Screening for pharmaceutical transformation products formed in river sediment by combining ultrahigh performance liquid chromatography/high resolution mass spectrometry with a rapid data-processing method

Comprehensive analysis of a widely pharmaceutical, furosemide, and its degradation products in aquatic systems: Occurrence, fate, and ecotoxicity

Many pharmaceutical compounds end up in the environment due to incomplete removal by wastewater treatment plants (WWTPs). Some compounds are sometimes present in significant concentrations and therefore represent a risk to the aquatic environment. Furosemide is one of the most widely used drugs in the world. Considered as an essential drug by the World Health Organization, this powerful loop diuretic is used extensively to treat hypertension, heart and kidney failure and many other purposes. However, this important consumption also results in a significant release of furosemide in wastewater and in the receiving environment where concentrations of a few hundred ng/L to several thousand have been found in the literature, making furosemide a compound of great concern. Also, during its transport in wastewater systems and WWTPs, furosemide can be degraded by various processes resulting in the production of more than 74 by-products. Furosemide may therefore present a significant risk to ecosystem health due not only to its direct cytotoxic, genotoxic and hepatotoxic effects in animals, but also indirectly through its transformation products, which are poorly characterized. Many articles classify furosemide as a priority pollutant according to its occurrence in the environment, its persistence, its elimination by WWTPs, its toxicity and ecotoxicity. Here, we present a state-of-the-art review of this emerging pollutant of interest, tracking it, from its consumption to its fate in the aquatic environment. Discussion points include the occurrence of furosemide in various matrices, the efficiency of many processes for the degradation of furosemide, the subsequent production of degradation products following these treatments, as well as their toxicity.

Occurrence, environmental impact and fate of pharmaceuticals in groundwater and surface water: a critical review

In many nations and locations, groundwater serves as the population's primary drinking water supply. However, pharmaceuticals found in groundwater and surface waters may affect aquatic ecosystems and public health. As a result, their existence in natural raw waters are now more widely acknowledged as a concern. This review summarises the evidence of research on pharmaceuticals' occurrence, impact and fate, considering results from different water bodies. Also, various analytical techniques were reviewed to compare different pharmaceuticals' detection frequencies in water bodies. These include liquid chromatography-mass spectrometry (LC-MS), high-performance liquid chromatography (HPLC), ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and gas chromatography-mass spectrometry (GC-MS). However, owing to LC-MS's high sensitivity and specification, it is the most reported instrument used for analysis. The PRISMA reviewing methodology was adopted based on relevant literature in order to focus on aim of the review. Among other pharmaceuticals reviewed, sulfamethoxazole was found to be the most frequently detected drug in wastewater (up to 100% detection frequency). The most reported pharmaceutical group in this review is antibiotics, with sulfamethoxazole having the highest concentration among the analysed pharmaceuticals in groundwater and freshwater (up to 5600 ng/L). Despite extensive study and analysis on the occurrence and fate of pharmaceuticals in the environment, appropriate wastewater management and disposal of pharmaceuticals in the water environment are not still monitored regularly. Therefore, there is a need for mainstream studies tailored to the surveillance of pharmaceuticals in water bodies to limit environmental risks to human and aquatic habitats in both mid and low-income nations.

Occurrence and fate of an emerging drug pollutant and its by-products during conventional and advanced wastewater treatment: Case study of furosemide

Conventional wastewater treatment systems are not designed to remove pharmaceutical compounds from wastewater. These compounds can be degraded into many other transformation products which are hardly, if at all, studied. In this context, we studied the occurrence and degradation of furosemide, a very frequently detected diuretic, along with its known degradation products in several types of wastewater. Influent and effluent from the Seine-Centre Wastewater Treatment Plant (WWTP) (Paris, France) as well as outlet of residential care homes (Dordogne, France) were analyzed by Ultra-Performance Liquid Chromatography-tandem Mass Spectrometry (UPLC-MS/MS) to quantify furosemide and its known degradation products, saluamine and pyridinium of furosemide. Oxidation experiments (chlorination, ozonation and UV photolysis with hydrogen peroxide) were then performed on furosemide solutions and on water from residential care facilities to study the degradation of furosemide by potential advanced processes, and also to identify unknown oxidation products by high-resolution mass spectrometry. Furosemide was well degraded in Seine-Centre WWTP (>75%) but did not increase the concentrations of its main degradation products. Saluamine and pyridinium of furosemide were already present at similar concentrations to furosemide in the raw wastewater (∼2.5-3.5 μg.L^-1), and their removal in the WWTPs were very high (>80%). Despite their removal, the three compounds remained present in treated wastewater effluents at concentrations of hundreds of nanograms per liter. Chlorination degraded furosemide without pyridinium production unlike the other two processes. Chlorination and ozonation were also effective for the removal of furosemide and pyridinium in residential care home water, but they resulted in the production of saluamine. To our knowledge this is the first evidence of saluamine and pyridinium of furosemide in real water samples in either the particulate or dissolved phase.

Identification and trend analysis of organic cationic contaminants via non-target screening in suspended particulate matter of the German rivers Rhine and Saar

Non-target screening of suspended particulate matter (SPM), collected from the German rivers Rhine and Saar, was conducted with the goal of identifying organic, permanent cationic contaminants and of estimating their temporal trends over an extended period. Therefore, annual composite samples of SPM, provided by the German Environmental Specimen Bank, were extracted and analyzed with high resolution LC-QToF-MS/MS. To facilitate the identification of substances belonging to the class "permanent cations", prioritization methods were applied utilizing the physicochemical properties of these compounds. These methods include both interactions of the analyte molecules with cation exchange resins and analyzing mass deviations when changing from non-deuterated to deuterated mobile phase solvents during LC-MS analysis. By applying both methods in a combined approach, 123 of the initially detected 2695 features were prioritized, corresponding to a 95% data reduction. This led to the identification of 22 permanent cationic species. The organic dyes Basic Yellow 28 and Fluorescent Brightener 363 as well as two quaternary ammonium compounds (QACs) were detected in environmental samples for the first time to best of or knowledge. The other compounds include additional QACs, as well as quaternary tri-phenylphosphonium compounds (QPC/TPP). In addition to identification, we determined temporal trends of all compounds over a period of 13 years and assessed their ecotoxicological relevance based on estimated concentrations. The two QACs oleyltrimethylammonium and eicosyltrimethylammonium show significant increasing trends in the Rhine SPM and maximum concentrations in the Saar SPM of about 900 and 1400 µg/kg, respectively. In the case of the dyes, constant trends have been observed at the end of the studied period, but also maximum concentrations of 400 µg/kg for Basic Yellow 28 in 2006 and 1000 µg/kg for Fluorescent Brightener 363 in 2015, potentially indicating a strong ecotoxicological risk.

