Quantitatively modeling soil-water distribution coefficients of three antibiotics using soil physicochemical properties

Global hierarchical meta-analysis to identify the factors for controlling effects of antibiotics on soil microbiota

It is widely known that antibiotics can affect the structure and function of soil microbial communities, but the specific degree of impact and controlled factors on different indicators remain inconclusive. We conducted a multiple hierarchical mixed effects meta-analysis on 2564 observations that were extracted from 60 publications, to comprehensively assess the impact of antibiotics on soil microbiota. The results showed that antibiotics had significant negative effects on soil microbial biomass, α-diversity and soil enzyme activity. Under neutral initial soil, when soil was derived from agricultural land or had a fine-textured, the negative impacts of antibiotics on soil microbial community were exacerbated. Both single and mixed additions of antibiotics had significant inhibitory effects on soil microbial enzyme activities. The Random Forest model predicted the following key moderators involved in the effects of antibiotics on the soil microbiome, and antibiotics type, soil texture were key moderators on the severity of soil microbial biomass changes. Soil texture, temperature and single or combined application constitute of antibiotics were the main drivers of effects on soil enzyme activities. The reported results can be helpful to assess the ecological risk of antibiotics in a soil environment and provides a scientific basis for the rational of antibiotics use in the soil environment.

Assessing sorption of fluoroquinolone antibiotics in soils from a Kd compilation based on pure organic and mineral components

The presence of fluoroquinolone (FQ) antibiotics in soils may cause a threat to human health due to overexposure and the generation of antibiotic resistance genes. Understanding their sorption behavior in soils is important to predict subsequent FQ (bio) availability. Here, FQ sorption in pure soil organic (i.e., humic substances) and mineral (i.e., metal oxides; phyllosilicates) components is evaluated through a solid-liquid distribution coefficient (Kd (FQ)) dataset consisting of 243 entries originated from 80 different studies, to elucidate their respective contribution to the overall Kd (FQ) in bulk soils. First, different factors affecting FQ sorption and desorption in each of these soil phases are critically discussed. The strong role of pH in Kd (FQ), due to the simultaneous effect on both FQ speciation and surface charge changes, encouraged the derivation of normalized sorption coefficients for the cationic, zwitterionic and anionic FQ species in humic substances and in different phyllosilicates. Kd (FQ) in metal oxides revealed a key role of metal nature and material specific surface area due to complexation sorption mechanisms at neutral pH. Cumulative distribution functions (CDF) were applied to each dataset to establish a sorption affinity range for each phase and to derive best estimate Kd (FQ) values for those materials where normalized sorption coefficients to FQ species were unavailable. The data analysis conducted in the different soil phases set the basis for a Kd (FQ) prediction model, which combined the respective sorption affinity of each phase for FQ and phase abundance in soil to estimate Kd (FQ) in bulk soils. The model was subsequently validated with sorption data in well characterized soils compiled from the literature.

The fate of pharmaceuticals and personal care products (PPCPs) in sewer sediments:Adsorption triggering resistance gene proliferation

In recent years, large quantities of pharmaceuticals and personal care products (PPCPs) have been discharged into sewers, while the mechanisms of PPCPs enrichment in sewer sediments have rarely been revealed. In this study, three PPCPs (tetracycline, sulfamethoxazole, and triclocarban) were added consecutively over a 90-day experimental period to reveal the mechanisms of PPCPs enrichment and the transmission of resistance genes in sewer sediments. The results showed that tetracycline (TC) and triclocarban (TCC) have higher adsorption concentration in sediments compared to sulfamethoxazole (SMX). The absolute abundance of Tets and suls genes increased in sediments under PPCPs pressure. The increase in secretion of extracellular polymeric substances (EPS) and the loosening of the structure exposed a large number of hydrophobic functional groups, which promoted the adsorption of PPCPs. The absolute abundance of antibiotic resistance genes (ARGs), EPS and the content of PPCPs in sediments exhibited significant correlations. The enrichment of PPCPs in sediments was attributed to the accumulation of EPS, which led to the proliferation of ARGs. These findings contributed to further understanding of the fate of PPCPs in sewer sediments and opened a new perspective for consideration of controlling the proliferation of resistance genes.

Multimedia distribution, partitioning, sources, comprehensive toxicity risk and co-occurrence network characteristics of trace elements in a typical Chinese shallow lake with high antibiotic risk

Although the combined pollution of trace elements and antibiotics has received extensive attention, the fate and toxicity risk of trace elements with high antibiotic risk are still unclear. The multimedia distributions, partitioning, sources, toxicity risks and co-occurrence network characteristics of trace elements in surface water (SW), overlying water (OW), pore water (PW) and sediment (Sedi) samples of 61 sites from Baiyangdian (BYD) Lake were investigated. The trace elements in the SW and OW are derived mainly from traffic and agricultural sources, and those in PW and Sedi samples are primarily from lithogenic and industrial sources. The total toxicity risk index (TRI) of nine trace elements (ΣTRI) in Sedi samples showed a very high toxicity risk (18.35 ± 8.84), and a high combined pollution toxicity risk (ΣΣTRI) was observed in PW (149.17 ± 97.52) and Sedi samples (46.37 ± 24.00). The co-occurrence network from SW to PW became more vulnerable. Generally, total antibiotics and TP may be keystones of trace elements in water and sediment. The high antibiotic risk significantly influenced ΣΣTRI in water samples but not in Sedi samples. The findings provide new implications for the monitoring and control of combined antibiotic-trace element pollution in shallow lakes.

Effects of antibiotics on the endophyte and phyllosphere bacterial communities of lotus from above and below surface water in a typical shallow lake

Antibiotics are ubiquitous pollutants that are widely found in aquatic ecosystems, where the bacterial community of aquatic plants is influenced by antibiotics. However, differences between endophyte and phyllosphere bacteria of Lotus from above and below surface water remains unclear. Lotus samples from above and below the surface water were collected to investigate the differences in endophyte and phyllosphere bacteria and dominant environmental factors in regions with low (L-) and high (H-) total antibiotic levels. There were significant differences in Shannon diversity between endophyte and phyllosphere bacteria except between the below-surface water phyllosphere bacteria and below-surface water endophytes in both L-antibiotic and H-antibiotic regions, with higher values for phyllosphere bacteria. The dominant phylum in all phyllosphere samples was Proteobacteria (76.1%-92.5%), while Cyanobacteria (47.8%-81.1%) was dominant in all endophyte samples. The dominant source of above-surface water endophytes was below-surface water endophytes (83.68-91.25%), below-surface water phyllosphere bacteria (48.43-55.91%) for above-surface water phyllosphere bacteria, and above-surface water endophytes (53.83-61.80%) for below-surface water endophytes, while the dominant contributor to the below-surface water phyllosphere bacteria was also below-surface water endophytes (52.96-61.00%) in two regions, indicating that antibiotic stress changed the sink‒source relationship between endophytes and phyllosphere bacteria. The physical-chemical properties of surface water and sediments could be responsible for the variations in the above- and below-surface water endophytes and phyllosphere bacteria in both regions. It is suggested that antibiotics may have a substantial effect on endophyte and phyllosphere bacterial community.

A comprehensive and global evaluation of residual antibiotics in agricultural soils: Accumulation, potential ecological risks, and attenuation strategies

The occurrence of antibiotics in agricultural soils has raised concerns due to their potential risks to ecosystems and human health. However, a comprehensive understanding of antibiotic accumulation, distribution, and potential risks to terrestrial ecosystems on a global scale is still limited. Therefore, in this study, we evaluated the accumulation of antibiotics and their potential risks to soil microorganisms and plants, and highlighted the driving factors of antibiotic accumulation in agricultural soils based on 134 peer-reviewed studies (between 2000 and 2022). The results indicated that 56 types of antibiotics were detected at least once in agricultural soils with concentrations ranging from undetectable to over 7000 µg/kg. Doxycycline, tylosin, sulfamethoxazole, and enrofloxacin, belonging to the tetracyclines, macrolides, sulfonamides, and fluoroquinolones, respectively, were the most accumulated antibiotics in agricultural soil. The accumulation of TCs, SAs, and FQs was found to pose greater risks to soil microorganisms (average at 29.3%, 15.4%, and 21.8%) and plants (42.4%, 26.0%, and 38.7%) than other antibiotics. East China was identified as a hot spot for antibiotic contamination due to high levels of antibiotic concentration and ecological risk to soil microorganisms and plants. Antibiotic accumulation was found to be higher in vegetable fields (245.5 µg/kg) and orchards (212.4 µg/kg) compared to croplands (137.2 µg/kg). Furthermore, direct land application of manure resulted in a greater accumulation of TCs, SAs, and FQs accumulation in soils than compost fertilization. The level of antibiotics decreased with increasing soil pH and organic matter content, attributed to decreasing adsorption and enhancing degradation of antibiotics. In conclusion, this study highlights the need for further research on the impacts of antibiotics on soil ecological function in agricultural fields and their interaction mechanisms. Additionally, a whole-chain approach, consisting of antibiotic consumption reduction, manure management strategies, and remediation technology for soil contaminated with antibiotics, is needed to eliminate the potential environmental risks of antibiotics for sustainable and green agriculture.

