Fate and effects of enrofloxacin in aquatic systems under different light conditions

Removal of enrofloxacin using Eichhornia crassipes in microcosm wetlands

The global consumption of antibiotics leads to their possible occurrence in the environment. In this context, nature-based solutions (NBS) can be used to sustainably manage and restore natural and modified ecosystems. In this work, we studied the efficiency of the NBS free-water surface wetlands (FWSWs) using Eichhornia crassipes in microcosm for enrofloxacin removal. We also explored the behavior of enrofloxacin in the system, its accumulation and distribution in plant tissues, the detoxification mechanisms, and the possible effects on plant growth. Enrofloxacin was initially taken up by E. crassipes (first 100 h). Notably, it accumulated in the sediment at the end of the experimental time. Removal rates above 94% were obtained in systems with sediment and sediment + E. crassipes. In addition, enrofloxacin was found in leaves, petioles, and roots (8.8-23.6 µg, 11-78.3 µg, and 10.2-70.7 µg, respectively). Furthermore, enrofloxacin, the main degradation product (ciprofloxacin), and other degradation products were quantified in the tissues and chlorosis was observed on days 5 and 9. Finally, the degradation products of enrofloxacin were analyzed, and four possible metabolic pathways of enrofloxacin in E. crassipes were described.

Geospatial and co-occurrence analysis of antibiotics, hormones, and UV filters in the Chesapeake Bay (USA) to confirm inputs from wastewater treatment plants, septic systems, and animal feeding operations

Previous studies have reported select contaminants of emerging concern (CECs) in limited areas of the Chesapeake Bay (USA), but no comprehensive efforts have been conducted. In this work, 43 antibiotics, 9 hormones, 11 UV filters, and sucralose, were measured in matched water, sediment, and oyster samples from 58 sites. The highest sucralose concentration was 3051 ng L-1 in a subwatershed with 4.43 million liters of wastewater effluent per day (MLD) and 4385 septic systems. Although antibiotic occurrence was generally low in subwatersheds located in less populated areas, 102 ng L-1 ciprofloxacin was detected downstream of 0.58 MLD wastewater effluent and 10 animal feeding operations. Hormones were not regularly detected in water (2%) or oysters (37%), but the high detection frequencies in sediment (74%) were associated with septic systems. UV filters were ubiquitously detected in oysters, and octisalate exhibited the highest concentration (423 ng g-1). Oyster-phase oxybenzone and aqueous-phase sucralose concentrations were significantly correlated to wastewater effluent and septic systems, respectively. Toxicity outcomes were predicted for homosalate and octisalate throughout the Bay, and antimicrobial resistance concerns were noted for the Chester River. The geospatial and co-occurrence relationships constitute crucial advances to understanding CEC occurrence in the Chesapeake Bay and elsewhere.

Antimicrobial Transformation Products in the Aquatic Environment: Global Occurrence, Ecotoxicological Risks, and Potential of Antibiotic Resistance

The global spread of antimicrobial resistance (AMR) is concerning for the health of humans, animals, and the environment in a One Health perspective. Assessments of AMR and associated environmental hazards mostly focus on antimicrobial parent compounds, while largely overlooking their transformation products (TPs). This review lists antimicrobial TPs identified in surface water environments and examines their potential for AMR promotion, ecological risk, as well as human health and environmental hazards using in silico models. Our review also summarizes the key transformation compartments of TPs, related pathways for TPs reaching surface waters and methodologies for studying the fate of TPs. The 56 antimicrobial TPs covered by the review were prioritized via scoring and ranking of various risk and hazard parameters. Most data on occurrences to date have been reported in Europe, while little is known about antibiotic TPs in Africa, Central and South America, Asia, and Oceania. Occurrence data on antiviral TPs and other antibacterial TPs are even scarcer. We propose evaluation of structural similarity between parent compounds and TPs for TP risk assessment. We predicted a risk of AMR for 13 TPs, especially TPs of tetracyclines and macrolides. We estimated the ecotoxicological effect concentrations of TPs from the experimental effect data of the parent chemical for bacteria, algae and water fleas, scaled by potency differences predicted by quantitative structure-activity relationships (QSARs) for baseline toxicity and a scaling factor for structural similarity. Inclusion of TPs in mixtures with their parent increased the ecological risk quotient over the threshold of one for 7 of the 24 antimicrobials included in this analysis, while only one parent had a risk quotient above one. Thirteen TPs, from which 6 were macrolide TPs, posed a risk to at least one of the three tested species. There were 12/21 TPs identified that are likely to exhibit a similar or higher level of mutagenicity/carcinogenicity, respectively, than their parent compound, with tetracycline TPs often showing increased mutagenicity. Most TPs with increased carcinogenicity belonged to sulfonamides. Most of the TPs were predicted to be mobile but not bioaccumulative, and 14 were predicted to be persistent. The six highest-priority TPs originated from the tetracycline antibiotic family and antivirals. This review, and in particular our ranking of antimicrobial TPs of concern, can support authorities in planning related intervention strategies and source mitigation of antimicrobials toward a sustainable future.

Mesocosm experiment to determine the contribution of adsorption, biodegradation, hydrolysis and photodegradation in the attenuation of antibiotics at the water sediment interface

To understand the fate of antibiotics in the aquatic environment, we need to evaluate to which extent the following processes contribute to the overall antibiotic attenuation: adsorption to river sediment, biodegradation, hydrolysis and photodegradation. A laboratory scale mesocosm experiment was conducted in 10 L reactors filled with river sediment and water. The reactors were spiked with four classes of antibiotics (fluoroquinolones, macrolides, sulfonamides, tetracyclines), as well as clindamycin and trimethoprim. The experimental-set-up was designed to study the attenuation processes in parallel in one mesocosm experiment, hence also considering synergetic effects. Our results showed that antibiotics belonging to the same class exhibited similar behavior. Adsorption was the main attenuation process for the fluoroquinolones and tetracyclines (44.4 to 80.0 %). For the sulfonamides, biodegradation was the most frequent process (50.2 to 65.1 %). Hydrolysis appeared to be significant only for tetracyclines (12.6 to 41.8 %). Photodegradation through visible light played a minor role for most of the antibiotics - fluoroquinolones, sulfonamides, and trimethoprim (0.7 to 24.7 %). The macrolides were the only class of antibiotics not affected by the studied processes and they persisted in the water phase. Based on our results, we propose to class the antibiotics in three groups according to their persistence in the water phase. Fluoroquinolones and tetracyclines were non-persistent (half-lives shorter than 11 d). Chlorotetracycline, sulfapyridine and trimethoprim showed a moderate persistence (half-lives between 12 and 35 d). Due to half-lives longer than 36 d sulfonamides and clindamycin were classified as persistent.

Seasonal variation and ecological risk assessment of Pharmaceuticals and Personal Care Products (PPCPs) in a typical semi-enclosed bay - The Bohai Bay in northern China

The Bohai Bay as a typical semi-enclosed bay in northern China with poor water exchange capacity and significant coastal urbanization, is greatly influenced by land-based inputs and human activities. As a class of pseudo-persistent organic pollutants, the spatial and temporal distribution of Pharmaceuticals and Personal Care Products (PPCPs) is particularly important to the ecological environment, and it will be imperfect to assess the ecological risk of PPCPs for the lack of systematic investigation of their distribution in different season. 14 typical PPCPs were selected to analyze the spatial and temporal distribution in the Bohai Bay by combining online solid-phase extraction (SPE) and HPLC-MS/MS techniques in this study, and their ecological risks to aquatic organisms were assessed by risk quotients (RQs) and concentration addition (CA) model. It was found that PPCPs widely presented in the Bohai Bay with significant differences of spatial and seasonal distribution. The concentrations of ∑PPCPs were higher in autumn than in summer. The distribution of individual pollutants also showed significant seasonal differences. The high values were mainly distributed in estuaries and near-shore outfalls. Mariculture activities in the northern part of the Bohai Bay made a greater contribution to the input of PPCPs. Caffeine, florfenicol, enrofloxacin and norfloxacin were the main pollutants in the Bohai Bay, with detection frequencies exceeding 80 %. The ecological risk of PPCPs to algae was significantly higher than that to invertebrates and fish. CA model indicated that the potential mixture risk of total PPCPs was not negligible, with 34 % and 88 % of stations having mixture risk in summer and autumn, respectively. The temporary stagnation of productive life caused by Covid-19 weakened the input of PPCPs to the Bohai Bay, reducing the cumulative effects of the pollutants. This study was the first full-coverage investigation of PPCPs in the Bohai Bay for different seasons, providing an important basis for the ecological risk assessment and pollution prevention of PPCPs in the bay.

