquatic environment under sunlight irradiation, engineered water oxidation systems, atmospheric water droplets, and biomedical systems. While the initial rate-determining charge-transfer reaction mechanisms and kinetics of ¹O₂ have been studied extensively, no comprehensive studies have been performed to elucidate the reaction mechanisms with organic compounds that have various functional groups. In this study, we use density functional theory calculations to determine elementary reaction mechanisms with a wide variety of organic compounds. The theoretically calculated aqueous-phase free energies of activation of single electron transfer and ¹O₂ addition reactions are compared to the experimentally determined rate constants in the literature to determine linear free-energy relationships. The theoretically calculated free energies of activation for the groups of phenolates and phenols show excellent correlations with the Hammett constants that accept electron densities by through-resonance. The dominant elementary reaction mechanism is discussed for each group of compounds. As a practical implication, we demonstrate the fate of environmentally relevant organic compounds induced by photochemically produced intermediate species at different pH and evaluate the impact of predicting rate constants to the half-life.

Photocatalytic mechanisms of 2,4-dinitroanisole degradation in water deciphered by C and N dual-element isotope fractionation

In surface water environments, photodegradation may be an important process for the natural attenuation of 2,4-dinitroanisole (DNAN). Understanding the photolysis and photocatalysis mechanisms of DNAN is difficult because the photosensitivity of nitro groups and the behavior of DNAN as a potential photosensitizer are unclear in aqueous solutions. Here, we investigate the degradation mechanisms of DNAN under UV-A (λ ~ 350 nm) and UV-C (λ ~ 254 nm) irradiation in a photolysis reactor where aqueous solution was continuously recycled through a UV-irradiated volume from a non-irradiated external reservoir. By tracking C and N isotopic fractionation in DNAN and its reaction products, we observed normal ¹³C fractionation (ε_C = -3.34‰) and inverse ¹⁵N fractionation (ε_N = +12.30‰) under UV-A (λ ~ 350 nm) irradiation, in contrast to inverse ¹³C fractionation (ε_C = +1.45‰) and normal ¹⁵N fractionation (ε_N = -3.79‰) under UV-C (λ ~ 254 nm) irradiation. These results indicate that DNAN can act as a photosensitizer and may follow a product-to-parent reversion mechanism in surface water environments. The data also indicate that photocatalytic degradation of DNAN in aqueous systems can be monitored via C and N stable isotope analysis.

Suspect and Nontarget Screening for Contaminants of Emerging Concern in an Urban Estuary

This study used suspect and nontarget screening with high-resolution mass spectrometry to characterize the occurrence of contaminants of emerging concern (CECs) in the nearshore marine environment of Puget Sound (WA). In total, 87 non-polymeric CECs were identified; those confirmed with reference standards (45) included pharmaceuticals, herbicides, vehicle-related compounds, plasticizers, and flame retardants. Eight polyfluoroalkyl substances were detected; perfluorooctanesulfonic acid (PFOS) concentrations were as high as 72-140 ng/L at one location. Low levels of methamphetamine were detected in 41% of the samples. Transformation products of pesticides were tentatively identified, including two novel transformation products of tebuthiuron. While a hydrodynamic simulation, analytical results, and dilution calculations demonstrated the prevalence of wastewater effluent to nearshore marine environments, the identity and abundance of selected CECs revealed the additional contributions from stormwater and localized urban and industrial sources. For the confirmed CECs, risk quotients were calculated based on concentrations and predicted toxicities, and eight CECs had risk quotients >1. Dilution in the marine estuarine environment lowered the risks of most wastewater-derived CECs, but dilution alone is insufficient to mitigate risks of localized inputs. These findings highlighted the necessity of suspect and nontarget screening and revealed the importance of localized contamination sources in urban marine environments.

Removal of epoxiconazole and pyraclostrobin from highly contaminated effluent (grams per liter level): Comparison between ozone and solar still decontamination using real field conditions

Brazilian environmental legislation obliges the aeroagriculture operators to treat the effluents generated after aircraft washing. This effluent commonly contains high levels of pesticides (g L^-1) with potential to produce point source pollution. In the present study, we evaluated the efficiency of two systems on the removal of the fungicides epoxiconazole and pyraclostrobin from these effluents. The first system is based on ozonation and is currently suggested by regulatory authority. The second system is based on a pyramid-shaped solar still. The pesticides removal was monitored using liquid chromatography mass spectrometry to determine the mass quantity of both molecules throughout the treatment. After treatment with ozone treatment, the total mass of epoxiconazole decreased by 73% and pyraclostrobin decreased by 90.8%. The solar distillation system removed epoxiconazole and pyraclostrobin by >99.995 and 99.99%, respectively. The both systems proved to be efficient in the treatment of effluent containing residues of the fungicide Opera®, a formulation containing epoxiconazole and pyraclostrobin. The solar distillation system showed a higher degree of removal and presents the advantage of operating without energy sources, reagents or consumables.

