Ultrasensitive detection of chlortetracycline in animal-origin food using molecularly imprinted electrochemical sensor based on SnS2/ZnCo-MOF and AuNPs.

The chlortetracycline (CTC) residue in food poses a threat to human health. Therefore, developing sensitive, convenient and selective analytical methods for CTC detection is crucial. This study innovatively uses tin disulfide/bimetallic organic framework (SnS2/ZnCo-MOF) nanocomposites in conjunction with gold nanoparticles (AuNPs) to co-modify a glassy carbon electrode (GCE). Further, a molecularly imprinted polymer (MIP)-based electrochemical sensing platform Au-MIP/SnS2/ZnCo-MOF/Au/GCE (AZG) was fabricated for selective CTC detection. SnS2/ZnCo-MOF enhanced the stability and surface area of the AZG sensor. The presence of AuNPs facilitated electron transport between the probe and the electrode across the insulating MIP layer. The fixation of AuNPs and MIP via electropolymerization enhanced the selective recognition of this sensor and amplified its output signal. The AZG sensor demonstrated a wide linear detection range (0.1-100 µM), low detection limit (0.072 nM), and high sensitivity (0.830 µA µM-1). It has been used for detecting CTC in animal-origin food with good recovery (96.08%-104.60%).

Biodegradation mechanism of chlortetracycline by a novel fungal Aspergillus sp. LS-1.

Chlortetracycline (CTC), a widely used typical tetracycline antibiotic, has raised increasing concerns due to its potential health and environmental risks. Biodegradation is considered an effective method to reduce CTC in environment. In this study, a strain Aspergillus sp. LS-1, which can efficiently degrade CTC, was isolated from CTC-rich activated sludge. Under optimal conditions, the maximum removal efficiency of CTC could reach 95.41%. Temperature was the most significant factor affecting the degradation efficiency of LS-1. The 19 products were identified in the CTC degradation by strain LS-1, and three degradation pathways were proposed. All the degradation pathways for CTC exhibited ring-cleaving, which may accelerate the mineralization of CTC. To gain more comprehensive insights into this strain, we obtained the genome of LS-1, which had high GC content (50.1%) and completeness (99.3%). The gene annotation revealed that LS-1 contains some vital enzymes and resistance genes that may carry functional genes involved in the CTC degradation. In addition, other antibiotic resistance genes were found in the genome of LS-1, indicating that LS-1 has the potential to degrade other antibiotics. This study provides a more theoretical basis for the investigation of CTC degradation by fungi and new insights into the biodegradation of CTC.

Synthesis of molecularly imprinted polymers based on nitrogen-doped carbon dots for specific detection of chlortetracycline by reversed phase microemulsion method.

Among the tetracycline antibiotics, chlortetracycline (CTC) is the most frequently used antibiotic except for tetracycline (TC) for enhancing the ability of the organism to fight bacterial infections. The poor metabolism and degradability of CTC can cause serious health effects. Most studies have focused on the detection and analysis of TC, and research on CTC is relatively scarce. This is because the structures of CTC and TC and oxytetracycline (OTC) are extremely similar, and even indistinguishable. In this study, CTC was used as a template molecule and a molecularly imprinted layer was coated on the surface of highly fluorescent N-CDs using a reversed-phase microemulsion method to form N-CDs@MIPs. It was possible to specifically identify CTC without the influence of TC and OTC, which are extremely similar in structure. By comparing with the non-imprinted polymer (N-CDs@NIPs), it exhibited high sensitivity and selectivity with an imprinting factor of 2.02. And it was used in the determination of CTC in milk with recoveries and relative standard deviations of 96.7%-109.8% and 0.64%-3.27%, respectively, with high accuracy and precision. The specificity of the measurement is excellent compared with other assays, and it is a valid and reliable assay.

Selectivity Quantification with the Fluorescent Quantitative Model-Assisted Semi-Selective Probe (Carbon Dots): Accurate Determination of Chlortetracycline in Aqueous Environments with Interference.

