Fate of drugs during wastewater treatment

Application of the HPLC-ELSD technique for the determination of major metabolites of ibuprofen and creatinine in human urine

The report presents robust and high throughput methods, based on liquid chromatography coupled with evaporative light scattering detection (HPLC-ELSD), for the simultaneous determination of major metabolites of ibuprofen (IBU), namely 2-hydroxyibuprofen and carboxyibuprofen (method A) as well as creatinine (Crn) (method B) in human urine. The assays primarily involve straightforward sample purification. For both methods, the chromatographic separation of the analytes is achieved within 8 min at room temperature on Poroshell 120 SB-C18 (75 × 4.6 mm, 2.7 µm) column using gradient elution. The eluents consisted of 0.1% formic acid in water and acetonitrile (method A) or water and methanol (method B) delivered at a flow rate of 1 or 0.5 mL/min, respectively. In relation to metabolites of IBU, the assay linearity was observed within 0.06-0.5 g/L in urine, while the Crn assay linearity was demonstrated within 0.5-30 mmol/L in urine. The limit of quantification for IBU metabolites was determined to be 0.06 g/L, and 0.5 mmol/L for Crn. These methods were successfully applied to urine samples delivered by ten apparently healthy donors showing that the HPLC-ELSD assays are suitable for human urine screening.

Management of hazardous fly-ash energy waste in the adsorptive removal of diclofenac by the use of synthetic zeolitic materials

Zeolite-carbon composites (Na-P1(C), Na-X(C)) and pure zeolites (Na-P1, Na-X) were synthesized from hazardous high-carbon fly ash waste (HC FA) via hydrothermal reaction with sodium hydroxide (NaOH). These solids were applied in the removal of diclofenac (DCF) from aqueous solution, with and without poly(acrylic acid) (PAA). The experiments included adsorption-desorption measurements, as well as electrokinetic and stability analyses. The obtained results showed that HC FA and Na-P1(C) had the greatest adsorption capacity towards DCF, i.e., 26.51 and 21.19 mg/g, respectively. PAA caused considerable decrease in the DCF adsorption due to the competition of both adsorbates of anionic character for active sites. For example, the adsorbed amount of DCF on Na-P1 without PAA was 14.11 mg/g, whereas the one measured with PAA was 5.08 mg/g. Most of prepared solids were effectively regenerated by the use of NaOH. Desorption degree reached even 73.65% in the single systems (with one adsorbate) and 97.24% in the mixed ones (with two adsorbates). Zeolitic materials formed suspensions of rather low stability, which underwent further deterioration in the organic molecules presence. All the results obtained in this study indicated that HC FA can be successfully managed in the removal of organic substances.

From the pills to environment - Prediction and tracking of non-steroidal anti-inflammatory drug concentrations in wastewater

The extend of environment pollution by pharmaceuticals is in a stage that required more automatic and integrated solutions. The non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most popular pharmaceutical in the world and emerging pollutants of natural waters. The aim of the paper was to check the correlation of the sales data of selected NSAIDs (ibuprofen, naproxen, diclofenac) and their concentration in the WWTP in order to enable predicting their loads, having only the sales data. For calculations, we apply three discharge scenarios (the fates between purchased to the presence in influents), having in mind that some part of sold mass can be improperly dispose to sewage system. To support predictions, chemical analysis was conducted in two conventional wastewater treatment plants (WWTPs) located in Poland during 2018 and 2020, thereby before and during pandemic situation. The NSAIDs concentration in the influent was higher than that which would be obtained if all of the administrated mass of the pharmaceutical went through the metabolic pathway of transformation. This means that substantial mass of sold NSAIDs in improperly dispose to sewage system, and this factor need to be taken into account in future predictions. Furthermore, results indicate that the variance of naproxen and diclofenac concentrations in the influent has no correlation with relatively stable sales throughout whole year. The pandemic situation had yet no direct effect to diclofenac concentrations in influents, despite observed increasing of sales. It was calculated that more than 60 kg of diclofenac was discharged into the Baltic Sea in 2018, and 20 kg in the first half of 2021 from two tested WWTPs. The presence of 4OH-diclofenac in effluents often in higher concentration compared to diclofenac mean that this still biologically active compound need to be taken into account in future risk assessment.

Assessment of the occurrence of 455 pharmaceutical compounds in sludge according to their physical and chemical properties: A review

Sludge agronomical reuse is of major interest due to the beneficial contribution of nutrients. However, it implies the introduction of unregulated pharmaceuticals into amended-soils and creates a controversial issue about sludge management. To limit their dissemination, it is essential to identify the compounds of interest and understand their attenuation mechanisms through the sludge processes. This paper summarizes the knowledge on 455 investigated pharmaceuticals among 32 therapeutical categories in amendable sludge matrices. It contributes to enlarging the list of commonly quantified compounds to 305 residues including 84 additional compounds compared to previous reviews. It highlights that sorption appears as the main mechanism controlling the occurrence of pharmaceuticals in sludge matrices and shows the considerable residual levels of pharmaceuticals reaching several mg/kg in dry weight. Antibiotics, stimulants, and antidepressants show the highest concentrations up to 232 mg/kg, while diuretics, anti-anxieties or anticoagulants present the lowest concentrations reaching up to 686 µg/kg. Collected data show the increase in investigated compounds as antifungals or antihistamines, and underline emerging categories like antidiabetics, antivirals, or antiarrhythmics. The in-depth analysis of the substantial database guides onto the pharmaceuticals that are the most likely to occur in these amendable matrices to assist future research.

Adsorption and desorption of antiviral drugs (ritonavir and lopinavir) on sewage sludges as a potential environmental risk

The aim of this work was to evaluate the adsorption capacity and mechanism of two antiviral drugs AVDs (lopinavir (LOP) and ritonavir (RIT)) on three various sewage sludges (SSLs). The results showed that SSLs differed in the structure and chemical composition and LOP and RIT had a high affinity to the studied SSLs (K_d in ranges 2076-3449 L/kg). The adsorption capacities differed between SSLs and ranged 7.55-8.71 mg/g (RIT) and 8.10-8.64 mg/g (LOP). The Freundlich model provided a best fitting of adsorption isotherms of all AVDs-SSLs. The adsorption kinetics were best described by pseudo-second order kinetic model. The adsorption of LOP and RIT on SSLs was exothermic, spontaneous, and thermodynamically feasible. The sorption of LOP and RIT to SSLs was complex due to the diverse chemical composition of SSLs and the differences in the chemical structure of AVDs. Analysis of binary solution of both AVDs showed the competition effect between AVDs and a decrease in adsorption efficiency (3-17%) compared to single solutions. The amount of desorbed AVDs from all SSLs was low (less than 15%). The findings of the present work are significant in the prediction of fate and persistence of AVDs on SSLs in the context of their further transmission and possible environmental contamination.

