Acesulfame and other artificial sweeteners in a wastewater treatment plant in Alberta, Canada: Occurrence, degradation, and emission

Acesulfame (ACE), sucralose (SUC), cyclamate (CYC), and saccharin (SAC) are widely used artificial sweeteners that undergo negligible metabolism in the human body, and thus ubiquitously exist in wastewater treatment plants (WWTPs). Due to their persistence in WWTPs, ACE and SUC are found in natural waters globally. Wastewater samples were collected from the primary influent, primary effluent, secondary effluent, and final effluent of a WWTP in Alberta, Canada between August 2022 and February 2023, and the artificial sweeteners concentrations were measured by LC-MS/MS. Using wastewater-based epidemiology, the daily per capita consumption of ACE in the studied wastewater treatment plant catchment was estimated to be the highest in the world. Similar to other studies, the removal efficiency in WWTP was high for SAC and CYC, but low or even negative for SUC. However, ACE removal remained surprisingly high (>96%), even in the cold Canadian winter months. This result may indicate a further adaptation of microorganisms capable of biodegrading ACE in WWTP. The estimated per capita discharge into the environment of ACE, CYC, and SAC is low in Alberta due to the prevalent utilization of secondary treatment throughout the province, but is 17.4-18.8 times higher in Canada, since only 70.3% of total discharged wastewater in Canada undergoes secondary treatment.

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.

Taste traces: Capsaicin and sweeteners as anthropogenic markers in municipal wastewater

Dietary-derived substances possess significant potential as anthropogenic markers owing to the large consumption and different intake habit. To investigate and evaluate such markers, wastewater samples from 35 wastewater treatment plants across 29 Chinese cities were collected to analyze artificial sweeteners (acesulfame and cyclamate) and natural spicy compounds (capsaicin and dihydrocapsaicin). Acesulfame (mean: 14.6 μg/L), cyclamate (mean: 24.3 μg/L), and capsaicin (mean: 101 ng/L) can be further investigated as anthropogenic markers due to their high detection frequency at high concentrations. Spatial use patterns revealed that acesulfame (5.31 g/d/1000 inhabitants (inh)) and cyclamate (8.16 g/d/1000 inh) use in northern China notably surpassed that in southern China (1.79 g/d/1000 inh and 3.23 g/d/1000 inh, p < 0.05). Conversely, chili pepper use was significantly higher (p < 0.05) in southern China (6702 g/d/1000 inh) than in northern China (2751 g/d/1000 inh), signifying a preference for sweetness in the northern regions and a predilection for spiciness in the southern regions. The total annual use of acesulfame (1842 t), cyclamate (3110 t), and chili (18.4 million tonnes) in China was estimated by this study, which was close to the national statistical production. In addition, sweetener use was negatively associated with the elderly population ratio, suggesting that the elderly population might not consume sweet foods. This study reveals the dietary sources of anthropogenic markers, highlighting the need for further research on the environmental implications of such markers.

Domesticating aquatic plants in hydroponic systems to demonstrate and advance phytoremediation of the artificial sweetener acesulfame

Artificial sweeteners (ASs) are ubiquitously detected in the global water system, among which acesulfame (ACE) is an emerging contaminant for its chemical and biological stability and unsatisfying removal by conventional or advanced treatment technologies. Phytoremediation is an effective and sustainable in-situ remediation technology that this study is the first to explore ACE removal by aquatic plants. The emergent plants, Scirpus Validus (S. validus), Phyllostachys heteroclada Oliver (P. heteroclada) and Acorus tatarinowii (A. tatarinowii) showed superior removal capability than eleven floating plants, and demonstrated high phytoremediation efficiencies (PEs) of up to 75 % after 28 d domestication. ACE removal by the three emergent plants increased during domestication, as the PEs after 28 d domestication were 5.6-6.5 times of 7 d domestication. Notably, the half-life of ACE was decreased from 20.0 to 33.1 d to 1.1-3.4 d in the plant-hydroponic system, compared with 481.0-1152.4 d in control water without plants. Moreover, A. tatarinowii demonstrated the highest removal capacity for ACE with 0.37 mg/g fresh biomass weight (FW), higher than S. validus (0.27 mg/g FW) and P. heteroclada (0.20 mg/g FW). It is worth noting that a mass balance analysis demonstrated that plant transpiration and plant uptake account for about 6.72 %-18.54 % and 9.69 %-21.67 % ACE removal, while hydrolysis only accounted for about 4 % and photolysis was negligible. The rest ACE may be used as a carbon source by endophytic bacteria and root microorganisms of plants. In addition, increased temperature, pH, and illumination intensity had a significant effect on phytoremediation. In the selected experimental range, the increase of temperature from 15 °C to 35 °C, illumination intensity from 1500 lx to 6000 lx, and pH from 5 to 9 generally accelerated the PEs of ACE during the domestication process. Though the mechanism still requires further investigation, the results provide scientific and feasible data for removal of ACE from water by diverse plants for the first time, and also revealed insights for in-situ treatment of ACE.

