Targeted and non-targeted liquid chromatography-mass spectrometric workflows for identification of transformation products of emerging pollutants in the aquatic environment
Introduction
The term “emerging pollutants” (EPs) [or “emerging contaminants” (ECs)] refers to compounds and their metabolites that are not currently covered by existing water-quality regulations, have not been studied often, are overlooked and are thought to be potential threats to environmental ecosystems and human health and safety. According to NORMAN (Network of reference laboratories, research centers and related organizations for monitoring emerging environmental substances), they are compounds that are not included in routine environmental monitoring programs and may be candidates for future legislation due to their adverse effects and/or persistency (http://www.norman-network.net/). Most regulating and implementation bodies, responsible for water and wastewater treatment, are working on the assumption that the so-called priority pollutants are responsible for the most significant share of environmental, human health and economic risk, even though they represent a minor fraction of the universe of known and yet-to be identified chemicals [1].
EPs encompass a diverse group of compounds, including pharmaceuticals and personal-care products (PPCPs), drugs of abuse (DoAs) and their metabolites, steroids and hormones, endocrine-disrupting compounds, surfactants, perfluorinated compounds, phosphoric ester flame retardants, industrial additives and agents (e.g., benzotriazoles and benzothiazoles), siloxanes, artificial sweeteners, and gasoline additives.
Once released into the environment, EPs are subject to biotic and abiotic transformation processes that are responsible for their transformation and/or elimination, according to their persistence, transport, and ultimate destination. Various transformations can take place, producing compounds that, to some extent, differ in their environmental behavior and ecotoxicological profile from the parent compound. Formation of transformation products (TPs) occurs mainly through oxidation, hydroxylation, hydrolysis, conjugation, cleavage, dealkylation, methylation and demethylation. EPs and their TPs can move vertically through the soil profile to groundwater and away from the source site with mobile groundwater. They also have the potential to reach surface water when they travel laterally as surface run-off or through sub-soil tile drains, entering streams, major rivers, reservoirs, and ultimately estuaries and oceans [2].
Since there is a gap in the information on the occurrence and the toxicity of TPs in the environment, we are unable to evaluate their significance in risk assessment [3], [4]. Standardized toxicity tests can provide quantitative information on the toxicity of the TP, compared to its parent compound, but these studies are limited [5], [6], [7]. In general, TPs are less toxic and more polar than the parent compounds. However, in some cases, they may be more persistent or exhibit higher toxicity or be present at much higher concentrations [8].
Although there is legislation regulating chemicals [e.g., pesticides, veterinary drugs, and persistent organic pollutants (POPs)], there is little mention of their TPs. Concerns over the TPs of pesticides in plants have been expressed since 1991 (European Directive 91/414/EEC), while the term “metabolite” appears in Regulation (EC) 1107/2009, concerning plant-protection products, and in Directives 2001/82/EC and 98/8/EC, concerning veterinary medical and biocidal products, respectively. European Medicines Agency (EMEA, 2006) also referred to the need for assessment of potential environmental risks of human medicinal products. However, in all these documents, there is no clarification on the determination, limits and toxicological effects of metabolites or TPs.
In OECD guidelines, concerning the Aerobic and Anaerobic Transformation in Aquatic Sediment Systems, adopted in 2002, it is claimed that TPs detected at ≥10% of the applied radioactivity should be identified. Meanwhile, EU Regulation 1907/2006 (REACH) requires identification of major TPs and degradation products for the registration of the substance. In the Regulation (EC) 850/2004 on POPs, a reference to their transformation processes also exists.
There is therefore a clear need to reveal the qualitative and quantitative occurrence of TPs in the environment, but this is only possible with continual development of instrumental analysis. Thereby, the range of identifiable chemicals is extended, and the quantification limits are lowered. With respect to obtaining a holistic view of risk, target-based environmental monitoring should be accompanied by non-target analysis using high-resolution (HR) hybrid mass spectrometers. The development of these highly resolved, accurate, hybrid, tandem mass spectrometers, and improved sophisticated software, has enabled more reliable, selective target analysis of highly polar compounds, and screening for unknown pollutants. The major benefit of full-scan and HR, accurate MS is that, within a single analytical run, target, suspect and non-target compounds can be analyzed or identified.
In the analysis of EPs, HR mass spectrometry (HR-MS) has been widely reported [3], [9], [10], [11], [12]. Moreover, for identification of TPs in environmental, food and biological samples, hybrid HR mass analyzers [e.g., linear ion trap Orbitrap MS and quadrupole time-of-flight MS (Q-TOF)] have been used, following specific workflows [12], [13], [14], [15], [16]. More specifically, human and microbial metabolites, oxidation and photodegradation TPs of pharmaceuticals have been discussed often [17], [18], [19], [20], [21]. Similarly, TPs of pesticides in biological (human metabolism, phase II), food and environmental samples have been reviewed [22], [23]. Furthermore, the TPs of anthelmintics [24], UV filters in the environment [25], [26] and steroidal compounds in biological samples [27] are included in recent review papers. An interesting fact concerning the analysis of EPs and their TPs is enantioselective biotransformation. Chiral EPs or chiral TPs formed may have enantioselective activity or toxicity, making chiral chromatography indispensable [28].