Spatial variability, source identification and risks assessment of antibiotics in multimedia of North China's largest freshwater lake using positive matrix factorization and Monte Carlo simulation

Antibiotics are widely found in aquatic ecosystems and pose a serious threat to human and the ecological system. Samples of surface water (SW), overlying water (OW), pore water (PW) and sediments (Sedi) were collected to investigate the spatial variability, potential sources, ecological risk (RQs) and health risks (HQs) of nine common antibiotics in Baiyangdian Lake using positive matrix factorization (PMF), and Monte Carlo simulation. Significant spatial autocorrelation of most antibiotics were observed in PW and Sedi samples rather than in SW and OW samples, and higher antibiotic levels were found in the northwest of waters and the southwest of sediments. Livestock (26.74-35.57%) and aquaculture (21.62-37.70%) were identified as primary sources of antibiotics in the water and sediments. Norfloxacin and roxithromycin showed high levels of RQ and HQ in more than 50% of samples, respectively. The combined RQ (ΣRQ) in the PW can be used as a sign of across multimedia risk. Notably, appreciable health risks were observed for the combined HQ (ΣHQ) in about 80% of samples, indicating the importance of taking health risk of antibiotics into consideration. The findings of this work provides a reference for antibiotics pollution control and risk management in shallow lake.

Adsorption behaviors and influencing factors of antibiotic norfloxacin on natural kaolinite-humic composite colloids in aquatic environment

Particles are ubiquitous and abundant in natural waters and play a crucial role in the fate and bioavailability of organic pollution. In the present study, natural mineral (kaolinites, KL), organic (humic/fulvic acid, HA/FA) and their composite particles were further separated into particles fractions (PFs, >1 μm) and colloidal fractions (CFs, 1 kDa-1 μm) by cross-flow ultrafiltration (CFUF). This research demonstrated the role of kaolinite-humic composite colloids on the adsorption of fluoroquinolone norfloxacin (NOR). The Freundlich model satisfactory described adsorption curves, showing strong affinity of NOR to CFs, with sorption capacity (K_F) between 8975.50 and 16638.13 for NOR. The adsorption capacities of NOR decreased with the particle size increasing from CFs to PFs. In addition, composite CFs showed excellent adsorption capacity, which was mainly attributed to the larger specific surface area of composite CFs and electronegativity and numerous oxygen-containing functional groups on the surfaces of the complexes, and electrostatic attraction, hydrogen bond and cation exchange could dominate the NOR adsorption onto the composite CFs. The best pH value under adsorption condition of composite CFs varied from weakly acidic to neutral with the increase of load amount of humic and fulvic acids on the surface of inorganic particles. The adsorption decreased with higher cation strength, larger cation radius and higher cation valence, which depended on the surface charge of colloids and the molecular shape of NOR. These results provided insight into the interfacial behaviors of NOR on the surfaces of natural colloids and promoted the understanding of the migration and transport of antibiotics in environmental systems.

Deriving parametric and probabilistic Kd values for fluoroquinolones in soils

The evaluation of the sorption affinity of fluoroquinolone antibiotics (FQs) in soils, by means of the derivation of solid-liquid distribution coefficients (K_d), is a valuable information for assessing their environmental mobility. Aiming to develop K_d (FQ) prediction tools in soils, in the first stage of this study we constructed a K_d (FQ) sorption dataset using current literature data. Furthermore, additional sorption and desorption data for norfloxacin were obtained in seven different soils of contrasting properties. Sorption isotherms of norfloxacin were linear under the experimental conditions tested and desorption percentages increased for scenarios in which low sorption was noted. Sorption tests in the same soils were then extended to ciprofloxacin, enrofloxacin and ofloxacin and pooled in the dataset, revealing comparable K_d (FQ) values among the FQ tested after analyzing the overall dataset consisting in 312 entries of K_d (FQ). A partial least square (PLS) regression model was then developed to predict values of K_d (FQ) based on specific relevant soil properties (i.e., pH, cation exchange capacity and organic carbon and texture information), and, for the first time, FQ properties (fraction of cationic FQ species) affecting sorption. Additionally, probabilistic, K_d (FQ) best estimates in soils were derived through cumulative distribution functions (CDFs) for the overall and for partial datasets created by grouping K_d (FQ) values according to key soil properties affecting FQ sorption (i.e., pH, organic carbon content and texture information). This latter approach permitted to derive more representative K_d (FQ) best estimates for the soils to be assessed, and with a lower related variability than that derived from the overall dataset. Best estimates K_d (FQ) values were > 1000 L kg^-1 for most acidic to neutral soils, suggesting strong sorption, although lower sorption and thus higher environmental mobility may be expected in scenarios with soils with alkaline pH, low OC and high sand contents. SYNOPSIS: This study aims to derive parametric and probabilistic K_d values for fluoroquinolone antibiotics in soils on the basis of a few relevant soil physicochemical properties.

Occurrence, bioaccumulation and ecological risks of antibiotics in the water-plant-sediment systems in different functional areas of the largest shallow lake in North China: Impacts of river input and historical agricultural activities

Antibiotics are widely used and ubiquitous in the environment, which in turn poses potential threat to human health. However, the effects of agricultural activities and river input on the fate and ecological risks of antibiotics in shallow lake are still poorly understood. Surface water, overlying water and pore water, sediments and aquatic plant samples in the historical planting subarea (PA), historical aquaculture subarea (AU), inflow subarea (IW), discharge subarea (DC), and conservation subarea (CK) of Baiyangdian Lake were collected and analyzed. Our results revealed that the total antibiotic concentrations ranged from 85.33 ng/L to 1631.47 ng/L in waters and from 66.90 ng/g to 177.03 ng/g in sediments. Generally, the total antibiotic concentrations introduced by planting activity in surface water, overlying water and sediments were higher and the levels of total antibiotics in pore water were more affected by river input. In addition, three quinolones (QNs) and two tetracyclines (TCs) were dominant antibiotics in almost five subareas. The pseudo-partitioning coefficient k_d(pw) and bioaccumulation factor (BAF) of antibiotics varied according to the effects of river input and historical agricultural activities. The ecological risk (RQ) of antibiotics from agricultural activities was higher than that from river input. The norfloxacin (NOR) in pore water showed high RQ, which contributed to a large proportion (>50 %) of the combined ecological risks (∑RQs) except for surface water. Therefore, NOR should be used as the primary ecological risk control index for antibiotic contamination management in the BYD. ∑RQs showed high risk in water in the five subareas. This study can act as a reference for governments to formulate effective management strategies for protecting the ecological health of lakes.

Characterizing bacterial communities in Phragmites australis rhizosphere and non-rhizosphere sediments under pressure of antibiotics in a shallow lake

Introduction

Antibiotics are ubiquitous pollutants and widely found in aquatic ecosystems, which of rhizosphere sediment and rhizosphere bacterial communities had certain correlation. However, the response of bacterial communities in Phragmites australis rhizosphere and non-rhizosphere sediments to antibiotics stress is still poorly understood.

Methods

To address this knowledge gap, the samples of rhizosphere (R) and non-rhizosphere (NR) sediments of P. australis were collected to investigate the differences of bacterial communities under the influence of antibiotics and key bacterial species and dominate environmental factors in Baiyangdian (BYD) Lake.

Results

The results showed that the contents of norfloxacin (NOR), ciprofloxacin (CIP) and total antibiotics in rhizosphere sediments were significantly higher than that in non-rhizosphere sediments, meanwhile, bacterial communities in non-rhizosphere sediments had significantly higher diversity (Sobs, Shannon, Simpsoneven and PD) than those in rhizosphere sediments. Furthermore, total antibiotics and CIP were found to be the most important factors in bacterial diversity. The majority of the phyla in rhizosphere sediments were Firmicutes, Proteobacteria and Campilobacterota, while Proteobacteria, Chloroflexi was the most abundant phyla followed by Bacteroidota, Actinobacteriota in non-rhizosphere sediments. The dominate factors of shaping the bacterial communities in rhizosphere were total antibiotics, pH, sediment organic matter (SOM), and NH₄-N, while dissolved organic carbon (DOC), NO₃-N, pH, and water contents (WC) in non-rhizosphere sediments.

Discussion

It is suggested that antibiotics may have a substantial effect on bacterial communities in P. australis rhizosphere sediment, which showed potential risk for ARGs selection pressure and dissemination in shallow lake ecosystems.

Enantioselective Behavior of Flumequine Enantiomers and Metabolites' Identification in Sediment

The enantioselective adsorption, degradation, and transformation of flumequine (FLU) enantiomers in sediment were investigated to elucidate the enantioselective environmental behaviors. The results of adsorption test showed that stereoselective differences of FLU enantiomers in sediment samples and the adsorbing capacity of S-(-)-FLU and R-(+)-FLU are higher than the racemate, and the pH values of the sediment determined the adsorption capacity. Enantioselective degradation behaviors were found under nonsterilized conditions and followed pseudo-first-order kinetic. The R-(+)-FLU was preferentially degraded, and there was significant enantioselectivity of the degradation of FLU. It can be concluded that the microorganism was the main reason for the stereoselective degradation in sediments. The physicochemical property of sediments, such as pH value and organic matter content, can affect the degradation rate of FLU. In addition, the process of transformation of FLU enantiomers in water-sediment system had enantioselective behavior, and R-(+)-FLU was preferential transformed. Meanwhile, the main metabolites of FLU in the sediment were decarboxylate and dihydroxylation products. This study contributes the evidence of comprehensively assessing the fate and risk of chiral FLU antibiotic and enantioselective behavior in the environment.