Seasonal biodegradation of the artificial sweetener acesulfame enhances its use as a transient wastewater tracer

The persistence of the artificial sweetener acesulfame potassium (ACE) during wastewater treatment and subsequently in the aquatic environment has made it a widely used tracer of wastewater inputs to both surface water and groundwater. However, the recently observed biodegradation of ACE during wastewater treatment has questioned the validity of this application. In this study, we assessed the use of ACE not only as a marker of wastewater, but also as a transient wastewater tracer that allows both the calculation of mixing ratios and travel times through the aquifer as well as the calibration of transient groundwater flow and mass transport models. Our analysis was based on data obtained in a nearly 8-year river water and groundwater sampling campaign along a confirmed wastewater-receiving riverbank filtration site located close to a drinking water supply system. We provide evidence that temperature controls ACE concentration and thus its seasonal oscillation. River water data showed that ACE loads decreased from 1.5-4 mg·s^-1 in the cold season (December to June; T<10 °C) to 0-0.5 mg·s^-1 in the warm season (July to November; T>10 °C). This seasonal variability of >600% was detectable in the aquifer and preserved >3 km, with ACE concentrations oscillating between <LOQ in the warm season up to 1 μg·L^-1 in the cold season. The large seasonal variation in ACE concentrations during wastewater treatment, compared to the other sweeteners (sucralose, cyclamate, and saccharin) and chloride enables its use as a transient tracer of wastewater inflows and riverbank filtration. In addition, the arrival time of the ACE concentration peak can be used to estimate groundwater flow velocity and mixing ratios, thereby demonstrating its potential in the calibration of groundwater numerical models.

Protein fractionation and shotgun proteomics analysis of enriched bacterial cultures shed new light on the enzymatically catalyzed degradation of acesulfame

The removal of organic micropollutants in municipal wastewater treatment is an extensively studied field of research, but the underlying enzymatic processes have only been elucidated to a small extent so far. In order to shed more light on the enzymatic degradation of the artificial sweetener acesulfame (ACE) in this context, we enriched two bacterial taxa which were not yet described to be involved in the degradation of ACE, an unknown Chelatococcus species and Ensifer adhaerens, by incubating activated sludge in chemically defined media containing ACE as sole carbon source. Cell-free lysates were extracted, spiked with ACE and analyzed via target LC-MS/MS, demonstrating for the first time enzymatically catalyzed ACE degradation outside of living cells. Fractionation of the lysate via two-dimensional fast protein liquid chromatography (FPLC) succeeded in a partial separation of the enzymes catalyzing the initial transformation reaction of ACE from those catalyzing the further transformation pathway. Thereby, an accumulation of the intermediate transformation product acetoacetamide-n-sulfonic acid (ANSA) in the ACE-degrading fractions was achieved, providing first quantitative evidence that the cleavage of the sulfuric ester moiety of ACE is the initial transformation step. The metaproteome of the enrichments was analyzed in the FPLC fractions and in the unfractionated lysate, using shotgun proteomics via UHPLC-HRMS/MS and label-free quantification. The comparison of protein abundances in the FPLC fractions to the corresponding ACE degradation rates revealed a metallo-β-lactamase fold metallo-hydrolase as most probable candidate for the enzyme catalyzing the initial transformation from ACE to ANSA. This enzyme was by far the most abundant of all detected proteins and amounted to a relative protein abundance of 91% in the most active fraction after the second fractionation step. Moreover, the analysis of the unfractionated lysate resulted in a list of further proteins possibly involved in the transformation of ACE, most striking a highly abundant amidase likely catalyzing the further transformation of ANSA, and an ABC transporter substrate-binding protein that may be involved in the uptake of ACE into the cell.

Assessing changes in nicotine consumption over two years in a population of Hanoi by wastewater analysis with benchmarking biomarkers

Monitoring the actual change in consumption of nicotine (a proxy for smoking) in the population is essential for formulating tobacco control policies. In recent years, wastewater-based epidemiology (WBE) has been applied as an alternative method to estimate changes in consumption of tobacco and other substances in different communities around the world, with high potential to be used in resource-scarce settings. This study aimed to conduct a WBE analysis in Hanoi, Vietnam, a lower-middle-income-country setting known for high smoking prevalence. Wastewater samples were collected at two sites along a sewage canal in Hanoi during three periods: Period 1 (September 2018), Period 2 (December 2018-January 2019), and Period 3 (December 2019-January 2020). Concentrations of cotinine, 3-hydroxycotinine, and nicotine ranged from 0.73 μg/L to 3.83 μg/L, from 1.09 μg/L to 5.07 μg/L, and from 0.97 μg/L to 9.90 μg/L, respectively. The average mass load of cotinine estimated for our samples was 0.45 ± 0.09 mg/day/person, which corresponds to an estimated daily nicotine consumption of 1.28 ± 0.25 mg/day/person. No weekly trend was detected over the three monitoring periods. We found the amount of nicotine consumption in Period 1 to be significantly lower than in Period 2 and Period 3. Our WBE estimates of smoking prevalence were slightly lower than the survey data. The analysis of benchmarking biomarkers confirmed that cotinine was stable in the samples similar to acesulfame, while paracetamol degraded along the sewer canal. Further refinement of the WBE approach may be required to improve the accuracy of analyzing tobacco consumption in the poor sewage infrastructure setting of Vietnam.

Persulfate-based strategy for promoted acesulfame removal during sludge anaerobic fermentation: Combined chemical and biological effects

The acesulfame (ACE) degradation in waste activated sludge (WAS) via direct anaerobic fermentation is difficult and the efficient elimination techniques are imperative for the ultimate safe WAS disposal. Persulfate (PS)-based approach was developed to promote the ACE removal during WAS anaerobic fermentation. Results demonstrated the effectiveness of PS-based treatments on ACE degradation, and the ACE removal efficiency was respectively 48.2% and 96.2% in the PS and PS/Fe-treated reactors while it was only 6.0% in the control reactor. Mechanism explorations revealed that the active free radicals (i.e. OH• and SO₄^•-) generated in the PS-based reactors were the key oxidative species for the ACE degradation. However, such effects were interfered by the released soluble substrates (i.e. protein, carbohydrate and inorganic ions) during anaerobic fermentation by competing and/or quenching free radicals, which caused the deceleration of the ACE removal efficiency. Moreover, the PS-based treatment facilitated the enrichment of functional microorganisms (i.e. Phyllobacteriaceae and Bradyrhizobiaceae) and upregulated the critical genes (i.e. pncB and nadE) involved in the ACE degradation. Based on the density functional theory (DFT) and metabolic intermediates analysis, the hydroxylation and oxidative ring-opening were the two main proposed metabolic pathways for ACE degradation. Overall, the combined chemical and biological metabolism effects collectively contributed to the efficient ACE degradation, and it provided a novel and effective strategy for refractory pollutants removal during WAS anaerobic fermentation.