Achievements, future trends and new developments in the analysis of EPs and their TPs were summarized by Farré et al. [29] and Fisher et al. [30]. Recently, highly sophisticated, comprehensive, step-wise workflows were also presented by Moschet et al. [31] and Hug et al. [32] for suspect and non-target screening of pesticides and EPs, including TPs in their suspect lists. However, it is still challenging to profile TPs in environment samples, since they are formed through many possible reactions, automatic workflows for the identification are not readily available, so manual data inspection is necessary, though time consuming, and, finally, there are no standards available.
The aim of this review is to compile the recent information regarding the background of (biotic and abiotic) transformation of EPs. We provide a brief overview of existing literature on transformation studies under biotic and abiotic conditions in recent years and we compile a list of all the EPs studied and comprehensive information for researchers in the field. We briefly summarize target analysis, since the development of accurate mass instruments and sophisticated computer tools has led to suspect and non-target analysis, even though all three procedures are indispensable parts of an integrated approach to determination of EPs and their TPs. We present the design of laboratory studies to facilitate identification of TPs by LC-MS and appropriate sample preparation. We thoroughly discuss target, suspect and non-target workflows using HR-MS/MS to identify new TPs.
Section snippets
Classification of transformation products (TPs)
TPs occurring in the environment can be classified into two main categories: biotransformation products formed by biotic or abiotic processes. This classification has subcategories that we describe in detail below, emphasizing the aquatic environment. The biotransformation products include human, animal and microbial metabolites in engineered and natural systems. The abiotic TPs are the outcome of hydrolysis, photolytic and photocatalytic degradation in the natural environment and
Identification approaches – laboratory studies
Simulation of the transformation processes in batch experiments under well-defined conditions with appropriate controls is a very common first approach for the identification of TPs. Batch experiments can be applied under biotic and abiotic conditions at high concentrations of the parent EPs.
For biodegradation experiments, samples can be provided directly from a wastewater-treatment plant (WWTP) or a pilot-scale WWTP (ps-WWTP) or from natural waters [33], [34], [51]. Moreover, the ability of
Identification approaches – analytical techniques
Nowadays, liquid chromatography (LC) coupled to MS (LC-MS) using a variety of mass analyzers is the technique of choice for the investigation of EPs and TPs in environmental samples.
LC is a suitable chromatographic technique for polar, thermo-labile compounds, thus for the identification of TPs, which are generally more polar than their parent molecules.
Mass analyzers commonly employed are triple quadrupole (QqQ), time-of-flight (TOF), ion-trap (IT), Orbitrap and hybrid [e.g., quadrupole
Future needs and trends
Development of generic and retrospective analytical techniques should permit the simultaneous determination of parent compounds and their TPs, within a single run. In the identification of TPs, the future lies in tiered approaches, which employ HR-MS, complementary techniques and advanced software tools. HR-MS outperforms LR-MS, regarding the level of identification of an unknown compound. Moreover, identification by HR-MS analysis has different levels of confidence, regarding the supporting
Acknowledgments
This project was implemented under the Greek Operational Program «Education and Lifelong Learning» and funded by the European Union (European Social Fund) and Greek National Resources (ARISTEIA 624).
References (92)
Non-regulated water contaminants: emerging research
Environ. Impact Assess. Rev
(2004)- et al.
Oxidation by-products and ecotoxicity assessment during the photodegradation of fenofibric acid in aqueous solution with UV and UV/H2O2
J. Hazar. Mat
(2011) - et al.
Photolysis of model emerging contaminants in ultra-pure water: kinetics, by-products formation and degradation pathways
Water Res
(2013) - et al.
Rapid automated screening, identification and quantification of organic micro-contaminants and their main transformation products in wastewater and river waters using liquid chromatography–quadrupole-time-of-flight mass spectrometry with an accurate-mass database
J. Chromatogr. A
(2010) - et al.
Accurate mass screening and identification of emerging contaminants in environmental samples by liquid chromatography–hybrid linear ion trap Orbitrap mass spectrometry
J. Chromatogr. A
(2009) - et al.
Application of advanced MS techniques to analysis and identification of human and microbial metabolites of pharmaceuticals in the aquatic environment
TRAC-Trend. Anal. Chem
(2007) - et al.
LC-MS for identifying photodegradation products of pharmaceuticals in the environment
TRAC-Trend. Anal. Chem
(2007) - et al.
Transformation products of pharmaceuticals in surface waters and wastewater formed during photolysis and advanced oxidation processes – degradation, elucidation of byproducts and assessment of their biological potency
Chemosphere
(2011) - et al.
Structure elucidation of phase II metabolites by tandem mass spectrometry: an overview
J. Chromatogr. A
(2005) - et al.
