Access the toxic effect of the antibiotic cefradine and its UV light degradation products on two freshwater algae

Joint toxicity mechanisms of binary emerging PFAS mixture on algae (Chlorella pyrenoidosa) at environmental concentration

Since traditional Per- and polyfluoroalkyl substances (PFAS) were banned in 2009 due to their bioaccumulation, persistence and biological toxicity, the emerging PFAS have been widely used as their substitutes and entered the aquatic environment in the form of mixtures. However, the joint toxicity mechanisms of these emerging PFAS mixtures to aquatic organisms remain largely unknown. Then, based on the testing of growth inhibition, cytotoxicity, photosynthesis and oxidative stress, and the toxicity mechanism of PFAS mixture (Perfluorobutane sulfonate and Perfluorobutane sulfonamide) to algae was explored using the Gene set enrichment analysis (GSEA). The results revealed that all three emerging PFAS treatments had a certain growth inhibitory effect on Chlorella pyrenoidosa (C. pyrenoidosa), but the toxicity of PFAS mixture was stronger than that of individual PFAS and showed a significant synergistic effect at environmental concentration. The joint toxicity mechanisms of binary PFAS mixture to C. pyrenoidosa were related to the damage of photosynthetic system, obstruction of ROS metabolism, and inhibition of DNA replication. Our findings are conductive to adding knowledge in understanding the joint toxicity mechanisms and provide a basis for assessing the environmental risk of emerging PFAS.

Effects of Enrofloxacin on the Epiphytic Algal Communities Growing on the Leaf Surface of Vallisneria natans

Enrofloxacin (ENR) is a member of quinolones, which are extensively used in livestock farming and aquaculture to fight various bacterial diseases, but its residues are partially transferred to surface water and affect the local aquatic ecosystem. There are many studies on the effect of ENR on the growth of a single aquatic species, but few on the level of the aquatic community. Epiphytic algae, which are organisms attached to the surface of submerged plants, play an important role in the absorption of nitrogen and phosphorus in the ecological purification pond which are mainly constructed by submerged plants, and are commonly used in aquaculture effluent treatment. Enrofloxacin (ENR) is frequently detected in aquaculture ponds and possibly discharged into the purification pond, thus imposing stress on the pond ecosystem. Here, we performed a microcosm experiment to evaluate the short-term effects of pulsed ENR in different concentrations on the epiphytic algal communities growing on Vallisneria natans. Our results showed an overall pattern of “low-dose-promotion and high-dose-inhibition”, which means under low and median ENR concentrations, the epiphytic algal biomass was promoted, while under high ENR concentrations, the biomass was inhibited. This pattern was mainly attributed to the high tolerance of filamentous green algae and yellow-green algae to ENR. Very low concentrations of ENR also favored the growth of diatoms and cyanobacteria. These results demonstrate a significant alteration of epiphytic algal communities by ENR and also spark further research on the potential use of filamentous green algae for the removal of ENR in contaminated waters because of its high tolerance.

Simultaneous electrochemical removal of Microcystis aeruginosa and sulfamethoxazole and its ecologic impacts on Vallisneria spiralis

In this study, the simultaneous removal effects of electrochemical oxidation with boron-doped diamond anodes at different current densities were tested on Microcystis aeruginosa and sulfamethoxazole. Flow cytometry and non-invasive micro-test technology were applied to study the physiological states of M. aeruginosa and Vallisneria spiralis leaf cells. As the current density increased, the degradation effect of electrochemical oxidation on sulfamethoxazole and microcystin-LR increased and exceeded 60% within 6 h. In addition, population density of M. aeruginosa, fluorescence response of chlorophyll a, and cytoplasmic membrane integrity decreased, whereas the proportion of cells with excessive accumulation of intracellular reactive oxygen species (ROS) increased. The effect of electrochemical oxidation on the cell population of M. aeruginosa continued after the power was turned off. The physiological state of V. spiralis leaf cells was not severely affected at 10 mA/cm² for 24 h. Higher current intensity and longer electrolysis time would induce apoptosis or necrosis. In order to achieve a higher target pollutant removal effect and simultaneously avoid damage to the lake ecosystem, the current intensity of the electrochemical oxidation device should not exceed 10 mA/cm², and a single electrolysis treatment should range from 6 h to 24 h.

