Sucralose and acesulfame as an indicator of domestic wastewater contamination in Wuhan surface water

Use of micropollutant indicator ratios to characterize wastewater treatment plant efficiency and to identify wastewater impact on groundwater

Contamination by wastewater has been traditionally assessed by measuring faecal coliforms, such as E. coli and entereococci. However, using micropollutants to track wastewater input is gaining interest. In this study, we identified nine micropollutant indicators that could be used to characterize water quality and wastewater treatment efficiency in pond-based wastewater treatment plants (WWTPs) of varying configuration. Of 232 micropollutants tested, nine micropollutants were detected in treated wastewater at concentrations and frequencies suitable to be considered as indicators for treated wastewater. The nine indicators were then classified as stable (carbamazepine, sucralose, benzotriazole, 4+5-methylbenzotriazole), labile (atorvastatin, naproxen, galaxolide) or intermediate/uncertain (gemfibrozil, tris(chloropropyl)phosphate isomers) based on observed removals in the pond-based WWTPs and correlations between micropollutant and dissolved organic carbon removal. The utility of the selected indicators was evaluated by assessing the wastewater quality in different stages of wastewater treatment in three pond-based WWTPs, as well as selected groundwater bores near one WWTP, where treated wastewater was used to irrigate a nearby golf course. Ratios of labile to stable indicators provided insight into the treatment efficiency of different facultative and maturation ponds and highlighted the seasonal variability in treatment efficiency for some pond-based WWTPs. Additionally, indicator ratios of labile to stable indicators identified potential unintended release of untreated wastewater to groundwater, even with the presence of micropollutants in other groundwater bores related to approved reuse of treated wastewater.

Obesogenic potentials of environmental artificial sweeteners with disturbances on both lipid metabolism and neural responses

Artificial sweeteners (ASs) entered the environments after application and emissions. Recent studies showed that some ASs had obesogenic risks. However, it remained unclear whether such risks are common and how they provoke such effects. Presently, the effects of 8 widely used ASs on lipid accumulation were measured in Caenorhabditis elegans. Potential mechanisms were explored with feeding and locomotion behavior, lipid metabolism and neural regulation. Results showed that acesulfame (ACE), aspartame (ASP), saccharin sodium (SOD), sucralose (SUC) and cyclamate (CYC) stimulated lipid accumulation at μg/L levels, showing obesogenic potentials. Behavior investigation showed that ACE, ASP, SOD, SUC and CYC biased more feeding in the energy intake aspect against the locomotion in the energy consumption one. Neotame (NEO), saccharin (SAC) and alitame (ALT) reduced the lipid accumulation without significant obesogenic potentials in the present study. However, all 8 ASs commonly disturbed enzymes (e.g., acetyl-CoA carboxylase) in lipogenesis and those (e.g., carnitine palmitoyl transferase) in lipolysis. In addition, ASs disturbed PPARγ (via expressions of nhr-49), TGF-β/DAF-7 (daf-7) and SREBP (sbp-1) pathways. Moreover, they also interfered neurotransmitters including serotonin (5-HT), dopamine (DA) and acetylcholine (ACh), with influences in Gsα (e.g., via expressions of gsα-1, ser-7), glutamate (e.g., mgl-1), and cGMP-dependent signaling pathways (e.g., egl-4). In summary, environmental ASs commonly disturbed neural regulation connecting behavior and lipid metabolism, and 5 out of 8 showed clear obesogenic potentials. ENVIRONMENTAL IMPLICATION: Artificial sweeteners (ASs) are become emerging pollutants after wide application and continuous emission. Recent studies showed that some environmental ASs had obesogenic risks. The present study employed Caenorhabditis elegans to explore the influences of 8 commonly used ASs on lipid metabolisms and also the underlying mechanisms. Five out of 8 ASs stimulated lipid accumulation at μg/L levels, and they biased energy intake against energy consumption. The other three ASs reduced the lipid accumulation. ASs commonly disturbed lipogenesis and lipolysis via PPARγ, TGF-β and SREBP pathways, and also influenced neurotransmitters with Gsα, glutamate and cGMP-dependent signaling pathways.