A multi-biomarker approach to assess toxicity of diclofenac and 4-OH diclofenac in Mytilus trossulus mussels - First evidence of diclofenac metabolite impact on molluscs

Although the presence of pharmaceuticals in the environment is an issue widely addressed in research over the past two decades, still little is known about their transformation products. However, there are indications that some of these chemicals may be equally or even more harmful than parent compounds. Diclofenac (DCF) is among the most commonly detected pharmaceuticals in the aquatic environment, but the potential effects of its metabolites on organisms are poorly understood. Therefore, the present study aimed to evaluate and compare the toxicity of DCF and its metabolite, 4-hydroxy diclofenac (4-OH DCF), in mussels using a multi-biomarker approach. Mytilus trossulus mussels were exposed to DCF and 4-OH DCF at 68.22 and 20.85 μg/L (measured concentrations at day 0), respectively, for 7 days. In our work, we showed that both tested compounds have no effect on most of the enzymatic biomarkers tested. However, it has been shown that their action can affect the protein content in gills and also be reflected through histological markers. ENVIRONMENTAL IMPLICATION: Studies in recent years clearly prove that pharmaceuticals can negatively affect aquatic organisms. In addition to parent compounds, metabolites of pharmaceuticals can also be a significant environmental problem. In the present work, the effects of diclofenac and its main metabolite, 4-hydroxy diclofenac, on marine mussels were evaluated. Both compounds showed negative effects on mussels, which was primarily observed through histological changes. The present study therefore confirms that not only diclofenac, but also its main metabolite can have negative effects on aquatic organisms.

In Silico Structure Predictions for Non-targeted Analysis: From Physicochemical Properties to Molecular Structures

While important advances have been made in high-resolution mass spectrometry (HRMS) and its applications in non-targeted analysis (NTA), the number of identified compounds in biological and environmental samples often does not exceed 5% of the detected chemical features. Our aim was to develop a computational pipeline that leverages data from HRMS but also incorporates physicochemical properties (equilibrium partition ratios between organic solvents and water; Ksolvent-water) and can propose molecular structures for detected chemical features. As these physicochemical properties are often sufficiently different across isomers, when put together, they can form a unique profile for each isomer, which we describe as the "physicochemical fingerprint". In our study, we used a comprehensive database of compounds that have been previously reported in human blood and collected their Ksolvent-water values for 129 partitioning systems. We used RDKit to calculate the number of RDKit fragments and the number of RDKit bits per molecule. We then developed and trained an artificial neural network, which used as an input the physicochemical fingerprint of a chemical feature and predicted the number and types of RDKit fragments and RDKit bits present in that structure. These were then used to search the database and propose chemical structures. The average success rate of predicting the right chemical structure ranged from 60 to 86% for the training set and from 48 to 81% for the testing set. These observations suggest that physicochemical fingerprints can assist in the identification of compounds with NTA and substantially improve the number of identified compounds.

Transformation products of pharmaceuticals in the environment: Their fate, (eco)toxicity and bioaccumulation potential

Nowadays, a huge scientific attention is being paid to the chemicals of emerging concern, which may pose a significant risk to the human and whole ecosystems. Among them, residues of pharmaceuticals are a widely investigated group of chemicals. In recent years it has been repeatedly demonstrated that pharmaceuticals are present in the environment and that some of them can be toxic to organisms as well as accumulate in their tissues. However, even though the knowledge of the presence, fate and possible threats posed by the parent forms of pharmaceuticals is quite extensive, their transformation products (TPs) have been disregarded for long time. Since last few years, this aspect has gained more scientific attention and recently published papers proved their common presence in the environment. Also the interest in terms of their toxicity, bioconcentration and stability in the environment has increased. Therefore, the aim of our paper was to revise and assess the current state of knowledge on the fate and effects resulting from the presence of the pharmaceuticals' transformation drugs in the environment. This review discusses the metabolites of compounds belonging to six major pharmaceutical groups: SSRIs, anticancer drugs, antibiotics, antihistamines, NSAIDs and opioids, additionally discussing other individual compounds for which literature data exist. The data presented in this paper prove that some TPs may be as harmful as their native forms, however for many groups of drugs this data is still insufficient to assess the risk posed by their presence in the environment.

What is in Nigerian waters? Target and non-target screening analysis for organic chemicals

Emerging organic contaminants (e.g., active pharmaceutical ingredients and personal care products ingredients) are ubiquitous in the environment and potentially harmful to ecosystems, have gained increasing public attention worldwide. Nevertheless, there is a scarcity of data on these contaminants in Africa. In this study, various types of water samples (wastewater, surface water and tap water) collected from Lagos, Nigeria were analyzed for these chemicals by both target and non-target analysis on an UHPLC-Orbitrap-MS/MS. In total, 109 compounds were identified by non-target screening using the online database mzCloud. Level 1 identification confidence was achieved for 13 compounds for which reference standards were available and level 2 was achieved for the rest. In the quantitative analysis, 18 of 38 target compounds were detected, including the parent compounds and their metabolites. Acetaminophen, sulfamethoxazole, acesulfame, and caffeine were detected in all samples with their highest concentrations at 8000, 5300, 16, and 7700 μg/L in wastewater, 140000, 3300, 7.7, and 12000 μg/L in surface water, and 66, 62, 0.17 and 1000 μg/L in tap water, respectively. The occurrence of psychoactive substances, anticancer treatments, antiretrovirals, antihypertensives, antidiabetics and their metabolites were reported in Nigeria for the first time. These results indicate poor wastewater treatment and management in Nigeria, and provide a preliminary profile of organic contaminants occurring in Nigerian waters. The findings from this study urge more future research on chemical pollution in the aquatic environments in Nigeria.