A Bioavailability Model to Predict the Impact of pH and Dissolved Organic Carbon on Ciprofloxacin Ecotoxicity to the Cyanobacterium Microcystis aeruginosa

Ciprofloxacin (CIP) is a pseudopersistent antibiotic detected in freshwater worldwide. As an ionizable chemical, its fate in freshwater is influenced by water chemistry factors such as pH, hardness, and dissolved organic carbon (DOC) content. We investigated the effect of pH, DOC, and Ca²⁺ levels on the toxicity of CIP to Microcystis aeruginosa and developed a bioavailability model on the basis of these experimental results. We found that the zwitterion (CIP^+/- ) is the most bioavailable species of CIP to M. aeruginosa, whereas DOC is the most dominant factor reducing CIP toxicity, possibly via binding of both CIP^+/- and CIP⁺ to DOC. pH likely also regulates CIP-DOC binding indirectly through its influence on CIP speciation. In addition, higher tolerance to CIP by M. aeruginosa was observed at pH < 7.2, but the underlying mechanism is yet unclear. Calcium was identified as an insignificant factor in CIP bioavailability. When parameterized with the data obtained from toxicity experiments, our bioavailability model is able to provide accurate predictions of CIP toxicity because the observed and predicted total median effective concentrations deviated by <28% from each other. Our model predicts that changes in pH and DOC conditions can affect CIP toxicity by up to 10-fold, suggesting that CIP in many natural environments is likely less toxic than in standard laboratory toxicity experiments. Environ Toxicol Chem 2022;41:2835-2847. © 2022 SETAC.

Antibiotics in aquaculture ponds from Guilin, South of China: Occurrence, distribution, and health risk assessment

Antibiotics have been widely used to prevent or treat bacterial infections in aquaculture in the past decades. However, large proportions of these compounds are excreted unchanged in feces and urine of animals, given incomplete metabolism, leading to the residual of unmetabolized compounds, and posing a potential risk to the environment. This study investigated the occurrence and distribution of seven antibiotics in surface water, sediments, fish muscle, and fish feed by high-performance liquid chromatography from the aquaculture areas in Guilin, South of China. The highest concentrations of the target antibiotics in water, sediment, fish muscle, and fish feed were 2047.53 ng/L, 13.32 μg/kg, 35.90 μg/kg, and 2203.97 μg/kg, respectively. In contrast, the most abundant antibiotic was enrofloxacin (ENR), followed by ofloxacin (OFL), sulfadimidine (SMZ), and ciprofloxacin (CIP). In this work, the concentrations of antibiotics were lower than those in other breeding areas. Correlation analyses showed significant relationships between sulfadiazine (SDZ) and TP, TN, and COD_Cr in water. In sediment, the release of SDZ was significantly related to TN, TP, and organic matter. The risk quotient (RQ) results revealed that sulfamethoxazole (SMX), CIP, and ENR were at high risk to microorganisms in water; while, SMX and NOR were at high risk in sediments. The result from the estimated daily intakes (health risk quotient, HQ < 1) suggested that the antibiotics might not pose a risk to human health by dietary exposure assessment; however, sediments may become an accumulation reservoir of antibiotics and cause secondary pollution, of which the local management should raise awareness.

Toxicity of fluoroquinolones on the cladoceran Daphnia magna

This study evaluates the acute and chronic toxicological effects of six fluoroquinolones on the mortality and growth of Daphnia magna. The NOECs calculated with the multivariate Probit regression model for the chronic study were 56 μg/L ciprofloxacin, 63 μg/L enrofloxacin, 78 μg/L levofloxacin, 85 μg/L marbofloxacin, 69 μg/L norfloxacin, and 141 μg/L ofloxacin. The risk quotients were determined using the measure environmental concentrations reported in water sources from different countries. The risks were low and moderate in water samples from rivers and lakes, although concentrations of ciprofloxacin, norfloxacin, and ofloxacin reported in some countries can cause toxicological damage to D. magna. In addition, urban wastewater and hospital wastewater samples constitute a threat to D. magna (high and moderate risks), requiring the treatment of these wastewater. PRACTITIONER POINTS: The NOECs calculated with the multivariate Probit model for the six fluoroquinolonas are between 56 μg/L ciprofloxacin and 141 μg/L ofloxacin. The levels of ciprofloxacin, norfloxacin, and ofloxacin in urban wastewater and hospital wastewater produce moderate and high risks for D. magna. Water and river samples from some countries containing ciprofloxacin, norlfoxacin, and ofloxacin present high risks for D. magna.

Fluoroquinolone antibiotics sensitized photodegradation of isoproturon

Fluoroquinolone (FQ) antibiotics are a group of contaminants of emerging environmental concern. In the present study, we demonstrated that norfloxacin (NORF) and ofloxacin (OFLO), two typical FQs, have photochemical reactivity analogous to chromophoric dissolved natural organic matter (DOM) in surface waters and can sensitize the photodegradation of isoproturon (IPU), a phenylurea herbicide. Such photochemical reactivity is ascribed to the quinolone chromophore that is excited to a triplet state (³FQ*) upon UV-A irradiation. ³FQ* further reacts with dissolved oxygen to give rise to singlet oxygen. ³FQ* steady-state concentrations of 6.72 × 10^-15 and 1.27 × 10^-15 M were measured in 10 μM NORF and OFLO solutions, respectively, under UV_365nm irradiation. The degradation of IPU was due to the reaction with ³FQ*, with bimolecular rate constants of 6.07 × 10⁹ and 1.51 × 10¹⁰ for ³NORF* and ³OFLO*, respectively. Intriguingly, NORF and OFLO per se were unstable and photolyzed during UV-A irradiation, but the photochemical reactivities of the solutions were not lost accordingly. High-resolution mass spectrometry analysis revealed that defluorination and piperazine moiety oxidation were the main photolysis pathways, while the core quinolone structure remained intact. Thus, the photolysis products largely inherited the photochemical reactivity of the parent compounds. Since all FQs share the same quinolone structure, similar photochemical reactivity is expected. The presence of FQs in surface water would affect the transformation and fate of coexisting compounds. To the best of our knowledge, this is the first study examining the environmental behavior of FQs as photosensitizers. The findings greatly advance the understandings of the influence of FQs in aquatic environment.

Performance and bacterial community dynamics of hydroponically grown Iris pseudacorus L. during the treatment of antibiotic-enriched wastewater at low/normal temperature

Antibiotics are widely detected in the water environment, posing a serious threat to the health of humans and animals. The effect of levofloxacin (LOFL) on pollutant removal and the difference in the influence mechanisms at normal and low temperatures in constructed wetlands are worth discussing. A hydroponic culture experiment was designed with Iris pseudacorus L. at low and normal temperatures. LOFL (0-100 µg/L) was added to the systems. The results indicated that the removal of pollutants was affected most by temperature, followed by LOFL concentration. At the same concentration of LOFL, the pollutant removal rate was significantly higher at normal temperature than at low temperature. Low concentrations of LOFL promoted the degradation of pollutants except TN under normal-temperature conditions. Compared with the results at low temperature, the bacterial community richness was higher and the diversity of bacterial communities was lower under normal-temperature conditions. The genera and the function of bacteria were greatly affected by antibiotic concentration, temperature and test time. A series of microorganisms resistant to antibiotics and low temperature were identified in this study. The results will provide valuable information and a reference for our understanding of the ecological effects of LOFL.