Review of aquatic toxicity of pharmaceuticals and personal care products to algae

Pharmaceuticals and Personal Care Products (PPCPs) have been frequently detected in the environment around the world. Algae play a significant role in aquatic ecosystem, thus the influence on algae may affect the life of higher trophic organisms. This review provides a state-of-the-art overview of current research on the toxicity of PPCPs to algae. Nanoparticles, contained in personal care products, also have been considered as the ingredients of PPCPs. PPCPs could cause unexpected effects on algae and their communities. Chlorophyta and diatoms are more accessible and sensitive to PPCPs. Multiple algal endpoints should be considered to provide a complete evaluation on PPCPs toxicity. The toxicity of organic ingredients in PPCPs could be predicted through quantitative structure-activity relationship model, whereas the toxicity of nanoparticles could be predicted with limitations. Light irradiation can change the toxicity through affecting algae and PPCPs. pH and natural organic matter can affect the toxicity through changing the existence of PPCPs. For joint and tertiary toxicity, experiments could be conducted to reveal the toxic mechanism. For multiple compound mixture toxicity, concentration addition and independent addition models are preferred. However, there has no empirical models to study nanoparticle-contained mixture toxicity. Algae-based remediation is an emerging technology to prevent the release of PPCPs from water treatment plants. Although many individual algal species are identified for removing a few compounds from PPCPs, algal-bacterial photobioreactor is a preferable alternative, with higher chances for industrial applications.

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.

Green and efficient degradation of cefoperazone sodium by Bi4O5Br2 leading to the production of non-toxic products: Performance and degradation pathway

Photocatalytic process represents a promising approach to overcome the pollution challenge associated with the antibiotics-containing wastewater. This study provides a green, efficient and novel approach to remove cephalosporins, particularly cefoperazone sodium (CFP). Bi₄O₅Br₂ was chosen for the first time to systematically study its degradation for CFP, including the analysis of material structure, degradation performance, the structure and toxicity of the transformation products, etc. The degradation rate results indicated that Bi₄O₅Br₂ had an excellent catalytic activity leading to 78% CFP removal compared with the pure BiOBr (38%) within 120 min of visible light irradiation. In addition, the Bi₄O₅Br₂ presents high stability and good organic carbon removal efficiency. The effects of the solution pH (3.12 - 8.75) on catalytic activity revealed that CFP was mainly photocatalyzed under acidic conditions and hydrolyzed under alkaline conditions. Combined with active species and degradation product identification, the photocatalytic degradation pathways of CFP by Bi₄O₅Br₂ was proposed, including hydrolysis, oxidation, reduction and decarboxylation. Most importantly, the identified products were all hydrolysis rather than oxidation byproducts transformed from the intermediate of β-lactam bond cleavage in CFP molecule, quite different from the mostly previous studies. Furthermore, the final products were demonstrated to be less toxic through the toxicity analysis. Overall, this study illustrates the detailed mechanism of CFP degradation by Bi₄O₅Br₂ and confirms Bi₄O₅Br₂ to be a promising material for the photodegradation of CFP.

Occurrence, fate, and risk assessment of typical tetracycline antibiotics in the aquatic environment: A review

Tetracyclines (TCs), used as human and veterinary medicines, are the most widely used antibiotics. More than 75% of TCs are excreted in an active form and released into the environment through human and animal urine and feces, causing adverse effects on the ecological system and human health. Few articles review the environmental occurrence and behaviors of TCs, as well as their risks and toxicities. Here, we comprehensively summarized the recent advances on the following important issues: (1) Environmental occurrence of TCs. TCs are used globally and their occurrence in the aquatic environment has been documented, including surface water, groundwater, drinking water, wastewater, sediment, and sludge. (2) Environmental behaviors of TCs, particularly the fate of TCs in wastewater treatment plants (WWTPs). Most WWTPs cannot effectively remove TCs from wastewater, so alternative methods for efficient removal of TCs need to be developed. The latest degradation methods of TCs are summarized, including adsorption, photocatalytic, photochemical and electrochemical, and biological degradations. (3) Toxicities and possible risks of TCs. The toxicological data of TCs indicate that several TCs are more toxic to algae than fish and daphnia. Risk assessments based on individual compound exposure indicate that the risks arising from the current concentrations of TCs in the aquatic environment cannot be ignored.

Transcriptomic analysis of Raphidocelis subcapitata exposed to erythromycin: The role of DNA replication in hormesis and growth inhibition

The occurrence of hormesis in the algal growth inhibition test is a major challenge in the dose-response characterization, whereas the molecular mechanism remains unraveled. The aim of this study is therefore to investigate the changes in the molecular pathways in a model green alga Raphidocelis subcapitata treated with erythromycin (ERY; 4, 80, 120 μg L^-1) by transcriptomic analysis. After 7 day exposure, ERY at 4 μg L^-1 caused hormetic effects (21.9 %) on cell density, whereas 52.0 % and 65.4 % were inhibited in two higher exposures. By using adj p < 0.05 and absolute log₂ fold change> 1 as a cutoff, we identified 218, 950, and 2896 differentially expressed genes in 4, 80, 120 μg L^-1 treatment groups, respectively. In two higher ERY treated groups, genes involved in phases I, II & III metabolism processes and porphyrin and chlorophyll metabolism pathway were consistently suppressed. Interestingly, genes (e.g., pri2, mcm2, and mcm6) enriched in DNA replication process were up-regulated in 4 μg L^-1 group, whereas these genes were all repressed in 120 μg L^-1 group. Alteration trend in gene expression was consistent with algal growth. Taken together, our results unveiled the molecular mechanism of action in ERY- stimulated/ inhibited growth in green alga.

