Occurrence of antibiotics and antibiotic resistance genes in soils from wastewater irrigation areas in the Pearl River Delta region, southern China

Antibiotic-metal complexes in wastewaters: fate and treatment trajectory

Unregulated usage, improper disposal, and leakage from pharmaceutical use and manufacturing sites have led to high detection levels of antibiotic residues in wastewater and surface water. The existing water treatment technologies are insufficient for removing trace antibiotics and these residual antibiotics tend to interact with co-existing metal ions and form antibiotic-metal complexes (AMCs) with altered bioactivity profile and physicochemical properties. Typically, antibiotics, including tetracyclines, fluoroquinolones, and sulphonamides, interact with heavy metals such as Fe²⁺, Co²⁺, Cu²⁺, Ni²⁺, to form AMCs which are more persistent and toxic than parent compounds. Although many studies have reported antibiotics detection, determination, distribution and risks associated with their environmental persistence, very few investigations are published on understanding the chemistry of these complexes in the wastewater and sludge matrix. This review, therefore, summarizes the structural features of both antibiotics and metals that facilitate complexation in wastewater. Further, this work critically appraises the treatment methods employed for antibiotic removal, individually and combined with metals, highlights the knowledge gaps, and delineates future perspectives for their treatment.

Individual and combined applications of biochar and pyroligneous acid mitigate dissemination of antibiotic resistance genes in agricultural soil

Remediation of agricultural soils polluted with antibiotic resistance genes (ARGs) is important for protecting food safety and human health. However, the feasibility of co-application of biochar and pyroligneous acid, two multifunctional soil amendments, for mitigating dissemination of soil ARGs is unknown. Thus, a woody biochar (BC450) and its by-product, pyroligneous acid (PA450) simultaneously produced at 450 °C from blended wood wastes, were used to compare their individual and combined effects on soil ARG abundance using a 65-day pot experiment planted with leafy vegetable Brassica chinensis L. The individual and combined applications of PA450 and BC450 significantly reduced the absolute abundance of ARGs by 65.7-81.4% and 47.5-72.9% in the corresponding rhizosphere and bulk soil. However, the co-application showed little synergistic effect, probably due to the counteractive effect of BC450 on the PA450-mitigated soil ARG proliferation, resulted from the promoted soil bacterial growth and/or adsorption of antimicrobial components of PA450 by BC450. The decreased abundances of mobile genetic element intI1 and Tn916/1545 in the PA450 treatments demonstrated the potential of PA450 for weakening horizontal gene transfer (HGT). Furthermore, weakened HGT by individual PA450, lowered availability of heavy metals by individual BC450, and different bacterial community (e.g., reduced ARGs bacterial host) together with improved soil properties from co-application of PA450 and BC450 all contributed to the reduced ARG level. This study highlighted the feasibility of co-applications of biochar and pyroligneous acid amendment for mitigating soil ARG pollution. These findings provide important information for developing eco-friendly technologies using biochar and pyroligneous acid in remediating ARG-contaminated soils.

Antibiotic resistance and class 1 integron genes distribution in irrigation water-soil-crop continuum as a function of irrigation water sources

The increasing demand for fresh water coupled with the need to recycle water and nutrients has witnessed a global increase in wastewater irrigation. However, the development of antibiotic resistance hotspots in different environmental compartments, as a result of wastewater reuse is becoming a global health concern. The effect of irrigation water sources (wastewater, surface water, fresh water) on the presence and abundance of antibiotic resistance genes (ARGs) (bla_CTX-m-32, tet-W, sul1, cml-A, and erm-B) and class 1 integrons (intI1) were investigated in the irrigation water-soil-crop continuum using quantitative real-time PCR (qPCR). Sul1 and bla_CTX-m-32 were the most and least abundant ARGs in three environments, respectively. The abundance of ARGs and intI1 significantly decreased from wastewater to surface water and then fresh water. However, irrigation water sources had no significant effect on the abundance of ARGs and intI1 in soil and crop samples. Principal component analysis (PCA) showed that UV index and air temperature attenuate the abundance of ARGs and intI1 in crop samples whereas the air humidity and soil electrical conductivity (EC) promotes the ARGs and intI1. So that the climate condition of semi-arid regions significantly affects the abundance of ARGs and intI1 in crop samples. The results suggest that treated wastewater might be safely reused in agricultural practice in semi-arid regions without a significant increase of potential health risks associated with ARGs transfer to the food chain. However, further research is needed for understanding and managing ARGs transfer from the agricultural ecosystem to humans through the food chain.

Metagenomic profiles and health risks of pathogens and antibiotic resistance genes in various industrial wastewaters and the associated receiving surface water

The aquatic environment may represent an essential route for transmission of antibiotic resistance to opportunistic human pathogens. Since industrial wastewater is discharged into the river after treatment, understanding the distribution of antibiotic resistance genes (ARGs) in river systems and the possibility of pathogens acquiring antibiotic resistance are challenges with far-reaching significance. This work mainly studied distribution profiles of pathogens and ARGs, and compared their health risk in various industrial wastewater with that of river water. Results showed that 166 pathogens were concurrently shared by the six water samples, with Salmonella enterica and Pseudomonas aeruginosa being the most abundant, followed by Fusarium graminearum and Magnaporthe oryzae. The similar composition of the pathogens suggests that pathogens in river water may mainly come from sewage discharge of slaughterhouses and that changes in water quality contribute significantly to the prevalence of these pathogens. Of the 57 ARG types detected, bacitracin was the most abundant, followed by sulfonamide, chloramphenicol, tetracycline, and aminoglycoside. Strikingly, the wastewater from a pharmaceutical factory producing Chinese medicine was also rich in bacA, sul1, mexW, mexB, mexF and oprn. It can be seen from the co-occurrence patterns that pathogens and the main ARGs have strong co-occurrence. Higher abundance of offensive virulence factors in industrial wastewater and their strong correlation with pathogens containing ARGs suggest higher microbiological risk. These findings highlight the need to assess ARG acquisition by pathogens in the surface water of human-impacted environments where pathogens and ARGs may co-thrive.

Does Irrigation with Treated and Untreated Wastewater Increase Antimicrobial Resistance in Soil and Water: A Systematic Review

Population growth and water scarcity necessitate alternative agriculture practices, such as reusing wastewater for irrigation. Domestic wastewater has been used for irrigation for centuries in many historically low-income and arid countries and is becoming more widely used by high-income countries to augment water resources in an increasingly dry climate. Wastewater treatment processes are not fully effective in removing all contaminants, such as antimicrobial resistant bacteria (ARB) and antimicrobial resistance genes (ARGs). Literature reviews on the impact of wastewater irrigation on antimicrobial resistance (AMR) in the environment have been inconclusive and mostly focused on treated wastewater. We conducted the first systematic review to assess the impact of irrigation with both treated or untreated domestic wastewater on ARB and ARGs in soil and adjacent water bodies. We screened titles/abstracts of 3002 articles, out of which 41 were screened in full text and 26 were included in this review. Of these, thirteen investigated irrigation with untreated wastewater, and nine found a positive association with ARB/ARGs in soil. Out of thirteen studies focused on treated wastewater, six found a positive association with ARB/ARGs while six found mixed/negative associations. Our findings demonstrate that irrigation with untreated wastewater increases AMR in soil and call for precautionary action by field workers, their families, and consumers when untreated wastewater is used to irrigate crops. The effect of irrigation with treated wastewater was more variable among the studies included in our review, highlighting the need to better understand to what extent AMR is disseminated through this practice. Future research should assess factors that modify the effect of wastewater irrigation on AMR in soil, such as the degree and type of wastewater treatment, and the duration and intensity of irrigation, to inform guidelines on the reuse of wastewater for irrigation.