Fate and ecological risks of antibiotics in water-sediment systems with cultivated and wild Phragmites australis in a typical Chinese shallow lake

River carrying antibiotics from upstream posed serious threats to receiving lake, and plants might had effects on antibiotics. Therefore, samples of waters, sediments and tissues of cultivated and wild Phragmites australis were collected to analyse antibiotics fate and ecological risks (RQs) in Zaozhadian Lake. Our results revealed that the total antibiotics showed an increasing tendency in surface/pore water and P. australis tissues and a decreasing tendency in overlying water and sediments from the lake entrance to the centre. The bioaccumulation factors (BAFs) of two sulfonamides (SAs) and three quinolones (QNs) increased in sediments and decreased in those of erythromycin in pore water from Site 1 to Site 11. Three QNs and two tetracyclines (TCs) were dominant antibiotics in pore water/sediment and surface/overlying water respectively. Higher levels of two SAs in surface/pore water and two macrolides (MAs) in overlying/pore water and sediments were observed in the wild P. australis region, while higher values of two TCs in overlying/pore water and three QNs in sediment were observed in the cultivated P. australis region. Higher BAFs of SAs and QNs in sediments were observed in the cultivated and wild P. australis region respectively. The RQs of oxytetracycline and two MAs posed moderate risks in surface/overlying water from more than 50% of sampling sites. Norfloxacin exhibited moderate RQ and low ∑RQ levels in sediments, and showed high risk in pore water. Our findings imply that much more attention should be given to the antibiotics from river inputs and management normatives to control antibiotic pollution.

Occurrence, Comparison and Priority Identification of Antibiotics in Surface Water and Sediment in Urbanized River: A Case Study of Suzhou Creek in Shanghai

Antibiotics in water have attracted increasing attention due to their potential threat to aquatic ecosystems and public health. Most previous studies have focused on heavily polluted environments, while ignoring urbanized rivers with high population density. Taking Suzhou Creek in Shanghai as an example, this study attempted to explore the antibiotic pollution characteristics of typical urbanized rivers. Further, it screened out priority antibiotics so as to provide reference for the regular monitoring of antibiotics in urban surface water in the study’s later stage. Four classes of 27 antibiotics in surface water samples and sediment samples were detected and analyzed by SPE-UPLC-MS/MS under both wet season and dry season. Results demonstrate that the total amount of antibiotics detected reached 1936.9 ng/L and 337.3 ng/g in water samples and sediment samples, respectively. Through Pearson correlation analysis, it can be shown that there is a very significant correlation between a variety of antibiotics in water and sediment. The results of ecological risk assessment based on risk quotient (RQ) show that certain antibiotics presented high and medium risk to the surrounding ecosystem. Finally, the priority antibiotics selected by optimized priority screening method were EM, SPD, CLR and RTM. Therefore, we have proven that the antibiotics being discharged in urbanized rivers show different types of antibiotics, while presenting a toxicological risk to certain species.

Sulfonamide antibiotics alter gaseous nitrogen emissions in the soil-plant system: A mesocosm experiment and meta-analysis

Veterinary antibiotics are widely used in many countries worldwide to treat diseases and protect the health of animals. However, the effects of sulfonamide antibiotics introduced via manure and wastewater irrigation on nitrogen (N) loss in the soil-plant system remain poorly understood. Here, we conducted a pot experiment to assess the effects of sulfamethazine (SMZ) and its degradation product (2-amino-4,6-dimethylpyrimidine, ADPD) at four concentration gradients (i.e., 0, 1, 10, 100 mg kg^-1) on nitrous oxide (N₂O) and ammonia (NH₃) emissions, and the abundances of N-cycling functional genes and sulfonamide resistance genes. We also collated 350 observations from 62 published papers and performed a meta-analysis of antibiotic addition effects on N₂O emission and soil net nitrification and denitrification. Antibiotics additions showed an inhibitory effect on N₂O emissions, which accords with the trend of our meta-analysis showing a significant decrease of 32%. The decreased N₂O emissions were attributed to the significant reduction in the abundances of total bacterial communities, ammonia oxidizers, and nir-type denitrifiers and to the resultant changes in soil inorganic N. N₂O emissions did not differ between non-environmentally relevant concentrations for SMZ but lowered with increasing ADPD concentrations. This discrepancy can be explained by differential responses of the gene abundances of ammonia oxidizers and nirK-type denitrifiers and the development of antibiotic resistance genes in the highest concentration following antibiotic additions. Antibiotic additions increased soil NH₃ volatilization but did not affect vegetable yield. Therefore, these findings provide insight into how the prevalence of antibiotics in soils could alter the N-cycling process and associated gas emissions, with implications for understanding the ecological risks of antibiotics in agriculture.

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

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

Shift in the distribution and fate of perfluoroalkyl acids by sluice gates in the multi-environment media of rivers

The impact of sluice operations on the distribution and fate of perfluoroalkyl acids (PFAAs) remains poorly understood. In this study, the distribution of PFAAs was investigated in water, suspended particles, sediment, and pore water from the upstream and downstream sections of six sluice gates along the Wangyu River, China. The target PFAAs were widely distributed in the dissolved phase (∑PFAAs: 447.61 ± 180.26 ng/L), particle phase (∑PFAAs: 2040.95 ± 1870.88 ng/g dw), sedimentary phase (∑PFAAs: 39.42 ± 35.38 ng/g dw), and pore water phase (∑PFAAs: 8172.54 ± 4278.60 ng/L). Our data suggest predominant detections of short-chain PFAAs such as perfluorobutanoic acid (PFBA) and perfluorohexanoic acid (PFHxA) in the four environmental media. Sediment pore water appeared as an essential repository and potential source for PFAA re-release to the river environment. The levels of PFAAs in the dissolved and suspended particle phase upstream of the sluices were significantly lower than those downstream, while the situation in the sediment and pore water phase was the opposite. Sluice operation caused PFAA redistribution among the multi-environment media but did not change the PFAA composition, which had the significant effect on the partition behavior of perfluoroalkyl carboxylic acids (PFCAs) between particles and water, as well as changed the migration pattern of PFOA, PFNA and PFOS from equilibrium to the migration state. Quantitative prediction models were developed for simulating fate of PFAAs in gate-controlled river, and the major factors affecting the distribution and fate of PFAAs were identified. Our findings provide insights into the redistribution mechanisms of PFAAs and an understanding of their environmental fate.

Dynamics of antibiotics and antibiotic resistance genes in four types of kitchen waste composting processes

Kitchen waste might be a potential source of antibiotics and antibiotic resistance genes. Composting is recognized as an effective way for kitchen waste disposal. However, the effects of different kitchen waste composting types on the removal of antibiotics and antibiotic resistance genes haven't been systematically studied. In this study, the dynamics of antibiotics and antibiotic resistance genes from kitchen waste of four composting processes were compared. Results showed that although kitchen waste was composted, it remained an underestimated source of antibiotics (25.9-207.3 μg/kg dry weight) and antibiotic resistance genes (10¹²-10¹⁷ copies/kg dry weight). Dynamic composting processes (i.e., dynamic pile composting and mechanical composting) decreased the antibiotic removal efficiency and increased the abundance of some antibiotic resistance genes (5.35-8534.7% enrichment). Partial least-squares path model analysis showed that mobile genetic elements played a dominant role in driving antibiotic resistance genes dynamics. Furthermore, redundancy analysis revealed that temperature, pH, and water content considerably affected the removal of antibiotics and mobile genetic elements. This study provides further insights into exploring the effective strategies in minimizing the risk of antibiotic resistance from kitchen waste via composting process.

Enhanced removal of sulfamethoxazole and tetracycline in bioretention cells amended with activated carbon and zero-valent iron: System performance and microbial community

Antibiotics, heavily used as medicine, enter the environment inevitably and raise concerns of the risk to the ecosystems. In this study, we explored the removal efficiency and mechanism of sulfamethoxazole (SMX) and tetracycline (TC) in activated carbon (AC) and AC-zero-valent iron amended bioretention cells (AC-BRC and AC-Fe-BRC) compared with a conventional bioretention cell (BRC). Moreover, the system performance of BRCs, the shifts of the microbial community, as well as the fate of corresponding antibiotic resistance genes (ARGs) were comprehensively investigated. The results showed that, exposed to antibiotics notwithstanding, AC-BRC and AC-Fe-BRC significantly outperformed BRC on total nitrogen (TN) removal (BRC: 70.36 ± 13.61%; AC-BRC: 91.43 ± 6.41%; AC-Fe-BRC: 83.44 ± 12.13%). Greater than 97% of the total phosphorous (TP) was removed in AC-Fe-BRC, remaining unimpacted despite of the selective pressure from SMX/TC. Excellent removals of antibiotics (above 99%) were achieved in AC-BRC and AC-Fe-BRC regardless of the types and initial concentrations (0.8 mg/L, 1.2 mg/L and 1.6 mg/L) of antibiotics, dwarfing the removal performance of BRC (12.2 ± 4.4%-64.2 ± 5.5%). The illumina high throughput sequencing analysis demonstrated the concomitant variations of microbial communities as SMX/TC was loaded. AC layers tended to alleviate the adverse effect of SMX/TC on microbial biodiversity. Proteobacteria (34.55-68.47%), Chloroflexi (7.13-33.54%), and Bacteroidetes (6.20-21.03%) were the top three dominant phyla in the anaerobic zone of the BRCs. The abundance of antibiotic resistance genes (ARGs) sulI, sulII and tetA genes were dramatically higher in AC-BRC and AC-Fe-BRC when exposed to 0.8 mg/L SMX/TC, which indicated that relatively low concentrations of SMX/TC induced the production of these three ARGs in the presence of AC. Although the amendment of AC led to highly efficient SMX/TC removals, further investigation is still required to improve the retention of ARGs in BRCs.