Antibiotics induced alterations in cell density, photosynthesis, microcystin synthesis and proteomic expression of Microcystis aeruginosa during CuSO4 treatment

Antibiotic contaminants have the potential to interfere with the control of cyanobacterial bloom through generating hormesis in cyanobacteria at current contamination level of ng L^-1. This study investigated the influence of a mixture of four frequently detected antibiotics, amoxicillin, ciprofloxacin, sulfamethoxazole and tetracycline, during the treatment of Microcystis aeruginosa by copper sulfate (CuSO₄) algaecide. CuSO₄ significantly (p <  0.05) inhibited cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability of M. aeruginosa in a dose-dependent manner at application doses of 0.01-0.05 mg L^-1. Besides, CuSO₄ inhibited oxidation-reduction process, photosynthesis and biosynthesis in M. aeruginosa at the proteomic level. Preventative application of CuSO₄ to a low density (4 × 10⁵ cells mL^-1) of M. aeruginosa effectively prevented the formation of bloom at low CuSO₄ doses, which is a possible route for eliminating the negative effects of CuSO₄ algaecide in aquatic environments. The presence of mixed antibiotics alleviated the toxicity of CuSO₄ in M. aeruginosa, through the downregulation of cation transport proteins and the upregulation of proteins related with chlorophyll a synthesis, photosynthesis, gene expression and oxidation-reduction. Mixed antibiotics also promoted microcystin synthesis in CuSO₄ treated cells through the upregulation of microcystin synthetases. Mixed antibiotics significantly (p <  0.05) increased cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability in CuSO₄ treated cells at test concentrations of 80 and 200 ng L^-1. A no-impact threshold of 20 ng L^-1 for mixed antibiotics (5 ng L^-1 for each antibiotic) was suggested for eliminating the interference of antibiotic contaminants on cyanobacterial bloom control.

Ecological risk assessment of fifty pharmaceuticals and personal care products (PPCPs) in Chinese surface waters: A proposed multiple-level system

Interest in the risks posed by trace concentrations of pharmaceuticals and personal care products (PPCPs) in surface waters is increasing, particularly with regard to potential effects of long-term, low-dose exposures of aquatic organisms. In most cases, the actual studies on PPCPs were risk assessments at screening-level, and accurate estimates were scarce. In this study, exposure and ecotoxicity data of 50 PPCPs were collected based on our previous studies, and a multiple-level environmental risk assessment was performed. The 50 selected PPCPs are likely to be frequently detected in surface waters of China, with concentrations ranging from the ng L^-1 to the low-g L^-1, and the risk quotients based on median concentrations ranged from 2046 for nonylphenol to 0 for phantolide. A semi-probabilistic approach screened 33 PPCPs that posed potential risks to aquatic organisms, among which 15 chemicals (nonylphenol, sulfamethoxazole, di (2-ethylhexyl) phthalate, 17β-ethynyl estradiol, caffeine, tetracycline, 17β-estradiol, estrone, dibutyl phthalate, ibuprofen, carbamazepine, tonalide, galaxolide, triclosan, and bisphenol A) were categorized as priority compounds according to an optimized risk assessment, and then the refined probabilistic risk assessment indicated 12 of them posed low to high risk to aquatic ecosystem, with the maximum risk products ranged from 1.54% to 17.38%. Based on these results, we propose that the optimized risk assessment was appropriate for screening priority contaminants at national scale, and when a more accurate estimation is required, the refined probability risk assessment is useful. The methodology and process might provide reference for other research of chemical evaluation and management for rivers, lakes, and sea waters.

Use of microalgae based technology for the removal of antibiotics from wastewater: A review

The antibiotic resistance induced by the release of antibiotics to the environment has urged research towards developing effective technologies for antibiotic removal from wastewater. Traditional technologies such as activated sludge processes are not effective for antibiotic removal. Recently, microalgae-based technology has been explored as a potential alternative for the treatment of wastewater containing antibiotics by adsorption, accumulation, biodegradation, photodegradation, and hydrolysis. In this review, the toxicities of antibiotics on microalgae, the mechanisms of antibiotic removal by microalgae, and the integration of microalgae with other technologies such as ultraviolet irradiation (photocatalysis), advanced oxidation, and complementary microorganism degradation for antibiotic removal were discussed. The limitations of current microalgae-based technology and future research needs were also discussed.

