Occurrence, distribution, and ecological risk of pharmaceuticals in a seasonally ice-sealed river: From ice formation to melting

Migration mechanism of atrazine in the simulated lake icing process at different freezing temperatures based on density function theory

Atrazine causes concern due to its resistant to biodegradation and could be accumulated in aquatic organisms, causing pollution in lakes. This study measured the concentration of atrazine in ice and the water under ice through a simulated icing experiment and calculated the distribution coefficient K to characterize its migration ability in the freezing process. Furthermore, density functional theory (DFT) calculations were employed to expatiate the migration law of atrazine during icing process. According to the results, it could release more energy into the environment when atrazine staying in water phase (-15.077 kcal/mol) than staying in ice phase (-14.388 kcal/mol), therefore it was beneficial for the migration of atrazine from ice to water. This explains that during the freezing process, the concentration of atrazine in the ice was lower than that in the water. Thermodynamic calculations indicated that when the temperature decreases from 268 to 248 K, the internal energy contribution of the compound of atrazine and ice molecule (water cluster) decreases at the same vibrational frequency, resulting in an increase in the free energy difference of the compound from -167.946 to -165.390 kcal/mol. This demonstrated the diminished migratory capacity of atrazine. This study revealed the environmental behavior of atrazine during lake freezing, which was beneficial for the management of atrazine and other pollutants during freezing and environmental protection.

Bromate-induced oxidation of carbamazepine and toxicity assessment of transformation products in the freezing-sunlight process: Effects of trivalent chromium

Bromate ()-induced pharmaceutical and personal care products (PPCPs) oxidation is enhanced in freezing systems. Reduced forms of metals are widely present, often coexisting with various contaminants. However, their effects on the interaction of PPCPs with in ice in cold regions may have been overlooked. Herein we investigated the effects of representative reducing metal Cr(III) on the interaction between the representative PPCP carbamazepine (CBZ) and in the freezing system. Our findings demonstrated that the degradation rate constants of CBZ by and Cr(III) were 29.4%-60.3% lower than those by in ice, revealing the inhibition of Cr(III) on CBZ degradation by in ice. In /freezing/sunlight system, contributed 62.8% to CBZ degradation. In /Cr(III)/freezing/sunlight system, Cr(III) promoted the generation of hydroxyl radical (·OH), leading to 51% contribution of ·OH to CBZ degradation. Oxidants were consumed by Cr(III) to form Cr(VI) rather than reacting with CBZ, thereby decreasing CBZ degradation by in ice. Due to sunlight-induced Cr(VI) reduction in ice, only 0.3% of Cr(III) was converted to Cr(VI) in /Cr(III)/freezing/sunlight system. -induced CBZ degradation rate in ice decreased in order of Fe(II), Cr(III), and Mn(II), which was due to the different reducing capabilities. An effective reduction in comprehensive toxicity of systems followed the freezing-sunlight process, even in the presence of Cr(III). This work sheds new light on the environmental behaviors and fate of PPCPs, brominated disinfection by-products, and reducing metals during seasonal freezing.

Application of RiTiCE in understanding hydro-meteorological controls on ice break-up patterns in River Tornionjoki

The Arctic region experiences significant annual hydrologic events, with the spring flood and ice break-up being the most prominent. River ice break-up, in particular, poses high socioeconomic and ecological expenses, including morphological changes and damage to riverine structures. This study aims to investigate the spatiotemporal patterns of river ice in the River Tornionjoki, including the timing of ice break-up at different latitudes. We utilized observation data and remote sensing techniques to track changes in ice patterns overtime on the River Tornionjoki. The study indicates that the ice break-up in the River Tornionjoki basin typically occurs during Apr-Jun based on the reach location in different latitudes; therefore, different stations behave according to their latitudinal location. We observed significant spatial variations in ice break-up timing across the basin, with an earlier break-up in the lower latitudes compared to the upper latitudes. The average ice break-up day in lower latitude stations ranges between 200-205, while in higher latitude stations the average ice break-up day ranges between 215-228.

Degradation of carbamazepine in ice with bromate and nitrite: Role of reactive nitrogen species