Probes such as carbon dots (C-dots) have extensive and important applications in the quantitative analysis of complex biological and environmental systems. However, the development of probes is often hindered by incomplete selectivity, i.e., a probe that responds to one substance is also prone to respond to coexisting structurally similar substances. Therefore, the above dilemma often leads to be developed as semi-selective probes, so that the development of probes is abandoned halfway. This work shows how a semi-selective probe can enhance selectivity by combining a proper multivariate calibration model. Primarily, we developed a semi-selective fluorescent probe that responded to tetracyclines (TCs) with discarded tobacco leaves. Then, we introduced the multivariate quantitative fluorescence model (QFM) to enhance its selectivity and solve the problem of fluorescence spectral shift. For the determination of chlortetracycline (CTC) with this semi-selective C-dots probe in mineral and lake water samples and compared to the traditional quantitative model, the introduced QFM resulted in an average relative predictive error (ARPE) in mineral water spiked samples decreased from 57.1 to 5.6%, which reduced the ARPE in the lake water spiked samples from 18.1 to 4.7%. The above results show that the QFM-assisted semi-selective probe C-dots strategy (QFMC-dots) can enhance selectivity, and QFMC-dots achieved high-selective and accurate determination of CTC in interfering mineral and lake water samples, with the limit of detection and limit of quantitation of 0.55 and 1.66 µM, respectively. The proposed strategy of enhancing selectivity by introducing a proper multivariate calibration model can reduce the difficulty and increase success rate of developing probes, which can be expected to provide an interesting alternative for the development of probes, especially when encountering semi-selective problems.

Mitigation effects and microbial mechanism of two ecological earthworms on the uptake of chlortetracycline and antibiotic resistance genes in lettuce.

The contamination of greenhouse vegetable soils with antibiotics and antibiotic resistance genes (ARGs), caused by the application of livestock and poultry manure, is a prominent environmental problem. In this study, the effects of two ecological earthworms (endogeic Metaphire guillelmi and epigeic Eisenia fetida) on the accumulation and transfer of chlortetracycline (CTC) and ARGs in a soil-lettuce system were studied via pot experiments. The results revealed that earthworm application accelerated the removal of the CTC from the soil and lettuce roots and leaves, with the CTC content reducing by 11.7-22.8 %, 15.7-36.1 %, and 8.93-19.6 % compared with that of the control, respectively. Both earthworms significantly reduced the CTC uptake by lettuce roots from the soil (P < 0.05) but did not change the CTC transfer efficiency from the roots to leaves. The high-throughput quantitative PCR results showed that the relative abundance of ARGs in the soil and lettuce roots and leaves decreased by 22.4-27.0 %, 25.1-44.1 %, and 24.4-25.4 %, respectively, with the application of earthworms. Earthworm addition decreased the interspecific bacterial interactions and the relative abundance of mobile genetic elements (MGEs), which helped reduce the dissemination of ARGs. Furthermore, some indigenous soil antibiotic degraders (Pseudomonas, Flavobacterium, Sphingobium, and Microbacterium) were stimulated by the earthworms. The results of redundancy analysis indicated that the bacterial community composition, CTC residues, and MGEs were the main parameters affecting the distribution of ARGs, accounting for 91.1 % of the total distribution. In addition, the bacterial function prediction results showed that the addition of earthworms reduced the abundance of some pathogenic bacteria in the system. Overall, our findings imply that earthworm application can substantially reduce the accumulation and transmission risk of antibiotics and ARGs in soil-lettuce systems, providing a cost-effective soil bioremediation practice for addressing antibiotic and ARGs contamination to guarantee the safety of vegetables and human health.

Potential output and risk of commonly administered veterinary antibiotics from small-scale livestock farms to surrounding areas in Northwest China.

