Transformation of acesulfame in chlorination: Kinetics study, identification of byproducts, and toxicity assessment

Acesulfame degradation by thermally activated persulfate: Kinetics, transformation products and estimated toxicity

The existence of the artificial sweetener acesulfame (ACE) in quantities of significance can negatively impact water quality, and its consumption has been associated with deleterious health effects. The present investigation explores the efficacy of heat-activated sodium persulfate (SPS) for eliminating ACE. The complete degradation of 0.50 mg L-1 of ACE was achieved within 45 min under a reaction temperature of 50 °C and 100 mg L-1 of SPS. The impact of thermal decomposition on ACE at a temperature of 60 °C was negligible. This study considers several factors, such as the SPS and ACE loading, the reaction temperature, the initial pH, and the water matrix of the reactor. The results indicate that the method's efficiency is positively correlated with higher initial concentrations of SPS, whereas it is inversely associated with the initial concentration of ACE. Furthermore, higher reaction temperatures and acidic initial pH levels promote the degradation of acesulfame. At the same time, certain constituents of the water matrix, such as humic acid, chlorides, and bicarbonates, can hinder the degradation process. Additionally, the data from LC-QToF-MS analysis of the samples were used to investigate transformation through suspect and non-target screening approaches. Overall, ACE's eight transformation products (TPs) were detected, and a potential ACE decomposition pathway was proposed. The concentration of TPs followed a volcano curve, decreasing in long treatment times. The ecotoxicity of ACE and its identified TPs was predicted using the ECOSAR software. The majority of TPs exhibited not harmful values.

Guidance document on the impact of water treatment processes on residues of active substances or their metabolites in water abstracted for the production of drinking water

This guidance document provides a tiered framework for risk assessors and facilitates risk managers in making decisions concerning the approval of active substances (AS) that are chemicals in plant protection products (PPPs) and biocidal products, and authorisation of the products. Based on the approaches presented in this document, a conclusion can be drawn on the impact of water treatment processes on residues of the AS or its metabolites in surface water and/or groundwater abstracted for the production of drinking water, i.e. the formation of transformation products (TPs). This guidance enables the identification of actual public health concerns from exposure to harmful compounds generated during the processing of water for the production of drinking water, and it focuses on water treatment methods commonly used in the European Union (EU). The tiered framework determines whether residues from PPP use or residues from biocidal product use can be present in water at water abstraction locations. Approaches, including experimental methods, are described that can be used to assess whether harmful TPs may form during water treatment and, if so, how to assess the impact of exposure to these water treatment TPs (tTPs) and other residues including environmental TPs (eTPs) on human and domesticated animal health through the consumption of TPs via drinking water. The types of studies or information that would be required are described while avoiding vertebrate testing as much as possible. The framework integrates the use of weight-of-evidence and, when possible alternative (new approach) methods to avoid as far as possible the need for additional testing.

A Critical Review on Chemical Speciation of Chlorine-Produced Oxidants (CPOs) in Seawater. Part 1: Chlorine Chemistry in Seawater and Its Consequences in Terms of Biocidal Effectiveness and Environmental Impact

Seawater chlorination has three main industrial uses: disinfection of water and installations, control of biofouling, and preventing the transport of aquatic invasive species. Once in contact with seawater, chlorine reacts rapidly with water constituents (e.g. bromide ions, ammonia, and nitrogen-containing compounds) to form a range of oxidative species (e.g. bromine and N-haloamines), termed "chlorine-produced oxidants" (CPOs) or "total residual oxidants" (TRO). The chemical nature of CPOs and their concentration are a function of two categories of parameters related to treatment modality (e.g. chlorine dose) and water quality (e.g. temperature, pH, ammonia concentration, and organic constituents). The chlorination process may result in continuous or intermittent releases of CPOs in seawater. The reactivity and potential ecotoxicity of CPO species largely depend on their physical and chemical properties. Therefore, evaluation of the biocidal effectiveness of chlorination and its potential impacts requires not only determining the sum of CPOs (via a bulk parameter), but also their chemical speciation. The aim of this article - which is the first of a trilogy dedicated to the chemical speciation of CPOs in seawater - is to provide an overview of current knowledge about chlorine chemistry in seawater and to discuss the biocidal efficacy and the environmental fate of resulting CPOs. The 2nd and 3rd articles delineate a comprehensive and critical review of analytical methods and approaches for the determination of CPOs in seawater.

