International audience | The reuse of treated wastewater (TWW) for irrigation is widely applied to alleviate pressure on freshwater resources. However, TWW contains antibiotics that once in soils, can exert selective pressure, promoting the emergence and spread of antimicrobial resistance (AMR) in the environment. Current environmental risk assessments for antibiotic residues rely on indicators such as Predicted No Effect Concentrations (PNECs), usually determined in liquid media. These PNECs aim to predict antibiotic concentrations that may promote resistance in the environment. Given the complexity of soil matrices, few studies have established PNEC values for soil, which likely differ significantly from aquatic environments.To address this gap, we developed a simplified experimental model using soil microcosms irrigated with TWW and the antibiotic sulfamethoxazole (SMX) to estimate threshold concentrations favouring resistance transfer or/and emergence within the soil microbiome. We identified SMX concentrations between 0.01 and 0.1 mg/kgdry soil that likely increased the abundance of sulfonamide resistance genes in soil. A time window of 1 to 7 days post-exposure showed a temporary rise in sul1 and intl1 gene abundance (over 1 log/soil 16S rDNA), the appearance of SMX transformation products, and an increase in some Rhodocyclaceae. After 1.5 months of incubation and complete SMX transformation, the relative abundance of sul1 and intl1 remained about 0.5 log higher than in SMX-free controls and soils with SMX levels below 0.1 mg/kg dry soil. A persistent transformation product, 4-N-glucuronide-SMX, was also observed.Here, the estimated PNEC for SMX in soil, between 0.01 and 0.1 mg/kg, exceeds typical SMX concentrations found in soils exposed to TWW. This may suggest low impact on resistance selection for this compound in the context of TWW exposure. However further studies on other soils, water, and antibiotics need to be conducted to expand our knowledge on soil PNECs.

Antibiotics are a contaminant class of worldwide concern as they are frequently detected in aquatic ecosystems. To better understand the impacts of antibiotics on aquatic ecosystems, we conducted an outdoor mesocosm experiment in which aquatic communities were exposed to different concentrations of the antibiotic sulfamethoxazole (0, 0.15, 1.5, 15 and 150 μg/L). These concentrations include mean (0.15 μg/L) and maximum detected concentrations (15 and 150 μg/L) in aquatic ecosystems worldwide. Sulfamethoxazole was applied once a week for eight consecutive weeks to 1530 L outdoor mesocosms in the Netherlands, followed by an eight-week recovery period. We evaluated phytoplankton-, bacterial- and invertebrate responses during and after sulfamethoxazole exposure and assessed impacts on organic matter decomposition. Contrary to our expectations, consistent treatment-related effects on algal and bacterial communities could not be demonstrated. In addition, sulfamethoxazole did not significantly affect zooplankton and macroinvertebrate communities. However, some effects on specific taxa were observed, with an increase in Mesostoma flatworm abundance (NOEC of <0.15 μg/L). In addition, eDNA analyses indicated negative impacts on the insects Odonata at a sulfamethoxazole concentration of 15 μg/L. Overall, environmentally relevant sulfamethoxazole concentration did not result in direct or indirect impairment of entire aquatic communities and ecological processes in our mesocosms. However, several specific macroinvertebrate taxa demonstrated significant (in)direct effects from sulfamethoxazole. Comparison of the results with the literature showed inconsistent results between studies using comparable, environmentally relevant, concentrations. Therefore, our study highlights the importance of testing the ecological impacts of pharmaceuticals (such as sulfamethoxazole) across multiple trophic levels spanning multiple aquatic communities, to fully understand its potential ecological threats.

We apply a tracer model linked with a 3D circulation model to simulate transport and fate of water-soluble persistent substances in the Black Sea that do not bioaccumulate to a considerable extent. The model uses specified degradation time and identical concentrations in the rivers to build a correlation between average concentration in the basin and half-life (DT50). The average concentration in certain sub-regions of the Black Sea can be estimated using an exponential dependence of DT50, if DT50 and concentration in rivers are known. Averaging is performed on the simulations from 2000 to 2019 with real atmospheric forcing and river runoff. A well-defined seasonal cycle is evident for the average shelf concentration, while the average concentration in the deep region does not show a pronounced seasonal cycle or inter-annual variations. With the help of the existing observational data, we estimate DT50 and concentration in the rivers for carbamazepine, sulfamethoxazole and terbuthylazine. Atrazine and simazine are believed to have accumulated in the basin for a long time due to their widespread use in the past and the slow rate of degradation in the marine environment.