Solar light-driven photocatalytic degradation and mineralization of beta blockers propranolol and atenolol by carbon dot/TiO2 composite

Herein improved solar light-driven photocatalytic degradation and mineralization of two emerging pollutants as well as recalcitrant beta blockers propranolol (PR) and atenolol (AT) have been demonstrated by metal-free carbon dot/TiO₂ (CDT) composite. Hydrothermally synthesized TiO₂ has been decorated with electrochemically synthesized carbon dots (CDs) and was well characterized by various analytical techniques viz. XRD, FTIR, Raman, XPS, UV-visible DRS, FESEM, and TEM. The optimized CDT composite, 2CDT (2 mL carbon dot/TiO₂), showed ~ 3.45- and ~ 1.75-fold enhancement in the photodegradation rate as compared to pristine TiO₂ for PR and AT respectively in 1 hour of irradiation along with complete degradation of PR and AT after 3 hours of irradiation. 2CDT exhibited 76% and 80% mineralization of PR and AT in contrast with 62% and 47% observed by pristine TiO₂. Further, the major reaction intermediates formed after degradation have been identified by HPLC/MS analysis, confirming more than 99% reduction of the parent compound for both PR and AT. Reusability of the optimized catalyst also showed successful degradation up to 3 cycles, showing reduction abilities of 97%, 95%, and 94% for 1st, 2nd, and 3rd cycle respectively. The enhanced degradation and mineralization efficiency of the 2CDT composite could be attributed to the excellent photosensitizer and electron reservoir properties of the CD along with upconverted photoluminescence behavior. The present study unlocks the possibility of using metal-free, facile CDT composite for effective degradation and mineralization of widely used beta blockers and other pharmaceuticals.

A two-year study of emerging micro-pollutants and drugs of abuse in two Western Cape wastewater treatment works (South Africa)

This study evaluated the occurrence and fate of fourteen contaminants of emerging concern (CECs) at two South African wastewater treatment works (WWTW). Daily loads of the drug targets were calculated in the aqueous phase of influent- and effluent wastewater to evaluate their fate at the treatment works, along with population-normalised daily loads in raw influent wastewater to identify community-wide substance use patterns in the two study areas. Environmental risk characterisation of the CECs at WWTW effluent discharge was done using conventional risk quotient (RQ) estimations. A significant reduction of most CECs was observed at both WWTW locations, except for some that have been previously recorded to persist through various WWTW processes globally, including the illicit drug methaqualone that was reported here for the first time to evaluate its fate during wastewater treatment, substance use trends, and potential toxicological risk. Moderate-to high-RQs were estimated for several target CECs during the sampling period for both treatment facilities. The results presented here suggest the need for a multi-disciplinary approach to WWTW monitoring of CECs and highlight the need for further refinement of risk assessment approaches to mitigate recalcitrant- or pseudo-persistent CECs in wastewater discharge. Such refinement should include: (1) identifying the potential ecological risk on a wider range of sentinel indicators, (2) interaction of CECs with various biochemical pathways (including sub-lethal toxicity responses), (3) identifying the persistence and toxicological risks of breakdown products and (4) partitioning of CECs in the aqueous environment and/or bioaccumulation in freshwater biota.

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 (K_d ) varies between different classes of antibiotics, with tetracyclines and fluoroquinolones showing the highest K_d values. The K_d 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 K_d ; therefore, several values exist in literature for the same compound. Environ Toxicol Chem 2021;40:3275-3298. © 2021 SETAC.

Time study on the uptake of four different beta-blockers in garden cress (Lepidium sativum) as a model plant

The aim of this study was to investigate the uptake of four beta-blockers by the model plant Lepidium sativum (garden cress) and their possible metabolization over a time period of 8 days. Therefore, cress was grown hydroponically in tap water for a week until they were matured, following irrigation with drug-containing water over the course of another 8 days. Samples were taken at days 1, 2, 4, and 8 after irrigation started. All four beta-blockers were taken up by the plants and the different octanol-water coefficients (log P) of the drugs have an influence on the uptake speed in the roots of the plants. The log P seems to have no influence on the translocation of the drugs from the root to the shoots. Furthermore, neither phase I nor phase II metabolization occurred inside the plants.

Removal of Pharmaceuticals from Water by Adsorption and Advanced Oxidation Processes: State of the Art and Trends

Pharmaceutical products have become a necessary part of life. Several studies have demonstrated that indirect exposure of humans to pharmaceuticals through the water could cause negative effects. Raw sewage and wastewater effluents are the major sources of pharmaceuticals found in surface waters and drinking water. Therefore, it is important to consider and characterize the efficiency of pharmaceutical removal during wastewater and drinking-water treatment processes. Various treatment options have been investigated for the removal/reduction of drugs (e.g., antibiotics, NSAIDs, analgesics) using conventional or biological treatments, such as activated sludge processes or bio-filtration, respectively. The efficiency of these processes ranges from 20–90%. Comparatively, advanced wastewater treatment processes, such as reverse osmosis, ozonation and advanced oxidation technologies, can achieve higher removal rates for drugs. Pharmaceuticals and their metabolites undergo natural attenuation by adsorption and solar oxidation. Therefore, pharmaceuticals in water sources even at trace concentrations would have undergone removal through biological processes and, if applicable, combined adsorption and photocatalytic degradation wastewater treatment processes. This review provides an overview of the conventional and advanced technologies for the removal of pharmaceutical compounds from water sources. It also sheds light on the key points behind adsorption and photocatalysis.