Young population consume twice as much artificial sweetener than the general population - A wastewater-based assessment in China

Understanding artificial sweetener consumption patterns and levels in different demographics is important for formulating public health policies on controlling sugar consumption. There is a considerable knowledge gap with respect to the pattern of artificial sweetener consumption in China. To narrow this gap, wastewater analysis was used to assess the temporal patterns of consumption of seven artificial sweeteners in an urban population and a university town in a megacity in South China over a one-year period. Daily influent wastewater samples were collected from an urban catchment and weekly samples collected from a university sub-catchment. Population normalized per capita consumption of the four detected artificial sweeteners (cyclamate, acesulfame, sucralose and saccharin) in the university catchment (1.0-5.9 mg d^-1 p^-1) was much higher than those in urban catchment (0.5-1.3 mg d^-1 p^-1), indicating younger population consume more artificial sweeteners than the general population. The daily consumption of artificial sweeteners was found to be stable throughout the week in the urban catchment. Time-series analysis showed that an average increase in temperature of 1 °C was associated with an increase consumption of 33 μg d^-1 p^-1 for acesulfame, 15 μg d^-1 p^-1 for sucralose and 14 μg d^-1 p^-1 for saccharin. This was the first study that objectively quantified the greater consumption of artificial sweeteners (proxy for consumption of artificially sweetened food and beverages) in a younger age group when compared to the general population, which could potentially pose a risk of health related diseases.

UV-induced activation of organic chloramine: Radicals generation, transformation pathway and DBP formation

Organic chloramines of little disinfection efficacy commonly exist in disinfection process (chlor(am)ination) due to the wide presence of organic amines in water, of which N-chlorodimethylamine (CDMA) is a typical one. For the first time, UV photolysis for the activation of CDMA was investigated. UV photolysis caused the cleavage of N-Cl bond in CDMA to form Cl^• and subsequently HO^•, both of which are dominant contributors to the destruction of model contaminant bisphenol A (BPA). Typical spectra of HO^• were detected by electron paramagnetic resonance (EPR) experiments, while spectra of reactive nitrogen species (RNS) were not detected during UV photolysis of CDMA. The increase of pH (6.0-8.0), HCO₃^-/CO₃^2-, Cl^- and nature organic matter inhibited the degradation of BPA. We proposed pathways of CDMA and BPA degradation based on the identified transformation products. UV photolysis of CDMA and BPA reduced the formation of N-nitrosodimethylamine (NDMA) at pH 8.0, but increased the formation of trichloronitromethane (TCNM) at pH 7.0 and 8.0. The increasing toxicity and the formation of TCNM and NDMA gave us a hint that formation of organic chloramines should be concerned.

UV/Chlorination of sulfamethazine (SMZ) and other prescription drugs: kinetics, transformation products and insights into the combined toxicological assessment

The UV/chlorination of three prescription drugs, sulfamethazine (SMZ), gemfibrozil (GEM) and antipyrine (ANT) were studied by the investigation of kinetics, transformation products and combined toxicological assessment. The degradation followed pseudo-first-order kinetics, with half-lives significantly affected by chlorine dosage, without being greatly influenced by pH value and bromide concentration. Based on the Frontier Orbital Theory, the structures of products by hydroxylation or chlorine substitution were proposed and the transformation pathways were introduced, with two, two and one never-before-reported products identified for SMZ, GEM and ANT, respectively. Compared to the results of the experiments with artificial water sample, the degradation kinetics of the three prescription drugs was observed with a prolonged half-lives in both Yangtze River and Taihu Lake water, suggesting that aromatic containing transformation products (TPs) may also exist in UV/chlorine treated natural waters. The results of combined toxicity on E. coli showed that the antagonism effect predominated in most binary and ternary combinations. However, the synergistic toxicity of combinations at low concentrations of prescription drugs subjected to UV/chlorine should be cautioned, which was more close to the natural concentration of prescription drugs in waters.