Occurrence and distribution of selected antibiotics in the surface waters and ecological risk assessment based on the theory of natural disaster

With increasing population growth and resource depletion, ecological health is a hotspot and urgent topic. Our study investigated the occurrence and distribution of five antibiotics, i.e., metronidazole (MET), sulfamethoxazole (SMZ), ciprofloxacin (CFX), norfloxacin (NFX), and enrofloxacin (EFX), in the surface water from Erlong Lake, China. With the seasonal and spatial variations of antibiotics, this study developed an interdisciplinary approach for the ecological risk of antibiotics considering the natural, human, and socioeconomic elements of watershed based on the risk theory of natural disaster. This approach integrates the geographic information system (GIS) spatial analysis tool, natural disaster theory, "driving force"-"pressure"-"state"-"impact"-"response" (DPSIR) model, and ordered weighted averaging (OWA) operators in terms of various environmental factors, representing a new ecological risk paradigm for environmental managers or decision-makers to identify environmental change. A total of 69 samples were collected in wet, dry, and normal seasons from 2017 to 2018, and laboratory analyses revealed that four antibiotics (MET, SMZ, CFX, and NFX) were widely detected in the lake. The mean concentrations decreased in the order of MET (1041.7 ng L^-1) > SMZ (771.4 ng L^-1) > CFX (646.4 ng L^-1) > NFX (179.0 ng L^-1) > EFX (15.3 ng L^-1), with their levels in natural surface waters higher than those in other studies. Antibiotic concentrations were higher in dry seasons than in other seasons, and the concentrations were strongly correlated with EC (electrical conductivity), pH, DOC (dissolved organic carbon), and TP (total phosphorus) according to redundancy analysis (RDA). Significant seasonal variations were found in CFX and EFX (ANOVA, p < 0.001). For the whole watershed, the ecological extremely and heavily vulnerable levels were concentrated in the central and northwest regions of the watershed, i.e., Changling county and Lishu county. Hence, the ecological distributions of extreme risk and heavy risk posed by the five selected antibiotics were assessed by using the mixture hazard quotient methods and DPSIR model which were also located in these counties in different seasons. The antibiotic results of ecosystem risk assessment can support decision-makers in identifying and prioritizing the necessary taking of specific measures and different risk attitudes to preserve the quality of ecological health for a city or multiple counties.

Effect of PHRs and PCPs on Microalgal Growth, Metabolism and Microalgae-Based Bioremediation Processes: A Review

In this review, the effect of pharmaceuticals (PHRs) and personal care products (PCPs) on microalgal growth and metabolism is reported. Concentrations of various PHRs and PCPs that cause inhibition and toxicity to growths of different microalgal strains are summarized and compared. The effect of PHRs and PCPs on microalgal metabolism (oxidative stress, enzyme activity, pigments, proteins, lipids, carbohydrates, toxins), as well as on the cellular morphology, is discussed. Literature data concerning the removal of PHRs and PCPs from wastewaters by living microalgal cultures, with the emphasis on microalgal growth, are gathered and discussed. The potential of simultaneously bioremediating PHRs/PCPs-containing wastewaters and cultivating microalgae for biomass production in a single process is considered. In the light of reviewed data, the feasibility of post-bioremediation microalgal biomass is discussed in terms of its contamination, biosafety and further usage for production of value-added biomolecules (pigments, lipids, proteins) and biomass as a whole.

The dual function of the algal treatment: Antibiotic elimination combined with CO2 fixation

The study provided an algal treatment to achieve dual function with antibiotic elimination and CO₂ fixation simultaneously. Two widely used antibiotics, cefradine and amoxicillin were selected as the target compounds. First of all, we assessed the influence of light intensity on algal growth and antibiotic removal efficiency to obtain the optimal light intensity. Secondly, after the algal antibiotic treatment, the CO₂ capture capacities at varied CO₂ volume concentrations were assessed and compared. Significant improvement in the removal efficiency of cefradine occurred when CO₂ was added into the treatment. Change in the content of photosynthetic pigments and the activities of RuBisCO and carbonic anhydrase occurred as the algal responses to the treatment condition. Our results showed that Chlorella pyrenoidosa performed better than Microcystis aeruginosa in both the antibiotic removal efficiency and the CO₂ capture capacity. In the integrated algal treatment, the remove rate of antibiotic has been improved by 30.16% and at the same time, the CO₂ absorption rate has been promoted by 10.94%. Metabolite analyses also revealed the mechanism involved, which proved the crucial role of the algae in the biodegradation of the target antibiotic.