Algae-induced photodegradation of antibiotics: A review

Antibiotics are a typical group of pharmaceutical and personal care products (PPCPs) with emerging pollutant effects. The presence of residual antibiotics in the environment is a prominent issue owing to their potential hazards, toxic effects, and persistence. Several treatments have been carried out in aquatic environments in order to eliminate antibiotic residues. Among these, photodegradation is regarded as an environmentally-friendly and efficient option. Indirect photodegradation is the main pathway for the degradation of residual antibiotics in natural water, as opposed to direct photodegradation. Algae, working as photosensitizers, play an important role in the indirect photolysis of residual antibiotics in natural water bodies. They promote this reaction by secreting extracellular organic matters (EOMs) and inducing the generation of active species. In order to provide a thorough understanding of the effects of algae on residual antibiotic degradation in the environment, this paper comprehensively reviews the latest research regarding algae-induced antibiotic photodegradation. The summary of the different pathways and photosensitive mechanisms involved in this process show that EOMs are indispensable to antibiotic photodegradation. The influencing factors of algae-induced photodegradation are also discussed here: these include algae species, antibiotic types, and environmental variables such as light source, ferric ion presence, temperature, and ultrasound treatment. Based on the review of existing literature, this paper also considers several pathways for the future study of algae-induced antibiotic photodegradation.

Modeling transport of antibiotic resistant bacteria in aquatic environment using stochastic differential equations

Contaminated sites are recognized as the "hotspot" for the development and spread of antibiotic resistance in environmental bacteria. It is very challenging to understand mechanism of development of antibiotic resistance in polluted environment in the presence of different anthropogenic pollutants. Uncertainties in the environmental processes adds complexity to the development of resistance. This study attempts to develop mathematical model by using stochastic partial differential equations for the transport of fluoroquinolone and its resistant bacteria in riverine environment. Poisson's process is assumed for the diffusion approximation in the stochastic partial differential equations (SPDE). Sensitive analysis is performed to evaluate the parameters and variables for their influence over the model outcome. Based on their sensitivity, the model parameters and variables are chosen and classified into environmental, demographic, and anthropogenic categories to investigate the sources of stochasticity. Stochastic partial differential equations are formulated for the state variables in the model. This SPDE model is then applied to the 100 km stretch of river Musi (South India) and simulations are carried out to assess the impact of stochasticity in model variables on the resistant bacteria population in sediments. By employing the stochasticity in model variables and parameters we came to know that environmental and anthropogenic variations are not able to affect the resistance dynamics at all. Demographic variations are able to affect the distribution of resistant bacteria population uniformly with standard deviation between 0.087 and 0.084, however, is not significant to have any biological relevance to it. The outcome of the present study is helpful in simplifying the model for practical applications. This study is an ongoing effort to improve the model for the transport of antibiotics and transport of antibiotic resistant bacteria in polluted river. There is a wide gap between the knowledge of stochastic resistant bacterial growth dynamics and the knowledge of transport of antibiotic resistance in polluted aquatic environment, this study is one step towards filling up that gap.

Degradation and metabolic pathways of sulfamethazine and enrofloxacin in Chlorella vulgaris and Scenedesmus obliquus treatment systems

The degradation and metabolic pathways of sulfamethazine (SMZ) and enrofloxacin (ENR) via microalgal treatment systems were investigated in this study. SMZ and ENR applied at 1-25 mg L^-1 did not significantly inhibit the growth of Chlorella vulgaris or Scenedesmus obliquus. SMZ and ENR exposure did not significantly alter the maximum quantum efficiencies of C. vulgaris and S. obliquus. When cultured at light intensities of 45-50 μmol photon m^-2 s^-1, the C. vulgaris and S. obliquus treatment systems achieved 24% and 11% degradation, respectively. The greatest removal of ENR was 52% and 43.3%, for C. vulgaris and S. obliquus treatment systems, respectively, after 15 days. The results indicated that the degradation of SMZ and ENR occurred by a combination of biodegradation and photolysis. Kinetic investigations revealed that the removal of SMZ and ENR (5 mg L^-1) followed a first-order model, with apparent rate constants (k) ranging from 0.0141 to 0.0048 day^-1 and 0.0132 to 0.0086 day^-1, respectively. Fifteen metabolites of SMZ and five intermediates of ENR were identified by UPLC-MS, and degradation pathways for SMZ and ENR were proposed. SMZ transformation reactions included ring cleavage, hydroxylation, methylation, and oxidation, whereas ENR was degraded by dealkylation, decarboxylation, and defluorination. Graphical abstract.

Evaluation of physiological changes induced by the fluoroquinolone antibiotic ciprofloxacin in the freshwater macrophyte species Lemna minor and Lemna gibba

The worldwide increase in the consumption of antibiotics is becoming a concern for the scientific community, since the presence of their residues in the wild poses specific challenges, especially in ecotoxicological terms. Currently, antibiotics are used for a wide range of purposes, being used against bacterial diseases but also as growth promoters. As a result, their environmental presence can affect wild organisms, especially those from the aquatic environment. This scenario leads to the need of characterizing the toxicity of antibiotics, especially towards non-target organisms. In this study we selected two species of aquatic macrophytes, Lemna minor and Lemna gibba, which are standard plant species inscribed in ecotoxicological testing guidelines. In this work we characterized the toxic effects of the quinolone antibiotic ciprofloxacin (in levels of 0.005, 0.013, 0.031, 0.078, and 0.195 mg/L), focusing on its potential toxicity towards photosynthetic mechanisms, and pro-oxidant effects. These objectives were attained by measuring the concentrations of chlorophyll a and b, and carotenoids levels. The determination of the quantum yield allowed assessing the effects of ciprofloxacin on the photochemical efficiency of the Photosystem II (PSII). The pro-oxidant effects induced by ciprofloxacin were evaluated by measuring oxidative stress biomarkers, such as catalase activity, and also by determining lipoperoxidation levels. The obtained results showed no differences in terms of the content of both chlorophylls a and b, or any change in the photochemical efficiency of the PSII; however, the global carotenoids content of L. gibba were significantly decreased. The activity of the anti-oxidant enzyme catalase was also significantly increased in L. minor. L. gibba showed a decrease in lipid peroxidation levels, but only for the two lowest concentrations of ciprofloxacin. The global set of data shows the activation of the anti-oxidant defensive system of both plant species, a response that was likely activated by the pro-oxidant character of ciprofloxacin. Our data demonstrate the interference of this therapeutic compound at different levels of plant metabolism, at ecologically relevant concentrations. In fact, the obtained results are of ecological relevance since they illustrate deleterious effects that may compromise the physiology of aquatic non-target plant species.

Enrofloxacin and Roundup® interactive effects on the aquatic macrophyte Elodea canadensis physiology

The co-occurrence of aquatic contaminants, such as antibiotics and herbicides, has motivated investigations into their interactive effects on aquatic organisms. We examined the combined effects of environmental concentrations of the antibiotic Enrofloxacin (Enro; 0-2.25 μg l-1) and Roundup OriginalDI (Roundup®; 0-0.75 μg active ingredient l-1), a glyphosate based-herbicide, on Elodea canadensis. Enro alone was not toxic, but the plants were highly sensitive to Roundup® whose toxicity is related to the induction of oxidative stress. The metabolism of Enro by plants into Ciprofloxacin (Cipro) was observed, and although former is not phytotoxic, oxidative events associated with Cipro generation were observed. The activity of cytochrome P450 was shown to be involved in Enro degradation in E. canadensis. As a cytochrome P450 inhibitor, Roundup® decreases Enro metabolism in plants. Enro, in turn, increases glyphosate uptake and toxicity, so that Enro and Roundup® have synergistic effects, disrupting the physiological processes of E. canadensis. Our results suggest E. canadensis as a potential candidate for the reclamation of Enro in contaminated waters, but not for Roundup® due to its high sensitivity to that herbicide.

