Chemical Fate and Partitioning Behavior of Antibiotics in the Aquatic Environment-A Review.

Antibiotics in the aquatic environment is a major problem because of the emergence of antibiotic resistance. The long-term ecological impact on the aquatic environment is unknown. Many sources allow entry of antibiotics into the environment, including wastewater-treatment plants (WWTPs), agricultural runoff, hospital effluent, and landfill leachate. Concentrations of antibiotics in the aquatic environment vary significantly; studies have shown fluoroquinolones, tetracycline, macrolides, sulfonamides, and penicillins to reach 2900, 1500, 9700, 21 400, and 1600 ng L-1 in wastewater effluent samples, respectively. However, concentrations are highly variable between different countries and depend on several factors including seasonal variation, prescription, and WWTP operating procedures. Likewise, the reported concentrations that cause environmental effects vary greatly between antibiotics, even within the same class; however, this predicted concentration for the antibiotics considered was frequently <1000 ngL-1 , indicating that when discharged into the environment along with treated effluent, these antibiotics have a potentially detrimental effect on the environment. Antibiotics are generally quite hydrophilic in nature; however, they can ionize in the aquatic environment to form charged structures, such as cations, zwitterions, and anions. Certain classes, particularly fluoroquinolones and tetracyclines, can adsorb onto solid matrices, including soils, sediment, and sludge, making it difficult to fully understand their chemical fate in the aquatic environment. The adsorption coefficient (Kd ) varies between different classes of antibiotics, with tetracyclines and fluoroquinolones showing the highest Kd values. The Kd values for fluoroquinolones, tetracyclines, macrolides, and sulfonamides have been reported as 54 600, 7600, 130, and 1.37 L kg-1 , respectively. Factors such as pH of the environment, solid matrix (sediment/soil sludge), and ionic strength can influence the Kd ; therefore, several values exist in literature for the same compound. Environ Toxicol Chem 2021;40:3275-3298. © 2021 SETAC.

Effect of eight common Brazilian drugs on Lemna minor and Salvinia auriculata growth.

The growth of two species of macrophytes (Lemna minor and Salvinia auriculata) under the effect of a mixture of amoxicillin, caffeine, carbamazepine, dipyrone, ibuprofen, losartan, omeprazole, and tenivastatin was investigated by bioassay. Three concentration levels were utilized in this study (10, 200, and 500 µg L-1) using a growth inhibition test based on the OECD 221/2006 guidelines. The frond number, total area, and chlorophyll a level were selected as suitable end points. For L. minor, at all concentrations, a significant difference in the total frond number was observed and the growth inhibition varied from 30 to 70% at the low and high concentrations, respectively. No significant growth change was observed to S. auriculata exposed to the mixture of drugs. Thus, individual drug tests were performed for L. minor which demonstrated stimulation in growth, when exposed to most drugs individually, except tenivastatin which was identified as the drug responsible for the significant growth inhibition seen in the mixture. The L. minor enhanced growth was probably caused by N molecule transformation to ammonium and nitrate, essential nutrients for plants.

Amoxicillin removal by pre-denitrification membrane bioreactor (A/O-MBR): Performance evaluation, degradation by-products, and antibiotic resistant bacteria.

Membrane bioreactors (MBRs) are one of the treatment technologies with the potential to remove emerging compounds from wastewater. The present work evaluated the efficiency of an MBR pilot system in removing amoxicillin from synthetic wastewater using a continuous flow pre-denitrification MBR (A/O-MBR) pilot unit. The system operated in three phases: (1) synthetic wastewater and hydraulic retention time (HRT) of 40 h; (2) adding amoxicillin 100 µg L-1 to the influent, and (3) varying flowrate to HRT of 20 h. Liquid chromatography coupled to high resolution mass spectrometry analysis confirmed the presence of five amoxicillin degradation by-products in the effluent. The addition of amoxicillin did not affect chemical oxygen demand (COD) or dissolved organic carbon (DOC) removal efficiencies. Respirometry showed that amoxicillin level did not inhibit heterotrophic bacteria metabolism. The change in HRT reduced the DOC removal (from 84% to 66%) but did not influence COD (>94%) or total nitrogen (>72%). The amoxicillin and by-products removal decreased from 80% to 54% with HRT change. Adsorption and biodegradation represented the largest removed fraction of the antibiotic in the A/O-MBR system (68%). Ecotoxicity assays showed P. fluorescens was more resistant and E. coli less resistant to amoxicillin residues at effluent sample matrix.

Mechanistic and ecotoxicological studies of amoxicillin removal through anaerobic degradation systems.

Many studies have been conducted on the evaluation and monitoring of micropollutants and by-products in wastewater treatment plants. Considering the increase in the production and consumption of emerging contaminants, such as drugs, personal care products, and plasticisers, it is necessary to conduct studies that support the elaboration of laws and regulations that promote the environmentally sustainable use of sludge and effluents. In this work, the biological degradation of amoxicillin was studied under two anaerobic conditions: i) using a 6 L reactor operated under semi-continuous flow; and ii) a batch system with 100 mL sealed glass syringes. According to the statistical analysis, amoxicillin was completely removed from the systems, but biogas production inhibition was observed (p < 0.05). Liquid chromatography-high-resolution mass spectrometry analysis identified amoxicillin penicilloic acid, amoxilloic acid, amoxicillin diketopiperazine and phenol hydroxypyrazine as by-products under anaerobic conditions. Ecotoxicity tests on effluent treated under the batch conditions showed that the addition of higher amounts of amoxicillin inhibited the target species Aliivibrio fischeri and Raphidocelis subcaptata, causing functional decreases of 28.5% and 22.2% when the antibiotic concentration was 2500 µg L-1. A. fischeri was the most sensitive organism to effluent treated under semi-continuous flow conditions; a continuous reduction in bioluminescence of up to 88.8% was observed after 39 days of feeding, which was associated with by-products accumulation due to unbalanced conditions during anaerobic digestion. Changes in the physico-chemical characteristics of the effluent caused the accumulation and removal of AMX-DKP IV and modified the toxicity to Lactuca sativa and R. subcapitata.

Ranking prescribed pharmaceuticals in terms of environmental risk: Inclusion of hospital data and the importance of regular review.

A newly available dataset on pharmaceuticals used in Scottish hospitals enabled an environmental risk assessment that includes hospital consumption of pharmaceuticals, as previous United Kingdom rankings have been based on community prescriptions only. Although health and the environment are devolved issues for the Scottish government, it is merited to consider a Scottish ranking separately; regional differentiation is particularly relevant in the spatial context of the European Commission's Water Framework Directive. Nine pharmaceuticals are identified as having a risk quotient greater than 1. Four of these, the antibacterials piperacillin, tazobactam, flucloxacillin, and ciprofloxacin, had high hospital contributions and had not been highlighted previously in rankings based on community prescriptions. Some drugs with a risk quotient < 0.1 are used almost exclusively in hospitals and could be more concentrated near effluents carrying hospital wastewater, where they may be of local concern. Although treating hospital effluents separately is a policy option, specifically including hospital consumption is important. Continually increasing the availability of ecotoxicological data and trends in consumption further contributes to a substantially different prioritization than in previous rankings. This leads the authors to conclude that regular review of risk is necessary.