Antibiotics: An overview on the environmental occurrence, toxicity, degradation, and removal methods

Antibiotics, as antimicrobial drugs, have been widely applied as human and veterinary medicines. Recently, many antibiotics have been detected in the environments due to their mass production, widespread use, but a lack of adequate treatment processes. The environmental occurrence of antibiotics has received worldwide attention due to their potential harm to the ecosystem and human health. Research status of antibiotics in the environment field is presented by bibliometrics. Herein, we provided a comprehensive overview on the following important issues: (1) occurrence of antibiotics in different environmental compartments, such as wastewater, surface water, and soil; (2) toxicity of antibiotics toward non-target organisms, including aquatic and terrestrial organisms; (3) current treatment technologies for the degradation and removal of antibiotics, including adsorption, hydrolysis, photodegradation and oxidation, and biodegradation. It was found that macrolides, fluoroquinolones, tetracyclines, and sulfonamides were most frequently detected in the environment. Compared to surface and groundwaters, wastewater contained a high concentration of antibiotic residues. Both antibiotics and their metabolites exhibited toxicity to non-target organisms, especially aquatic organisms (e.g., algae and fish). Fluoroquinolones, tetracyclines, and sulfonamides can be removed through abiotic process, such as adsorption, photodegradation, and oxidation. Fluoroquinolones and sulfonamides can directly undergo biodegradation. Further studies on the chronic effects of antibiotics at environmentally relevant concentrations on the ecosystem were urgently needed to fully understand the hazards of antibiotics and help the government to establish the permissible limits. Biodegradation is a promising technology; it has numerous advantages such as cost-effectiveness and environmental friendliness.

Adsorption behaviours and transfer simulation of levofloxacin in silty clay

Fluoroquinolone antibiotics in soil can cause serious antibiotic pollution. Adsorption is the main factor that influences their destination and transport of antibiotics. Therefore, research on the behaviour of antibiotics once they reach the soil environment is meaningful to design appropriate measures to reduce their potential risks. This research took levofloxacin (LVFX) as the research object and used a static adsorption experiment to study the adsorption behaviour of the vadose zone of silty clay on the North China Plain. The results showed that LVFX had high retention in silty clay, with an average adsorption ratio of more than 90%. Adsorption of LVFX on silty clay reached equilibrium in 24 h with an adsorption amount of 93.5 mg/kg at an initial LVFX concentration of 10 mg/L. Acidity, cations and soil organic matter could affect the adsorption of LVFX, with adsorption variation ratio of 3.3%, 3.4% and 0.6%, respectively. In addition, numerical simulation with Hydrus-1D was utilized, and the results show that LVFX may infiltrate into underground water through silty clay after 28 days and completely penetrate in 100 days.

The role of soils in regulation of freshwater and coastal water quality

Water quality regulation is an important ecosystem service function of soil. In this study, the mechanism by which soil regulates water quality was reviewed, and the effects of soil management on water quality were explored. A scientometrics analysis was also conducted to explore the research fields and hotspots of water quality regulation of soil in the past 5 years. This review found that the pollutants entering the soil can be mitigated by precipitation, adsorption and desorption, ion exchange, redox and metabolic decomposition. As an optimal substrate, soil in constructed wetlands has perfect performance in the adsorption and passivation of pollutants such as nitrogen, phosphorus and heavy metals in water, and degradation of pesticides and emerging contaminants. Mangrove wetlands play an important role in coastal zone protection and coastal water quality restoration. However, the excessive application of agricultural chemicals causes soil overload, which leads to the occurrence of agricultural non-point source pollution. Under the dual pressures of climate change and food insecurity in the future, developing environmentally friendly and economically feasible sustainable soil management measures is crucial for maintaining the water purification function of soil by relying on the accurate quantification of soil function based on big data and modelling. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People'.

Electrocatalytic oxidation of ciprofloxacin by Co-Ce-Zr/γ-Al2O3 three-dimensional particle electrode

In this work, Co-Ce-Zr/γ-Al₂O3₃ particle electrodes were prepared for the efficient degradation of ciprofloxacin (CIP). Co-Ce-Zr/γ-Al₂O₃ particle electrodes were analyzed with a scanning electron microscope (SEM), X-Ray Diffraction (XRD), X-Ray Fluorescence Spectrometer (XRF), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). According to the results, significant amounts of Co₃O₄, CeO₂, and ZrO₂ were formed on the Co-Ce-Zr/γ-Al₂O₃ particle electrodes. It was shown that when the conditions of the reaction system were at pH=6, conductivity of 4 ms/cm, current of 0.2 A, initial pollutant concentration of 100 mg/L, and material dosage of 15 g, CIP could be completely degraded within 40 min, and the energy consumed in the reaction was 41.3 kWh/kg CIP. The rate of total organic carbon (TOC) removal by Co-Ce-Zr/γ-Al₂O₃ particle electrodes was recorded to be approximately 52.6%. Using a response surface methodology, we explored the optimal operating conditions. At the same time, we also explored the influence of inorganic anions in water and actual water medium on the rate of CIP removal. In addition, the ESR data proved that the main active substance in the reaction system was ·OH. The degradation intermediates were investigated, and the possible mechanism was proposed. Thus, this research provided a new solution for the treatment of antibiotic-containing wastewater.

Persistence and spread of tetracycline resistance genes and microbial community variations in the soil of animal corrals in a semi-arid planted forest

At the spring, goat and sheep herds are transferred to planted forests, in a semi-arid region in the northern Negev Desert, Israel, to reduce herbaceous biomass and, fire risk. The herds are held overnight in corrals for about 4 months, enriching the soil with organic matter and nitrogen. This research examined the effect of these enrichments on soil bacterial community structure (BCS) and the abundance of tetracycline resistance genes (TRGs) in active and abandoned corrals (1-10-years-old). Based on 16S rRNA gene sequences, the Proteobacteria and Actinobacteria phyla dominated the soil of all corrals. The Actinobacteria were less abundant in the active and 1-year-old corrals (23-26%) than in the other corrals and the control (33-38%). A principal component analysis showed that, the BCS in the active and the 1-year-old abandoned corrals was significantly different from that in the older corrals and the control. The Firmicutes phylum constituted 28% of the BCS in the active corrals, 12.5% in the 1-year-old corrals and 2% in the older corrals and the control. In contrast, the Acidobacteria phylum was hardly detected in the active and 1-year-old abandoned corrals and constituted 10% of the BCS in the older corrals. Genes conferring resistance to tetracycline were detected in high numbers. The tetG and tetW genes were detected in the active and abandoned corrals (1-10 years). The tetQ gene was detected only in the active and 1-year-old abandoned corrals. None of the genes were detected in the control soil. The three genes were detected outside an active corral, in the downstream section of an ephemeral tributary. The results prove that abandoned and unobserved periodic animal corrals are an environmental reservoir for TRGs.

Coexisting antibiotic changes the persistence and metabolic profile of atrazine in the environment

Pesticides are widely used in agriculture to control weeds, pests and plant diseases. Antibiotics may be introduced to the agricultural environment by manure fertilizer or wastewater irrigation. Co-existence of antibiotics in field may lead to profound impacts on pesticide residue. In this study, the impacts of oxytetracycline on the environmental fate and metabolic profile of atrazine was investigated, and the disturbance of oxytetracycline on functional genes related to atrazine degradation in soils was also studied. Oxytetracycline could inhibit the degradation of atrazine significantly and prolong the half-life to 1.27 and 1.59 times longer at 5 mg/kg and 50 mg/kg. Also, oxytetracycline altered the composition of atrazine metabolites, including three chloro-s-triazine metabolites (DEA, DIA, DDA) and three hydroxyl metabolites (OH-ATZ, OH-DEA, OH-DIA). Oxytetracycline decreased the ratio of hydroxyl metabolites, while increased the chloro-s-triazine metabolites which had higher toxicity and were easily leached in soil. Atrazine hydrolase genes atzA and trzN were down-regulated by oxytetracycline, which might decrease the hydroxyl metabolite formation and detoxification of atrazine. Oxytetracycline changed the degradation of atrazine and the composition of the metabolites probably by altering the soil microorganisms. The increased persistence and the percentage of the chloro-s-triazine metabolites induced by oxytetracycline might result in increased environmental problems.

