Occurrence, Seasonal Variation and Risk Assessment of Antibiotics in Qingcaosha Reservoir

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.

Occurrence, removal, emission and environment risk of 32 antibiotics and metabolites in wastewater treatment plants in Wuhu, China

Wastewater treatment plants (WWTPs) are considered important sources of antibiotics and metabolites in aquatic environments and pose a serious threat to the safety of aquatic organisms. In this study, we investigated the seasonal occurrence, removal, emission, and environmental risk assessment (ERA) of 32 antibiotics and metabolites at four WWTPs located in Wuhu, China. The main findings of this study are as follows: Ofloxacin concentrations dominated all WWTPs, and large quantities of sulfachinoxalin were only detected in WWTP 2 treating mixed sewage. The average apparent removal of individual parent antibiotics or metabolites ranged from -94.7 to 100 %. There was a noticeable seasonal emission pattern (independent t-test, t = 9.89, p < 0.001), with lower emissions observed during summer. WWTPs discharged 85.2 ± 43.8 g of antibiotics and metabolites each day. Approximately 87 % of emissions were discharged into the mainstream of the Yangtze River, while the remainder were discharged into its tributary, the Zhanghe River. The total emissions of 21 parent antibiotics were approximately 18 % of the prescription data, indicating that a considerable and alarming amount of prototype drugs entered the receiving water body. Based on the risk quotient (RQ) of the ERA, the Zhanghe River has a moderate risk of ofloxacin (RQ = 0.111-0.583), a low or insignificant risk of sulfamethoxazole (RQ = 0.003-0.048), and an insignificant risk of other antibiotics or metabolites. However, the risk of antibiotics or metabolites in the mainstream of Yangtze River is insignificant. This study could help understand the seasonal emission patterns of antibiotics and metabolites, as well as more antibiotics sensitive of environmental risks in tributary than that in mainstream.

Four antibiotics and copper interactive effects on the growth and physiological characteristics of Hydrilla verticillata (L.f.) Royle

Co-pollution of antibiotics and heavy metal copper (Cu) is common in freshwater environments because of their wide use as antimicrobial agents, especially in aquaculture. However, the toxic effects of coexisting antibiotics and heavy metals on aquatic plants remain unclear. This study investigated the effect of four antibiotics (i.e., enrofloxacin, ENR; tetracycline, TC; sulfamethoxazole, SMX; erythromycin, ERY), Cu, and their mixture on the growth and physiological responses of Hydrilla verticillata (L.f.) Royle. Results showed that the four antibiotics exhibited toxic effects on the growth and physiological indicators of H. verticillata, and root elongation was the most sensitive endpoint of the phytotoxicity test. The median effect concentration (EC50) of root elongation indicated that TC (EC50 = 10.05 mg/L) has the highest level of growth toxicity, and the toxicity of ENR to aquatic plants was close to TC (EC50 = 10.44 mg/L), followed by SMX (EC50 = 20.08 mg/L). However, there was no significant toxic effect of 20 mg/L ERY on the root elongation. Hydrophobicity may be a key factor affecting the phytotoxicity of antibiotics. Moreover, antagonistic toxic effects were observed under ENR + Cu, TC + Cu, SMX + Cu, and ERY + Cu co-exposures at all the experimental concentrations (0.01-20 mg/L). Due to the concentrations of antibiotics in natural waters usually with ng/L levels, our results suggested that environmental antibiotic concentrations probably pose low ecological risk to aquatic plants and indicated the H. verticillata could be used as phytoremediation candidate to remove antibiotic or antibiotic-Cu pollutions in general nature water.