Determination of contaminants of emerging concern and their transformation products in treated-wastewater irrigated soil and corn

In many parts of the world, clean water has become increasingly scarce. Irrigation of agricultural land with treated wastewater is commonly used in response to water shortages but there is concern about the environmental fate and transport of contaminants present in the irrigation wastewater. This study aimed to examine the presence of wastewater sourced contaminants in soil and field grown corn (Zea mays) crops spray irrigated with treated wastewater. Soil, corn grain, leaves, and roots were sampled and tested from a long-term wastewater irrigation site as well as a non-irrigated control site in close geographic proximity. Samples were analyzed using comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry (GC × GC-TOFMS) and both targeted and non-targeted analyses were conducted to determine chemical differences between the wastewater irrigated and control samples. Target compounds detected and quantified in the samples include herbicides, phthalates, and polycyclic aromatic hydrocarbons. Non-targeted analysis showed chemical differences between each the wastewater irrigated and control samples. Furthermore, new chloro-dimethyl-benzotriazole compounds, which are suspected to be transformation products created by the chlorine disinfection process of the wastewater treatment plant, were tentatively identified in the wastewater effluent. Twenty of these new benzotriazoles were detected and semi-quantified in the wastewater irrigated soil samples at a maximum concentration of 472 ng/g. Eight of the most abundant benzotriazoles were also detected in the corn roots at concentrations up to 56 ng/g.

Bromine and iodine species in drinking water supply system along the Changjiang River in China: Occurrence and transformation

Bromine (Br) and iodine (I) in source water can form highly toxic brominated or iodinated disinfection byproducts in treatment plants. For the first time, the occurrence of Br and I speciation and their proportion, transformation in the drinking water supply system along the Changjiang River were investigated. 96 water samples were collected from eight drinking water treatment plants under conditions of low, normal, and flood water regimes. Total Br (TBr) and total I (TI) concentrations were quantified by inductively coupled plasma mass spectrometry (ICPMS) and inorganic Br/I forms (bromide, bromate, iodide, and iodate) were determined by high-performance liquid chromatography coupled with ICPMS. Concentrations of organic Br/I were calculated as the difference between total Br/I and inorganic Br/I. Water regimes had different effect on Br and I species, and there were different rules in untreated and treated water samples. Apparent increase of TBr and TI concentrations after water treatment were observed, which indicated the possibility of Br/I introduction by chlorine-containing disinfectant. The occurrence of TBr, TI, bromide, and total organic I in the river were investigated to increase with the direction of flow. In addition, TBr and TI concentrations correlated with the concentrations of artificial sweeteners (e.g., acesulfame and sucralose, a kind of wastewater indicator), suggesting the influence of domestic sewage on Br and I in the river. In untreated water, bromide was the main Br species, and after treatment more than 50% was transformed into organic Br. Iodoorganics were the majority of I species in raw water and were partly transformed into iodate after treatment. Overall, the Br/I species have accumulation potential in the Changjiang River and organic forms occupy high proportion in treated water samples, which should be paid more attention.

Artificial sweeteners in end-use biosolids in Australia

Artificial sweeteners are contaminants of emerging concern that can enter the aquatic and terrestrial environments via wastewater effluent discharge and the environmental application of biosolids. The release of artificial sweeteners from the use of biosolids in Australia was assessed. The concentration of seven artificial sweeteners was quantified in biosolids samples collected from 71 wastewater treatment plants (WWTPs) across Australia during Census 2016. Sucralose, saccharin, acesulfame, aspartame and cyclamate were detected in biosolids samples at median concentrations ranging from 0.18 ng/g (dry weight) (range: <LOQ-34 ng/g) for cyclamate to 220 ng/g (range: <LOQ -3,670 ng/g) for sucralose, while neotame and neohesperidin dihydrochalcone were not detected. The relationship between the concentration of artificial sweeteners in biosolids and moisture content was assessed with the concentration of artificial sweeteners decreasing as dewatering time increased in a biosolids drying hall. The geometric means (± standard deviation) for per capita loads of individual artificial sweeteners ranged from 8.7 (1.6, 48) µg year^-1 person^-1 for cyclamate to 4,000 (1,000, 15,000) µg year^-1 person^-1 for sucralose with 223 kg of artificial sweeteners released to terrestrial environment from biosolids end-use annually in Australia. Due to the low loads of artificial sweeteners in biosolids compared with wastewater effluent, risks associated with artificial sweeteners in biosolids are likely limited.