Calibration and field validation of POCIS passive samplers for tracking artificial sweeteners as indicators of municipal wastewater contamination in surface waters

Polar organic chemical integrative samplers (POCIS) are widely used to track contaminants in surface waters. However, POCIS have not been used previously to monitor for artificial sweeteners as an indicator of wastewater pollution. In this study, we report for the first time the POCIS sampling rates (Rs_cal) for four artificial sweetener compounds, acesulfame (0.001 L/day), sucralose (0.114 L/day), cyclamate (0.001 L/day), and saccharin (0.002 L/day). We also prepared a modified POCIS with Strata X-AW anion exchange resin as a sorbent (i.e., ax-POCIS) and determined the sampling rates for sucralose (0.060 L/day) and acesulfame (0.128 L/day). Rs_cal values were adjusted according to the rate of loss of the performance reference compound, metoprolol-d₆ from deployed POCIS to yield field sampling rates (i.e., Rs_field). Field validation of the monitoring method was conducted in Presqu'ile Bay on the north-central coast of Lake Ontario that is impacted by discharges from a sewage lagoon. POCIS were deployed at four sites within the bay and in the lagoon discharge. The four artificial sweeteners, as well as caffeine, ibuprofen, and other microcontaminants of sewage origin, were present throughout the bay at estimated concentrations in the ng/L range, and in the lagoon discharge at estimated concentrations higher by approximately one order of magnitude. Because acesulfame is present in ionic form over the pH range of natural waters, there are uncertainties related to the sampling rates using the standard POCIS. Sucralose is recommended as the best choice for source tracking using POCIS. There was good agreement between the concentrations of sucralose estimated from POCIS and the measured concentrations in grab samples of surface water in the bay. The present study provides key data for monitoring artificial sweeteners using POCIS.

Variation in septic system effluent inputs to tributaries in multiple subwatersheds and approaches to distinguish contributing pathways and areas

Quantifying the contribution of septic systems to contaminant, including nutrient, loading to streams is needed in many watersheds to inform water quality management programs. However, this quantification is challenging due to the distributed locations of septic systems and uncertainties regarding the pathways delivering effluent from septic systems (functioning and failing) to a stream. The objectives of this study were firstly to evaluate how septic effluent inputs to streams vary with stream discharge conditions for multiple subwatersheds with different characteristics (i.e., geology, septic system density, and typical age), and secondly to examine new approaches for distinguishing the pathways and the contributing areas delivering septic effluent to streams. These approaches use the artificial sweetener acesulfame as a conservative tracer for septic effluent in applications of: (i) stream concentration-discharge (C-Q) relationships using low frequency sampling data, (ii) hysteresis behavior in event-based C-Q relationships, and (iii) longitudinal stream sampling. For all nine subwatersheds studied, the amount of septic effluent reaching the subwatershed outlets was considerably higher during high stream discharge (event) conditions compared to low discharge (baseflow) conditions, suggesting pathways other than groundwater may also be important. Generally, the percentage of septic effluent reaching the outlets was less for subwatersheds with newer households compared to those with older households. The combined interpretation of low frequency and event-based C-Q relationships indicate that complex pathways control the delivery of septic effluent to the subwatershed outlets. The interpretations suggest that groundwater pathways may dominate in some subwatersheds, while more rapid pathways associated with failing septic systems (e.g., overland runoff) may be important in others. Finally, longitudinal stream sampling illustrate the potential of acesulfame data to identify key areas contributing septic effluent to the stream. The novel approaches used here can be applied to guide future investigations aiming to quantify and manage water quality impairment from septic systems.

Acesulfame aerobic biodegradation by enriched consortia and Chelatococcus spp.: Kinetics, transformation products, and genomic characterization

The artificial sweetener Acesulfame (ACE) has been frequently detected in wastewater treatment plants (WWTPs) and is regarded as an emerging pollutant due to its low biodegradability. However, recent observations of ACE biodegradation in WWTPs have stimulated interest in the ACE-degrading bacteria and mineralization pathways. In this study, next-generation sequencing methods, Illumina and Nanopore sequencing, were combined to explore the ACE-degrading communities enriched from the activated sludge of six municipal wastewater treatment plants. Metagenomic investigations indicated that all enrichments were similarly dominated by the phyla Proteobacteria and Planctomycetes. Notably, at the species level, four metagenome-assembled genomes (MAGs) were shared by six enriched communities with considerable abundances, indicating that they may be responsible for ACE biodegradation in the enrichments. Besides, two ACE-degrading pure strains, affiliated to the genus Chelatococcus, were isolated from the enrichment. The genomic analysis showed that these two isolates were the new species that were genetically distinct from their relatives. Two type strains, Chelatococcus asaccharovorans DSM 6462 and Chelatococcus composti DSM 101465, could not degrade ACE, implying that the ACE-degrading capability was not shared among the different species in the genus Chelatococcus. The results of the degradation experiment showed that the two isolates could use ACE as the sole carbon source and mineralize ~90% of the total organic carbon. Three biotransformation products (TP96, TP180B, and TP182B) were demonstrated by UPLC-QTOF-MS. The results of this study provide valuable insights into ACE biodegradation and its biotransformation products.

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.