Photolysis of enrofloxacin, pefloxacin and sulfaquinoxaline in aqueous solution by UV/H2O2, UV/Fe(II), and UV/H2O2/Fe(II) and the toxicity of the final reaction solutions on zebrafish embryos

In this work, the photolysis of enrofloxacin (ENR), pefloxacin (PEF), and sulfaquinoxaline (SQX) in aqueous solution by UV combined with H₂O₂ or ferrous ions (Fe(II)), as well as Fenton (Fe(II)/H₂O₂) processes, was investigated. In addition, the toxicity of the final reaction solution after UV/H₂O₂/Fe(II) treatment toward zebrafish embryos was determined. The degradation of the test compounds followed pseudo-first-order reaction kinetics. The optimum concentrations of H₂O₂ for ENR, PEF and SQX removal under UV/H₂O₂ treatment were 20, 20 and 5 mM, respectively. The optimum concentrations of Fe(II) for ENR, PEF and SQX removal in the UV/Fe(II) system were 0.25, 10, and 1 mM, respectively. For the UV/H₂O₂/Fe(II) system, pH = 3 is the best initial pH for the degradation of ENR, PEF and SQX with the degradation efficiencies at 100%, 79.1% and 100% after 180 min, respectively. Considering the degradation rate and electrical energy per order of the test compounds, the UV/H₂O₂/Fe(II) process was better than the UV/H₂O₂ and UV/Fe(II) processes because of the greater OH generation. Based on major transformation products of ENR, PEF, and SQX detected during UV/H₂O₂/Fe(II) treatment, the probable degradation pathway of each compound is proposed. The fluorine atom of ENR and PEF was transformed into fluorine ion, and the sulfur atom was transformed into SO₂/SO₄^2-. The nitrogen atom was mainly transformed into NH₃/NH₄⁺. Formic acid, acetic acid, oxalic acid, and fumaric acid were identified in the irradiated solutions and all the test compounds and their intermediates can be finally mineralized. In addition, after the UV/H₂O₂/Fe(II) process, the acute toxicity of the final reaction solutions on zebrafish embryos was lower than that of the initial solution without any treatment. In summary, UV/H₂O₂/Fe(II) is a safe and efficient technology for antibiotic degradation.

DFT/TDDFT insights into effects of dissociation and metal complexation on photochemical behavior of enrofloxacin in water

Elucidation of the mechanisms underlying the effects of different dissociated forms and metal ion complexation on the photochemical behavior of antibiotics in aqueous media is a key problem and requires further research. We examined the mechanism of the direct photolysis of enrofloxacin (ENRO) in different dissociated forms in water and the impact of metal ions (Mg²⁺) on the photolysis of ENRO using density functional theory and time-dependent density functional theory. The results showed that different dissociated forms of ENRO exhibited diverse maximum electronic absorbance wavelengths (ENRO³⁺ (264 nm) < ENRO^- (278 nm) < ENRO⁰ (280 nm) < ENRO²⁺ (282 nm) < ENRO⁺ (306 nm)). The calculations of the reaction pathways and activation energies (E_a) in the photolysis of ENRO⁰/ENRO⁺/ENRO^- showed that defluorination was the main reaction pathway. The removal of cyclopropane was the main reaction pathway for the direct photolysis of ENRO²⁺/ENRO³⁺. Furthermore, the presence of Mg²⁺ was observed to change the order of the maximum electronic absorbance wavelengths and increases the intensities of the ENRO absorbance peaks. Calculations of the photolysis reaction pathways showed that the presence of Mg²⁺ increased the E_a for the most direct photolysis pathways of ENRO, while its presence decreased the E_a for several partial direct photolysis pathways such as the pathway in which the piperazine ring moiety of ENRO⁰/ENRO³⁺ is damaged and the pathway in which cyclopropane is released from ENRO³⁺. The findings on the photolysis behavior of ENRO in water system have provided useful information on the risk assessment of antibiotics.

Mathematical model for the transport of fluoroquinolone and its resistant bacteria in aquatic environment

Development of antibiotic resistance in environmental bacteria is a direct threat to public health. Therefore, it becomes necessary to understand the fate and transport of antibiotic and its resistant bacteria. This paper presents a mathematical model for spatial and temporal transport of fluoroquinolone and its resistant bacteria in the aquatic environment of the river. The model includes state variables for organic matter, fluoroquinolone, heavy metals, and susceptible and resistant bacteria in the water column and sediment bed. Resistant gene is the factor which makes bacteria resistant to a particular antibiotic and is majorly carried on plasmids. Plasmid-mediated resistance genes are transferable between different bacterial species through conjugation (horizontal resistance transfer). This model includes plasmid dynamics between susceptible and resistant bacteria by considering the rate of horizontal resistance gene transfer among bacteria and the rate of losing resistance (segregation). The model describes processes which comprise of advection, dispersion, degradation, adsorption, diffusion, settling, resuspension, microbial growth, segregation, and transfer of resistance genes. The mathematical equations were solved by using numerical methods (implicit-explicit scheme) with appropriate boundary conditions. The development of the present model was motivated by the fact that the Musi River is heavily impacted by antibiotic pollution which led to the development of antibiotic resistance in its aquatic environment. The model was simulated for hypothetical pollution scenarios to predict the future conditions under various pollution management alternatives. The simulation results of the model for different cases show that the concentration of antibiotic, the concentration of organic matter, segregation rate, and horizontal transfer rate are the governing factors in the variation of population density of resistant bacteria. The treatment of effluents for antibiotics might be costly for the bulk drug manufacturing industries, but the guidelines can be made to reduce the organic matter which can limit the growth rate of microbes and reduce the total microbial population in the river. The reduction in antibiotic concentration can reduce the selection pressure on bacteria and can limit the population of resistant culture and its influence zone in the river stretch; however, complete removal of antibiotics may not result in complete elimination of antibiotic-resistant bacteria.

Effects of temperature, genetic variation and species competition on the sensitivity of algae populations to the antibiotic enrofloxacin

Primary producers are amongst the most sensitive organisms to antibiotic pollution in aquatic ecosystems. To date, there is little information on how different environmental conditions may affect their sensitivity to antibiotics. In this study we assessed how temperature, genetic variation and species competition may affect the sensitivity of the cyanobacterium Microcystis aeruginosa and the green-algae Scenedesmus obliquus to the antibiotic enrofloxacin. First, we performed single-species tests to assess the toxicity of enrofloxacin under different temperature conditions (20°C and 30°C) and to assess the sensitivity of different species strains using a standard temperature (20°C). Next, we investigated how enrofloxacin contamination may affect the competition between M. aeruginosa and S. obliquus. A competition experiment was performed following a full factorial design with different competition treatments, defined as density ratios (i.e. initial bio-volume of 25/75%, 10/90% and 1/99% of S. obliquus/M. aeruginosa, respectively), one 100% S. obliquus treatment and one 100% M. aeruginosa treatment, and four different enrofloxacin concentrations (i.e. control, 0.01, 0.05 and 0.10mg/L). Growth inhibition based on cell number, bio-volume, chlorophyll-a concentration as well as photosynthetic activity were used as evaluation endpoints in the single-species tests, while growth inhibition based on measured chlorophyll-a was primarily used in the competition experiment. M. aeruginosa photosynthetic activity was found to be the most sensitive endpoint to enrofloxacin (EC50-72h =0.02mg/L), followed by growth inhibition based on cell number. S. obliquus was found to be slightly more sensitive at 20°C than at 30°C (EC50-72h cell number growth inhibition of 38 and 41mg/L, respectively), whereas an opposite trend was observed for M. aeruginosa (0.047 and 0.037mg/L, respectively). Differences in EC50-72h values between algal strains of the same species were within a factor of two. The competition experiment showed that M. aeruginosa growth can be significantly reduced in the presence of S. obliquus at a density ratio of 75/25% M. aeruginosa/S. obliquus, showing a higher susceptibility to enrofloxacin than in the single-species test. The results of this study confirm the high sensitivity of cyanobacteria to antibiotics and show that temperature and inter-strain genetic variation may have a limited influence on their response to them. The results of the competition experiment suggest that the structure of primary producer communities can be affected, at least temporarily, at antibiotic concentrations close to those that have been measured in the environment.