Degradation of acesulfame in UV/monochloramine process: Kinetics, transformation pathways and toxicity assessment

UV/monochloramine (UV/NH₂Cl) is an emerging advanced oxidation process that can generate various reactive species like reactive chlorine species (RCS) and hydroxyl radicals for micropollutant removal. This study investigated the potential toxicity of transformation products resulting from UV/NH₂Cl treatment of acesulfame (ACE), as an example of micropollutant, found in worldwide aquatic environment. Compared with UV photolysis and chloramination, the UV/NH₂Cl process more effectively degraded ACE. The transformation products of ACE treated with the UV/NH₂Cl process were identified and characterized with high resolution mass spectrometry. The formation of chlorinated-TPs indicated the role of RCS in UV/NH₂Cl transformation even though UV photolysis was predominantly responsible for the ACE degradation. The Vibrio fischeri bioluminescence inhibition assay revealed a higher toxicity of TPs derived from UV/NH₂Cl than from UV photolysis. The increased toxicity could be attributed to most of the generated chlorinated-TPs (Cl-TPs), in particular those halo-alcohols. The ECOSAR program predicts that halo-alcohol TPs are more toxic than their non-chlorinated analogues and other Cl-TPs. This study provides insight into the important role of reactive species in the micropollutants' transformation of UV/NH₂Cl process. It further provides information relevant to the potential risk when applying the process for micropollutant removal in water treatment.

Unraveling the chemodiversity of halogenated disinfection by-products formed during drinking water treatment using target and non-target screening tools

To date, there is no analytical approach available that allows the full identification and characterization of highly complex disinfection by-product (DBP) mixtures. This study aimed at investigating the chemodiversity of drinking water halogenated DBPs using diverse analytical tools: measurement of adsorbable organic halogen (AOX) and mass spectrometry (MS)-based target and non-target analytical workflows. Water was sampled before and after chemical disinfection (chlorine or chloramine) at four drinking water treatment plants in Sweden. The target analysis had the highest sensitivity, although it could only partially explain the AOX formed in the disinfected waters. Non-target Fourier transform ion cyclotron resonance (FT-ICR) MS analysis indicated that only up to 19 Cl and/or Br-CHO formulae were common to all disinfected waters. Unexpectedly, a high diversity of halogenated DBPs (presumed halogenated polyphenolic and highly unsaturated compounds) was found in chloraminated surface water, comparable to that found in chlorinated surface water. Overall, up to 86 DBPs (including isobaric species) were tentatively identified using liquid chromatography (LC)-Orbitrap MS. Although further work is needed to confirm their identity and assess their relevance in terms of toxicity, they can be used to design suspect lists to improve the characterization of disinfected water halogenated mixtures.

National wastewater reconnaissance of artificial sweetener consumption and emission in Australia

Artificial sweeteners are used as sugar substitutes in our daily lives yet consumption and release patterns are currently unknown in Australia. The spatial distribution of artificial sweetener consumption and WWTP effluent emission in Australia was estimated by wastewater analysis. Wastewater influent and effluent samples were collected from 69 WWTPs across Australia during the week of the 2016 Australian census. Mean population-weighted per capita loads for individual artificial sweeteners (cyclamate, aspartame, acesulfame, sucralose, saccharin) ranged from 0.12 ± 0.14 mg d^-1p^-1 for aspartame to 6.9 ± 2.8 mg d^-1p^-1 for acesulfame with 1004 kg of these artificial sweeteners being consumed daily in Australia. Significant removal of aspartame (100%), cyclamate (92 ± 18%) and saccharin (88 ± 21%) was observed during wastewater treatment. The average per capita release to the environment for individual artificial sweeteners (cyclamate, acesulfame, sucralose, saccharin) ranged from 230 ± 780 mg d^-1 1000p^-1 (cyclamate) to 3800 ± 1400 mg d^-1 1000p^-1 (sucralose). The daily release of artificial sweeteners from Australian WWTPs was estimated to be 142 kg suggesting that 14% of the artificial sweeteners consumed in Australia are released into the environment. To the best of our knowledge, this is the first wastewater study to estimate the occurrence and population-normalized artificial sweetener consumption and emission in Australia.

