Comprehensive study on the potential environmental risk of temporal antibiotic usage through wastewater discharges

Occurrence, Removal, and Risk Assessment of Antimicrobials and Their Transformation Products in Effluent from Australian Wastewater Treatment Plants

Despite Australia's high antimicrobial use, their residues in wastewater and their impacts on receiving waters remain largely unknown. This study assessed the occurrence, removal, and risk for antimicrobial resistance (AMR) of 102 antimicrobial substances and selected transformation products (TPs) in wastewater effluent from 47 wastewater treatment plants (WWTPs) across Australia. Thirty-two antimicrobials and 13 TPs were detected, with 14 analytes occurring at >80% frequencies. Ampicillin, penicillin V, penicilloic V acid, fluconazole, and tazobactam M1 were observed with high median concentrations of >0.2 μg/L. Collectively, the WWTPs released 5.4 kg/day or 0.54 g/day/1000 inhabitants of antimicrobials/TPs into natural waters, with β-lactams, quinolones, nitroimidazoles/azoles, and sulfonamides comprising high volumes, which was correlated with the population's socioeconomic statuses. Thirty-seven analytes were removed at rates >80% post-treatment, whereas quinolones, nitroimidazoles/azoles, lincosamides, and macrolide TPs were observed with poor removal efficiencies, which were affected by treatment processes and regional climate. Comparing measured concentrations with the predicted no-effect concentrations for AMR selection (PNECAMR), 7 antimicrobials exerted selection risk for resistant bacteria. Concerningly, ciprofloxacin posed medium/high risk in most of the assessed WWTPs. The accumulative effects of antimicrobial classes and certain TPs might further aggravate adverse impacts on AMR development. Our study provides insights into the presence and AMR implications of antimicrobials in treated wastewater, aiming to safeguard public health and ecosystems.

Integrated ecological-health risk assessment of ofloxacin

Antibiotics are emerging contaminants of significant concern, while previous research has mostly focused on their ecological or health impacts in isolation. This limited systematic research on its overall risk and the uncertainty relating to the risk evaluation is also unclear. This study addressed this gap by examining both ecological or health impacts by integrating interspecies correlation models, species sensitivity distribution curves, and health risk evaluation. Then comprehensive risk of antibiotics was calculated using economic approaches. The Wenyu River basin in China and ofloxacin were chosen as the study area and target antibiotic, respectively. The results indicate that both the ecological and health risk quotients for ofloxacin were manageable, and the level of urbanization was found to correlate with increased antibiotic risk. The economic impact on population health was greater than on ecosystems. The presence of ofloxacin in the watershed still resulted in more than $200,000 in annual economic losses, affecting both human society and the ecosystem. The assessment process, including the evaluation object, extrapolated data, and fitted curves, contributed to uncertainty in the results. These findings provide valuable insights for addressing the challenges in assessing the risks of antibiotics, emphasizing the need for integrated assessment frameworks.

Environmental and toxicological aspects of sulfamethoxazole photodegradation in the presence of oxidizing agents

Sulfamethoxazole (SMX) is a popular active substance, which is extensively applied to treat bacterial infections in humans and animals. Due to its widespread use, SMX enters the natural environment, where it can undergo degradation. Similarly to other emerging contaminants, SMX photodegradation and the use of oxidants in wastewater treatment processes can lead to the formation of potentially adverse transformation products for ecosystems. This study investigated the efficiency of SMX photodegradation in the presence of oxidizing agents (H2O2 and Fenton reagent). The potential environmental consequences of degradation product formation were analyzed based on experimental toxicity characterization. Standardized tests employing diverse organisms were utilized: Alivibrio fischeri (Microtox®), Daphnia magna (Daphtoxkit F®), and Lemna minor (Lemna sp. GIT). The potential environmental impact of the products identified in the reaction mixtures was evaluated using parameters describing aqueous solubility, hydrophobicity, toxicity, bioconcentration, persistence, and mobility. The analysis revealed that photodegradation produces transformation products with higher toxicity than SMX, as confirmed by in vitro tests of the reaction mixtures. Most of the detected compounds were found to have low mobility potential. The formation rates of key environmentally relevant transformation products, such as 1,4-benzoquinone, aniline, and phenol, were also discussed. The changes in total organic carbon (TOC) affected by photodegradation under the influence of the considered oxidizing agents were characterized.