Fluoroquinolones (FQs) in the environment: A review on their abundance, sorption and toxicity in soil

The use of fluoroquinolones (FQs) antibiotics as therapeutic agents and growth promoters is increasing worldwide; however their extensive uses are also resulting in antibiotic resistance among world communities. FQs have also become one of the major contaminants in the waste water bodies, which are not even completely removed during the treatment processes. Furthermore, their abundance in agricultural resources, such as the irrigation water, the bio-solids and the livestock manure can also affect the soil micro-environment. These antibiotics in soil tend to interact in several different ways to affect soil flora and fauna. The current review endeavors to highlight the some critical aspects of FQs prevalence in the environment. The review presents a detailed discussion on the pathways and abundance of FQs in soil. The discussion further spans the issue of sorption and FQs transformation into the soil better understand of their behavior and their toxicity to soil flora and fauna.

Assessing the presence of enrofloxacin and ciprofloxacin in piggery wastewater and their adsorption behaviour onto solid materials, with a newly developed chromatographic method

Veterinary antibiotics could enter the environment after the application of manure or farm wastewater on soil as fertilizer. In this study, a UPLC-MS/MS analytical method was developed and validated for the simultaneous determination of enrofloxacin (ENR) and ciprofloxacin (CIP) at environmental relevant concentrations in piggery wastewater, piggery wastewater solids, agricultural soil and ground water with good performance characteristics. The method recovery for ENR and CIP was 94.2 and 89.9% in the filtered piggery wastewater, 81.3 and 82% in the wastewater solid material, 78.1 and 76.8% in the soil and 95.6 and 97.3% in the ground water. The Limit of Detection (LOD) and Limit of Quantification (LOQ) for ENR were 21 and 64 ng L^-1 and for CIP was 18 and 54 ng L^-1, respectively. The method was implemented to monitor ENR and CIP in the wastewater of a piggery facility in Cyprus which applied anaerobic treatment before the final disposal of the reclaimed water. The highest antibiotic concentrations were measured in the wastewater samples collected from the nursery, where ENR is continuously used, with average concentration 31.4 μg L^-1 for ENR and 16.0 μg L^-1 for CIP. After the anaerobic digester, the two antibiotics were found only on the solid matter of the treated wastewater with an average concentration of 1.7 μg kg^-1 for ENR and 1.0 μg kg^-1 for CIP. The antibiotics adsorption at pH = 7 on clay soil, quartz sand and on solid matter isolated from the piggery wastewater was found to be higher than 95% for all solid materials. The concentration of the antibiotics in soil samples taken from a field where reclaimed piggery wastewater was applied for 10 years and in samples of groundwater from a nearby well was found for all samples below the LOD.

Direct Photolysis of Fluoroquinolone Antibiotics at 253.7 nm: Specific Reaction Kinetics and Formation of Equally Potent Fluoroquinolone Antibiotics

Three fluoroquinolone-to-fluoroquinolone antibiotic transformations were monitored during UV-C irradiation processes. In particular, the following reactions were observed: enrofloxacin-to-ciprofloxacin, difloxacin-to-sarafloxacin, and pefloxacin-to-norfloxacin. The apparent molar absorptivity and fluence-based pseudo-first-order rate constants for transformation of the six fluoroquinolones by direct photolysis at 253.7 nm were determined for the pH 2-12 range. These parameters were deconvoluted to calculate specific molar absorptivity and fluence-based rate constants for cationic, zwitterionic, and anionic fluoroquinolone species. For a typical disinfection fluence of 40 mJ/cm(2), the apparent transformation efficiencies were inflated by 2-8% when fluoroquinolone products were not considered; moreover, the overall transformation efficiencies at 400 mJ/cm(2) varied by up to 40% depending on pH. The three product antibiotics, namely ciprofloxacin, sarafloxacin, and norfloxacin, were found to be equally or more potent than the parent fluoroquinolones using an Escherichia coli-based assay. UV treatment of a solution containing difloxacin was found to increase antimicrobial activity due to formation of sarafloxacin. These results highlight the importance of considering antibiotic-to-antibiotic transformations in UV-based processes.

Role of humic substances in the degradation pathways and residual antibacterial activity during the photodecomposition of the antibiotic ciprofloxacin in water

This study focuses on the photo-transformation, in presence of humic substances (HSs), of ciprofloxacin (CIP), a commonly-used fluoroquinolone antibiotic whose presence in aquatic ecosystems is a health hazard for humans and other living organisms. HSs from the International Humic Substances Society (Elliott humic acid and fulvic acid, Pahokee peat humic acid and Nordic lake) and a humic acid extracted from modified coal (HACM) were tested for their ability to photodegrade CIP. Based on kinetic and analytical studies, it was possible to establish an accelerating effect on the rate of CIP decomposition caused by the humic substances. This effect was associated with the photosensitized capacity of the HSs to facilitate energy transfer from an excited humic state to the ground state of ciprofloxacin. Except for Nordic lake, which experienced a lower positive effect, no significant differences in the CIP transformation were found among the different humic acids examined. The photochemistry of CIP can be modified by parameters such as pH, CIP or oxygen concentration. The irradiation of this antibiotic in the presence of HACM showed that antimicrobial activity was negligible after 14 h for E. coli and 24 h for S. aureus. In contrast, the antimicrobial activity was only slightly decreased after 24 h of irradiation by direct photolysis. Although mineralization of CIP irradiation in the presence of a HACM solution was not achieved, biodegradability was achieved after 12 h of irradiation, indicating that microorganisms within the environment can easily degrade CIP photochemical by-products.

Evaluation of the oxidation of enrofloxacin by permanganate and the antimicrobial activity of the products

Permanganate [Mn(VII)] oxidation of the fluoroquinolone (FQ) antibiotic enrofloxacin (ENR) was investigated with respect to kinetics and mechanisms, and the products were evaluated for residual antibacterial activity. The degradation of ENR by Mn(VII) obeyed second-order kinetics. A modern liquid chromatography coupled to a hybrid quadrupole time-of-flight mass spectrometer (LC-Q-TOF) was used to determine the accurate mass of the measured degradation products. The structures of nine oxidation products were identified at a neutral pH, one of which was an N-oxide product formed from the oxidation of tertiary amines. One proposed plausible reaction pathway was that the oxidation occurred on the piperazine ring; the C-H adjacent to the amine group was attacked by Mn(VII). The identified products from ENR arose through four pathways involving two mechanisms of N-dealkylation, C-hydroxylation and the reactions of amine oxides. The quinolone core remained intact for all of the products. The residual antibacterial activity of the oxidative reaction byproducts against the nonresistant Escherichia coli (G(-)) reference strain DH5ɑ was evaluated by quantifying the bacterial colonies. The oxidation products exhibited reduced antibacterial activity compared with their parent compound.

Response of a salt marsh microbial community to antibiotic contamination

Salt marsh plants and associated microorganisms can have an important role in contaminant removal from estuaries, through bioremediation processes. Nevertheless, the interaction between emerging contaminants, namely antibiotics, and plant-microorganism associations in estuarine environment are still scarcely known. In this vein, the aim of the present study was to evaluate, in controlled conditions, the response of a salt marsh plant-microorganism association to a contamination with a veterinary antibiotic. For that a salt marsh plant (Phragmites australis) and its respective rhizosediment were collected in a temperate estuary (Lima estuary, NW Portugal) and exposed for 7 days to enrofloxacin (ENR) under different nutritional conditions in sediment elutriates. Response was evaluated in terms of ENR removal and changes in microbial community structure (evaluated by ARISA) and abundance (estimated by DAPI). In general, no significant changes were observed in microbial abundance. Changes in bacterial richness and diversity were observed but only in unplanted systems. However, multivariate analysis of ARISA profiles showed significant effect of both the presence of plant and type of treatment on the microbial community structure, with significant differences among all treatment groups. In addition, plants and associated microorganisms presented a potential for antibiotic removal that, although highly dependent on their nutritional status, can be a valuable asset to recover impacted areas such as estuarine ones.