Carbamazepine and Diclofenac Removal Double Treatment: Oxidation and Adsorption

In the present research, the effect of two hybrid treatments, ozone followed by powdered activated carbon (PAC) or PAC followed by ozone (O₃), was studied for the removal of two drugs present in water: diclofenac and carbamazepine. In the study, two initial concentrations of each of the contaminants, 0.7 mg L^-1 and 1.8 mg L^-1, were used. Different doses of PAC between 4-20 mg L^-1 were studied as variables, as well as different doses of O₃ between 0.056-0.280 mg L^-1. The evolution of the concentration of each contaminant over time was evaluated. From the results obtained, it was concluded that the combined treatment with ozone followed by PAC reduces between 50% and 75% the time required to achieve 90% removal of diclofenac when compared with the time required when only activated carbon was used. In the case of carbamazepine, the time required was 97% less. For carbamazepine, to achieve reduction percentages of up to 90%, O₃ treatment followed by PAC acted faster than PAC followed by O₃. In the case of diclofenac, PAC treatment followed by O₃ was faster to reach concentrations of up to 90%. However, to reach yields below 80%, O₃ treatment followed by PAC was more efficient.

Automated method to determine pharmaceutical compounds in wastewater using on-line solid-phase extraction coupled to LC-MS/MS

An automated method was developed using on-line solid-phase extraction (SPE) as a sample preparation step, coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS), for determination of pharmaceutical compounds in wastewater samples at nanograms per liter to micrograms per liter concentration levels. This method is suitable for use in routine analysis, especially in environmental applications, avoiding cross-contamination and requiring minimal sample handling. Results can be obtained rapidly, with a chromatographic run time of only 24 min (including sample preparation and chromatographic analysis). Using a 50 μL injection volume, the method was validated according to international guidelines, considering parameters included in terms of method detection (MDL) and quantification limit (MQL), linearity, inter-day and intra-day precisions, and matrix effects. Assessment of chromatographic efficiency considered peak resolution and asymmetry, and carryover was evaluated to ensure analytical reliability and the ability to reuse the SPE cartridge. The intra- and inter-day precisions were lower than 10 and 17%, respectively. The MDL values ranged from 1×10^-6 to 1 μg L^-1, while the MQL values were from 0.001 to 3 μg L^-1. Matrix effects were minimized by isotope dilution calibration. Application of the method to 20 wastewater samples showed that caffeine was the most frequently detected compound, with the highest concentration of 715 μg L^-1, while other pharmaceutical compounds were detected in fewer samples and at lower concentrations (up to 8.51 μg L^-1).

Pharmaceuticals Market, Consumption Trends and Disease Incidence Are Not Driving the Pharmaceutical Research on Water and Wastewater

Pharmaceuticals enhance our quality of life; consequently, their consumption is growing as a result of the need to treat ageing-related and chronic diseases and changes in the clinical practice. The market revenues also show an historic growth worldwide motivated by the increase on the drug demand. However, this positivism on the market is fogged because the discharge of pharmaceuticals and their metabolites into the environment, including water, also increases due to their inappropriate management, treatment and disposal; now, worldwide, this fact is recognized as an environmental concern and human health risk. Intriguingly, researchers have studied the most effective methods for pharmaceutical removal in wastewater; however, the types of pharmaceuticals investigated in most of these studies do not reflect the most produced and consumed pharmaceuticals on the market. Hence, an attempt was done to analyze the pharmaceutical market, drugs consumption trends and the pharmaceutical research interests worldwide. Notwithstanding, the intensive research work done in different pharmaceutical research fronts such as disposal and fate, environmental impacts and concerns, human health risks, removal, degradation and development of treatment technologies, found that such research is not totally aligned with the market trends and consumption patterns. There are other drivers and interests that promote the pharmaceutical research. Thus, this review is an important contribution to those that are interested not only on the pharmaceutical market and drugs consumption, but also on the links, the drivers and interests that motivate and determine the research work on certain groups of pharmaceuticals on water and wastewater.

A fast-screening approach for the tentative identification of drug-related metabolites from three non-steroidal anti-inflammatory drugs in hydroponically grown edible plants by HPLC-drift-tube-ion-mobility quadrupole time-of-flight mass spectrometry

The (tentative) identification of unknown drug-related phase II metabolites in plants upon drug uptake remains a challenging task despite improved analytical instrument performance. To broaden the knowledge of possible drug metabolization, a fast-screening approach for the tentative identification of drug-related phase II metabolites is presented in this work. Therefore, an in silico database for the three non-steroidal anti-inflammatory drugs (ketoprofen, mefenamic acid, and naproxen) and a sub-group of their theoretical phase II metabolites (based on combinations with glucose, glucuronic acid, and malonic acid) was created. Next, the theoretical exact masses (protonated species and ammonia adducts) were calculated and used as precursor ions in an autoMS/MS measurement method. The applicability of this workflow was tested on the example of eleven edible plants, which were hydroponically grown in solutions containing the respective drug at a concentration level of 20 mg/L. For the three drugs investigated this led to the tentative identification of 41 metabolites (some of them so far not described in this context), such as combinations of hydroxylated mefenamic acid with up to four glucose units or hydroxylated mefenamic acid with two glucose and three malonic acid units.

Detection of pharmaceuticals in wastewater effluents-a comparison of the performance of Chemcatcher® and polar organic compound integrative sampler

Chemcatcher^® and POCIS passive sampling devices are widely used for monitoring polar organic pollutants in water. Chemcatcher^® uses a bound Horizon Atlantic™ HLB-L sorbent disk as receiving phase, whilst the POCIS uses the same material in the form of loose powder. Both devices (n = 3) were deployed for 21 days in the final effluent at three wastewater treatment plants in South Wales, UK. Following deployment, sampler extracts were analysed using liquid chromatography time-of-flight mass spectrometry. Compounds were identified using an in-house database of pharmaceuticals using a metabolomics workflow. Sixty-eight compounds were identified in all samplers. For the POCIS, substantial losses of sorbent (11-51%) were found during deployment and subsequent laboratory analysis, necessitating the use of a recovery factor. Percentage relative standard deviations varied (with 10 compounds exceeding 30% in both samplers) between individual compounds and between samplers deployed at the three sites. The relative performance of the two devices was evaluated using the mass of analyte sequestered, measured as an integrated peak area. The ratio of the uptake of the pharmaceuticals for the POCIS versus Chemcatcher^® was lower (1.84x) than would be expected on the basis of the ratio of active sampling areas (3.01x) of the two devices. The lower than predicted uptake may be attributable to the loose sorbent material moving inside the POCIS when deployed in the field in the vertical plane. In order to overcome this, it is recommended to deploy the POCIS horizontally inside the deployment cage.