The concern over antibiotic pollution from animal husbandry has significantly increased over recent years. However, few studies on output and environmental risk of veterinary antibiotics (VAs) throughout different exposure matrices from small-scale livestock farms (SSLFs) have been explored. This study explored the output and environmental risk of three classes of VAs (sulfonamides (SAs), tetracyclines (TCs), fluoroquinolones (FQs)) in three different types of environmental media (manure, soil, and plants/vegetables) derived from four livestock feedlots in the Hexi Corridor of Northwest China. Following, a risk assessment was conducted to identify the hazardous potential of these VAs on the ecological health of the surrounding environment. A total of 108 soil, 36 manure, 12 plants/vegetables, and 15 animal product samples were collected from the animal feedlots for analysis. The results showed that each of the three groups of VAs were detected in the soil, manure and plant samples derived from all four feedlots in varying levels. In the soil samples, the detection rate of SAs (68%) was higher than the TCs (57%) and the FQs (27%). The total concentration of VAs ranged from not detected (n.d.) to 275 ng/g, while chlortetracycline (CTC) was the most abundant (275 ng/g) of the VAs in soil samples. The SAs had the highest detection rate (100%), followed by TCs (89%), and FQs (78%) in manure samples. The total concentration of VAs residues ranged from n. d. to 105 ng/g, of which CTC was as high as 91 ng/g in manures. In the plant/vegetable samples, the TCs had the highest detection rate (58%), while sulfamethazine (SDM) was the most abundant (32 ng/g). The total concentration of the VAs ranged from n. d. to 65 ng/g in the plant/vegetable samples. The target VAs were not detected in animal products. Measurements of the composition of VAs in soil samples at different vertical depths as well as horizontal distances from the manure accumulation sites showed that VAs were partially retained in the soil of the feedlots and were distributed into the surrounding environment both horizontally and vertically. It is suspected that the detected VAs could be accumulated in agricultural soils since they could be found in most of the sampled manures and soils in SSLFs. These results highlighted the necessity of considering SSLF practices to mange the accumulation and disposal of manure mitigating and controlling VA pollution.

Association between antibiotic exposure and the risk of infertility in women of childbearing age: A case-control study.

BACKGROUND: Based on self-report questionnaires, two previous epidemiological studies investigated the association between the exposure of women to antibiotics and their fertility. However, biomonitoring studies on low-dose antibiotic exposure, mainly from food and water, and its relation to the risk of infertility are missing. METHODS: Based on a case-control study design, 302 women with infertility (144 primary infertility, 158 secondary infertility) and 302 women with normal fertility, all aged 20-49 years, were recruited from Anhui Province, China, in 2020 and 2021. A total of 41 common antibiotics and two antibiotic metabolites in urine samples were determined by liquid chromatography-triple quadrupole tandem mass spectrometry (LC-QqQ-MS/MS). RESULTS: Twenty-eight antibiotics with detection rates from 10% to 100% in both cases (median concentration: ∼2.294 ng/mL) and controls (∼1.596 ng/mL) were included in the analysis. Logistic regression analysis revealed that after controlling for confounding factors, high concentrations of eight individual antibiotics (sulfamethoxazole, sulfaclozine, sulfamonomethoxine, penicillin G, chlorotetracycline, ofloxacin, norfloxacin, and cyadox) and four antibiotic classes (sulfonamides, tetracyclines, quinoxalines, and veterinary antibiotics) were related to a high risk of female infertility, with odds ratios (ORs) ranging from 1.30 to 2.86, except for chlorotetracycline (OR = 6.34), while another nine individual antibiotics (sulfamethazine, azithromycin, cefaclor, amoxicillin, oxytetracycline, pefloxacin, sarafloxacin, enrofloxacin, and florfenicol) and classes of chloramphenicol analogs and human antibiotics were related to a reduced risk of infertility, with ORs ranging from 0.70 to 0.20. Based on restricted cubic spline models after controlling for confounding factors, we observed that the relationship between all of the above protective antibiotics and infertility was nonlinear: A certain concentration could reduce the risk of female infertility while exceeding a safe dose could increase the risk of infertility. CONCLUSION: These results provide preliminary evidence that the effects of antibiotics on female fertility vary based on the active ingredient and usage and imply the importance of exposure dose. Future studies are needed to verify these results by controlling for multiple confounding factors.

Bridging of a Liquid Chromatography-Tandem Mass Spectrometry Method for Oxytetracycline, Chlortetracycline, and Tetracycline in Bovine Kidney with the Official Microbial Growth Inhibition Assay.

BACKGROUND: Oxytetracycline (OTC), chlortetracycline (CTC), and tetracycline (TC) are approved antibiotics used to treat bacterial infections in cattle. To ensure human food safety, a tolerance has been established for the sum of these three TC residues as 12 parts per million in bovine kidney in the United States The current official regulatory method for quantifying these antibiotics in the target organ is a labor-intensive microbiological assay. OBJECTIVE: Our laboratory developed and validated a fast, selective, and less laborious method utilizing LC-tandem mass spectrometry for the determination and confirmation of the three tetracyclines (TET) in bovine kidney. METHODS: Briefly, homogenized kidney tissue was spiked with an internal standard (ISTD), and then was extracted with 1% phosphate buffer. The crude extract was cleaned up using solid-phase extraction cartridges before instrumental analysis. RESULTS: Accuracies for quantifying these three drugs in fortified kidney homogenate were between 99.9 and 110% at multiple concentrations, with respective CVs all below 9.5%. Quantitative correlation between the two methods (bridging) was evaluated with incurred bovine kidney samples for each of the three tetracyclines separately. The results were statistically evaluated using a measurement model called Functional Relationship Estimation by Maximum Likelihood. CONCLUSION: A linear quantitative relationship was demonstrated between the two methods within the concentration range of regulatory relevance. HIGHLIGHTS: This instrumental method is in addition to the established microbial assay for the detection of tetracyclines residue in beef kidney to ensure the food safety of cattle products.

