On-site removal of antibiotics and antibiotic resistance genes from leachate by aged refuse bioreactor: Effects of microbial community and operational parameters

Distribution, removal and potential factors affecting antibiotics occurrence in leachate from municipal solid waste incineration plants in China

Leachate from municipal solid waste (MSW) incineration harbors a plethora of contaminants, including antibiotics and antibiotic resistance genes (ARGs). However, the understanding of such leachate is markedly scant in comparison to that of landfill leachate. In this study, the distribution and removal of 8 sulfonamides (SAs), 4 quinolones (FQs), and 4 macrolides (MLs) antibiotics in leachate from 14 MSW incineration plants in representative cities across different regions of China were investigated. In addition, potential factors affecting the contamination levels of antibiotics and ARGs in fresh leachate were evaluated. The results showed that the total concentration of target antibiotics in fresh leachate ranged from 4406.1 to 14,930.6 ng/L. Notably, the antibiotic distribution in leachate exhibited regional disparities, influenced by economic status, climatic conditions, and waste separation policies. The absolute abundance of total ARGs ranged from 1.3 × 107-4.0 × 108 copies/mL, with the mobile genetic elements intl1 facilitates the dissemination of qnrS, sul1 and sul2. No distinct regional distribution of the ARGs was observed among different cities. Antibiotic and ARGs distributions were significantly correlated with total organic carbon, pH, ammonia nitrogen, heavy metals, and microbial communities. Moreover, SAs were identified as contributors to the proliferation and spread of corresponding ARGs. Fourteen typical "anaerobic-anoxic/aerobic-anoxic/aerobic-ultrafiltration-nanofiltration " treatment processes removed the target antibiotics effectively (76.1 %-97.0 %). Biodegradation was considered to be the dominant antibiotic removal pathway, removing 62.0 %-90.9 % of antibiotics, while sludge adsorption removed only 1.0 %-11.7 %. This research furnishes valuable insights into the fate of antibiotics in MSW incineration leachate.

Contaminant-degrading bacteria are super carriers of antibiotic resistance genes in municipal landfills: A metagenomics-based study

Municipal landfills are hotspot sources of antimicrobial resistance (AMR) and are also important habitats of contaminant-degrading bacteria. However, high diversity of antibiotic resistance genes (ARGs) in landfills hinders assessing AMR risks in the affected environment. More concerned, whether there is co-selection or enrichment of antibiotic-resistant bacteria and contaminant-degrading bacteria in these extremely polluted environments is far less understood. Here, we collected metagenomic datasets of 32 raw leachate and 45 solid waste samples in 22 municipal landfills of China. The antibiotic resistome, antibiotic-resistant bacteria and contaminant-degrading bacteria were explored, and were then compared with other environmental types. Results showed that the antibiotic resistome in landfills contained 1,403 ARG subtypes, with the total abundance over the levels in natural environments and reaching the levels in human feces and sewage. Therein, 49 subtypes were listed as top priority ARGs for future surveillance based on the criteria of enrichment in landfills, mobilizable and present in pathogens. By comparing to those in less contaminated river environments, we elucidated an enrichment of antibiotic-resistant bacteria with contaminant-degrading potentials in landfills. Bacteria in Pseudomonadaceae, Moraxellaceae, Xanthomonadaceae and Enterobacteriaceae deserved the most concerns since 72.2 % of ARG hosts were classified to them. Klebsiella pneumoniae, Acinetobacter nosocomialis and Escherichia coli were abundant multidrug-resistant pathogenic species in raw leachate (∼10.2 % of total microbiomes), but they rarely carried contaminant-degradation genes. Notably, several bacterial genera belonging to Pseudomonadaceae had the most antibiotic-resistant, pathogenic, and contaminant-degrading potentials than other bacteria. Overall, the findings highlight environmental selection for contaminant-degrading antibiotic-resistant pathogens, and provide significant insights into AMR risks in municipal landfills.

Integrating advanced techniques and machine learning for landfill leachate treatment: Addressing limitations and environmental concerns

This review article explores the challenges associated with landfill leachate resulting from the increasing disposal of municipal solid waste in landfills and open areas. The composition of landfill leachate includes antibiotics (0.001-100 μg), heavy metals (0.001-1.4 g/L), dissolved organic and inorganic components, and xenobiotics including polyaromatic hydrocarbons (10-25 μg/L). Conventional treatment methods, such as biological (microbial and phytoremediation) and physicochemical (electrochemical and membrane-based) techniques, are available but face limitations in terms of cost, accuracy, and environmental risks. To surmount these challenges, this study advocates for the integration of artificial intelligence (AI) and machine learning (ML) to strengthen treatment efficacy through predictive analytics and optimized operational parameters. It critically evaluates the risks posed by recalcitrant leachate components and appraises the performance of various treatment modalities, both independently and in tandem with biological and physicochemical processes. Notably, physicochemical treatments have demonstrated pollutant removal rates of up to 90% for various contaminants, while integrated biological approaches have achieved over 95% removal efficiency. However, the heterogeneous nature of solid waste composition further complicates treatment methodologies. Consequently, the integration of advanced ML algorithms such as Support Vector Regression, Artificial Neural Networks, and Genetic Algorithms is proposed to refine leachate treatment processes. This review provides valuable insights for different stakeholders specifically researchers, policymakers and practitioners, seeking to fortify waste disposal infrastructure and foster sustainable landfill leachate management practices. By leveraging AI and ML tools in conjunction with a nuanced understanding of leachate complexities, a promising pathway emerges towards effectively addressing this environmental challenge while mitigating potential adverse impacts.

Environmental pitfalls and associated human health risks and ecological impacts from landfill leachate contaminants: Current evidence, recommended interventions and future directions

The improper management of solid waste, particularly the dumping of untreated municipal solid waste, poses a growing global challenge in both developed and developing nations. The generation of leachate is one of the significant issues that arise from this practice, and it can have harmful impacts on both the environment and public health. This paper presents an overview of the primary waste types that generate landfill leachate and their characteristics. This includes examining the distribution of waste types in landfills globally and how they have changed over time, which can provide valuable insights into potential pollutants in a given area and their trends. With a lack of specific regulations and growing concerns regarding environmental and health impacts, the paper also focuses on emerging contaminants. Furthermore, the environmental and ecological impacts of leachate, along with associated health risks, are analyzed. The potential applications of landfill leachate, suggested interventions and future directions are also discussed in the manuscript. Finally, this work addresses future research directions in landfill leachate studies, with attention, for the first time to the potentialities that artificial intelligence can offer for landfill leachate management, studies, and applications.

Antibiotic resistance genes and heavy metals in landfill: A review

Landfill is reservoir containing antibiotic resistance genes (ARGs) that pose a threat to human life and health. Heavy metals impose lasting effects on ARGs. This review investigated and analyzed the distribution, composition, and abundance of heavy metals and ARGs in landfill. The abundance ranges of ARGs detected in refuse and leachate were similar. The composition of ARG varied with sampling depth in refuse. ARG in leachate varies with the distribution of ARG in the refuse. The ARG of sulI was associated with 11 metals (Co, Pb, Mn, Zn, Cu, Cr, Ni, Sb, As, Cd, and Al). The effects of the total metal concentration on ARG abundance were masked by many factors. Low heavy metal concentrations showed positive effects on ARG diffusion; conversely, high heavy metal concentrations showed negative effects. Organic matter had a selective pressure effect on microorganisms and could provide energy for the diffusion of ARGs. Complexes of heavy metals and organic matter were common in landfill. Therefore, the hypothesis was proposed that organic matter and heavy metals have combined effects on the horizontal gene transfer (HGT) of ARGs during landfill stabilization. This work provides a new basis to better understand the HGT of ARGs in landfill.