The negative impact of antibiotic pollution on the agricultural system and human health is a hot issue in the world. However, little information is available on the antibiotics toxicity mechanism and the role of silicon (Si) to alleviate the antibiotics toxicity. In this study, strawberry (Fragaria ananassa) showed excitatory response to low-dose SMZ (1 mg L⁻¹), but strawberry root and photosynthetic efficiency were damaged under high level. When SMZ level exceeded 10 mg L⁻¹, H₂0₂, O₂⁻, MDA and relative conductivity increased, while SOD and CAT activities first increased and then decreased. SMZ accumulated more in roots and fruits, but less in stems, and the accumulation increased with the increase of SMZ-dose. Under 1 mg L⁻¹ SMZ, the SMZ accumulation in fruits was 110.54 μg kg⁻¹, which exceeded the maximum residue limit. SMZ can induce the expression of sul1, sul2 and intI1, and intI1 had the highest abundance. Exogenous application of Si alleviated the toxicity of SMZ, which is mainly related to the degradation of SMZ in soil and the reduction of SMZ absorption by strawberry. In addition, Si relieved root damage, promoted the increase of photosynthetic efficiency, and improved the antioxidant system to resist SMZ toxicity.

Aquatic pollution from emerging organic contaminants (EOCs) is of key environmental importance in India and globally, particularly due to concerns of antimicrobial resistance, ecotoxicity and drinking water supply vulnerability. Here, using a broad screening approach, we characterize the composition and distribution of EOCs in groundwater in the Gangetic Plain around Patna (Bihar), as an exemplar of a rapidly developing urban area in northern India. A total of 73 EOCs were detected in 51 samples, typically at ng.L⁻¹ to low μg.L⁻¹ concentrations, relating to medical and veterinary, agrochemical, industrial and lifestyle usage. Concentrations were often dominated by the lifestyle chemical and artificial sweetener sucralose. Seventeen identified EOCs are flagged as priority compounds by the European Commission, World Health Organisation and/or World Organisation for Animal Health: namely, herbicides diuron and atrazine; insecticides imidacloprid, thiamethoxam, clothianidin and acetamiprid; the surfactant perfluorooctane sulfonate (and related perfluorobutane sulfonate, perfluorohexane sulfonate, perfluorooctanoic acid and perfluoropentane sulfonate); and medical/veterinary compounds sulfamethoxazole, sulfanilamide, dapson, sulfathiazole, sulfamethazine and diclofenac. The spatial distribution of EOCs varies widely, with concentrations declining with depth, consistent with a strong dominant vertical flow control. Groundwater EOC concentrations in Patna were found to peak within ∼10 km distance from the River Ganges, indicating mainly urban inputs with some local pollution hotspots. A heterogeneous relationship between EOCs and population density likely reflects confounding factors including varying input types and controls (e.g. spatial, temporal), wastewater treatment infrastructure and groundwater abstraction. Strong seasonal agreement in EOC concentrations was observed. Co-existence of limited transformation products with associated parent compounds indicate active microbial degradation processes. This study characterizes key controls on the distribution of groundwater EOCs across the urban to rural transition near Patna, as a rapidly developing Indian city, and contributes to the wider understanding of the vulnerability of shallow groundwater to surface-derived contamination in similar environments.

Constructed wetlands integrated with microbial fuel cells (MFC-CWs) have been recently developed and tested for removing antibiotics. However, the effects of carbon source availability, electron transfer flux and cathode conditions on antibiotics removal in MFC-CWs through co-metabolism remained unclear. In this study, four experiments were conducted in MFC-CW microcosms to investigate the influence of carbon source species and concentrations, external resistance and aeration duration on sulfamethoxazole (SMX) and tetracycline (TC) removal and bioelectricity generation performance. MFC-CWs supplied with glucose as carbon source outperformed other carbon sources, and moderate influent glucose concentration (200 mg L⁻¹) resulted in the best removal of both SMX and TC. Highest removal percentages of SMX (99.4%) and TC (97.8%) were obtained in MFC-CWs with the external resistance of 700 Ω compared to other external resistance treatments. SMX and TC removal percentages in MFC-CWs were improved by 4.98% and 4.34%, respectively, by increasing the aeration duration to 12 h compared to no aeration. For bioelectricity generation performance, glucose outperformed sodium acetate, sucrose and starch, with the highest voltages of 386 ± 20 mV, maximum power density (MPD) of 123.43 mW m⁻³, and coulombic efficiency (CE) of 0.273%. Increasing carbon source concentrations from 100 to 400 mg L⁻¹, significantly (p < 0.05) increased the voltage and MPD, but decreased the internal resistance and CE. The highest MPD was obtained when the external resistance (700 Ω) was close to the internal resistance (600.11 Ω). Aeration not only improved the voltage and MPD, but also reduced the internal resistance. This study demonstrates that carbon source species and concentrations, external resistances and aeration duration, all play vital roles in regulating SMX and TC removal in MFC-CWs.