Sources, Environmental Fate, and Ecological Risks of Antibiotics in Sediments of Asia's Longest River: A Whole-Basin Investigation.

This study conducted the first extensive and comprehensive investigation of the whole-scale sedimentary antibiotic concentration, possible drivers, environmental fate, and potential ecological risks in the Yangtze River. Totally, 20 antibiotics were detected in the sediments. Results revealed that the order of antibiotic abundance in sediment was fluoroquinolones > tetracyclines > macrolides > sulfonamides > amphenicols. The total antibiotic concentrations were 0.10-134.4 ng/g (mean: 11.88 ng/g). Of these, fluoroquinolones and tetracyclines were the two dominant antibiotic categories. The dominant occurrence of fluoroquinolones and tetracyclines in sediments suggested that the distribution coefficient (Kd) was one of the important factors to determine their fate. Correlation analysis demonstrated that antibiotic contamination was largely influenced by the local scale of animal husbandry, and the positive correlation between antibiotics and heavy metals was likely driven by their common source of contamination and the complexation. Environmental risk assessment showed that tetracycline and chlortetracycline exhibited potential risks from medium to high in the Yangtze River, although most of the compounds posed minimal and low risks. This work provided a valuable large-scale data set across the whole Yangtze River and revealed the contamination profile of antibiotics. Mitigation and management measures to reduce antibiotic inputs are needed for the Yangtze River basin.

Response of microbial interactions in activated sludge to chlortetracycline.

Chlortetracycline (CTC) has attracted increasing attention due to its potential environmental risks. However, its effects on bacterial communities and microbial interactions in activated sludge systems remain unclear. To verify these issues, a lab-scale sequencing batch reactor (SBR) exposed to different concentrations of CTC (0, 0.05, 0.5, 1 mg/L) was carried out for 106 days. The results showed that the removal efficiencies of COD, TN, and TP were negatively affected, and the system functions could gradually recover at low CTC concentrations (≤0.05 mg/L), but high CTC concentrations (≥0.5 mg/L) caused irreversible damage. CTC significantly altered bacterial diversity and the overall bacterial community structure, and stimulated the emergence of many taxa with antibiotic resistance. Molecular ecological network analysis showed that low concentrations of CTC increased network complexity and enhanced microbial interactions, while high concentrations of CTC had the opposite effect. Sub-networks analysis of dominant phyla (Bacteriodota, Proteobacteria, and Actionobacteriota) and dominant genera (Propioniciclava, a genus from the family Pleomorphomonadaceae and WCHB1-32) also showed the same pattern. In addition, keystone species identified by Z-P analysis had low relative abundance, but they were important in maintaining the stable performance of the system. In summary, low concentrations of CTC enhanced the complexity and stability of the activated sludge system. While high CTC concentrations destabilized the stability of the overall network and then caused effluent water quality deterioration. This study provides insights into our understanding of response in the bacteria community and their network interactions under tetracycline antibiotics in activated sludge system.

An exhaustive investigation on antibiotics contamination from livestock farms within sensitive reservoir water area: Spatial density, source apportionment and risk assessment.

