Mechanism for the primary transformation of acetaminophen in a soil/water system

A review on reactive oxygen species-induced mechanism pathways of pharmaceutical waste degradation: Acetaminophen as a drug waste model

Innately designed to induce physiological changes, pharmaceuticals are foreknowingly hazardous to the ecosystem. Advanced oxidation processes (AOPs) are recognized as a set of contemporary and highly efficient methods being used as a contrivance for the removal of pharmaceutical residues. Since reactive oxygen species (ROS) are formed in these processes to interact and contribute directly toward the oxidation of target contaminant(s), a profound insight regarding the mechanisms of ROS leading to the degradation of pharmaceuticals is fundamentally significant. The conceptualization of some specific reaction mechanisms allows the design of an effective and safe degradation process that can empirically reduce the environmental impact of the micropollutants. This review mainly deliberates the mechanistic reaction pathways for ROS-mediated degradation of pharmaceuticals often leading to complete mineralization, with a focus on acetaminophen as a drug waste model.

Delineating acetaminophen biodegradation kinetics and metabolomics using bacterial community

Acetaminophen [N-(4-hydroxyphenyl) acetamide, APAP] is an extensively and frequently consumed over-the-counter analgesic and antiphlogistic medication. It is being regarded as an emerging pollutant due to its continuous increment in the environment instigating inimical impacts on humans and the ecosystem. Considering its wide prevalence in the environment, there is an immense need of appropriate methods for the removal of APAP. The present study indulged screening and isolation of APAP degrading bacterial strains from pharmaceuticals-contaminated sites, followed by their molecular characterization via 16S rRNA sequencing. The phylogenetic analyses assigned the isolates to the genera Pseudomonas, Bacillus, Paracoccus, Agrobacterium, Brucella, Escherichia, and Enterobacter based on genetic relatedness. The efficacy of these strains in batch cultures tested through High-performance Liquid Chromatography (HPLC) revealed Paracoccus sp. and Enterobacter sp. as the most promising bacterial isolates degrading up to 88.96 and 85.92%, respectively of 300 mg L-1 of APAP within 8 days of incubation. Michaelis-Menten kinetics model parameters also elucidated the high degradation potential of these isolates. The major metabolites identified through FTIR and GC-MS analyses were 4-aminophenol, hydroquinone, and 3-hydroxy-2,4-hexadienedioic. Therefore, the outcomes of this comprehensive investigation will be of paramount significance in formulating strategies for the bioremediation of acetaminophen-contaminated sites through a natural augmentation process via native bacterial strains.

Effects of Tryptophan and Tyrosine on the Transformation of Monophenols in Chromophoric Dissolved Organic Matter Solutions: Enhance the Forward Transformation and Reduce the Reverse Transformation

Tryptophan (Trp) and tyrosine (Tyr) are the primary precursors of protein-like components in dissolved organic matter. Phenolic compounds are ubiquitous in aquatic environments and are considered the main electron donor in chromophoric dissolved organic matter (CDOM). Our results showed that Trp and Tyr (50 μM) enhanced the transformation of six monophenols (20 μM) with varying numbers of -CH3 and -OCH3 substituent groups by a factor of 1.0-1.8. The enhancement factor increased with the ratio of Trp (Tyr) to monophenols. In four different CDOM solutions (5 mg C/L, pH 8.0), a maximum enhancement factor of 3.2-6.7 was observed at a Trp/monophenol concentration ratio of 50. Conversely, monophenols greatly inhibited the transformation of Trp or Tyr. The enhancement factor decreased as the initial pH increased from 3.0 to 10.0. Additionally, the enhancement factor was not directly proportional to the oxidation potential of monophenol. We propose that the promotion effects are generated through the direct oxidation of monophenols by Trp (Tyr) radicals as well as through the reaction between Trp (Tyr) radicals and the one-electron reductant of CDOM.

Biodegradation of acetaminophen: Microcosm centric genomic-proteomic-metabolomics evidences

Acetaminophen (APAP) is a frequently used, over-the-counter analgesic and antipyretic medication. Considering increase in global consumption, its ubiquity in environment with potential toxic impacts has become a cause of great concern. Hence, bioremediation of this emerging contaminant is of paramount significance. The present study incorporates a microcosm centric omics approach to gain in-depth insights into APAP degradation by Paracoccus sp. APAP_BH8. It can metabolize APAP (300 mg kg-1) within 16 days in soil microcosms. Genome analysis revealed potential genes capable of mediating degradation includes M20 aminoacylase family protein, guanidine deaminase, 4-hydroxybenzoate 3-monooxygenase, and 4-hydroxyphenylpyruvate dioxygenase. Whole proteome analysis showed differential expression of enzymes and bioinformatics provided evidence for stable binding of intermediates at the active site of considered enzymes. Metabolites identified were 4-aminophenol, hydroquinone, and 3-hydroxy-cis, cis-muconate. Therefore, Paracoccus sp. APAP_BH8 with versatile enzymatic and genetic attributes can be a promising candidate for formulating improved in situ APAP bioremediation strategies.