Variable persistence of artificial sweeteners during wastewater treatment: Implications for future use as tracers

For more than a decade the artificial sweeteners acesulfame (ACE) and sucralose (SUC) have been applied as tracers of the input of wastewater to environmental waters. Recently concerns have been raised that degradation of ACE during treatment may hinder or restrict its use as a wastewater tracer. In this study the value of ACE and SUC as tracers was reassessed based on samples of wastewater at 12 municipal wastewater treatment (MWWT) plants and from 7 septic systems and associated septic plumes in groundwater. The results indicated stability of SUC during MWWT at most plants, and variable removal of both sweeteners during some MWWT and in the septic wastewater systems. However, the residual concentrations of ACE and SUC in municipal effluent and in septic plumes indicate that both sweeteners remain valuable wastewater tracers. The mass ratio SUC/ACE was found to be a useful parameter for examining the relative persistence of these sweeteners.

Under the radar - Exceptionally high environmental concentrations of the high production volume chemical sulfamic acid in the urban water cycle

Elevated concentrations of sulfamate, the anion of sulfamic acid, were found in surface waters and finished drinking water in Germany with concentrations up to 580 μg/L and 140 μg/L, respectively. Wastewater treatment plant (WWTP) effluent was identified as the dominant source of sulfamate in the urban water cycle, as sulfamate concentrations correlated positively (0.77 > r < 0.99) with concentrations of the wastewater tracer carbamazepine in samples from different waterbodies. Ozonation and activated sludge experiments proved that sulfamate can be formed from chemical and biological degradation of various precursors. Molar sulfamate yields were highly compound-specific and ranged from 2% to 56%. However, the transformation of precursors to sulfamate in WWTPs and wastewater-impacted waterbodies was found to be quantitatively irrelevant, since concentrations of sulfamate in these compartments are already high, presumably due to its primary use as an acidic cleaning agent. Sulfamate concentrations in the influent and effluent of studied WWTPs ranged from 520 μg/L to 1900 μg/L and from 490 μg/L to 1600 μg/L, respectively. Laboratory batch experiments were performed to assess the recalcitrance of sulfamate for chemical oxidation. In combination with the results from sampling conducted at full-scale waterworks, it was shown that common drinking water treatment techniques, including ozonation and filtration with activated carbon, are not capable to remove sulfamate. The results of biodegradation tests and from the analysis of samples taken at four bank filtration sites indicate that sulfamate is attenuated in the sediment/water interface of aquatic systems and during aquifer passage under aerobic and anaerobic conditions. Sulfamate concentrations decreased by between 62% and 99% during aquifer passage at the bank filtration sites. Considering the few data on short term ecotoxicity, about 30% of the presented sulfamate levels in ground and surface water samples did exceed the predicted no-effect concentration (PNEC) of sulfamate, and thus effects of sulfamate on the aquatic ecosystem of wastewater-impacted waterbodies in Germany cannot be excluded so far. Toxicological estimations suggest that no risk to human health is expected by concentrations of sulfamate typically encountered in tap water.