Although the studies on antibiotic contamination are common at present, large-scale sampling studies drawing highly representative conclusions are still scarce. This study conducted a comprehensive investigation on a total of 1183 samples from 70 livestock farms within a sensitive area around reservoir waters. 45 types of antibiotics belonging to 5 different classes were monitored. This is the first analysis to comprehensively investigate the density distribution, source apportionment, ecological and health risk of antibiotics in an entire area of sensitive waters. The results showed that the layer manure samples had highest detection rate of antibiotics (0.0 %-96.1 %, average value = 30.7 %) followed by pig manure samples. Oxytetracycline had the highest concentration of 712.16 mg/kg in a pig manure sample. Different from using antibiotic concentration as a proxy for pollution level, the spatial density was calculated by averaging antibiotic concentration to area and converting different livestock to pig equivalent. The spatial density of pig equivalent can more realistically reflect the pollution caused by different breeds of livestocks. It was shown that the pig farms contributed higher to total antibiotic density than the layer and cattle farms did. After assessed, a few antibiotics (oxytetracycline, chlorotetracycline and tetracycline) have posed high ecological risks to soil around the farms. However, none of them caused hazard quotient (HQ) risk and carcinogenic risk (CR) to human health in the water of reservoir. Children were more likely to be at hazard risk than adults. Antibiotic mass fluctuation rules were analyzed along the chain (feed → livestock waste → soil → surface water). Feed, livestock waste and soil had similar diversity, but the antibiotic concentrations continued to decline, implying the possible sources of antibiotic residues were similar. Thus, it is important to reduce unnecessary antibiotic use to prevent the potential long-term risk of antibiotics.

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.

Field study on loss of tetracycline antibiotics from manure-applied soil and their risk assessment in regional water environment of Guangzhou, China.

Tetracycline antibiotics (TCs) introduced into agricultural fields via manure application tend to accumulate in soils and further reach water environments via surface runoff and leachate, posing potential risks to regional water environment. This study investigated the loss of tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) in surface runoff and leachate samples collected from a vegetable farmland with manure application in Guangzhou, South China. A risk assessment method was constructed for evaluating the ecological and health risks of manure-associated antibiotics released from soil into water environment. The results showed that the concentrations of three TCs in surface runoff, 30-cm leachate, and 60-cm leachate after the first rainfall event were 2.79-35.97, 1.71-18.44, and 0.4-2.66 µg/L, respectively, which all decreased with sampling depth and the time after rainfall events. Up to 0.13% of TCs were transported into the surface water through surface runoff, while less than 0.01% of TCs were transported into the groundwater through leachate at 60 cm. OTC had a higher total mass percentage (0.13%) into surface water via runoff than CTC (0.11%) and TC (0.07%) likely due to its smallest Kd value and largest input mass. Based on loss percentages, their predicted environmental concentrations (PEC) ranged from 4.87 (TC) to 16.91 (OTC) ng/L in regional surface water and 1.42 (TC) to 5.20 (CTC) ng/L in regional groundwater. The risk assessment based on PEC results suggested non-negligible health risk (HQ > 1.0 × 10-6) and low ecological risk (RQ < 0.1) in both regional surface water and groundwater, drawing concerns on the potential hazards of TCs released from manure-amended soil into water environments.

Effective degradation of Chlortetracycline using dual bio catalyst.

Chlortetracycline (CTC) degradation using potential microbial consortia or individual bacterial strains was useful method for improving bioremediation potential. The co-culture (Klebsiella pneumoniae CH3 and Bacillus amyloliquefaciens CS1) of bacterial strains have the ability to degrade chlortetracycline (91.8 ± 1.7%), followed by sulfamethoxazole (62.1 ± 1.2%) and amoxicillin (73.9 ± 3.3%). It was observed that the degradation potential was maximum after 10 days incubation, 8-10% inoculum, pH 7.5, and antibiotic concentration ranged from 150 to 200 mg/L. The initial concentrations of CTC significantly affected CTC degradation. In strain CH3, maximum biodegradation of CTC (99.4 ± 2.3%) was observed at 200 mg/L initial CTC concentrations. In CS1, maximum biodegradation of CTC was obtained at 150 mg/L concentration (80.5 ± 3.2%) after 10 days of culture. Alkaline pH was found to be suitable for the degradation of antibiotic than acidic range. After initial optimization by one factor at a time approach in free cells, the bacterial strains (CH3 and CS1) were co-immobilized. The co-immobilized bacterial cells showed improved degradation potential than free cells. To determine the biodegradation potential of immobilized cells, the selected strains were immobilized in polymer beads and treated with CTC with 175 mg/L initial concentration. The experimental results revealed that after 3 days of treatment the residual CTC concentration was 150.1 ± 3.2 mg/L and it decreased as 1.28 ± 0.01 mg/L after 10 days of treatment. The present study confirmed the effectiveness and feasibility of biodegradation ability of K. pneumoniae CH3 and B. amyloliquefaciens CS1 immobilized for CTC degradation in wastewater.