The changes in antibiotic resistance genes during 86 years of the soil ripening process without anthropogenic activities

This study aimed to reveal the baseline of natural variations in antibiotic resistance genes (ARGs) in soil without anthropogenic activities over the decades. Nine soil samples with different time of soil formation were taken from the Yancheng Wetland National Nature Reserve, China. ARGs and mobile genetic elements (MGEs) were characterized using metagenomic analysis. A total of 196 and 192 subtypes of ARGs were detected in bulk soil and rhizosphere, respectively. The diversity and abundance of ARGs were stable during 69 years probably due to the alkaline pH soil environment but not due to antibiotics. Increases in ARGs after 86 years were probably attributed to more migrant birds inhabited compared with other sampling sites. Multidrug was the most abundant type, and largely shared by soil samples. It was further shown that soil samples could not be clearly distinguished, suggesting a slow process of succession of ARGs in the mudflat. The variation partitioning analysis revealed that the ARG profile was driven by the comprehensive effects exhibited by the bacterial community, MGEs, and environmental factors. Besides, pathogenic bacteria containing ARGs mediated by migrant birds in the area with 86 years of soil formation history nearing human settlements needed special attention. This study revealed the slow variations in ARGs in the soil ripening process without anthropogenic activities over decades, and it provided information for assessing the effect of human activities on the occurrence and dissemination of ARGs.

Fate of Macrolide Antibiotics with Different Wastewater Treatment Technologies

This comprehensive study addressed the occurrence, seasonal changes, removal efficiencies, and environmental risk assessments of three macrolide antibiotics in five wastewater treatment plants (WWTPs) with conventional and different additional treatment processes. A 1-year monitoring study was conducted, and influents and effluents were collected from Guangzhou (GZ), Shenzhen (SZ), Tai Po (TP), Shatin (ST), and Stonecutters Island (SI) WWTPs. Solid phase extraction and HPLC-MS/MS were used for the pretreatment and determination. The detection limits for azithromycin (AZI), erythromycin (ERY), and roxithromycin (ROX) ranged from 0.80 to 2.13 ng/L for the influent and effluent water samples. AZI was the most abundant antibiotic found in the influents, with average concentrations ranging from 571 ng/L to 1046 ng/L at all the target WWTPs. The seasonal average AZI concentration was the highest in all five WWTPs with the concentration of 984 ng/L in autumn, 849 ng/L in winter, 741 ng/L in summer, and 533 ng/L in spring. The seasonal AZI removal rates in the WWTPs were similar, with an average removal rate above 63.3% from spring to winter. All the treatments in the five WWTPs showed removal abilities for AZI, ERY, and ROX, regardless of the three phase treatments, namely, the UV disinfection process and conventional or chemically enhanced process within the WWTPs. For ERY and ROX, the average total removal rates were significantly decreased in the spring among all five WWTPs, at 53.1% and 57.8%, respectively. The GZ and SZ WWTPs displayed better removal rates than the TP, ST, and SI WWTPs, because the activity underlying the modified A2/O process in the GZ and SZ WWTPs has important effects on the antibiotic removal because the bacteria could produce compact granules and make the antibiotics settle faster in the wastewater. The additional UV disinfection in the SZ WWTP improved the removal efficiencies of the target antibiotics; it enhanced the biodegradability of residual organic pollutants in the WWTP effluent. Moreover, the corresponding environmental risks have been assessed and are viewed as a necessary component of future research.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11270-021-05053-y.

Study on the Electrochemical Removal Mechanism of Oxytetracycline by a Ti/IrO2-Ta2O5 Plate

In this study, a Ti/IrO₂-Ta₂O₅ anode was prepared by a hydrothermal method, and the prepared electrode was characterized by techniques such as scanning electron microscopy, X-ray diffraction, and electron dispersive spectroscopy. At the same time, the anode characteristics before and after electrochemical experiments were analyzed. The electrode gradation mechanism of oxytetracycline is discussed. In the whole experimental process, the range of electrolysis conditions was determined by single factor experiment, and then the optimal removal condition of oxytetracycline was determined by orthogonal experiments. The removal rate of oxytetracycline reached 99.02% after 20 min of electrolysis under the following optimal conditions: a current of 0.500 A, plate spacing of 2 cm, Na₂SO₄ electrolyte concentration of 4 g/L, and solution pH of 3. Additionally, the mechanism of oxytetracycline removal was explored, free radical scavenging experiments were performed, and the degradation mechanism was inferred based on the changes in the ultraviolet absorption of the oxytetracycline solution before and after electrolysis. Then, based on the liquid chromatography-mass spectrometry data, seven possible compounds and five possible removal pathways were proposed.

Large-scale biogeographical patterns of antibiotic resistome in the forest soils across China

Soil is a reservoir of environmental resistomes. Information about their distribution, profiles, and driving forces in undisturbed environments is essential for understanding and managing modern antibiotic resistance genes (ARGs) in human disturbed environments. However, knowledge about the resistomes in pristine soils is limited, particularly at national scale. Here, we conducted a national-scale investigation of soil resistomes in pristine forests across China. Although the antibiotics content was low and ranged from below limit of detection (LOD) to 0.290 μg/kg, numerous detected ARGs conferring resistance to major classes of modern antibiotics were identified and indicated forest soils as a potential source of resistance traits. ARGs ranged from 6.20 × 10^-7 to 2.52 × 10^-3 copies/16S-rRNA and were predominated by those resisting aminoglycoside and encoding deactivation mechanisms. Low abundance of mobile genetic elements (MGEs) and its scarcely positive connections with ARGs suggest the low potential of horizontal gene transfer. The geographic patterns of ARGs and ARG-hosts in pristine forest soils were mainly driven by soil physiochemical variables and followed a distance-decay relationship. This work focusing on pristine soils can provide valuably new information for our understanding of the ARGs in human disturbed environments.

Effect of antibiotic type and vegetable species on antibiotic accumulation in soil-vegetable system, soil microbiota, and resistance genes

Antibiotic accumulation in soil and plants is an escalating problem in agriculture and is receiving increasing attention. However, the effect of plant species on the fate of different types of antibiotics in a soil-vegetable system and soil resistome has not been adequately explored. To this end, greenhouse pot experiments were conducted to simulate contamination by ciprofloxacin (CIP), oxytetracycline (OTC), sulfamethoxazole (SMZ), and tylosin (TY) at 1 mg kg^-1 in the soils in which cabbage, endive, and spinach were grown. We investigated antibiotic persistence in soils and accumulation in vegetables (i.e., spinach, endive, and cabbage), microbial community profiles, and the abundance of 17 antibiotic resistance genes (ARGs) in contaminated soils. After 40 days, the residues of CIP and OTC in soil and their accumulation in vegetables were significantly higher than those of SMZ and TY. Of all vegetables, spinach had the highest antibiotic accumulation. Further, antibiotic contamination had no significant effect on soil microbial abundance; however, soil microbial diversity significantly decreased in soils amended with TY. The antibiotic type more significantly affected microbial composition than the kind of vegetable species. The relative abundances of some ARGs significantly increased in contaminated soils. Particularly, in endive soil, quinolone-associated cmlA, cmlA2, and qnrS1 increased with CIP contamination, OTC contamination increased tetG2 and otrA, SMZ increased sul1, and TY increased macrolide-related carB and msrc-01 relative abundance. However, some individual ARGs declined upon antibiotic contamination. Our results indicated that antibiotic type and vegetable species jointly shape the profiles of soil microorganisms and ARGs.

Sources of Antibiotic Resistant Bacteria (ARB) and Antibiotic Resistance Genes (ARGs) in the Soil: A Review of the Spreading Mechanism and Human Health Risks

Soil is an essential part of our ecosystem and plays a crucial role as a nutrient source, provides habitat for plants and other organisms. Overuse of antibiotics has accelerated the development and dissemination of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). ARB and ARGs are recognized as emerging environmental contaminants causing soil pollution and serious risks to public health. ARB and ARGs are discharged into soils through several pathways. Application of manure in agriculture is one of the primary sources of ARB and ARGs dissemination in the soil. Different sources of contamination by ARB and ARGs were reviewed and analyzed as well as dissemination mechanisms in the soil. The effects of ARB and ARGs on soil bacterial community were evaluated. Furthermore, the impact of different sources of manure on soil microbial diversity as well as the effect of antibiotics on the development of ARB and ARGs in soils was analyzed. Human health risk assessments associated with the spreading of ARB and ARGs in soils were investigated. Finally, recommendations and mitigation strategies were proposed.