Pathogens and antibiotic resistance genes during the landfill leachate treatment process: Occurrence, fate, and impact on groundwater

Landfill leachate is an essential source of pathogens and antibiotic resistance genes (ARGs) in the environment. However, information on the removal behavior of pathogens and ARGs during the leachate treatment and the impact on surrounding groundwater is limited. In this study, we investigated the effects of leachate treatment on the removal of pathogens and ARGs with metagenomic sequencing, as well as the impact of landfill effluent on groundwater. It is shown that the leachate treatment could not completely remove pathogens and ARGs. Twenty-nine additional pathogens and twenty-nine ARGs were newly identified in the landfill effluent. The relative abundance of pathogens and multiple antibiotic resistance genes decreased after ultrafiltration but relative abundance increased after reverse osmosis. In addition, the relative abundances of Acinetobacter baumannii, Erwinia amylovora, Escherichia coli, Fusarium graminearum, Klebsiella pneumoniae, and Magnaporthe oryzae, as well as mdtH, VanZ, and blaOXA-53 increased significantly in the landfill effluent compared to the untreated leachate. The relative abundance of some mobile genetic elements (tniA, tniB, tnpA, istA, IS91) in leachate also increased after ultrafiltration and reverse osmosis. The size of pathogens, the size and properties of ARGs and mobile genetic elements, and the materials of ultrafiltration and reverse osmosis membranes may affect the removal effect of pathogens, ARGs and mobile genetic elements in leachate treatment process. Interestingly, the pathogens and ARGs in landfill effluent were transferred to groundwater according to SourceTracker. The ARGs, mobile genetic elements, and pathogens that are difficult to remove in the leachate treatment process, provide a reference for optimizing the leachate treatment process and improving the control of pathogens and ARGs. Furthermore, this study clarifies the effect of landfill leachate sources of pathogens and ARGs in groundwater.

The influence of combined treatment of municipal wastewater and landfill leachate on the spread of antibiotic resistance in the environment - A preliminary case study

Environmentally-friendly management of landfill leachate (LL) poses a challenge, and LL is usually co-treated with municipal wastewater in wastewater treatment plants (WWTPs). The extent to which the co-treatment of LL and municipal wastewater influences the spread of antibiotic resistance (AR) in the environment has not been examined to date. Two WWTPs with similar wastewater composition and technology were studied. Landfill leachate was co-treated with wastewater in one of the studied WWTPs. Landfill leachate, untreated and treated wastewater from both WWTPs, and river water sampled upstream and downstream from the wastewater discharge point were analyzed. Physicochemical parameters, microbial diversity, and antibiotic resistance genes (ARGs) abundance were investigated to determine the impact of LL co-treatment on chemical and microbiological contamination in the environment. Landfill leachate increased pollutant concentrations in untreated wastewater and river water. Cotreatment of LL and wastewater could affect the abundance and diversity of microbial communities and the interactions between microbial species. Co-treatment also decreased the stability of microbial co-occurrence networks in the examined samples. The mexF gene was identified as a potential marker of environmental pollution with LL. This is the first study to explore the impact of LL on the occurrence of AR determinants in wastewater and rivers receiving effluents.

Comparative insight into the effects of different carbon source supplement on antibiotic resistance genes during whole-run and short-cut nitrification-denitrification processes

Mature landfill leachate is known for nitrogen-removal challenging and meantime was considered as an important sink of antibiotic resistance genes (ARGs). The added external carbon sources, enabling the short-cut nitrification and denitrification, may facilitate the proliferation of bacteria that possibly carry ARGs. However, this speculation has yet to be studied. Here, we explored the effects of glucose, sodium acetate, and methanol supplements on ARGs during whole-run and short-cut treatment processes. The results showed that sodium acetate supplement during short-cut process efficiently reduced the abundances of total ARGs (0.84-1.99 copies/16S rRNA) and integrons (0.59-1.20 copies/16S rRNA), which were highly enhanced by methanol addition during whole-run treatment process (total ARGs: 3.60-11.01 copies/16S rRNA, integrons: 1.20-4.69 copies/16S rRNA). Indirect gradient analysis showed that the variation of ARGs was not correlated with the supplement of different external carbon source. Correlation analysis indicated that dominant intl1 (55.99 ± 17.61% of integrons) showed positively significant correlations with all detected ARGs expect for sul2 and ermB (p < 0.05), suggesting the significant role on ARGs dissemination. Redundancy analysis illustrated that the potential hosts of intl1, intl2, sul1, tetQ, tetM, mefA, and mexF were dominant Bacteroidetes and Actinobacteria. Interestingly, the numbers and significant extent of correlations under the supplement of sodium acetate during short-cut denitrification process were obviously declined, and it was in accordance with ARGs reduced by sodium acetate supplement, suggesting sodium acetate displayed the efficient ARGs reduction during short-cut process. In summary, this study provides a comparative understanding of the effects on ARGs by different carbon source supplements during nitrification-denitrification processes of leachate; sodium acetate is the optimal carbon source.

Antibiotic resistance genes in landfill leachates from seven municipal solid waste landfills: Seasonal variations, hosts, and risk assessment

Landfills are reservoir of antibiotics and antibiotic resistance. Antibiotic resistance would transport to the environment through landfill leachate, posing threaten to the environment. However, long term monitoring on antibiotic resistance genes in landfill leachate transportation is limited. Furthermore, antibiotic resistance gene hosts and their risk assessment are lacking. In this study, we investigated the seasonal variation of ARGs sulI, tetO and tetW in seven Chinese municipal solid waste landfill leachates over two years (2017-2018) by quantitative polymerase chain reaction. We also evaluated the associated bacterial hosts and their risk levels based on metagenomics and omics-based framework for assessing the health risk of antimicrobial resistance genes, respectively. Because sulI, tetO and tetW are abundant and the most frequently detected ARGs in global landfill system, they are selected as target ARGs. Results showed that the relative content of target ARGs in 2017 was 100 times higher than that in 2018, suggesting ARGs attenuation. The hosts of sulI were phyla of Lentisphaerae and Proteobacteria, whereas the hosts of tetO and tetW were Bacteroidetes and Firmicutes. Remarkably, the host species include pathogenic bacterium (Salmonella enterica, Labilibaculum filiforme, Bacteroidales bacterium, Anaeromassilibacillus senegalensis, and Pseudochrobactrum sp. B5). ARGs tetO and tetW belong to the Rank II level with characters of enrichment in the human-associated environment and gene mobility, and sulI ranked as Rank VI. In addition, among 1210 known ARGs in the landfill leachate, 78 ARGs belonged to risk Rank I (enrichment in human-associated environment, gene mobility and pathogenicity), demonstrating high health risk of landfill system. These results demonstrate that antibiotic resistance in landfill and landfill leachate have high health risk and the kind of ARGs with high abundance in human-associated environment, gene mobility and pathogenicity should be paid more attention.

Effects of Pyroligneous Acid on Diversity and Dynamics of Antibiotic Resistance Genes in Alfalfa Silage

Antibiotic resistance genes (ARGs) are recognized as contaminants due to their potential risk for human and environment. The aim of the present study is to investigate the effects of pyroligneous acid (PA), a waste of biochar production, on fermentation characteristics, diversity, and dynamics of ARGs during ensiling of alfalfa using metagenomic analysis. The results indicated that PA decreased (P < 0.05) dry matter loss, pH value, gas production, coliform bacteria count, protease activity, and nonprotein-N, ammonia-N, and butyric acid contents and increased (P < 0.05) lactic acid content during ensiling. During fermentation, Bacteria, Firmicutes, and Lactobacillus were the most abundant at kingdom, phylum, and genus levels, respectively. Pyroligneous acid reduced the relative abundance of Bacteria and Firmicutes and increased that of Lactobacillus. The detected ARGs belonged to 36 drug classes, including mainly macrolides, tetracycline, lincosamides, and phenicol. These types of ARGs decreased during fermentation and were further reduced by PA. These types of ARGs were positively correlated (P < 0.05) with fermentation parameters like pH value and ammonia-N content and with bacterial communities. At the genus level, the top several drug classes, including macrolide, tetracycline, lincosamide, phenicol, oxazolidinone, streptogramin, pleuromutilin, and glycopeptide, were positively correlated with Staphylococcus, Streptococcus, Listeria, Bacillus, Klebsiella, Clostridium, and Enterobacter, the potential hosts of ARGs. Overall, ARGs in alfalfa silage were abundant and were influenced by the fermentation parameters and microbial community composition. Ensiling could be a feasible way to mitigate ARGs in forages. The addition of PA could not only improve fermentation quality but also reduce ARG pollution of alfalfa silage.

