Toxicity of tetracycline and its transformation products to a phosphorus removing Shewanella strain

Persistence and potential risks of tetracyclines and their transformation products in two typical different animal manure composting treatments

Abundant residues of tetracyclines in animal manures and manure-derived organic fertilizers can pose a substantial risk to environments. However, our knowledge on the residual levels and potential risk of tetracyclines and their transformation products (TPs) in manure and manure-derived organic fertilizers produced by different composting treatments is still limited. Herein, the occurrence and distribution of four veterinary tetracyclines (tetracycline, oxytetracycline, chlortetracycline, and doxycycline) and ten of their TPs were investigated in paired samples of fresh manure and manure-derived organic fertilizers. Tetracyclines and TPs were frequently detected in manure and manure-derived organic fertilizer samples in ranging from 130 to 118,137 μg·kg-1 and 54.6 to 104,891 μg·kg-1, respectively. Notably, the TPs concentrations of tetracycline and chlortetracycline were comparable to those of the parent compounds, with 4-epimers being always dominant and retained antibacterial potency. Based on paired-sampling strategy, the removal efficiency of tetracyclines and TPs in thermophilic composting was higher than that in manure storage. Toxicological data in the soil environment and the data derived from equilibrium partitioning method, indicated that tetracyclines and some TPs like 4-epitetracycline, 4-epichlortetracycline and isochlortetracycline could pose median to high ecological risk to terrestrial organisms. Total concentrations of TPs in manure-derived organic fertilizers were significantly correlated with the absolute abundance of tet(X) family genes, which provide evidence to evaluate the effects of TPs on the levels of antibiotic resistance in the environment. Among them, the 4-epitetracycline could pose ecological risk and retain antibacterial potency. Our findings emphasize the importance of monitoring and controlling the prevalence of tetracyclines and their TPs in livestock-related environments.

Efficient mitigation of emerging antibiotics residues from water matrix: Integrated approaches and sustainable technologies

The prevalence of antibiotic traces in the aquatic matrices is a concern due to the emanation of antibiotic resistance which requires a multifaceted approach. One of the potential sources is the wastewater treatment plants with a lack of advance infrastructure leading to the dissemination of contaminants. Continuous advancements in economic globalization have facilitated the application of several conventional, advanced, and hybrid techniques for the mitigation of rising antibiotic traces in the aquatic matrices that have been thoroughly scrutinized in the current paper. Although the implementation of existing mitigation techniques is associated with several limiting factors and barriers which require further research to enhance their removal efficiency. The review further summarizes the application of the microbial processes to combat antibiotic persistence in wastewater establishing a sustainable approach. However, hybrid technologies are considered as most efficient and environmental-benign due to their higher removal efficacy, energy-efficiency, and cost-effectiveness. A brief elucidation has been provided for the mechanism responsible for lowering antibiotic concentration in wastewater through biodegradation and biotransformation. Overall, the current review presents a comprehensive approach for antibiotic mitigation using existing methods however, policies and measures should be implemented for continuous monitoring and surveillance of antibiotic persistence in aquatic matrices to reduce their potential risk to humans and the environment.

Effect and mechanism of simultaneous cadmium-tetracycline removal by a self-assembled microbial-photocatalytic coupling system

Electrochemical bacteria Shewanella oneidensis MR-4 (MR-4) was used to biologically generate cadmium sulfide (bio-CdS) nanocrystals and construct a self-assembled intimately coupled photocatalysis-biodegradation system (SA-ICPB) to remove cadmium (Cd) and tetracycline hydrochloride (TCH) from wastewater. The characterization using EDS, TEM, XRD, XPS, and UV-vis confirmed the successful CdS bio-synthesis and its visible-light response capacity (520 nm). 98.4% of Cd²⁺ (2 mM) was removed during bio-CdS generation within 30 min. The electrochemical analysis confirmed the photoelectric response capability of the bio-CdS as well as its photocatalytic efficiency. Under visible light, SA-ICPB entirely eliminated TCH (30 mg/L). In 2 h, 87.2% and 43.0% of TCH were removed separately with and without oxygen. 55.7% more chemical oxygen demand (COD) was removed with oxygen participation, indicating the degradation intermediates elimination by SA-ICPB required oxygen participation. Biodegradation dominated the process under aerobic circumstances. Electron paramagnetic resonance analysis indicated that h⁺ and ·O₂^- played a decisive role in photocatalytic degradation. Mass spectrometry analysis proved that TCH was dehydrated, dealkylated, and ring-opened before mineralizing. In conclusion, MR-4 can spontaneously generate SA-ICPB and rapidly-deeply eliminate antibiotics by coupling photocatalytic and microbial degradation. Such an approach was efficient for the deep degradation of persistent organic pollutants with antimicrobial properties.