Comprehensive analysis and risk assessment of Antibiotic contaminants, antibiotic-resistant bacteria, and resistance genes: Patterns, drivers, and implications in the Songliao Basin

The pervasive use of antibiotics has raised substantial environmental concerns, especially regarding their temporal and spatial distribution across diverse water systems. This study addressed the gap in comprehensive research on antibiotic contamination during different hydrological periods, focusing on the Jilin section of the Songliao Basin in Northeast China, an area with severe winter ice cover. The study examined the occurrence, distribution, influencing factors, and potential ecological risks of prevalent antibiotic contaminants. Findings revealed antibiotic concentrations ranging from 239.64 to 965.81 ng/L, with antibiotic resistance genes (ARGs) at 5.22 × 10-2 16S rRNA-1 and antibiotic-resistant bacteria (ARB) up to 5.76 log10 CFU/mL. Ecological risk assessments identified significant risks to algae from oxytetracycline, erythromycin, and amoxicillin. Redundancy analysis and co-occurrence networks with ordinary least squares (OLS) demonstrated that the dispersion of ARGs and ARB is significantly influenced by environmental factors such as total organic carbon (TOC), total phosphorus (TP), total nitrogen (TN), fluoride (F⁻), and nitrate (NO₃⁻). These elements, along with mobile genetic elements (MGEs), play crucial roles in ARG patterns (R2 = 0.94, p ≤ 0.01). This investigation offers foundational insights into antibiotic pollution dynamics in cold climates, supporting the development of targeted mitigation strategies for aquatic systems.

Enhanced Degradation of Norfloxacin Under Visible Light by S-Scheme Fe2O3/g-C3N4 Heterojunctions

S-scheme Fe2O3/g-C3N4 heterojunctions were successfully fabricated by the ultrasonic assistance method to remove norfloxacin (NOR) under visible light irradiation. The synthesized catalysts were well studied through various techniques. The obtained Fe2O3/g-C3N4 heterojunctions exhibited an optimal photocatalytic degradation of 94.7% for NOR, which was 1.67 and 1.28 times higher than using Fe2O3 and g-C3N4 alone, respectively. In addition, the kinetic constant of NOR removal with Fe2O3/g-C3N4 composites was about 0.6631 h-1, and NOR photo-deegradation was still 86.7% after four cycles. The enhanced photocatalytic activity may be mainly attributed to the formation of S-scheme Fe2O3/g-C3N4 heterojunctions with built-in electric fields, which were beneficial to the separation and transfer of photostimulated charge carriers. Furthermore, a possible photo-degradation mechanism of NOR for S-scheme Fe2O3/g-C3N4 heterojunctions is described.

Occurrence of emerging contaminants in three river basins impacted by wastewater treatment plant effluents: Spatio-seasonal patterns and environmental risk assessment

The concern on the fate and distribution of contaminants of emerging concern (CECs) is a burning topic due to their widespread occurrence and potential harmful effects. Particularly, antibiotics have received great attention due to their implications in antimicrobial resistance occurrence. The impact of wastewater treatment plants (WWTP) is remarkable, being one of the main pathways for the introduction of CECs into aquatic systems. The combination of novel analytical methodologies and risk assessment strategies is a promising tool to find out environmentally relevant compounds posing major concerns in freshwater ecosystems impacted by those wastewater effluents. Within this context, a multi-target approach was applied in three Spanish river basins affected by different WWTP treated effluents for spatio-temporal monitoring of their chemical status. Solid phase extraction followed by ultra-high-performance liquid chromatography were used for the quantification of a large panel of compounds (n = 270), including pharmaceuticals and other consumer products, pesticides and industrial chemicals. To this end, water samples were collected in four sampling campaigns at three locations in each basin: (i) upstream from the WWTPs; (ii) WWTP effluent discharge points (effluent outfall); and (iii) downstream from the WWTPs (500 m downriver from the effluent outfall). Likewise, 24-h composite effluent samples from each of the WWTPs were provided in all sampling periods. First the occurrence and distribution of these compounds were assessed. Diverse seasonal trends were observed depending on the group of emerging compounds, though COVID-19 outbreak affected variations of certain pharmaceuticals. Detection frequencies and concentrations in effluents generally exceeded those in river samples and concentrations measured upstream WWTPs were generally low or non-quantifiable. Finally, risks associated with maximum contamination levels were evaluated using two different approaches to account for antibiotic resistance selection as well. From all studied compounds, 89 evidenced environmental risk on at least one occasion in this study.

Norfloxacin affects inorganic nitrogen compound transformation in tailwater containing Corbicula fluminea

The Asian clam, Corbicula fluminea, commonly used in engineered wetlands receiving tailwater, affects nitrogen compound transformation in water. This study investigates how a commonly observed antibiotic in tailwater, norfloxacin, impact nitrogen compound transformation in tailwater containing C. fluminea. The clam was exposed to artificial tailwater with norfloxacin (0, 0.2, 20, and 2000 μg/L) for 15 days. Water properties, C. fluminea ecotoxicity responses, microorganism composition and nitrification- or denitrification-related enzyme activities were measured. Results revealed norfloxacin-induced increases and reductions in tailwater NH4+ and NO2- concentrations, respectively, along with antioxidant system inhibition, organ histopathological damage and disruption of water filtering and digestion system. Microorganism composition, especially biodiversity indices, varied with medium (clam organs and exposure water) and norfloxacin concentrations. Norfloxacin reduced NO2- content by lowering the ratio between microbial nitrifying enzyme (decreased hydroxylamine oxidoreductase and nitrite oxidoreductase activity) and denitrifying enzyme (increased nitrate reductase and nitrite reductase activity) in tailwater. Elevated NH4+ content resulted from upregulated ammonification and inhibited nitrification of microorganisms in tailwater, as well as increased ammonia emission from C. fluminea due to organ damage and metabolic disruption of the digestion system. Overall, this study offers insights into using benthic organisms to treat tailwater with antibiotic residues, especially regarding nitrogen treatment.