IMPORTANCE Antibiotic resistance genes (ARGs) are considered environmental pollutants posing a potential human health risk. Silage is an important and traditional feed, mainly for ruminants. ARGs in silages might influence the diversity and distribution of ARGs in animal intestinal and feces and then the manure and the manured soil. However, the diversity and dynamics of ARGs in silage during fermentation are still unknown. We ensiled alfalfa, one of the most widely used forages, with or without pyroligneous acid (PA), which was proved to have the ability to reduce ARGs in soils. The results showed that ARGs in alfalfa silage were abundant and were influenced by the fermentation parameters and microbial community. The majority of ARGs in alfalfa silage reduced during fermentation. The addition of PA could improve silage quality and reduce ARG pollution in alfalfa silage. This study can provide useful information for understanding and controlling ARG pollution in animal production.

Abundance and diversity of antibiotic resistance genes and bacterial communities in the western Pacific and Southern Oceans

This study investigated the abundance and diversity of antibiotic resistance genes (ARGs) and the composition of bacterial communities along a transect covering the western Pacific Ocean (36°N) to the Southern Ocean (74°S) using the Korean icebreaker R/V Araon (total cruise distance: 14,942 km). The relative abundances of ARGs and bacteria were assessed with quantitative PCR and next generation sequencing, respectively. The absolute abundance of ARGs was 3.0 × 10⁶ ± 1.6 × 10⁶ copies/mL in the western Pacific Ocean, with the highest value (7.8 × 10⁶ copies/mL) recorded at a station in the Tasman Sea (37°S). The absolute abundance of ARGs in the Southern Ocean was 1.8-fold lower than that in the western Pacific Ocean, and slightly increased (0.7-fold) toward Terra Nova Bay in Antarctica, possibly resulting from natural terrestrial sources or human activity. β-Lactam and tetracycline resistance genes were dominant in all samples (88-99%), indicating that they are likely the key ARGs in the ocean. Correlation and network analysis showed that Bdellovibrionota, Bacteroidetes, Cyanobacteria, Margulisbacteria, and Proteobacteria were positively correlated with ARGs, suggesting that these bacteria are the most likely ARG carriers. This study highlights the latitudinal profile of ARG distribution in the open ocean system and provides insights that will help in monitoring emerging pollutants on a global scale.

The panorama of antibiotics and the related antibiotic resistance genes (ARGs) in landfill leachate

Landfill leachate is an important source and sink of antibiotics and antibiotic resistance genes (ARGs), which poses a potential threat to human health and ecological environment. Ten antibiotics and 8 ARGs in leachates collected from Zhejiang Province, China, were systematically investigated. The effects of multiple factors were considered: leachate age, season when the leachate was sampled (dry or rainy), heavy metal concentrations, and leachate quality parameters. Leachate age was crucial to the profile of the detectable antibiotics and ARGs. The total concentration of antibiotics were in the order of macrolides > sulfonamides > tetracyclines and they decreased significantly with leachate age. Similarly, fewer ARGs were harbored in aged leachate; the order of abundance of the ARGs was mexF (11.92 ± 0.22 log₁₀ gene copies/L) > sul2 > Intl1 > sul1 > ermB > mefA > tetM > tetQ (9.57 ± 1.32 log₁₀ gene copies/L). The extreme abundances (i.e., the maxima and minima) of ARGs relating to the same class of antibiotic were always surprisingly similar and appeared in leachate of the same age. Seasonal variation greatly affected the concentrations of antibiotics in the leachate-the concentration difference between the dry and rainy seasons could reach two orders of magnitude. Heavy metal concentrations and leachate quality parameters also had important effects on the distribution of antibiotics and ARGs. Overall, the profile of antibiotics and ARGs in leachates was influenced by numerous factors, and the pollution of antibiotics and ARGs may be reduced and controlled by adjusting the environmental factors.

Antibiotics and antibiotic resistance genes in landfills: A review

Landfill are important reservoirs of antibiotics and antibiotic resistance genes (ARGs). They harbor diverse contaminants, such as heavy metals and persistent organic chemicals, complex microbial consortia, and anaerobic degradation processes, which facilitate the occurrence, development, and transfer of ARGs and antibiotic resistant bacteria (ARB). The main concern is that antibiotics and developed ARGs and ARB may transfer to the local environment via leachate and landfill leakage. In this paper, we provide an overview of established studies on antibiotics and ARGs in landfills, summarize the origins and distribution of antibiotics and ARGs, discuss the linkages among various antibiotics, ARGs, and bacterial communities as well as the influencing factors of ARGs, and evaluate the current treatment processes of antibiotics and ARGs. Finally, future research is proposed to fill the current knowledge gaps, which include mechanisms for the development and transmission of antibiotic resistance, as well as efficient treatment approaches for antibiotic resistance.

Profiles of antibiotic resistance genes in an inland salt-lake Ebinur Lake, Xinjiang, China: The relationship with antibiotics, environmental factors, and microbial communities

Lakes in arid northwestern China, as the main pollutant-holding water bodies in the typical ecologically fragile areas, are facing the unknown risk of exposure to antibiotics and antibiotic resistance genes (ARGs). In this study, five ARGs and one mobile genetic element (intI1) and their relation with antibiotics, microbial communities and water quality were investigated in Ebinur Lake Basin, a typical salt-lake of China. Quantitative PCR analysis indicated that ARGs decreasing order in both surface water and sediment was sul1 >sul2 >tetW>ermB>qnrS, which means sulfonamide resistance genes were the main pollution ARGs. Macrolide antibiotics were the predominant antibiotics in the surface water and sediment in winter, while sulfonamides and quinolones accounted for a high proportion in summer. There was a non-corresponding relationship between ARGs and antibiotics. Moreover, the relationship between ARGs and microbial communities were defined. Sulfonamide resistance genes were carried by a greater diversity of potential host bacteria (76 genera) than other ARGs (9 genera). And their positive correlation with intI1 (p < 0.05) which promotes their migration and provides possibility of their co-occurrence in bacterial populations (e.g., Nitrospira). Bacterial genera were the main driver of ARGs distribution pattern in highly saline lake sediment. Environmental factors like salinity, total nitrogen and organic matter could have a certain influence on the occurrence of ARGs by affecting microorganisms. The results systematically show the distribution and propagation characteristics of ARGs in typical inland salt-lakes in China, and preliminarily explored the relationship between ARGs and antibiotics, resistance genes and microorganisms in lakes in ecologically fragile areas.

Study on antibiotics, antibiotic resistance genes, bacterial community characteristics and their correlation in the landfill leachates

AIM

This study aimed to investigate the contamination levels of antibiotics and antibiotic resistance genes (ARGs) in the landfill leachates and their correlations with the bacteria.