Amended Vegetation Filters as Nature-Based Solutions for the Treatment of Pharmaceuticals: Infiltration Experiments Coupled to Reactive Transport Modelling

In small populations and scattered communities, wastewater treatment through vegetation filters (VFs), a nature-based solution, has proved to be feasible, especially for nutrient and organic matter removal. However, the presence of pharmaceuticals in wastewater and their potential to infiltrate through the vadose zone and reach groundwater is a drawback in the evaluation of VF performances. Soil amended with readily labile carbon sources, such as woodchips, enhances microbial activity and sorption processes, which could improve pharmaceutical attenuation in VFs. The present study aims to assess if woodchip amendments to a VF's soil are able to abate concentrations of selected pharmaceuticals in the infiltrating water by quantitatively describing the occurring processes through reactive transport modelling. Thus, a column experiment using soil collected from an operating VF and poplar woodchips was conducted, alongside a column containing only soil used as reference. The pharmaceuticals acetaminophen, naproxen, atenolol, caffeine, carbamazepine, ketoprofen and sulfamethoxazole were applied daily to the column inlet, mimicking a real irrigation pattern and periodically measured in the effluent. Ketoprofen was the only injected pharmaceutical that reached the column outlet of both systems within the experimental timeframe. The absence of acetaminophen, atenolol, caffeine, carbamazepine, naproxen and sulfamethoxazole in both column outlets indicates that they were attenuated even without woodchips. However, the presence of 10,11-epoxy carbamazepine and atenolol acid as transformation products (TPs) suggests that incomplete degradation also occurs and that the effect of the amendment on the infiltration of TPs is compound-specific. Modelling allowed us to generate breakthrough curves of ketoprofen in both columns and to obtain transport parameters during infiltration. Woodchip-amended columns exhibited Kd and μw values from one to two orders of magnitude higher compared to soil column. This augmentation of sorption and biodegradation processes significantly enhanced the removal of ketoprofen to over 96%.

Pharmaceutically active compounds (PhACs) in surface water: Occurrence, trends and risk assessment in the Tagus River Basin (Spain)

In this study, the presence of 23 pharmaceutically active compounds (PhACs) including antibiotics, analgesics, anti-inflammatories, psychiatric and cardiovascular drugs, antifungals and metabolites was investigated in surface waters. A total of 89 samples were collected during 3 years (2020, 2021 and 2022) from a European representative river basin (Tagus, Spain). To elucidate PhAC potential sources, sampling points located in areas with low, median and high anthropogenic influence were selected. The analytical method based on solid phase extraction (SPE) followed by UHPLC-MS/MS analysis was validated meeting SANTE/2020/12830 and SANTE/12682/2019 performance criteria. PhACs were quantified above limits of quantification (LOQs) in 96 % of water samples, being the antihypertensives valsartan (648 ng/L, 87 % quantification frequency) and irbesartan (390 ng/L, 75 %) and the antidepressant o-desmethylvenlafaxine (495 ng/L, 76 %) the predominant pollutants. The rest of the target PhACs showed median concentrations between 4 and 172 ng/L with quantification frequencies ranging from 35 to 75 %. ∑PhAC concentrations did not show temporal or seasonal trends. However, valsartan and naproxen presented lower levels in drier (spring and summer) compared to the wetter. Source identification revealed a clear anthropogenic origin since concentrations obtained in highly populated areas were statistically higher (p < 0.01) than those quantified in sparsely populated ones. This finding was also confirmed by calculating PhACs mass flow rates, which ranged between 1.4 and 235 kg/y. Finally, data generated were used to estimate the potential risk to the aquatic ecosystem for three trophic levels (phototrophic, invertebrate and vertebrate organisms). Risk quotient ratios (RQs) were calculated for all PhACs at the median (P50) and worst-case (max) scenarios. Up to 7 PhACs (acetaminophen, carbamazepine, gemfibrozil, ibuprofen, irbesartan, ketoprofen and venlafaxine) showed high risk for the highest trophic level (fish) in >45 % of investigated locations.

Paracetamol ecotoxicological bioassay using the bioindicators Lens culinaris Med. and Pisum sativum L

Paracetamol is one of the most widely used drugs worldwide, yet its environmental presence and hazardous impact on non-target organisms could rapidly increase. In this study, the possible cytotoxic effects of paracetamol were evaluated using two bioindicator plants Lens culinaris and Pisum sativum. Concentrations of 500, 400, 300, 200, 100, 50, 25, 5, 1 mg L-1, and a control (distilled water) were used for a total of 10 treatments, which were subsequently applied on seeds of Lens culinaris Med. and Pisum sativum L.; after 72 h of exposure, root growth, mitotic index, percentage of chromosomal abnormalities, and the presence of micronucleus were evaluated. The cytotoxic effect of paracetamol on L. culinaris and P. sativum was demonstrated, reporting the inhibition of root growth, the presence of abnormalities, and a significant micronucleus index at all concentrations used, which shows that this drug has a high degree of toxicity.