Seasonal freezing of waters occurs during winter in cold regions. Bromate ( [Formula: see text] ) is a disinfection by-product generated during water treatment, its interaction with emerging contaminants may be affected by freezing. Nitrite ( [Formula: see text] ) is widely distributed in the environment, whereas its effect on the interaction of emerging contaminants and [Formula: see text] in ice may have been overlooked. Herein carbamazepine (CBZ) was selected as a model emerging contaminant to elucidate the role of reactive nitrogen species (RNS) in contaminant transformation during the reduction of [Formula: see text] by [Formula: see text] in ice. Results indicated that freezing significantly enhanced CBZ degradation by [Formula: see text] . The CBZ degradation by [Formula: see text] and [Formula: see text] in ice was 25.4 %-27.8 % higher than that by [Formula: see text] . Contributions of hydroxyl radical (•OH), bromine radical (•Br), and RNS to CBZ degradation in freezing/dark or sunlight systems were 8.1 % or 15.9 %, 25.4 % or 7.2 %, and 66.5 % or 76.9 %, respectively. Most CBZ was degraded by RNS generated during the reduction of [Formula: see text] by [Formula: see text] in ice, resulting in 16.4 % of transformation products being nitro-containing byproducts. Hybrid toxicity of CBZ/ [Formula: see text] / [Formula: see text] system was reduced effectively after the freezing-sunlight process. This study can provide new insights into the environmental fate of emerging contaminants, [Formula: see text] , and [Formula: see text] in cold regions.

Comparing the photodegradation of typical antibiotics in ice and in water: Degradation kinetics, mechanisms, and effects of dissolved substances

New antibiotic contaminants have been detected in both surface waters and natural ice across cold regions. However, few studies have revealed distinctions between their ice and aqueous photochemistry. In this study, the photodegradation and effects of the main dissolved substances on the photolytic kinetics were investigated for sulfonamides (SAs) and fluoroquinolones (FQs) in ice/water under simulated sunlight. The results showed that the photolysis of sulfamethizole (SMT), sulfachloropyridazine (SCP), enrofloxacin (ENR) and difloxacin (DIF) in ice/water followed the pseudo-first-order kinetics with their quantum yields ranging from 4.93 × 10-3 to 11.15 × 10-2. The individual antibiotics experienced disparate photodegradation rates in ice and in water. This divergence was attributed to the concentration-enhancing effect and the solvent cage effect that occurred in the freezing process. Moreover, the main constituents (Cl-, HASS, NO3- and Fe(III)) exhibited varying degrees of promotion or inhibition on the photodegradation of SAs and FQs in the two phases (p < 0.05), and these effects were dependent on the individual antibiotics and the matrix. Extrapolation of the laboratory data to the field conditions provided a reasonable estimate of environmental photolytic half-lives (t1/2,E) during midsummer and midwinter in cold regions. The estimated t1/2,E values ranged from 0.02 h for ENR to 14 h for SCP, which depended on the reaction phases, latitudes and seasons. These results revealed the similarities and differences between the ice and aqueous photochemistry of antibiotics, which is important for the accurate assessment of the fate and risk of these new pollutants in cold environments.

Assessing the ecotoxicity of florfenicol exposure at environmental levels: A case study of histology, apoptosis and microbiota in hepatopancreas of Eriocheir sinensis

The intensification of production practices in the aquaculture industry has led to the indiscriminate use of antibiotics to combat diseases and reduce costs, which has resulted in environmental pollution, posing serious threats to aquaculture sustainability and food safety. However, the toxic effect of florfenicol (FF) exposure on the hepatopancreas of crustaceans remains unclear. Herein, by employing Chinese mitten crab (Eriocheir sinensis) as subjects to investigate the toxic effects on histopathology, oxidative stress, apoptosis and microbiota of hepatopancreas under environment-relevant (0.5 and 5 μg/L), and extreme concentrations (50 μg/L) of FF. Our results revealed that the damage of hepatopancreas tissue structure caused by FF exposure in a dose-and time-dependent manner. Combined with the increased expression of apoptosis-related genes (Caspase 3, Caspase 8, p53, Bax and Bcl-2) at mRNA and protein levels, activation of catalase (CAT) and superoxide dismutase (SOD), and malondialdehyde (MDA) accumulation, FF exposure also induced oxidative stress, and apoptosis in hepatopancreas. Interestingly, 7 days exposure triggered more pronounced toxic effect in crabs than 14 days under environment-relevant FF concentration. Integrated biomarker response version 2 (IBRv2) index indicated that 14 days FF exposure under extreme concentration has serious toxicity effect on crabs. Furthermore, 14 days exposure to FF changed the diversity and composition of hepatopancreas microbiota leading remarkable increase of pathogenic microorganism Spirochaetes following exposure to 50 μg/L of FF. Taken together, our study explained potential mechanism of FF toxicity on hepatopancreas of crustaceans, and provided a reference for the concentration of FF to be used in culture of Chinese mitten crab.