Antibiotic residues of drinking-water and its human exposure risk assessment in rural Eastern China

Trace levels of antibiotics were frequently found in drinking-water, leading a growing concern that drinking-water is an important exposure source to antibiotics in humans. In this study, we investigated antibiotics in tap water and well water in two rural residential areas in Eastern China to assess the related human health exposure risks in drinking-water. Twenty-seven antibiotics were analyzed using ultra performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UPLC-MS/MS). The average daily dose (ADD) and the health risk quotient (HRQ) for exposure to antibiotics in humans were evaluated using 10000 times of Monte Carlo simulations. Ten antibiotics were detected in drinking-water samples, with the maximum concentrations of antibiotic mixture of 8.29 ng/L in tap water and 2.95 ng/L in well water, respectively. Macrolides and sulfonamides were the predominant contaminants and showed the seasonality. Azithromycin had the highest detection frequencies (79.71-100%), followed by roxithromycin (25.71-100%) and erythromycin (21.43-86.96%). The estimated ADD and HRQ for human exposure to antibiotic mixture through drinking-water was less than 0.01 μg/kg/day and 0.01, respectively, which varied over sites, water types, seasons and sex. Ingestion route was more important than dermal contact route (10-6 to 10-4 μg/kg/day magnitude vs. 10-11 to 10-8 μg/kg/day magnitude). Macrolides also contributed mainly to health exposure risks to antibiotics through drinking-water, whose HRQ accounted for 46% to 67% of the total HRQs. Although the individual antibiotic and their combined effects contributed to acceptable health risks for human, the long-term exposure patterns to low-dose antibiotics in drinking-water should not be ignored.

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.

Comparison and prioritization of antibiotics in a reservoir and its inflow rivers of Beijing, China

The occurrence of antibiotics in drinking water resources, like reservoirs, is of considerable concern due to their potential risks to ecosystem, human health, and antimicrobial resistance development. Here, we quantified 83 antibiotics in water and sediments of wet and dry seasons from the Miyun reservoir and its inflow rivers in Beijing, China. Twenty-four antibiotics were detected in water with concentrations of ND-11.6 ng/L and 19 antibiotics were observed in sediments with concentrations of ND-6.50 ng/g. Sulfonamides (SAs) were the dominated antibiotics in water in two seasons. SAs and quinolones (QNs) in wet season and macrolides (MLs) and QNs in dry season predominated in sediments. The reservoir and inflow rivers showed significant differences in antibiotic concentrations and compositions in water and sediments. As an important input source of reservoir, the river water showed significantly higher total antibiotic concentrations than those in the reservoir. In contrast, the reservoir sediments are the sink of antibiotics, and had higher total antibiotic concentrations compared with rivers. A prioritization approach based on the overall risk scores and detection frequencies of antibiotics was developed, and 3 (sulfaguanidine, anhydroerythromycin, and sulfamethoxazole) and 5 (doxycycline, sulfadiazine, clarithromycin, roxithromycin, and flumequine) antibiotics with high and moderate priority, respectively, were screened. The study provides a comprehensive insight of antibiotics in the Miyun Reservoir and its inflow rivers, and is significant for future monitoring and pollution mitigation of antibiotics.

Concentrations and Risk Assessments of Antibiotics in an Urban-Rural Complex Watershed with Intensive Livestock Farming

Antibiotics used for the treatment of humans and livestock are released into the environment, whereby they pose a grave threat to biota (including humans) as they can cause the emergence of various strains of resistant bacteria. An improved understanding of antibiotics in the environment is thus vital for appropriate management and mitigation. Herein, surface water and groundwater samples containing antibiotics were analyzed in an urban-rural complex watershed (Cheongmi Stream) comprising intensive livestock farms by collecting samples across different time points and locations. The spatiotemporal trends of the residual antibiotics were analyzed, and ecological and antibiotic resistance-based risk assessments were performed considering their concentrations. The results showed that the concentrations and detection frequencies of the residual antibiotics in the surface water were affected by various factors such as agricultural activities and point sources, and were higher than those found in groundwater; however, frequent detection of antibiotics in groundwater showed that residual antibiotics were influenced by factors such as usage pattern and sewage runoff. Furthermore, few antibiotics posed ecological risks. The risk assessment methods adopted in this study can be applied elsewhere, and the results can be considered in the environmental management of residual antibiotics in the Cheongmi Stream watershed.