Acetaminophen Levels Found in Recycled Wastewater Alter Soil Microbial Community Structure and Functional Diversity

The practice of using recycled wastewater (RWW) has been successfully adopted to address the growing demand for clean water. However, chemicals of emerging concern (CECs) including pharmaceutical products remain in the RWW even after additional cleaning. When RWW is used to irrigate crops or landscapes, these chemicals can enter these and adjacent environments. Unfortunately, the overall composition and concentrations of CECs found in different RWW sources vary, and even the same source can vary over time. Therefore, we selected one compound that is found frequently and in high concentrations in many RWW sources, acetaminophen (APAP), to use for our study. Using greenhouse grown eggplants treated with APAP concentrations within the ranges found in RWW effluents, we investigated the short-term impacts of APAP on the soil bacterial population under agricultural settings. Using Illumina sequencing-based approaches, we showed that APAP has the potential to cause shifts in the microbial community most likely by positively selecting for bacteria that are capable of metabolizing the breakdown products of APAP such as glycosides and carboxylic acids. Community-level physiological profiles of carbon metabolism were evaluated using Biolog EcoPlate as a proxy for community functions. The Biolog plates indicated that the metabolism of amines, amino acids, carbohydrates, carboxylic acids, and polymers was significantly higher in the presence of APAP. Abundance of microorganisms of importance to plant health and productivity was altered by APAP. Our results indicate that the soil microbial community and functions could be altered by APAP at concentrations found in RWW. Our findings contribute to the knowledge base needed to guide policies regulating RWW reuse in agriculture and also highlight the need to further investigate the effects of CECs found in RWW on soil microbiomes.

Novel composite of Zn/Ti-layered double hydroxide coupled with MXene for the efficient photocatalytic degradation of pharmaceuticals

In the present study, a hybrid photocatalyst of Zn/Ti layered double hydroxide (LDH) coupled with MXene - Ti₃C₂ was synthesized for the first time and applied in photocatalytic degradation of acetaminophen and ibuprofen, two commonly present in the natural environment and prone to accumulate in the aquatic ecosystem pharmaceuticals. The effect of MXene content (0.5 wt%, 2.5 wt%, and 5 wt%) on the photocatalytic activity of LDH/MXene composite was investigated. The composite of LDH/MXene containing 2.5 wt% of MXene revealed the highest photocatalytic activity in the degradation of acetaminophen (100% within 40 min) and ibuprofen (99.7% within 60 min). Furthermore, an improvement in acetaminophen and ibuprofen mineralization was observed for the composite material. Meanwhile, the introduction of interfering ions (Na⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-) in the model seawater did not affect the removal efficiency of both pharmaceuticals. The photocatalytic experiment performed in the four subsequent cycles, as well as FTIR, TEM, and XPS analyses after the photodegradation process confirmed the excellent stability and reusability of the prepared composite material. In order to evaluate the effect of various reactive oxidizing species (ROS) on the photocatalytic process, the trapping experiment was applied. It was noticed that •O₂^- had the main contribution in photocatalytic degradation of acetaminophen, while •OH and h⁺ mainly affected the degradation of ibuprofen. Finally, based on the results of Mott Schottky analysis, bandgap calculation, and ROS trapping experiment, the possible mechanism for pharmaceuticals degradation was proposed. This research illustrates the feasibility and novelty of the treatment of pharmaceuticals by LDH/MXene composites, implying that MXene plays a significant role in the electron-hole separation and thus high photocatalytic activity.

Sodium tetraborate simultaneously enhances the degradation of acetaminophen and reduces the formation potential of chlorinated by-products with heat-activated peroxymonosulfate oxidation

In this study, sodium tetraborate (Na₂B₄O₇) was introduced to enhance the degradation of acetaminophen (ACT) in heat-activated peroxymonosulfate (PMS) process. The elimination of ACT in Na₂B₄O₇/heat/PMS process followed the pseudo-first order kinetics. The corresponding k_obs value with 10 mM Na₂B₄O₇ was 33.1 times higher than that in heat/PMS process. ¹O₂ and HO· were identified as primary reactive species via quenching experiments and electron paramagnetic resonance technology. B(OH)₄^-, the hydrolysis product of Na₂B₄O₇, reacted with PMS to generate HOOB(OH)₃^-. ¹O₂ was generated by the self-decomposition of PMS using B(OH)₄^- as catalyst, while HO· was produced via the breakage of peroxide bond of PMS and HOOB(OH)₃^-under high temperature. ACT was degraded by reactive species via the pathways of -NH- bond breakage, -OH replacement, -NH₂ oxidation and benzene ring cleavage. Nine transformation intermediates were detected by LC/Q-TOF/MS, and the toxicity of reaction solution decreased significantly with the elimination of ACT. Increasing Na₂B₄O₇ dosage, PMS concentration, initial pH and reaction temperature were conducive to ACT elimination. Humic acid, Cl^- and CO₃^2- inhibited the degradation of ACT heavily, while SO₄^2- and NO₃^- had the negligible effects. Moreover, B(OH)₄^- could react with free chlorine to the inert B(OH)₃OCl^- and further significantly suppress the formation of chlorinated by-products for the treatment of Cl^--containing water in Na₂B₄O₇/heat/PMS process. This study provided an effective way to enhance the oxidation capacity of heat/PMS process and suppress the formation of chlorinated by-products in chloride-containing water, and the findings had important implications for using borate buffer in the studies of PMS-based advanced oxidation processes.