Investigation of pesticide metabolites in food and water by LC-TOF-MS
Trends Anal. Chem
(2008)
Determination of pesticide transformation products: a review of extraction and detection methods
J. Chromatogr. A
Biological transformations of steroidal compounds: a review
Steroids
Enantioselective chromatography-A powerful tool for the discrimination of biotic and abiotic transformation processes of chiral environmental pollutants
J. Chromatogr. A
Achievements and future trends in the analysis of emerging organic contaminants in environmental samples by mass spectrometry and bioanalytical techniques
J. Chromatogr. A
Identification of novel micropollutants in wastewater by a combination of suspect and nontarget screening
Environ. Pollut
Degradation of carbamazepine by Trametes versicolor in an air pulsed fluidized bed bioreactor and identification of intermediates
Water Res
Degradation of the tricyclic antipsychotic drug chlorpromazine under environmental conditions, identification of its main aquatic biotic and abiotic transformation products by LC–MSn and their effects on environmental bacteria
J. Chromatogr. B
Degradation of the drug sodium diclofenac by Trametes versicolor pellets and identification of some intermediates by NMR
J. Hazar. Mat
Metabolism of polybrominated diphenyl ethers and tetrabromobisphenol A by fish liver subcellular fractions in vitro
Aquat. Toxicol
6:2 Fluorotelomer alcohol biotransformation in an aerobic river sediment system
Chemosphere
5:3 Polyfluorinated acid aerobic biotransformation in activated sludge via novel ‘‘one-carbon removal pathways
Chemosphere
Degradation of UV filters in sewage sludge and 4-MBC in liquid medium by the ligninolytic fungus Trametes versicolor
J. Environ. Manage
Incomplete aerobic degradation of the antidiabetic drug Metformin and identification of the bacterial dead-end transformation product Guanylurea
Chemosphere
Pathways and metabolites of microbial degradation of selected acidic pharmaceutical and their occurrence in municipal wastewater treated by a membrane bioreactor
Water Res
Continuous degradation of a mixture of sulfonamides by Trametes versicolor and identification of metabolites from sulfapyridine and sulfathiazole
J. Hazar. Mat
Anaerobic testosterone degradation in Steroidobacter denitrificans – identification of transformation products
Environ. Pollut
Enhanced transformation of triclosan by laccase in the presence of redox mediators
Water Res
Triclosan susceptibility and co-metabolism – a comparison for three aerobic pollutant-degrading bacteria
Bioresour. Technol
Investigating the biodegradability of perfluorooctanoic acid
Chemosphere
Photochemical reactivity of perfluorooctanoic acid (PFOA) in conditions representing surface water
Sci. Total Environ
De-conjugation behavior of conjugated estrogens in the raw sewage, activated sludge and river water
J. Hazar. Mat
Occurrence and reductions of pharmaceuticals and personal care products and estrogens by municipal wastewater treatment plants in Ontario, Canada
Sci. Total Environ
Liquid chromatography/quadrupole-time-of-flight mass spectrometry with metabolic profiling of human urine as a tool for environmental analysis of Dextromethorphan
J. Chromatogr. A
Cross-species comparison of fluoxetine metabolism with fish liver microsomes
Chemosphere
Photodegradation of azithromycin in various aqueous systems under simulated and natural solar radiation: kinetics and identification of photoproducts
Chemosphere
Identification of ozonation by-products of 4- and 5-methyl- 1H-benzotriazole during the treatment of surface water to drinking water
Water Res
Investigation of degradation products of cocaine and benzoylecgonine in the aquatic environment
Sci. Total Environ
Photolytic and photocatalytic degradation of quinclorac in ultrapure and paddy field water: identification of transformation products and pathways
Chemosphere
Degradation and removal methods of antibiotics from aqueous matrices – a review
J. Environ. Manage
Kinetic assessment and modeling of an ozonation step for full-scale municipal wastewater treatment: micropollutant oxidation, by-product formation and disinfection
Water Res
Formation of chlorinated by-products during photo-Fenton degradation of pyrimethanil under saline conditions. Influence on toxicity and biodegradability
J. Hazard. Mater
The degradation products of UV filters in aqueous and chlorinated aqueous solutions
Water Res
Mechanism of phenol photodegradation in the presence of pure and modified-TiO2: a review
Water Res
A new approach to data evaluation in the non-target screening of organic trace substances in water analysis
Chemosphere
The Handbook of Environmental Chemistry
New trends in the analytical determination of emerging contaminants and their transformation products in environmental waters
Environ. Sci. Pollut. Res
Cited by (264)
Occurrence, source apportionment and risk assessment of selected pharmaceuticals and their transformation products in the effluent-impacted rivers
2024, Regional Studies in Marine ScienceAnalysis of chemical contaminants in fish using high resolution mass spectrometry – A review
2024, Trends in Environmental Analytical ChemistryPesticide residues in animal-derived food: Current state and perspectives
2024, Food Chemistry