Photodegradation for different dissociated species of norfloxacin and ofloxacin in water ice under solar irradiation

Ice is an important medium that regulates the transformation of organic contaminants. Nonetheless, photodegradation of emerging fluoroquinolone (FQ) antibiotics in the ice, particularly those with varying dissociated species, remains inadequately explored. In this study, the photodegradation of norfloxacin (NOR) and ofloxacin (OFL) in different dissociated species in water ice were investigated. Results indicated that the quantum yield of the zwitterion for NOR in the ice was 1.7-5.0 times higher than that of the cation, and 1.3 times higher than that of the anion. The quantum yield of the zwitterion for OFL in the ice was 2.5-3.4 times higher than that of the cation, and 1.4 times higher than that of the anion. The degradation pathways of NOR and OFL with different dissociated species depended on their molecular structure. Most products possessed lower developmental toxicity than parent NOR and OFL, respectively. OFL showed a higher inhibitory rate of Escherichia coli activity at the initial time of photodegradation, which was higher than that of NOR. This study offers novel insights into the impact of dissociated species on the photodegradation of FQs in ice and contributes to understanding the environmental behavior of fluorinated pharmaceuticals in the cryosphere.

Spatiotemporal variability and environmental effects of greenhouse gases, nutrients, and dissolved carbons in an ice-covered reservoir

Ice cover restructures the distribution of substances in ice and underlying water and poses non-negligible environmental effects. This study aimed to clarify the spatiotemporal variability and environmental effects of methane (CH4), nitrous oxide (N2O), total nitrogen (TN), total phosphorus (TP), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) in ice and water columns during different ice-covered periods. We surveyed the ice-growth, ice-stability, and ice-melt periods in an ice-covered reservoir located in Northeast China. The results showed that underlying water (CH4: 1218.9 ± 2678.9 nmol L-1 and N2O: 19.3 ± 7.3 nmol L-1) and ice (CH4: 535.2 ± 2373.1 nmol L-1 and N2O: 9.9 ± 1.5 nmol L-1) were sources of atmospheric greenhouse gases. N2O concentrations were the highest in the bottom water of the reservoir while CH4 accumulated the most below the ice in the riverine zone. These can be attributed to differences in the solubilities and relative molecular masses of the two gases. Higher concentrations of N2O, TN, TP, DOC, and DIC were recorded in the underlying water than those in the ice due to the preferential redistribution of these substances in the aqueous phase during ice formation. Additionally, we distinguished between bubble and no-bubble areas in the riverine zone and found that the higher CH4 concentrations in the underlying water than those in the ice were due to CH4 bubbles. In addition, we reviewed various substances in ice-water systems and found that the substances in ice-water systems can be divided into solute exclusion and particle entrapment, which are attributed to differences between dissolved and particulate states. These findings are important for a comprehensive understanding of substances dynamics during ice-covered periods.

Selection of priority emerging contaminants in surface waters of India, Pakistan, Bangladesh, and Sri Lanka

The challenge of emerging contaminants (ECs) in global surface water bodies and particularly in low- and middle-income countries such as India, Pakistan, Bangladesh, and Sri Lanka, is evident from the literature. The complexity arises from the high costs involved in EC analysis and the extensive list of ECs, which complicates the selection of essential compounds for scientific and regulatory investigations. Consequently, monitoring programs often include ECs that may have minimal significance within a region and do not pose known or suspected ecological or human health risks. This study aims to address this issue by employing a multi-risk assessment approach to identify priority ECs in the surface waters of the aforementioned countries. Through an analysis of occurrence levels and frequency data gathered from published literature, an optimized risk quotient (RQ) was derived. The findings reveal a priority list of 38 compounds that exhibit potential environmental risks and merit consideration in future water quality monitoring programs. Furthermore, the majority of antibiotics in India (12 out of 17) and Pakistan (7 out of 17) exhibit a risk quotient for antimicrobial resistance selection (RQAMR) greater than 1, highlighting the need for devising effective strategies to mitigate the escalation of antibiotic resistance in the environment.

Freezing degradation of the anticonvulsant oxcarbazepine by bromate in water ice under sunlight irradiation

Ice plays a crucial role in contaminant transformation in seasonally ice-covered waters. In this study, the characteristics and mechanisms of an emerging contaminant oxcarbazepine (OXC) degradation by a disinfection by-product bromate ( [Formula: see text] ) in ice were explored via combined experiments and theoretical calculations. Results showed that 74.0 % and 86.4 % of OXC was degraded by [Formula: see text] in ice after 140 min in dark and 120 min under solar irradiation, respectively, while the reaction was negligible in water. The oxidation-reduction potential of [Formula: see text] solution at 1000 μmol L-1 was 56.9 % higher than that at 50 μmol L-1. The oxidation-reduction potential of [Formula: see text] solution at pH 2 was 14.8 %-109.5 % higher than those at other pH values. Enhanced OXC degradation by [Formula: see text] in ice could be attributed to increased [Formula: see text] oxidation capacity resulting from locally elevated [Formula: see text] and H+ concentrations. Hypobromous acid (HOBr), •OH, and Br• generated by direct photolysis under solar irradiation further promoted the OXC degradation in ice. Br• formed by the direct photolysis of accumulated HOBr under solar irradiation caused the generation of bromine-containing degradation products. Bromine-containing degradation products possessed higher potential toxicities, which could contribute to increase the secondary pollution of water environment.