Paracetamol degradation pathways in soil after biochar addition

Little is known about the effect of biochar on the degradation of paracetamol in soil, considering the ubiquity of this pollutant in the environment. Given the importance of the electrochemical properties of biochar for contaminant remediation, we investigated the influence of raw and designer redox-active biochars on paracetamol degradation in soil. Metabolite quantification indicated that a minimum of 53% of the spiked paracetamol was transformed in biochar-amended soil, resulting in the accumulation of different degradation products. The identification of these products allowed us to chart paracetamol degradation pathways in soil with and without biochar amendment. Some of the major degradation routes were observed to proceed via catechol and phenol, despite being previously described as having only a minor role in paracetamol metabolism. Additionally, a new transformation route from paracetamol to NAPQI was discovered in anaerobic soil originating from direct redox reactions on the surface of the designer biochars. These results may contribute to change our understanding of the environmental fate of paracetamol in soil and the role of biochar in its biodegradation.

High-efficiency degradation of phthalic acid esters (PAEs) by Pseudarthrobacter defluvii E5: Performance, degradative pathway, and key genes

Phthalic acid esters (PAEs) are a class of biologically accumulated carcinogenic and teratogenic toxic chemicals that exist widely in the environment. This study, Pseudarthrobacter defluvii E5 was isolated from agricultural soils and showed efficient PAEs-degradation and -mineralization abilities for five PAEs, and encouraging PAEs tolerance and bioavailable range for dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) (0.25-1200 mg/L). The complete catalytic system in E5 genome enables PAEs to be degraded into monoester, phthalate (PA) and Protocatechuic acid (PCA), which eventually enter the tricarboxylic acid cycle (TCA cycle). The preferred PAEs-metabolic pathway in soil by E5 is the metabolism induced by enzymes encoded by pehA, mehpH, pht Operon and pca Operon. For the first time, two para-homologous pht gene clusters were found to coexist on the plasmid and contribute to PAEs degradation. Further study showed that P. defluvii E5 has a broad application prospect in microplastics-contaminated environments.

Two transformation pathways of Acetaminophen with Fe3+ saturated clay particles in dark or light

Acetaminophen (AP) has been frequently detected in different environments due to its wide usage as a common analgesic and antipyretic pharmaceutical. Excess residual of AP in the environment may cause biological risk. However, information about its environmental behaviors was limited, especially the interactions with clay minerals. In this study, AP transformation mediated by Fe³⁺ saturated clay particles was systematically investigated. The results showed 47.6 ± 1.1% or 78.9 ± 0.5% of AP was removed in the presence of Fe³⁺-montmorillonite respectively in dark or under simulated sunlight irradiation after 10 h. The hypothesized mechanism was that exchangeable ferric ions can either obtain electron from AP to form AP radical, or produce ^•OH under light, which can further react with AP. In dark condition, AP radicals could cross-couple with each other to form dimers, while oxidation products were also detected under light irradiation due to ^•OH attacking. Moreover, higher concentration of dissolved oxygen (DO) facilitated Fe³⁺ regeneration on clay surfaces and more reactive Fe species distributed in lower pH, which could significantly enhance the removal of AP both in dark and light. Results of this study revealed that clay minerals played important roles in the abiotic transformation of AP either in dark or under light irradiation, and oligomerization other than mineralization were the dominant processes.

Enhanced dissipation of trace level organic contaminants by floating treatment wetlands established with two macrophyte species: A mesocosm study

This study evaluated removal efficiencies of six contaminants of emerging concern (CECs) in floating treatment wetland (FTW) mesocosms established with either Japanese Sweetflag (Acorus gramineus Sol. ex Aiton) or canna lilies (Canna Hybrida L. 'Orange King Humbert'). The CECs included: acetaminophen (APAP), atrazine (ATZ), carbamazepine (CBZ), perfluorooctanoic acid (PFOA), sulfamethoxazole (SMX), and 17β-estradiol (E2). Each treatment was planted with different numbers of plants (i.e., 0, 10, 15, and 20), and the experiments lasted for 17 weeks. Dissipation of CECs was greater in planted treatments than in non-planted controls, and the planting number had little effect on dissipation of CECs. All residues of APAP and E2 dissipated rapidly within 2 weeks in all planted treatments. At the end of the experiment, residues of ATZ and SMX completely dissipated in the canna treatments, but not in the sweetflag treatments (75.8-87.6% and 96.3-97.1%, respectively). During the 17 week study, moderate dissipation of CBZ was observed in treatments including cannas (79.5-82.6%) and sweetflag (69.4-82.3%), while less dissipation was observed for PFOA (9.0-15.0% with sweetflag and 58.4-62.3% with cannas). Principal component analysis indicates that aqueous persistency of CECs and species of plants used influenced the dissipation of CECs in FTWs. Of the two species evaluated, canna was the most promising plant species for FTW systems designed to remove these CECs from surface water.