METHODS AND RESULTS

Using HPLC-MS, quantitative PCR and high-throughput sequencing, we measured the pollution levels of 14 antibiotics and 10 ARGs in the leachates of the landfill in Taiyuan, China, and analysed changes in the bacterial community and the correlations of bacteria with antibiotics and ARGs. The main results showed high levels of antibiotics (like enrofloxacin, pefloxacin and oxytetracycline) and ARGs (like sulfonamides, tetracycline, macrolides, quinolones and β-lactam-resistance genes) in the landfill leachates, along with higher diversity and richness of the bacteria. Some types of antibiotics had positive correlations with their corresponding ARGs. The dominant bacteria in the landfill leachates were Pseudomonas, Defluviitoga and Sulfurimonas, which correlated with the antibiotics and ARGs and might have potential effects on degrading them.

CONCLUSIONS

Antibiotics and ARG pollution existed in the landfill leachates, while bacteria were closely associated with them.

SIGNIFICANCE AND IMPACT OF THE STUDY

It will provide helpful information for the potential application of the bacteria in antibiotics and ARGs pollution control and landfill leachate management.

Rainfall Influences Occurrence of Pharmaceutical and Personal Care Products in Landfill Leachates: Evidence from Seasonal Variations and Extreme Rainfall Episodes

Unused or expired pharmaceutical and personal care products (PPCPs) are usually discharged into municipal solid wastes, then travel to landfills, and eventually percolate into leachates. However, knowledge of their occurrence and temporal dynamics in leachates is limited, making landfill leachate an underappreciated emission source of PPCPs. Furthermore, the differences in PPCP variations in landfill leachates emphasize the necessity for identifying the influencing factors and elucidating the mechanisms for PPCP fluctuations. In this study, successive monthly monitoring of PPCPs in leachates throughout an entire year was performed to determine their seasonal variations and identify their influencing factors. Furthermore, five pairs of additional sampling campaigns were conducted before and after rainfall events during wet seasons to elucidate the influencing mechanisms. The results showed that there was a distinct seasonal variation in PPCPs in landfill leachates-elevated levels during the wet period (from April to September, with a mean concentration of 17.0 μg/L for total monitored PPCPs)-when compared to other months (mean concentration of 3.8 μg/L). Rainfall played a considerable role in mediating PPCP concentrations in leachates. The PPCP responses to five rainfall episodes further verified the influence of rainfall and demonstrated that the tendency to PPCP concentration increase was related to rainfall precipitation. Torrential rain events (i.e., 24 h cumulative precipitation of 50-99.9 mm) led to the most significant increases in PPCP concentrations in landfill leachates. In addition, the hydrophilicity of PPCPs contributed to the different fluctuations during the 1 year investigation and different responses to rainfall. To the best of our knowledge, this study provides the first direct evidence supporting the influence of rainfall on PPCPs in landfill leachates, which can help better understand the occurrence and behavior of emerging contaminants in this underappreciated emission source.

Antibiotic resistance contamination in four Italian municipal solid waste landfills sites spanning 34 years

Municipal solid waste landfill is now recognized as a significant reservoir of antibiotics and antibiotic resistance genes (ARGs). This study investigates the contamination of antibiotics resistance, in 10 leachate samples collected from four MSW landfills in north Italy spanning 34 years, including ARGs as well as mobile genetic element (MGEs). Antibiotics (0-434740 ng/L) and ARGs (5.56-6.85 × 10⁵copies/μL leachate) were found in leachate. Abundances of the measured ARGs were found to be clustered into two groups with different changing tendencies with landfilling age in different landfills. Even though some antibiotics were banned or limited in Italy, they were found to still occur in landfills and drive the long-term contamination of ARGs indirectly, indicating the persistence of antibiotic resistance. What's more, the complexity of antibiotic resistance in leachate was found to synthetically relate to antibiotics, metals, microbes and MGEs presenting that Mn, SMX and EFC influence positively (p < 0.01) the contamination of tetW, tetQ, tetM, tetA, ermB, and cat, contributing importantly in new leachate. This study discusses the AR pollution of leachate in Italy where antibiotics are used the most in Europe, less reported in literatures. Our results suggest that a full-scale view for landfill antibiotics resistance should be considered with history of landfills, use of antibiotics and different phase in landfills, with both "relative static" and "dynamic tracking" perspective to focus on the principal antibiotic-resistance pollutants for leachate treatment, and raise the attention for landfill post-closure care and landfill mining.

Distinct effects of hypochlorite types on the reduction of antibiotic resistance genes during waste activated sludge fermentation: Insights of bacterial community, cellular activity, and genetic expression

The effectiveness of hypochlorites (NaClO and Ca(ClO)₂) on the reduction of antibiotic resistance genes (ARGs) during waste activated sludge (WAS) fermentation was determined by the quantitative PCR. NaClO and Ca(ClO)₂ exhibited distinct effects on ARGs fates. Ca(ClO)₂ was effective in removing all investigated ARGs, and the efficiency was highly dose-dependent. Unexpectedly, the NaClO treatment attenuated ARGs with lower efficiency and even caused the propagation of certain ARGs (i.e., aadA1 and tetQ) at higher doses. The extracellular polymeric substances dissolution and membrane integrity suggested that unstable NaClO had acute effects on bacteria initially, while it was ineffective to further attenuate ARGs released from hosts due to the rapid consumption of oxidative ClO^-. Without lasting and strong oxidative stress, the microbial activities of tolerant ARGs hosts will partially recover and then contribute to the ARGs dissemination across genera. In contrast, solid-state Ca(ClO)₂ was slowly released and exhibited prolonged effects on bacteria by disrupting cell membranes and removing the susceptible ARGs released from hosts. Furthermore, bacterial taxa-ARG network analysis indicated that Ca(ClO)₂ reduced the abundance of potential hosts, and the metabolic pathway and gene expression related to ARGs propagation were significantly downregulated by Ca(ClO)₂, which contributed to efficient ARGs attenuation.

Microbial community and molecular ecological network in the EGSB reactor treating antibiotic wastewater: Response to environmental factors

In this study, one lab-scale EGSB reactor (1.47 L volume) was designed to treat the antibiotic wastewater under different environmental factors, including the addition of cephalexin (CFX), Temperature (T) and Hydraulic Retention Time (HRT). The microbial community structure in EGSB reactor was analyzed with high-throughput sequencing technology to investigate their response to environmental factors changes, and then the random-matrix-theory (RMT)-based network analysis was used to investigate the microbial community's molecular ecological network in EGSB systems treating antibiotics wastewater. Moreover, the explanatory value of each environmental factor on the change of microbial community structure was obtained through the result of redundancy analysis (RDA). The results showed that the addition of cephalexin (CFX), decline of T and decline of HRT (8 h) would decrease the removal efficiency of COD decreasing. And the removal efficiency of CFX would not be affected by decline of T and HRT, except the producing and degrading process of CFX by-products was changed obviously. The result of RDA analysis suggested the environmental factors mainly affected bacterial and fungal microbial community structure but not archaeal ones. The result of high-throughput sequencing showed the relative abundance (RA) of Firmicutes had been obviously affected by T and HRT, which might be main reason leading to the decrease of COD removal efficiency. In addition, molecular ecological network analysis showed the growth of Bacteroidetes occupied the niche of functional microorganism and led to the unstable operation of EGSB when T declined. What's more, the molecular ecological network analysis revealed that Exophiala which belonged to fungi Ascomycota phylum was the hub genus to degrade complex refractory organic pollutants, and Aceticlastic methanogens Methanosaeta was the core functional archaea genus.