Cephalosporin antibiotics in the aquatic environment: A critical review of occurrence, fate, ecotoxicity and removal technologies

Due to their widespread occurrence in the aquatic environment, human and veterinary cephalosporin antibiotics have been studied as water pollutants. In order to characterize environmental risks of this compound class, this review evaluates relevant data about physicochemical properties, occurrence, ecotoxicity and degradation of cephalosporins. Although application of cephalosporins is rather low compared to other antibiotics and their environmental life-time is believed to be short (i.e. days), the available data is insufficient to draw conclusions on their environmental relevance. Few studies concerning the fate of cephalosporins in soil are available, while hydrolysis and photo-degradation are suggested as the main attenuation processes in the aquatic environment. Cephalosporins have been detected in different aqueous matrices in concentrations ranging from 0.30 ng L^-1 to 0.03 mg L^-1, with sewage and wastewater being the main matrices with positive findings. For wastewater treatment purposes, several technologies have been tested for the abatement of cephalosporins, including photolysis and adsorption. In most cases, the technology employed led to complete or significant removal (>95%) of parental drugs but few authors reported on cephalosporins' metabolites and transformation products. Furthermore, the present ecotoxicological data are insufficient for comprehensive ecological risk quotient calculations. Considering the total of 53 cephalosporins, effective values (EC, LC, NOAEC, NOAEL, etc.) are only available for around 30% of parental drugs and are very scarce for cyanobacteria, which is considered to be the most sensitive group of organisms to antibiotics. Furthermore, it has been demonstrated that cephalosporins' transformation products can be more toxic and more persistent than the parental drugs. Few investigations considering this possibility are available. Consequently, more effort on ecotoxicological data generation and verification of biological inactivation of cephalosporins-related products is needed. Likewise, the lack of natural depletion rates and knowledge gaps on mixture effects for cephalosporins' degradation and toxicity have to be overcome.

Comprehensive assessment of three typical antibiotics on cyanobacteria (Microcystis aeruginosa): The impact and recovery capability

This innovative study provided a comprehensive evaluation of the effects of three typical antibiotics exposures (cefradine, norfloxacin and amoxicillin) on Microcystis aeruginosa in two periods (exposure and post-exposure) at a new perspective. The results indicated that the irreversible growth inhibition of M. aeruginosa attributed to the norfloxacin in the exposure and the re-exposure stages. In contrast, although the algal cell size recovered to the control level after the exposure of 20 mg/L of cefradine, the significant stimulation on glutathione (GSH) still persisted even if the contaminants were removed. On the other hand, amoxicillin inhibited the activities of superoxide dismutase (SOD), GSH contents and the algal cell size in the exposure period while malonaldehyde (MDA) contents increased significantly in two periods.

Study on the interaction mechanism between cefradine and Chlamydomonas reinhardtii in water solutions under dark condition

Our research investigated the hormesis effect of cefradine on the specific growth rates (μ) of single-celled algae (Chlamydomonas reinhardtii) from aqueous solutions. We found the specific growth rate of C. reinhardtii slightly increased with cefradine concentrations within the range 0.5-10 mg/L. Effects of algae density, initial solution pH, and temperature on the adsorption batch assays were investigated. The optimum conditions for cefradine adsorption occurred at a density of 5 × 10⁶ algae cells/mL, a solution pH of 7.0, and a temperature of 25.0 °C. A Box-Behnken design was employed to evaluate correlations between influential factors and cefradine adsorption. The results showed a significant interaction between algae density and temperature. The maximum removal rate could reach 50.13% under the optimal conditions. Additionally, the adsorption mechanisms were explored through Langmuir and Freundlich isotherm equations, adsorption kinetics, and thermodynamics. The results suggested that the adsorption process was monolayer, spontaneous, and endothermic with an increase in randomness at the algae-solution interface, which followed a pseudo-second-order model. All the data indicated that the alga performed a better removal capacity in the antibiotic-containing wastewater treatment process. This study lays the groundwork for a better understanding of the interaction mechanism between cefradine and Chlamydomonas reinhardtii in water solutions under dark condition.

Ecotoxicity of the two veterinarian antibiotics ceftiofur and cefapirin before and after photo-transformation

The release of antibiotics into the environment may lead to deleterious effects in non-target organisms as well as pressure in antimicrobial resistance acquirement. Ceftiofur (CEF) and cefapirin (CEPA) are veterinary cephalosporins used for recurrent and economically relevant infections. Both antibiotics have been detected in aquatic environments and their fate during drinking water processing is still unknown. This work investigated the acute and chronic toxicities of CEF and CEPA towards aquatic organisms including stability tests. Complementary, the effects of water disinfection radiation (UV-C, 254nm) on ecotoxicological responses were studied. CEF and CEPA have significant decay during Daphnia magna tests, portraying half-lives (t_1/2) of 49 and 53h, respectively. During tests with green algae (Scenedesmus spec.), CEPA was more instable (t_1/2 88h) than CEF (t_1/2 267h). CEF and its presumable hydrolysis products induced deleterious effects in Daphnia magna (48h EC₅₀ 139, LC₅₀ 179 in μM), which was not observed with Scenedesmus spec. (72h NOAEC 82.5±2.5μM). In the case of CEPA, no toxic effects were observed in either test (48h EC-LC₅₀>510 and 72h NOAEC 57±6, in μM). Photolysis of CEPA resulted in toxic products, which were effective for the cladoceran but not for the green algae. On the other hand, the different radiation doses studied did not affect CEF ecotoxicity. This investigation illustrates the importance of cephalosporin hydrolysis during standard toxicity tests. Furthermore, the potential formation of species-specific toxic compounds during water processing is demonstrated, highlighting the need of further assessing toxicity of both cephalosporins and their transformation products.