Occurrence, distribution, and potential ecological risks of antibiotics in a seasonal freeze-thaw basin

Antibiotics have gained increasing attention as pharmaceuticals widely existing in human society. Under low temperature conditions, antibiotics tend to have higher environmental persistence, which poses a potential threat to ecological environment, but research on antibiotics in low-temperature basins is still lacking. Therefore, for investigating occurrence, spatio-temporal distributions, and ecological risks of antibiotics in a seasonal freeze-thaw basin, rivers in Tumen River basin were selected and sampled, including 25 samples during the river-freezing season and 27 samples during the non-freezing season. Overall, climate characteristics of different latitudes and renewal frequency of antibiotics are important factors that lead to diversity of antibiotics in basins. Eleven target antibiotics were detected and their average concentrations during the river-freezing season (0.83-27.5 ng L-1) were lower than that during the non-freezing season (2.80-45.30 ng L-1), severely impacted by river flow, ice sealed-melting, and local feeding practices. In addition, total antibiotic concentrations are usually highest in downstream areas of human settlements, receiving input from husbandry and sewage, respectively. Through ecological risk assessment, norfloxacin and amoxicillin posed high risks to algae, which were identified as high-risk pollutants in basin.

Coupled multimedia fate and bioaccumulation models for predicting fate of florfenicol and fluoroquinolones in water and fish organs in the seasonal ice-sealed reservoir

Ice formation in reservoirs could promote the accumulation of antibiotics in fish, potentially leading to elevated concentrations in fish muscles, kidneys, and livers. However, for the seasonal ice-sealed reservoirs, antibiotic sampling and detecting conditions in water and fish are normally limited by the ice cover. Additionally, previous studies on the prediction of antibiotics accumulated in seasonal ice-sealed reservoir fish are scarce. This study presents a coupled model incorporating a multimedia fate model and a bioaccumulation model to predict antibiotic fate in water and the muscles, kidneys, and livers of fish in seasonal ice-sealed reservoirs. Prediction concentrations of florfenicol were higher than those of ofloxacin and norfloxacin in both water and fish from the seasonal ice-sealed reservoir. Log bioaccumulation factors of antibiotics in Cyprinus carpio and Hypophthalmichthys nobilis in January 2021 were higher than those in October 2020 by 21.5% and 12.6%, respectively. Antibiotics mean transfer fluxes from water to fish muscles, kidneys, and livers increased owing to the reservoir ice-cover formation date advancing by 13.0%, 77.1%, and 61.0%, respectively. This work provides a modeling tool for investigating the fate and mass transfer flux of antibiotics in biological and environmental phases in seasonal ice-sealed reservoirs.

Co single atoms anchored on straw biochar as an efficient peroxydisulfate activator for ultrafast removal of antibiotics

The removal efficiency of antibiotics decreases at low temperature, which is an urgent problem to be solved in cold regions. This study prepared a low-cost single atom catalyst (SAC) from straw biochar, which can rapidly degrade antibiotics at different temperatures by activating peroxydisulfate (PDS). Co SA/CN-900 + PDS system can degrade 100% of tetracycline hydrochloride (TCH, 10 mg/L) in 6 min. The high concentration of TCH (25 mg/L) was degraded by 96.3% in 10 min at 4 °C. The system was also tested in simulated wastewater and showed a good removal efficiency. TCH was primarily degraded by 1O2 and direct electron transfer pathway. Electrochemical experiments and density functional theory (DFT) calculations showed that CoN4 improved the electron transfer capacity of biochar and thus enhanced the oxidation capacity of Co SA/CN-900 + PDS complex. This work optimizes the application of agricultural waste biochar and provides a design strategy of efficient heterogenous Co SACs to degrade antibiotics in cold regions.