Occurrence and Health Risks of Organic Micropollutants in Tap Water in Dalian

Organic micropollutants (OMPs) in tap water may pose risks to human health. Previous studies on the potential health risks of OMPs in tap water may have underestimated the potential health risks of OMPs due to their limited coverage in target pollutants and incomplete toxicity data. In this study, tap water samples were collected in 37 sampling sites in Dalian, China. More than 1,200 target pollutants were screened by combining screening analysis and target analysis. A total of 93 OMPs were detected, with concentration summation ranging from 157 to 1.7 × 104 ng/L among different sampling sites. A total of 17 OMPs (12 agrochemicals, 3 pharmaceuticals and personal care products, and 2 other compounds) were detected in over 80% of the sampling sites. Especially, imidacloprid, tebuconazole, and atrazine-desethyl were found in all the sampling sites. Computational toxicology models were adopted to predict the missing toxicity threshold values of the identified chemicals. Noncarcinogenic risks were estimated to be negligible among all the sampling sites, while carcinogenic risks at six sites were above 10-6 but below 10-4, indicating non-negligible risks. Griseofulvin contributed the most to the carcinogenic risk. This study offers valuable insights that can guide future initiatives to safeguard tap water safety.

Influence of sucralose, acesulfame-k, and their mixture on brain's fish: A study of behavior, oxidative damage, and acetylcholinesterase activity in Daniorerio

Sucralose (SUC) and acesulfame-k (ACE-K) are widely used artificial sweeteners worldwide; however, they are frequently detected in aquatic environments due to their low metabolism and inadequate removal during wastewater treatment. The harmful effects of these compounds on hydrobionts have yet to be fully understood, as data on their toxicity is limited and inconclusive. This research aimed to determine the impact of SUC (50, 75, 125 μg/L) and ACE-K (50, 75, 125 μg/L), individually and in combination, on fish's swimming behavior, acetylcholinesterase activity, and oxidative stress response after four months of exposure. Following exposure, adult Danio rerio displayed anxiety-like behavior, as evidenced by increased freezing time and decreased swimming activity. Additionally, analysis of fish brain tissue revealed a disruption of REDOX homeostasis, leading to oxidative stress, which may be responsible for the observed inhibition of AChE activity. The results indicated that ACE-K was more toxic than SUC, and the mixture of both compounds produced a more detrimental effect than when each compound was administered alone. These findings highlight the hazardous impacts of SUC and ACE-K on fish in environmentally relevant concentrations, suggesting that these compounds should be added to the priority pollutant list.

Understanding common population markers for SARS-CoV-2 RNA normalization in wastewater - A review

Wastewater monitoring and epidemiology have seen renewed interest during the recent COVID-19 pandemic. As a result, there is an increasing need to normalize wastewater-derived viral loads in local populations. Chemical tracers, both exogenous and endogenous compounds, have proven to be more stable and reliable for normalization than biological indicators. However, differing instrumentation and extraction methods can make it difficult to compare results. This review examines current extraction and quantification methods for ten common population indicators: creatinine, coprostanol, nicotine, cotinine, sucralose, acesulfame, androstenedione 5-hydroindoleacetic acid (5-HIAA), caffeine, and 1,7-dimethyluric acid. Some wastewater parameters such as ammonia, total nitrogen, total phosphorus, and daily flowrate were also evaluated. The analytical methods included direct injection, dilute and shoot, liquid/liquid, and solid phase extraction (SPE). Creatine, acesulfame, nicotine, 5-HIAA and androstenedione have been analysed by direct injection into LC-MS; however, most authors prefer to include SPE steps to avoid matrix effects. Both LC-MS and GC-MS have been successfully used to quantify coprostanol in wastewater, and the other selected indicators have been quantified successfully with LC-MS. Acidification to stabilize the sample before freezing to maintain the integrity of samples has been reported to be beneficial. However, there are arguments both for and against working at acidic pHs. Wastewater parameters mentioned earlier are quick and easy to quantify, but the data does not always represent the human population effectively. A preference for population indicators originating solely from humans is apparent. This review summarises methods employed for chemical indicators in wastewater, provides a basis for choosing an appropriate extraction and analysis method, and highlights the utility of accurate chemical tracer data for wastewater-based epidemiology.