Acesulfame as a suitable sewer tracer on groundwater pollution: A case study before and after the 2016 Mw 7.0 Kumamoto earthquakes

On April 14th and 16th, 2016, two large-scale earthquakes (M_w 6.2 and 7.0) occurred in Kumamoto, Japan. The sewer system was seriously damaged and there were concerns about groundwater pollution by sewer exfiltration. In this study, artificial sweeteners including acesulfame (ACE) in groundwater were analyzed before and after the earthquakes to evaluate sewage pollution and its temporal variation. Before the earthquakes, ACE was detected in 31 of 49 groundwater samples analyzed, indicating that wastewater may have leaked into groundwater. Groundwater was sampled from the same locations 2, 7, 12, and 30 months after the earthquakes. The detection frequency and median concentration of ACE in groundwater increased significantly 7 months after the earthquakes, from several tens to maximumly 189 times greater than the pre-earthquake concentrations. This suggests the earthquakes caused serious damage to sewer pipes and groundwater may be polluted. However, ACE concentrations drastically decreased or remained low 30 months after the earthquakes, probably due to the recovery and restoration work of sewer infrastructure. This study shows that ACE is an excellent tracer for evaluating sewer exfiltration to groundwater. In addition, it is important to obtain data on sewage tracers under normal condition as part of preparations for large-scale earthquakes.

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.

Performance of ultraviolet/persulfate process in degrading artificial sweetener acesulfame

The degradation of the artificial sweetener acesulfame (ACE) was investigated using an ultraviolet (UV)₃₆₅-activated peroxydisulfate (PDS) process. The results demonstrated that the ACE reaction rate with the UV/PDS process followed pseudo first-order kinetics (R² > 0.9) under various conditions. A high dosage of PDS, alkaline condition, and the existence of NO₃^- and Cl^- enhanced ACE degradation; however, a high dosage of ACE, the existence of HCO₃^-, humic acid, and fulvic acid, and a real water matrix did not facilitate the degradation of ACE. Four types of transformation products were detected in the degradation of ACE by UV/PDS, and the primary degradation pathways were oxidation, hydroxyl substitution, hydrolysis, and hydration. The hydroxyl radicals played a predominant role (71.31%) in the degradation of ACE by the UV/PDS process, followed by sulfate radicals (14.57%) and UV photolysis (8.83%). Both the degradation and mineralization rates of ACE using the UV/PDS process had significant advantages over that of the UV/H₂O₂ process regarding ACE degradation, indicating that the UV/PDS process is more promising for treating water containing ACE.

Comprehensive investigations about the binding interaction of acesulfame with human serum albumin

In this work, the binding interaction of an artificial sweetener, acesulfame (ACS) with human serum albumin (HSA) are investigated at the molecular level by using spectral methods and molecular modeling. ACS has the ability to induce static quenching of the intrinsic fluorescence of HSA by a complex formed between HSA and ACS through weak multi-noncovalent forces including hydrophobic, hydrogen bond and van der Waals forces. ACS enters subdomain IIA of HSA to induce the tertiary structure changes of HSA and decreased the hydrophobicity of protein. In addition, ACS binding does not obviously alter the secondary structure of HSA. This study is hoped to provide some crucial information for further investigations of the biosafety of sweetener.

Effects of heavy metals released from sediment accelerated by artificial sweeteners and humic acid on a green algae Scenedesmus obliquus

Artificial sweeteners (ASs) are emerging polar organic contaminants, which can chelate with heavy metals in the environment. Recently, the ASs have been widely detected in the aquatic environment. However, little is known about the influence of ASs on the mobility and toxicity of heavy metals associated in sediment. In the present study, the release of heavy metals from a lake sediment and the toxicity to a green algae Scenedesmus obliquus were examined in the presence of two most frequently detected ASs, acesulfame and sucralose, and humic acid (HA), respectively. The existence of 1.00-100 mg/L of acesulfame, sucralose, and HA enhanced the release rates (R_release) of Cd, Cu, and Pb from the virgin lake sediment significantly by up to 46.7%, 86.0%, and 79.9%, respectively. Further, the results from microcosm experiments revealed that the existence of 1.00-10.0 mg/L of acesulfame, sucralose, and HA in the water phase prompted the release and toxicity of heavy metals associated with Cd- and Cu-spiked sediment, and the promotion capacity followed the order of HA > acesulfame > sucralose. The inhibitions on cell-specific growth rate (μ) of the algae were found increasing significantly with the elevated levels of acesulfame and HA (p < 0.05). Additionally, photosynthesis of the algae was affected by the co-existence of ASs or HA and heavy metals released from sediments, as indicated by the changes in fluorescence parameters. The present study provides valuable insight into the likelihood of the combined effect of ASs and heavy metals on aquatic organisms.

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.

Estimating cumulative wastewater treatment plant discharge influences on acesulfame and Escherichia coli in a highly impacted watershed with a fully-integrated modelling approach

Wastewater treatment plant (WWTP) discharge is often considered a principal source of surface water contamination. In this study, a three-dimensional fully-integrated groundwater-surface water model was used to simulate the transport characteristics and cumulative loading of an artificial sweetener (acesulfame) and fecal indicator bacteria (Escherichia coli) from WWTPs within a 6800 km² mixed-use, highly impacted watershed in Ontario, Canada. The model, which employed 3.5 × 10⁶ computational nodes and 15 layers, facilitated a comprehensive assessment of groundwater-surface water interactions under high and low flow conditions; processes typically not accounted for in WWTP cumulative effects models. Simulations demonstrate that the model had significant capacity in reproducing the average and transient multi-year groundwater and surface water flow conditions in the watershed. As a proxy human-specific conservative tracer, acesulfame was useful for model validation and to help inform the representation of watershed-scale transport processes. Using a uniform WWTP acesulfame loading rate of 7.14 mg person^-1 day^-1, the general spatial trends and magnitudes of the acesulfame concentration profile along the main river reach within the watershed were reproduced; however, model performance was improved by tuning individual WWTP loading rates. Although instream dilution and groundwater-surface water interactions were strongly dependent on flow conditions, the main reach primarily consisted of groundwater discharge zones. For this reason, hydrodynamic dispersion in the hyporheic zone is shown as the predominant mechanism driving acesulfame into near-stream shallow groundwater, while under high flow conditions, the simulations demonstrate the potential for advective flushing of the shallow groundwater. Regarding the cumulative impact of the WWTPs on E. coli concentrations in the surface flow system, simulated transient E. coli levels downstream of WWTPs in the watershed were significantly lower than observed values, thus highlighting the potential importance of other sources of E. coli in the watershed.