The formation mechanism of antibiotic-resistance genes associated with bacterial communities during biological decomposition of household garbage

Food wastes are significant reservoir of antibiotic-resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) available for exchange with clinical pathogens. However, food wastes-related changes of antibiotic resistance in long-period decomposition have been overlooked. Here, we evaluated the comprehensive ARG profile and its association with microbial communities, explained how this might vary with household garbage decomposition. Average of 128, 150 and 91 ARGs were detected in meat, vegetable and fruit wastes, respectively, with multidrug and tetracycline as the predominant ARG types. ARG abundance significantly increased at initial stage of waste fermentation and then decreased. High abundance of Eubacterium-coprostanoligenes, Sporanaerobacter, Peptoniphilus, Peptostreptococcus might be explained for the high relative abundance of ARGs in meat, while high abundance of Advenella, Prevotella, Solobacterium was attributed to the high diversity of ARGs in vegetables. Significant correlations were observed among volatile organic compounds, mobile genetic elements and ARGs, implying that they might contribute to transfer and transport of ARGs. Network analysis revealed that aph(2')-Id-01, acrA-05, tetO-1 were potential ARG indicators, while Hathewaya, Paraclostridium and Prevotellaceae were possible hosts of ARGs. Our work might unveil underlining mechanism of the effects of food wastes decomposition on development and spread of ARGs in environment and also clues to ARG mitigation.

Municipal Solid Waste Landfills: An Underestimated Source of Pharmaceutical and Personal Care Products in the Water Environment

Pharmaceutical and personal care products (PPCPs) have been the focus of increasing concern in recent decades due to their ubiquity in the environment and potential risks. Out-of-date PPCPs are usually discharged into municipal solid wastes (MSWs), enter the leachates in MSW landfills, and have serious adverse effects on the surrounding water environment. However, the occurrence and removal of PPCPs from landfill leachates have rarely been examined to date. This lack of knowledge makes the landfill an underestimated source of PPCPs in the environment. In this review, we collected the relevant publications of PPCPs in landfill leachates, systematically summarized the occurrence of PPCPs in landfill leachates globally, evaluated the removal performances for various PPCPs by different types of on-site full-scale leachate treatment processes, and assessed the impacts of landfill leachates on PPCPs in the adjacent groundwater. In particular, influencing factors for PPCPs in landfill leachates, including the physicochemical properties of PPCPs, climate conditions, and characteristics of landfill sites (i.e., landfill ages) as well as sociological factors (i.e., economic development), were extensively discussed to understand their occurrence patterns. Future perspectives were also proposed in light of the identified knowledge gaps. To the best of our knowledge, this is the first review regarding the occurrence and removal of PPCPs from landfill leachates worldwide.

Vessel transport of antibiotic resistance genes across oceans and its implications for ballast water management

The emergence and spread of antibiotic resistance are major threats to ecosystems and human health. Transoceanic channels (e.g., ship ballast water) can transfer harmful aquatic organisms across geographically isolated waters. However, the occurrence of antibiotic resistance genes (ARGs) in ship ballast water and their relationship with microbial communities and environmental factors remain unknown. In this study, ballast water from 28 vessels sailing to Shanghai and Jiangyin (China) were collected, and the ARGs in these water samples were investigated. Considerable levels of ARGs and integrase of the class-I integrons (intI1) were detected in all ballast water samples. sul1 and tetQ were the most and least abundant ARGs in ballast water samples, respectively. The ARGs were strongly correlated with those of the 16S rRNA and intI1 genes. Ballast water exchange can reduce the absolute abundance of some kinds of ARGs while increasing the relative abundance of several ARGs (e.g., mefA, mexF, strB, sul1, and tetQ). Moreover, the bacterial hosts of ARGs were generally different in the unexchanged ballast water (UEBW) and exchanged ballast water (EBW). In particular, Leisingera and unclassified_Erythrobacteraceae were the main ARGs-associated genera in the EBW, while Pseudohongiella, Cycloclasticus, OM43_clade, norank_f_Rhodospirillaceae, and norank_f_Rhodobacteraceae were the dominant ARGs hosts in the UEBW. Overall, ship ballast water is an effective moving carrier for the global transference of ARGs, and its sufficient management is required for mitigating ARGs propagation across oceans.

Characterization of antibiotic resistance genes and bacterial community in selected municipal and industrial sewage treatment plants beside Poyang Lake

Sewage treatment plants (STPs) are significant reservoirs of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB). Municipal STPs (MSTPs) and industrial STPs (ISTPs) are the two most important STP types in cities. In this study, the ARGs, mobile genetic elements (MGEs), and bacterial communities of selected STPs, including two MSTPs and one ISTP, in the vicinity of Poyang Lake were comprehensively investigated through high-throughput qPCR and high-throughput Illumina sequencing. The results showed that the profiles of ARGs, MGEs and bacteria differed between the ISTP and the two MSTPs, most likely due to differences in influent water quality, such as the Pb that characterized in the ISTP's influent. The longer hydraulic retention times (HRTs) of the two MSTPs than of the ISTP may also have accounted for the different profiles. Thus, a prolonged HRT in the CASS process seems to allow a more extensive removal of ARGs and bacteria in ISTPs with similar treatment process. By providing comprehensive insights into the characteristics of ARGs, MGEs and the bacterial communities of the selected MSTPs and ISTP, our study provides a scientific basis for controlling the propagation and diffusion of ARGs and ARB in different types of STPs.

Fate of antibiotics and antibiotic resistance genes in a full-scale restaurant food waste treatment plant: Implications of the roles beyond heavy metals and mobile genetic elements

Is our food safe and free of the crisis of antibiotics and antibiotic resistance (AR)? And will the derived food waste (FW) impose AR risk to the environment after biological treatment? This study used restaurant FW leachates flowing through a 200 tons-waste/day biological treatment plant as a window to investigate the fate of antibiotics and antibiotic-resistance genes (ARGs) during the acceptance and treatment of FW. Sulfonamides (sulfamethazine, sulfamethoxazole) and quinolones (ciprofloxacin, enrofloxacin, ofloxacin) were detected during FW treatment, while tetracyclines, macrolides and chloramphenicols were not observable. ARGs encoding resistance to sulfonamides, tetracyclines and macrolides emerged in FW leachates. Material flow analysis illustrated that the total amount of antibiotics (except sulfamethazine) and ARGs were constant during FW treatment processes. Both the concentration and total amount of most antibiotics and ARGs fluctuated during treatment, physical processes (screening, centrifugation, solid-liquid and oil-water separation) did not decrease antibiotic or ARGs concentrations or total levels permanently; the affiliated wastewater treatment plant appeared to remove sulfonamides and most ARGs concentrations and total amount. Heavy metals Ni, Co and Cu were important for disseminating antibiotics concentrations and MGEs for distributing ARGs concentrations. Humic substances (fulvic acids, hydrophilic fractions), C-associated and N-associated contents were essential for the distribution of the total amounts of antibiotics and ARGs. Overall, this study implied that human food might not be free of antibiotics and ARGs, and FW was an underestimated AR pool with various determinants. Nonetheless, derived hazards of FW could be mitigated through biological treatment with well-planned daily operations.

Anaerobic/aerobic conditions determine antibiotic resistance genes removal patterns from leachate by affecting bacteria taxa-genes co-occurrence modules

Landfill treatment of municipal solid waste treatment produces a large amount of leachate, which has been an important hotspot of ARGs. This study aimed to investigate the ARGs removal potential, kinetics and mechanism from leachate in aerobic and anaerobic conditions. Simulated landfill reactors showed the efficacy in reducing ARGs, and the removal efficiencies depended on ARGs types and aerobic/anaerobic conditions. The ARGs tetQ and bla_CTX-M were more likely to attenuate with the log-removal efficiencies of 1.50-3 order of magnitude. The ARGs removal kinetic was well fitted by modified Collins-Selleck model, and aerobic condition showed better removal capacities and kinetics than anaerobic condition. Among the ARGs with great removal performance, sul2, aadA1and bla_CTX-M were eliminated from leachate and refuse simultaneously, but tetM, ermB, and mefA were removed from leachate but enriched in refuse. Aerobic/anaerobic states might drive the bacterial community shift of leachate and refuse, and topology property comparison of co-occurrence networks suggested that refuse had a closer non-random host relationship between ARGs and microbial taxa than leachate. Further module analyses revealed that ARGs removal efficiencies depended on the taxonomy of host bacteria in leachate, while the refuse taxa-ARGs correlation determined ARGs removal patterns. By selecting distinct bacteria cluster in different conditions, aerobic treatment benefited ARGs reduction in leachate and refuse, while anaerobic treatment enhanced the enrichment of ARGs in refuse. These findings can potentially foster the understanding of ARGs removal mechanism in biological treatment processes.