Transformation of bromophenols by aqueous chlorination and exploration of main reaction mechanisms

Bromophenols (BPs) are ubiquitous phenolic contaminants and typical halogenated disinfection byproducts (DBPs) that are commonly detected in aquatic environments. The transformation of 2,4-dibromophenol (2,4-DBP) during chlorination process was fully explored in this research. It was found that active chlorine can react with 2,4-DBP effectively in a wide pH range of 5.0-11.0, with an apparent second-order rate constant (k_app) varying from 0.8 M^-1 s^-1 to 110.3 M^-1 s^-1. The addition of 5 mM ammonium ions almost completely suppressed the reaction via competitive consumption of free chlorine. With the concentration of HA increasing from 1.0 to 10.0 mg L^-1, the inhibition on the degradation of 2,4-DBP increased from 8.7% to 63.4%. By contrast, bromide ions at a concentration of 5 mM accelerated the process by about 4 times, due to the formation of hypobromous acid. On the basis of the eleven products (with eight nominal masses) identified by LC-TOF-MS, electrophilic substitution reactions and single-electron transfer reactions were mainly involved in the chlorination process. The concentration of primary chlorine-substituted products was about 4 times that of the dimer products, demonstrating that electrophilic substitution reaction was predominant during chlorination of 2,4-DBP. Density functional theory (DFT) based calculations revealed that HOCl is the dominant active oxidizing species for elimination of 2,4-DBP and coupling reaction occurs more easily at para and ortho position of hydroxyl group in the phenolic moiety. These findings could provide some new insights into the environmental fate of bromophenols during chlorine disinfection of water and wastewaters.

Detoxification and bioaugmentation potential for acetaminophen and its derivatives using Ensifer sp. isolated from activated sludge

Acetaminophen (APAP), a widely used analgesic-antipyretic drug, is frequently detected in the environment and may pose ecological risks to aquatic communities. In this work, an APAP-degrading organism, designated as Ensifer sp. POKHU, was isolated from activated sludge (AS) enriched with APAP. POKHU degraded up to 630 mg/L of APAP without substrate inhibition. The bacterium metabolized APAP to hydroquinone (HQ) via 4-aminophenol (4-AP). APAP derivatives, 4AP, HQ, and 1,4-benzoquinone (BQ), frequently detected in the environment, were found to inhibit nitrogen metabolism (ammonium oxidation) to a greater extent than APAP. POKHU had the ability to degrade varying levels (0.4-40 mg/L) of 4-AP, HQ, and BQ, which indicated a great potential for detoxification in environments contaminated with both APAP and its derivatives. The addition of POKHU to fresh AS samples taken from a wastewater treatment plant greatly increased the biotransformation rates of APAP from 5.6 d^-1 (no POKHU augmentation) to >20.0 d^-1 (5% POKHU). Bioaugmentation with POKHU reduced 400 μg/L of APAP to levels below its ecotoxicity threshold within 4 h, which is shorter than the typical hydraulic retention times for full-scale AS processing. Overall, this study identified a new auxiliary biological agent for APAP detoxification, which could degrade both APAP and its metabolic derivatives (those that can be more toxic than the parent contaminant, APAP). The results have practical implications for developing a biological means (detoxification and bioaugmentation) of treating high-strength pharmaceutical waste streams, such as wastewater from hospitals and drug manufactures, and of landfill leachates.

Activated sludge-degrading analgesic drug acetaminophen: Acclimation, microbial community dynamics, degradation characteristics, and bioaugmentation potential

This study identified specific bacterial populations that play a key role in detoxifying acetaminophen (N-acetyl-p-aminophenol, APAP) in activated sludge (AS) microbial communities. An AS bioreactor was established by feeding 100 mg/L of APAP as a sole carbon, nitrogen, and energy source. While the bioreactor increased APAP biotransformation rates significantly (0.7 d^-1 to 6.1 d^-1) over a month of acclimation, it selected for Pseudomonas by significantly reducing community diversity by 40% and richness by 47%. A Pseudomonas population (designated PCO) isolated from the APAP-degrading community was phylogenetically distinct from other Pseudomonas spp. previously reported as APAP-degrading isolates. PCO could remove APAP at levels up to 590 mg/L without inhibition and could also metabolize APAP-derived metabolites, 4-aminophenol, hydroquinone, and 1,4-benzoquinone at varying levels. PCO was introduced to AS at various volumes (5, 25, and 50% of the total), showing significantly enhanced APAP transformation rates (1.5, 1.9, and 2.3 d^-1) compared to the control (1.2 d^-1) without PCO inoculation. Overall, our study provides new insights into the phylogenetic and metabolic features of a key species population predominantly accelerating APAP breakdown in the context of AS microbial communities, which will help in the design of a biological means (bioaugmentation) of treating APAP-bearing waste streams.