New insights into the aquatic photochemistry of fluoroquinolone antibiotics: Direct photodegradation, hydroxyl-radical oxidation, and antibacterial activity changes

The ubiquity and photoreactivity of fluoroquinolone antibiotics (FQs) in surface waters urge new insights into their aqueous photochemical behavior. This study concerns the photochemistry of 6 FQs: ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin and enrofloxacin. Methods were developed to calculate their solar direct photodegradation half-lives (td,E) and hydroxyl-radical oxidation half-lives (tOH,E) in sunlit surface waters. The td,E values range from 0.56 min to 28.8 min at 45° N latitude, whereas tOH,E ranges from 3.24h to 33.6h, suggesting that most FQs tend to undergo fast direct photolysis rather than hydroxyl-radical oxidation in surface waters. However, a case study for levofloxacin and sarafloxacin indicated that the hydroxyl-radical oxidation induced risky photochlorination and resulted in multi-degradation pathways, such as piperazinyl hydroxylation and clearage. Changes in the antibacterial activity of FQs caused by photodegradation in various waters were further examined using Escherichia coli, and it was found that the activity evolution depended on primary photodegradation pathways and products. Primary intermediates with intact FQ nuclei retained significant antibacterial activity. These results are important for assessing the fate and risk of FQs in surface waters.

Human-use antibacterial residues in the natural environment of China: implication for ecopharmacovigilance

Antibacterial residues in the natural environment have been of increasing concern due to their impact on bacteria resistance development and toxicity to natural communities and ultimately to public health. China is a large country with high production and consumption of antibacterials for its population growth and economic development in recent years. In this article, we summarized the current situation of human-use antibacterial pollution in Chinese water (wastewaters, natural and drinking waters) and solid matrices (sludge, sediment, and soil) reported in 33 peer-reviewed papers. We found that, although there are adequate wastewater treatment systems in China, human-use antibacterial residues in the natural environment were reported almost throughout the whole country. Three most frequently prescribed classes of antibacterials in China, including quinolones, macrolides, and β-lactam, were also the predominant classes of residues in Chinese environment, manifested as the high concentration and detection frequency. In view of this alarming situation, we have presented that ecopharmacovigilance (EPV) might be implemented in the antibacterial drug administration of China, as the active participation of the pharmaceutical industry and drug regulatory authorities from the diffuse source of antibacterial pollution. Considering EPV experience of developed countries together with the actual conditions of China, we have identified some approaches that can be taken, including:• Focus on education;• Further strengthening and persevering the antibacterial stewardship strategies and pharmaceutical take-back programs in China;• Designing greener antibacterials with better degradability in the environment;• Implementing environmental risk assessment prior to launch of new drugs;• Strengthening collaboration in EPV-related areas.

Effects of enrofloxacin, ciprofloxacin, and trimethoprim on two generations of Daphnia magna

Multigenerational tests on Daphnia magna were performed exposing two subsequent generation to enrofloxacin (EFX) and its metabolite ciprofloxacin (CPX), and to trimethoprim (TMP). Mortality rate of 100% and 50% was detected in F0 at concentrations of ≥ 13 mgL(-1) (EFX) and 50 mgL(-1) (TMP), respectively. In F1 with respect to F0, both for growth and reproduction, a worsening trend of the response with EFX, a similar response with CPX and an attenuating trend with TMP was observed. Furthermore, the lowest EC20 for reproduction inhibition (1.3 mgL(-1)) was calculated for F1 exposed to EFX. However, other experimentations, longer and more complex, are necessary in order to confirm that EFX is more hazardous to daphnids than CPX and TMP. EC50 measured for the three assayed antibacterials were in the 6.5-37 mgL(-1) range therefore environmental unrealistic, except in case of exceptional contaminations that may occur in relation to poorly controlled wastewaters from pharmaceutical factories or excessive use of prophylactic treatments in aquaculture.

Environmental photochemistry of fluoroquinolones in soil and in aqueous soil suspensions under solar light

The photodegradation fate of widely used fluoroquinolone (FQ) drugs has been studied both at the water-soil interface and in soil at actual concentrations (500 ng g(-1)) under natural solar light. Both human and veterinary drugs have been examined, namely ciprofloxacin, danofloxacin, enrofloxacin, levofloxacin, marbofloxacin and moxifloxacin. After spiking and irradiation, samples were submitted to microwave-assisted extraction and analyzed by high-performance liquid chromatography coupled to fluorescence detection (HPLC-FD). FQs degradation was faster in aqueous soil suspension than in neat soil (but lower than in "clean" water). A number of byproducts were identified by HPLC electrospray ionization tandem mass spectrometry after a post-extraction cleanup based on a molecularly imprinted polymer phase, for a more accurate detection. The distribution in the suspension was intermediate between those observed in soils and in aqueous solutions.

Fluoroquinolone antibiotics: an emerging class of environmental micropollutants

The aim of this review paper is to provide a comprehensive overview of different chemical and environmental aspects concerning fluoroquinolone antibiotics as emerging contaminants. A literature survey has been performed based on 204 papers from 1998 to mid-2013, resulting in a dataset consisting out of 4100 data points related to physical-chemical properties, environmental occurrence, removal efficiencies, and ecotoxicological data. In a first part, an overview is given on relevant physical-chemical parameters to better understand the behavior of fluoroquinolones during wastewater treatment and in the environment. Secondly, the route of these antibiotics after their application in both human and veterinary surroundings is discussed. Thirdly, the occurrence of fluoroquinolone residues is discussed for different environmental matrices. The final part of this review provides a tentative risk assessment of fluoroquinolone compounds and their transformation products in surface waters by means of hazard quotients. Overall, this review shows that fluoroquinolone antibiotics have a wide spread use and that their behavior during wastewater treatment is complex with an incomplete removal. As a result, it is observed that these biorecalcitrant compounds are present in different environmental matrices at potentially hazardous concentrations for the aquatic environment. The latter calls for actions on both the consumption as well as the wastewater treatment aspect to diminish the discharge of these biological active compounds.

The sensitivity of Daphnia magna and Daphnia curvirostris to 10 veterinary antibacterials and to some of their binary mixtures

Aim of this study was to evaluate the suitability of Daphnia curvirostris for the acute toxicity test usually performed on Daphnia magna, and to compare the sensitivity of the two species toward 10 antibacterials [enrofloxacin (EFX), ciprofloxacin(CPX), sulfaguanidine (SGD), sulfadiazine (SDZ), sulfamethazine (SMZ), sulfaquinoxaline (SQO), sulfaclozine (SCZ), sulfamerazine (SMA), sulfadimethoxine (SDM) and trimethoprim (TMP)] and some of their binary mixtures. Furthermore, a tentative prolonged-toxicity test (lasting 13d) was settled up in order to evidence toxic responses with drug concentrations that were uneffective in the classic 48h immobilization test. Results showed that D. curvirostris was more sensitive than D. magna to the majority of compounds (6 out of 10). Lowest 48h EC50s were obtained with EFX (4.3mgL(-1) in D. curvirostris) and SGD (6.2mgL(-1) in D. magna). The toxicity of paired compounds was always concentration-additive or less than concentration-additive. In the prolonged-toxicity test mortality and/or reproduction inhibition were constantly observed. It was concluded that: (1) D. curvirostris could be a suitable model for the evaluation of acute toxicity of antibacterials since its sensitivity was generally greater than that of D. magna; (2) the toxicity of EFX and SGD should be given special attention as the two compounds, in the prolonged test, showed to be active at concentrations of 0.9mgL(-1) and 2.5mgL(-1), respectively; (3) the concentration addition is usually a reasonable worst case estimation of the environmental impact of antibacterial mixtures.