Comparison of the regulatory outline of ecopharmacovigilance of pharmaceuticals in Europe, USA, Japan and Australia

Pharmaceuticals are known to improve the quality of life by curing and preventing diseases. However, these pharmaceutical products, when it diffuses through the environment by various routes, can cause severe harmful effects to the living organisms. During the last several years, the coping with the impact of pharmaceuticals on the environment was one of the challenging tasks for the pharmaceutical industries. These concerns about the environmental health and safety risks paved the way in developing a proper regulatory framework for environmental risk assessment of pharmaceutical products. In the US, EU, and Canada, most improvements have been made in the regulation of Environmental Risk Assessment (ERA) for pharmaceuticals. Many countries and organizations like the Organization for Economic Cooperation and Development (OECD), had adapted these ERA procedures to fulfil the purpose. At present, there are no specific guidelines for ERA of pharmaceuticals in Japan, Australia and many other countries. Nevertheless, it is expected that they will have strict regulations and legal requirements in the future. The purpose of this study is to understand and compare the ERA regulation in Europe, USA, Japan and Australia. In this review, we have summarized the knowledge on ERA of pharmaceuticals and its consequences on the environment. It is therefore necessary to establish an eco-pharmacovigilance system for monitoring and collection of data, which would eradicate the risk of pharmaceuticals entering into the surroundings.

Evaluation of the Possibility of Using Hydroponic Cultivations for the Removal of Pharmaceuticals and Endocrine Disrupting Compounds in Municipal Sewage Treatment Plants

The problem of the presence of pharmaceuticals and endocrine disrupting compounds (EDCs) in the environment is closely related to municipal wastewater and in consequence to municipal wastewater treatment plants (MWWTPs) because wastewater is the main way in which these compounds are transferred to the ecosystem. For this reason, the development of cheap, simple but very effective techniques for the removal of such residues from wastewater is very important. In this study, the analysis of the potential of using three new plants: Cyperus papyrus (Papyrus), Lysimachia nemorum (Yellow pimpernel), and Euonymus europaeus (European spindle) by hydroponic cultivation for the removal of 15 selected pharmaceuticals and endocrine disrupting compounds (EDCs) in an MWWTP is presented. In order to obtain the most reliable data, this study was performed using real WWTP conditions and with the determination of the selected analytes in untreated sewage, treated sewage, and in plant materials. For determining the target compounds in plant materials, an Accelerated Solvent Extraction (ASE)-Solid-Phase Extraction (SPE)-GC-MS(SIM) method was developed and validated. The obtained data proved that the elimination efficiency of the investigated substances from wastewater was in the range of 35.8% for diflunisal to above 99.9% for paracetamol, terbutaline, and flurbiprofen. Lysimachia nemorum was the most effective for the uptake of target compounds among the tested plant species. Thus, the application of constructed wetlands for supporting conventional MWWTPs allowed a significant increase in their removal from the wastewater stream.

Bioremediation of bezafibrate and paroxetine by microorganisms from estuarine sediment and activated sludge of an associated wastewater treatment plant

The present work aimed to explore the potential of autochthonous microorganisms from an urban estuary and from activated sludge of an associated wastewater treatment plant (WWTP), for biodegradation of an antidepressant drug, paroxetine, and on a cholesterol-lowering agent, bezafibrate. These compounds were chosen as representatives of extensively used pharmaceuticals. Autochthonous microorganisms from the indicated sources were exposed to the target pharmaceuticals (1 mg/L) in co-metabolism with sodium acetate (500 mg/L) along a two-weeks period, for a total of 7 two-weeks periods (here referred as cycles). Exposures were carried out in batch mode, under different incubation conditions (agitation vs. static). Removal of pharmaceuticals was monitored at the end of each cycle, by analysing the culture medium. For paroxetine, fluoride ion release was also followed as an indicator of defluorination of the molecule. The structure of the bacterial communities was analysed by ARISA (Automated rRNA Intergenic Spacer Analysis), at the beginning of the experiment and at the end of the first and the last cycles to identify substantial changes associated with the time of exposure, the incubation conditions and the presence and type of pharmaceuticals. Incubation conditions affected not only the bacterial community structure, but also the biodegradation efficiency. At the beginning of the experiment, removal of target pharmaceuticals was found to be lower under agitation than under static conditions, but at the end of the experiment, results showed high removal of the pharmaceuticals from the culture medium (>97%) under both conditions, mainly by microbiological processes. For paroxetine, adsorption and abiotic processes also had an important influence on its removal, but defluorination only occurred in the presence of microorganisms. These results highlight that autochthonous microorganisms from estuarine sediments and WWTP sludge have high ability to remove the selected pharmaceuticals with relevant implications for the development of new bioremediation tools for environmental restoration.

Emerging contaminants of high concern and their enzyme-assisted biodegradation - A review