Exposure of Mytilus trossulus to diclofenac and 4'-hydroxydiclofenac: Uptake, bioconcentration and mass balance for the evaluation of their environmental fate

Diclofenac (DIC) is one of the most widely consumed drugs in the world, and its presence in the environment as well as potential effects on organisms are the subject of numerous recent scientific works. However, it is becoming clear that the risk posed by pharmaceuticals in the environment needs to be viewed more broadly and their numerous derivatives should also be considered. In fact, already published results confirm that the transformation products of NSAIDs including DIC may cause a variety of potentially negative effects on marine organisms, sometimes showing increased biological activity. To date, however, little is known about bioconcentration of DIC and DIC metabolites and the role of sex in this process. Therefore, the present study for the first time evaluates sex-related differences in DIC bioconcentration and estimates bioconcentration potential of DIC metabolite, 4-OH DIC, in the Mytilus trossulus tissues. In the experiment lasting 7 days, mussels were exposed to DIC and 4-OH DIC at concentrations 68.22 and 20.85 μg/L, respectively. Our study confirms that DIC can be taken up by organisms not only in its native form, but also as a metabolite, and metabolised further. Furthermore, in the present work, mass balance was performed and the stability of both studied compounds under experimental conditions was analysed. Obtained results suggest that DIC is more stable than its derivative under the tested conditions, but further analyses of the environmental fate of these compounds are necessary.

Transformation of organic micropollutants along hyporheic flow in bedforms of river-simulating flumes

Urban streams receive increasing loads of organic micropollutants from treated wastewaters. A comprehensive understanding of the in-stream fate of micropollutants is thus of high interest for water quality management. Bedforms induce pumping effects considerably contributing to whole stream hyporheic exchange and are hotspots of biogeochemical turnover processes. However, little is known about the transformation of micropollutants in such structures. In the present study, we set up recirculating flumes to examine the transformation of a set of micropollutants along single flowpaths in two triangular bedforms. We sampled porewater from four locations in the bedforms over 78 days and analysed the resulting concentration curves using the results of a hydrodynamic model in combination with a reactive transport model accounting for advection, dispersion, first-order removal and retardation. The four porewater sampling locations were positioned on individual flowpaths with median solute travel times ranging from 11.5 to 43.3 h as shown in a hydrodynamic model previously. Highest stability was estimated for hydrochlorothiazide on all flowpaths. Lowest detectable half-lives were estimated for sotalol (0.7 h) and sitagliptin (0.2 h) along the shortest flowpath. Also, venlafaxine, acesulfame, bezafibrate, irbesartan, valsartan, ibuprofen and naproxen displayed lower half-lives at shorter flowpaths in the first bedform. However, the behavior of many compounds in the second bedform deviated from expectations, where particularly transformation products, e.g. valsartan acid, showed high concentrations. Flowpath-specific behavior as observed for metformin or flume-specific behavior as observed for metoprolol acid, for instance, was attributed to potential small-scale or flume-scale heterogeneity of microbial community compositions, respectively. The results of the study indicate that the shallow hyporheic flow field and the small-scale heterogeneity of the microbial community are major controlling factors for the transformation of relevant micropollutants in river sediments.

Assessment of the presence of transformation products of pharmaceuticals in agricultural environments irrigated with reclaimed water by wide-scope LC-QTOF-MS suspect screening

The transformation that pharmaceuticals can undergo during the water reclamation cycle, or by biotic/abiotic reactions when reclaimed water (RW) is used for irrigation, can lead to the presence of transformation products (TPs) in agricultural environments. However, data on TPs in real crops are scarce. Herein, a suspect screening approach was applied for the comprehensive investigation of 262 potential TPs, associated with 20 prioritised pharmaceuticals found in real tomato crops exposed to long-term RW irrigation. The occurrence and fate of the TPs was evaluated by the retrospective analysis of RW, soil, leave and tomato samples from 4 intensive production greenhouses. Sample analysis was accomplished by liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS). Up to 18 TPs were tentatively identified, of which 2 were not previously reported. 7 TPs were finally confirmed with analytical standards. 5 TPs were determined in RW, 15 TPs in soil and 2 TPs in leaves. Remarkably, the investigated TPs were not found in tomato fruits. These results shed light on the variety of TPs that can be found in the water reuse cycle and contribute to the assessment of the global risks of wastewater reuse and the safety of the vegetable and fruit production system.

An integrated approach to MS-based identification and risk assessment of pharmaceutical biotransformation in wastewater

The omnipresence of pharmaceuticals at relatively high concentrations (μg/L) in environmental compartments indicated their inadequate removal by wastewater treatment plants. As such, batch reactors seeded with activated sludge were set up to assess the biotransformation of metformin, ranitidine, lidocaine and atorvastatin. The main objective was to identify transformation products (TPs) through the establishment of an integrated workflow for suspect and non-target screening based on reversed phase liquid chromatography quadrupole-time-of-flight mass spectrometry. To support the identification, hydrophilic interaction liquid chromatography (HILIC) was used as a complementary tool, in order to enhance the completeness of the developed workflow by identifying the more polar TPs. The structure assignment/elucidation of the candidate TPs was mainly based on interpretation of MS/MS spectra. Twenty-two TPs were identified, with fourteen of them reaching high identification confidence levels (level 1: confirmed structure by reference standards and level 2: probable structure by library spectrum match and diagnostic evidence). Finally, retrospective analysis in influent and effluent wastewater was performed for the TPs for four consecutive years in wastewater sampled in Athens, Greece. The potential toxicological threat of the compounds to the aquatic environment was assessed and atorvastatin with two of its TPs showed a potential risk to the aquatic organisms.

Occurrence of carbamazepine, diclofenac, and their related metabolites and transformation products in a French aquatic environment and preliminary risk assessment

With questions emerging on the presence and risks associated with metabolites and transformation products (TPs) of organic contaminants in the aquatic environment, progress has been made in terms of monitoring and regulation of pesticide metabolites. However, less interest is shown for pharmaceutical residues, although their pseudo-persistence and adverse effects on non-target organisms are proven. This study provides original knowledge about the contamination of ten sites located along three French rivers (water, sediments, biofilms, clams) by pharmaceutical metabolites and TPs, as well as a preliminary environmental risk assessment. Studied compounds included carbamazepine with five metabolites and TPs, and diclofenac with three metabolites and TPs. Results show that metabolites and TPs are present in all studied compartments, with mean concentrations up to 0.52 µg L^-1 in water, 229 ng g^-1 in sediments, 2153 ng g^-1 in biofilms, and 1149 ng g^-1 in clams. QSAR estimations (OECD toolbox) were involved to predict the studied compounds ecotoxicities. QSAR models showed that diclofenac and its metabolites and TPs could be more toxic than carbamazepine and its metabolites and TPs to three aquatic species representing green algae, invertebrates, and fish. However, real ecotoxicological effects are still to be determined. The environmental risk assessment showed that hydroxydiclofenac, 2-[(2-chlorophenyl)-amino]-benzaldehyde and dibenzazepine could present a greater risk than other studied compounds for aquatic organisms. In addition, the risk associated with a mixture of diclofenac and its related metabolites and TPs has been found to be greater than that of the compounds considered individually.