Antibiotic Residues and Resistance in Three Wastewater Treatment Plants in Romania

This study evaluates antibiotic residues and bacterial loads in influent and effluent samples from three wastewater treatment plants (WWTPs) in Romania, across four seasons from 2021 to 2022. Analytical methods included solid-phase extraction and high-performance liquid chromatography (HPLC) to quantify antibiotic concentrations, while microbiological assays estimated bacterial loads and assessed antibiotic resistance patterns. Statistical analyses explored the impact of environmental factors such as temperature and rainfall on antibiotic levels. The results showed significant seasonal variations, with higher antibiotic concentrations in warmer seasons. Antibiotic removal efficiency varied among WWTPs, with some antibiotics being effectively removed and others persisting in the effluent, posing high environmental risks and potential for antibiotic resistance development. Bacterial loads were higher in spring and summer, correlating with increased temperatures. Eight bacterial strains were isolated, with higher resistance during warmer seasons, particularly to amoxicillin and clarithromycin.

Understanding associations between antimicrobial agents usage and antimicrobial resistance genes prevalence at the community level using wastewater-based epidemiology: A Spanish pilot study

Understanding the development and spread of antimicrobial resistance (AMR) is important for combating this global threat for public health. Wastewater-based epidemiology (WBE) is a complementary approach to current surveillance programs that minimizes some of the existing limitations. The aim of the present study is to explore WBE for monitoring antibiotics and antibiotic resistance genes (ARGs) in wastewater samples collected during 2021/2022 from the city of Castellon (Spain). Eighteen commonly prescribed antibiotics have been selected and measured by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), with triple quadrupole mass analysers. Moreover, qPCR for specific ARGs has been performed to obtain information of these genes in co-presence with antibiotics. All selected ARGs, along with a total of 11 antibiotics, were identified. The highest population-normalized daily loads were observed for the macrolide azithromycin, followed by the quinolones ciprofloxacin and levofloxacin. Subsequently, daily consumption estimates based on wastewater data were compared with prescription data of antibiotics. Statistical analyses were conducted to explore if there is correlation between antibiotics and ARGs. While no correlations were found between antibiotics and their corresponding ARGs, certain correlations (p < 0.05) were identified among non-corresponding ARGs. In addition, a strong positive correlation was found between the sum of all antibiotics and the intl1 gene. Moreover, population-normalized ARG loads significantly correlate with the 16S rRNA-normalized ARG loads, serving as an indicator for population size. Results provide a baseline for future work and a proof-of-concept emphasising the need for future work and long-term surveillance, and highlight the need of similar programs at a regional and global levels worldwide.

An evaluation of conventional and nature-based technologies for controlling antibiotic-resistant bacteria and antibiotic-resistant genes in wastewater treatment plants

Antibiotic resistance is a globally recognized health concern which leads to longer hospital stays, increased morbidity, increased mortality, and higher medical costs. Understanding how antibiotic resistance persists and exchanges in environmental systems like soil, water, and wastewater are critically important for understanding the emergence of pathogens with new resistance profiles and the subsequent exposure of people who indirectly/directly come in contact with these pathogens. There are concerns about the widespread application of prophylactic antibiotics in the clinical and agriculture sectors, as well as chemicals/detergents used in food and manufacturing industries, especially the quaternary ammonium compounds which have been found responsible for the generation of resistant genes in water and soil. The rates of horizontal gene transfer increase where there is a lack of proper water/wastewater infrastructure, high antibiotic manufacturing industries, or endpoint users - such as hospitals and intensive agriculture. Conventional wastewater treatment technologies are often inefficient in the reduction of ARB/ARGs and provide the perfect combination of conditions for the development of antibiotic resistance. The wastewater discharged from municipal facilities may therefore be enriched with bacterial communities/pathogens and provide a suitable environment (due to the presence of nutrients and other pollutants) to enhance the transfer of antibiotic resistance. However, facilities with tertiary treatment (either traditional/emerging technologies) provide higher rates of reduction. This review provides a synthesis of the current understanding of wastewater treatment and antibiotic resistance, examining the drivers that may accelerate their possible transmission to a different environment, and highlighting the need for tertiary technologies used in treatment plants for the reduction of resistant bacteria/genes.