Effect of biodegradation on haloacetic acid formation potentials of anthropogenic compounds during chlorination

During drinking water treatment processes, anthropogenic compounds act as important precursors of disinfection by-products such as haloacetic acids (HAAs). Several transformations in these precursors occur prior to the disinfection stage, such as partial biodegradation. We hypothesized that this partial biodegradation of anthropogenic compounds potentially affects their HAA formation potentials (HAAFPs). In this study, the HAAFPs of 51 anthropogenic compounds after short-term contact (less than 1 h) and long-term contact (24 h) with activated sludge were compared. Considerable changes were observed particularly in trichloroacetic acid (TCAA) formation potentials (FPs) of phenols, demonstrating that biodegradation should be considered in investigations of potential precursors of HAAs. Phenols with low HAAFPs, such as hydroquinone, show higher HAAFPs after biodegradation, but HAAFPs of most phenols and anilines decreased after biodegradation. Thus, biodegradation will most likely have a positive impact on water quality from the standpoint of HAAFP reduction. For most aliphatic compounds, changes in HAAFP were negligible, but the dichloroacetic acid (DCAA) FP of acrylic acid largely increased. This study illustrates that biodegradation may have a large effect on the HAAFPs of anthropogenic compounds.

Artificial Sweeteners in Pig Feed: A Worldwide Survey and Case Study in Pig Farms in Tianjin, China

Some artificial sweeteners (ASs) are used in pig feeds, although little is known on this regard. An investigation was conducted by determining seven common ASs in pig feed, manure, wastewater, compost, and soil from 16 pig farms in Tianjin, China. Saccharin (SAC) was predominant in feed (1.41-326 mg/kg) and manure samples (1.06-401 mg/kg). The annual mass loads of ASs in pig feeds were estimated at 5.69-119, 4.92-149, and 1.29-35 kg per 10³ piglets, hogs, and sows, respectively. The annual emission of ASs via biowaste (i.e., manure) was estimated at 3.58-85.2, 0.04-26.2, and 0.08-9.97 kg per 10³ capita for the three dominant ASs, i.e., SAC, neotame (NEO), and cyclamate (CYC). On a global scale, SAC was also widely detected at concentrations of 0.01-326 mg/kg in pig feed from China, Switzerland, Japan, Chile, and the United States, suggesting the worldwide use of ASs in pig feed. NEO and CYC were found in 41% and 30% of the feed samples, respectively, at concentrations of 0.05-70 mg/kg, whereas other ASs were barely found with rather lower concentrations. The annual mass loads of ASs consumed via pig feed consumption were estimated at 2400 tons worldwide. Thus, pig farming is an important source of ASs to the environment.

Transformations of organic micropollutants undergoing permanganate/bisulfite treatment: Kinetics, pathways and toxicity

Permanganate/bisulfite (PM/BS) is a relatively new advanced oxidation process that can degrade organic micropollutants at extraordinary high rates. In this study, the degradability of PM/BS process towards different representative types of compounds was studied by investigating the kinetics, reaction site specificity and transformation chemistry. Acesulfame (ACE) and carbamazepine (CBZ) were two typical compounds containing olefinic moieties. Sucralose (SUC) was selected as a reference compound, and it is without aromatic and olefinic moieties. The kinetics results indicated that ACE and CBZ were effectively degraded while SUC was not. Preferred reaction sites of Mn³⁺ species was elucidated by identification of the ACE-transformation products (TPs) and CBZ-TPs with UHPLC-QTOF-MS. Seventeen ACE-TPs including two new compounds and eleven CBZ-TPs produced during the PM/BS process were identified and characterized. Transformation pathways revealed that cleavage of olefinic double bonds was the main reaction mechanism. Chemical structures containing electron-donating groups preferentially reacted with electrophilic Mn³⁺ species during the process. In addition, transformation products of ACE and CBZ during PM/BS process did not induce higher toxicity. This study provides a preliminary interpretation on the selectivity of PM/BS process according to the micropollutants' chemical structures, which hope to shed light on the future development of PM/BS treatment.

Removing acesulfame with the peroxone process: Transformation products, pathways and toxicity

Emerging contaminants (ECs) are receiving considerable attention because of their widespread occurrence, persistence and potential threat to the environment, wildlife and humans. Acesulfame (ACE), an extensively used artificial sweetener, is the most worrisome example of ECs. The photolysis/photocatalysis, chlorination and/or permanganate oxidation of ACE produces transformation products (TPs) that are more persistent and toxic than precursors. Thus, an alternative treatment method to treat ACE is required; oxidation by the peroxone process could be that method and was systematically investigated, as reported here. During the peroxone process, ACE degradation followed pseudo-first-order kinetics, with a rate that was significantly higher than after conventional ozonation. The hydroxyl radical was the major reactive species. Amount of hydrogen peroxide (H₂O₂) used, pH and type of water matrix showed significant influence on ACE degradation. Fifteen TPs in ultrapure water extracts, including four newly reported compounds, were identified and characterized by high resolution mass spectrometry (HR-MS) based on accurate mass measurements and MS/MS fragmentation. The reduced toxicity compared to other reported treatments of ACE was likely due to different transformation pathways and TPs generated. The peroxone process therefore appears to be one viable choice for safe removal of ACE.