Recognition of typical antibiotic residues in environmental media related to groundwater in China (2009-2019)

The potential adverse environmental and health-related impacts of antibiotics are becoming more and more concerning. China is globally the largest antibiotic producer and consumer, possibly resulting in the ubiquity and high detection levels of antibiotics in environmental compartments. Clear status on the concentration levels and spatial distribution of antibiotic contamination in China's environment is necessary to gain insight into the establishment of legal and regulatory frameworks. This study collects information from over 170 papers reporting the occurrence and distribution of antibiotics in China's environment. A total of 110 antibiotics were detected, and 28 priority antibiotics were ubiquitous in China in almost all compartments of the environment, excluding the atmosphere. Seven dominant antibiotics in all environment compartments were identified by cluster analysis, including tetracycline, oxytetracycline, chlortetracycline, ofloxacin, enrofloxacin, norfloxacin, and ciprofloxacin. Meanwhile, sulfamethoxazole, sulfadiazine, and sulfamethazine were also frequently found in aqueous phases. Among the main basins where antibiotics were detected, the Haihe River Basin had higher median antibiotic concentrations in surface water compared to other basins, while the Huaihe River Basin had higher median concentrations in sediment. The median values of antibiotic concentrations in the sources were as follows: animal manure, 39 μg/kg (microgram per kilogram); WWTP (wastewater treatment plant) sludge, 39 μg/kg; animal wastewater, 156 ng/L (nanogram per liter); WWTP effluent: 15 ng/L. These concentrations are 1 - 2 orders of magnitude higher than that of the receptors (soil, 2.1 μg/kg; sediment, 4.7 μg/kg; surface water, 8.1 ng/L; groundwater, 2.9 ng/L), whether in solid or aqueous phases. Based on the number of detected antibiotics in various environmental compartments, animal farms and WWTPs are the main sources of antibiotics, and surface water and sediment are the main receptors of antibiotics. Hierarchical clustering identified the two main pathways of antibiotic transfer in various environmental compartments, which are from animal wastewater/WWTP effluent to surface water/sediment and from animal manure/WWTP sludge to soil/groundwater.

Antibiotics in soil and water in China-a systematic review and source analysis

With the high production and consumption of antibiotics in recent years due to increasing economic development and improving population health, China is facing serious antibiotic pollution in the environment, and it is becoming a significant threat to ecology and human health. This study explores the spatial distribution patterns of 65 antibiotics in soil, surface water and coastal water based on a systematic review. Potential emission sources of antibiotics are also analyzed using data extracted from the reviewed literature. The results suggest that China has very high antibiotic detection rates of 100%, 98.0% and 96.4% for soil, surface water and coastal water, respectively. Regions with high antibiotic levels are mainly located in Bohai Bay, including the Beijing‒Tianjin‒Hebei region, Liaoning and Shandong Provinces, and Yangtze River. Tetracyclines (TCs) and quinolones (QNs) are the dominant antibiotics observed in soil and are mainly attributed to the use of manure as fertilizer and the reuse of domestic wastewater. Sulfonamides (SAs), macrolides (MLs), TCs and QNs are the dominant antibiotics observed in surface water and are mainly attributed to aquaculture and the emission of domestic sewage. QNs are the dominant antibiotics observed in coastal water and are mainly attributed to marine cultivation. The detection frequencies and concentrations of TCs, QNs, SAs and MLs in both soil and water are much higher than those in other developed countries. Suggestions including restricting antibiotic usages in livestock farming and aquaculture, innovation of wastewater treatment technology to improve antibiotic removal rate, and establishing guidelines on antibiotic concentration for wastewater discharge and organic fertilizer are provided.

Antibiotic resistance genes (ARGs) in agricultural soils from the Yangtze River Delta, China

As an important reservoir of intrinsic antimicrobial resistance, soil is subjected to increasing anthropogenic activities that creates sustained selection pressure for the prevalence of antibiotic resistance genes (ARGs), thus constituting an important environmental dissemination pathway to human exposure. This study investigated the levels and spatial distributions of three classes of ARGs in relation to a range of co-occurring chemical mixtures and soil properties at a regional scale of the Yangtze River Delta (YRD), China. The selected eight ARGs were all detected in 241 agricultural soil samples with relative abundances ranging from 1.01 × 10^-7 to 2.31 × 10^-1 normalized to the 16S rRNA gene. The sulII and tetG were the dominant ARGs with a mean relative abundance of 6.67 × 10^-3 and 5.25 × 10^-3, respectively. The ARGs were mainly present in agricultural soils alongside Taihu Lake and Shanghai municipality, the most agriculturally and economically vibrant area of the YRD region. Antibiotics, rather than other co-occurring pollutants and soil properties, remain to be the dominant correlate to the ARGs, suggesting their co-introduction into the soils via irrigation and manure application or the sustained selection pressure of antibiotics from these sources for the proliferation of ARGs in the soils. While the current dataset provided useful information to assess the ARGs pollution for mitigation, future studies are warranted to reveal the complete picture on the potential transfer of antimicrobial resistance from soil to agricultural produces to human consumption and associated health implications.

Boosting photocatalytic degradation of antibiotic wastewater by synergy effect of heterojunction and phosphorus doping

Phosphorus-doped g-C₃N₄/ZnIn₂S₄ (PCN/ZIS) heterojunction photocatalysts were constructed by solvothermal method. The physical and chemical properties were investigated with X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), etc. The degradation of antibiotic wastewater was used to investigate the photocatalytic activities of composites under visible-light irradiation. The 10% PCN/ZIS had the best photocatalytic degradation performance for tetracycline with a photodegradation rate of 0.0874 min^-1, which is respectively about 2.9 and 52.0 times than that of pure ZIS and PCN. Meanwhile, it was concluded that the holes and ⋅O₂^- (superoxide radicals) play dominant roles in the photocatalytic reactions through radicals trapping experiments, while ⋅OH (hydroxyl radicals) has a negative effect. In addition, 10%PCN/ZIS, with excellent stability and recyclability, also exhibited high photocatalytic activity for terramycin, chlortetracycline and ofloxacin. Overall, with the enhanced photocatalytic performance, PCN/ZIS could be potentially applied for photocatalytic degradation of antibiotic wastewater.

Screening of Bacterial Endophytes Able to Promote Plant Growth and Increase Salinity Tolerance

Bacterial endophytes can colonize plant tissues without harming the plant. Instead, they are often able to increase plant growth and tolerance to environmental stresses. In this work, new strains of bacterial endophytes were isolated from three economically important crop plants (sorghum, cucumber and tomato) grown in three different regions in soils with different management. All bacterial strains were identified by 16S rRNA sequencing and characterized for plant beneficial traits. Based on physiological activities, we selected eight strains that were further tested for their antibiotic resistance profile and for the ability to efficiently colonize the interior of sorghum plants. According to the results of the re-inoculation test, five strains were used to inoculate sorghum seeds. Then, plant growth promotion activity was assessed on sorghum plants exposed to salinity stress. Only two bacterial endophytes increased plant biomass, but three of them delayed or reduced plant salinity stress symptoms. These five strains were then characterized for the ability to produce the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which is involved in the increase of stress tolerance. Pseudomonas brassicacearum SVB6R1 was the only strain that was able to produce this enzyme, suggesting that ACC deaminase is not the only physiological trait involved in conferring plant tolerance to salt stress in these bacterial strains.

A critical review on the occurrence of resistomes in the environment and their removal from wastewater using apposite treatment technologies: Limitations, successes and future improvement

Recent reports are pointing towards the potential increasing risks of resistomes in human host. With no permissible limit in sight, resistomes are continually multiplying at an alarming rate in the ecosystem, with a disturbing level in drinking water source. The morphology and chemical constituent of resistomes afford them to resist degradation, elude membrane and counter ionic charge, thereby, rendering both conventional and advanced water and wastewater treatment inefficient. Water and wastewater matrix may govern the propagation of individual resistomes sub-type, co-selection and specific interaction towards precise condition may have enhanced the current challenge. This review covers recent reports (2011-2019) on the occurrence of ARB/ARGs and ease of spread of resistance genes in the aquatic ecosystem. The contributions of water matrix to the spread and mitigation, treatment options, via bulk removal or capture, and intracellular and extracellular DNA lysis were discussed. A complete summary of recent occurrences of ARB/ARGs, fate after disinfection and optimum conditions of individual treatment technology or in tandem, including process limitations, with a brief assessment of removal or degradation mechanism were highlighted.