Untreated wastewater impact and environmental risk assessment of artificial sweeteners in river water and sediments of the Danube River Basin in Serbia

Artificial sweeteners are receiving increasing attention as newly recognized emerging contaminants that mainly reach the aquatic environment through the discharge of municipal wastewater containing large amount of these compounds. In this study, the impact of raw untreated wastewater discharges on the levels and the water/sediment distribution of artificial sweeteners in the Danube River and its largest tributaries in Serbia was evaluated, and a comprehensive assessment of environmental risks for freshwater and benthic organisms was performed. Acesulfame and sucralose were detected in all river water samples (100%), while saccharin (59%) and cyclamate (12%) were less frequently found, indicating long-term continuous sewage-derived pollution. Aspartame (100%) and neotame (60%) were the only artificial sweeteners recorded in the sediment samples due to their preference to sorb to particulate matter in the water/sediment system. In terms of ecotoxicological risk, a low risk for aquatic organisms was determined at the detected levels of saccharin in river water, while a high to medium risk was found for benthic biota at the concentrations of neotame and aspartame detected in sediments. The largest contribution to the pollution of the Danube River Basin with artificial sweeteners, and consequently the highest environmental risk, was determined in the two largest cities, the capital Belgrade and Novi Sad, which raises the issue of transboundary pollution.

Air quality characteristics during 2016-2020 in Wuhan, China

Implementation of a clean air policy in China has high national importance. Here, we analyzed tempo-spatial characteristics of the concentrations of PM_2.5 (PM_2.5_C), PM₁₀ (PM₁₀_C), SO₂ (SO₂ _C), NO₂ (NO₂ _C), CO (CO _C), and maximum 8-h average O₃ (O₃_8h_C), monitored at 22 stations throughout the mega-city of Wuhan from January 2016 to December 2020, and their correlations with the meteorological and socio-economic factors. PM_2.5_C, PM₁₀_C, SO₂ _C, NO₂ _C, and CO _C showed similar monthly and seasonal trends, with minimum value in summer and maximum value in winter. However, O_{3_}8h_C showed an opposite monthly and seasonal change pattern. In 2020, compared to the other years, the annual average PM_2.5_C, PM₁₀_C, SO₂ _C, NO₂ _C, and CO _C were lower. PM_2.5_C and PM₁₀_C were higher in urban and industrial sites and lower in the control site. The SO₂_C was higher in industrial sites. The NO₂_C was lower, and O_{3_}8h_C was higher in suburban sites, while CO showed no spatial differences in their concentrations. PM_2.5 _C, PM₁₀ _C, SO₂ _C, NO₂ _C, and CO _C had positive correlations with each other, while O_{3_}8h_C showed more complex correlations with the other pollutants. PM_2.5_C, PM₁₀_C, SO₂ _C, and CO _C presented a significantly negative association with temperature and precipitation, while O₃ was significantly positively associated with temperature and negatively associated with relative air humidity. There was no significant correlation between air pollutants and wind speed. Gross domestic product, population, number of automobiles, and energy consumption play an important role in the dynamics of air quality concentrations. These all provided important information for the decision and policy-makers to effectively control the air pollution in Wuhan.

Acesulfame allows the tracing of multiple sources of wastewater and riverbank filtration