Modelling the photochemistry of imazethapyr in rice paddy water

In this work the photochemistry of imazethapyr, an imidazolinone herbicide used in rice crops, was modelled in rice paddy water. The photochemical half-life time of the herbicide was assessed by means of the APEX software (Aqueous Photochemistry of Environmentally occurring Xenobiotics) taking into account the direct photolysis, the reactions with hydroxyl radicals (HO) and, in some cases, the reactions with the excited triplet states of chromophoric dissolved organic matter (³CDOM*). We found that direct photolysis and HO reaction can account for a half-life time ranging between 8 and 11 days in May, which is in quite good agreement with the half-life times measured in the field and reported in the literature. These findings suggest that direct photolysis and reaction with HO are important degradation pathways for imazethapyr in paddy water. Dissolved organic matter (DOM) has been reported in the literature to decrease the imazethapyr photodegradation rate. Our model computations confirm this finding but, upon comparison of model predictions with experimental data from the literature, we provide evidence of a non-negligible role of DOM-photosensitised processes in imazethapyr degradation, particularly in DOM-rich waters. We also assess an upper limit (10⁸ L mol^-1 s^-1) for the second-order rate constant of the reaction between imazethapyr and ³CDOM*. Furthermore, on the basis of literature-reported photodegradation pathways and by using both APEX and the US-EPA ECOSAR V2.0 software, we assess that the direct photolysis by-products of imazethapyr could pose a potential ecotoxicological threat to aquatic systems.

Exposure to solar light reduces cytotoxicity of sewage effluents to mammalian cells: Roles of reactive oxygen and nitrogen species

Sewage effluents can contain hundreds of toxic pollutants, making them a risk to humans when involved in drinking water. It is therefore important to evaluate the cytotoxicity of sewage effluents to mammalian cells. Solar light might influence the water quality of sewage effluents after their discharge into lakes or rivers, altering their cytotoxicity. In this study, natural solar light was found to lower the cytotoxicity of sewage effluents to Chinese hamster ovary (CHO) cells. Cytotoxicity of different samples decreased by 31%-65% after 12 h of simulated irradiation. Ultraviolet in sunlight was the major contributor to the cytotoxicity reduction. Aquatic reactive oxygen species (ROS), including singlet oxygen, superoxide anions, hydrogen peroxide, and hydroxyl radicals, were generated in the effluents under irradiation and they contributed to part of cytotoxicity reduction. Pollutants in sewage effluents induced cytotoxicity by simultaneously elevating the levels of intracellular ROS and intracellular reactive nitrogen species (RNS) in CHO cells. Solar light and the aquatic ROS formed under irradiation reduced the cytotoxicity because the transformed pollutants in sewage effluents increased lower intracellular ROS and RNS levels. These results help reveal the detoxification mechanism of sewage effluents in natural environment.

Contribution of the Excited Triplet State of Humic Acid and Superoxide Radical Anion to Generation and Elimination of Phenoxyl Radical

Contributions of excited triplet state of humic acid (³HA*) and superoxide radical anion (O₂^•-), which is mainly generated via the reaction of O₂ with HA-derived reducing intermediates (HA^•-), to phenol transformation were revealed using acetaminophen, 2,4,6-trimethylphenol and tyrosine as probe molecules. Phenol transformation was initiated by ³HA*, leading to the formation of the phenoxyl radical (PhO•), but the distribution of transformation intermediates was codetermined by ³HA* and HA^•-. The influence of HA^•- essentially resulted from the production of O₂^•-, which affected the fate of PhO•. PhO• could undergo dimerization, or react with O₂^•-, leading to either phenol peroxide formation (radical addition) or phenol regeneration (electron transfer). In addition, PhO• could bind to HA or react with HA radicals, particularly in the absence of O₂ and O₂^•-. These PhO• reactions were dependent on the reduction potential and structure of PhO•. This study also proved that the reaction of phenol with ¹O₂ and the reaction of PhO• with O₂^•- lead to the same oxidation product. The contributions of ³HA* and its generated ¹O₂, HA^•- and its generated O₂^•- to phenol transformation were pH-dependent.