Occurrence of super antibiotic resistance genes in the downstream of the Yangtze River in China: Prevalence and antibiotic resistance profiles

The super antibiotic resistance genes (SARGs) demonstrate more severe threats than other antibiotic resistance genes while have not received enough attention in the environment. The study explored the prevalence and the antibiotic tolerance profiles of two typical SARGs, MCR-1 and NDM-1, and their hosting bacteria in the downstream of the Yangtze River and the nearby wastewater treatment plant (WWTP) and drinking water treatment plant (DWTP). Results indicated that MCR-1 and NDM-1 were prevalent in the influent and biological units of the WWTP. Their hosting bacteria were effectively removed, but 2.49 × 10⁸ copies/L MCR-1 and 7.00 × 10⁶ copies/L NDM-1 were still persistent in the effluent. In the Yangtze River, MCR-1 and NDM-1 were detected with higher abundance and antibiotic tolerance than the WWTP effluent and were significantly affected by nearby water contamination and human activities. In the DWTP, MCR-1 and NDM-1 were detected with average values 5.56 × 10⁷ copies/L and 2.14 × 10⁵ copies/L in the influent. Their hosting bacteria were undetectable in the effluent, but the two SARGs were still persistent with 1.39 × 10⁷ copies/L and 6.29 × 10⁴ copies/L, and were greatly enriched in the sludge. Molecular ecological networks demonstrated wide hosting relationships between MCR-1/NDM-1 and bacteria community in the DWTP. Redundancy analysis found that MCR-1 positively correlated with COD and NH₃-N, while negatively correlated with turbidity. Additionally, MCR-1 hosting bacteria positively correlated with NO₃^--N and negatively correlated with COD and NH₃-N. NDM-1 positively correlated with turbidity and NDM-1 hosting bacteria positively correlated with COD and NO₂^--N. The study demonstrated that the WWTP could not effectively remove SARGs with high amount of them being discharged into the Yangtze River. Then they were transported into the DWTP and the persistent SARGs in the effluent would probably be transferred into human, thus imposing great threats on public health.

Comparative network analysis revealing the mechanisms of antibiotic resistance genes removal by leachate recirculation under different hydraulic loadings

The wide dissemination of antibiotic resistance is a pervasive global health threat, and landfill leachate has been an important hotspot of antibiotic resistance genes (ARGs). This study aimed to investigate the removal performance and mechanism of ARGs from leachate under different hydraulic loadings. ARGs removal efficiencies were dependent on hydraulic loadings and ARGs types other than operating time, and reactors operated with hydraulic loadings of 25 and 50 L·m^-3·d^-1 exhibited greater removal potential than 100 L·m^-3·d^-1. ARGs removal patterns varied from different subtypes, for genes sul2, tetQ, aadA1 and bla_CTX-M were eliminated from both leachate and refuse, and tetM, ermB, mefA, and strB were removed from leachate but enriched in refuse. Under different hydraulic loadings, bacterial communities shift shaped ARGs fates in leachate, but refuse had more stable antibiotic resistome and community structure. The topology comparison analysis of co-occurrence network suggested a closer hosting relationship between ARGs and genera in refuse than leachate. Furthermore, taxonomic category of host bacteria other than diversity of host genera determined the ARGs removal, and the ARGs harbored in phyla Cyanobacteria, Tenericutes and Acidobacteria were more likely to be removed. These findings can potentially foster the understanding of ARGs removal mechanism in biological treatment processes under different operating conditions.

Effects of long-lasting nitrogen and organic shock loadings on an engineered biofilter treating matured landfill leachate

The decentralized bioreactor is a promising process for landfill leachate (LL) treatment, however, it is often confronted with various forms of shock loadings. To explore the robustness of bioreactors to the long-lasting substrate shocks, a long-term study of over 90 days was carried out to investigate the effects of nitrogen (mainly ammonium nitrogen, NH₄-N) and organic (in terms of chemical oxygen demand, COD) shock loading on an engineered zeolite-based biofilter with alternative soil-mixed block (SMB) (EZS-biofilter) for treating matured LL. The low-, mid-, and high-strength intensity of matured LL was theoretical defined mainly according to the content of total nitrogen (TN) and COD. The experiment proved that the EZS-biofilter could effectively absorb the substrate shocks in a range of 104, 408, and 1357 mg/L as TN and 178, 590, and 1050 mg/L as COD, corresponding to the low-, medium-, and high-strength LL, respectively. A modified sensitivity index reflected that the nitrogen shock loadings exerted much more predominant influence than COD shock due to the great variation of nitrification/denitrification. The provided information in this study are beneficial for the practical engineered operation of biofilters for treating matured LL.

Simultaneous degradation of tetracycline and denitrification by a novel bacterium, Klebsiella sp. SQY5

Polluted waters with a high residue of tetracycline also have a high concentration of nitrate. Thus, screening for both, highly efficient tetracycline biodegradation and nitrate transformation, is a key technical strategy. In this study, a novel tetracycline degrading strain, SQY5, which was identified as Klebsiella sp., was isolated from municipal sludge. Biodegradation characteristics of tetracycline were studied under various environmental conditions; including inoculation dose (v/v), initial tetracycline concentration, temperature, and pH. Response surface methodology (RSM) analysis demonstrated that the maximum degradation ratio of tetracycline can be obtained under the condition with an initial tetracycline concentration of 61.27 mg L^-1, temperature of 34.96 °C, pH of 7.17, and inoculation dose of 29.89%. Furthermore, this was the first report on the relationship between the degradation of tetracycline and the denitrification effect, showing that a maximum tetracycline reduction rate of 0.113 mg L^-1·h^-1 and denitrification rate of 4.64 mg L^-1·h^-1 were observed within 32 h and 92 h of SQY5 inoculation, respectively. The data of this study has the potential for use in engineering processes designed for the simultaneous biological removal of nitrates while degrading antibiotics.

Metagenomic analysis of antibiotic resistance genes (ARGs) during refuse decomposition

Landfill is important reservoirs of residual antibiotics and antibiotic resistance genes (ARGs), but the mechanism of landfill application influence on antibiotic resistance remains unclear. Although refuse decomposition plays a crucial role in landfill stabilization, its impact on the antibiotic resistance has not been well characterized. To better understand the impact, we studied the dynamics of ARGs and the bacterial community composition during refuse decomposition in a bench-scale bioreactor after long term operation (265d) based on metagenomics analysis. The total abundances of ARGs increased from 431.0ppm in the initial aerobic phase (AP) to 643.9ppm in the later methanogenic phase (MP) during refuse decomposition, suggesting that application of landfill for municipal solid waste (MSW) treatment may elevate the level of ARGs. A shift from drug-specific (bacitracin, tetracycline and sulfonamide) resistance to multidrug resistance was observed during the refuse decomposition and was driven by a shift of potential bacteria hosts. The elevated abundance of Pseudomonas mainly contributed to the increasing abundance of multidrug ARGs (mexF and mexW). Accordingly, the percentage of ARGs encoding an efflux pump increased during refuse decomposition, suggesting that potential bacteria hosts developed this mechanism to adapt to the carbon and energy shortage when biodegradable substances were depleted. Overall, our findings indicate that the use of landfill for MSW treatment increased antibiotic resistance, and demonstrate the need for a comprehensive investigation of antibiotic resistance in landfill.