Influence of hydraulic loading rate on antibiotics removal and antibiotic resistance expression in soil layer of constructed wetlands

Behavior of veterinary antibiotics, the corresponding resistant genes in soil layer of constructed wetlands (red soil), and their response to different hydraulic loading rates (HLR) (2, 5, and 10 cm/d) were investigated. Results indicated that the soil layer had perfect performance for oxytetracycline and ciprofloxacin, yet sulfamethazine removal was unsatisfactory. Detection rates of oxytetracycline, ciprofloxacin and sulfamethazine in the effluent of simulation systems of soil layer were 8.33-36.36%, 8.33-47.83% and 100%, respectively. The model analysis of adsorption and hydrolysis indicated that physical adsorption, which was controlled by exchange reaction process based on diffusion, was the primary adsorption mechanism of target antibiotics in red soil, and the hydrolysis half-life values of antibiotics in the water of soil layer were shorter than them in wastewater. The removal response of oxytetracycline and ciprofloxacin to change of HLR was insignificant, yet the respective effluent concentrations of sulfamethazine at HLR of 2-10 cm/d were 41.90, 61.35 and 73.54 μg/L during treating synthetic livestock wastewater, which revealed significant positive correlation (P < 0.05). The relative abundances of each target resistance genes in soil showed significant increase after treating wastewater (10^-5-10^-6 to 10^-4-10^-1), and the total level of those at different HLRs (2, 5, and 10 cm/d) were 3.02 × 10^-2, 7.54 × 10^-2 and 8.65 × 10^-1, respectively. In summary, HLR could affect the removal efficiency of partial antibiotic in soil layer of constructed wetlands, and the expression of antibiotic resistance in the soil gradually increased with increase in the HLR.

Evaluation of wetland substrates for veterinary antibiotics pollution control in lab-scale systems

The behaviors of typical veterinary antibiotics (oxytetracycline, ciprofloxacin and sulfamethazine) and 75 types of corresponding antibiotic resistant genes (ARGs) in four substrate systems (zeolite, gravel, red brick, and oyster shell) were investigated in this study. The results indicated that during treating synthetic livestock wastewater with individual antibiotic influent concentration of 100 μg/L, the effluent contained oxytetracycline and ciprofloxacin concentrations of 0.7-1.5 μg/L and 1.0-1.9 μg/L, respectively, in the zeolite and red brick systems, which were significantly lower than those of the other substrate systems (4.6-14.5 μg/L). Statistical correlation analyses indicated that the difference regarding oxytetracycline and ciprofloxacin removal among the four substrates was determined by their adsorption capacity which was controlled by the chemisorption mechanism. The average removal efficiency of sulfamethazine in the gravel system (48%) was higher than that of the other substrate systems (34-45%), and biodegradation may alter the sulfamethazine performance because of its co-metabolism process. Although tetG, floR, sul1, and qacEΔ1 were the dominant ARGs in all substrate systems (8.74 × 10^-2-6.34 × 10^-1), there was difference in the total ARG enrichment levels among the four substrates. Oyster shell exhibited the lowest total relative abundance (1.56 × 10⁰) compared to that of the other substrates (1.82 × 10⁰-2.27 × 10⁰), and the ARG total relative abundance exhibited significant negative and positive correlations with the substrate pH and system bacterial diversity (P < 0.05), respectively. In summary, this study indicated that due to the difference of adsorption capacity and residual abundant nutrient in wastewater, the wetland substrate selection can affect the removal efficiency of veterinary antibiotics, and antibiotics may not be the determining factor of ARG enrichment in the substrate system.

Tetracycline and Sulfonamide Antibiotics in Soils: Presence, Fate and Environmental Risks

Veterinary antibiotics are widely used worldwide to treat and prevent infectious diseases, as well as (in countries where allowed) to promote growth and improve feeding efficiency of food-producing animals in livestock activities. Among the different antibiotic classes, tetracyclines and sulfonamides are two of the most used for veterinary proposals. Due to the fact that these compounds are poorly absorbed in the gut of animals, a significant proportion (up to ~90%) of them are excreted unchanged, thus reaching the environment mainly through the application of manures and slurries as fertilizers in agricultural fields. Once in the soil, antibiotics are subjected to a series of physicochemical and biological processes, which depend both on the antibiotic nature and soil characteristics. Adsorption/desorption to soil particles and degradation are the main processes that will affect the persistence, bioavailability, and environmental fate of these pollutants, thus determining their potential impacts and risks on human and ecological health. Taking all this into account, a literature review was conducted in order to shed light on the current knowledge about the occurrence of tetracycline and sulfonamide antibiotics in manures/slurries and agricultural soils, as well as on their fate in the environment. For that, the adsorption/desorption and the degradation (both abiotic and biotic) processes of these pollutants in soils were deeply discussed. Finally, the potential risks of deleterious effects on human and ecological health associated with the presence of these antibiotic residues were assessed. This review contributes to a deeper understanding of the lifecycle of tetracycline and sulfonamide antibiotics in the environment, thus facilitating decision-making for the application of preventive and mitigation measures to reduce its negative impacts and risks to public health.

Pharmaceuticals and personal care products in a drinking water resource of Yangtze River Delta Ecology and Greenery Integration Development Demonstration Zone in China: Occurrence and human health risk assessment

The occurrence, partition, and human health risk of thirteen pharmaceuticals and personal care products (PPCPs) have been investigated in surface water, overlying water, pore water and sediment samples from Dianshan Lake of Yangtze River Delta Ecology and Greenery Integration Development Demonstration Zone in China. PPCPs were ubiquitous in aqueous phase and sediments from Dianshan Lake. Sulfamethazine (SMZ) was dominated in surface water and overlying water, while ketoprofen (KPF) was rich in sediment. The total concentration of PPCPs ranged from 0.38-85.27 ng/L, 24.26-130.03 ng/L and 5.39-149.84 μg/kg in surface water, overlying water and sediment, respectively, which were in middle levels compared with these reported in other aquatic environment in China. Naproxen (NPX), sulfadimethoxine (SDM), sulfamethoxazole (SMX) and sulfamethazine (SMZ) in surface water showed a relatively higher level in lake side than those in lake center suggesting that a mixed containment source of human- and animal-derived from the areas around lake. The significant season variations of most PPCPs were mainly attributed to their usage, water temperature and dilution effect. The partition behaviors of PPCPs in sediment-overlying water and sediment-pore water system were mainly affected by their logK_ow values, and showed weak correlation with total organic carbon (TOC) content in sediment and molecular weights of PPCPs. Preliminary results indicated that PPCPs in Dianshan Lake have not posed a high risk to human health by exposure to drinking water for all age groups. Nevertheless, their potential to cause the mixture toxicity and resistance genes cannot be neglected. This work will contribute to the clear picture of PPCPs contamination in drinking water source in the Demonstration Zone, and provide reliable and simple-to-use information to regulators on the exposure and risk levels of PPCPs, as well as recommendations for future research.

Effect of biosolids characteristics on retention and release behavior of azithromycin and ciprofloxacin

Azithromycin (AZ) and ciprofloxacin (CIP) are commonly prescribed antibiotics frequently detected in municipal biosolids and identified by the USEPA as contaminants of emerging concern. The land application of municipal biosolids is an agronomically beneficial practice but is also a potential pathway of CIP and AZ release into the environment. Understanding retention-release behavior is crucial for assessing the environmental fate of and risks from land-applied biosolids-borne target antibiotics. Here, we used batch equilibrations to assess retention and release of environmentally relevant concentrations of CIP and AZ in ten different biosolids. The biosolids included Class A and Class B materials with a range of physiochemical characteristics (e.g. pH, cation exchange capacity (CEC), organic matter content (OM), and iron (Fe) and aluminum (Al)) expected to influence retention and release of AZ and CIP. Retention was linear (R² > 0.99 for AZ and >0.96 for CIP) and sorption coefficients (K_d) ranged from 52 to 370 L kg^-1 for AZ and 430-2300 L kg^-1 for CIP. Desorption also varied but was highly hysteretic, with hysteresis coefficients (H) ranging 0.01 to 0.15 for AZ and ≤0.01 for CIP, suggesting limited bioaccessibility. The penalized and shrinkage method least absolute shrinkage and selection operator (LASSO) was used to produce models describing AZ and CIP sorption behavior based on any given biosolids physiochemical characteristics. Multiple linear regression analysis linked AZ sorption behavior to total Fe content, likely due to a predisposition of AZ to participate in reactions with in situ Fe species. CIP sorption behavior was linked to oxalate extractable Al and total phosphorus (P) content, suggesting CIP bonding with amorphous forms of Al and a potential relationship between CIP sorption to biosolids and biosolids production processes, as manifested by correlation of CIP sorption with total P content.