Toxicity of single and combined 4-epianhydrotetracycline and cadmium at environmentally relevant concentrations on the zebrafish embryos (Danio rerio)

The combined pollution of antibiotics and heavy metals has attracted a worldwide attention in the recent years. 4-epianhydrotetracycline (EATC) is the major degradation product of tetracycline (TC), which has been detected frequently in environment and its concentration is even higher than TC under some circumstances. Cadmium (Cd) is a common heavy metal contaminant and has highly toxic to organisms, plants and humans even at low doses. In the present study, zebrafish (Danio rerio) embryo toxicity test was performed to investigate the single and combined effects of EATC and Cd on aquatic organisms. Exposure to EATC and Cd at environmentally relevant concentrations had a series of hazardous impacts on the embryonic development, including lethality, hatching rate, heart rate and teratogenic effects. Compared to the contaminant existed alone, combined pollution produced stronger toxicity, which appeared as the decreasing of heart rate and hatching rate, and the increasing of malformation of zebrafish embryos. After 96 h exposure, the reactive oxygen species (ROS) levels in zebrafish embryos were increased significantly, revealing that EATC-Cd co-exposure resulted in potential oxidative stress-induced damage. Acridine orange (AO) staining showed that combined exposure resulted in stronger cell apoptosis. The potential health risks of the combined pollution of EATC and Cd should be paid more attention to higher level vertebrates and humans.

Transformation products of tetracyclines in three typical municipal wastewater treatment plants

Antibiotics in the environment could undergo various processes with formation of transformation products, but little has been known about their occurrence and (eco)toxicological consequences. Here we investigated the occurrence and fate of nine transformation products of four tetracyclines (tetracycline, oxytetracycline, chlortetracycline and doxycycline) in three municipal wastewater treatment plants (WWTPs) in Guangzhou, China. The results showed the detection of all the tetracyclines and their transformation products in the WWTPs, with mean concentrations ranging from 17.8 ng/L (anhydrotetracycline) to 49.1 ng/L (oxytetracycline) in influent, 3.03 ng/L (tetracycline) to 6.94 ng/L (4-epi-chlortetracycline) in effluent, and 19.8 ng/g (isochlortetracycline) to 503 ng/g (4-epi-tertracycline) in sludge, respectively. The transformation products of tetracycline, oxytetracycline, chlortetracycline and doxycycline accounted for 73%-83%, 26%-52%, 70%-73% and 69%-74% of total concentrations, respectively. The aqueous removal rates of tetracyclines and their transformation products in the three WWTPs ranged from 18.4% (demethyl-chlortetracycline) to 93.7% (oxytetracycline). Mass balance analysis based on both aqueous and solid phase showed that their removals were mainly attributed to the sludge adsorption. Residual tetracyclines and their transformation products in the effluents would pose no obvious ecological risks to three aquatic organisms (green algae, daphnia and fish). However, 43.5% of sludge samples had high risks from these tetracyclines and transformation products, especially the compounds with poor biodegradability. The results from this study suggest that transformation products should be included in future environmental monitoring and control.

Effects of 4-epianhydrotetracycline on oxidative stress in zebrafish (Danio rerio) embryos

4-Epianhydrotetracycline (4-EATC) is a major intermediate product of tetracycline during its degradation progress in the natural environment, which is frequently detected in aquatic environments and poses a potential threat to aquatic organisms. In the present study, the ecotoxicity of 4-EATC have been studied from the perspective of oxidative stress by using zebrafish embryos. After 96 h exposure, the reactive oxygen species (ROS) levels, malondialdehyde (MDA) concentrations and protein carbonyl (PC) contents in zebrafish embryos in the lower-concentration 4-EATC treatment groups (1.25 mg/L and 2.50 mg/L) showed no significant differences compared with the negative control group. However, the total superoxide dismutase (SOD) activity was increased significantly. After exposed to the higher-concentration of 4-EATC (5.00, 10.0 and 20.0 mg/L) resulted in a significant increase in ROS levels, MDA concentrations and PC contents, in contrast, a significant decrease in SOD activities. The results indicate that exposure to high concentrations of 4-EATC (5.00, 10.0 and 20.0 mg/L) could disrupt the redox equilibrium in zebrafish embryos, leading to the occurrence of oxidative damage. Apoptosis of the embryonic cells could be induced by 4-EATC exposure at different concentration and the rate of apoptosis enhanced with the increase of 4-EATC concentration. The pericardium was the most frequent site of apoptosis. The present study points out that more attention should be paid to the potential ecological risks of antibiotic degradation products.