Occurrence and Distribution of Tetracycline Antibiotics and Resistance Genes in Longshore Sediments of the Three Gorges Reservoir, China

The widespread use of antibiotics and the induced antibiotic resistance genes have attracted much attention in recent years. The longshore sediments in the water-level-fluctuating zone of the Three Gorges Reservoir were selected to investigate the spatial-temporal distribution of antibiotics and antibiotic resistance genes in two different operation stages (low-water level in summer and high-water level in winter). Three kinds of tetracycline antibiotics (tetracycline, oxytetracycline, and chlortetracycline) and three kinds of tetracycline resistance genes [tet(A), tet(C), and tet(M)] were analyzed and quantified. The results showed that the distribution of tetracyclines and resistance genes in riverine, transition and lacustrine zones showed a certain regularity, and the tetracycline antibiotics concentration and the total abundance of the tetracycline resistance genes were highest in the transition zone, and then the riverine zone. Meanwhile, there were significant seasonal variations of tetracycline and the resistance genes. The concentrations of the tetracycline and resistance genes were higher in summer than those in winter, while the relative abundance of resistance genes was higher in winter. It was suggested that the different seasonal distribution of antibiotics and resistance genes may be correlated with the reservoir operation in the Three Gorges Reservoir and the higher use of antibiotics in winter. In addition, Pearson correlation analysis showed that the concentrations of the tetracycline, class 1 integron and 16S rRNA were positively correlated with the abundance of the tetracycline resistance genes.

Abundances and profiles of antibiotic resistance genes as well as co-occurrences with human bacterial pathogens in ship ballast tank sediments from a shipyard in Jiangsu Province, China

Ship ballasting operations may transfer harmful aquatic organisms across global ocean. This study aims to reveal the occurrences and abundances of antibiotic resistance genes (ARGs) and human bacterial pathogens (HBPs) in ballast tank sediments. Nine samples were collected and respectively analyzed by real-time quantitative PCR and high-throughput sequencing technologies. Ten ARGs (aadA1, blaCTX-M, blaTEM, ermB, mefA, strB, sul1, sul2, tetM, and tetQ) and the Class-I integron gene (intI1) were highly prevalent (10⁵-10⁹ gene copies/g) in ballast tank sediments. The sul1 was the most abundant ARG with the concentration of 10⁸-10⁹ copies/g and intI1 was much more abundant than the ARGs in ballast tank sediments. The strong positive correlations between intI1 and ARGs (blaCTX-M, sul1, sul2 and tetM) indicated the potential spread of ARGs via horizontal gene transfer. In ballast tank sediments, 44 bacterial species were identified as HBPs and accounted for 0.13-21.46% of the total bacterial population although the three indicator pathogenic microbes (Vibrio cholerae, Escherichia coli, and Enterococci) proposed by the International Maritime Organization were not detected. Pseudomonas pseudoalcaligenes, Enterococcus hirae, Shigella sonnei and Bacillus anthracis were the dominant pathogens in ballast tank sediments. Zn and P in sediments had positive effects on the ARGs. Network analysis results indicated that sul1 and sul2 genes existed in several bacterial pathogens. Ballast tank sediments could be regarded as a carrier for the migration of ARGs. It is important to manage ballast tank sediments reasonably in order to prevent the dissemination of ARGs and bacterial pathogens.

Nanocomposite thin films Ag0(NP)/TiO2 in the efficient removal of micro-pollutants from aqueous solutions: A case study of tetracycline and sulfamethoxazole removal

The aim of this communication is to synthesize novel Nanocomposite thin film materials (Ag⁰(NP)/TiO₂) using the template process. Surface morphology of materials was obtained by the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses. The presence of doped Ag-nanoparticles was confirmed by the TEM images along with the SEM-EDX analyses. The Atomic Force Microscopic images were demonstrated the surface roughness and thickness of Nanocomposite thin films. X-ray diffraction analysis confirmed that TiO₂ was predominantly present to its anatase mineral phase. The Fourier Transform Infra-red analysis conducted to obtain the functional groups present with the solid. The specific surface area and pore sizes of Nanocomposites were obtained by the BET (Brunauer, Emmett, and Teller) analysis. Further, the Nanocomposite thin film photocatalysts were successfully employed in the degradation of emerging micro-pollutants viz., the antibiotics tetracycline and sulfamethoxazole from aqueous solutions using less harmful UV-A light (λ_max 330 nm). The effect of solution pH (pH 4.0-8.0) and pollutant concentrations (1.0 mg/L-20.0 mg/L (for tetracycline) and (0.5 mg/L-15.0 mg/L (for sulfamethoxazole)) was extensively studied in the photocatalytic removal of these antibiotics. A significant decrease in percentage of non-purgeable organic carbon removal indicated that the micro-pollutants was substantially mineralized by the photocatalytic treatment. The stability of thin film was assessed by the repeated use of Nanocomposite thin films and results were indicated that the degradation of tetracycline or sulfamethoxazole was almost unaffected at least for six cycles of photocatalytic operations. The presence of several cations and anions in the degradation of these antibiotics was studied. Additionally, the presence of 2-propanol and EDTA inhibited significantly the degradation of these micro-pollutants i.e., the percentage of degradation was decreased by 31.8 and 24.2% (for tetracycline) and 42.8 and 39.9% (for sulfamethoxazole), respectively. This indicated that the degradation of tetracycline or sulfamethoxazole was predominantly proceeded by the OH radicals; generated at the valance and conduction band of semiconductor. Similarly, the presence of sodium azide inhibited the percentage removal of these antibiotics.

Research progress on distribution, migration, transformation of antibiotics and antibiotic resistance genes (ARGs) in aquatic environment

Antimicrobial and antibiotics resistance caused by misuse or overuse of antibiotics exposure is a growing and significant threat to global public health. The spread and horizontal transfer of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) by the selective pressure of antibiotics in an aquatic environment is a major public health issue. To develop a better understanding of potential ecological risks die to antibiotics and ARGs, this study mainly summarizes research progress about: (i) the occurrence, concentration, fate, and potential ecological effects of antibiotics and ARGs in various aquatic environments, (ii) the threat, spread, and horizontal gene transfer (HGT) of ARGs, and (iii) the relationship between antibiotics, ARGs, and ARB. Finally, this review also proposes future research direction on antibiotics and ARGs.

Antibiotic resistome in landfill leachate from different cities of China deciphered by metagenomic analysis

High throughput sequencing-based metagenomic analysis and network analysis were applied to investigate the broad-spectrum profiles of ARGs in landfill leachate from 12 cities in China. In total, 526 ARG subtypes belonging to 21 ARG types were detected with abundances ranging from 1.1 × 10^-6 to 2.09 × 10^-1 copy of ARG/copy of 16S rRNA gene. 68 ARG subtypes that accounted for 73.4%-93.4% of the total ARG abundances were shared by all leachate samples. The four most abundant ARGs, sul1, sul2, aadA and bacA can be served as ARG indicators to quantitatively predict the total abundances by linear functions (r² = 0.577-0.819, P < 0.001). No distinct regional distribution pattern of the ARGs was observed among different cities in China, while the ARG compositions of the leachate were clearly distinct from those of other environmental sample types. Nearly 90% ARG subtypes in the anaerobic digestion sludge from sewage treatment plants (STPADS) were shared by the leachate and the abundances of leachate and STPADS ARGs generalists accounted for 84.5% and 87.7% of total abundances in these two types of anaerobic samples, respectively. Furthermore, Procrustes analysis suggested that microbial community composition might be the determining factor of ARG compositions in landfill leachate. ARGs within the same type or among the different types showed higher incidences of non-random co-occurrence and 17 genera might be potential hosts of multiple ARGs. This study highlighted that landfill leachate is an important reservoir of various ARGs and provided a useful reference for the surveillance and risk management of ARGs in landfill environments.