The widespread occurrence and adverse environmental and health-related impacts of various types of emerging contaminants (ECs) have become an issue of high concern. With ever increasing scientific knowledge, socio-economic awareness, health-related problems and ecological apprehensions, people are more concerned about the widespread ECs, around the globe. Among ECs, biologically active compounds from pharmaceutical, cosmeceutical, biomedical, personal care products (PPCPs), endocrine-disrupting chemicals (EDCs), and flame-retardants are of paramount concern. The presence and persistence of ECs in water bodies are of continued and burning interest, worldwide. Various types of ECs are being discharged knowingly/unknowingly with/without partial treatments into the aquatic environments that pose serious health issues and affects the entire living ecosystem. So far, various approaches have been developed for ECs degradation and removal to diminish their adverse impact. Many previous and/or ongoing studies have focused on contaminants degradation and efficient removal via numerous treatment strategies, i.e. (1) physical, (2) chemical and (3) biological. However, the experimental evidence is lacking to enable specific predictions about ECs mechanistic degradation and removal fate across various in-practice systems. In this context, the deployment oxidoreductases such as peroxidases (lignin peroxidases, manganese-dependent peroxidases, and horseradish peroxidase), aromatic dioxygenases, various oxygenases, laccases, and tyrosinases have received considerable research attention. Immobilization is highlighted as a promising approach to improve enzyme catalytic performance and stabilization, as well as, to protect the three-dimensional structure of the enzyme against the undesirable consequences of harsh reaction environment. This work overviews the current and state-of-the-art critical aspect related to hazardous pollutants at large and ECs in particular by the immobilized oxidoreductase enzymes. The first part of the review focuses on the occurrence, physiochemical behavior, potent sources and significant routes of ECs. Following that, environmentally-related adverse impacts and health-related issues of ECs are discussed in the second part. In the third part, biodegradation and removal strategies with a comparative overview of several conventional vs. non-conventional methods are presented briefly. The fourth part majorly focuses on operational modes of different oxidoreductase enzyme-based biocatalytic processes for the biodegradation and biotransformation of a wide array of harmful environmental contaminants. Finally, the left behind research gaps, concluding remarks as well as future trends and recommendations in the use of carrier-immobilized oxidoreductases for environmental perspective are also discussed.

Analytical and legislative challenges of sewage sludge processing and management

ABSTRACT

This article presents the most popular methods of sewage sludge management and analytical techniques which could be a powerful tool in designing new sewage sludge management methods. Chemical analysis is also described as a vital point at the subsequent stages of technological processes control and sewage sludge quality assessment. It is also an instrument essential to maintaining control of processed sewage sludge introduced to the environment as ready-to-use materials. The sludge management method is conditioned by the compliance with legal acts concerning sludge management. The most important of these contain information regarding allowable concentrations of pollutants which can be released into the environment, and the most important declarations concerning sewage sludge management. Various analytical techniques and preparation methods that can be used during the monitoring of the managed and processed sewage sludge are described. The most important are chromatographic techniques, methods based on inductively coupled plasma, and mass spectrometry based methods.

GRAPHICAL ABSTRACT

Behaviour of aqueous sulfamethizole solution and temperature effects in cold plasma oxidation treatment

The increase in volume and variety of pharmaceuticals found in natural water bodies has become an increasingly serious environmental problem. The implementation of cold plasma technology, specifically gas-phase pulsed corona discharge (PCD), for sulfamethizole abatement was studied in the present work. It was observed that sulfamethizole is easily oxidized by PCD. The flow rate and pH of the solution have no significant effect on the oxidation. Treatment at low pulse repetition frequency is preferable from the energy efficiency point of view but is more time-consuming. The maximum energy efficiency was around 120 g/kWh at half-life and around 50 g/kWh at the end of the treatment. Increasing the solution temperature from room temperature to 50 °C led to a significant reaction retardation of the process and decrease in energy efficiency. The pseudo-first order reaction rate constant (k₁) grows with increase in pulse repetition frequency and does not depend on pH. By contrast, decreasing frequency leads to a reduction of the second order reaction rate constant (k₂). At elevated temperature of 50 °C, the k₁, k₂ values decrease 2 and 2.9 times at 50 pps and 500 pps respectively. Lower temperature of 10 °C had no effect on oxidation efficiency compared with room temperature.

Targeted eco-pharmacovigilance for ketoprofen in the environment: Need, strategy and challenge

Implementing "targeted" eco-pharmacovigilance(EPV) which focuses on individual or specific pharmaceuticals on a prioritised basis is a feasible, economical and customized approach to reduce the environmental concentrations and risks of pharmaceuticals. Non-steroidal anti-inflammatory drugs(NSAIDs) remaining in environment are a kind of priority hazard substances, due to a notable case that diclofenac residues caused the loss of more than 99% of vultures across the Indian sub-continent. Ketoprofen, as another widely used NSAID with comparable or even higher global consumption than diclofenac, in the environment has been shown to present a potential risk to non-target terrestrial and aquatic species. Based on the review of 85 articles reporting the analyses of ketoprofen residues in environment since 2010, we found that this NSAID frequently present in various environmental compartments around the world. Therefore, it is urgent to implement EPV targeting ketoprofen pollution. Here, we provide some recommendations for implementing the targeted EPV for ketoprofen, including: Closely monitoring ketoprofen in the natural environment; Reducing the residues of ketoprofen through source control; Encouraging urine source separation and treatment; Limiting the application of veterinary ketoprofen; Designing and constituting a framework system of targeted EPV. But some challenges, such as ambiguity in the accountability of the main bodies responsible for continued monitoring of ketoprofen residues, the lack of optimized urine source separation scenarios and procedure, the need for detailed design and application schemes of the framework system of targeted EPV, etc. should be addressed.

Study of pharmaceuticals in surface and wastewater from Cuernavaca, Morelos, Mexico: Occurrence and environmental risk assessment

The present work describes the first known study to date on the occurrence of pharmaceuticals in surface water and wastewater of Cuernavaca, the capital of the state of Morelos (México). Selected pharmaceuticals (a total of 35) were extracted from the collected water samples with a generic solid phase extraction (SPE) protocol and determined in the sample extracts by means of high-performance liquid chromatography coupled to electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS). A screening level risk assessment combining the measured environmental concentrations (MECs) with dose-response data based on predicted no-effect concentrations (PNECs) was also applied to estimate Hazard Quotients (HQs) for the pharmaceuticals detected in the investigated area. A total of twelve pharmaceuticals were found in the water samples analyzed, with detection frequencies above 78% and in most cases of 100%. Overall, the most abundant pharmaceuticals in surface water were the analgesic and anti-inflammatory drugs naproxen (732-4880ng/L), acetaminophen (354-4460ng/L), and diclofenac (258-1398ng/L), and the lipid regulator bezafibrate (286-2100ng/L). On the contrary, other compounds like the β-blocker atenolol and the psychiatric drug carbamazepine were found at only a few ng or tens of ng per liter in the Apatlaco River. Despite the fact that some of the most abundant compounds showed good removal (>97%) during wastewater treatment, concentrations downstream the WWTP were only slightly lower than upstream. This indicates the existence of additional inputs of untreated wastewater into the river. Based on the obtained HQ-values, the concentrations of ibuprofen, sulfamethoxazole, diclofenac and naproxen present in the river could pose a high toxicity risk for the aquatic ecosystem. These findings highlight these pharmaceuticals as relevant organic contaminants in the area of study and the need to further monitor them in order to adopt appropriate measures to safeguard the ecosystem, and eventually human health.