Sulfamethoxazole affects the microbial composition and antibiotic resistance gene abundance in soil and accumulates in lettuce

Pot experiments were set up to simulate the soil contamination by three initial concentrations of sulfamethoxazole (SMX) (S1, 100 mg/kg; S2, 200 mg/kg; S3, 300 mg/kg). The content of SMX in soil and its accumulation in lettuce were analysed. Additionally, the effects of SMX on soil microorganisms and antibiotic resistance genes were studied by Illumina high-throughput sequencing and droplet digital polymerase chain reaction (ddPCR). The results demonstrated that the SMX content in soil reduced by 97%, 86% and 75% in the S1, S2 and S3 treatment groups after 120 days, respectively. The accumulated SMX in lettuce was positively correlated with the initial concentration of SMX in soil. SMX contamination significantly reduced the bacterial diversity and altered the composition of bacterial and fungal communities in soil. The dominant bacterial and fungal genera in the SMX-contaminated soil were obviously different from those in the control soil. The relative abundance of sul1 (sulfonamide resistance gene) remarkably increased in the SMX-contaminated soil, while that of other ARGs, such as sul2 and tetracycline and quinolone resistance genes, showed no significant change.

Escherichia coli as a carrier of tetracyclines and penicillins resistance in wild pheasant (Phasianus colchicus)

Wild animals like pheasant seem to be a good source of information about human activities. Therefore, the wild pheasants and relative stable appendix microcenosis were selected for antibiotic resistance testing. Penicillin resistance by MALDI-TOF Mass Spectrometry and tetracyclines resistance by genetic methods using specific primers were tested. Differences between tetracycline and penicillin resistance were detected. Results showed high prevalence of resistant Escherichia coli isolated from wild pheasant appendix. E. coli isolated from wild pheasant appendix carried plasmids for penicillins and tetracyclines resistance where they were responsible for enzymatic degradation of penicillin and carried genes for regulating efflux pumps for tetracyclines. Results showed that tetracyclines and penicillins resistance is widespread between wild pheasants with a carrier as Escherichia coli isolated from relative stable microcenosis of appendix.

Single and joint toxic effects of four antibiotics on some metabolic pathways of zebrafish (Danio rerio) larvae

In China, antibiotics are commonly used for human and veterinary medicine, and they are present in various environmental media. Thus, the toxic effects of antibiotics on organisms have attracted the attention of society and scientists alike. In this study, zebrafish embryos were used to test the single and joint toxicity of four antibiotics, sulfamonomethoxine (SMM), cefotaxime sodium (CFT), tetracycline (TC), enrofloxacin (ENR), and their combinations, combining the results of experimental and omics techniques. Following exposure to antibiotics for 120 h, the body lengths of zebrafish larvae in all 100 μg/L antibiotic groups were significantly shortened, and the reactive oxygen species (ROS) content in the 100 μg/L Mix group was significantly increased. Transcriptome sequencing (RNA-seq) showed that the mRNA level of numerous genes was significantly changed in the five antibiotic treatment groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of the differentially expressed genes revealed a significant enrichment of the steroid biosynthesis and other metabolism pathways. Hub gene analysis highlighted dhcr24, acat1, aldh1a2, aldh8a1, suclg2, hadh, and hsdl2 as the key genes, and hub gene expression changes because of the antibiotic treatment suggested that the metabolic system of the zebrafish larvae was severely disrupted by the interaction with other genes. In conclusion, single or joint exposure to different antibiotics at environmental concentrations affected the early development and metabolic system of zebrafish larvae, and our results provide fundamental evidence for future studies of antibiotic toxicity in aquatic organisms.

Treated wastewater used in fresh produce irrigation in Nsukka, Southeast Nigeria is a reservoir of enterotoxigenic and multidrug-resistant Escherichia coli

Background

Occurrences of pathogens in environmental and irrigation waters, as well as the use of inadequately treated sewage for fresh produce constitute potential public health threats worldwide.

Objective

To investigate the treated wastewater used in fresh produce irrigation in Nsuskka, Southeastern Nigeria, as a reservoir enterotoxigenic and multidrug-resistant Escherichia coli.

Methods

Treated wastewater (from the sewage treatment facility at Nsukka, Southeast Nigeria), soil and irrigated vegetable samples were collected and analyzed using standard procedures. Escherichia coli isolated from the samples were screened for the presence of enterotoxigenic E. coli strain encoding lt gene and profiled for antibiotic resistance using the conventional PCR and standardized agar disk diffusion assays respectively.

Results

Of the total presumptive 103 isolates, PCR detected uidA gene in 87 (84 %), of which 23 (26 %) harboured the lt encoding ETEC gene. Generally, imipenem, cefuroxime and norfloxacin proved to be most effective of all the antibiotics employed. Wastewater isolates were variously susceptible to ciprofloxacin (95 %), norfloxacin (95 %), cefuroxime (93 %), chloramphenicol (93 %), trimethoprim and tetracycline (88 %), soil isolates to streptomycin (75 %) and vegetable isolates to cefuroxime (90 %), norfloxacin (86 %), ciprofloxacin (81 %) and chloramphenicol. Contrariwise, high resistances observed to other antibiotics were in the order; ampicillin (95 %), penicillin (93 %), erythromycin (90 %) and clarithromycin (83 %) among wastewater isolates, ciprofloxacin and norfloxacin (75 %) in soil isolates; penicillin, vancomycin and erythromycin (98 %), rifampicin and clarithromycin (93 %), sulphamethoxazole (83 %), ampicillin (81 %), tetracycline and imipenem (76 %), trimethoprim (72 %) and amoxicillin (71 %) among vegetable isolates, with multidrug resistance patterns ranging from three to seventeen.

Conclusions

Our results reveal the treated wastewater as a reservoir of enterotoxigenic E. coli as well as multidrug resistance that may pose a health hazard for humans and animals when released to the natural environment. Hence, there is need to develop management strategies and ensure compliance in order to prevent water-borne diarrhoea caused by ETEC and reduce the menace of antibiotic resistance in the environment.

Occurrence and distribution of priority pharmaceuticals in the Yellow River and the Huai River in Henan, China

The occurrence and spatial distribution of priority pharmaceuticals (PPs) in water samples from the Yellow River and the Huai River in the Henan region of China were investigated in this study. The concentration of the total PPs (ΣPPs; sum of the 10 observed PPs) ranged from not detected to 3474 ng L^-1 in samples from the Yellow River and from 4.35 to 146 ng L^-1 in samples from the Huai River. The level of the ΣPPs in the Huai River was much lower than that found in the Yellow River. The composition of the PPs differed between the two rivers. Norfloxacin, carbamazepine, and 5,5-diphenylhydantoin were detected at high concentrations in the Yellow River, whereas sulfamethazine, ampicillin trihydrate, carbamazepine, and 5,5-diphenylhydantoin were the dominant species in the Huai River, suggesting there were different pollution sources. In comparison to other studies around China, most of the PPs in water samples from the Yellow River and the Huai River were at low concentrations, except for norfloxacin and ofloxacin. There were significant seasonal variations among the PPs in water samples from the Huai River, whereas spatial distinctions were recorded among the PPs in the Yellow River. Dissolved organic carbon content did not correlate with the PPs in the studied area.

Airborne antibiotic resistance genes in Hong Kong kindergartens

Antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) have become a critical global public health issue in this century. There is increasing evidence for the presence and transmission of ARGs by air transmission. In this research, ARGs and ARB in air conditioner filter dust (AC dust) and urine samples from 55 kindergarten children in 17 kindergartens and nearby 10 soil samples in Hong Kong were analyzed. The results showed the presence of 16 ARG subtypes and the mobile genetic element (MGE) intI1 in AC dust, and 12 ARG subtypes in the soil samples. ARGs presenting resistance to sulfonamide (6.9 × 10^-3-0.17) (expressed as relative abundance of the 16 S rRNA genes) were most abundant followed by macrolides (1.8 × 10^-3-3.3 × 10^-2), sul1, sul2 (sulfonamide), ermF (macrolides) and intI1 genes in AC dust in 17 kindergartens. For soil samples, 12 ARG subtypes and the intI1 were detected, and the genes providing resistance to sulfonamide (1.6 × 10^-3-2.7 × 10^-1) were the most abundant ARGs in the 10 soil samples, followed by tetracycline (ND-1.4 × 10^-2). Multi-resistant bacteria with sul1, sul2, intI1, or tetQ were detected in all AC dust samples and some urine samples. Based on bacterial genera and ARG co-occurrence network analysis and Hong Kong's special geographical location and cultural environment, there might be two origins for the ARGs detected in the kindergartens: β-lactam/macrolide ARGs mainly derived from human medicine use and tetracycline/sulfonamide ARGs mainly from other areas, as well as IntI1 may play a role in the spread of ARGs in Hong Kong. The widely detection of ARGs in AC dust in kindergartens in Hong Kong highlights the need for the improvement of management measures.