Performance of full scale constructed wetlands in removing antibiotics and antibiotic resistance genes

Additional treatment of wastewater, such as constructed wetlands (CWs), is a possible solution to reduce the discharge of antibiotics and antibiotic resistance genes (ARGs) from households and industry to the environment. This study aims to investigate the occurrence and removal of antibiotics and ARGs by two full scale CWs operated at different hydraulic retention times (HRT), namely 1 day and 3 days. Both CWs were receiving the same wastewater treatment plant (WWTP) effluent. Temporally and spatially distributed sampling of water and sediment was conducted for one year and samples were analyzed for antibiotics and ARGs by using LC-MS/MS and qPCR. Results showed that both CWs removed antibiotics significantly with a comparable overall removal of 28%-100%, depending on the type of antibiotics. However, some of the antibiotics showed higher concentration after the CW treatment. Five antibiotics (tiamulin, tylosin, oxytetracycline, sulfamethoxazole and trimethoprim) were the most abundant (>1500 ng/l on average) in winter. Meanwhile, ermB was the most abundant (average of 5.0 log) in winter compared to summer (average of 3.5 log). Other ARGs did not show a significant increase or decrease between winter and summer. ARGs were removed from the wastewater by 0.8 to 1.5 log. The HRT did not influence the removal of either the antibiotics or the ARGs. A strong correlation was found between sul genes and intI1. The results also revealed a positive and a negative relationship from sampling point 1 to sampling point 5: a positive relation between abundance of antibiotics, ARGs, and of NO₃-N, NH₄-N, TP, COD and a negative relation between antibiotics, ARGs and temperature. This relationship showed the effect between antibiotics and ARGs concentrations with physicochemical parameters and nutrients. The ability of CWs to reduce the input of micropollutants into the environment makes CWs a potential post treatment to WWTP.

Strong links between load and manure and a comprehensive risk assessment of veterinary antibiotics with low KOW in intensive livestock farming watersheds

Various veterinary antibiotics (VAs) are used in large quantities as an essential component for intensive livestock farming, and can flow into the environment from various pollution sources. In this study, VAs in surface water and groundwater in the Gwangcheon stream watershed, an intensive livestock farming area in Korea, were analyzed using ultra-high-performance liquid chromatograph-quadrupole orbitrap high-resolution mass spectrometer with online solid phase extraction. Although the selected VAs are relatively mobile and have low K_OW values it is significant to assess their fates and ecological risks in the environment. The concentration of VAs in the surface water was higher than that in groundwater by approximately 23-fold, indicating that the former were directly introduced from pollution sources such as livestock manure. An analysis of the correlation between livestock manure production and the residuals of VAs in the stream showed a high linearity (R² > 0.70), confirming that livestock excreta significantly contributed to the VAs in the watershed. A combined evaluation of environmental behaviors and ecological risks of VAs was performed for the first time using persistence, bioaccumulation potential, and toxicity properties and risk quotient values of VAs. Trimethoprim showed persistence and a potential impact on the ecosystem. The cumulative risk quotient values at one sampling point exceeded 1 indicating that several VAs can cumulatively cause local risk. The risk assessment method considering pollution sources, different locations, and correlation analysis applied in this study will be useful in evaluating the impacts of trace pollutants in watersheds.

Remoción de cinco productos farmacéuticos catalogados como contaminantes emergentes en medio acuoso utilizando la especie vetiver (Chrysopogon zizanioides)