Aquifers providing drinking water are increasingly threatened by emerging contaminants due to wastewater inputs from multiple sources. These inputs have to be identified, differentiated, and characterized to allow an accurate risk assessment and thus ensure the safety of drinking water through appropriate management. We hypothesize, that in climates with seasonal temperature variations, the sweetener acesulfame potassium (ACE) provides new pathways to study wastewater inputs to aquifers. Specifically, this study investigates the temperature-driven seasonal oscillation of ACE to assess multiple sources of wastewater inputs at a riverbank filtration site. ACE concentrations in the river water varied from 0.2 to 1 μg L^-1 in the cold season (T < 10 °C) to 0-0.1 μg L^-1 in the warm season (T > 10 °C), due to temperature-dependent biodegradation during wastewater treatment. This oscillating signal could be traced throughout the aquifer over distances up to 3250 m from two different infiltration sources. A transient numerical model of groundwater flow and ACE transport was calibrated over hydraulic heads and ACE concentrations, allowing the accurate calculation of mixing ratios, travel times, and flow-path directions for each of the two infiltration sources. The calculated travel time from the distant infiltration source was of 67 days, while that from the near source was of 20 days. The difference in travel times leads to different potential degradation of contaminants flowing into the aquifer from the river, thus demonstrating the importance of individually assessing the locations of riverbank infiltration. The calibrated ACE transport model allowed calculating transient mixing ratios, which confirmed the impact of river stage and groundwater levels on the mixing ratio of the original groundwater and the bank filtrate. Therefore, continuous monitoring of ACE concentrations can help to optimize the management of the water works with the aim to avoid collection of water with very short travel times, which has important regulative aspects. Our findings demonstrate the suitability of ACE as a transient tracer for identifying multiple sources of wastewater, including riverbank filtration sites affected by wastewater treatment plant effluents. ACE seasonal oscillation tracking thus provides a new tool to be used in climates with pronounced seasonal temperature variations to assess the origins of contamination in aquifers, with time and cost advantages over multi-tracer approaches.

Magnetic Solid-Phase Extraction Based on Silica and Graphene Materials for Sensitive Analysis of Emerging Contaminants in Wastewater with the Aid of UHPLC-Orbitrap-MS

With the advancement of technology and nanotechnology, new extraction sorbents have been created and effectively used for the magnetic solid-phase extraction of target analytes. Some of the investigated sorbents have better chemical and physical properties, exhibiting high extraction efficiency and strong repeatability, combined with low detection and quantification limits. In this study graphene oxide (GO) magnetic composites were prepared and used as magnetic solid-phase extraction (MSPE) adsorbents along with synthesized silica based magnetic nanoparticles (MNPs) functionalized with the C18 group for the preconcentration of emerging contaminants (ECs) in wastewater samples generated from hospital and urban facilities. The sample preparation with magnetic materials was followed by UHPLC-Orbitrap MS analysis for the accurate identification and determination of trace amounts of pharmaceutical active compounds and artificial sweeteners in effluent wastewater. Optimal conditions were used for the extraction of ECs from the aqueous samples, prior to UHPLC-Orbitrap MS determination. The proposed methods achieved low quantitation limits between 1.1-33.6 ng L^-1 and 1.8-98.7 ng L^-1 and satisfactory recoveries in the range of 58.4%-102.6%. An intra-day precision of less than 23.1% was achieved, while inter-day RSD% values in the range of 5.6-24.8% were observed. These figures of merit suggest that our proposed methodology is suitable for the determination of target ECs in aquatic systems.

Seasonal occurrence, removal and mass loads of artificial sweeteners in the largest water reclamation plant in China

Artificial sweeteners (ASs) are of growing concern as an emerging contaminant. In the study, the seasonal occurrence, removal and mass load of six ASs in sewage, suspended particulate matter (SPM) and sludge were investigated throughout the treatment process of the largest water reclamation plant in China. The highest ASs concentrations in the influent (13.0 μg/L), effluent (2.22 μg/L), SPM (4.48 μg/g) and sludge (0.15 μg/g) were observed in the dry season, which were 1.24- to 5.0-fold higher than in the normal season and 1.06- to 37.5-fold higher than the flood season. Following treatment, ASs concentrations decreased by 24.3 %, 51.7 % and 5.1 % (on average) in primary, secondary and reclaimed processes, respectively. Among the investigated ASs, acesulfame (93.1 %) and cyclamate (98.4 %) were removed most efficiently, with removal occurring mainly in secondary processes, while sucralose exhibited the lowest removal efficiency (38.7 %). Seasonal characteristics affect the consumption of ASs, which subsequently changes the input and discharge ASs loads of STPs. The maximum mass load of ASs occurred in the dry season, ranging from 0.002 (neotame) to 1.33 mg/d/person (cyclamate), while the maximum emission load occurred in the flood season, ranging from 0.003 (neotame) to 0.83 mg/d/person (sucralose). The mass and emission load of ASs in Beijing is significantly lower than in European or the United States, due to Beijing having low per capita consumption of ASs (5.50 mg/d/person). The highest ASs risk in the receiving water occurred in the flood season due to the input of other pollution sources by rainfall runoff. Meanwhile, attention should be paid to the risk of receiving water close to the STP outlet in the dry seasons for the highest ASs concentration in the STP effluent in the season. The present study provides important guidance on controlling the input and reducing the emission of ASs in different seasons.