Large-scale patterns of soil antibiotic resistome in Chinese croplands

Soil is a vital reservoir of antibiotic resistance genes (ARGs), but we still know little about their distribution in cropland soils and the main driving forces. Here we performed an investigation for ARGs patterns in 105 cropland soils (planted with maize, peanut or soybean) along a 2, 200 km transect in China using high-throughput quantitative PCR approaches. Totally, 204 ARGs were detected, with a higher diversity found in central China than that in northeast and south China. The most abundant (top 50%) and highly shared (present in >50% samples) ARGs regarded as core resistome were dominated by multidrug resistance genes such as oprJ, acrA-05 and acrA-04. Regressive analyses revealed that the relative abundance of total ARGs and core resistome both had significant relationships with mobile genetic elements (MGEs). Anthropogenic factors including the consumption of plastic films and soil properties including heavy metals showed good correlations with the diversity of ARGs. Structural equation modelling analysis further explained that anthropogenic factors were the main forces shaping the ARGs patterns. These findings highlight the importance of human activities in shaping soil antibiotic resistome in the croplands, providing potential management strategies to mitigate the dissemination of ARGs to humans via food chain.

Fabrication of sustainable manganese ferrite modified biochar from vinasse for enhanced adsorption of fluoroquinolone antibiotics: Effects and mechanisms

An effective adsorbent towards fluoroquinolone antibiotics was synthesized via a facile two-step approach, the co-precipitation of Fe, Mn with vinasse wastes and then pyrolysis under controlled conditions which denoted as FMB. Its adsorption behavior was examined based on a batch adsorption experiment of fluoroquinolone antibiotics pefloxacin (PEF) and ciprofloxacin (CIP). Experimental factors, such as pH, adsorbent dose, ionic strength, contact time and temperature have done a great deal to influence the adsorption of PEF and CIP. The FMB demonstrated excellent performance in reusability tests towards to both PEF and CIP, which showed that the recycling efficiency of PEF and CIP could remain ~55% and ~80% after five recycle cycles, respectively. The dominated adsorption mechanisms included pore filling effect, π-π stacking interaction, π-π EDA, hydrogen bonding and hydrophobicity. Overall, this work presented FMB was recognized as an effective, environmental-friendly and magnetically separable adsorbent for alleviating fluoroquinolone antibiotics contamination from water.

Zoonosis: An Emerging Link to Antibiotic Resistance Under "One Health Approach"

Current scenario in communicable diseases has generated new era that identifies the "One health" approach to understand the sharing and management of etiological agents with its impact on ecosystem. Under this context the relevance of zoonotic diseases generates major concern. The indiscriminate and higher use of antibiotics in animal husbandry creates substantial pressure on the gut microbiome for development of resistance due to shorter generation time and high density. Thus, gut works as a bioreactor for the breeding of ARBs in this scenario and are continuously released in different niches. These ARBs transfer resistance genes among native flora through horizontal gene transfer events, vectors and quorum sensing. About 60% of infectious diseases in human are caused by zoonotic pathogens have potential to carry ARGs which could be transmitted to humans. The well documented zoonotic diseases are anthrax cause by Bacillus anthracis, bovine tuberculosis by Mycobacterium tuberculosis, brucellosis by Brucella abortus, and hemorrhagic colitis by Escherichia coli. Similarly, most of the antibiotics are not completely metabolized and released in unmetabolized forms which enters the food chain and affect various ecological niches through bioaccumulation. The persistence period of antibiotics ranges from < 1 to 3466 days in environment. The consequences of misusing the antibiotic in livestock and their fate in various ecological niches have been discussed in this review. Further the light sheds on antibiotics persistence and it biodegradation through different abiotic and biotic approaches in environment. The knowledge on personnel hygiene and strong surveillance system for zoonotic disease including ARBs transmission, prevention and control measures should be established to regulate the spread of AMR in the environment and subsequently to the human being through a food web.

Minimizing the residual antimicrobial activity of tetracycline after adsorption into the montmorillonite: Effect of organic modification

Variety of adsorbents have been developed and used for antibiotic separations (e.g. tetracycline), however, there is not enough information about the residual antimicrobial activity of adsorbed antibiotics. In this study, montmorillonite was modified using HDTMA and applied for adsorption of tetracycline in order to minimize the residual antimicrobial activity of tetracycline. Results revealed that despite the high adsorption capacity of the non-modified montmorillonite for tetracycline, high residual antimicrobial activity still remained which was probably correlated to the partial release of tetracycline from the montmorillonite structure. On the other hand, the adsorbed tetracycline onto HDTMA-modified montmorillonite had much weaker residual antimicrobial activity due to the strong attraction force between HDTMA and the tetracycline which minimize the chance of its desorption when releasing the complex in the environment. A series of changes on the HDTMA-modification process (by improvement of HDTMA arrangement in the interlayers of montmorillonite) enhanced the adsorption of tetracycline in the interlayer spaces of montmorillonite with the least residual antimicrobial activity of tetracycline and HDTMA-modified montmorillonite complex. Results of this study present a great enhancement in the adsorption of antibiotics to minimize the effect of antibiotics such as the development of antibiotic-resistant bacteria.

Occurrence and human health risk assessment of pharmaceuticals and personal care products in real agricultural systems with long-term reclaimed wastewater irrigation in Beijing, China

Reclaimed wastewater (RW) is increasingly used to irrigate agricultural land and to alleviate agricultural water shortages worldwide. This usage has resulted in concerns about soil contamination by pharmaceuticals and personal care products (PPCPs) and the human health risks associated with dietary crop intake. In this study, we systematically analysed the occurrence and accumulation of 11 PPCPs and one active metabolite in soils and various crops (cucumber, eggplant, long bean and wheat) from realistic RW irrigation fields with different irrigation histories (20, 30 and 40 years) in Beijing and evaluated the human health risks associated with the consumption of these crops. The 11 PPCPs and one active metabolite were detected at concentrations ranging from 0.67 to 22.92 ng L^-1 in RW, 0.029-28.13 μg kg^-1 in irrigated soil, and <0.01-28.01 μg kg^-1 in crops. The concentrations of N4-acetyl-sulfamethoxazole and triclosan were higher than those of other PPCPs, with respective concentrations of 14.39-31.44 ng L^-1 and 15.93-26.23 ng L^-1 in RW, 10.92-23.29 μg kg^-1 and 20.22-28.13 μg kg^-1 in irrigated soil and 17.92-28.01 μg kg^-1 and 8.92-14.91 μg kg^-1 in crops. However, the estimated threshold of toxicological concern (TTC) and hazard quotient (HQ) values revealed that the concentrations of N4-acetyl-sulfamethoxazole and triclosan in crops irrigated with RW should be considered a de minimis risk to human health. The concentrations of 11 PPCPs and one active metabolite in soils and crops and the calculated fruit bioconcentration factors (BCFs) did not display obvious increases associated with the duration of RW irrigation in real agricultural systems (P > 0.05). The concentrations of the studied PPCPs in the RW used for irrigation followed different patterns from the concentrations detected in the irrigated soils and crops. Although the concentrations of sulfamethoxazole, sulfisoxazole, sulfamethazine and trimethoprim in RW were higher than those of many other studied PPCPs, their respective values in the irrigated soils and crops did not display a similar tendency. The uptake and accumulation of PPCPs varied among the crop species (P < 0.05). Although PPCPs were detected in eggplant, long bean and wheat (BCFs: not applicable-1.67, 0.03-1.35 and 0.01-5.01, respectively), PPCPs accumulated at increased levels in cucumber (BCFs 0.03-18.98). The estimated TTC and HQ values showed that the consumption of crops irrigated long-term with RW presents a de minimis risk to human health. However, further studies with more PPCPs and additional crop species need to be conducted, the synergistic effects of chemical mixtures of multiple PPCPs and the toxic effects of PPCP metabolites should be elucidated to obtain more reliable information on the safety of wastewater reuse for irrigation.