Fate of Trace Organic Compounds in Hyporheic Zone Sediments of Contrasting Organic Carbon Content and Impact on the Microbiome

The organic carbon in streambed sediments drives multiple biogeochemical reactions, including the attenuation of organic micropollutants. An attenuation assay using sediment microcosms differing in the initial total organic carbon (TOC) revealed higher microbiome and sorption associated removal efficiencies of trace organic compounds (TrOCs) in the high-TOC compared to the low-TOC sediments. Overall, the combined microbial and sorption associated removal efficiencies of the micropollutants were generally higher than by sorption alone for all compounds tested except propranolol whose removal efficiency was similar via both mechanisms. Quantitative real-time PCR and time-resolved 16S rRNA gene amplicon sequencing revealed that higher bacterial abundance and diversity in the high-TOC sediments correlated with higher microbial removal efficiencies of most TrOCs. The bacterial community in the high-TOC sediment samples remained relatively stable against the stressor effects of TrOC amendment compared to the low-TOC sediment community that was characterized by a decline in the relative abundance of most phyla except Proteobacteria. Bacterial genera that were significantly more abundant in amended relative to unamended sediment samples and thus associated with biodegradation of the TrOCs included Xanthobacter, Hyphomicrobium, Novosphingobium, Reyranella and Terrimonas. The collective results indicated that the TOC content influences the microbial community dynamics and associated biotransformation of TrOCs as well as the sorption potential of the hyporheic zone sediments.

TiO2 and N-TiO2-photocatalytic degradation of salicylic acid in water: characterization of transformation products by mass spectrometry

The aim of this work is to study the byproducts formed as a result of the photocatalytic process under different conditions of light wavelength and photocatalyst doping, rendering valuable information about the fate of pollutants for water treatment applications. Salicylic acid was selected as a model emerging pollutant and powders of nitrogen-doped titanium dioxide (N-TiO₂) and TiO₂ were prepared by the sol-gel process, using TiO₂ P-25 Degussa as benchmark. Two light sources, UVA fluorescent tubes (372 nm) and blue LEDs (462 nm), were employed for photolysis and photocatalysis experiments. Transformation products formed during the process were studied by high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS). Major differences were found in the amount and identity of the transformation products due to the different light sources, detecting similar transformation products among the studied catalysts. Under UVA light, hydroxylated and carbonylated byproducts were the first intermediates to reach maximum abundances whereas presumed ring opening products were the last ones. On the other hand, under blue LED illumination byproducts accumulated with decreased mineralization. Photocatalytic degradation pathways were proposed based on the findings.

Application of a non-target workflow for the identification of specific contaminants using the example of the Nidda river basin

Non-target screening of water samples from the Nidda river basin in central Germany was conducted with the goal to identify previously unknown chemical contaminants and their emission sources. The focus was on organic, water-borne contaminants which were not typical to municipal wastewater. Grab samples of river water from 13 locations on the Nidda and 15 of its tributaries, in sum 112 samples, were analysed with high resolution LC-QToF-MS/MS. To facilitate the identification of substances, features originating from the same compound such as adducts and isotopologues as well as in-source fragments and species with multiple charge states were registered and grouped by a componentization step utilizing both retention times and peak shapes of the features to combine them in a single component. This led to a reduction of the number of features by an average of 1235 per sample (46%). These grouped features were prioritized if these were detected only in specific tributaries or specific river sections, reducing the number of components by an average of 913 per sample (78%). In addition, grouped features were labelled as typically found in municipal wastewater by combining data from 16 wastewater treatment plants located across Germany and Switzerland and comparing this to components detected in the Nidda basin. These were removed, leading to a further reduction of components by an average of 72 per sample (30%) for an average total reduction of 2536 per sample (93%). Finally, nine compounds, with emission sources in three specific tributaries, were identified, including the textile additive Nylostab S-EED®, which was previously not known to be an environmental contaminant, as well as naturally occurring compounds such as highly toxic microcystins.

Bacterial Diversity Controls Transformation of Wastewater-Derived Organic Contaminants in River-Simulating Flumes

Hyporheic zones are the water-saturated flow-through subsurfaces of rivers which are characterized by the simultaneous occurrence of multiple physical, biological, and chemical processes. Two factors playing a role in the hyporheic attenuation of organic contaminants are sediment bedforms (a major driver of hyporheic exchange) and the composition of the sediment microbial community. How these factors act on the diverse range of organic contaminants encountered downstream from wastewater treatment plants is not well understood. To address this knowledge gap, we investigated dissipation half-lives (DT50s) of 31 substances (mainly pharmaceuticals) under different combinations of bacterial diversity and bedform-induced hyporheic flow using 20 recirculating flumes in a central composite face factorial design. By combining small-volume pore water sampling, targeted analysis, and suspect screening, along with quantitative real-time PCR and time-resolved amplicon Illumina MiSeq sequencing, we determined a comprehensive set of DT50s, associated bacterial communities, and microbial transformation products. The resulting DT50s of parent compounds ranged from 0.5 (fluoxetine) to 306 days (carbamazepine), with 20 substances responding significantly to bacterial diversity and four to both diversity and hyporheic flow. Bacterial taxa that were associated with biodegradation included Acidobacteria (groups 6, 17, and 22), Actinobacteria (Nocardioides and Illumatobacter), Bacteroidetes (Terrimonas and Flavobacterium) and diverse Proteobacteria (Pseudomonadaceae, Sphingomonadaceae, and Xanthomonadaceae). Notable were the formation of valsartan acid from irbesartan and valsartan, the persistence of N-desmethylvenlafaxine across all treatments, and the identification of biuret as a novel transformation product of metformin. Twelve additional target transformation products were identified, which were persistent in either pore or surface water of at least one treatment, indicating their environmental relevance.