Combined effects of binary antibiotic mixture on growth, microcystin production, and extracellular release of Microcystis aeruginosa: application of response surface methodology

The interactive effects of binary antibiotic mixtures of spiramycin (SP) and ampicillin (AMP) on Microcystis aeruginosa (MA) in terms of growth as well as microcystin production and extracellular release were investigated through the response surface methodology (RSM). SP with higher 50 and 5% effective concentrations in MA growth was more toxic to MA than AMP. RSM model for toxic unit approach suggested that the combined toxicity of SP and AMP varied from synergism to antagonism with SP/AMP mixture ratio decreasing from reversed equitoxic ratio (5:1) to equitoxic ratio (1:5). Deviations from the prediction of concentration addition (CA) and independent action (IA) model further indicated that combined toxicity of target antibiotics mixed in equivalent ratio (1:1) varied from synergism to antagonism with increasing total dose of SP and AMP. With the increase of SP/AMP mixture ratio, combined effect of mixed antibiotics on MA growth changed from stimulation to inhibition due to the variation of the combined toxicity and the increasing proportion of higher toxic component (SP) in the mixture. The mixture of target antibiotics at their environmentally relevant concentrations with increased total dose and SP/AMP mixture ratio stimulated intracellular microcystin synthesis and facilitated MA cell lysis, thus leading to the increase of microcystin productivity and extracellular release.

Occurrence and ecological hazard assessment of selected antibiotics in the surface waters in and around Lake Honghu, China

The occurrence and temporal-spatial distributions of 13 antibiotics (tetracyclines, sulfonamides, and fluoroquinolones) in the water of a high-intensity aquaculture lake, Honghu Lake, and its associated river network and ponds were investigated. Tetracycline, oxytetracycline, chlortetracycline, and sulfadiazine are the four dominant antibiotics in this region, with maximum and median concentrations of 1454.8 and 304.8ng/L, 2796.6 and 161.9ng/L, 1431.3 and 349.9ng/L, and 499.5 and 106.5ng/L, respectively. The median concentrations of the other nine antibiotics are lower than 57.1ng/L. The highest contaminated sites are located in the Four-lake main canal and its lake inlets. Antibiotic concentrations were higher in November than in May and the concentrations were strongly correlated with water temperature, dissolved oxygen, and nitrates according to redundancy analysis. The source analysis indicated that besides untreated domestic and husbandry sewage, the aquaculture in the lake and ponds is a main source of antibiotics in the study region. The environmental hazards posed by the selected antibiotics were assessed by using the methods of hazard quotient and mixture hazard quotient. The results suggested that tetracycline, oxytetracycline, sulfadiazine, and ciprofloxacin pose medium to high ecological hazard to algae in almost all of the water samples, and the high combination ecological hazards of antibiotics are mainly posed by the high individual hazard quotient of tetracycline in the study area.

Effects of benzophenone-3 on the green alga Chlamydomonas reinhardtii and the cyanobacterium Microcystis aeruginosa

Effects of benzophenone-3 (BP-3) on the green alga, Chlamydomonas reinhardtii, and the cyanobacterium, Microcystis aeruginosa, were investigated. The tested organisms were exposed to environmental levels of BP-3 for 10 days, at nominal concentrations from 0.01 to 5000μgL^-1. Specific growth rate and photosynthetic pigments were employed to evaluate the toxic responses. The two tested algae had distinct toxic responses towards BP-3 stress, with the green alga C. reinhardtii being more sensitive than the cyanobacterium M. aeriginosa, based on EC₂₀ and EC₅₀ values. Uptake of BP-3 from the medium occurred in both species, with M. aeruginosa showing greater overall uptake (27.2-77.4%) compared to C. reinhardtii (1.1-58.4%). The effects of BP-3 on C. reinhardtii were variable at concentrations lower than 100μgL^-1. At higher concentrations, the specific growth rate of C. reinhardtii decreased following a reduction in chlorophyll a (chl-a) content. Further experiments showed that BP-3 regulated the growth of C. reinhardtii by affecting the production of chl-a, chlorophyll b and carotenoids. In M. aeruginosa, specific growth rate was only moderately affected by BP-3. Additionally, the production of chl-a was significantly inhibited over the different exposure concentrations, while the production of carotenoids was stimulated. These results indicate a potential detrimental effect on prokaryotes and eukaryotes and that the mechanism of action varies with species.