Development of a semi-quantitative risk assessment model for evaluating environmental threat posed by the three first EU watch-list pharmaceuticals to urban wastewater treatment plants: An Irish case study

Contamination of receiving waters with pharmaceutical compounds is of pressing concern. This constitutes the first study to report on the development of a semi-quantitative risk assessment (RA) model for evaluating the environmental threat posed by three EU watch list pharmaceutical compounds namely, diclofenac, 17-beta-estradiol and 17-alpha-ethinylestradiol, to aquatic ecosystems using Irish data as a case study. This RA model adopts the Irish Environmental Protection Agency Source-Pathway-Receptor concept to define relevant parameters for calculating low, medium or high risk score for each agglomeration of wastewater treatment plant (WWTP), which include catchment, treatments, operational and management factors. This RA model may potentially be used on a national scale to (i) identify WWTPs that pose a particular risk as regards releasing disproportionally high levels of these pharmaceutical compounds, and (ii) help identify priority locations for introducing or upgrading control measures (e.g. tertiary treatment, source reduction). To assess risks for these substances of emerging concern, the model was applied to 16 urban WWTPs located in different regions in Ireland that were scored for the three different compounds and ranked as low, medium or high risk. As a validation proxy, this case study used limited monitoring data recorded at some these plants receiving waters. It is envisaged that this semi-quantitative RA approach may aid other EU countries investigate and screen for potential risks where limited measured or predicted environmental pollutant concentrations and/or hydrological data are available. This model is semi-quantitative, as other factors such as influence of climate change and drug usage or prescription data will need to be considered in a future point for estimating and predicting risks.

Bioaccumulation of pharmaceutically active compounds and endocrine disrupting chemicals in aquatic macrophytes: Results of hydroponic experiments with Echinodorus horemanii and Eichhornia crassipes

Information regarding the bioaccumulation behaviour of pharmaceutically active compounds (PhACs) and endocrine disrupting chemicals (EDCs) in aquatic plants is limited. The present study involved controlled hydroponic experiments to assess uptake and elimination rate constants (k_u, k_e), bioconcentration factors (BCFs) and translocation factors (TFs) of several PhACs and EDCs in two aquatic macrophyte species, including one submerged species (Echinodorus horemanii) and one free-floating species (Eichhornia crassipes). The results revealed that the studied compounds are readily taken up in these aquatic plants. While bioconcentration factors (BCFs) and translocation factors (TFs) of the test compounds varied substantially, no discernible relationship with physicochemical properties such as octanol-water distribution coefficient (D_ow), membrane-water distribution coefficient (D_mw) and organic carbon-water partition coefficient (K_oc). Diphenhydramine and triclosan exhibited the highest degree of uptake and bioaccumulation potential. For example, the whole-plant BCF of triclosan in E. horemanii was 4390L/kg, while the whole-plant BCF of diphenhydramine in E. crassipes was 6130L/kg. BCFs of 17β-estradiol (E2), 17α-ethinylestradiol (EE2), estrone (E1) and bisphenol A (BPA) were relatively low (2-150L/kg). BCFs were generally higher in free-floating aquatic macrophyte species compared to the submerged species. For the free-floating species, E. crassipes, the majority of PhACs and EDCs were more allocated in roots compared to leaves, with TFs<1. However, some compounds such as caffeine, atrazine, diphenhydramine, E2 and carbamazepine were more allocated in leaf tissue (TFs>1). The study findings may be useful for design and implementation of phytoremediation systems, as well as aid future modeling and risk assessment initiatives for these emerging organic contaminants.

Combined adsorption and degradation of the off-flavor compound 2-methylisoborneol in sludge derived from a recirculating aquaculture system

Off-flavor in fish poses a serious threat for the aquaculture industry. In the present study, removal of 2-methylisoborneol (MIB), an off-flavor causing compound, was found to be mediated by adsorption and bacterial degradation in sludge derived from an aquaculture system. A numerical model was developed which augmented Langmuir equations of kinetics of adsorption/desorption of MIB with first order degradation kinetics. When laboratory-scale reactors, containing sludge from the aquaculture system, were operated in a recirculating mode, MIB in solution was depleted to undetectable levels within 6 days in reactors with untreated sludge, while its depletion was incomplete in reactors with sterilized sludge. When operated in an open flow mode, removal of MIB was significantly faster in reactors with untreated sludge. Efficient MIB removal was evident under various conditions, including ambient MIB levels, flow velocities and sludge loads. When operated in an open flow mode, the model successfully predicted steady MIB removal rates with time. During steady state conditions, most of the MIB removal was found to be due to microbial degradation of the adsorbed MIB. Findings obtained in this study can be used in the design of reactors for removal of off-flavor compounds from recirculating aquaculture systems.

Monitoring, sources, receptors, and control measures for three European Union watch list substances of emerging concern in receiving waters - A 20year systematic review

Pollution of European receiving waters with contaminants of emerging concern (CECs), such as with 17-beta-estradiol (a natural estrogenic hormone, E2), along with pharmaceutically-active compounds diclofenac (an anti-inflammatory drug, DCL) and 17-alpha-ethynylestradiol (a synthetic estrogenic hormone, EE2)) is a ubiquitous phenomenon. These three CECs were added to the EU watch list of emerging substances to be monitoring in 2013, which was updated in 2015 to comprise 10 substances/groups of substances in the field of water policy. A systematic literature review was conducted of 3952 potentially relevant articles over period 1995 to 2015 that produced a new EU-wide database consisting of 1268 publications on DCL, E2 and EE2. European surface water concentrations of DCL are typically reported below the proposed annual average environmental quality standard (AA EQS) of 100ng/l, but that exceedances frequently occur. E2 and EE2 surface water concentrations are typically below 50ng/l and 10ng/l respectively, but these values greatly exceed the proposed AA EQS values for these compounds (0.04 and 0.035ng/l respectively). However, levels of these CECs are frequently reported to be disproportionately high in EU receiving waters, particularly in effluents at control points that require urgent attention. Overall it was found that DCL and EE2 enter European aquatic environment mainly following human consumption and excretion of therapeutic drugs, and by incomplete removal from influent at urban wastewater treatment plants (WWTPs). E2 is a natural hormone excreted by humans which also experiences incomplete removal during WWTPs treatment. Current conventional analytical chemistry methods are sufficiently sensitive for the detection and quantification of DCL but not for E2 and EE2, thus alternative, ultra-trace, time-integrated monitoring techniques such as passive sampling are needed to inform water quality for these estrogens. DCL appears resistant to conventional wastewater treatment while E2 and EE2 have high removal efficiencies that occur through biodegradation or sorption to organic matter. There is a pressing need to determine fate and behaviour of these CECs in European receiving waters such as using GIS-modelling of river basins as this will identify pressure points for informing priority decision making and alleviation strategies for upgrade of WWTPs and for hospital effluents with advanced treatment technologies. More monitoring data for these CECs in receiving waters is urgently needed for EU legislation and effective risk management.