Evaluation of the fate of nutrients, antibiotics, and antibiotic resistance genes in sludge treatment wetlands

The aim of this research was to analyze the elimination of nutrients, antibiotics as well as antibiotic resistance genes (ARGs) in different sludge treatment wetlands (STWs) with or without reeds and aeration tubes. Five antibiotics, including oxytetracycline, tetracycline, azithromycin, sulfamethoxazole, and sulfadiazine; five ARGs, including two tetracycline ARGs (tetC and tetA), one macrolide ARGs (ermB), and two sulfonamide ARGs (sul1 and sul2); and one integrase gene (intI1) were determined in the surface and bottom layers of three STWs, respectively. The removal efficiencies of antibiotics in the bottom layer were lower than that in the surface layer, while the elimination efficiencies of ARGs showed opposite trend. Strong correlations were observed among the contents of antibiotics as well as related ARGs, and the abundance of ARGs had a strong correlation with intI1. The results demonstrated that the contents of these pollutants decreased during the resting period in all the STWs, while the wetland had reeds and aeration tubes performed the best.

Constructed Wetland Revealed Efficient Sulfamethoxazole Removal but Enhanced the Spread of Antibiotic Resistance Genes

Constructed wetlands (CWs) could achieve high removal efficiency of antibiotics, but probably stimulate the spread of antibiotic resistance genes (ARGs). In this study, four CWs were established to treat synthetic wastewater containing sulfamethoxazole (SMX). SMX elimination efficiencies, SMX degradation mechanisms, dynamic fates of ARGs, and bacterial communities were evaluated during the treatment period (360 day). Throughout the whole study, the concentration of SMX in the effluent gradually increased (p < 0.05), but in general, the removal efficiency of SMX remained at a very high level (>98%). In addition, the concentration of SMX in the bottom layer was higher compared with that in the surface layer. The main byproducts of SMX degradation were found to be 4-amino benzene sulfinic acid, 3-amino-5-methylisoxazole, benzenethiol, and 3-hydroxybutan-1-aminium. Temporally speaking, an obvious increase of sul genes was observed, along with the increase of SMX concentration in the bottom and middle layers of CWs. Spatially speaking, the concentration of sul genes increased from the surface layer to the bottom layer.

Quinolones antibiotics in the Baiyangdian Lake, China: Occurrence, distribution, predicted no-effect concentrations (PNECs) and ecological risks by three methods

The occurrence, distribution, and ecological risk of 10 quinolones (QNs) were investigated in the water and sediment samples from Baiyangdian Lake, China. The field samplings were conducted in April (dry season) and August (wet season) 2018, the results showed that QNs was extensively distributed in the Baiyangdian Lake. For the occurrence, Flumequine (FLU) and Ofloxacin (OFL) were the most detected QNs in Baiyangdian Lake. For the temporal variation, the sum concentration of QNs in water and sediment were ranged from 153 ng/L to 3093 ng/L and from 40.1 ng/g to 1475 ng/g in April, while ranged from 3.83 ng/L to 769 ng/L and from 20.3 ng/g to 373 ng/g in August. For the spatial variation, all of QNs exhibited significance difference in concentration at different sampling areas. Furthermore, PNEC plays an important role in ecological risk assessment, thus the PNECs of FLU and OFL were derived by assessment factors (AF), species sensitivity distribution (SSD), and AQUATOX model methods. The results showed that: PNEC_AFs, PNEC_SSDs, and PNEC_AQUATOXs were 18.7 μg/L, 196 μg/L, and 128 μg/L for FLU, respectively; and were 0.021 μg/L, 4.40 μg/L, and 3.00 μg/L for OFL, respectively. The PNECs for FLU and OFL derived by three approaches showed the rank of: PNEC_SSDs > PNEC_AQUATOXs > PNEC_AFs; while the risk quotients (RQs) followed the other rank of: RQ_SSDs < RQ_AQUATOXs < RQ_AFs. The results was indicated that the indirect ecological effects plays an important role in the derived PNECs for QNs, without considering the indirect ecological effects in natural ecosystem can lead to under-protective or over-protective PNECs (RQs) for chemicals. Therefore, AQUATOX model can be applied in deriving PNECs during the ecological risk assessment.

Distribution, residue level, sources, and phase partition of antibiotics in surface sediments from the inland river: a case study of the Xiangjiang River, south-central China

In view of the increasing attention on antibiotic contamination and their scarce data in the inland river (especially for the sediment), the occurrence of 28 antibiotics in sediments from the Xiangjiang River was comprehensively analyzed, and 22 antibiotics were detected with a total concentration ranging from 4.07 to 2090 ng g^-1. The residue was almost at a moderate or higher level in the aquatic environment around the world. Fluoroquinolones and tetracyclines were the dominant detected antibiotics, and the maximum total concentration could reach to 2085 ng g^-1, though that in surface water was just 33.4 ng L^-1. Oxytetracycline and chlortetracycline could be detected with high concentration in areas with lower population density. Usage profile of each antibiotic may be responsible for the spatial variation. Principal component analysis-multiple linear regression model indicated that direct discharge of domestic wastewater and livestock or aquaculture sewage could contribute 94.2% of the pollution. Redundancy analysis was used to screen out the environment variables, which were closely related to the pseudo-partitioning coefficients (K_d) of antibiotics in sediment and surface water for the first time, and showed that the K_d was correlated with sediment pH negatively and organic carbon, total phosphorus, and conductivity of the sediments positively. High sedimentary organic carbon was considered to promote the higher K_d in this river. This study would deepen the understanding of the occurrence of antibiotics in sediments from the inland rivers and provide scientific support for controlling the antibiotic contamination.

Occurrence of antibiotics and their associations with antibiotic resistance genes and bacterial communities in Guangdong coastal areas

The concentration of 8 antibiotics and 21 antibiotic resistance genes were investigated in the coastal areas of Guangdong, China. Total concentrations of antibiotics ranged from 0.43 ng/L to 1040.31 ng/L. The concentrations of tetracyclines were much higher than that of sulfonamides in most sampling sites. The abundance of target antibiotic resistance genes ranged from 1.82 × 10⁵ to 5.9 × 10⁹ copies/mL and tetM accounted for the highest percentages of detected antibiotic resistance genes in most sampling sites. Furthermore, the dominant phyla in water samples were Proteobacteria, Bacteroidetes and Actinobacteria. The relationship between antibiotics, antibiotic resistance genes, and bacterial communities was also investigated. As a result, the abundance of sul1 was positively correlated with the concentration of sulfadiazine, sulfamethoxazole and sulfonamide p-methyl oxypyrimidine. Besides, sulfonamide p-methyl oxypyrimidine, sulfadiazine and p-aminobenzenesulfonamide were significantly correlated with the bacterial communities. These findings suggested that the residues of antibiotics in coastal areas of Guangdong affect the distribution of antibiotic resistance genes and alter the microbial communities.

Evaluation of the Sorption Potential of Mineral Materials Using Tetracycline as a Model Pollutant

Tetracycline (TC) is among the most used antibiotics in animal feedstock in the EU. Antibiotics’ persistence as emerging pollutants in the environment is evidenced by their long half-life in residual organic-mineral sediments and waters. The risk associated with this persistence favours antibiotic-resistant microbiota, affecting human health and ecosystems. The purpose of the present work is to assess the adsorption of TC into natural clay minerals, synthetic iron hydroxides and calcined sewage sludge. TC adsorption isotherms were performed in three replicated batch tests at three different pH values (4, 6, 8) and TC concentrations (33–1176 mg·L−1). X-Ray diffraction (XRD) mineralogy, cation exchange capacity (CEC), Brunauer, Emmett and Teller specific surface area (BET-SSA) and point of zero charge salt effect (PZSE) were determined for the characterization of materials. Sorption was analysed by means of fitting Langmuir and Freundlich adsorption models, which showed good fitting parameters for the studied materials. Low-charge montmorillonite (LC Mnt) is displays the best sorption capacity for TC at maximum TC concentration (350–300 mgTC·g−1) in the whole range of pH (4–8). Sepiolite and smectites adsorbed 200–250 mgTC·g−1, while illite, calcined sludge or iron hydroxides present the lowest adsorption capacity (<100 mgTC·g−1). Nevertheless, illite, sepiolite and ferrihydrite display high adsorption intensities at low to medium TC concentrations (<300 mg·L−1), even at pH 8, as is expected in wastewater environmental conditions.

Predicting distribution coefficients for antibiotics in a river water-sediment using quantitative models based on their spatiotemporal variations

Antibiotics are widely used in humans and animals, but their presence in environmental matrices after use is of great concern. Distribution behavior of antibiotics in natural water-sediment systems is influenced by sediment properties, but how these properties, such as surface area, affect their distribution between water and sediment phases remains unclear. The concentrations of antibiotics also vary both spatially and temporally. In this study, a solid/liquid distribution coefficient Kd(pre) was proposed and evaluated in 12 quantitative predicting models based on aquatic field data compared with a bulk coefficient Kd. Results confirmed by the occurrence pattern, concentration levels and spatiotemporal distributions indicated that the characteristics of antibiotics pollution in rural northwestern Guangzhou were generally consistent with previous investigations, suggesting that this investigation was representative of the present aquatic pollution status of antibiotics. The median concentrations were <100 ng·L^-1 and 220 ng·g^-1 (d.w.) in the water and sediments, respectively. The most pronounced high concentrations of total antibiotic residue found were 778.0 ng·L^-1 for sulfonamides (SAs) in water and 1596.9 ng·g^-1 (d.w.) for fluoroquinolones (FQs) in sediments at site 13 in December of 2016, probably due to its dense population, high frequency of antibiotic use and low water flow. Moreover, 12 quantitative models were established with a high level of robustness and ability to spatiotemporally predict the Kd for each of the 12 antibiotics. The models revealed that pH, organic matter and specific surface area of sediments played significant roles in influencing the adsorption of SAs, FQs, tetracyclines (TCs) and (macrolides) MLs. Our findings provide insights into the effects of physicochemical properties on distribution of antibiotics, predicting their fate and transport, as well as assessments of exposure and risk of these emerging pollutants to aquatic ecosystems.