Approach for analytical characterization and toxicological assessment of ozonation products in drinking water on the example of acesulfame

The monitoring and control of drinking water quality is generally important as it significantly contributes to the health of the population. In this context, particular attention has to be paid to the use of treatment techniques during drinking water treatment. It is known that the formation of reaction products (transformation products) has to be taken into account when oxidizing agents such as ozone are used. Different transformation products are classified as critical to health and require analytical examination. The risk assessment for previously unknown transformation products can be difficult as far as not all transformation products are present as single substances or the individual substances are not present in a sufficient high concentration or cannot be isolated from the original solution. The aim of this work is to show exemplarily the identification and quantification of ozonation products (OPs) after ozonation and their toxicological characterization, using the artificial sweetener acesulfame. It was shown that OPs can be fully characterized using ion chromatography in combination with different detection systems. A major OP could be recovered as a pure substance by crystallization and direct genotoxicological testing was possible without previous enrichment processes. Acesulfame samples of different concentrations in ultrapure and in drinking water after ozonation were tested in several genotoxicity tests. These tests revealed genotoxic effects of acesulfame after ozonation in ultrapure water in several genotoxicological test systems (micronucleus test, umu test, Ames-fluctuation-test and comet assay). In contrast, the crystallized ozonation product OP168 did not show any positive effects. Therefore, it seems likely that the observed effect was caused by the second major product OP170. However, a sufficiently large amount of analytically pure substance OP170 could not be obtained. It was also shown that the rate of the OP170 formation in drinking water is significantly lower than in ultrapure water and that ozonation in drinking water did not induce genotoxic effects.

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.

Detection of artificial sweeteners and iodinated X-ray contrast media in wastewater via LC-MS/MS and their potential use as anthropogenic tracers in flowing waters

The detection of wastewater impact on stream chemistry is often hindered by high background concentrations of ubiquitous solutes. In the present study we tested the applicability of artificial sweeteners (AS) and iodinated X-ray contrast media (ICM) as tracers to detect this impact by examining wastewater treatment plant (WWTP) effluents and surface water samples. The developed direct injection LC-MS/MS method enabled the detection of these anthropogenic micropollutants in aqueous samples down to trace level concentrations. The 2-h-composite sampling of WWTP effluent revealed fluctuating ICM concentrations between and within days with highest concentrations at the end of the week. Diatrizoic acid (DTZ) and iopromide (IOP) were the predominant ICM with concentrations up to 7 μg/L. Concentrations of the AS acesulfame (ACE) fluctuated between 0.5 μg/L and 1 μg/L. Concentrations of AS and ICM in surface water were both associated with wastewater impact. DTZ contamination was more widespread whereas some sampling points exhibited a more pronounced contamination with non-ionic ICM. Surface water was frequently contaminated with AS. Particularly ACE was detected in every surface water sample indicating that it is chemically stable and that inputs to the aquatic environment via WWTP effluents are widespread. The broad application of ACE as food additive enables its application as a tracer throughout Germany. Furthermore, the developed LC-MS/MS method enables rapid detection of ACE down to the low ng/L-range. Nonetheless, DTZ or IOP could be used in addition to ACE to verify anthropogenic influences on natural waters.

Ecotoxicity and environmental fates of newly recognized contaminants-artificial sweeteners: A review

Artificial sweeteners (ASs) are used in countless application in daily life. ASs are newly recognized as pollutants due to their high detection frequency in various environmental media, which has aroused great concern. This review presents the current knowledge of AS ecotoxicity and possible elimination routes in the environment. The obtained results indicate that the negative impacts of ASs are more severe than previously expected. More attention should be paid to the chronic and metabolite toxicities of ASs. Moreover, numerous processes (physical, chemical and biological) have been reported to be able to degrade ASs. However, the elimination efficiency varies greatly depending on the specific AS and the particular experimental conditions. Cyclamate and saccharin are easily removed, while sucralose and acesulfame are generally persistent. Additionally, there is a large gap in the ASs removal efficiency between bench tests and full-scale studies. The potential for microbial degradation of persistent ASs was reported in some regions, but clarification of the underlying mechanisms is necessary to increase the likelihood of using this approach in wide applications with a satisfactory performance.

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.

Characterization of a managed aquifer recharge system using multiple tracers

Knowledge about the residence times of artificially infiltrated water into an aquifer and the resulting flow paths is essential to developing groundwater-management schemes. To obtain this knowledge, a variety of tracers can be used to study residence times and gain information about subsurface processes. Although a variety of tracers exists, their interpretation can differ considerably due to subsurface heterogeneity, underlying assumptions, and sampling and analysis limitations. The current study systematically assesses information gained from seven different tracers during a pumping experiment at a site where drinking water is extracted from an aquifer close to contaminated areas and where groundwater is artificially recharged by infiltrating surface water. We demonstrate that the groundwater residence times estimated using dye and heat tracers are comparable when the thermal retardation for the heat tracer is considered. Furthermore, major ions, acesulfame, and stable isotopes (δ²H and δ¹⁸O) show that mixing of infiltrated water and groundwater coming from the regional flow path occurred and a vertical stratification of the flow system exist. Based on the concentration patterns of dissolved gases (He, Ar, Kr, N₂, and O₂) and chlorinated solvents (e.g., tetrachloroethene), three temporal phases are observed in the ratio between infiltrated water and regional groundwater during the pumping experiment. Variability in this ratio is significantly related to changes in the pumping and infiltration rates. During constant pumping rates, more infiltrated water was extracted, which led to a higher dilution of the regional groundwater. An infiltration interruption caused however, the ratio to change and more regional groundwater is extracted, which led to an increase in all concentrations. The obtained results are discussed for each tracer considered and its strengths and limitations are illustrated. Overall, it is demonstrated that aquifer heterogeneity and various subsurface processes necessitate application of multiple tracers to quantify uncertainty when identifying flow processes.