Toxicity and combined effects of antibiotics and nano ZnO on a phosphorus-removing Shewanella strain in wastewater treatment

Antibiotics and nanoparticles, which are emerging contaminants, can occur simultaneously in biological wastewater treatment systems, potentially resulting in complex interactive effects. This study investigated the effects of individual and complex zinc oxide nanoparticles (nZnO) and antibiotics (quinolone and sulfonamide), on the Shewanella strain used to remove phosphorus (PO₄^3-), metabolic processes, as well as its complexing and toxicity mechanisms. The inhibition of PO₄^3- removal increased from 30.7% to 100.0% with increased nZnO concentrations (half maximal effective concentration (EC50) = 1.1 mg Zn/L) by affecting poly-p and glycogen metabolites. The combined exposure to nZnO and ciprofloxacin/norfloxacin (CIP/NOR) had a significant antagonistic effect on the removal of PO₄^3- and on the metabolism of poly-p and glycogen in phosphate-accumulating organisms (PAOs), whereas the complexing of sulfonamide and nZnO had no significant additional effect. Thus, the complexing of nanoparticles and antibiotics exhibited different toxicity effects from the antibiotic structure-based complex reactions. These results can be used to improve wastewater treatment processes and reduce risks associated with wastewater discharge.

Tetracyclines in the environment: An overview on the occurrence, fate, toxicity, detection, removal methods, and sludge management

Tetracyclines (TCs) are a group of broad-spectrum antibiotics having vast human, veterinary, and aquaculture applications. The continuous release of TCs residues into the environment and the inadequate removal through the conventional treatment systems result in its prevalent occurrence in soil, surface water, groundwater, and even in drinking water. As aqueous TCs contamination is the tip of the iceberg, and TCs possess good sorption capacity towards soil, sediments, sludge, and manure, it is insufficient to rely on the sorptive removal in the conventional water treatment plants. The severity of the TCs contamination is evident from the emergence of TCs resistance in a wide variety of microorganisms. This paper reviews the recent research on the TCs occurrence in the environmental matrices, fate in natural systems, toxic effects, and the removal methods. The high performance liquid chromatography (HPLC) determination of TCs in environmental samples and the associated technology developments are analyzed. The benefits and limitations of biochemical and physicochemical removal processes are also discussed. This work draws attention to the inevitability of proper TC sludge management. This paper also gives insight into the limitations of TCs related research and the future scope of research in environmental contamination by TCs residues.

Environmental and health impacts of contaminants of emerging concerns: Recent treatment challenges and approaches

In the past few decades, new contaminants of emerging concern (CECs) in the air, water, and soil have gained significant attention due to their adverse impact on human health and the environment. The sources of CECs have been identified in different forms from domestic and industrial activities such as personal care products and pharmaceuticals. It has been established that aqueous medium plays a major role in the dissemination of various contaminants, like drinking water, reservoirs, lakes, rivers and waste with water medium. There remains inadequate technology for the treatment of CECs in the wastewater systems. Though different techniques have advanced for the treatment of CECs, they still pose a severe threat to human health and disturb the ecological balance. In this review, the characteristics, recent technologies, risk assessment and management of CECs have been discussed. The primary aim is to highlight the new innovative and cost-effective technologies for the remediations of CECs in all forms. Biochar is readily and economically available in abundance and an economical adsorbent with 100% adsorptive removal for H₂PO₄^-. The bibliometric analysis also performed to understand the emerging research trends on the treatment techniques, which can help in developing a guiding pathway to modern research in academia and industry.

Nanorod bundle-like silver cyanamide nanocrystals for the high-efficiency photocatalytic degradation of tetracycline

Silver cyanamide (Ag₂NCN) is a type of functional semiconductor material with a visible-light response. Ag₂NCN nanocrystals with nanorod bundle-like (RB) or straw bundle-like (SB) assemblies were successfully prepared, and it was found that the as-prepared Ag₂NCN nanorod bundle (RB) samples had a narrower bandgap of 2.16 eV, which was lower than those reported. As a result, RB samples demonstrated a higher photocatalytic activity towards tetracycline (TC) degradation. The analyses of active species confirmed that both the photo-generated holes and ˙O₂ ^- radicals of the RB sample played significant roles during the process of photocatalytic degradation of TC, and the holes were the main active species. These results indicated that effective charge separation could be achieved by adjusting the morphologies of Ag₂NCN nanocrystals. This study provides a new approach to prepare Ag₂NCN nanocrystals with a narrower bandgap and strong visible-light response towards antibiotic degradation.