Occurrence and removal of organic micropollutants: An overview of the watch list of EU Decision 2015/495

Although there are no legal discharge limits for micropollutants into the environment, some regulations have been published in the last few years. Recently, a watch list of substances for European Union-wide monitoring was reported in the Decision 2015/495/EU of 20 March 2015. Besides the substances previously recommended to be included by the Directive 39/2013/EU, namely two pharmaceuticals (diclofenac and the synthetic hormone 17-alpha-ethinylestradiol (EE2)) and a natural hormone (17-beta-estradiol (E2)), the first watch list of 10 substances/groups of substances also refers three macrolide antibiotics (azithromycin, clarithromycin and erythromycin), other natural hormone (estrone (E1)), some pesticides (methiocarb, oxadiazon, imidacloprid, thiacloprid, thiamethoxam, clothianidin, acetamiprid and triallate), a UV filter (2-ethylhexyl-4-methoxycinnamate) and an antioxidant (2,6-di-tert-butyl-4-methylphenol) commonly used as food additive. Since little is known about the removal of most of the substances included in the Decision 2015/495/EU, particularly regarding realistic concentrations in aqueous environmental samples, this review aims to: (i) overview the European policy in the water field; (ii) briefly describe the most commonly used conventional and advanced treatment processes to remove micropollutants; (iii) summarize the relevant data published in the last decade, regarding occurrence and removal in aqueous matrices of the 10 substances/groups of substances that were recently included in the first watch list for European Union monitoring (Decision 2015/495/EU); and (iv) highlight the lack of reports concerning some substances of the watch list, the study of un-spiked aquatic matrices and the assessment of transformation by-products.

Competitive adsorption of a pool of pharmaceuticals onto a raw clay mineral

The removal of a Pharmaceutically Active Compound (PhAC) pool using a well referenced clay mineral from Wyoming (SWy-2) as a geosorbent was studied for a better understanding of the environmental fate.

Removal of steroid estrogens from municipal wastewater in a pilot scale expanded granular sludge blanket reactor and anaerobic membrane bioreactor

Anaerobic treatment of municipal wastewater offers the prospect of a new paradigm by reducing aeration costs and minimizing sludge production. It has been successfully applied in warm climates, but does not always achieve the desired outcomes in temperate climates at the biochemical oxygen demand (BOD) values of municipal crude wastewater. Recently the concept of 'fortification' has been proposed to increase organic strength and has been demonstrated at the laboratory and pilot scale treating municipal wastewater at temperatures of 10-17°C. The process treats a proportion of the flow anaerobically by combining it with primary sludge from the residual flow and then polishing it to a high effluent standard aerobically. Energy consumption is reduced as is sludge production. However, no new treatment process is viable if it only addresses the problems of traditional pollutants (suspended solids - SS, BOD, nitrogen - N and phosphorus - P); it must also treat hazardous substances. This study compared three potential municipal anaerobic treatment regimes, crude wastewater in an expanded granular sludge blanket (EGSB) reactor, fortified crude wastewater in an EGSB and crude wastewater in an anaerobic membrane bioreactor. The benefits of fortification were demonstrated for the removal of SS, BOD, N and P. These three systems were further challenged with the removal of steroid estrogens at environmental concentrations from natural indigenous sources. All three systems removed these compounds to a significant degree, confirming that estrogen removal is not restricted to highly aerobic autotrophs, or aerobic heterotrophs, but is also a faculty of anaerobic bacteria.

A review on emerging contaminants in wastewaters and the environment: current knowledge, understudied areas and recommendations for future monitoring

This review identifies understudied areas of emerging contaminant (EC) research in wastewaters and the environment, and recommends direction for future monitoring. Non-regulated trace organic ECs including pharmaceuticals, illicit drugs and personal care products are focused on due to ongoing policy initiatives and the expectant broadening of environmental legislation. These ECs are ubiquitous in the aquatic environment, mainly derived from the discharge of municipal wastewater effluents. Their presence is of concern due to the possible ecological impact (e.g., endocrine disruption) to biota within the environment. To better understand their fate in wastewaters and in the environment, a standardised approach to sampling is needed. This ensures representative data is attained and facilitates a better understanding of spatial and temporal trends of EC occurrence. During wastewater treatment, there is a lack of suspended particulate matter analysis due to further preparation requirements and a lack of good analytical approaches. This results in the under-reporting of several ECs entering wastewater treatment works (WwTWs) and the aquatic environment. Also, sludge can act as a concentrating medium for some chemicals during wastewater treatment. The majority of treated sludge is applied directly to agricultural land without analysis for ECs. As a result there is a paucity of information on the fate of ECs in soils and consequently, there has been no driver to investigate the toxicity to exposed terrestrial organisms. Therefore a more holistic approach to environmental monitoring is required, such that the fate and impact of ECs in all exposed environmental compartments are studied. The traditional analytical approach of applying targeted screening with low resolution mass spectrometry (e.g., triple quadrupoles) results in numerous chemicals such as transformation products going undetected. These can exhibit similar toxicity to the parent EC, demonstrating the necessity of using an integrated analytical approach which compliments targeted and non-targeted screening with biological assays to measure ecological impact. With respect to current toxicity testing protocols, failure to consider the enantiomeric distribution of chiral compounds found in the environment, and the possible toxicological differences between enantiomers is concerning. Such information is essential for the development of more accurate environmental risk assessment.