Environmental availability of sulfamethoxazole and its acetylated metabolite added to soils via sludge compost or bovine manure

The fate of antibiotics and their metabolites in soils after application of organic waste depends on their environmental availability, which depends on the quality and biodegradability of the added exogenous organic matter (EOM). This study aimed at better understanding the fate of sulfamethoxazole (SMX) and N-acetyl-sulfamethoxazole (AcSMX) metabolite added to soils via sludge compost or cow manure application, during a 28-day incubation. Experimental results obtained for mineralized, extractable, and non-extractable fractions as well as EOM mineralization were used to couple SMX and AcSMX dynamics to the EOM evolution using the COP-Soil model. According to various mechanisms of extraction, CaCl₂, EDTA and cyclodextrin solutions extracted contrasted available fractions (31-96% on day 0), resulting in different sets of parameter values in the model. CaCl₂ extraction was the best method to assess the sulfonamide availability, leading to low relative root mean squared errors and best simulations of SMX and AcSMX dynamics. The decrease of SMX and AcSMX availability over time went with the formation of non-extractable residues, mostly of physicochemical origin. Using the COP-Soil model, the co-metabolism was assumed to be responsible for the formation of biogenic non-extractable residues and the low mineralization of SMX and AcSMX.

Retention-release of ciprofloxacin and azithromycin in biosolids and biosolids-amended soils

Ciprofloxacin (CIP) and azithromycin (AZ) are commonly prescribed antibiotics, often found at elevated concentrations in treated sewage sludge (biosolids), and could pose human and ecological risks when land applied. Limited retention-release data preclude assessing potential risks from the target antibiotics in biosolids and biosolids-amended soils. The present work assessed sorption-desorption of CIP and AZ in biosolids and biosolids-amended soils using the "traditional" batch equilibration method. The batch equilibration method also included un-amended soils for comparison. Release potentials of the biosolids-borne antibiotics were assessed via multiple desorption equilibrations in the presence of CaCl₂, soils, PbCl₂, or competing antibiotic (CIP versus AZ) solutions. Desorption kinetics of CIP from biosolids were also evaluated by the diffusive gradient in thin films technique (DGT), coupled with a diffusion transport-exchange model available in 2D-DIFs. Sorption of both antibiotics followed linear models with partitioning coefficient (K_d) values for CIP ranging between 40 and 334 L kg^-1 in soils and 357 L kg^-1 in biosolids, and values for AZ ranging between 11 and 202 L kg^-1 in soils and 428 L kg^-1 in biosolids. Antibiotic desorption from the biosolids was highly hysteretic (hysteresis coefficients < 0.003) and desorption of the biosolids-borne chemicals was extremely small (<3%) using any of the various desorption equilibration approaches. Desorption was hysteric in soils too; where desorption percentages were 4, 5, and 26% for CIP and 6, 32, and 50% for AZ in the silt loam soil, manured sand, and sand, respectively. CIP release from biosolids determined by DGT was also small (<1%), ascribed to low dissolved and labile concentrations in the solid phase and a small effective diffusion coefficient. Results obtained using equilibrium and dynamic approaches suggest that the target antibiotic bioaccessibilities from biosolids and finer-textured (typical agricultural) soils would be minimal and that biosolids (not soils) control desorption of the two biosolids-borne chemicals.

Dynamics of oxytetracycline, sulfamerazine, and ciprofloxacin and related antibiotic resistance genes during swine manure composting

Understanding the dynamics of veterinary antibiotic and related antibiotic resistance genes (ARGs) during swine manure composting is crucial in assessing the environmental risk of antibiotics, which could effectively reduce their impact in natural environments. This study investigated the dissipation of oxytetracycline (OTC), sulfamerazine (SM1) and ciprofloxacin (CIP) as well as the behaviour of their corresponding ARGs during swine manure composting. These antibiotics were added at two concentration levels and two different methods of addition (single/mixture). The results indicated that the removal efficiency of antibiotics by composting were ≥85%, except for the single-SM1 treatment. The tetracycline resistance genes (TRGs) encoding ribosomal protection proteins (RPP) and efflux pump (EFP) and fluoroquinolone resistance genes (FRGs) could be effectively removed after 42 days. On the contrary, the TRGs encoding enzymatic inactivation (EI) and sulfonamide resistance genes (SRGs) were enriched up to 31-fold (sul 2 in single-low-SM1). Statistical analyses indicated that the behaviour of these class antibiotics and ARGs were controlled by microbial activity and significantly influenced by environmental factors (mainly C/N, moisture and pH) throughout the composting process.

Plant toxicity and accumulation of biosolids-borne ciprofloxacin and azithromycin

Trace organic chemicals (TOrCs) in land applied biosolids can cause phytotoxicities and contaminate human and animal food chains. Information on phytotoxicity and phytoaccumulation of environmentally relevant concentrations of two antibiotic TOrCs, ciprofloxacin (CIP) and azithromycin (AZ), from biosolids-amended soils is limited. Greenhouse studies were conducted to assess the plant toxicity and accumulation of a range of environmentally relevant concentrations of biosolids-borne CIP and AZ in biosolids-amended soils. Separate studies assessed phytotoxicity potential of soil-borne CIP and AZ (soils directly spiked with the target antibiotics without biosolids) at concentrations much greater than those of environmental relevance in biosolids-amended soils. Both the biosolids-borne and the soil-borne antibiotic studies involved three plants (radish (Raphanus sativus), lettuce (Lactuca sativa), and tall fescue grass (Festuca arundinacea)) of different morphologies, physiologies, and chemical exposure scenarios. Phytotoxicity and phytoaccumulation from the biosolids-borne antibiotics were minimal at environmentally relevant concentrations, even in sand. The separate phytotoxicity experiments involving the soil-borne antibiotics revealed no observed adverse effect concentration (NOAEC) of 3.2 mg kg-1 (AZ) and 36.1 mg kg-1 (CIP) for the three plants grown in soils mimicking typical agricultural soils. These NOAEC values are about 100-fold greater than the antibiotic concentrations expected in biosolids-amended soils. NOAEC values under an unrealistic worst-case where the antibiotics were directly spiked to sand (NOAEC = 3.2 mg kg-1 for AZ; and ≥0.36 mg kg-1 for CIP) were also greater than the environmentally relevant concentrations of the biosolids-borne antibiotics. The results suggest that land application of biosolids-borne CIP and AZ pose De minimis risks to plants. Point estimates of plant bioaccumulation factors (dry weight basis) were 0.01 (CIP) and 0.1 (AZ), suggesting minimal impacts of the target TOrCs on human and/or animal food chains.

Quantitative models for predicting adsorption of oxytetracycline, ciprofloxacin and sulfamerazine to swine manures with contrasting properties

Understanding antibiotic adsorption in livestock manures is crucial to assess the fate and risk of antibiotics in the environment. In this study, three quantitative models developed with swine manure-water distribution coefficients (LgK_d) for oxytetracycline (OTC), ciprofloxacin (CIP) and sulfamerazine (SM1) in swine manures. Physicochemical parameters (n=12) of the swine manure were used as independent variables using partial least-squares (PLSs) analysis. The cumulative cross-validated regression coefficients (Q²_cum) values, standard deviations (SDs) and external validation coefficient (Q²_ext) ranged from 0.761 to 0.868, 0.027 to 0.064, and 0.743 to 0.827 for the three models; as such, internal and external predictability of the models were strong. The pH, soluble organic carbon (SOC) and nitrogen (SON), and Ca were important explanatory variables for the OTC-Model, pH, SOC, and SON for the CIP-model, and pH, total organic nitrogen (TON), and SOC for the SM1-model. The high VIPs (variable importance in the projections) of pH (1.178-1.396), SOC (0.968-1.034), and SON (0.822 and 0.865) established these physicochemical parameters as likely being dominant (associatively) in affecting transport of antibiotics in swine manures.

Occurrence and partitioning behavior of organophosphate esters in surface water and sediment of a shallow Chinese freshwater lake (Taihu Lake): Implication for eco-toxicity risk

Organophosphate esters (OPEs) are ubiquitous in the aquatic environment, which have been considered or suspected as carcinogens and neurotoxicants. In this study, the occurrence, spatial distribution, potential sources, partitioning character and potential risks of OPEs in the surface water and sediment collected from Taihu Lake were investigated. The concentrations of ∑12 OPEs varied from 1.0 × 10² to 1.7 × 10³ ng/L for the surface water and from 8.1 to 4.2 × 10² ng/g dw for the sediment. Trimethyl phosphate (TEP) was the predominant congener in the surface water, while Tris(2-ethylhexyl) phosphate (TEHP) in the sediment. Positive correlations between OPEs indicated that they may have the same sources and/or similar environmental behavior. The pseudo-partitioning values of OPEs ranged from 0.59 to 6.5 × 10⁴ L/kg. TEHP has the highest pseudo-partitioning coefficient, which indicated that TEHP inclined to be enriched in the sediment in Taihu Lake. Risk assessment (RQ) showed that individual OPEs in the surface water and sediment posed no/low risk to aquatic organisms, except 2-Ethylhexyl diphenyl phosphate (EHDPP) (moderate risk) in water.