Enhanced freezing-induced carbamazepine degradation by bromate under solar irradiation via the formation of hypobromous acid and hydroxyl radical

Ice is a crucial medium in cold regions and plays an important role in the transformation of pollutants. When waters receiving treated wastewater freeze in cold regions during winter, the emerging contaminant carbamazepine (CBZ) and the disinfection by-product bromate ( [Formula: see text] ) can coexist in ice. However, their interaction in ice remains poorly understood. Here, CBZ degradation by [Formula: see text] in ice was investigated via a simulation experiment. Results showed that 96% of CBZ was degraded by [Formula: see text] after 90 min in ice in dark, while the degradation was negligible in water. The time required for nearly 100% CBZ degradation by [Formula: see text] in ice under solar irradiation was 22.2% shorter than in dark. The production of hypobromous acid (HOBr) was responsible for the gradually accelerated CBZ degradation rate in ice. The HOBr generation time in ice under solar irradiation was 50% shorter than in dark. The formation of HOBr and hydroxyl radical by the direct photolysis of [Formula: see text] under solar irradiation enhanced the CBZ degradation in ice. CBZ was mainly degraded by deamidation, decarbonylation, decarboxylation, hydroxylation, molecular rearrangement, and oxidation reactions. Furthermore, 18.5% of degradation products exhibited lower toxicity than their parent CBZ. This work can provide new insights into the environmental behaviors and fate of emerging contaminants in cold regions.

Optimizing the multimedia fate model for characterizing environmental risks of florfenicol in seasonally ice-covered reservoirs

Seasonally ice-covered reservoirs have both freeze-thaw and artificial regulation characteristics which could cause the accumulation of antibiotics. Florfenicol, one of the most widely used veterinary antibiotics, with an environmental persistence due to its fluorinated substituents has been detected in the suburban drinking water source reservoirs. In this study, a four-level fugacity model that is appropriate for ice-water-sediment systems was developed to predict the fate of florfenicol and assess its ecological risk in seasonally ice-covered reservoirs. The effects of freeze-thaw and artificial regulation processes on the volume variation of ice and water were considered by the model. The simulation accuracies in ice and water in the model were improved by 3.9% and 17.7%, respectively, compared with the traditional model. The results of mass transfer analysis showed that the inflow of florfenicol in tributaries and the volume variation of ice and water were the major factors influencing the concentration variation of florfenicol in the seasonally ice-covered reservoir. Additionally, ecological risk analysis showed that the values of risk quotients ranged from 0.019 to 0.038 which was consistently at a low ecological risk level. Our findings provide a modeling tool for predicting the fate of antibiotics with persistence and assessing their ecological risks in seasonally freeze-thaw reservoirs in cold regions.

A comprehensive study of the source, occurrence, and spatio-seasonal dynamics of 12 target antibiotics and their potential risks in a cold semi-arid catchment

Antibiotics are widely consumed and are ubiquitous in aquatic ecosystems, such as in agricultural and fishery lake catchments, for prophylactic treatment. However, there are very few comprehensive studies reporting all seasonal occurrences, spatiotemporal dynamics, and risk assessments of antibiotics in agricultural lake catchments, especially in cold regions during the winter season. This study measured seasonality in the concentrations of 12 antibiotics belonging to seven different classes in the surface waters (tributary rivers and lakes) of the Chagan lake catchment in northeast China. All antibiotics were detected in most of the water samples across most seasons, with concentrations varying for different compounds, locations, and seasons. These levels were discussed in terms of the main sources at different sampling sites, including agriculture, fish farming, municipal wastewater, and others. In general, the highest concentrations of most compounds were observed during the freeze-thaw periods. The number of antibiotic resistance genes (ARGs) correlated with compound lipophilicity and half-life. Based on the ecological risks of antibiotics and the relative abundance of ARGs, a hierarchical control priority list (HCPL) of antibiotics was determined, considering four levels (critical, high, medium, and low). To further strengthen the control and effectively manage antibiotics, we highly recommend the reduction and selective use of veterinary antibiotics in winter and spring during the freeze-thaw periods in the Chagan lake catchment.

Antibiotics in a seasonal ice-sealed reservoir: Occurrence, temporal variation, prioritization, and source apportionment

Antibiotics are prevalent in the aquatic environment as emerging contaminants. Their knowledge of seasonal ice-sealed reservoirs, however, is limited. The occurrence, temporal variation, and prioritization of twenty-three antibiotics in Shitoukoumen Reservoir during its ice-free and ice-sealed periods, as well as the source apportionment of the high-priority antibiotics, were investigated in this study. The results showed that florfenicol was the dominant antibiotic in Shitoukoumen Reservoir, with different median concentrations of 75.0 ± 6.5 ng L^-1 and 7.0 ± 1.7 ng kg^-1 in the water and ice, respectively. The concentrations of florfenicol, sulfaguanidine, and sulfamonomethoxine in the water of the reservoir water varied over time, but their monthly mass loads from inflow rivers were similar during ice-free and ice-sealed periods. This indicated that other factors, such as aquacultural practice, non-point source rain runoff, and the blocking effect of ice, determined the temporal variations of the three antibiotics and resulted in their relatively high concentrations during the ice-free period. High-priority antibiotics included erythromycin, florfenicol, ofloxacin, sarafloxacin, sulfaquinoxaline, thiamphenicol, and tylosin. Aquaculture was the primary source of high-priority antibiotics, accounting for 67.3 % and 59.4 % of the total high-priority antibiotic concentrations during ice-free and ice-sealed periods, respectively. The findings suggest that aquaculture, rain runoff, and ice blocking should all be considered as factors influencing antibiotic variations in a seasonal ice-sealed reservoir.