Comparing non-targeted chemical persistence assessed using an unspiked OECD 309 test to field measurements

Previous research has shown that unspiked OECD 309 tests can be used to quantify chemical biodegradation in surface waters, relying on chemical residues already present in the water. Here we test the hypothesis that unspiked OECD 309 tests can quantitatively predict chemical persistence in the environment by comparing chemical half-lives assessed in the laboratory against those measured in the field. The study object was a Swedish lake heavily impacted by treated municipal wastewater. Half-lives in the field were measured by mass balance over 12 weeks. In parallel, half-lives in the lab were determined with an unspiked OECD 309 test run for 60 days. Chemical analysis was conducted using a non-target screening approach. The field study yielded a half-life <100 days for 38 chemicals for which the dominant source was wastewater; 32 of these were also detected in the lab test, whereby 18 had half-lives with a well-constrained uncertainty that did not intersect infinity. For 14 of the 18 chemicals, the field and lab half-lives agreed within a factor 3. In summary, the lab test predicted chemical attenuation in the field well. Limitations of the approach include the need for measurable chemical concentrations in the water body and failure to account for some attenuation mechanisms like phototransformation.

Using recirculating flumes and a response surface model to investigate the role of hyporheic exchange and bacterial diversity on micropollutant half-lives

Enhancing the understanding of the fate of wastewater-derived organic micropollutants in rivers is crucial to improve risk assessment, regulatory decision making and river management. Hyporheic exchange and sediment bacterial diversity are two factors gaining increasing importance as drivers for micropollutant degradation, but are complex to study in field experiments and usually ignored in laboratory tests aimed to estimate environmental half-lives. Flume mesocosms are useful to investigate micropollutant degradation processes, bridging the gap between the field and batch experiments. However, few studies have used flumes in this context. We present a novel experimental setup using 20 recirculating flumes and a response surface model to study the influence of hyporheic exchange and sediment bacterial diversity on half-lives of the anti-epileptic drug carbamazepine (CBZ) and the artificial sweetener acesulfame (ACS). The effect of bedform-induced hyporheic exchange was tested by three treatment levels differing in number of bedforms (0, 3 and 6). Three levels of sediment bacterial diversity were obtained by diluting sediment from the River Erpe in Berlin, Germany, with sand (1 : 10, 1 : 1000 and 1 : 100 000). Our results show that ACS half-lives were significantly influenced by sediment dilution and number of bedforms. Half-lives of CBZ were higher than ACS, and were significantly affected only by the sediment dilution variable, and thus by bacterial diversity. Our results show that (1) the flume-setup is a useful tool to study the fate of micropollutants in rivers, and that (2) higher hyporheic exchange and bacterial diversity in the sediment can increase the degradation of micropollutants in rivers.

Using carbon substrate as a selection pressure to enhance the potential of aerobic granular sludge microbial communities for removing contaminants of emerging concern

The ability of aerobic granular sludge (AGS) technology to biotransform contaminants of emerging concern (CECs) is largely unknown. AGS supplemented with either acetate, 2-propanol, glycerol, or a 1:1:1 mixture of all three, were cultivated to investigate the link between carbon supplements and biotransformation of six CECs. Carbon substrate had a significant effect on the microbial community composition, as assessed by 16S rRNA gene sequence analyses. Substrate degradation requiring a larger number of catabolic reactions (i.e., glycerol and the mix) was associated with greater microbial richness. The biotransformation of CECs was 45.9% greater in communities supplemented with glycerol (60.3 ± 30.2 µg L^-1 VSS^-1) compared to acetate (20.9 ± 29.7 µg L^-1 VSS^-1). Database surveys of metabolic reactions indicate that microbial communities supplemented with glycerol have the greatest capacity for the degradation of aromatic compounds, while those supplemented with acetate community have the lowest.

Spatial and Temporal Variability in Attenuation of Polar Organic Micropollutants in an Urban Lowland Stream

Contamination of rivers by trace organic compounds (TrOCs) poses a risk for aquatic ecosystems and drinking water quality. Spatially- and temporally varying environmental conditions are expected to play a major role in controlling in-stream attenuation of TrOCs. This variability is rarely captured by in situ studies of TrOC attenuation. Instead, snap-shots or time-weighted average conditions and corresponding attenuation rates are reported. The present work sought to investigate this variability and factors controlling it by analysis of 24 TrOCs over a 4.7 km reach of the River Erpe (Berlin, Germany). The factors investigated included sunlight and water temperature as well as the presence of macrophytes. Attenuation rate constants in 48 consecutive hourly water parcels were tracked along two contiguous river sections of different characteristics. Section 1 was less shaded and more densely covered with submerged macrophytes compared to section 2. The sampling campaign was repeated after macrophyte removal from section 1. The findings show, that section 1 generally provided more favorable conditions for both photo- and biodegradation. Macrophyte removal enhanced photolysis of some compounds (e.g., hydrochlorothiazide and diclofenac) while reducing the biodegradation of metoprolol. The transformation products metoprolol acid and valsartan acid were formed along the reach under all conditions.

Determination of polar organic micropollutants in surface and pore water by high-resolution sampling-direct injection-ultra high performance liquid chromatography-tandem mass spectrometry

Hyporheic zones (HZs) are dynamic and complex transition regions between rivers and aquifers which are thought to play an important role in the attenuation of environmental micropollutants. Non-steady state and small-scale hyporheic processes which affect micropollutants in the HZ are poorly characterized due to limitations in existing analytical methodologies. In this work we developed a method for high spatio-temporal resolution analysis of polar organic micropollutants (POMs) in hyporheic pore- and surface waters by combining (semi-) automatic low volume sampling techniques with direct-injection ultra-high performance liquid chromatography tandem mass spectrometry. The method is capable of quantifying 25 parent compounds and 18 transformation products (TPs) using only 0.4 mL of water and few preparation steps. Application of the method to both surface and pore water revealed significant (i.e. > an order of magnitude) differences in POM concentrations over small time and spatial scales (i.e. < a few hours and tens of cm, respectively). Guanylurea, a TP of the antidiabetic drug metformin was detected at unprecedentedly high concentrations. Collectively, this method is suitable for in situ characterization of POMs at high spatial and temporal resolution and with minimal disturbance of natural flow paths and infiltration of surface water.

High-throughput evaluation of organic contaminant removal efficiency in a wastewater treatment plant using direct injection UHPLC-Orbitrap-MS/MS

The removal efficiency (RE) of organic contaminants in wastewater treatment plants (WWTPs) is a major determinant of the environmental impact of these contaminants. However, RE data are available for only a few chemicals due to the time and cost required for conventional target analysis. In the present study, we applied non-target screening analysis to evaluate the RE of polar contaminants, by analyzing influent and effluent samples from a Swedish WWTP with direct injection UHPLC-Orbitrap-MS/MS. Matrix effects were evaluated by spiking the samples with isotope-labeled standards of 40 polar contaminants. For 85% of the compounds, the matrix effects in the influent and effluent were not significantly different. Approximately 10 000 compounds were detected in the wastewater, of which 319 were identified by using the online database mzCloud. Level 1 identification confidence was achieved for 31 compounds for which we had reference standards, and level 2 was achieved for the remainder. RE was calculated from the ratio of the peak areas in the influent and the effluent from the non-target analysis. Good agreement was found with RE determined from the target analysis of the target compounds. The method generated reliable estimates of RE for large numbers of contaminants with comparatively low effort and is foreseen to be particularly useful in applications where information on a large number of chemicals is needed.