Vertical up-flow constructed wetlands exhibited efficient antibiotic removal but induced antibiotic resistance genes in effluent

The intensive use of antibiotics results in their continuous release into the environment and the subsequent widespread dissemination of antibiotic resistance genes (ARGs), thus posing potential risks for public health. Although vertical up-flow constructed wetlands (VUF-CWs) have been widely used to treat wastewater in remote or rural regions, few studies have assessed the potential risks of ARG dissemination when VUF-CWs are applied to treat wastewaters containing antibiotics. In this study, the removal performance of two typical antibiotics (sulfamethoxazole (SMX) and tetracycline (TC)) and the fate of ARGs were evaluated in three lab-scale VUF-CWs. The results indicated that high removal efficiencies (>98%) could be achieved for both SMX and TC. However, the exposure of antibiotics resulted in harboring abundant ARGs (mainly sul- and tet-related genes), even with increasing abundances with operation time. The abundances of ARGs had a positive correlation with the accumulation of SMX and TC in different layers of VUF-CWs, where the tet and sul genes have the highest abundance in the bottom layer due to the highest antibiotic exposure concentration. Positive correlations were observed between the abundance of tet gene and antibiotic concentration in effluent. Although the effluent had lower abundances of the ARGs than that in the wetland media, the occurrence of ARGs in effluent might still pose risk for public health. Further studies are required to explore effective control strategies to eliminate ARGs from VUF-CWs.

Distribution and Risk Assessment of Antibiotics in a Typical River in North China Plain

We evaluated the occurrence and distribution of 12 antibiotics from the sulfonamide (SAs), fluoroquinolone (FQs) and tetracycline (TCs) groups in the Weihe River, North China. The total antibiotic concentrations in surface water, pore water, and sediment samples ranged from 11.1 to 173.1 ng/L, 5.8 to 103.9 ng/L, and 9.5 to 153.4 μg/kg, respectively. The values of the sediment-water partitioning coefficient in the Weihe River varied widely, from not detected to 943, 2213, and 2405 L/kg for SAs, FQs, and TCs, respectively. The values of the partitioning coefficients between sediment and surface water were generally lower than those between sediment and pore water, which indicated ongoing inputs to the water. The risk assessment showed that there were relatively high ecological risks to aquatic algae in this area from sulfamethoxazole, norfloxacin, tetracycline, ofloxacin, and ciprofloxacin.

Behavior of tetracycline and sulfamethoxazole and their corresponding resistance genes in three-dimensional biofilm-electrode reactors with low current

Antibiotics and antibiotic resistance genes (ARGs) have become major health concerns. In this study, three-dimensional biofilm-electrode reactors (3D-BERs) under low current were designed to assess their performance in removing tetracycline (TC) and sulfamethoxazole (SMX) from synthetic wastewater. In addition, the fates of the corresponding ARGs in microbial communities were investigated. The mass removal ratios of TC and SMX by the 3D-BERs were 82.6-97.3% and 72.2-93.2%, respectively. There were obvious increases in the relative abundances of all target genes after ∼2 months. The tet and sul genes were significantly upregulated by high concentrations of antibiotics in the cathode layer, and higher ARG levels were evident in the cathodes than in the anodes. High-throughput sequencing identified Methylotenera, Candidatus Accumulibacter, Limnohabitans, Dechloromonas, Crenothrix, and Caldilinea as the dominant genera in the samples at the end of the experiment, after ∼8 months, and these bacteria potentially exhibited antibiotic resistance. The relative abundances and compositions of the dominant microbial populations changed throughout the course of antibiotic removal in the 3D-BERs.

The effect of iron plaque on uptake and translocation of norfloxacin in rice seedlings grown in paddy soil

Although the role of iron plaque on rice root surface has been investigated in recent years, its effect on antibiotic uptake remains uncertain. In the study, pot experiment was conducted to investigate the effect of iron plaque on uptake and translocation of norfloxacin (adding 10 and 50 mg·kg^-1 treatments) in rice seedlings grown in paddy soil. Iron plaque was induced by adding different amounts of Fe(II) in soil. The results showed that the presence of norfloxacin can decrease the amount of iron plaque induced. After rice with iron plaque induced, norfloxacin was mainly accumulated in iron plaque on root surface, followed by inside root, but its translocation from root to other rice tissues is not observed. Iron plaque played the role of a barrier for norfloxacin uptake into rice roots under high norfloxacin concentration of 50 mg·kg^-1, however not that under low concentration of 10 mg·kg^-1. And the barrier function was the most strongest with adding Fe(II) of 30 mg·kg^-1 as combined action of iron plaque and rhizosphere effect. Fluorescence microscope analysis showed that norfloxacin mainly distributed in the outside of root cell, which showed its translocation as apoplastic pathway in rice. Comparing with non-rhizosphere, more norfloxacin was accumulated in rhizosphere soil. Maybe, strong root oxidization (high Eh values) induced more iron oxide formation in rhizosphere and on root surface, which led to norfloxacin's mobility towards to rhizosphere through its strong adsorption of iron oxides and then promoted its uptake by rice on root surface.

Influence of the natural colloids on the multi-phase distributions of antibiotics in the surface water from the largest lake in North China

Understanding antibiotic adsorption on natural colloids is crucial for prediction of the behavior, bioavailability and toxicity of antibiotics in natural waters. In the present study, the filtered water (dissolved phase, <0.7μm) was further separated into colloidal phase (1kDa-0.7μm) and soluble phase (<1kDa) by cross-flow ultrafiltration (CFUF), and the spatial-temporal variation and distribution of six antibiotics in multi-phases were investigated in Baiyangdian Lake. Results indicated that antibiotic concentrations differed significantly with sampling location and time. The mean concentrations of antibiotics ranged between 13.65 and 320.44ngL^-1 in the dissolved phase, and the colloidal phase accounted for 4.7-49.8% of all antibiotics, suggesting that natural colloids play an important role as carriers of antibiotics in aquatic environments. Because of the influence of colloids, the partition coefficients of antibiotics between suspended particulate matter (SPM) and soluble phase (intrinsic partition coefficients, K_p^int) were found to be 6.18-109.60% higher than corresponding observed partition coefficients (K_p^obs, between SPM and dissolved phase). The mean partition coefficients between colloidal and soluble phase (K_col.) ranged between 6218 and 117,374Lkg^-1, which were 1-2 orders of magnitude greater than K_p^int values. In order to explore the adsorption mechanism of antibiotics on colloids, Pearson's correlations were performed. The results showed that log K_col. were negatively correlated with cations in natural colloids; especially with Mg (r, -0.643, P<0.01) for oxytetracycline (OTC), and with both Ca (-0.595, P<0.01) and Mg (-0.593, P<0.01) in the case of ofloxacin (OFL). This result revealed that the competitive effect between cations and antibiotics was the main factor influencing the adsorption behavior of antibiotics on natural colloids in the lake.

Effect of electrical stimulation on the fate of sulfamethoxazole and tetracycline with their corresponding resistance genes in three-dimensional biofilm-electrode reactors

Three-dimensional biofilm-electrode reactors (3D-BERs), which possess a large effective area to drive the reductive degradation of contaminants, have recently attracted attention for wastewater treatment. There have been few studies of the potential and risks of the application of this system on the removal of antibiotics. Here four 3D-BERs were designed to initially assess the potential for electrical stimulation to remove sulfamethoxazole (SMX), tetracycline (TC) and chemical oxygen demand, and to study the fate of the corresponding antibiotic resistance genes. The results indicated that the 3D-BER could significantly reduce antibiotic concentrations in wastewater, achieving removal rates of 88.9-93.5% and 89.3-95.6% for SMX and TC, respectively. The concentrations of target genes (sulI, sulII, sulIII, tetA, tetC, tetO, tetQ, and tetW) in a granular-activated carbon (GAC) cathode were higher than those in a GAC anode in the 3D-BR (reactor with biological sludge and no voltage) and 3D-BER. An obvious increasing trend in the relative abundances of all target genes was observed in the GAC. A low current density could not increase the development of sul and tet genes in the 3D-BER. The total resistance was in the following order: 3D-BER > 3D-BR > 3D-ER (reactor with 0.8 V and without biological sludge). In addition, the dehydrogenase activity of the microorganisms in the 3D-BER was significantly higher than in the 3D-BR (p < 0.05). High-throughput sequencing revealed that the microbial communities and relative abundance at the phyla level were affected by current stimulation.