Use, fate and ecological risks of antibiotics applied in tilapia cage farming in Thailand

The use, environmental fate and ecological risks of antibiotics applied in tilapia cage farming were investigated in the Tha Chin and Mun rivers in Thailand. Information on antibiotic use was collected through interviewing 29 farmers, and the concentrations of the most commonly used antibiotics, oxytetracycline (OTC) and enrofloxacin (ENR), were monitored in river water and sediment samples. Moreover, we assessed the toxicity of OTC and ENR on tropical freshwater invertebrates and performed a risk assessment for aquatic ecosystems. All interviewed tilapia farmers reported to routinely use antibiotics. Peak water concentrations for OTC and ENR were 49 and 1.6 μg/L, respectively. Antibiotics were most frequently detected in sediments with concentrations up to 6908 μg/kg d.w. for OTC, and 2339 μg/kg d.w. for ENR. The results of this study indicate insignificant short-term risks for primary producers and invertebrates, but suggest that the studied aquaculture farms constitute an important source of antibiotic pollution.

Photo-transformation of pharmaceutically active compounds in the aqueous environment: a review

In the past few years, the fate and transportation of pharmaceutically active compounds (PhACs) in aqueous environments have raised significant concerns among the public, scientists and regulatory groups. Photodegradation is an important removal process in surface waters. This review summarizes the last 10 years (2003-2013) of studies on the solar or solar-simulated photodegradation of PhACs in aqueous environments. The PhACs covered include: beta-blockers, antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs), histamine H₂-receptor antagonists, lipid regulators, carbamazepine, steroid hormones, and X-ray contrast media compounds. Kinetic studies, degradation mechanisms and toxicity removal are the three major topics involved in this review. The quantum yield for the direct photolysis of PhACs and the bimolecular reaction rate constants of PhACs with reactive oxygen species (ROS), such as the ˙OH radical and singlet oxygen, are also summarized. This information is not only important to predict the PhAC photodegradation fate, but also is very useful for advanced treatment technologies, such as ozone or advanced oxidation processes.

Effects of the antibiotic enrofloxacin on the ecology of tropical eutrophic freshwater microcosms

The main objective of the present study was to assess the ecological impacts of the fluoroquinolone antibiotic enrofloxacin on the structure and functioning of tropical freshwater ecosystems. Enrofloxacin was applied at a concentration of 1, 10, 100 and 1,000 μg/L for 7 consecutive days in 600-L outdoor microcosms in Thailand. The ecosystem-level effects of enrofloxacin were monitored on five structural (macroinvertebrates, zooplankton, phytoplankton, periphyton and bacteria) and two functional (organic matter decomposition and nitrogen cycling) endpoint groups for 4 weeks after the last antibiotic application. Enrofloxacin was found to dissipate relatively fast from the water column (half-dissipation time: 11.7h), and about 11% of the applied dose was transformed into its main by-product ciprofloxacin after 24h. Consistent treatment-related effects on the invertebrate and primary producer communities and on organic matter decomposition could not be demonstrated. Enrofloxacin significantly affected the structure of leaf-associated bacterial communities at the highest treatment level, and reduced the abundance of ammonia-oxidizing bacteria and ammonia-oxidizing archaea in the sediments, with calculated NOECs of 10 and <1 μg/L, respectively. The ammonia concentration in the microcosm water significantly increased in the highest treatment level, and nitrate production was decreased, indicating a potential impairment of the nitrification function at concentrations above 100 μg/L. The results of this study suggest that environmentally relevant concentrations of enrofloxacin are not likely to result in direct or indirect toxic effects on the invertebrate and primary producer communities, nor on important microbially mediated functions such as nitrification.

Investigation of residual fluoroquinolones in a soil-vegetable system in an intensive vegetable cultivation area in Northern China

One of the largest vegetable cultivation field sites in Northeast China was selected to investigate the occurrence and distribution pattern of fluoroquinolones (FQs) in the soil-vegetable system. A total of 100 surface soil samples and 68 vegetable samples were collected from this study area. The antibiotic concentration was analyzed using high-performance liquid chromatography tandem mass spectrometry. Results indicated the presence of FQs in all soil samples. Ciprofloxacin (CIP) had the highest mean concentration, at 104.4 μg · kg(-1) in the soil, a level that represents a relatively high risk to the environment and to human health. However, in the vegetable samples, norfloxacin (NOR) was significantly higher than CIP and enrofloxacin (ENR), ranging from 18.2 to 658.3 μg · kg(-1). The transfer ability of NOR in soil-vegetables is greater than that of CIP and ENR. Moreover, we found that the solanaceous fruits had a higher antibiotic accumulation ability than the leafy vegetables. Taken together, these data indicate that greater attention should be paid to the region in which vegetables with higher accumulation ability are grown.

Degradation of the potential rodent contraceptive quinestrol and elimination of its estrogenic activity in soil and water

Quinestrol has shown potential for use in the fertility control of the plateau pika population of the Qinghai-Tibet Plateau. However, the environmental safety and fate of this compound are still obscure. Our study investigated degradation of quinestrol in a local soil and aquatic system for the first time. The results indicate that the degradation of quinestrol follows first-order kinetics in both soil and water, with a dissipation half-life of approximately 16.0 days in local soil. Microbial activity heavily influenced the degradation of quinestrol, with 41.2% removal in non-sterile soil comparing to 4.8% removal in sterile soil after incubation of 10 days. The half-lives in neutral water (pH 7.4) were 0.75 h when exposed to UV light (λ = 365 nm) whereas they became 2.63 h when exposed to visible light (λ > 400 nm). Acidic conditions facilitated quinestrol degradation in water with shorter half-lives of 1.04 and 1.47 h in pH 4.0 and pH 5.0 solutions, respectively. Moreover, both the soil and water treatment systems efficiently eliminated the estrogenic activity of quinestrol. Results presented herein clarify the complete degradation of quinestrol in a relatively short time. The ecological and environmental safety of this compound needs further investigation.

The potential environmental risks of pharmaceuticals in Vietnamese aquatic systems: case study of antibiotics and synthetic hormones

Presently, many pharmaceuticals are listed as emerging contaminants since they are considered to be great potential threats to environmental ecosystems. These contaminants, thus, present significant research interest due to their extensive use and their physicochemical and toxicological properties. This review discusses a whole range of findings that address various aspects of the usage, occurrence, and potentially environmental risks of pharmaceuticals released from various anthropogenic sources, with emphasis on the aquatic systems in Vietnam. The published information and collected data on the usage and occurrence of antibiotics and synthetic hormone in effluents and aquatic systems of Vietnam is reported. This is followed by a potential ecological risk assessment of these pollutants. The extensive use of antibiotics and synthetic hormones in Vietnam could cause the discharge and accumulation of these contaminants in the aquatic systems and potentially poses serious risks for ecosystems. Vietnam is known to have extensively used antibiotics and synthetic hormones, so these contaminants are inevitably detected in aquatic systems. Thus, an appropriate monitoring program of these contaminants is urgently needed in order to mitigate their negative effects and protect the ecosystems.

Antibiotics in riverine runoff of the Pearl River Delta and Pearl River Estuary, China: concentrations, mass loading and ecological risks

Ten antibiotics belonging to three groups (macrolides, fluoroquinolones and sulfonamides) were investigated in riverine runoff of the Pearl River Delta (PRD) and Pearl River Estuary (PRE), South China for assessing the importance of riverine runoff in the transportation of contaminants from terrestrial sources to the open ocean. All antibiotics were detected in the eight outlets with concentrations ranging from 0.7 to 127 ng L(-1). The annual mass loadings of antibiotics from the PRD to the PRE and coast were 193 tons with 102 tons from the fluoroquinolone group. It showed that antibiotics decreased from the riverine outlets to the PRE and open ocean. Risk assessment showed that most of these antibiotics showed various ecological risks to the relevant aquatic organisms, in which ofloxacin (OFL), erythromycin (ETM) and ciprofloxacin (CIP) posed high ecological risks to the studied aquatic environments.