Time-course evolution of bacterial community tolerance to tetracycline antibiotics in agricultural soils: A laboratory experiment.

The presence of antibiotics in soils may increase the selection pressure on soil bacterial communities and cause tolerance to these pollutants. The temporal evolution of bacterial community tolerance to different concentrations of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) was evaluated in two soils. The results showed an increase of soil bacterial community tolerance to TC, CTC and OTC only in samples polluted with the highest antibiotic concentrations tested (2000 mg kg-1). The magnitude of those increases was higher in the soil with the lower organic carbon content (1.6%) than in the soil with an organic carbon content reaching 3.4%. In the soil with low organic carbon content, the time-course evolution showed a maximum increase in the tolerance of bacterial communities to tetracycline antibiotics between 45 and 100 incubation days, while for longer incubation times (360 days) the tolerance decreased. In the soil with high organic carbon content, a similar behavior was found for OTC. However, for CTC and TC, slightly increases and decreases (respectively) were found in the bacterial community tolerance at intermediate incubation times, followed by values close to zero for TC after 360 days of incubation, while for CTC they remained higher than in the control. In conclusion, soil pollution due to tetracyclines may cause bacterial community tolerance to these antibiotics when present at high concentrations. In addition, the risk is higher in soils with low organic matter content, and it decreases with time.

One-step synthesis of N, S-doped carbon dots with orange emission and their application in tetracycline antibiotics, quercetin sensing, and cell imaging.

Water soluble N, S-doped carbon dots (N, S-CDs) with orange emission were synthesized from basic fuchsin and sulfosalicylic acid by the typical hydrothermal route. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline antibiotics (for example, chlortetracycline (CTC)) and quercetin. The proposed sensor was utilized to realize the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm) with satisfactory recoveries and relative standard deviations (RSD). The linear range and detection limit (LOD) of CTC is 1.24-165 µM and 32.36 nM, respectively. For quercetin, the linear ranges are 0.98-34 µM and 34-165 µΜ, and the LOD is 6.87 nM (3σ/m). By virtue of the good biocompatibility and long-wavelength emission, N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bio-imaging and sensing. In this paper, N, S-doped carbon dots (N, S-CDs) with orange emission (λem = 605 nm) were synthesized from basic fuchsin and sulfosalicylic acid. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for the sensing of tetracycline antibiotics (for example: chlortetracycline (CTC)) and quercetin. The sensor has been successfully applied to the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm). The linear range and detection limit (LOD) of CTC is 1.24-165 µM and 32.36 nM respectively. For quercetin, the linear ranges are 0.98-34 µM and 34-165 µΜ, and the LOD is 6.87 nM (3σ/m). In addition, due to the characteristics of good biocompatibility and long-wavelength emission, the N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bioimaging and sensing.

Persistence and fate of chlortetracycline in the aquatic environment under sub-tropical conditions: generation and dissipation of metabolites.

The persistence of chlortetracycline in the aquatic environment, including the generation and dissipation of its metabolites, were investigated over a period of 90 days using microcosm experiments, with a view to establishing the metabolites generated and their persistence under conditions closely resembling the actual aquatic environment in terms of chemical and microbial composition. The concentrations of chlortetracycline and its metabolites were monitored in the water phase as well as the sediment phase. Data are presented showing that the degradation of chlortetracycline in each phase conforms to a triphasic linear rate law, confirming the existence of three speciation forms in each phase, attributed to one free dissolved form, and two colloidal particle adsorbed forms. Data are also presented showing that the two adsorbed forms are the most persistent, with life-times of 204.1 and 20.3 days respectively in the water phase, and 215.1 and 19.8 days respectively in the sediment phase. Life-times of 5.01 and 3.7 days respectively were obtained for the free dissolved forms in the water phase and sediment phase respectively. Data are further presented showing that of the several metabolites of chlortetracycline reported previously, only 4-epi-chlortetracycline and iso-chlortetracycline could be detected, and that these two degradation products undergo microbial mineralization without transformation to other intermediate degradation products in significant or detectable amounts.

Competitive adsorption and desorption of three tetracycline antibiotics on bio-sorbent materials in binary systems.