Priority screening of contaminant of emerging concern (CECs) in surface water from drinking water sources in the lower reaches of the Yangtze River based on exposure-activity ratios (EARs)

Surface water provides ecological services such as drinking water supply. However, contaminants of emerging concern (CECs) are rising concerns because they are ubiquitously detected in surface water and pose potential risks to the aquatic environment and human health. This study investigated the occurrence of 165 CECs in surface water from drinking water source areas along the lower reaches of the Yangtze River to prioritize the CECs and to estimate potential biological activity based on exposure-activity ratio (EAR). A total of 70 CECs were detected in the surface water at least once at the selected 17 sampling sites, and their concentrations ranged from 0.592 to 4650 ng/L. Twenty-four CECs were detected at each site, and these were mostly pharmaceutical and personal care products and pesticides. Sucralose, 1H-benzotriazole and carbendazim were the most common CECs with high median concentrations in the study area. Specifically, sucralose, an artificial sweetener, was presented at each site with the highest median concentration (3010 ng/L), which indicated that anthropogenic inputs are an important source of contaminants. Medroxyprogesterone and trenbolone were identified as the priority contaminants of interest, with maximum EAR_chemical values of 0.389 and 0.183, respectively. Among all the sites, the higher cumulative EAR_mixture value was found from Nantong City (0.765), which indicated that this site could have a relatively greater potential for biological effects, and these effects were mainly due to medroxyprogesterone and trenbolone. In regard to the bioactivity of all detected CECs, nuclear receptors showed the greatest potential bioactivity in this region, particularly androgen receptor-mediated bioactivity, which is most likely affected organisms residing in the source water area. These results suggest that the drinking water sources from the studied region are contaminated with CECs, and highlight the prioritization of future monitoring and research to protect source waters.

Acute exposure to environmentally relevant concentrations of sucralose disrupts embryonic development and leads to an oxidative stress response in Danio rerio

Sucralose (SUC) is the most consumed artificial sweetener worldwide, not metabolized by the human body, and barely eliminated from water in wastewater treatment plants. Although different studies have reported high concentrations of this sweetener in aquatic environments, limited to no information is known about the toxic effects this drug may produce over water organisms. Moreover, most of the current studies have used non-environmentally relevant concentrations of SUC for these effects. Herein, we aimed to evaluate the harmful effects that environmentally relevant concentrations of SUC may induce in the early life stages of Danio rerio. According to our results, SUC altered the embryonic development of D. rerio, producing several malformations that led to their death. The major malformations were scoliosis, pericardial edema, yolk deformation, and tail malformation. However, embryos also got craniofacial malformations, eye absence, fin absence, dwarfism, delay of the hatching process, and hypopigmentation. SUC also generated an oxidative stress response in the embryos characterized by an increase in the levels of lipid peroxidation, hydroperoxides, and carbonyl proteins. To overcome this oxidative stress response, we observed a significant increase in the levels of antioxidant enzymes superoxide dismutase and catalase. Moreover, a significant boost in the expression of antioxidant defense-related genes, Nuclear respiratory factor 1a (Nrf1a) and Nuclear respiratory factor 2a (Nrf2a), was also observed at all concentrations. Concerning apoptosis-related genes, we observed the expression of Caspase 3 (CASP3) and Caspase 9 (CASP9) was increased in a concentration-dependent manner. Overall, we conclude environmentally relevant concentrations of SUC are harmful to the early life stages of fish as they produce malformations, oxidative stress, and increased gene expression of apoptosis-related genes on embryos.