Los productos farmacéuticos constituyen un grupo único de contaminantes emergentes de gran interés, debido a que se ha determinado su presencia frecuente en aguas superficiales, subterráneas y agua potable. Debido al metabolismo y la absorción incompletos en el organismo humano, una cantidad significativa de estos fármacos se excretan y liberan al ambiente a través de las aguas residuales. Por lo que el objetivo de este trabajo fue evaluar el potencial de la especie vetiver (Chrysopogon zizanioides) para eliminar del medio acuoso cinco productos farmacéuticos comúnmente recetados y de venta libre como ciprofloxacina, ibuprofeno, sulfametaxazol, diclofenaco y acetaminofén. La especie fue aclimatada en invernado, donde se llevó a cabo los experimentos en condiciones controladas de temperatura y a un pH de 6,5. Las muestras fueron analizadas utilizando espectrofotometría UV-Vis para leer en forma directa las absorbancias de cada producto farmacéutico. Para el análisis estadístico de los datos se empleó la metodología de superficies de respuesta con el fin de encontrar los modelos que ayuden a determinar tiempos y concentraciones óptimas donde se maximiza la absorción de cada fármaco, así como la obtención de las pendientes de crecimiento para determinar hacia donde se deberá buscar el óptimo. Se utilizó el software estadístico R versión 3.6.0 y RStudio versión 1.1.453. Los resultados obtenidos indican que C. zizanioides removió de manera más eficiente ciprofloxacina (98,3%) a una concentración de 3mg/L en un tiempo de 149h, seguido por ibuprofeno y diclofenaco con un máximo de remoción de 73,33% y sulfametaxazol con 66,53%, obteniéndose el menor porcentaje de remoción para acetaminofén de 38,49% a las 192h, donde se realizó toma de muestras cada 48 horas de las soluciones de cada fármaco a diferentes concentraciones (3 mg/L, 6 mg/L, 9 mg/L, 12 mg/L). En este trabajo de investigación se demostró la capacidad removedora de Chrysopogon zizanioides de los cinco fármacos estudiados en medio acuoso en condiciones controladas, vislumbrando un gran potencial en el ámbito de la biotecnología ambiental para el tratamiento terciario de aguas residuales.

Presencia de productos farmacéuticos en el agua y su impacto en el ambiente

Los productos farmacéuticos (PFs) constituyen un grupo importante de los contaminantes emergentes (CE), debido a su potencial para inducir efectos fisiológicos adversos a bajas concentraciones en humanos y animales. Muchos estudios alrededor del mundo han reportado la presencia de un sin número de estos compuestos en diferentes medios acuáticos, lo que genera preocupación por los posibles efectos negativos que se producen en el agua, en la salud humana y la vida silvestre. En este contexto, este artículo tiene por objetivo presentar una revisión de los aspectos más relevantes sobre la presencia de PFs en el agua en un ámbito global desde el año 2010 hasta el 2019. El mayor número de estudios reportan presencia de contaminantes emergentes incluyendo fármacos de diferentes tipos en aguas superficiales, aguas subterráneas, aguas residuales y agua potable. Las principales fuentes de ingreso de fármacos en los sistemas acuáticos provienen de las aguas residuales que recogen aguas domésticas, efluentes hospitalarios y efluentes de fábricas sin tratamiento o inadecuadamente tratadas antes de ser liberadas a ríos y mares. La presencia de PFs en el ambiente acuático preocupa por su persistencia, la bioacumulación, la toxicidad y la generación de resistencia a antibióticos de muchos microorganismos, entre otras consecuencias aún no estudiadas en el ambiente.

Fate of antibiotics and antibiotic resistance genes during conventional and additional treatment technologies in wastewater treatment plants