Distribution of florfenicol and norfloxacin in ice during water freezing process: Dual effects by fluorine substituents

Distribution in ice is regarded as one of important transport modes for pollutants in seasonal freeze-up waters in cold regions. However, the distribution characteristics and mechanisms of fluorinated antibiotics as emerging contaminants during the water freezing process remain unclear. Here, florfenicol and norfloxacin were selected as model fluorinated antibiotics to investigate their ice-water distribution. Effects of antibiotic molecular structure on the distribution were explored through comparative studies with their non-fluorinated structural analogs. Results showed that phase changes during the ice growth process redistributed the antibiotics, with antibiotic concentrations in water 3.0-6.4 times higher than those in ice. The solute-rich boundary layer with a concentration gradient was presented at the ice-water interface and controlled by constitutional supercooling during the freezing process. The ice-water distribution coefficient (K_IW) values of antibiotics increased by 34.8%-38.0% with a doubling of the cooling area. The solute distribution coefficient (K_bs) values of antibiotics at -20 °C were 65.6%-70.3% higher than at -10 °C. The K_IW and K_bs values of all antibiotics were negatively correlated with their water solubilities. The fluorine substituents influenced the binding energies between antibiotics and ice, resulting in a 1.1-fold increase in the binding energy of norfloxacin on the ice surface relative to its structural analog pipemidic acid. The results provide a new insight into the transport behaviors of fluorinated pharmaceuticals in ice-water systems.

The Migration Pattern of Atrazine during the Processes of Water Freezing and Thawing

Atrazine, one of the most commonly used herbicides in the world, is of concern because of its frequent occurrence in various water bodies and the potential threat it constitutes to ecosystems. The transport of contaminants in seasonally ice-covered lakes is an important factor affecting the under-ice water environment, and changes in phase during ice growth and melting cause redistribution of atrazine between ice and water phases. To explore the migration pattern of atrazine during freezing and thawing, laboratory simulation experiments involving freezing and thawing were carried out. The effects of ice thickness, freezing temperature, and initial concentration on the migration ability of atrazine during freezing were investigated. The results showed that the relationship between the concentration of atrazine in ice and water during freezing was ice layer < water before freezing < water layer under the ice. Atrazine tended to migrate to under-ice water during the freezing process, and the intensity of migration was positively correlated with the ice thickness, freezing temperature, and initial concentration. During the thawing phase, atrazine trapped in the ice was released into the water in large quantities in the early stages. The first 20% of meltwater concentration was significantly higher than the average concentration in ice, with the highest case being 2.75 times the average concentration in ice. The results reported in this study are a useful reference for planning possible pollution control measures on such lakes during their freeze-thaw process.

Derivation of Water Quality Criteria for Carbamazepine and Ecological Risk Assessment in the Nansi Lake Basin

Carbamazepine, as one of several pharmaceutical and personal care products, has gained much attention in recent years because of its continuous discharge in natural waters and toxicity to aquatic ecosystems. However, it is difficult to evaluate and manage carbamazepine pollution because of the lack of a rational and scientific Water Quality Criteria (WQC) of carbamazepine. In this study, the carbamazepine toxicity data of thirty-five aquatic species from eight taxonomic groups were selected, and the species sensitivity distribution (SSD) method was applied to derive the WQC for carbamazepine based on the Log-logistic model, which was 18.4 ng/L. Meanwhile, the occurrence and distribution of carbamazepine in the Nansi Lake basin was studied. Results showed that concentrations of carbamazepine in 29 sampling sites were in the range of 3.3 to 128.2 ng/L, with the mean of 17.3 ng/L. In general, the levels of carbamazepine in tributaries were higher than those in the lakes. In addition, qualitative and quantitative ecological risk assessment methods were applied to assess the adverse effect of carbamazepine on aquatic systems. The hazard quotient (HQ) method showed that there were 24 and 5 sampling sites, in which risk levels were low and moderate, respectively. The joint probability curve (JPC) method indicated that ecological risks might exist in 1.4% and 1.0% of surface water, while a 5% threshold and 1% threshold were set up to protect aquatic species, respectively. Generally, carbamazepine posed a low risk to the aquatic organisms in the Nansi Lake basin.