Fluoroquinolones and β-lactam antibiotics and antibiotic resistance genes in autumn leachates of seven major municipal solid waste landfills in China

Landfills are reservoirs of antibiotics, heavy metals, disinfectants and other emerging contaminants, and they are closely associated with the increasing prevalence of antibiotic-resistance genes (ARGs). In this study, two classes of clinical use antibiotics, i.e., fluoroquinolones (FQs) and β-lactams (BLs), twelve subtypes of their parallel ARGs, and five mobile genetic elements (MGEs), were measured in municipal solid waste (MSW) landfill leachates from seven mega-cities in China. The highest concentration of FQs was detected in Shanghai (48,326.67 ng/L), and the highest concentration of BLs was detected in Hangzhou (1304 ng/L). In landfill leachates in Suzhou, the total contents of targeted ARGs subtypes ((1.44 ± 4.64) × 10-4 (ARGs/16S)) and MGEs (7.88 × 10-2 ± 1.18 × 10-1 (ARGs/16S)) were the highest. The relative abundance of ARGs and MGEs was significantly correlated with the contents of As and Cr, and the presence of MGEs was highly correlated with the content of Cd (r = -0.438, p = 0.475). Linear regression analysis showed that MGEs are closely associated with the abundance of genes resistant to FQs and BLs. These results suggest that the occurrences of FQs and BLs ARGs in the landfills of China are substantially influenced by heavy metals and MGEs. Regional differences concerning the antibiotics and ARGs contents in leachates were observed across seven mega-cities, and FQs were significantly correlated with the local population level (p < 0.01). Further, the nitrogen input to the landfills contributes significantly to the elevated levels of target ARGs.

Extracellular polymeric substances affect the responses of multi-species biofilms in the presence of sulfamethizole

The occurrence and transportation of antibiotics in biofilms from natural and engineered sources have attracted increasing interests. Nevertheless, the effects of extracellular polymeric substances (EPS) on the responses of biofilms to the exposure to antibiotics are not clear. In this study, the effects of EPS on the sorption and biological responses to one representative antibiotic, sulfamethizole (STZ), in model biofilms were investigated. Proteins dominated the interactions between the EPS and the STZ and the EPS from a moving bed biofilm reactor exhibited the strongest interaction with the STZ. The EPS served as important reservoirs for the STZ and the tested biofilms all showed reduced sorption capacities for the STZ after the EPS were extracted. The respiratory rates and typical enzymatic activities were reduced after the EPS were extracted. High-throughput 16S rRNA gene sequencing results confirmed that the bacterial community in the biofilm without the EPS was more vulnerable to antibiotic shock as indicated by the community diversity and richness indices. A greater increase in the abundance of susceptible species was observed in the natural biofilm. The results comprehensively suggested that the EPS played important role in biosorption of STZ and alleviated the direct damage of the antibiotic to the cells; in addition the extent of the bacterial community response was associated with the origins of the biofilms. Our study provided details on the responses of multi-species biofilms to the exposure to an antibiotic and highlighted the role of the EPS in interacting with the antibiotic, thereby providing a deeper understanding of the bioremediation of antibiotics in real-life natural and engineered biofilm systems.

Bacterial community structure and abundances of antibiotic resistance genes in heavy metals contaminated agricultural soil

Soil contamination with heavy metals is a worldwide problem especially in China. The interrelation of soil bacterial community structure, antibiotic resistance genes, and heavy metal contamination in soil is still unclear. Here, seven agricultural areas (G1-G7) with heavy metal contamination were sampled with different distances (741 to 2556 m) to the factory. Denaturing gradient gel electrophoresis (DGGE) and Shannon index were used to analyze bacterial community diversity. Real-time fluorescence quantitative PCR was used to detect the relative abundance of ARGs sul1, sul2, tetA, tetM, tetW, one mobile genetic elements (MGE) inti1. Results showed that all samples were polluted by Cadmium (Cd), and some of them were polluted by lead (Pb), mercury (Hg), arsenic (As), copper (Cu), and zinc (Zn). DGGE showed that the most abundant bacterial species were found in G7 with the lightest heavy metal contamination. The results of the principal component analysis and clustering analysis both showed that G7 could not be classified with other samples. The relative abundance of sul1 was correlated with Cu, Zn concentration. Gene sul2 are positively related with total phosphorus, and tetM was associated with organic matter. Total gene abundances and relative abundance of inti1 both correlated with organic matter. Redundancy analysis showed that Zn and sul2 were significantly related with bacterial community structure. Together, our results indicate a complex linkage between soil heavy metal concentration, bacterial community composition, and some global disseminated ARG abundance.

Responses of biofilm microorganisms from moving bed biofilm reactor to antibiotics exposure: Protective role of extracellular polymeric substances

EPS can affect the migration of antibiotics in biofilm reactors, however the roles of biofilm EPS on the fate of antibiotics and the protective mechanisms to bacterial community remain unknown. We investigated the transport of three representative antibiotics in the biofilm suspension from a moving bed biofilm reactor. Spectral analysis suggested that proteins dominated the interactions between EPS and antibiotics. The adsorbed amounts of antibiotics onto EPS accounted for 14.5%, 88.2% and 13.1% of total concentration for sulfamethizole, tetracycline and norfloxacin, respectively at the biodegradation stage. The respiratory rates and representative enzymatic activities all experienced declines for biofilm without EPS in exposure to antibiotics. Gene sequencing results indicated that the bacterial community in biofilm without EPS was more vulnerable to antibiotics shocks. Our results demonstrated the protective roles of biofilm EPS in resisting antibiotics stresses, which provides important implications for understanding the bioremediation of antibiotics in biofilm systems.

Evolution of microbial communities during electrokinetic treatment of antibiotic-polluted soil

The evolution of microbial communities during the electrokinetic treatment of antibiotic-polluted soil (EKA) was investigated with chlortetracycline (CTC), oxytetracycline (OTC) and tetracycline (TC) as template antibiotics. The total population of soil microorganisms was less affected during the electrokinetic process, while living anti-CTC, anti-OTC, anti-TC and anti-MIX bacteria were inactivated by 10.48%, 31.37%, 34.76%, and 22.08%, respectively, during the 7-day treatment compared with antibiotic-polluted soil without an electric field (NOE). Accordingly, samples with NOE treatment showed a higher Shannon index than those with EKA treatment, indicating a reduction of the microbial community diversity after electrokinetic processes. The major taxonomic phyla found in the samples of EKA and NOE treatment were Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria. And the distribution of Actinobacteria, Cyanobacteria, and Chloroflexi was greatly decreased compared with blank soil. In the phylum Proteobacteria, the abundance of Alphaproteobacteria was greatly reduced in the soils supplemented with antibiotics (from 13.40% in blank soil to 6.43-10.16% after treatment); while Betaproteobacteria and Deltaproteobacteria showed a different trend with their abundance increased compared to blank soil, and Gammaproteobacteria remained unchanged for all treatments (2.36-2.78%). The varied trends for different classes indicated that the major bacterial groups changed with the treatments due to their different adaptability to the antibiotics as well as to the electric field. SulI being an exception, the reduction ratio of the observed antibiotic resistance genes (ARGs) including tetC, tetG, tetW, tetM, intI1, and sulII in the 0-2cm soil sampled with EKA versus NOE treatment reached 55.17%, 3.59%, 99.26%, 89.51%, 30.40%, and 27.92%, respectively. Finally, correlation analysis was conducted between antibiotic-resistant bacteria, ARGs and taxonomic bacterial classes. It was found that sulII was the most representative of many different bacteria among the seven ARGs studied. This is the first report on the changes in microbial communities before and after EKA, and the present results demonstrated that the application of EKA is a useful and effective approach to suppressing both antibiotic resistant microorganisms and ARGs.