Multi-residue analysis of pharmaceuticals in wastewater by liquid chromatography-magnetic sector mass spectrometry: method quality assessment and application in a Belgian case study

Through systematic research a novel analytical method using solid-phase extraction (SPE) and liquid chromatography magnetic sector mass spectrometry was developed for the measurement of 43 pharmaceuticals in wastewater. A thorough method validation quantified the contribution of both the extraction recovery and matrix effects in the overall method process efficiency, and a detailed uncertainty analysis was performed to elaborate a quality labelling strategy to be used in data interpretation. Compounds for which a precise (relative standard deviation<20%) process efficiency between 60% and 140% was determined, were labelled as 'quantitative' whereas the results for other compounds should be interpreted as 'indicative'. Method application on influent and effluent samples of (i) a conventional active sludge system and (ii) a parallel membrane bioreactor/conventional active sludge wastewater treatment plant in Belgium revealed the occurrence of 22 pharmaceuticals. The anti-inflammatory drug diclofenac and the antidepressant venlafaxine were measured in the effluents at concentrations ranging from 0.5 to 1.8 μg L(-1) and 0.2 to 0.5 μg L(-1), respectively, which indicated to be of high potential environmental risk for the receiving river Dender, Belgium.

Obtaining process mass balances of pharmaceuticals and triclosan to determine their fate during wastewater treatment

To better understand pharmaceutical fate during wastewater treatment, analysis in both aqueous and particulate phases is needed. Reported herein is a multi-residue method for the determination of ten pharmaceutical drugs and the personal care product triclosan in wastewater matrices. Method quantitation limits ranged from 7.6 to 76.6 ng l(-1) for aqueous phases and from 7.0 to 96.7 ng g(-1) for particulate phases. The analytical method was applied to attain a complete process mass balance of a pilot-scale activated sludge plant (ASP) operated under controlled conditions. The mass balance (inclusive of aqueous and particulate concentrations at all sample points) was used to diagnose removal, revealing pharmaceuticals to be separable into three fate pathways: (a) biological degradation, (b) sorption onto activated sludge and (c) resistant to removal from the aqueous phase. These differences in fate behaviour explained a broad range of secondary removal observed (-8 to 99%). The ASP was also simultaneously compared to a full-scale trickling filter (TF) works whilst receiving the same influent wastewater. Performance of the ASP and TF was similar, achieving total pharmaceutical removals of 253 and 249 μg g(-1) biochemical oxygen demand (BOD) removed, respectively. This corresponded with reductions in total pharmaceutical load of 91 and 90% (ANOVA, p-value>0.05). Interestingly, despite low suspended solid concentrations final effluents of both the ASP and TF contained significant concentrations of some chemicals in the particulate phase. Individually, triclosan and the antibiotics ofloxacin and ciprofloxacin were within the particulate phase of effluents at concentrations ranging from 26 to 296 ng l(-1).

Assessing potential modifications to the activated sludge process to improve simultaneous removal of a diverse range of micropollutants

It is proposed that wastewater treatment facilities meet legislated discharge limits for a range of micropollutants. However, the heterogeneity of these micropollutants in wastewaters make removal difficult to predict since their chemistry is so diverse. In this study, a range of organic and inorganic micropollutants known to be preferentially removed via different mechanisms were selected to challenge the activated sludge process (ASP) and determine its potential to achieve simultaneous micropollutant removal. At a fixed hydraulic retention time (HRT) of 8 h, the influence of an increase in solids retention time (SRT) on removal was evaluated. Maximum achievable micropollutant removal was recorded for all chemicals (estrogens, nonylphenolics and metals) at the highest SRT studied (27 days). Also, optimisation of HRT by extension to 24 h further augmented organic biodegradation. Most notable was the enhancement in removal of the considerably recalcitrant synthetic estrogen 17α-ethinylestradiol which increased to 65 ± 19%. Regression analysis indicates that this enhanced micropollutant behaviour is ostensibly related to the concomitant reduction in food: microorganism ratio. Interestingly, extended HRT also initiated nonylphenol biodegradation which has not been consistently observed previously in real wastewaters. However, extending HRT increased the solubilisation of particulate bound metals, increasing effluent aqueous metals concentrations (i.e., 0.45 μm filtered) by >100%. This is significant as only the aqueous metal phase is to be considered for environmental compliance. Consequently, identification of an optimum process condition for generic micropollutant removal is expected to favour a more integrated approach where upstream process unit optimisation (i.e., primary sedimentation) is demanded to reduce loading of the particle bound metal phase onto the ASP, thereby enabling longer HRT in the ASP to be considered for optimum removal of organic micropollutants.

A review on removing pharmaceutical contaminants from wastewater by constructed wetlands: design, performance and mechanism

This paper presents a comprehensive review of the current state of research activities on the application of constructed wetlands for removing pharmaceutical contaminants from wastewater. The focus of the review was placed on the application of constructed wetlands as an alternative secondary wastewater treatment system or as a wastewater polishing treatment system. The design parameters of the reported constructed wetlands including the physical configuration, hydraulic mode, vegetation species, and targeting pharmaceuticals were summarized. The removal efficiencies of pharmaceuticals under different conditions in the wetlands were evaluated at the macroscopic level. In addition, the importance of the three main components of constructed wetlands (substrate, plants and microbes) for pharmaceutical removal was analyzed to elucidate the possible removal mechanisms involved. There is a general consensus among many researchers that constructed wetlands hold great potential of being used as an alternative secondary wastewater treatment system or as a wastewater polishing treatment system for the removal of pharmaceuticals, but relevant reported studies are scarce and are not conclusive in their findings. Current knowledge is limited on the removal efficiencies of pharmaceuticals in constructed wetlands, the removal mechanisms involved, the toxicity to constructed wetlands caused by pharmaceuticals, and the influences of certain important parameters (configuration design, hydraulic mode, temperature and seasonality, pH, oxygen and redox potential, etc.). This review promotes further research on these issues to provide more and better convincing evidences for the function and performance of larger laboratory-scale, pilot-scale or full-scale constructed wetlands.