Information on the removal of antibiotics and ARGs in full-scale WWTPs (with or without additional treatment technology) is limited. However, it is important to understand the efficiency of full-scale treatment technologies in removing antibiotics and ARGs under a variety of conditions relevant for practice to reduce their environmental spreading. Therefore, this study was performed to evaluate the removal of antibiotics and ARGs in a conventional wastewater treatment plant (WWTP A) and two full-scale combined with additional treatment technologies. WWTP B, a conventional activated sludge treatment followed by an activated carbon filtration step (1-STEP® filter) as a final treatment step. WWTP C, a treatment plant using aerobic granular sludge (NEREDA®) as an alternative to activated sludge treatment. Water and sludge were collected and analysed for 52 antibiotics from four target antibiotic groups (macrolides, sulfonamides, quinolones, tetracyclines) and four target ARGs (ermB, sul 1, sul 2 and tetW) and integrase gene class 1 (intI1). Despite the high removal percentages (79-88%) of the total load of antibiotics in all WWTPs, some antibiotics were detected in the various effluents. Additional treatment technology (WWTP C) showed antibiotics removal up to 99% (tetracyclines). For ARGs, WWTP C reduced 2.3 log followed by WWTP A with 2.0 log, and WWTP B with 1.3 log. This shows that full-scale WWTP with an additional treatment technology are promising solutions for reducing emissions of antibiotics and ARGs from wastewater treatment plants. However, total removal of the antibiotics and ARGS cannot be achieved for all types of antibiotics and ARGs. In addition, the ARGs were more abundant in the sludge compared to the wastewater effluent suggesting that sludge is an important reservoir representing a source for later ARG emissions upon reuse, i.e. as fertilizer in agriculture or as resource for bioplastics or bioflocculants. These aspects require further research.

Spatial and seasonal variations and risk assessment for heavy metals in surface sediments of the largest river-embedded reservoir in China

The sediment acts as not only sink but also source of heavy metals in aquatic environment, which may cause the endogenous pollution in drinking water reservoirs. In this work, we collected the surface sediments from Qingcaosha Reservoir, the largest river-embedded reservoir in China, and investigated the spatial distribution, risk, and sources of heavy metals in four seasons. Significant spatial and seasonal heterogeneity could be found in the distribution of five heavy metals (Cr, Cu, Mn, Zn, and Ni) in the surface sediments. The highest concentrations of the five metals were detected in the sediments from the reservoir downstream, especially in summer and next spring. The geo-accumulation index (I_geo) and enrichment factor (EF) suggest that the sediment pollution caused by single metal was heavier in summer than in other seasons. Also, the Nemerow pollution index (PI_N) manifests that the synergetic pollution induced by five metals was most serious in summer, followed by next spring. However, the potential ecological risk index (PERI) indicates that none of these metals caused potential ecological risk in four seasons. Comprehensive analysis demonstrates that the sediment pollution gradually increased from autumn to winter and then to next spring. Principal component analysis shows that the main pollution source of five heavy metals may come from industrial wastewater and domestic sewage, which was almost independent of seasons. This work can provide data support for the subsequent seasonal optimization of drinking water quality and reservoir management.

Occurrence and fate of antibiotic residues and antibiotic resistance genes in a reservoir with ecological purification facilities for drinking water sources

Antibiotics and antibiotic resistance genes (ARGs) are emerging contaminants in surface waters, especially drinking water sources, where they can pose a risk to human health and aquatic ecology. The ecological purification facilities constructed in the drinking water reservoirs are intended to safeguard water quality. However, their ability to remove antibiotics and ARGs from the water and the presence of ARGs in such river-reservoir systems have not been comprehensively characterized yet. The occurrence, distribution and spatiotemporal variations in antibiotics, ARGs, and mobile genetic elements (MGEs) were investigated in a representative river-reservoir system in Shanghai, China. A total of 283 ARGs and 12 MGEs were detected in the water using high- throughput quantitative PCR analysis. Antibiotic residues and the absolute abundance of total ARGs and MGEs in reservoir inflow were significantly reduced when water from the river passed through the ecological purification processes in the reservoir. Antibiotics in this river-reservoir system posed only limited risks to the aquatic ecosystem and human health. No significant correlation was observed between the distribution pattern of ARGs and spatiotemporal factors. The dominant ARGs were strongly and significantly correlated with integrons. Through redundancy analysis and variation partitioning analysis, we determined that MGEs were the major driver shifting the distribution of ARGs, and the effects of environmental factors and antibiotic residues were reflected in the joint effects with MGEs. The small ecological reservoir was verified as an effective engineering to mitigate ecological risk in the drinking water source.