What is in Nigerian waters? Target and non-target screening analysis for organic chemicals

Emerging organic contaminants (e.g., active pharmaceutical ingredients and personal care products ingredients) are ubiquitous in the environment and potentially harmful to ecosystems, have gained increasing public attention worldwide. Nevertheless, there is a scarcity of data on these contaminants in Africa. In this study, various types of water samples (wastewater, surface water and tap water) collected from Lagos, Nigeria were analyzed for these chemicals by both target and non-target analysis on an UHPLC-Orbitrap-MS/MS. In total, 109 compounds were identified by non-target screening using the online database mzCloud. Level 1 identification confidence was achieved for 13 compounds for which reference standards were available and level 2 was achieved for the rest. In the quantitative analysis, 18 of 38 target compounds were detected, including the parent compounds and their metabolites. Acetaminophen, sulfamethoxazole, acesulfame, and caffeine were detected in all samples with their highest concentrations at 8000, 5300, 16, and 7700 μg/L in wastewater, 140000, 3300, 7.7, and 12000 μg/L in surface water, and 66, 62, 0.17 and 1000 μg/L in tap water, respectively. The occurrence of psychoactive substances, anticancer treatments, antiretrovirals, antihypertensives, antidiabetics and their metabolites were reported in Nigeria for the first time. These results indicate poor wastewater treatment and management in Nigeria, and provide a preliminary profile of organic contaminants occurring in Nigerian waters. The findings from this study urge more future research on chemical pollution in the aquatic environments in Nigeria.

Anthropogenic impacts on isotopic and geochemical characteristics of urban streams: a case study in Wuhan, China

Urbanization and human activities have significantly modified the geochemical signatures of urban streams worldwide. However, the geochemical characteristics of urban streams in Wuhan, one of the core cities in the Yangtze River Economic Belt in China, remain largely unstudied. Here, we examined the stable isotopes and geochemistry of urban streams at 73 locations in the central districts in Wuhan during May 2019. Maps of isotopic signatures reflected a non-free-flowing state in part of the urban stream system in Wuhan. A lower DO and a higher EC level were found in urban streams relative to the adjacent Yangtze River. The Na⁺, K⁺, and Cl^- concentrations in urban streams were > 3.0 times as high as those in the Yangtze River, and there was a slight increasing trend between 1.1 and 1.4 times for other major ions. The mildly elevated Fe concentration (1.3 times) and markedly elevated Mn concentration (> 5.0 times) were observed in urban streams. Spearman's correlation analysis indicated strong positive bivariate correlations among Na⁺, K⁺, and Cl^- in urban streams, and an urban geochemical principal component was identified by principal component analysis. Plotting Na/(Na + Ca) versus total dissolved solids (TDS) indicated a potential risk of "urban stream syndrome." These findings can enhance the knowledge of anthropogenic impacts on current urban stream water quality and provide reference for the restoration and improvement of water ecology functions of the urban stream system in Wuhan.

Tracking the fate of artificial sweeteners within the coastal waters of Shenzhen city, China: From wastewater treatment plants to sea

Artificial sweeteners (ASs), as a new emerging pollutant, the fate from wastewater treatment plants (WWTPs) to sea is growing concerned. In this study, the distribution and polluted loading of six typical ASs were analyzed based on the measurement in influent, primary effluent, secondary effluent, tertiary effluent, suspended particulate matter (SPM), and sludge from four WWTPs and receiving waters near the coast of Shenzhen city, China. Elevated levels of ASs were detected in WWTPs located near a highly populated area (about 14,000 people km^-2). Sucralose was predominant in all water samples (0.1-22.2 μg L^-1), and had a 1.6-704.0 times higher concentration than the means of other ASs detected. Aspartame were mainly distributed in SPM and sludge, and the fractions in offshore water exceeded 45%. Acesulfame, sucralose, cyclamate and saccharin could be effectively removed by secondary biochemical treatment. The average daily loading (4.2 g d^-1 1000people^-1) and discharge loading (0.4 g d^-1 1000people^-1) of sucralose in WWTPs was higher than those of the other ASs. Dissolved organic carbon and UV₂₅₄ can affect the fate of ASs, and SPM mainly affects the distributions of aspartame and neotame. As a potential sewage indicator, neotame deserves further attention.