Potential use of floating treatment wetlands established with Canna flaccida for removing organic contaminants from surface water

Surface water bodies worldwide may be contaminated with various organic contaminants. In many cases, the actual toxicity thresholds to nontarget organisms are unknown, thus presenting unknown risks. This study evaluated the potential use of floating treatment wetlands (FTWs) planted with Canna flaccida (common name: Canna) for removing two pharmaceuticals (acetaminophen and carbamazepine) and one herbicide (atrazine) from contaminated water. Triplicate FTWs with varying plant densities were established in 378 L mesocosms. After dosing the mesocosms with the contaminants, water samples were collected over a 12-week period for analysis. The planted FTWs showed differing abilities for removing acetaminophen, atrazine, and carbamazepine. Plant densities on the FTWs did not affect dissipation of acetaminophen or atrazine, but did carbamazepine. All acetaminophen residues were removed from the water within 2 weeks, while all atrazine residues were removed within 12 weeks. Approximately, 79-92% of these residues removed were associated with the FTWs. In contrast, all of the carbamazepine was not removed after 12 weeks, at which time only 29-36.7% of the total removed was associated with the FTWs. Overall results suggest that FTWs established with C. flaccida are promising for removing trace concentrations of acetaminophen, atrazine, and carbamazepine from surface water.

Characterization, optimization and kinetics study of acetaminophen degradation by Bacillus drentensis strain S1 and waste water degradation analysis

Background

In this study, the biodegradation of N-acetyl-para-aminophenol also known as acetaminophen (APAP, paracetamol) was studied by bacterial strain Bacillus drentensis strain S1 (accession no. KY623719) isolated from sewage sample.

Results

The Bacillus drentensis strain S1 was isolated from the sewage sample using the enrichment culture method. As per our knowledge this is the first Bacillus drentensis strain reported for the degradation of APAP. In this study a 20-L batch reactor was employed for degradation of APAP. The maximum specific growth rate (μmax) was observed at 400 mg/L concentration of APAP. The pilot-scale anaerobic batch reactor of was stable and self-buffered. The degradation in pilot-scale reactor was slow as compared to batch experiments due to fluctuation in pH and exhaustion of nutrients. Design-Expert® software was used for optimization of conditions for APAP degradation; such as temperature (40 °C), pH (7.0), concentration of APAP (300 g/L) and agitation speed (165 rpm). The FTIR and GC–MS were used to identify the degradation metabolites. The intermediates of degradation like 2-isopropyl-5-methylcyclohexanone and phenothiazine were observed, based on these results the metabolic pathway has been predicted.

Conclusions

The optimization, kinetic, batch study and pilot study indicates the potential of Bacillus drentensis strain S1 for degradation of acetaminophen. The experimental design, optimization and statistical analysis were performed by Design Expert® software. The optimal growth condition for Bacillus drentensis strain S1 was found to be at temperature 40 °C, pH 7, acetaminophen at concentration of 300 (mg/L) and agitation speed 165 rpm. The GC–MS and FTIR was used for identification of metabolites produced during acetaminophen degradation and the partial metabolic pathway for degradation of acetaminophen was also proposed .

Biotransformation of Acetaminophen by intact cells and crude enzymes of bacteria: A comparative study and modelling

Acetaminophen (APAP), which is an active ingredient of many analgesic drugs, is one of the contaminants of emerging concern in the environment. Although APAP is biodegradable, it is frequently detected in treatment plant effluents, surface water and soil suggesting that there are factors affecting the fate of APAP in the environment. In this study, four strains of bacteria that can degrade APAP were isolated from soil. Those strains belonged to Rhodococcus, Pseudomonas, Flavobacterium, and Sphingobium genera of Bacteria. A series of kinetic experiments were performed on the isolates in shake-flasks to determine biodegradation rate constant as well as the effect of temperature, APAP concentration and cell density on the biodegradation rates. APAP biodegradation follows the first order reaction kinetics which is coupled with cell growth. The specific APAP biodegradation rate constant (k) for all strains was similar and equal to 0.19 ± 0.01 h^-1. The temperature, at which APAP biodegradation rate was maximum, was 35 °C. APAP biodegradation rate was linearly correlated with both the initial APAP concentration and the cell density. Initial step of the APAP biodegradation was hydrolysis of the amide bond which resulted in formation and accumulation of p-aminophenol suggesting that aryl acylamidase enzyme is responsible for the biotransformation. In addition, free and immobilized crude enzymes of the isolates transformed APAP at similar rates, comparable to the intact cells. This study showed that APAP biodegradation is achieved by a diverse group of bacteria having a similar enzyme operating at a constant kinetics which is very slow at environmentally relevant APAP concentrations. Natural removal of APAP in the environment is limited by kinetics, therefore APAP-bearing waste streams should be treated in adsorption enhanced biological systems before discharged into the environment.

Acetaminophen micropollutant: Historical and current occurrences, toxicity, removal strategies and transformation pathways in different environments

Acetaminophen (ACT) is commonly used as a counter painkiller and nowadays, it is increasingly present in the natural water environment. Although its concentrations are usually at the ppt to ppm levels, ACT can transform into various intermediates depending on the environmental conditions. Due to the complexity of the ACT degradation products and the intermediates, it poses a major challenge for monitoring, detection and to propose adequate treatment technologies. The main objectives of this review study were to assess (i) the occurrences and toxicities, (2) the removal technologies and (3) the transformation pathways and intermediates of ACT in four environmental compartments namely wastewater, surface water, ground water, and soil/sediments. Based on the review, it was observed that the ACT concentrations in wastewater can reach up to several hundreds of ppb. Amongst the different countries, China and the USA showed the highest ACT concentration in wastewater (≤300 μg/L), with a very high detection frequency (81-100%). Concerning surface water, the ACT concentrations were found to be at the ppt level. Some regions in France, Spain, Germany, Korea, USA, and UK comply with the recommended ACT concentration for drinking water (71 ng/L). Notably, ACT can transform and degrade into various metabolites such as aromatic derivatives or organic acids. Some of them (e.g., hydroquinone and benzoquinone) are toxic to human and other life forms. Thus, in water and wastewater treatment plants, tertiary treatment systems such as advanced oxidation, membrane separation, and hybrid processes should be used to remove the toxic metabolites of ACT.