Size-dependent adsorption of antibiotics onto nanoparticles in a field-scale wastewater treatment plant

This work present aims to evaluate the effect of a conventional wastewater treatment process on the number of nanoparticles, and the role of nanoparticles as a carrier of antibiotics. A set of methods based on asymmetrical flow field flow fractionation coupled with multi-angle light scattering to separate and quantify nanoparticles in real wastewater was established. The characterization of nanoparticles was conducted by transmission electron microscopy, energy dispersive spectrometer, UV-visible spectrophotometer and three-dimensional excitation-emission matrix fluorescence spectroscopy. The adsorption of different sizes of nanoparticles separated from the real wastewater for four targeted antibiotics (sulfadiazine, ofloxacin, tylosin and tetracycline) was studied. The results show that the number of nanoparticles were increased in the wastewater treatment process and the size range between 60 and 80 nm was predominant in wastewater samples. The nanoparticles were mainly composed of O, Si, Al and Ca elements and organic components were in the size range of 0-10 nm. Targeted antibiotics were dominantly adsorbed onto nanoparticles with 60-80 nm size range at each stage. The concentrations of tetracycline adsorbed on nanoparticles were surprisingly increased in the end of the treatment process, while ofloxacin and tylosin had the completely opposite phenomenon to tetracycline. The pH and ionic strength definitely affected the aggregation of nanoparticles and interaction with the antibiotics. It is of great significance to give insights into nanoparticle-antibiotic assemblages for the effective treatment and avoiding the water risks due to nanoparticles' ubiquitous and their risks of carrying antibiotics.

Monitoring Antimicrobial Resistance Dissemination in Aquatic Systems

This special issue on Antimicrobial Resistance in Environmental Waters features 11 articles on monitoring and surveillance of antimicrobial resistance (AMR) in natural aquatic systems (reservoirs, rivers), and effluent discharge from water treatment plants to assess the effectiveness of AMR removal and resulting loads in treated waters. The occurrence and distribution of antimicrobials, antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) was determined by utilizing a variety of techniques including liquid chromatography—mass spectrometry in tandem (LC-MS/MS), traditional culturing, antibiotic susceptibility testing (AST), molecular and OMIC approaches. Some of the key elements of AMR studies presented in this special issue highlight the underlying drivers of AMR contamination in the environment and evaluation of the hazard imposed on aquatic organisms in receiving environments through ecological risk assessments. As described in this issue, screening antimicrobial peptide (AMP) libraries for biofilm disruption and antimicrobial candidates are promising avenues for the development of new treatment options to eradicate resistance. This editorial puts into perspective the current AMR problem in the environment and potential new methods which could be applied to surveillance and monitoring efforts.

Comparison of chlorination behaviors between norfloxacin and ofloxacin: Reaction kinetics, oxidation products and reaction pathways

Fluoroquinolones (FQs) are very ubiquitous in water environment in China. The commonly application of free available chlorine (FAC) during water treatment stimulated the focus on the transformation of FQs during chlorination. Among these FQs, norfloxacin (NOR) and ofloxacin (OFL) are the representatives of secondary amine FQs and tertiary amine FQs, respectively. To better understand the difference between secondary amine FQs and tertiary amine FQs during chlorination, reaction kinetics, products and mechanisms were determined. The maximum k_app of NOR were four orders of magnitude higher than that of OFL. Moreover, eleven products of NOR and twelve products of OFL were obtained by LC-MS/MS analysis. For the two FQs, the common reactive sites were three nitrogen atoms, benzene ring, carboxyl group and double bond by chlorination. For OFL, the ether ring was also active in aqueous system. The formation mechanisms of these products were presented in this study. The main reaction pathways were electrophilic addition to nitrogen, nucleophilic substitution to benzene ring, halodecarboxylation of carboxyl group and hydrolysis of ether ring. Na₂S₂O₃ as a reducing agent had large effect on the chlorination of secondary amine FQ, but no effect on tertiary amine FQ. Be different to secondary amine FQ, the opening of quinolone ring happened in tertiary amine FQ after halodecarboxylation of carboxyl group.