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

Acesulfame (ACE) is one of the most commonly used artificial sweeteners. Because it is not metabolized in the human gut, it reaches the aquatic environment unchanged. In the present study, the reactivity of ACE in free chlorine-containing water was investigated for the first time. The degradation of ACE was found to follow pseudo-first-order kinetics. The first-order rate increased with decreasing pH from 9.4 to 4.8 with estimated half-lives from 693 min to 2 min. Structural elucidation of the detected transformation products (TPs) was performed by ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry. Integration of MS/MS fragments, isotopic pattern and exact mass allowed the characterization of up to 5 different TPs in the ultrapure water extracts analyzed, including two proposed new chlorinated compounds reported for the first time. Unexpectedly, several known and regulated disinfection by-products (DBPs) were present in the ACE chlorinated solution. In addition, two of the six DBPs are proposed as N-DBPs. Time-course profiles of ACE and the identified by-products in tap water and wastewater samples were followed in order to simulate the actual disinfection process. Tap water did not significantly affect degradation, but wastewater did; it reacted with the ACE to produce several brominated-DBPs. A preliminary assessment of chlorinated mixtures by luminescence inhibition of Vibrio fischeri showed that these by-products were up to 1.8-fold more toxic than the parent compound. The generation of these DBPs, both regulated and not, representing enhanced toxicity, make chlorine disinfection a controversial treatment for ACE. Further efforts are urgently needed to both assess the consequences of current water treatment processes on ACE and to develop new processes that will safely treat ACE. Human health and the health of our aquatic ecosystems are at stake.

Oxidative transformation of artificial sweetener acesulfame by permanganate: Reaction kinetics, transformation products and pathways, and ecotoxicity

Acesulfame has attracted much attention due to its wide application, environmental persistence and potential safety risk of transformation products (TPs). Little information is known on acesulfame transformation in the presence of oxidants/disinfectants. The acesulfame oxidation by permanganate (Mn(VII)) in water under environmentally relevant conditions was systematically evaluated. The pH of water showed negligible influence in acesulfame oxidation. Inorganic ligand (pyrophosphate) exhibited insignificant effect whereas organic ligands (oxalate, ethylene diamine tetraacetic acid, and humic acid) exerted obvious suppression on acesulfame oxidation. Natural organic matter in real water had important influence in acesulfame oxidation by Mn(VII). Acesulfame transformation pathways were initiated by the attack of Mn(VII) on double bond of ring via [3+2] addition electrocyclic reaction and rich electron of N moiety through electrophilic reaction, followed by oxidation and hydrolysis reactions to produce TPs. Among them, five TPs were for the first time identified. The ecotoxicity tests uncover higher toxicity of the TPs than acesulfame itself. The study on oxidative transformation of acesulfame by Mn(VII) would illumine comprehensive evaluation of this emerging contaminant. Water treatment plants need to consider cautiously to protect the safety of downstream system when using Mn(VII) to dispose the water resource containing acesulfame or other artificial sweeteners.

Biodegradation of the artificial sweetener acesulfame in biological wastewater treatment and sandfilters

A considerable removal of the artificial sweetener acesulfame (ACE) was observed during activated sludge processes at 13 wastewater treatment plants (WWTPs) as well as in a full-scale sand filter of a water works. A long-term sampling campaign over a period of almost two years revealed that ACE removal in WWTPs can be highly variable over time. Nitrifying/denitrifying sequencing batch reactors (SBR) as well as aerobic batch experiments with activated sludge and filter sand from a water works confirmed that both activated sludge as well as filter sand can efficiently remove ACE and that the removal can be attributed to biologically mediated degradation processes. The lab results strongly indicated that varying ACE removal in WWTPs is not associated with nitrification processes. Neither an enhancement of the nitrification rate nor the availability of ammonium or the inhibition of ammonium monooxygenase by N-allylthiourea (ATU) affected the degradation. Moreover, ACE was found to be also degradable by activated sludge under denitrifying conditions, while being persistent in the absence of both dissolved oxygen and nitrate. Using ion chromatography coupled with high resolution mass spectrometry, sulfamic acid (SA) was identified as the predominant transformation product (TP). Quantitative analysis of ACE and SA revealed a closed mass balance during the entire test period and confirmed that ACE was quantitatively transformed to SA. Measurements of dissolved organic carbon (DOC) revealed an almost complete removal of the carbon originating from ACE, thereby further confirming that SA is the only relevant final TP in the assumed degradation pathway of ACE. A first analysis of SA in three municipal WWTP revealed similar concentrations in influents and effluents with maximum concentrations of up to 2.3 mg/L. The high concentrations of SA in wastewater are in accordance with the extensive use of SA in acid cleaners, while the degradation of ACE in WWTPs adds only a very small portion of the total load of SA discharged into surface waters. No removal of SA was observed by the biological treatment applied at these WWTPs. Moreover, SA was also stable in the aerobic batch experiments conducted with the filter sand from a water works. Hence, SA might be a more appropriate wastewater tracer than ACE due to its chemical and microbiological persistence, the negligible sorbing affinity (high negative charge density) and its elevated concentrations in WWTP effluents.