Effect of fulvic acid concentration levels on the cleavage of piperazinyl and defluorination of ciprofloxacin photodegradation in ice

Ice is an important physical and chemical sink for various pollutants in cold regions. The photodegradation of emerging fluoroquinolone (FQ) antibiotic contaminants with dissolved organic matter (DOM) in ice remains poorly understood. Here, the photodegradation of ciprofloxacin (CIP) and fulvic acid (FA) in different proportions as representative FQ and DOM in ice were investigated. Results suggested that the photodegradation rate constant of CIP in ice was 1.9 times higher than that in water. When C_FA/C_CIP ≤ 60, promotion was caused by FA sensitization. FA increased the formation rate of cleavage in the piperazine ring and defluorination products. When 60 < C_FA/C_CIP < 650, the effect of FA on CIP changed from promoting to inhibiting. When 650 ≤ C_FA/C_CIP ≤ 2600, inhibition was caused by both quenching effects of 143.9%-51.3% and light screening effects of 0%-48.7%. FA inhibited cleavage in the piperazine ring for CIP by the scavenging reaction intermediate of aniline radical cation in ice. When C_FA/C_CIP > 2600, the light screening effect was greater than the quenching effect. This work provides new insights into how DOM affects the FQ photodegradation with different concentration proportions, which is beneficial for understanding the environmental behaviors of fluorinated pharmaceuticals in cold regions.

Antibiotics in fish caught from ice-sealed waters: Spatial and species variations, tissue distribution, bioaccumulation, and human health risk

Antibiotics are increasingly detected in fish caught in ice-free waters, but information on fish caught in ice-sealed waters is insufficient. The concentrations of 23 antibiotics in the gills, muscles, kidneys, livers, biles, and brains of Cyprinus carpio and Hypophthalmichthys nobilis caught during winter fish-hunting activities in Chagan Lake, Haernao Reservoir, and Shitoukoumen Reservoir were systematically studied to ascertain the variations among fish species and fishing regions, tissue distribution, and bioaccumulation, as well as the potential risk to humans via the consumption of contaminated fish. The results indicated that the individual antibiotic concentration in tissues ranged from undetectable to 35.0 ng/g ww. The total antibiotic concentration in fish muscles from Shitoukoumen Reservoir was lower than that from Chagan Lake and Haernao Reservoir, but showed no significant difference between Cyprinus carpio and Hypophthalmichthys nobilis. Chloramphenicols had a high proportion in most fish tissues ranging from 28.3% to 44.0%, and the antibiotics were mainly distributed in the livers with a total concentration of 54.8 ± 9.9 ng/g ww. The mean values of bioaccumulation factors (BAF) of antibiotics in tissues ranged from 79.4 to 1000 L/kg, with the higher values found in the fish livers. The hazard quotient and hazard index value of antibiotics in the muscles of fish from ice-sealed were less than 1, indicating a negligible risk to human health via the consumption of fish muscles. This study revealed that the total antibiotic concentration in muscles showed spatial variations but not fish species-dependence. The antibiotics mainly accumulated in the livers. In addition, the target antibiotic concentrations in the muscles of fish from ice-sealed waters met the safe for consumption criteria.

New insights into thiamphenicol biodegradation mechanism by Sphingomonas sp. CL5.1 deciphered through metabolic and proteomic analysis

Biological treatment is an efficient and economical process to remove thiamphenicol (TAP) residues from the environment. The discovery of TAP-degrading bacteria and the decryption of its biodegradation mechanism will be beneficial to enhance the biological removal of TAP. In this study, Sphingomonas sp. CL5.1 was found to be capable of catabolizing TAP as the sole carbon, nitrogen, and energy source. This strain could degrade 93.9% of 25 mg/L TAP in 36 h, and remove about 11.9% of the total organic carbon of TAP. A novel metabolism pathway of TAP was constructed, and the enzymes involved in TAP metabolism in strain CL5.1 were predicted via proteomic and metabolic analysis. TAP was proposed to be transformed to O-TAP via oxidation of C₃-OH and DD-TAP via dehydration of C₃-OH and dehydrogenation of C₁-OH. A novel glucose-methanol-choline (GMC) family oxidoreductase CapO was predicted to be involved in the oxidation of C₃-OH. O-TAP was supposed to be further cleaved into DCA, glycine, and PMB. Glycine might be a pivotal direct nitrogen source for strain CL5.1, and it could be involved in nitrogen metabolism through the glycine cleavage system or directly participate in the biosynthetic processes.