Unravelling Contaminants in the Anthropocene Using Statistical Analysis of Liquid Chromatography-High-Resolution Mass Spectrometry Nontarget Screening Data Recorded in Lake Sediments

The significant increase in traces of human activity in the environment worldwide provides evidence of the beginning of a new geological era, informally named the Anthropocene. The rate and variability of these human modifications at the local and global scale remain largely unknown, but new analytical methods such as high-resolution mass spectrometry (HRMS) can help to characterize chemical contamination. We therefore applied HRMS to investigate the contamination history of two lakes in Central Europe over the preceding 100 years. A hierarchical clustering analysis (HCA) of the collected time series data revealed more than 13 000 profiles of anthropogenic origin in both lakes, defining the beginning of large-scale human impacts during the 1950s. Our results show that the analysis of temporal patterns of nontarget contaminants is an effective method for characterizing the contamination pattern in the Anthropocene and an important step in prioritizing the identification of organic contaminants not yet successfully targeted by environmental regulation and pollution reduction initiatives. As proof of the concept, the success of the method was demonstrated with the identification of the pesticide imazalil, which probably originated from imported fruits. This new approach applicable to palaeoarchives can effectively be used to document the time and rate of change in contamination over time and provide additional information on the onset of the Anthropocene.

A strategic screening approach to identify transformation products of organic micropollutants formed in natural waters

Many transformation products (TPs) from organic micropollutants are not included in routine environmental monitoring programs due to limited knowledge of their occurrence and fate. An efficient method to identify and prioritize critical compounds in terms of environmental relevance is needed. In this study, we applied a strategic screening approach based on a case-control concept to identify TPs formed along wastewater-impacted rivers. Time-integrated samples were collected over one week at both ends of a river stretch downstream of a wastewater treatment plant (WWTP) outfall and were analyzed by ultrahigh performance liquid chromatography interfaced with quadrupole time-of-flight mass spectrometry (UHPLC-QToF-MS/MS). The screening procedure of the high-resolution MS (HRMS) datasets consisted of three major steps: (i) screening for parent compounds (PCs) attenuated along the stretch; (ii) prediction of potential TPs from these PCs; and (iii) screening for TPs from this list with an increasing trend along the stretch. In total, 32 PCs decreased along the investigated river stretches. From these PCs, eight TPs had increasing concentrations along the studied stretches and could be tentatively identified. The identification of one TP (benzamide) was confirmed by its corresponding reference standard, while no standards were available for the remaining TPs.

Microbial biotransformation of furosemide for environmental risk assessment: identification of metabolites and toxicological evaluation

Some widely prescribed drugs are sparsely metabolized and end up in the environment. They can thus be a focal point of ecotoxicity, either themselves or their environmental transformation products. In this context, we present a study concerning furosemide, a diuretic, which is mainly excreted unchanged. We investigated its biotransformation by two environmental fungi, Aspergillus candidus and Cunninghamella echinulata. The assessment of its ecotoxicity and that of its metabolites was performed using the Microtox test (ISO 11348-3) with Vibrio fischeri marine bacteria. Three metabolites were identified by means of HPLC-MS and ¹H/¹³C NMR analysis: saluamine, a known pyridinium derivative and a hydroxy-ketone product, the latter having not been previously described. This hydroxy-ketone metabolite was obtained with C. echinulata and was further slowly transformed into saluamine. The pyridinium derivative was obtained in low amount with both strains. Metabolites, excepting saluamine, exhibited higher toxicity than furosemide, being the pyridinium structure the one with the most elevated toxic levels (EC₅₀ = 34.40 ± 6.84 mg L^-1). These results demonstrate that biotic environmental transformation products may present a higher environmental risk than the starting drug, hence highlighting the importance of boosting toxicological risk assessment related to the impact of pharmaceutical waste.

Exploring Trends of C and N Isotope Fractionation to Trace Transformation Reactions of Diclofenac in Natural and Engineered Systems

Although diclofenac ranks among the most frequently detected pharmaceuticals in the urban water cycle, its environmental transformation reactions remain imperfectly understood. Biodegradation-induced changes in ¹⁵N/¹⁴N ratios (ε_N = -7.1‰ ± 0.4‰) have indicated that compound-specific isotope analysis (CSIA) may detect diclofenac degradation. This singular observation warrants exploration for further transformation reactions. The present study surveys carbon and nitrogen isotope fractionation in other environmental and engineered transformation reactions of diclofenac. While carbon isotope fractionation was generally small, observed nitrogen isotope fractionation in degradation by MnO₂ (ε_N = -7.3‰ ± 0.3‰), photolysis (ε_N = +1.9‰ ± 0.1‰), and ozonation (ε_N = +1.5‰ ± 0.2‰) revealed distinct trends for different oxidative transformation reactions. The small, secondary isotope effect associated with ozonation suggests an attack of O₃ in a molecular position distant from the N atom. Model reactants for outer-sphere single electron transfer generated large inverse nitrogen isotope fractionation (ε_N = +5.7‰ ± 0.3‰), ruling out this mechanism for biodegradation and transformation by MnO₂. In a river model, isotope fractionation-derived degradation estimates agreed well with concentration mass balances, providing a proof-of-principle validation for assessing micropollutant degradation in river sediment. Our study highlights the prospect of combining CSIA with transformation product analysis for a better assessment of transformation reactions within the environmental life of diclofenac.

Fate of Pharmaceuticals and Their Transformation Products in Four Small European Rivers Receiving Treated Wastewater

A considerable knowledge gap exists with respect to the fate and environmental relevance of transformation products (TPs) of polar organic micropollutants in surface water. To narrow this gap we investigated the fate of 20 parent compounds (PCs) and 11 characteristic TPs in four wastewater-impacted rivers. Samples were obtained from time-integrated active sampling as well as passive sampling using polar organic chemical integrative samplers (POCIS). Seventeen out of the 20 PCs were detected in at least one of the rivers. All the PCs except acesulfame, carbamazepine, and fluconazole were attenuated along the studied river stretches, with the largest decrease found in the smallest river which had an intense surface water-pore water exchange. Seven TPs were detected, all of which were already present directly downstream of the WWTP outfall, suggesting that the WWTPs were a major source of TPs to the recipients. For anionic compounds, attenuation was the highest in the two rivers with the lowest discharge, while the pattern was not as clear for neutral or cationic compounds. For most compounds the results obtained from active sampling were not significantly different from those using POCIS, demonstrating that the cost and labor efficient POCIS is suitable to determine the attenuation of organic micropollutants in rivers.