Degradation of artificial sweeteners via direct and indirect photochemical reactions

We studied the direct and indirect photochemical reactivity of artificial sweeteners acesulfame, saccharin, cyclamic acid and sucralose in environm entally relevant dilute aqueous solutions. Aqueous solutions of sweeteners were irradiated with simulated solar radiation (>290 nm; 96 and 168 h) or ultraviolet radiation (UVR; up to 24 h) for assessing photochemical reactions in surface waters or in water treatment, respectively. The sweeteners were dissolved in deionised water for examination of direct photochemical reactions. Direct photochemical reactions degraded all sweeteners under UVR but only acesulfame under simulated solar radiation. Acesulfame was degraded over three orders of magnitude faster than the other sweeteners. For examining indirect photochemical reactions, the sweeteners were dissolved in surface waters with indigenous dissolved organic matter or irradiated with aqueous solutions of nitrate (1 mg N/L) and ferric iron (2.8 mg Fe/L) introduced as sensitizers. Iron enhanced the photodegradation rates but nitrate and dissolved organic matter did not. UVR transformed acesulfame into at least three products: iso-acesulfame, hydroxylated acesulfame and hydroxypropanyl sulfate. Photolytic half-life was one year for acesulfame and more than several years for the other sweeteners in surface waters under solar radiation. Our study shows that the photochemical reactivity of commonly used artificial sweeteners is variable: acesulfame may be sensitive to photodegradation in surface waters, while saccharin, cyclamic acid and sucralose degrade very slowly even under the energetic UVR commonly used in water treatment.

Evaluation of polar organic micropollutants as indicators for wastewater-related coastal water quality impairment

Results from coastal water pollution monitoring (Lesvos Island, Greece) are presented. In total, 53 samples were analyzed for 58 polar organic micropollutants such as selected herbicides, biocides, corrosion inhibitors, stimulants, artificial sweeteners, and pharmaceuticals. Main focus is the application of a proposed wastewater indicator quartet (acesulfame, caffeine, valsartan, and valsartan acid) to detect point sources and contamination hot-spots with untreated and treated wastewater. The derived conclusions are compared with the state of knowledge regarding local land use and infrastructure. The artificial sweetener acesulfame and the stimulant caffeine were used as indicators for treated and untreated wastewater, respectively. In case of a contamination with untreated wastewater the concentration ratio of the antihypertensive valsartan and its transformation product valsartan acid was used to further refine the estimation of the residence time of the contamination. The median/maximum concentrations of acesulfame and caffeine were 5.3/178 ng L(-1) and 6.1/522 ng L(-1), respectively. Their detection frequency was 100%. Highest concentrations were detected within the urban area of the capital of the island (Mytilene). The indicator quartet in the gulfs of Gera and Kalloni (two semi-enclosed embayments on the island) demonstrated different concentration patterns. A comparatively higher proportion of untreated wastewater was detected in the gulf of Gera, which is in agreement with data on the wastewater infrastructure. The indicator quality of the micropollutants to detect wastewater was compared with electrical conductivity (EC) data. Due to their anthropogenic nature and low detection limits, the micropollutants are superior to EC regarding both sensitivity and selectivity. The concentrations of atrazine, diuron, and isoproturon did not exceed the annual average of their environmental quality standards (EQS) defined by the European Commission. At two sampling locations irgarol 1051 exceeded its annual average EQS value but not the maximum allowable concentration of 16 ng L(-1).

Photocatalytic transformation of acesulfame: Transformation products identification and embryotoxicity study

Artificial sweeteners have been recognized as emerging contaminants due to their wide application, environmental persistence and ubiquitous occurrence. Among them, acesulfame has attracted much attention. After being discharged into the environment, acesulfame undergoes photolysis naturally. However, acesulfame photodegradation behavior and identity of its transformation products, critical to understanding acesulfame's environmental impact, have not been thoroughly investigated. The present study aimed to fill this knowledge gap by a laboratory simulation study in examining acesulfame transformation products and pathways under UV-C photolysis in the presence of TiO2. Photodegradation products of acesulfame were isolated and analyzed using the LC-IM-QTOF-MS coupled with LC Ion Trap MS in the MS(n) mode. Our results show six new transformation products that have not been previously identified. The molecular structures and transformation pathways were proposed. Further embryotoxicity tests showed that acesulfame transformation products at the low g L(-1) level produced significant adverse effects in tail detachment, heart rate, hatching rate and survival rate during fish embryo development. The identification of additional transformation products with proposed transformation pathways of acesulfame, the increased toxicity of acesulfame after photolysis, and the fact that the accumulation of acesulfame transformation products is increasingly likely make acesulfame contamination even more important. Water resource control agencies need to consider legislation regarding acesulfame and other artificial sweeteners, while further studies are carried out, in order to protect the safety of this most vital resource.

Sources of aminomethylphosphonic acid (AMPA) in urban and rural catchments in Ontario, Canada: Glyphosate or phosphonates in wastewater?

Correlation analysis suggests that occurrences of AMPA in streams of southern Ontario are linked mainly to glyphosate in both urban and rural settings, rather than to wastewater sources, as some previous studies have suggested. For this analysis the artificial sweetener acesulfame was analyzed as a wastewater indicator in surface water samples collected from urban and rural settings in southern Ontario, Canada. This interpretation is supported by the concurrence of seasonal fluctuations of glyphosate and AMPA concentrations. Herbicide applications in larger urban centres and along major transportation corridors appear to be important sources of glyphosate and AMPA in surface water, in addition to uses of this herbicide in rural and mixed use areas. Fluctuations in concentrations of acesulfame and glyphosate residues were found to be related to hydrologic events.