Batch-type experiments were used to study competitive adsorption/desorption for the antibiotics tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), onto by-products from forest and food industries (oak ash, pine bark, and mussel shell). These antibiotics are frequently present in manures and slurries spread on agrosystems. Binary competitive systems were performed by setting the dose of one antibiotic to 200 µmol L-1, and varying the concentration of a second antibiotic from 50 to 600 µmol L-1. In the cases where a concentration of 200 µmol L-1 was used for each antibiotic, the results of the binary experiments were also compared with those obtained in parallel tests corresponding to simple and ternary systems using the same concentration. The results indicated that pine bark can adsorb most of the antibiotics added, with desorption being less than 5% in most cases. Oak ash showed high adsorption for all three antibiotics in the simple systems (100% of CTC, 90% of TC, and 80% of OTC), but clearly decreased in the binary systems (up to values below 40%), especially for higher antibiotics concentrations, although desorption was generally less than 5%. Mussel shell showed adsorption results lesser than 25% for OTC and CT in simple systems, while increased up to 65% in binary systems in which CTC was present at high concentrations, but desorption was generally very high. CTC was the antibiotic with the highest adsorption onto all three by-products, and the one showing less decrease for its adsorption in the binary systems. Overall, the smallest differences among the various competitive systems were obtained when the adsorbent used was pine bark, and especially for the CTC antibiotic. These results could aid to develop management practices, based on the use of low-cost bio-sorbents, which would decrease risks of pollution due to tetracycline antibiotics spread in agroecosystems and affecting the environment.

Simultaneous determination of olaquindox, oxytetracycline and chlorotetracycline in feeds by high performance liquid chromatography with ultraviolet and fluorescence detection adopting online synchronous derivation and separation.

Olaquindox, oxytetracycline and chlorotetracycline were widely used in feed as antibiotics and growth promoter to improve feed conversion efficiency and increase the rate of weight gain for animals. However, the use of these antibiotics in feed was gradually prohibited because of concerns about contamination and resistance in animals. A quantitative and confirmatory method for determining the presence of olaquindox, oxytetracycline and chlorotetracycline in feed by high performance liquid chromatography equipped with ultraviolet detector in series with fluorescence detector (HPLC-UVD-FLD) was developed, optimized, and validated in three different matrices (compound, concentrated and premix feed). The analytes extraction was performed with a mixture of acetonitrile and 0.1 mol/L ethylenediamine tetraacetic acid disodium-Mcllvaine buffer (1:4, v/v) by one step sample preparation procedure. The validated method presented a broad linear range and good linearity with weighted least square method. The decision limit of the analytes ranged from 0.61 to 0.77 mg/kg for olaquindox, 0.90 to 1.2 mg/kg for oxytetracycline and 1.3 to 2.0 mg/kg for chlorotetracycline. The average recovery values found in intermediate precision conditions were ranged from 88.0 to 99.7% for olaquindox with RSD lower than 11.1%, from 84.4 to 99.0% for oxytetracycline with RSD lower than 9.6%, from 83.8 to 97.5% for chlorotetracycline with RSD lower than 10.0%. By Youden test and bottom-up method, the method was proved to be sufficiently robust and had a small uncertainty for different concentration levels. The developed method was successfully utilized for commercial feed samples to monitor complex cross contamination and residue conditions. Online synchronous derivation and separation using ultraviolet detector in series with fluorescence detector can effectively prevent false positive of chlorotetracycline in feed caused by vegetable meal. Since olaquindox, oxytetracycline and chlorotetracycline are widely used in feed, the developed method provide an important and analytical tool for the simultaneous identification and quantification of them in feed to monitor its risk of cross contamination and excessive content.

Nitrogen-doped carbon dots from rhizobium as fluorescence probes for chlortetracycline hydrochloride.

Fluorescent nitrogen-doped carbon dots (CDs) were prepared via hydrothermal method at 190 °C for 10 h using rhizobium from soy as the carbon and nitrogen source. Their optical properties, structure, morphology, and functional groups were characterized in detail and the results showed that they possess unique excitation-dependent fluorescence behavior, with average diameter 4.5 ± 2.0 nm and good water dispersibility. Due to the overlap of the UV-vis absorbance of chlortetracycline hydrochloride (CCH) and the fluorescence excitation band of CDs, the fluorescence of the prepared CDs can be quenched by CCH selectively and sensitively. The changes of the fluorescence intensity of CDs have a good linear relationship with the concentration of CCH in a wide concentration range of 5-100 µM, with a detection limit of 0.254 µM. This present method has been successfully applied to determine the CCH in water with recovery ranging from 96.0% to 100.7%.