Integrated biomarker response index to assess toxic effects of environmentally relevant concentrations of paracetamol in a neotropical catfish (Rhamdia quelen)

The nonsteroidal anti-inflammatory drugs (NSAIDs) are amongst the most commonly detected classes of pharmaceuticals in freshwater environments, with paracetamol being the most abundant. The aim of this study was to evaluate the possible toxic effects of environmentally relevant concentrations (0.25, 2.5 and 25 μg.L^-1) of paracetamol in Rhamdia quelen fish exposed for 14 days using different biomarkers. The total count of leukocytes and thrombocytes was reduced at the highest concentration. In the gills, all concentrations of paracetamol reduced the glutathione S-transferase (GST) activity and the reduced glutathione (GSH) levels compared to the control group. The activity of catalase (CAT) was not altered and glutathione peroxidase (GPx) activity increased at the highest concentrations. The superoxide dismutase (SOD) activity decreased at 25 μg.L^-1 and the LPO levels increased at 2.5 μg.L^-1 when compared to the control group. The concentration of ROS was not different among the groups. In the posterior kidney the activities of GST (2.5 μg.L^-1), CAT (2.5 μg.L^-1 and at 25 μg. L^-1) and GPx and GSH levels increased at all concentrations when compared to the control group. The SOD activity and LPO levels did not change. Paracetamol caused genotoxicity in the blood and gills at concentrations of 2.5 μg.L^-1 and in the posterior kidney at 2.5 and 25 μg.L^-1. An osmoregulatory imbalance in plasma ions and a reduction in the carbonic anhydrase activity in the gills at 0.25 μg.L^-1 were observed. Histopathological alterations occurred in the gills of fish exposed to 25 μg.L^-1 and in the posterior kidney at 0.25 and 25 μg.L^-1 of paracetamol. The integrated biomarker index showed that the stress caused by the concentration of 25 μg.L^-1 was the highest one. These results demonstrated toxic effects of paracetamol on the gills and posterior kidneys of fish, compromising their physiological functions and evidencing the need for monitoring the residues of pharmaceuticals released into aquatic environment.

Transformation of acetaminophen in natural surface water and the change of aquatic microbes

The kinetics and transformation pathway of acetaminophen (APAP) in natural surface water (one sample from the Yangtze River and three others from different lakes), and the changes of aquatic microbes in surface water were revealed in this study. Both photochemical and microbial reactions contributed to the transformation of APAP under irradiance of 1.0-250 mW/cm². Microbial compositions were significantly different among surface water, and same microbial transformation product (1,4-bezoquinone) was detected as the predominant biotransformation intermediate in four studied surface water, but the lag phase (12-50-h) for the transformation was highly dependent on the aquatic microbial abundance and composition. The lag phase no longer existed with irradiance increased to 5.9 mW/cm². Aquatic microbial abundance and composition were influenced by the presence of APAP and radiation, and the influence extent was dependent on microbial species. The findings demonstrated that the individual contribution of biotic and abiotic process to the overall transformation of APAP and maybe other phenol in surface water varied as the background composition of surface water and the external environment changed, and biotransformation dominated (>73%) the overall transformation of APAP in surface water.

Contribution of the Excited Triplet State of Humic Acid and Superoxide Radical Anion to Generation and Elimination of Phenoxyl Radical

Contributions of excited triplet state of humic acid (³HA*) and superoxide radical anion (O₂^•-), which is mainly generated via the reaction of O₂ with HA-derived reducing intermediates (HA^•-), to phenol transformation were revealed using acetaminophen, 2,4,6-trimethylphenol and tyrosine as probe molecules. Phenol transformation was initiated by ³HA*, leading to the formation of the phenoxyl radical (PhO•), but the distribution of transformation intermediates was codetermined by ³HA* and HA^•-. The influence of HA^•- essentially resulted from the production of O₂^•-, which affected the fate of PhO•. PhO• could undergo dimerization, or react with O₂^•-, leading to either phenol peroxide formation (radical addition) or phenol regeneration (electron transfer). In addition, PhO• could bind to HA or react with HA radicals, particularly in the absence of O₂ and O₂^•-. These PhO• reactions were dependent on the reduction potential and structure of PhO•. This study also proved that the reaction of phenol with ¹O₂ and the reaction of PhO• with O₂^•- lead to the same oxidation product. The contributions of ³HA* and its generated ¹O₂, HA^•- and its generated O₂^•- to phenol transformation were pH-dependent.