Effects of chronic exposure to cefadroxil and cefradine on Daphnia magna and Oryzias latipes

Cefadroxil and cefradine have frequently been detected in surface waters, however toxicological studies in aquatic organisms have mostly been limited to acute lethal effects. In the present study, endocrine disruption caused by cefadroxil and cefradine, and its underlying mechanism were investigated by chronic exposure of Daphnia magna (21 d) and Oryzias latipes (120 d). In medaka fish, the effects on growth, mortality, and reproduction, as well as on the levels of hormones and genes related to the hypothalamic-pituitary-gonad (HPG) axis, were investigated after 120 d exposure. In D. magna, the chronic effects on growth were observed at the highest concentration of 83.0 mg L^-1 cefadroxil and 80.8 mg L^-1 cefradine. The growth of juvenile fish was significantly impaired by exposure to cefradine. Following exposure to cefadroxil and cefradine for 120 d, sex-dependent changes in E2 hormones were observed and their levels were supported by the regulation of genes along the HPG axis. We found that chronic exposure to cefadroxil and cefradine impaired growth and reproduction in a freshwater invertebrate and fish, and altered the levels of sex hormones and genes associated with the HPG axis in fish.

Toxin Release of Cyanobacterium Microcystis aeruginosa after Exposure to Typical Tetracycline Antibiotic Contaminants

The global usage of veterinary antibiotics is significant. Antibiotics can be released into aquatic environments and elicit toxic effects on non-target organisms. In this study, the growth characteristics and toxin release of the cyanobacterium Microcystis aeruginosa (M. aeruginosa) were examined to investigate the physiological effects of tetracycline antibiotics on aquatic life. Results showed that the degree of toxicities of the following target antibiotics was TC (tetracycline hydrochloride) > CTC (chlortetracycline hydrochloride) > OTC (oxytetracycline hydrochloride) in terms of growth parameters, EC10 (0.63, 1.86, and 3.02 mg/L, respectively), and EC20 (1.58, 4.09, and 4.86 mg/L, respectively) values. These antibiotics inhibited the production of microcystin-LR (MC-LR) to varying degrees. CTC interfered M. aeruginosa cells and decreased their ability to release MC-LR, but this antibiotic stimulated the ability of these cells to synthesize MC-LR at 2 and 5 mg/L. OTC elicited a relatively weaker toxicity than CTC did and reduced MC-LR release. TC was the most toxic among the three antibiotics, and this antibiotic simultaneously reduced intracellular and extracellular MC-LR equivalents. Our results helped elucidate the effects of tetracycline antibiotics on M. aeruginosa, which is essential for environmental evaluation and protection. Our results are also helpful for guiding the application of veterinary antibiotics in agricultural settings.

Effects of artemisinin sustained-release granules on mixed alga growth and microcystins production and release

To safely and effectively apply artemisinin sustained-release granules to control and prevent algal water-blooms, the effects of artemisinin and its sustained-release granules on freshwater alga (Scenedesmus obliquus (S. obliquus) and Microcystis aeruginosa (M. aeruginosa)), as well as the production and release of microcystins (MCs) were studied. The results showed that artemisinin sustained-release granules inhibited the growth of M. aeruginosa (above 95% IR) and S. obliquus (about 90% IR), with M. aeruginosa more sensitive. The artemisinin sustained-release granules had a longer inhibition effect on growth of pure algae and algal coexistence than direct artemisinin dosing. The artemisinin sustained-release granules could decrease the production and release of algal toxins due to the continued stress of artemisinin released from artemisinin sustained-release granules. There was no increase in the total amount of MC-LR in the algal cell culture medium.

Algal Feedback and Removal Efficiency in a Sequencing Batch Reactor Algae Process (SBAR) to Treat the Antibiotic Cefradine

Many previous studies focused on the removal capability for contaminants when the algae grown in an unexposed, unpolluted environment and ignored whether the feedback of algae to the toxic stress influenced the removal capability in a subsequent treatment batch. The present research investigated and compared algal feedback and removal efficiency in a sequencing batch reactor algae process (SBAR) to remove cefradine. Three varied pollution load conditions (10, 30 and 60 mg/L) were considered. Compared with the algal characteristics in the first treatment batch at 10 and 30 mg/L, higher algal growth inhibition rates were observed in the second treatment batch (11.23% to 20.81%). In contrast, algae produced more photosynthetic pigments in response to cefradine in the second treatment batch. A better removal efficiency (76.02%) was obtained during 96 h when the alga treated the antibiotic at 60 mg/L in the first treatment batch and at 30 mg/L in the second treatment batch. Additionally, the removal rate per unit algal density was also improved when the alga treated the antibiotic at 30 or 60 mg/L in the first treatment batch, respectively and at 30 mg/L in the second treatment batch. Our result indicated that the green algae were also able to adapt to varied pollution loads in different treatment batches.

