| Recently, artificial sweeteners (ASs) have become increasingly popular. Globally, these sugar substitutes areconsumed in substantial quantities in food, beverages, pharmaceuticals, personal care products, and even in animal feed. Recent publications indicate that ASs occur widespread in surface waters, groundwater, drinking water, and wastewater treatment plants (WWTPs)in Europe and North America. However, no reports on the occurrence of ASs in China and other Asian countries have been published, where food habits are quite different from those in western countries. Majority of field investigations and laboratory studies on ASs have been concentrated on aquatic environment due to their high water solubility, no information is available regarding on the environmental level of ASs in soil or other media, and little is known regarding their fate under environmentally relevant conditions, which is important for understanding the fate and eco-risk of ASs. Therefore, based on a novel analytical method developed, seven ASs, including acesulfame, sucralose, saccharin, cyclamate, neotame, aspartame, and neohesperidin dihydrochalcone (NHDC), were investigated in Chinese surface water, groundwater, tap water, precipitation, soil, outdoor dust and atmosphere samples. Besides, the fate of the ASs inWWTP and drinking water treatment processes (DWTP) were assessed. Finally, the fate of acesulfame in river water under environmentally relevant conditions was systematically evaluated.Firstly, a highly sensitive method for the simultaneous trace (ng/L) quantification of the seven ASs in a variety of water samples using solid-phase extraction and ion-pair high-performance liquid chromatography (HPLC) triple quadrupole mass spectrometer with an electrospray ionization source in negative ion multiple reaction monitoring mode (ESI-MS) was developed. The composition of the mobile phases and the parameters of the detector were optimized for instrumental analysis. Ten solid phase extraction cartridges were tested to evaluate their applicability for the pre-concentration of the analytes, and their loading and eluting parameters were optimized. Satisfactory recoveries (77-99%) of all of the studied ASs were obtained using a Poly-Sery PWAX cartridge with25mM sodium acetate solution (pH4) as wash buffer and methanol containing1mM tris (hydroxymethyl) amino methane (TRIS) as eluent. The method is sound and does not require pH adjustment or buffering of water samples. The HPLC separation was performed on an Athena C18-WP column with water and acetonitrile, both containing5mM ammonium acetate and1mM TRIS as mobile phases, in gradient elution mode. The method was fully validated and presents good linearity, accuracy and precision. Method quantification limits (MQL) varied between0.4and7.5ng/L for different water samples. The post-extraction spike method was applied to assess matrix effects, and quantification was achieved using internal standard calibration to overcome the unavoidable matrix effects during ESI-MS analysis. The method was applied to the analysis of thirteen water samples from Tianjin, China, including wastewater, tap water, surface water, and groundwater. The method described here is time-saving, accurate and precise, and is suitable for monitoring artificial sweeteners in different water matrices.Based on the novel method developed, the occurrence and removal of the ASs, in WWTPand DWTP were assessed. All of the seven investigated ASs were detected in the influent of WWTP, with concentrations in the range of6.4-31,700ng/L; while acesulfame, sucralose, saccharin and cyclamate were detected in the effluent, with concentrations in the range of32.4-11,200ng/L, which might be a contaminant source for surface water. Acesulfame, sucralose, saccharin, cyclamate, neotame were found in source water of DWTP, with concentrations between<MQL and579ng/L. Acesulfame, sucralose, saccharin and cyclamate were detected in drinking water, with concentrations in the range of23.3-504ng/L. The sedimentation, flocculation, and chlorination in DWTP could not significantly eliminate the investigated ASs. Compared with saccharin, cyclamate, aspartame, neotame, and NHDC, sucralose and acesulfame were proved to be very persistent against microbial degradation, and their elimination rates in WWTP were less than20%.In order to understand the levels of ASs in Chinese aquatic environment, seventy different types of water samples, including wastewaters, tap waters, fresh surface waters, coastal waters, groundwaters, and precipitation samples, from Tianjin, China, were analyzed for the seven ASs. The concentrations of the investigated ASs were generally in the order of WWTP influent> WWTP effluent> surface water> tap water> groundwater≈precipitation, while the composition profiles of ASs varied in different waters. Acesulfame, sucralose, cyclamate, and saccharin were consistently detected in surface waters and ranged from50ng/L to0.12mg/L, while acesulfame was the dominant sweetener in surface and tap waters. Aspartame was found in all of the surface waters at a concentration up to0.21μg/L, but was not found in groundwaters and tap waters. Neotame and NHDC were less frequently detected and the concentrations were low. The concentrations of the ASs in some of the surface waters were of the same order with those in the WWTP influents, but not with the effluents, indicating there are probably untreated discharges into the surface waters. ASs were found in groundwater, but