Removal of acetaminophen in water by laccase immobilized in barium alginate

This research has focused on the optimization of immobilized laccase condition and utilization in degradation of acetaminophen contaminated in aqueous solution. Laccase from Lentinus polychrous was immobilized in barium alginate. The effects of laccase immobilization such as sodium alginate concentration, barium chloride concentration and gelation time were studied. The optimal conditions for immobilization were sodium alginate 5% (w/v), barium chloride 5% (w/v) and gelation time of 60 min. Immobilized laccase was then used for acetaminophen removal. Acetaminophen was removed quickly in the first 50 min. The degradation rate and percentage of removal increased when the enzyme concentration increased. Immobilized laccase at 0.57 U/g-alginate showed the maximum removal at 94% in 240 min. The removal efficiency decreased with increasing initial acetaminophen concentration. The K_m value for immobilized laccase (98.86 µM) was lower than that of free laccase (203.56 µM), indicating that substrate affinity was probably enhanced by immobilization. The immobilized enzyme exhibited high activity and good acetaminophen removal at pH 7 and temperature of 35°C. The activation energies of free and immobilized laccase for degradation of acetaminophen were 8.08 and 17.70 kJ/mol, respectively. It was also found that laccase stability to pH and temperature increased after immobilization. Furthermore, immobilized laccase could be reused for five cycles. The capability of removal and enzyme activity were retained above 70%.

Degradation of acetaminophen in aqueous solution under visible light irradiation by Bi-modified titanate nanomaterials: morphology effect, kinetics and mechanism

Three morphologies of Bi-modified titanate nanomaterials were prepared using the hydrothermal method and controlled parameters to degrade acetaminophen.

Significant changes in the photo-reactivity of TiO2 in the presence of a capped natural dissolved organic matter layer

Natural dissolved organic matter (NDOM) in surface waters has a high sorption affinity for TiO₂ during long contact. An attached NDOM layer can act as a conduction band electron and/or valance band hole acceptor, and NDOM can also decrease the concentration of hydroxyl radicals (OH) in the bulk phase. Therefore, the degradation kinetics and mechanism for degradation of acetaminophen on NDOM capped TiO₂ (NDOM-TiO₂) are significantly different from those on raw TiO₂. Quantum calculation results suggest that hydroxylation to the ortho position in relation to the acetamide group is more favorable. Although OH induced hydroxylation is the predominant pathway for degradation of acetaminophen on TiO₂, one-electron oxidation of acetaminophen by a valance band hole, excited triplet NDOM or NDOM radical cation is the major degradation pathway on NDOM-TiO₂. This study is the first to detect and confirm APAP oligomers as intermediates during the degradation of acetaminophen by TiO₂ photocatalysis, especially when using NDOM-TiO₂ as a catalyst. The results suggest the reactivity of TiO₂ could change significantly after long exposure to natural water, which need to be concerned about for removal of micropollutants in surface water by TiO₂ photocatalysis.

Photosensitized degradation of acetaminophen in natural organic matter solutions: The role of triplet states and oxygen

The photolysis of acetaminophen, a widely used pharmaceutical, in simulated natural organic matter solutions was investigated. The triplet states of natural organic matter (³NOM*) were found to play the dominant role in its photodegradation, while the contributions from hydroxyl radicals and singlet oxygen were negligible. Dissolved oxygen (DO) plays a dual role. From anaerobic to microaerobic (0.5 mg/L DO) conditions, the degradation rate of acetaminophen increased by 4-fold. That suggests the involvement of DO in reactions with the degradation intermediates. With increasing oxygen levels to saturated conditions (26 mg/L DO), the degradation rate became slower, mainly due to DO's quenching effect on ³NOM*. Superoxide radical (O₂^-) did not react with acetaminophen directly, but possibly quenched the intermediates to reverse the degradation process. The main photochemical pathways were shown to involve phenoxyl radical and N-radical cations, finally yielding hydroxylated derivatives, dimers and nitrosophenol. A reaction mechanism involving ³NOM*, oxygen and O₂^- is proposed.

Effects of Engineered Nanoparticles on the Enantioselective Transformation of Metalaxyl Agent and Commercial Metalaxyl in Agricultural Soils

The adsorption coefficient of racemic metalaxyl onto an agriculture soil was small and nonenantioselective. Biotransformation was the predominant pathway for the elimination of R-metalaxyl, while abiotic and biotransformation made a comparable contribution to the degradation of S-metalaxyl. Metalaxyl acid was the main transformation intermediate. The enantiomer fraction of metalaxyl decreased with an increase in its initial spike concentration or the presence of the co-constituents in metalaxyl commercial products. Under simulated solar irradiation, the presence of TiO₂ promoted the overall transformation kinetics through enhanced biotransformation and extra photoinduced chemical reactions. The promotion was enantioselective and thereafter changed the enantiomer fraction. The results obtained in this study showed that some achiral parameters, although they have no direct impact on enantioselective reactions with enantiomers, can significantly affect the enantioselective transformation of racemic metalaxyl. Thus, our results indicate that the contribution of chemical interactions on the enantioselective transformation of chiral pesticides may be underestimated.