Removing tetracycline and Hg(II) with ball-milled magnetic nanobiochar and its potential on polluted irrigation water reclamation

The feasibility of ball-milled magnetic nanobiochars (BMBCs) derived from wheat straw for adsorptive removal of tetracycline (TC) and Hg(II) from aqueous solution was assessed against that of pristine magnetic biochars (PMBCs). Ball milling conversion of PMBCs into BMBCs greatly improved TC and Hg(II) removal, and ≥ 99% TC and Hg(II) were adsorbed by BMBC prepared at 700 °C (BMBC700) within 12 h. The maximum adsorptive removal capacities of BMBC700 for TC and Hg(II) were 268.3 and 127.4 mg/g, respectively. The amounts of TC and Hg(II) removed by BMBC700 decreased gradually as the ionic strength of the solution increased, but increased as the solution temperature increased from 25 to 45 °C. The further FTIR and XPS analysis confirmed removal of TC was predominately regulated by the combination of electrostatic interactions, hydrogen bonds, and Cπ-Cπ interaction, while, the adsorption of Hg(II) was mainly governed by several mechanisms, including electrostatic attractions, Hg-Cπ bond formation, and surface complexation. Overall, BMBC700 presented great potential for TC and Hg(II) removal from polluted irrigation water and exhibited acceptable recyclability performance as well as magnetic separation advantage in use.

An innovative modeling approach of linking land use patterns with soil antibiotic contamination in peri-urban areas

Due to the intensive use and continuous release, high and persistent concentrations of antibiotics are found in soils worldwide. This severe contamination elevates the risks associated with antibiotic exposure and resistance for soil ecosystems and human health. Estimating antibiotic concentrations in soils is a complex and important challenge because the limited information is available on antibiotic use and emission and the high exposure risk to human health occurred in peri-urban areas. In this study, soil antibiotic contamination was linked with land use patterns in a data-scarce peri-urban area in four different seasons, and we established a modeling framework based on land use to estimate spatially explicit distribution of antibiotics in soils. The soil antibiotic concentration was found to be substantially affected by surrounding land use patterns in buffer zones with a radius of 350 m. Agricultural land was the main source of antibiotics entering the soil. Notably, road networks also had considerable impacts on antibiotic residues in soils. Then, a statistical model was developed in describing the linkage between land use patterns and soil antibiotic concentration. Model evaluation suggested that the proposed model successfully simulated the variation of antibiotics in soil with good statistical performance (R² > 0.7). Finally, the model was extrapolated to investigate detailed distribution of antibiotics in soils. Clear spatial and seasonal dynamics can be found in soil antibiotic concentration. To our knowledge, this was the first attempt to adopt a model focusing on land use pattern to estimate the spatially explicit distribution of antibiotics in soils. Despite of some uncertainties, the research provides a land-use-based modeling approach as a reference for preventing and controlling soil antibiotic contamination in the future.

Raw wastewater irrigation for urban agriculture in three African cities increases the abundance of transferable antibiotic resistance genes in soil, including those encoding extended spectrum β-lactamases (ESBLs)

A study was conducted to investigate the impact of raw wastewater use for irrigation on dissemination of bacterial resistance in urban agriculture in African cities. The pollution of agricultural fields by selected antibiotic residues was assessed. The structure and functions of the soil microbial communities, presence of antibiotic resistance genes of human clinical importance and Enterobacteriaceae plasmid replicons were analysed using high throughput metagenomic sequencing. In irrigated fields, the richness of Bacteroidetes and Firmicutes phyla increased by 65% and 15.7%, respectively; functions allocated to microbial communities' adaptation and development increased by 3%. Abundance of antibiotic resistance genes of medical interest was 27% greater in irrigated fields. Extended spectrum β-lactamase genes identified in irrigated fields included bla_CARB-3, bla_OXA-347, bla_OXA-5 and bla_Rm3. The presence of ARGs encoding resistance to amphenicols, β-lactams, and tetracyclines were associated with the higher concentrations of ciprofloxacin, enrofloxacin and sulfamethoxazole in irrigated fields. Ten Enterobacteriaceae plasmid amplicon groups involved in the wide distribution of ARGs were identified in the fields. IncQ2, ColE, IncFIC, IncQ1, and IncFII were found in both farming systems; IncW and IncP1 in irrigated fields; and IncY, IncFIB and IncFIA in non-irrigated fields. In conclusion, raw wastewater irrigated soils in African cities could represent a vector for the spread of antibiotic resistance, thus threatening human and animal health. Consumers of products from these farms and farmers could be at risk of acquiring infections due to drug-resistant bacteria.

Research and Technological Advances Regarding the Study of the Spread of Antimicrobial Resistance Genes and Antimicrobial-Resistant Bacteria Related to Animal Husbandry

The extensive use of antimicrobials in animal farms poses serious safety hazards to both the environment and public health, and this trend is likely to continue. Antimicrobial resistance genes (ARGs) are a class of emerging pollutants that are difficult to remove once introduced. Understanding the environmental transfer of antimicrobial-resistant bacteria (ARB) and ARGs is pivotal for creating control measures. In this review, we summarize the research progress on the spread and detection of ARB and ARG pollution related to animal husbandry. Molecular methods such as high-throughput sequencing have greatly enriched the information about ARB communities. However, it remains challenging to delineate mechanisms regarding ARG induction, transmission, and tempo-spatial changes in the whole process, from animal husbandry to multiple ecosystems. As a result, future research should be more focused on the mechanisms of ARG induction, transmission, and control. We also expect that future research will rely more heavily on metagenomic -analysis, metatranscriptomic sequencing, and multi-omics technologies

Current progress in the adsorption, transport and biodegradation of antibiotics in soil

Antibiotic residues in soil may cause potential risks to human health and soil ecosystems. To avoid these potential risks, comprehensive study of the adsorption, transport and biodegradation of antibiotics in soil is very imperative. This review provided current views about the most recent studies, which have been conducted toward the adsorption, transport and biodegradation of antibiotics in soil. The influencing factors affecting the adsorption behaviors of antibiotics in soil, including the antibiotics properties (e.g., molecular structure, hydrophobicity, polarity, polarizability, and spatial configuration) and the soil characteristics (e.g., soil type, soil pH, coexisting ions, and soil organic matter), were discussed. The effects of fertilizer colloids, porous media, and pH of soil on the transport behaviors of antibiotics were analyzed. The biodegradation of antibiotics in soil were also highlighted by investigating the effects of soil microbiome, soil pH, soil temperature, and interactions between antibiotics. Prospects of antibiotics adsorption, transport and biodegradation were also proposed.

Prevalence of Antibiotic Resistance Genes and Their Association with Antibiotics in a Wastewater Treatment Plant: Process Distribution and Analysis

Effluents from wastewater treatment plants has been identified as a main point-source of antibiotics and antibiotic resistance genes in natural water environments. In this study, a typical municipal sewage treatment system in south China was taken as the research object to investigate the effects of each treatment unit on eight target antibiotics (sulfamethoxazole, sulfamethazine, tetracycline hydrochloride, oxytetracycline dihydrate, norfloxacin, ofloxacin, clarithromycin, roxithromycin), 17 antibiotic resistance genes (ARGs) and class 1 integron genes in the system using Accelerated Solvent Extraction-Solid phase extraction-Ultra high Performance Liquid Chromatography-Tandem mass spectrometry (ASE-SPE-UPLC-MS/MS) and real-time fluorescent quantitative PCR (qPCR) and the correlation between them. Seven antibiotics (mainly sulfonamides and tetracyclines, 4.19–141.97 ng·L−1) were detected in the influent, while only sulfamethoxazole, sulfamethazine, ofloxacin, and clarithromycin were detected in the effluent (3.11–16.61 ng·L−1). The tetracycline antibiotics in the wastewater treatment plant (WWTP) were transferred to the sludge phase by adsorption, in which tetracycline hydrochloride and oxytetracycline dihydrate were mostly removed in the aerobic and anaerobic stages, while sulfamethoxazole was mainly removed through biological transformation. Sul I was the most abundant resistance gene, but the WWTP had no obvious effect on its removal. Anaerobic treatment was found to play an important role in tetA, tetQ, and tetX removal. Moreover, correlation analysis revealed that the relative abundance of tetX was significantly correlated with clarithromycin (p = 0.039) and ofloxacin (p = 0.028), while that of tetQ was significantly correlated with sulfamethazine (p = 0.007) and sulfamethoxazole (p = 0.001), and that of tetC was significantly correlated with the class 1 integron gene (p = 0.014). Overall, the results presented herein provide a reference for improving the antibiotics and ARGs removal efficiency of WWTPs in south China.