Evaluation of the effects of three sulfa sweeteners on the lifespan and intestinal fat deposition in C. elegans

High sugar content in beverage or food can affect the aging process, and thus natural/artificial sweeteners are widely used as substitutes. However, whether sweeteners have such adverse effects as sugar remains to be clarified. Therefore, in the current study, three sulfa sweeteners, namely, saccharin sodium salt hydrate (SAC²), sodium cyclamate (CYC³) and acesulfame potassium (AceK⁴) were evaluated for their effects on the lifespan, deposition of lipofuscin, exercise activity, food intake, and intestinal fat deposition (IFD⁵) of Caenorhabditis elegans (C. elegans⁶). It was shown that SAC at 0.3 and 10 mg/mL shortened the lifespan of C. elegans and impaired the exercise capacity, while at other concentrations no significant effects were observed. In contrast, CYC at 0.1, 1 and 10 mg/mL prolonged the lifespan of C. elegans. On the other hand, AceK at 1 mg/mL increased the lifespan of C. elegans, and could decrease both lipofuscin deposition and IFD in a dose-dependent manner. Taken together, these results indicated that although SAC, CYC, and AceK all belong to the sulfa sweeteners, each has distinct effects on different physiological activities associated with aging, at least in C. elegans.

Redox mediators and irradiation improve fenton degradation of acesulfame

Widely recognized as a promising approach to degrading recalcitrant pollutants, Advanced Oxidation Processes (AOPs) have drawn much attention for their effectiveness and efficiency. Among all the AOPs, the Fenton system has been widely applied for oxidation and mineralization of micropollutants due to its ease of implementation and high catalytic efficiency. However, the necessity of preceding acidification, together with rapid consumption and slow regeneration of Fe(II) resulting in deterioration of reactivity, has reduced its competitiveness as a practical option for water treatment. Acknowledging the above drawbacks, this study investigates the potential viable option to enhance the Fenton system. Acesulfame was chosen as the model compound due to its ubiquitous occurrence and persistence in the environment. UV-assisted photo-Fenton treatment was found to remove the parent compound effectively; the transformation profile of acesulfame was identified and elucidated with the ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Prolonged UV photo-Fenton treatment was effective for mineralization of the majority of the transformation products, without increasing the overall toxicity as indicated by Vibrio fischeri bioluminescence assay. The positive effects of the addition of redox mediators to Fenton systems at neutral pH were confirmed in this study. The results could be the basis for further development of homogeneous catalytic degradation techniques for the oxidation of environmental contaminants at circumneutral pHs to neutral pHs.

Transformation of naproxen during the chlorination process: Products identification and quantum chemistry validation

The by-products produced by pharmaceutically active compounds (PhACs) during chlorination are attracting wide concern. Thus, the transformation and toxicity of naproxen (NAP) during the chlorination process were assessed in this study. The transformation of NAP was found to follow pseudo-first-order kinetics, and the first-order rate constant was improved by increasing the NaOCl dose. High-resolution mass spectrometry (HRMS) was successfully applied to identify 14 chlorination products. This study represents the first elucidation and report of the exact structure of the primary chlorine substitution product ((2S)-2-(5-chloro-6-methoxy-2-naphthyl)propionic acid) based on HRMS and ¹H NMR. Chlorine will primarily substitute the hydrogen atom on the C7 position of the naphthalene ring to form the mono-chlorine substitution product, as further validated at the theoretical level by quantum chemical calculations. A series of HOCl-induced reactions, including substitution, demethylation, and dehydrogenation, led to the transformation of NAP during the chlorination process. ECOSAR program revealed that the potential aquatic toxicity of the transformation products is significantly higher than that of the parent NAP. Their introduction into the environment may still pose potential risks.