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.

Quantification of four artificial sweeteners in Finnish surface waters with isotope-dilution mass spectrometry

The artificial sweeteners sucralose (SCL), acesulfame (ACS), saccharin (SAC), and cyclamate (CYC) have been detected in environmental waters in Europe and North America. Higher environmental levels are expected in view of the increasing consumption of these food additives. In this study, an isotope-dilution mass spectrometry (IDMS) LC-MS/MS method was developed and validated for quantifying the four artificial sweeteners in boreal lakes (n = 3) and rivers (n = 12). The highest concentrations of ACS, SAC, CYC and SCL were 9,600, 490, 210 and 1000 ng/L, respectively. ACS and SAC were detected in all studied samples, and CYC and SCL in 98% and 56% of the samples. Seasonal trends of ACS and SAC were observed in some rivers. ACS and SCL concentrations in rivers correlated linearly with population equivalents of the wastewater treatment plants in the catchment areas, whereas SAC and CYC concentrations depend more on the source.

Quantification of long-term wastewater fluxes at the surface water/groundwater-interface: an integrative model perspective using stable isotopes and acesulfame

The suitability of acesulfame to trace wastewater-related surface water fluxes from streams into the hyporheic and riparian zones over long-term periods was investigated. The transport behavior of acesulfame was compared with the transport of water stable isotopes (δ(18)O or δ(2)H). A calibrated model based on a joint inversion of temperature, acesulfame, and piezometric pressure heads was employed in a model validation using data sets of acesulfame and water stable isotopes collected over 5months in a stream and groundwater. The spatial distribution of fresh water within the groundwater resulting from surface water infiltration was estimated by computing groundwater ages and compared with the predicted acesulfame plume obtained after 153day simulation time. Both, surface water ratios calculated with a mixing equation from water stable isotopes and simulated acesulfame mass fluxes, were investigated for their ability to estimate the contribution of wastewater-related surface water inflow within groundwater. The results of this study point to limitations for the application of acesulfame to trace surface water-groundwater interactions properly. Acesulfame completely missed the wastewater-related surface water volumes that still remained in the hyporheic zone under stream-gaining conditions. In contrast, under stream-losing conditions, which developed after periods of stagnating hydraulic exchange, acesulfame based predictions lead to an overestimation of the surface water volume of up to 25% in the riparian zone. If slow seepage velocities prevail a proportion of acesulfame might be stored in smaller pores, while when released under fast flowing water conditions it will travel further downstream with the groundwater flow direction. Therefore, under such conditions acesulfame can be a less-ideal tracer in the hyporheic and riparian zones and additional monitoring with other environmental tracers such as water stable isotopes is highly recommended.

Occurrence and fate of the angiotensin II receptor antagonist transformation product valsartan acid in the water cycle--a comparative study with selected β-blockers and the persistent anthropogenic wastewater indicators carbamazepine and acesulfame

The substantial transformation of the angiotensin II receptor antagonist valsartan to the transformation product 2'-(2H-tetrazol-5-yl)-[1,1'-biphenyl]-4-carboxylic acid (referred to as valsartan acid) during the activated sludge process was demonstrated in the literature and confirmed in the here presented study. However, there was a severe lack of knowledge regarding the occurrence and fate of this compound in surface water and its behavior during drinking water treatment. In this work a comparative study on the occurrence and persistency of valsartan acid, three frequently used β-blockers (metoprolol, atenolol, and sotalol), atenolol acid (one significant transformation product of atenolol and metoprolol), and the two widely distributed persistent anthropogenic wastewater indicators carbamazepine and acesulfame in raw sewage, treated wastewater, surface water, groundwater, and tap water is presented. Median concentrations of valsartan acid in the analyzed matrices were 101, 1,310, 69, <1.0, and 65 ng L(-1), respectively. Treated effluents from wastewater treatment plants were confirmed as significant source. Regarding concentration levels of pharmaceutical residues in surface waters valsartan acid was found just as relevant as the analyzed β-blockers and the anticonvulsant carbamazepine. Regarding its persistency in surface waters it was comparable to carbamazepine and acesulfame. Furthermore, removal of valsartan acid during bank filtration was poor, which demonstrated the relevance of this compound for drinking water suppliers. Regarding drinking water treatment (Muelheim Process) the compound was resistant to ozonation but effectively eliminated (≥90%) by subsequent activated carbon filtration. However, without applying activated carbon filtration the compound may enter the drinking water distribution system as it was demonstrated for Berlin tap water.

An artificial sweetener and pharmaceutical compounds as co-tracers of urban wastewater in groundwater

Groundwater in urban areas can be affected by numerous wastewater sources. Distinguishing these sources can facilitate better management of urban water resources and wastewater, and protection of urban aquatic environments. A single wastewater tracer, even if ideal (i.e. low background levels, non-reactive, low detection limits, etc.), would be unable to accomplish this task. Here, we investigated the potential advantages of using a suite of anthropogenic chemicals as co-tracers to distinguish wastewater sources that contribute to groundwater contamination at two urban sites. We considered both relatively ubiquitous and non-ubiquitous tracers in wastewater. At the Jasper (Alberta, Canada) site, concentrations of an artificial sweetener, two pharmaceutical compounds, and a degradate of nicotine in groundwater were strongly correlated as co-tracers. This evidence, along with the similar spatial distributions of these co-tracers could be used to delineate and distinguish a single municipal wastewater plume. At the Barrie (Ontario, Canada) site, there was moderate to strong correlation of the wastewater co-tracers, but local differences in their distributions and in the ratios of their concentrations could be used to infer that mixtures of two or more domestic septic plumes were present in the groundwater at this site. This study demonstrates the benefit of applying a suite of tracers to urban groundwater affected by wastewater contamination. This approach should be applicable at other urban sites.