Occurrence and ecological risk assessment of selected antibiotics in the freshwater lakes along the middle and lower reaches of Yangtze River Basin

Lakes are regarded as copious antibiotic reservoirs because the antibiotics discharged by human activities mostly end up in lakes and further threaten the aqueous ecosystem. Antibiotic contamination in lakes is mostly attributed to wastewater treatment plant effluents, which change the water quality and pose ecological risks. This study investigated the concentration of 10 selected antibiotics in 17 lakes along the middle and lower reaches of the Yangtze River Basin. The correlation between antibiotics and water quality parameters were analyzed. Seven out of the 10 selected antibiotics were detected in almost all the 17 lakes with the highest concentration at 1139.40 ng/L. Sulfamethoxazole (SMZ) and erythromycin (ERY) had relatively higher concentration compared with other antibiotics. Antibiotic detection frequency was approximately 40%-100% in all 17 lakes. Ofloxacin (OFX) and naproxen (NPX) were negatively correlated (p < 0.05) with redox potential, indicating their oxidation potential in freshwater lakes. OFX showed high or medium short-term risks in some of the lakes and low or insignificant long-term risks in the corresponding lakes, respectively. In contrast, sulfadiazine and SMZ exerted low and medium short-term ecological risks and medium and high long-term risks, respectively. Roxithromycin (ROX) showed low short-term risk in seven of the 17 lakes and medium long-term risk in the corresponding lakes. NPX showed insignificant short-term and long-term risks in almost all the 17 lakes. This study fills the gap on antibiotic ecological risk assessment along the Yangtze River Basin and reveal the importance of SMZ control in the research area.

Antibiotic resistance and class 1 integron gene dynamics along effluent, reclaimed wastewater irrigated soil, crop continua: elucidating potential risks and ecological constraints

Reuse of municipal wastewater is a growing global trend, but currently there is lack of consensus regarding the potential dissemination of antibiotic resistance elements by treated wastewater irrigation. We tracked intI1, a proxy for anthropogenic pollution, and an assemblage of antibiotic resistance genes associated with mobile elements and/or wastewater (bla_GES, bla_OXA2, bla_OXA10, bla_TEM, bla_CTX-M-32 and qnrS) in treated wastewater effluents, effluent stabilization reservoirs, and along irrigation water-soil-crop continua in experimental lysimeters and large-scale commercial fields. While several of the targeted antibiotic resistance genes were profuse in effluents, there was almost no correlation between gene abundance in irrigation water and those detected in soil, and no evidence of systematic gene transfer to irrigated soil or crops. In contrast, soil intI1 abundance correlated strongly to irrigation water levels in lysimeters and sandy field soils, but this was not the case for clay-rich soils or for most of the analyzed crops, suggesting that intI1 may not always be a reliable marker for tracking the impact of treated wastewater irrigation. We hypothesize that "ecological boundaries" expedited by biotic and abiotic factors constrain dissemination of antibiotic resistance elements, and assert that a more holistic perception of these factors is crucial for understanding and managing antibiotic resistance dissemination.

Influence of Two-Stage Combinations of Constructed Wetlands on the Removal of Antibiotics, Antibiotic Resistance Genes and Nutrients from Goose Wastewater

Antibiotic and antibiotic resistance genes (ARGs) have been considered as emerging environmental contaminants and possess potential crisis to global public health. However, little is known about the differences between various configurations of two-stage combinations of constructed wetlands (CWs) on antibiotics and ARG removal from wastewater. In the study, three configurations of two-stage hybrid CWs (horizontal subsurface flow-down-flow vertical subsurface flow CWs, HF-DVF; horizontal subsurface flow-up-flow vertical subsurface flow CWs, HF-UVF; down-flow vertical subsurface flow-up-flow vertical subsurface flow CWs, DVF-UVF) were operated to evaluate their ability to remove high-concentration antibiotics (tilmicosin-TMS and doxycycline-DOC), ARGs (seven tet genes and three erm genes), intI1, 16S rRNA, and nutrients from goose wastewater. The results showed that all three hybrid CWs could remove more than 98% of TMS and DOC from wastewater, without significant difference among treatments (p > 0.05). For ARGs, DVF-UVF showed significantly higher removal efficiencies of intI1, ermB, ermC, ermF, tetW, and tetG compared to HF-UVF (p < 0.05), mainly because they might remove and arrest growth of bacteria. The relatively high removal efficiencies of NH₄⁺-N, NO₃^-N, and NO₂^--N were also observed from DVF-UVF, ranging from 87% to 95% (p > 0.05), indicating that anaerobic ammonium oxidation (anammox) might be established in the CWs. Our results demonstrate that the removal performances of antibiotics using two-stage hybrid CWs are not affected by the combined configuration, whereas the combination of DVF and UVF CWs perform better on the removal of ARGs and nutrients compared with HF-DVF and HF-UVF CWs.

Occurrence and spatial variation of antibiotic resistance genes (ARGs) in the Hetao Irrigation District, China

The prevalence and proliferation of antibiotic resistance genes (ARGs) has been identified as an emerging contaminant of concern and a crucial threat to public health worldwide. To determine the occurrence and distribution of ARGs in artificial agricultural irrigation systems, we designed eight sample sites of farmland drainage in the Hetao Irrigation District, Inner Mongolia, China. Results indicated that the distribution of ARGs in sub-drainage canals is influenced by the local urban area, agriculture, and animal husbandry structure. The bla_TEM gene was predominant in the water samples (up to 8.98 ARG copies/16S rRNA genes). The average ARG abundance in drainage channel sampling sites was significantly higher than the influent water from the Yellow River, which means that the artificial agricultural irrigation system enhances the abundance of resistance genes in the study area. Moreover, the effluent water of the whole irrigation system presented a lower abundance of ARGs than the influent water. This demonstrates that the Wuliangsuhai watershed ecosystem plays an important role in regulating the abundance of ARGs in the area. In our study, the mobile gene elements correlated with trB, emrD, mexF, and vanC (P < 0.001) in the irrigation system. Additionally, different correlations exist between other special subtypes of ARGs. These findings provided deeper insights into mitigating the propagation of ARGs and the associated risks to public health.

Occurrence and distribution of antibiotics and antibiotic resistant genes in water and sediments of urban rivers with black-odor water in Guangzhou, South China

Urban rivers in some countries have been heavily polluted and the water became black and odor. Nevertheless, only few studies reported the occurrence of antibiotics and their corresponding antibiotic resistant genes (ARGs) in urban rivers with black-odor water with and without remediation. In this study, nine antibiotics (belonging to sulfonamides, tetracyclines, quinolones, and macrolides) and their corresponding ARGs in water and sediments of six urban rivers in Guangzhou, South China were analyzed to investigate their spatial distribution and the influence of water remediation. The concentrations of individual antibiotics varied from ND (not detectable) to 2702 ng/L and ND to 449 μg/kg in surface water and sediments, respectively. Norfloxacin displayed the highest average concentrations, followed by ciprofloxacin. The relative abundance of quinolone-resistance gene qnrA (~10³ ARGs/16S rRNA) was the highest, followed by tetracyclines-resistance genes tetC (~10^-2 ARGs/16S rRNA). The antibiotics and ARGs in sediments from various rivers exhibited distinct spatial distribution with large variation from upstream to downstream. Generally, levels of antibiotics and tetracyclines-resistance genes (tetA, tetC and tetM) in urban rivers with black-odor water (affected by industrial and domestic sewage) were higher than those in remediated urban rivers. Significant positive correlations were observed only between the relative abundances of tetA (or tetC) with the concentrations of some antibiotics (e.g., ciprofloxacin and norfloxacin). TetA was also significantly positively correlated with the concentrations of Ni, Cr, and As in sediments. This study found that urban rivers remediated with dredging might lower antibiotic levels in sediment, but high relative abundance of certain ARGs (e.g., tetB, qnrA) may still exist.