A paradoxical impact of high rates of production and consumption of antibiotics is their widespread release in the environment. Consequently, low concentrations of antibiotics and their byproducts have been routinely identified from various environmental settings especially from aquatic environments. However, the impact of such low concentrations of antibiotics on the exposed host especially in early life remains poorly understood. We exposed zebrafish to two different environmental concentrations of oxytetracycline and sulfamethoxazole, from larval stage to adulthood (∼120 days) and characterized their impact on the taxonomic diversity, antibiotic resistance genes, and metabolic pathways of the gut microbiome using metagenomic shotgun sequencing and analysis. Long term exposure of environmental concentrations of oxytetracycline and sulfamethoxazole significantly impacted the taxonomic composition and metabolic pathways of zebrafish gut microbiome. The antibiotic exposed samples exhibited significant enrichment of multiple flavobacterial species, including Flavobacterium sp. F52, Flavobacterium johnsoniae and Flavobacterium sp. Fl, which are well known pathogenic bacteria. The relative abundance of antibiotic resistance genes, especially several tetratcycline and sulfonamide resistance genes were significantly higher in the exposed samples and showed a linear correlation with the antibiotic concentrations. Furthermore, several metabolic pathways, including folate biosynthesis, oxidative phosphorylation, and biotin metabolism pathways, showed significant enrichment in the antibiotic exposed samples. Collectively, our results suggest that early life exposure of the environmental concentrations of antibiotics can increase the abundance of unfavorable bacteria, antibiotic resistance genes and associated pathways in the gut microbiome of zebrafish.

A three-dimensional hydrodynamic-antibiotic model is developed to investigate the transport and dilution of sulfamethoxazole (SMX) in the Upper Gulf of Thailand (UGoT). The simulation produced a spatially averaged annual mean SMX concentration of 0.58 μgm−3, which varied slightly between seasons assuming a temporally constant river SMX loading observed in August. In contrast, the horizontal distribution of SMX concentrations strongly varied with season because of the changing residual currents. In addition, SMX is diluted to concentrations lower than 10% of those in river waters a short distance offshore of the estuaries. To better understand this behavior, we examined the relationship between salinity and SMX concentrations in the UGoT. The annual budget demonstrates that 98% of SMX in the UGoT is removed by natural decomposition. As the concentrations of fluvial pollutants in the UGoT depend on their river loading and decomposition rates, functions were derived to predict pollutant concentrations and flushing times based on the river input flux and half-life.

Recently, the widespread use of antibiotic has raised concerns about the potential health risks associated with their microbiological effect. In the present study, we investigated 990 elderly individuals (age ≥ 60 years) from the Cohort of Elderly Health and Environment Controllable Factors in West Anhui, China. A total of 45 representative antibiotics and two antibiotic metabolites were monitored in urine samples through liquid chromatography electrospray tandem mass spectrometry. The results revealed that 34 antibiotics were detected in 93.0% of all urine samples and the detection frequencies of each antibiotic varied between 0.2% and 35.5%. The overall detection frequencies of seven human antibiotics (HAs), 10 veterinary antibiotics (VAs), three antibiotics preferred as HAs (PHAs), and 14 preferred as VAs (PVAs) in urines were 27.4%, 62.9%, 30.9% and 72.7%, respectively. Notably, the samples with concentrations of six PVAs (sulfamethoxazole, trimethoprim, oxytetracycline, danofloxacin, norfloxacin and lincomycin) above 5000 ng/mL accounted for 1.7% of all urine samples. Additionally, in 62.7% of urine samples, the total antibiotic concentration was in the range of the limits of detection to 20.0 ng/mL. Furthermore, the elderly individuals with the sum of estimated daily intakes of VAs and PVAs more than 1 μg/kg/day accounted for 15.2% of all participants, and a health risk related to change in gut microbiota under antibiotic stimulation was expected in 6.7% of the elderly individuals. Especially, ciprofloxacin was the foremost contributor to the health risk, and its hazard quotient value was more than one in 3.5% of all subjects. Taken together, the elderly Chinese people were extensively exposed to VAs, and some elderly individuals may have a health risk associated with dysbiosis of the gut microbiota.

Pharmaceutically active compounds (PhACs) are widely found in the environment due to vast human consumption. Lots of work has been devoted to investigating the occurrence and seasonal variations globally. To fully understand characteristics and cross-year variation of PhACs in Beijing, 35 PhACs were analyzed in 46 sites across Beijing from both urban and suburban areas. Concentrations of target PhACs were ranged from levels of ng L⁻¹ to μg L⁻¹. Metoprolol (524 ng L⁻¹), caffeine (390 ng L⁻¹) and acetaminophen (156 ng L⁻¹) were the three most abundant non-antibiotics with the highest median concentration, and nalidixic acid (135 ng L⁻¹), erythromycin (64 ng L⁻¹) and sulfamethoxazole (77 ng L⁻¹) were the most abundant antibiotics. Urban and suburban areas are distinguished by PhAC composition in cluster analysis due to different wastewater collection rate. The ratio of easily removable compound group and hardly removable group was then proposed to reflect the wastewater collection rate. The compositional comparison of PhACs in WWTPs’ effluents and their receiving rivers further illustrates the impact of WWTPs in urban area. Higher proportion of antibiotics (>30%) in suburban area reflected the impact of presence of livestock farms, which should be concerned. Further statistical analyses show an improving trend of wastewater collection rate, and excluding metoprolol, an anti-hypertension medicine, the total concentration of 13 target PhACs was reduced by 72% during 2013–2017.