Compound-Specific Stable Isotope Fractionation of Pesticides and Pharmaceuticals in a Mesoscale Aquifer Model

Compound-specific isotope analysis (CSIA) receives increasing interest for its ability to detect natural degradation of pesticides and pharmaceuticals. Despite recent laboratory studies, CSIA investigations of such micropollutants in the environment are still rare. To explore the certainty of information obtainable by CSIA in a near-environmental setting, a pulse of the pesticide bentazone, the pesticide metabolite 2,6-dichlorobenzamide (BAM), and the pharmaceuticals diclofenac and ibuprofen was released into a mesoscale aquifer with quasi-two-dimensional flow. Concentration breakthrough curves (BTC) of BAM and ibuprofen demonstrated neither degradation nor sorption. Bentazone was transformed but did not sorb significantly, whereas diclofenac showed both degradation and sorption. Carbon and nitrogen CSIA could be accomplished in similar concentrations as for "traditional" priority pollutants (low μg/L range), however, at the cost of uncertainties (0.4-0.5‰ (carbon), 1‰ (nitrogen)). Nonetheless, invariant carbon and nitrogen isotope values confirmed that BAM was neither degraded nor sorbed, while significant enrichment of (13)C and in particular (15)N corroborated transformation of diclofenac and bentazone. Retardation of diclofenac was reflected in additional (15)N sorption isotope effects, whereas isotope fractionation of transverse dispersion could not be identified. These results provide a benchmark on the performance of CSIA to monitor the reactivity of micropollutants in aquifers and may guide future efforts to accomplish CSIA at even lower concentrations (ng/L range).

Oxidation of cetirizine, fexofenadine and hydrochlorothiazide during ozonation: Kinetics and formation of transformation products

The efficiency of wastewater ozonation for the abatement of three nitrogen-containing pharmaceuticals, two antihistamine drugs, cetirizine (CTR) and fexofenadine (FXF), and the diuretic drug, hydrochlorothiazide (HCTZ), was investigated. Species-specific second-order rate constants for the reactions of the molecular, protonated (CTR, FXF) or deprotonated (HCTZ) forms of these compounds with ozone were determined. All three compounds are very reactive with ozone (apparent second order rate constants at pH 7: kO3,pH7 = 1.7·10(5) M(-1)s(-1), 8.5·10(4) M(-1)s(-1) and 9.0·10(3) M(-1)s(-1) for CTR, HCTZ and FXF, respectively). Transformation product (TP) structures were elucidated using liquid chromatography coupled with high-resolution tandem mass spectrometry, including isotope-labeled standards. For cetirizine and hydrochlorothiazide 8 TPs each and for fexofenadine 7 TPs were identified. The main TPs of cetirizine and fexofenadine are their respective N-oxides, whereas chlorothiazide forms to almost 100% from hydrochlorothiazide. In the bacteria bioluminescence assay the toxicity was slightly increased only during the ozonation of cetirizine at very high cetirizine concentrations. The main TPs detected in bench-scale experiments were also detected in full-scale ozonation of a municipal wastewater, for >90% elimination of the parent compounds.

Non-target time trend screening: a data reduction strategy for detecting emerging contaminants in biological samples

Non-targeted mass spectrometry-based approaches for detecting novel xenobiotics in biological samples are hampered by the occurrence of naturally fluctuating endogenous substances, which are difficult to distinguish from environmental contaminants. Here, we investigate a data reduction strategy for datasets derived from a biological time series. The objective is to flag reoccurring peaks in the time series based on increasing peak intensities, thereby reducing peak lists to only those which may be associated with emerging bioaccumulative contaminants. As a result, compounds with increasing concentrations are flagged while compounds displaying random, decreasing, or steady-state time trends are removed. As an initial proof of concept, we created artificial time trends by fortifying human whole blood samples with isotopically labelled standards. Different scenarios were investigated: eight model compounds had a continuously increasing trend in the last two to nine time points, and four model compounds had a trend that reached steady state after an initial increase. Each time series was investigated at three fortification levels and one unfortified series. Following extraction, analysis by ultra performance liquid chromatography high-resolution mass spectrometry, and data processing, a total of 21,700 aligned peaks were obtained. Peaks displaying an increasing trend were filtered from randomly fluctuating peaks using time trend ratios and Spearman’s rank correlation coefficients. The first approach was successful in flagging model compounds spiked at only two to three time points, while the latter approach resulted in all model compounds ranking in the top 11 % of the peak lists. Compared to initial peak lists, a combination of both approaches reduced the size of datasets by 80–85 %. Overall, non-target time trend screening represents a promising data reduction strategy for identifying emerging bioaccumulative contaminants in biological samples.

Graphical abstract

Biodegradation of sulfamethoxazole photo-transformation products in a water/sediment test

Occurrence of the antibiotic sulfamethoxazole (SMX) in the aquatic environment is of concern due to its potential to induce antibiotic resistance in pathogenic bacteria. While degradation of SMX can occur by numerous processes, the environmental fate of its transformation products (TPs) remains poorly understood. In the present work, biodegradation of SMX photo-TPs was investigated in a water/sediment system. Photo-TPs were produced by exposing SMX to artificial sunlight for 48 h. The resulting mixture of 8 photo-TPs was characterized using a combination of ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry and tandem mass spectrometry, and then used in biodegradation experiments. Significant differences in transformation among SMX photo-TPs were observed in the water/sediment system, with four photo-TPs displaying evidence of biodegradation (dissipation half-lives [DT50] of 39.7 d for 3-amino-5-methylisoxazole, 12.7 d for 4-nitro-sulfamethxoazole, 7.6 d for an SMX isomer and 2.4 d for [C10H13N3O4S]), two displaying primarily abiotic degradation (DT50 of 31 d for sulfanilic acid and 74.9 d for 5-methylisoxazol-3-yl-sulfamate), and two photo-TPs behaving largely recalcitrantly. Remarkably, TPs previously reported to be photo-stable also were persistent in biodegradation experiments. The most surprising observation was an increase in SMX concentrations when the irradiated solution was incubated, which we attribute to back-transformation of certain photo-TPs by sediment bacteria (85% from 4-nitro-sulfamethoxazole). This process could contribute to exposure to SMX in the aquatic environment that is higher than one would expect based on the fate of SMX alone. The results highlight the importance of considering TPs along with their parent compounds when characterizing environmental risks of emerging contaminants.