Spatial variation of dissolved organic nitrogen in Wuhan surface waters: Correlation with the occurrence of disinfection byproducts during the COVID-19 pandemic

Intensified sanitization practices during the recent coronavirus disease-2019 (COVID-19) led to the release of chlorine-based disinfectants in surface water, potentially triggering the formation of disinfection byproducts (DBPs) in the presence of dissolved organic nitrogen (DON). Thus, a comprehensive investigation of DON's spatial distribution and its association with DBP occurrence in the surface water is urgently needed. In this study, a total of 51 water samples were collected from two rivers and four lakes in May 2020 in Wuhan to explore the regional variation of nitrogen (N) species, DON's compositional characteristics, and the three classes of DBP occurrence. In lakes, 53.0% to 86.3% of N existed as DON, with its concentration varying between 0.3-4.0 mg N/L. In contrast, NO₃^--N was the dominant N species in rivers. Spectral analysis revealed that DON in the lakes contained higher humic and fulvic materials with higher A₂₅₄, A₂₅₃/A_203, SUVA₂₅₄, and P_III+IV/P_I+II+V ratios, while rivers had higher levels of hydrophilic compounds. Trihalomethanes (THMs) were the most prevalent DBPs in the surface waters, followed by N-nitrosamines and haloacetonitriles (HANs). The levels of N-nitrosamines (23.1-97.4 ng/L) increased significantly after the outbreak of the COVID-19 pandemic. Excessive DON in the surface waters was responsible for the formation of N-nitrosamines. This study confirmed that the presence of DON in surface water could result in DBP formation, especially N-nitrosamines, when disinfectants were discharged into surface water during the COVID-19 pandemic.

Sucralose Affects Thyroid Hormone Signaling in American Bullfrog [Rana (Lithobates) catesbeiana] Tadpoles

Nonnutritive sweeteners used in food and beverage products are widespread, persistent aquatic pollutants. Despite this, their impact on aquatic organisms, particularly vertebrates, is not well-studied. Recent findings in rodents suggest sucralose, a chlorinated disaccharide, alters thyroid hormone (TH) metabolism. Because amphibian tadpole metamorphosis is TH-dependent, we hypothesized sucralose may alter signaling for this postembryonic developmental process. The present study used the American bullfrog, Rana (Lithobates) catesbeiana, as a sensitive, environmentally relevant model for testing TH disruption in the absence and presence of thyroxine (T₄), a hormone that induces metamorphosis. Premetamorphic R. catesbeiana tadpoles were immersed in 1-, 15-, and 32-mg/L sucralose solutions ± 5 nM (3.9 µg/L) thyroxine (T₄) for 48 h. RNA transcripts encoding thyroid hormone receptors alpha and beta (thra and thrb) and TH-induced basic region leucine zipper protein (thibz) were analyzed in four tissues: back skin, liver, olfactory epithelium, and tail fin, using reverse transcription quantitative real-time PCR (RT-qPCR). We found that sucralose altered the expression of fundamental TH-response genes involved in anuran metamorphosis in a tissue- and TH-status dependent manner. As organochlorines induce xenobiotic metabolism, we isolated and characterized three novel R. catesbeiana gene transcripts involved in xenobiotic metabolism: pregnane X receptor (nr1i2), constitutive androstane receptor (nr1i3), and cytochrome p450 3a4 (cyp3a4). We analyzed their expression using RT-qPCR and found evidence of their modulation by sucralose. To our knowledge, these data are the first to show xenobiotic and thyroid-disrupting activities in amphibians and further investigations into cumulative effects of environmental sucralose exposure are warranted.

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.