Temporal-spatial variation and partitioning prediction of antibiotics in surface water and sediments from the intertidal zones of the Yellow River Delta, China

As special zones, the intertidal zones of the Yellow River Delta (YRD) are highly variable along with time and space. Fluvial-marine and land-ocean interactions which frequently occur in these areas have a great impact on the fate of pollutants. Antibiotics, which contribute to antibiotic-resistant genes (ARGs), are widely detected in wastewater, natural water, soil, sediments, and even drinking water. Therefore, it is meaningful to investigate the occurrence and fate of antibiotics in these special zones. In this study, eight antibiotics belonging to tetracyclines (TCs), fluoroquinolones (FQs), and macrolides (MLs) were detected in the surface water and sediments from the intertidal zones of YRD during two seasons. Two models were established to predict the partitioning coefficients of norfloxacin (NOR) and erythromycin (ETM) using physicochemical properties of sediments, respectively. The total concentrations of these antibiotics were 82.94-230.96ng·L(-1) and 40.97-207.44ng·g(-1), respectively, in the surface water and sediments. Seasonal variation was mainly influenced by the frequency of antibiotics use and environment factors. The regions with river supply exhibited the highest concentrations of antibiotics in surface water and sediments. Meanwhile, particle-size fractions, cation exchange capability (CEC), and metal ions content played dominant roles in the partitioning behaviors of NOR and ETM between the surface water and sediments. Both models established in this study featured accuracy and feasibility, which provided the methods for predicting the partitioning coefficients of emerging contaminants similar in structures to NOR and ETM in the intertidal zones.

Not All Antibiotic Use Practices in Food-Animal Agriculture Afford the Same Risk

The World Health Organization has identified quinolones, third- and fourth-generation cephalosporins, and macrolides as the most important antibiotics in human medicine. In the context of agricultural use of antibiotics, the principle zoonotic agents of concern are , spp., , and spp. Antibiotic exposure provides a selective advantage to resistant strains of these bacteria relative to their susceptible conspecifics. This is a dose-dependent process, and consequently antibiotic use practices that involve higher doses will exert greater and longer-lasting selective pressure in favor of resistant bacterial populations and will therefore increase the probability of transmission to people and other animals. Oral administration has a greater impact on enteric flora with the exception of fluoroquinolone treatments, which appear to affect the enteric flora equally if administered orally or parenterally. The use of quinolones in agriculture deserves heightened scrutiny because of the ease with which these broad-spectrum antibiotics favor spontaneously resistant bacteria in exposed populations. When present at sufficient concentrations, excreted antibiotics have the potential to selectively favor resistant bacteria in the environment and increase the probability of transmission to people and animals. The bioavailability of antibiotics varies greatly: some antibiotics remain active in soils (florfenicol, β-lactams), whereas others may be rapidly sorbed and thus not bioavailable (tetracycline, macrolides, quinolones). When considering the risks of different antibiotic use practices in agriculture, it would be prudent to focus attention on practices that involve high doses, oral delivery, and residues of antibiotics that remain active in soils.

Occurrence and spatial distribution of emerging contaminants in the unsaturated zone. case study: Guadalete River basin (Cadiz, Spain)

Irrigation with reclaimed water is becoming a common practice in arid- and semi-arid regions as a consequence of structural water resource scarcity. This practice can lead to contamination of the vadose zone if sewage-derived contaminants are not removed properly. In the current work, we have characterized soils from the Guadalete River basin (SW Spain), which are often irrigated with reclaimed water from a nearby wastewater treatment plant and amended using sludge. Physico-chemical, mineralogical and hydraulic properties were measured in soil samples from this area (from surface up to 2 m depth). Emerging contaminants (synthetic surfactants and pharmaceutically active compounds, or PhACs) were also determined. Synthetic surfactants, widely used in personal care products (PCPs), were found in a wide range of concentrations: 73-1300 μg kg(-1) for linear alkylbenzene sulfonates (LAS), 120-496 μg kg(-1) for alkyl ethoxysulfates (AES), 19-1090 μg kg(-1) for alcohol polyethoxylates (AEOs), and 155-280 μg kg(-1) for nonylphenol polyethoxylates (NPEOs). The presence of surfactant homologues with longer alkyl chains was predominant due to their sorption capacity. A positive correlation was found between LAS and AEOs and soil organic carbon and clay content, respectively. Out of 64 PhACs analyzed, only 7 were detected occasionally (diclofenac, metoprolol, fenofibrate, carbamazepine, clarithromycin, famotidine and hydrochlorothiazide), always at very low concentrations (from 0.1 to 1.3 μg kg(-1)).

The kinetics and QSAR of abiotic reduction of mononitro aromatic compounds catalyzed by activated carbon

The kinetics of abiotic reduction of mono-nitro aromatic compounds (mono-NACs) catalyzed by activated carbon (AC) in an anaerobic system were examined. There were 6 types of substituent groups on nitrobenzene, including methyl, chlorine, amino, carboxyl, hydroxyl and cyanogen groups, at the ortho, meta or para positions. Our results showed that reduction followed pseudo-first order reaction kinetics, and that the rate constant (logkSA) varied widely, ranging between -4.77 and -2.82, depending upon the type and position of the substituent. A quantitative structure-activity relationship (QSAR) model using 15 theoretical molecular descriptors and partial-least-squares (PLS) regression was developed for the reduction rates of mono-NACs catalyzed by AC. The cross-validated regression coefficient (Qcum(2), 0.861) and correlation coefficient (R(2), 0.898) indicated significantly high robustness of the model. The VIP (variable importance in the projection) values of energy of the lowest unoccupied molecular orbital (ELUMO) and the maximum net atomic charge on the aromatic carbon bound to the nitro group (QC(-)) were 1.15 and 1.01, respectively. These values indicated that the molecular orbital energies and the atomic net charges might play important roles in the reduction of mono-NACs catalyzed by AC in anaerobic systems.

Evaluation of antibiotic mobility in soil associated with swine-slurry soil amendment under cropping conditions

Interest in identifying pools of antibacterial-resistance genes has grown over the last decade, with veterinary antibiotics (VAs) receiving particular attention. In this paper, a mesoscale study aimed at evaluating the vertical transport of common VAs-namely, fluoroquinolones, tetracyclines, sulfonamides, and lincosamides in agricultural soil subjected to drip irrigation-was performed under greenhouse conditions. Accordingly, leachates of cropped and uncropped soil, amended with swine-slurry leading to 19-38 μg kg(-1) (dry mass) antibiotics in the soil, were analyzed over the course of the productive cycle of a lettuce (42 days) with three sampling campaigns (N = 24). High lincomycin (LCM) concentrations (30-39 μg L(-1)) were detected in the leachates collected from the swine-slurry-amended soil. The highest LCM mass recovered in the leachates (30.1 ± 1.63 %) was obtained from cropped experimental units. In addition, the LCM leaching constant and its leaching potential as obtained from the first-order model were higher in the leachates from the cropped experimental units. Lower concentrations of sulfadimethoxine were also detected in leachates and in soil. Enrofloxacin and oxytetracycline occurred only in soil, which is consistent with high soil interaction.

Behavior of tetracycline and sulfamethazine with corresponding resistance genes from swine wastewater in pilot-scale constructed wetlands

Four pilot-scale constructed wetlands (free water surface, SF; horizontal subsurface flow, HSF; vertical subsurface flows with different water level, VSF-L and VSF-H) were operated to assess their ability to remove sulfamethazine (SMZ) and tetracycline (TC) from wastewaters, and to investigate the abundance level of corresponding resistance genes (sulI, sulII, tetM, tetW and tetO) in the CWs. The results indicated that CWs could significantly reduce the concentration of antibiotics in wastewater, and the mass removal rate range of SMZ and TC were respectively 11%-95% and 85%-95% in the four systems on the basis of hydraulic equilibrium; further relatively high removal rate was observed in VSF with low water level. Seasonal condition had a significant effect on SMZ removal in the CWs (especially SMZ in SF), but TC removal in VSFs were not considered to have statistically significant differences in winter and summer. At the end period, the relative abundances of target genes in the CWs showed obvious increases compared to initial levels, ranging from 2.98 × 10(-5) to 1.27 × 10(-1) for sul genes and 4.68 × 10(-6) to 1.54 × 10(-1) for tet genes after treatment, and those abundances showed close relation to both characteristic of wastewater and configuration of CWs.

Distribution and risk assessment of quinolone antibiotics in the soils from organic vegetable farms of a subtropical city, Southern China

Organic fertilizer or manure containing antibiotics has been widely used in organic farms, but the distribution and potential impacts of antibiotics to the local environment are not well understood. In this study, four quinolone antibiotics in soil samples (n=69) from five organic vegetable farms in a subtropical city, Southern China, were analyzed using high performance liquid chromatography-tandem mass spectrometry. Our results indicated that quinolone compounds were ubiquitous in soil samples (detection frequency>97% for all compounds), and their concentrations ranged from not detectable to 42.0 μg/kg. Among the targets, enrofloxacin (ENR) was the dominant compound, followed by ciprofloxacin (CIP) and norfloxacin (NOR). The average total concentrations of four compounds in the soils were affected by vegetable types and species cultivated, decreasing in the order of fruit>rhizome>leaf vegetables. Moreover, the average concentrations of quinolone compounds (except ENR) in open-field soils were higher than those in greenhouse soils. The concentrations of quinolone antibiotics in this study were lower than the ecotoxic effect trigger value (100 μg/kg) proposed by the Veterinary Medicine International Coordination commission. Risk assessment based on the calculated risk quotients indicated that NOR, CIP, and ENR posed mainly medium to low risks to bacteria.