Photodegradation of norfloxacin in ice: Role of the fluorine substituent

Ice is an important medium in cold regions, because it regulates the environmental behaviors and the fate of pollutants. The photodegradation of fluoroquinolone (FQ) antibiotics as emerging contaminants of concern in ice remains poorly understood. Here, the photodegradation of fluorine-containing norfloxacin (NOR) as one model of FQs in ice formed from freezing solutions was investigated. Pipemidic acid (PPA) as a structural analogue of NOR was selected to compare the effect of molecular structure on the antibiotic photodegradation in the ice. Results suggested that the photodegradation rate constant of NOR in ice relative to pure water increased by 40.0%. Both the absorbance in the absorption spectra and quantum yields of NOR in ice over water increased by 1.4 times. Direct photodegradation mainly caused the defluorination of NOR, which was more important than cleavage and oxidation of the piperazine ring by self-sensitized photooxidation in ice. The defluorination rate of NOR in the ice relative to water increased by about 12.7%. The fluorine substituent played a more important role in the NOR photodegradation in the ice, resulting in a 1.6-fold increase in the photodegradation rate constant of NOR relative to PPA. This work provides a new insight into the role of fluorine substituents in the photodegradation of fluorinated pharmaceuticals in cold regions.

Removal of antibiotic thiamphenicol by bacterium Aeromonas hydrophila HS01

Thiamphenicol (TAP) is an amphenicol antibiotic, which has a broad-spectrum inhibitory effect on both gram-positive and gram-negative bacteria. Since it is widely used in animals and aquaculture, its residues in environment may bring potential risk for human health and ecosystems. While TAP can be removed through conventional physical or chemical methods, its bioremediation using microorganisms is less studied. Here, we report the removal of TAP by a bacterial strain, Aeromonas hydrophila HS01, which can remove more than 90.0% of TAP in a living cell-dependent manner. Our results indicated that its removal efficiency can be greatly affected by the growth condition. Proteomics studies revealed a number of differentially expressed proteins of HS01 in the presence of TAP, which may play critical roles in the transportation and degradation of TAP. All these results indicate bacterial strain A. hydrophila HS01 is a new microbial resource for efficiently removing TAP, and may shed new insights in developing bioremediation approaches for TAP pollution.

Comparison of the degradation of multiple amine-containing pharmaceuticals during electroindirect oxidation and electrochlorination processes in continuous system

The degradation of pharmaceuticals by electrochemical oxidation (EO) in simulated wastewater containing multiple pharmaceuticals was compared between batch and continuous reactors. Despite the excellent efficiencies achieved in batch experiments, the practical/large-scale applications of EO-degrading amine-containing pharmaceuticals has not yet been accomplished. This paper presents the results of continuous experiments with one of the most promising electrochemical configurations of Pt/Ti electrodes before proceeding to application. In the continuous electrooxidation system (without chloride), direct oxidation on the electrode surface and oxidation by hydroxyl radicals were the main pathways. Due to their short lifespans, the radicals could not be transferred to the bulk solution, and the removal of pharmaceuticals followed the order of sulfamethoxazole (SMX) > paracetamol (PAR) > diclofenac (DIC). In the electrochlorination system (with chloride), oxidation by residual chlorine was the main pathway. The removal of pharmaceuticals followed the order of sulfamethoxazole (SMX) > diclofenac (DIC) > paracetamol (PAR). High SMX removal was realized because of the high reaction rate of SMX with free chlorine. Among the pharmaceuticals, PAR had the lowest removal because it is a neutral species with a low mass transfer rate without the attraction of electrostatic force. These results are consistent with the predictions from our previous batch-scale study, which showed that the reaction rate of dissociated compounds could be increased by the addition of electrostatic force. Furthermore, multiple coexisting pharmaceuticals, such as SMX and PAR or DIC, may form dimers that can be transferred to complex structures and cause higher toxicity.

Screening and ecological risk of 1200 organic micropollutants in Yangtze Estuary water

The Yangtze River, the third largest river in the world, has been polluted by various organic chemicals. In 2018, China decided to implement ecological restoration of the Yangtze River to protect the river. However, except for some conventional pollution indices such as COD (Chemical Oxygen Demand) and NH₄⁺-N, the overall levels and risks of a wide variety of organic micropollutants (OMPs) in the Yangtze Estuary is not clear. Herein, results from a wide-range screening on levels and risks of OMPs in the Yangtze Estuary water were reported. 36 water samples were collected at 9 sites in the Yangtze Estuary in 2012 and 2013. Approximately 1200 OMPs were screened. A total of 131 OMPs were detected with total concentrations ranging from 1.8×10³ to 9.7×10³ ng/L. A tiered strategy was proposed to simplify the assessment of multi-substance ecological risks. Results showed that risk quotient (RQ) for 77% of the OMPs was less than 0.1. For 20 OMPs with RQ ≥ 0.1, joint probabilistic risks were assessed by species sensitivity distribution models. The joint risks as expressed by multi-substance potentially affected fractions are > 5%, and are not insignificant. The results may serve as a benchmark for protecting biodiversity in the Yangtze Estuary, as China motivated to have a fundamental improvement on the environmental quality by 2035.