the levels were quite low with a maximum concentration of less than0.10μg/L. Relatively higher concentrations of acesulfame, sucralose, and saccharin were found in the tap water samples. Besides, acesulfame was found persistent to cover long transport distances. The ASs were detected in precipitation samples with high frequency, and acesulfame, saccharin, and cyclamate were the predominant ASs, with concentrations ranging from3.5ng/L to1.3μg/L. The percentage compositions of saccharin, cyclamate, and acesulfame in precipitation samples were similar to particulate phase samples and some of the surface water samples, indicating a similar pollution source. A gross estimation revealed that precipitation may act as a source for saccharin and cyclamate in the surface environment of Tianjin city. Moreover, the presence of ASs in the atmosphere was primarily assessed by taking4air samples to evaluate their potential source in precipitation. Generally,ASs with a high particle-associated fraction, i.e., saccharin, cyclamate, and acesulfame were detected in the precipitation samples at high concentrations. Therefore, we supposed that ASs may enter the atmosphere in a particle-associated form with airborne dust.To give a picture on AS distribution and source in the whole environment, the concentrations and seasonal variations of ASs in atmosphere, soil, and water samplesfrom Tianjin were studied. The AS levels were significantly higher in Haihe river at TJW (a sampling site of central city in Tianjin) in winter, and the lower AS levels in summer at TJW may be ascribed to photo-induced degradation or biodegradation accelerated by higher temperature. No obviously seasonal trends were obtained at BYL (close to a AS factory in Tianjin) and WWTP (in Tianjin), suggesting the input of the ASs to receiving waters were similar between winter and summer. Saccharin, cyclamate, and acesulfame were the dominant ASs in both gas and particulate phase in Tianjin, with concentrations varying from0.02to1940pg/m. Generally, gas phase concentrations of the ASs were relatively higher in summer, while opposite results were acquired for particulate phase. This is due to the influence of temperature on phase distribution. Both the AS factory and WWTP could or may act as atmospheric sources of the ASs in the investigatedarea. Wet and dry deposition fluxes were calculated based on the measured AS levels. The results indicated that both wet and dry deposition could efficiently remove ASs in the atmosphere and act as important pollutant sources for the ASs in surface environment.To clarify whether the ASs occur widespread in soil and atmospheric fall dust, a nationwide investigation on the occurrence of ASs was conducted by collecting98paired outdoor dust and soil samples from mainland China, and the levels of perchlorate in these samples were studied in parallel.Saccharin, cyclamate, and acesulfame were detected in all of Chinese atmospheric dry deposition and soil samples, at concentrations up to1860,6450, and861ng/g, respectively, while the other four ASs were less or not found in the dust or soil samples. No significant difference in the dust AS concentrations was found between Northern and Southern China, nor was for those in the soil.Perchlorate was detected in all of the soil and outdoor dust samples. High levels of perchlorate were found in soil, ranging from0.001to216mg/kg in Northern China and from0.001to25.8mg/kg in Southern China. Even higher perchlorate concentrations were detected in dust samples, with concentrations ranging from0.132to5300mg/kg in Northern China, and from0.270to3700mg/kg in Southern China. The high perchlorate levels in soil and dust may raise concern on the potential risk for organisms and human.Significant correlative relationships were found between the main ASs (saccharin, cyclamate, and acesulfame) and perchlorate in the dust samples, indicating that similar factors, such as population density and economic level, control the release of these two classes of contaminants. However, owing to biodegradation of the ASs in soil, no remarkable relationships were observed between the soil AS and perchlorate concentrations, nor was for those between the dust and soil AS levels.In the final, 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 a pH of4with a rate constant of0.0355d-1in deionized water. No significant decrease in the 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 photo-induced biodegradation was the primary degradation process for acesulfame removal. The near-surface summer half-life of acesulfame in the water from the Haihe River was9d. Both photolysis and photo-induced biodegradation were sensitive to light intensity. Specific experiments revealed the involvement of1O2/3DOM*in acesulfame photolysis, whereas·OH exhibited only a slight contribution due to the scavenging effect of bicarbonate. Ten transformation intermediates (TIs) were identified in the simulated samples under simulated sunlight irradiation based on the mass spectrometry. As indicated by the total organic carbon data, no significant mineralization occurred in either photolysis or photo-induced biodegradation of acesulfame within7d under simulated sunlight irradiation, suggesting the generation of more persistent intermediates. Finally, major TIs were analyzed, and the degradation pathways of acesulfame under environmentally relevant conditions were proposed for the first time. |
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