Direct photochemistry of three fluoroquinolone antibacterials: norfloxacin, ofloxacin, and enrofloxacin

Fluoroquinolone (FQ) antibacterial compounds are frequently detected in the aquatic environment, and photodegradation is expected to play an important role in FQ fate in some sunlit surface waters. This study investigated the direct aquatic photochemistry of three FQs: norfloxacin, ofloxacin, and enrofloxacin. The direct photolysis rate of each drug exhibited strong pH dependence when exposed to simulated sunlight. For each FQ, direct photolysis rates and total light absorbance were used to calculate quantum yields for each of three environmentally relevant protonation states: a cationic, a zwitterionic, and an anionic form. In each case, quantum yields of the species varied significantly. The quantum yield for the zwitterionic form was 2-3 times higher than that of the anionic form and over an order of magnitude higher than that of the cationic form. Antibacterial activity assays were used to determine whether the loss of parent FQ due to photolysis led to loss of activity. Norfloxacin and ofloxacin photoproducts were found to be inactive, whereas enrofloxacin photoproducts were found to retain significant activity. These results are important for aiding in predictions of the potential impacts of FQs in surface waters.

Trimethoprim: kinetic and mechanistic considerations in photochemical environmental fate and AOP treatment

Trimethoprim (TMP), a bacteriostatic antibiotic, has recently been detected in wastewater and surface waters. In this study the sunlight mediated photochemical fate, and treatment using advanced oxidation and reduction (free radical) processes, have been investigated with respect to their effect on TMP. Photochemical fate, in the presence of humic acid, and advanced oxidation treatment both involve the hydroxyl radical (OH) as one of the reactive species of interest. Another reactive oxygen species, singlet oxygen (1O2), may also be important in the photochemical fate of TMP. The bimolecular reaction rate constants of TMP with 1O2 and OH were evaluated to be (3.2±0.2)×10(6) M(-1) s(-1) and 8.66×10(9) M(-1) s(-1), respectively. The reaction kinetics for the sub-structural moieties of TMP, 1,2,3-trimethoxybenzene (TMBz) and 2,4-diaminoprimidine (DAP), was evaluated to facilitate an understanding of the loss mechanisms. For TMBz and DAP the reaction rate constants with 1O2 were <1.0×10(4) and (3.0±0.1)×10(6) M(-1) s(-1), while with OH they were 8.12×10(9) and 1.64×10(9) M(-1) s(-1), respectively. The data suggests that the 1O2 attacks the DAP and the OH radical attacks the TMBz moiety. However, for TMP, 1O2 and OH reactions accounted for only ∼19% and ∼6%, of its total photodegradation, respectively. Therefore, the reaction of TMP with excited state natural organic matter is postulated as a significant degradation pathway for the loss of TMP in sunlit waters containing natural organic matter. There was no effect of pH on the direct or indirect photolysis of TMP. To complete the study for reductive treatment processes, the solvated electron reaction rates for the destruction of TMP, TMBz and DAP were also evaluated. The absolute bimolecular reaction rates obtained were, (13.6±0.01)×10(9), (6.36±0.11)×10(7) and (10.1±0.01)×10(9) M(-1) s(-1), respectively.

Toxicity of the fluoroquinolone antibiotics enrofloxacin and ciprofloxacin to photoautotrophic aquatic organisms

The present study investigated the growth inhibition effect of the fluoroquinolone antibiotics enrofloxacin and ciprofloxacin on four photoautotrophic aquatic species: the freshwater microalga Desmodesmus subspicatus, the cyanobacterium Anabaena flos-aquae, the monocotyledonous macrophyte Lemna minor, and the dicotyledonous macrophyte Myriophyllum spicatum. Both antibiotics, which act by inhibiting the bacterial DNA gyrase, demonstrated high toxicity to A. flos-aquae and L. minor and moderate to slight toxicity to D. subspicatus and M. spicatum. The cyanobacterium was the most sensitive species with median effective concentration (EC50) values of 173 and 10.2 µg/L for enrofloxacin and ciprofloxacin, respectively. Lemna minor proved to be similarly sensitive, with EC50 values of 107 and 62.5 µg/L for enrofloxacin and ciprofloxacin, respectively. While enrofloxacin was more toxic to green algae, ciprofloxacin was more toxic to cyanobacteria. Calculated EC50s for D. subspicatus were 5,568 µg/L and >8,042 µg/L for enrofloxacin and ciprofloxacin, respectively. These data, as well as effect data from the literature, were compared with predicted and reported environmental concentrations. For two of the four species, a risk was identified at ciprofloxacin concentrations found in surface waters, sewage treatment plant influents and effluents, as well as in hospital effluents. For ciprofloxacin the results of the present study indicate a risk even at the predicted environmental concentration. In contrast, for enrofloxacin no risk was identified at predicted and measured concentrations.

Occurrence and distribution of antibiotics in coastal water of the Bohai Bay, China: impacts of river discharge and aquaculture activities

The presence of 21 antibiotics in six different groups was investigated in coastal water of the Bohai Bay. Meantime, to illuminate the potential effects caused by the river discharge and aquaculture activities, wastewater from three breeding plants and surface water from six rivers flowing into the Bohai Bay were also analyzed for the selected antibiotics. The result revealed that measured antibiotics in the North Bobai Bay were generally higher than those in the South, highlighting the remarkable effects of high density of human activities on the exposure of antibiotics in environment. The antibiotics found in the six rivers were generally higher than those in the Bohai Bay reflecting the important antibiotics source of river discharge. This study reveals that the high consumption of some antibiotics in aquaculture activities may pose high ecological risk to the bay.

Photolysis of Enrofloxacin in aqueous systems under simulated sunlight irradiation: Kinetics, mechanism and toxicity of photolysis products

Photolysis of Enro in water was investigated under simulated sunlight irradiation using a Xenon lamp. The results showed that Enro photolysis followed apparent first-order kinetics. Increasing Enro concentration from 5.0 to 40.0 mg L⁻¹ led to the decrease of the photolysis rate constant from 1.6 × 10⁻² to 3.0 × 10⁻³ min⁻¹. Compared with the acidic and basic conditions, the photolysis rate was faster at neutral condition. Both of nitrate and humic acid can markedly decrease the photolysis rate of Enro because they can competitively absorb photons with Enro. The electron spin resonance and reactive oxygen species scavenging experiments indicated that Enro underwent self-sensitized photooxidation via OH and ¹O₂. After irradiation for 90 min, only 13.1% reduction of TOC occurred in spite of fast photolysis of 58.9% of Enro, indicating that Enro was transformed into intermediates without complete mineralization. The photolysis of Enro involved three main pathways: decarboxylation, defluorination, and piperazinyl N⁴-dealkylation. The bioluminescence inhibition rate using Vibrio fischeri increased to 67.2% at 60 min and then decreased to 56.9% at 90 min, indicative of the generation of some more toxic intermediates than Enro and then the degradation of the intermediates. The results will help us understand fundamental mechanisms of Enro photolysis and provide insight into the potential fate and transformation of Enro in surface waters.

Antibiotic contaminants in coastal wetlands from Vietnamese shrimp farming

BACKGROUND AND PURPOSE

Shrimp culture has been expanded rapidly in recent years in coastal wetland zone of Vietnam due to favorable natural conditions. However, this industry has caused several negative impacts to the environment. One of the critical issues is the excessive application of antibiotics including human medicines. These chemicals could be released from shrimp ponds and then accumulated and contaminated of the ecosystem. This review article discusses a whole range of findings that address various aspects of the usage, occurrence and potentially environmental risks of antibiotics released from shrimp farming, with emphasis on the South Vietnam coastal wetland.

METHODS

The published information on the usage and occurrence of antibiotics in Vietnamese shrimp farming has been reviewed. A global comparison was also carried out. This follows by a brief overview of the transport and fate of these antibiotics in the environment.

RESULTS

Several antibiotics commonly used in Vietnamese shrimp culture have been detected in wastewater and sediment of the ponds, as well as in surrounding coastal wetlands, resulting in the existence of antibiotic-resistant bacteria. However, their transport and fate could not be clearly defined.

CONCLUSIONS

The well-documented accumulation of antibiotics in mud and sediments in Vietnamese coastal wetlands potentially poses serious risks for the local wetland ecosystems. Thus, research on the transport and fate of antibiotics' residues from the ponds into the surrounding environment is urgently needed.