Identification of transformation products from β-blocking agents formed in wetland microcosms using LC-Q-ToF

Identification of degradation products from trace organic compounds, which may retain the biological activity of the parent compound, is an important step in understanding the long-term effects of these compounds on the environment. Constructed wetlands have been successfully utilized to remove contaminants from wastewater effluent, including pharmacologically active compounds. However, relatively little is known about the transformation products formed during wetland treatment. In this study, three different wetland microcosm treatments were used to determine the biotransformation products of the β-adrenoreceptor antagonists atenolol, metoprolol and propranolol. LC/ESI-Q-ToF run in the MS(E) and MS/MS modes was used to identify and characterize the degradation products through the accurate masses of precursor and product ions. The results were compared with those of a reference standard when available. Several compounds not previously described as biotransformation products produced in wetlands were identified, including propranolol-O-sulfate, 1-naphthol and the human metabolite N-deaminated metoprolol. Transformation pathways were significantly affected by microcosm conditions and differed between compounds, despite the compounds' structural similarities. Altogether, a diverse range of transformation products in wetland microcosms were identified and elucidated using high resolving MS. This work shows that transformation products are not always easily predicted, nor formed via the same pathways even for structurally similar compounds.

LC-MS screening techniques for wastewater analysis and analytical data handling strategies: Sartans and their transformation products as an example

A large number of anthropogenic trace contaminants such as pharmaceuticals, their human metabolites and further transformation products (TPs) enter wastewater treatment plants on a daily basis. A mixture of known, expected, and unknown molecules are discharged into the receiving aquatic environment because only partial elimination occurs for many of these chemicals during physical, biological and chemical treatment processes. In this study, an array of LC-MS methods from three collaborating laboratories was applied to detect and identify anthropogenic trace contaminants and their TPs in different waters. Starting with theoretical predictions of TPs, an efficient workflow using the combination of target, suspected-target and non-target strategies for the identification of these TPs in the environment was developed. These techniques and strategies were applied to study anti-hypertensive drugs from the sartan group (i.e., candesartan, eprosartan, irbesartan, olmesartan, and valsartan). Degradation experiments were performed in lab-scale wastewater treatment plants, and a screening workflow including an inter-laboratory approach was used for the identification of transformation products in the effluent samples. Subsequently, newly identified compounds were successfully analyzed in effluents of real wastewater treatment plants and river waters.

Flume experiments to investigate the environmental fate of pharmaceuticals and their transformation products in streams

The hyporheic zone—the transition region beneath and alongside the stream bed—is a central compartment for attenuation of organic micropollutants in rivers. It provides abundant sorption sites and excellent conditions for biotransformation. We used a bench-scale flume to study the fate of 19 parent pharmaceuticals (PPs) and the formation of 11 characteristic transformation products (TPs) under boundary conditions similar to those in hyporheic zones. The persistence of PPs ranged from readily degradable with a dissipation half-life (DT50) as short as 1.8 days (acetaminophen, ibuprofen) to not degradable (chlorthalidone, fluconazole). The temporal and spatial patterns of PP and TP concentrations in pore water were heterogeneous, reflecting the complex hydraulic and biogeochemical conditions in hyporheic zones. Four TPs (carbamazepine-10,11-epoxide, metoprolol acid, 1-naphthol, and saluamine) were exclusively formed in the sediment compartment and released to surface water, highlighting their potential to be used as indicators for characterizing hyporheic transformation of micropollutants in streams. The accumulation of certain TPs over the experimental period illustrates that we might face a peak of secondary contamination by TPs far from the point of release of the original contaminants into a stream. Such TPs should be considered as priority candidates for a higher-tier environmental risk assessment.

Lessons learned from water/sediment-testing of pharmaceuticals

Previous studies revealed large differences in the transformation of pharmaceuticals in rivers with similar characteristics. The present work aimed at answering the question whether these differences are related to the transformation capacity of the specific river sediments. More generally, we also aimed at evaluating the overall diagnostic power of water/sediment tests. Incubation experiments with 9 pharmaceuticals were carried out with sediments sampled from three rivers. All compounds expect carbamazepine were removed at dissipation half-lives between 2.5 and 56 days; biotransformation was identified as the major removal process. Interestingly, sediment from river Roter Main was more efficient in removing pharmaceuticals than sediment from river Gründlach, while the opposite pattern was observed in previous field studies. Obviously, the physical boundary conditions are governing the actual elimination of pharmaceuticals and not the transformation potential of the specific sediments. In a separate experiment, an immediate onset of transformation was observed after introducing oxygen to an anoxic water/sediment system. Transformation rates in sediments sampled from several sites within one river varied up to a factor of 2.5. This considerable in-stream variability is a critical factor for environmental risk assessment where single cutoff values are being used for evaluating a compound's persistence.

C & N isotope analysis of diclofenac to distinguish oxidative and reductive transformation and to track commercial products

Although diclofenac is frequently found in aquatic systems, its degradability in the environment remains imperfectly understood. On the one hand, evidence from concentration analysis alone is inconclusive if an unknown hydrology impedes a distinction between degradation and dilution. On the other hand, not all transformation products may be detectable. As a new approach, we therefore developed GC-IRMS (gas chromatography-isotope-ratio mass-spectrometry) analysis for carbon and nitrogen isotope measurements of diclofenac. The method uses a derivatization step that can be conducted either online or offline, for optimized throughput or sensitivity, respectively. In combination with on-column injection, the latter method enables determination of diclofenac isotope ratios down to the sub-μgL(-1) range in environmental samples. Degradation in an aerobic sediment-water system showed strong nitrogen isotope fractionation (εN = -7.1‰), whereas reductive diclofenac dechlorination was associated with significant carbon isotope fractionation (εC = -2.0‰). Hence dual element isotope analysis bears potential not only to detect diclofenac degradation, but even to distinguish both transformation pathways in the environment. In an explorative survey, analysis of commercial diclofenac products showed significant differences in carbon and nitrogen isotope ratios, demonstrating a further potential to track, and potentially even to authenticate, commercial production batches.