Photocatalytic Degradation of 4-Nitrophenol by C, N-TiO2: Degradation Efficiency vs. Embryonic Toxicity of the Resulting Compounds

The photocatalytic activity of TiO₂ based photocatalysts can be improved by structural modification and elemental doping. In this study, through rational design, one type of carbon and nitrogen co-doped TiO₂ (C, N-TiO₂) photocatalyst with mesoporous structure was synthesized with improved photocatalytic activity in degrading 4-nitrophenol under simulated sunlight irradiation. The photocatalytic degradation efficiency of the C, N-TiO₂ was much higher than the anatase TiO₂ (A-TiO₂) based on absorbance and HPLC analyses. Moreover, using zebrafish embryos, we showed that the intermediate degradation compounds generated by photocatalytic degradation of 4-nitrophenol had higher toxicity than the parent compound. A repeated degradation process was necessary to render complete degradation and non-toxicity to the zebrafish embryos. Our results demonstrated the importance of evaluating the photocatalytic degradation efficiency in conjunction with the toxicity assessment of the degradation compounds.

Vibrio fischeri bioluminescence inhibition assay for ecotoxicity assessment: A review

Vibrio fischeri bioluminescence inhibition bioassay (VFBIA) has been widely applied for the monitoring of toxicity on account of multiple advantages encompassing shorter test duration, sensitive, cost-effective and ease of operation. Moreover, this bioassay found to be equally applicable to all types of matrices (organic & inorganic compounds, metals, wastewater, river water, sewage sludge, landfill leachate, herbicides, treated wastewater etc.) for toxicity monitoring. This review highlights the apparent significance of Vibrio fischeri bioluminescence inhibition assay for ecotoxicological screening and evaluation of diverse chemical substances toxicity profile. The biochemical and genetic basis of the bioluminescence assay and its regulatory mechanism have been concisely discussed. The basic test protocol with ongoing improvements, widespread applications, typical advantages and probable limitations of the assay have been overviewed. The sensitivity of VFBIA and toxicity bioassays has also been compared.

Elimination of chlorine-refractory carbamazepine by breakpoint chlorination: Reactive species and oxidation byproducts

Breakpoint chlorination can be commonly observed in the chlorination of water treatments when ammonia is present. In this study, it was found that breakpoint chlorination can remarkably eliminate a ubiquitous and chlorine-refractory micropollutant, carbamazepine (CBZ), with the removal of 72% at neutral condition. At neutral pH, low CBZ elimination was observed at a chlorine/ammonia molar ratio (Cl/N) of 1.0 and higher CBZ elimination was observed as Cl/N ratio increased from 1.0 to 1.6 (breakpoint), indicating that CBZ elimination was closely related to the generation and decomposition of chloramines. The chloramines generation and decomposition rates were affected by the pH, so that the CBZ elimination rate was highest at pH 7.0 and lower in acidic and basic solutions (pH 5.5 and pH 9.5, respectively). The CBZ elimination at pH 7.0 was 72.4% after 10 min of breakpoint chlorination, while reaction times about 30 min and 60 min were required to achieve the same elimination at pH 5.5 and pH 9.5, respectively. Breakpoint chlorination of CBZ was strongly suppressed by radical scavenger tBuOH and moderately suppressed by N₂ purging, the inhibiting ratios being 87.7% and 27.8% at breakpoint, respectively. Electron spin resonance experiments suggested that unidentified radicals were generated by breakpoint chlorination. The OH and unidentified radical species contributions to CBZ elimination were <23.7% and >76.3%, respectively, when a pseudo steady state breakpoint chlorination was performed in a microinjection system with nitrobenzene as OH probe. Although CBZ were efficiently eliminated, breakpoint chlorination of CBZ generated adsorbable organic chlorine. The cytotoxicity of the CBZ solution was therefore increased by breakpoint chlorination, suggesting that biological risk caused by the breakpoint chlorination of micropollutants should be taken into consideration.