Cellular and transcriptional responses in Microcystis aeruginosa exposed to two antibiotic contaminants

The responses of Microcystis aeruginosa under exposure to spiramycin and amoxicillin were investigated on both cellular and genetic levels through a 7-day exposure test. Algal growth was inhibited by spiramycin while promoted by amoxicillin at test concentrations of 0.6-1.8 μg L(-1), indicating a higher toxicity of spiramycin than amoxicillin. During the whole exposure period, the chlorophyll a content and expression levels of psbA, psaB, and rbcL were significantly inhibited by spiramycin at test concentrations of 1.2 and 1.8 μg L(-1) (p < 0.05) and stimulated by 0.6-1.8 μg L(-1) of amoxicillin (p < 0.05), with respective decreases of up to 26, 75, 72, and 82% compared to the control and respective increases of 20, 70, 135, and 55%. During the 4 to 7 days of exposure, the microcystin-LR content and expression levels of mcyB and grpE were reduced by up to 66, 47, and 72% in spiramycin-treated algal cells, respectively, and stimulated by up to 1.3-, 1.4-, and 1.5-folds in amoxicillin-treated algal cells, respectively. Elevated recA expression was only observed in 1.2 and 1.8 μg L(-1) of spiramycin-treated algal cells, indicating severe DNA damage due to the high toxicity. Target antibiotics were suspected to regulate the growth and microcystin-production in M. aeruginosa via the photosynthesis system.

Physiological effects of tetracycline antibiotic pollutants on non-target aquatic Microcystis aeruginosa

This study aimed to evaluate the aquatic toxicity of three typical tetracycline antibiotics, including tetracycline, oxytetracycline, and chlortetracycline, on the cyanobacterium Microcystis aeruginosa. The cell density, chlorophyll a content, protein content, and enzymatic antioxidant activities were determined. The results showed that the cell growth was significantly inhibited by the three compounds at a low concentration. The chlorophyll a and protein content decreased significantly after exposure to 0.05 mg L(-1) of each compound for 9 d. When exposed to 0.2-1 mg L(-1) of tetracycline, the superoxide dismutase (SOD) activity increased, but peroxidase (POD) and catalase (CAT) activities decreased. In contrast, when exposed to oxytetracycline and chlortetracycline at different concentrations ranging from 0.2 to 1 mg L(-1) and from 0.01 to 0.05 mg L(-1), the SOD activity decreased, but the POD and CAT activities increased. These findings indicate that tetracycline antibiotics influence cell growth and protein synthesis, and they also induce oxidative stress in M. aeruginosa at environmentally similar concentrations. Thus, this study may provide further insights into the toxic effects of tetracycline antibiotics and the controlled use of antibiotics.

Combined effects of two antibiotic contaminants on Microcystis aeruginosa

Combined toxicity of spiramycin and amoxicillin was tested in Microcystis aeruginosa. The respective 50% effective concentrations (EC50mix) expressed in toxic unit (TU) values were 1.25 and 1.83 for spiramycin and amoxicillin mixed at 1:7 and 1:1, suggesting an antagonistic interaction at the median effect level. Deviations from the prediction of concentration addition (CA) and independent action (IA) models further indicated that combined toxicity of two antibiotics mixed at 1:1 varied from synergism to antagonism with increasing test concentration. Both the EC50mix of 0.86 (in TU value) and the deviation from two models manifested a synergistic interaction between spiramycin and amoxicillin mixed at 7:1. At an environmentally relevant concentration of 800ngL(-1), combined effect of mixed antibiotics on algal growth changed from stimulation to inhibition with the increasing proportion of higher toxic component (spiramycin). Chlorophyll-a content and expression levels of psbA, psaB, and rbcL varied in a similar manner as growth rate, suggesting a correlation between algal growth and photosynthesis under exposure to mixed antibiotics. The stimulation of microcystin-production by mixed antibiotics was related with the elevated expression of mcyB. The mixture of two target antibiotics with low proportion of spiramycin (<50%) could increase the harm of M. aeruginosa to aquatic environments by stimulating algal growth and production and release of microcystin-LR at their current contamination levels.

Green tide deactivation with layered-structure cuboids of Ag/CaTiO3 under UV light

In this work, an alternative to deactivate noxious green tide Tetraselmis suecica in the short-term is proposed by employing Perovskite-like cube-shaped, crystalline CaTiO3 semiconductors functionalized with atomic silver nanoparticles. CaTiO3 was prepared by a microwave-assisted hydrothermal method and then Ag(0)NPs (1 wt% of CaTiO3), were added by the photoreduction method. The XRD results show that crystalline CaTiO3 has an orthorhombic unit cell with a Perovskite-like structure. Images obtained by FESEM and HRTEM microscopies show well-faceted CaTiO3 rectangular prismatic morphology functionalizated with silver nanoparticles ≈ 13.5 nm. XPS and EDS-FESEM has confirmed the composition of CaTiO3 and silver occurring mainly as reduced metal. The UV inactivation of noxious T. suecica with Ag/CaTiO3 nanocomposites formed on bare materials results in complete deactivation of the algae in 12 min. The direct contact between harmful algae and Ag/CaTiO3 nanocomposite is necessary to deactivate the algae and inhibits algae viability.