Interaction between tetracycline and microorganisms during wastewater treatment: A review

Tetracycline (TC) is a commonly used human and veterinary antibiotic that is mostly discharged into wastewater in the form of the parent compounds. At present, wastewater treatment plants (WWTPs) use activated sludge processes that are not specifically designed to remove such pollutants. Considering the biological toxicity of TC in aquatic environment, the migration and fate of TC in the process of wastewater treatment deserve attention. This paper reviews the influence of TC on the functional bacteria in the sludge matrix and the development of tetracycline-resistant genes, and also discusses their adsorption removal rates, their adsorption kinetics and adsorption isotherm models, and infers their adsorption mechanism. In addition, the biodegradation of TC in the process of biological treatment is reviewed. Co-metabolism and the role of dominant bacteria in the degradation process are described, along with the formation of degradation byproducts and their toxicity. Furthermore, the current popular integrated coupling-system for TC degradation is also introduced. This paper systematically introduces the interaction between TC and activated sludge in WWTPs. The review concludes by providing directions to address research and knowledge gaps in TC removal from wastewater.

Effect of sulfamethoxazole and oxytetracycline on enhanced biological phosphorus removal and bacterial community structure

The individual and combined effects of sulfamethoxazole (SMX) and oxytetracycline (OTC) on an enhanced biological phosphorus removal (EBPR) system was investigated. OTC at 5 mg/L resulted in filamentous bulking with a collapse of EBPR system. P removal decreased to 44.8% and COD was mostly removed during the aerobic phase. SMX and OTC had antagonistic effects in EBPR system. The inhibitory effect of SMX and SMX + OTC on P removal, COD removal, glycogen transformation and extracellular polymeric substances content was reversible with prolonged operation, accompanied with increase of polyphosphate accumulating organisms. The presence of nitrification inhibitor allylthiourea, high pH and low tetX abundance limited the removal of SMX and OTC. The bacterial community structure, antibiotic resistance genes abundances and genes functions were also investigated by metagenomic analysis. The results of this study offer insights into the individual and combined environmental risks of SMX and OTC, and their impact on EBPR.

Developmental toxicity and transcriptome analysis of 4-epianhydrotetracycline to zebrafish (Danio rerio) embryos

As a primary degradation by-product of tetracycline (TC), 4-Epianhydrotetracycline (4-EATC) has been detected frequently in the aquatic environment, which may pose a potential environmental risk to aquatic organisms. Up to now, however, the toxicology study on 4-EATC to aquatic organisms is limited. In the present study, in order to better understand the toxic mechanism of 4-EATC, developmental toxicity including lethal and sublethal effects of 4-EATC and TC were investigated. The results showed that the developmental toxicity of 4-EATC to zebrafish embryos was stronger than that of TC. The 96 h LC₅₀ value of 4-EATC to zebrafish embryos was 29.13 mg/L. Malformations seemed to be the most sensitive sublethal endpoint of 4-EATC exposure, and the 96 h EC₅₀ value was 8.57 mg/L. Transcriptome response of 4-EATC to zebrafish embryos was determined. The results showed that 430 different expression genes (DEGs) caused by 4-EATC, and most enriched in tryptophan (TRP) metabolism pathway. Annotation of DEGs in the TRP metabolism demonstrated that expression of 4 gene products in tryptophan metabolized along the kynurenine (KYN) pathway were changed. Disorder of TRP catabolism in KYN pathway was a potential mechanism of 4-EATC toxicity to zebrafish embryos.

Microbial degradation of tetracycline in the aquatic environment: a review

Tetracycline residues have frequently been detected in multi-environmental media, and it could induce antibiotic resistance genes (ARGs) in microorganisms, which has attracted great attention. Where biodegradation processes may be a promising strategy to remove tetracycline. Thus, this study mainly considers: (i) the degradation of tetracycline by microorganisms including single microorganisms and microbial flora; (ii) the elimination of tetracycline during biochemical treatment processes and advanced treatment systems in wastewater treatment plants (WWTPs) and constructed wetlands (CWs); (iii) the degradation of tetracycline by biological coupling processes; (iv) the confusion and problem of tetracycline biodegradation. Furthermore, the characteristics and comparison of tetracycline biodegradation have been discussed in detail. Additionally, future research directions are suggested to reduce tetracycline in the aquatic environment, especially tetracycline biodegradation and the nitrogen conversion process. Highlights Degradation of tetracycline by pure culture strains and microflora was significant. Degradation of tetracycline by biochemical treatment process was summarized. Advanced treatment process in CWs could eliminate tetracycline. Future research directions on biodegradation of tetracycline are proposed.