Fate and toxicity of emerging pollutants, their metabolites and transformation products in the aquatic environment
Introduction
Emerging pollutants are defined as compounds that are not currently covered by existing water-quality regulations, have not been studied before, and are thought to be potential threats to environmental ecosystems and human health and safety (Table 1). They encompass a diverse group of compounds, including pharmaceuticals, drugs of abuse, personal-care products (PCPs), steroids and hormones, surfactants, perfluorinated compounds (PFCs), flame retardants, industrial additives and agents, and gasoline additives, as well as their transformation products (TPs) (Table 1). In addition, three new classes have to be added to the list of emerging pollutants: nanomaterials, 1,4-dioxane and swimming pool disinfection by-products (DBPs) [1].
The way that organic compounds enter the environment depends on their pattern of usage and mode of application (e.g., disposal of municipal, industrial and agricultural wastes, excretion of pharmaceuticals and accidental spills). Once in the environment, they can be widely distributed at some time between their production through to use and disposal. Because most emerging pollutants are from human use, their emissions are an issue for some wastewater processes, so the study of the fate of the emerging pollutants in wastewater-treatment plants (WWTP) is important.
Once released into the environment, emerging pollutants are subject to processes (e.g., biodegradation, and chemical and photochemical degradation) that contribute to their elimination. Depending on the compartment in which synthetic chemicals are present in the environment (e.g., groundwater, surface water and sediment) or in the technosphere (e.g., WWTPs and drinking-water facilities), different transformations can take place, sometimes producing products that can differ in their environmental behavior and ecotoxicological profile. For example, TPs of some pollutants are often more persistent than their corresponding parent compounds [2] and exhibit greater toxicity (e.g., the major biodegradation product of nonylphenol ethoxylates, nonylphenol, which is much more persistent than the parent compound and can mimic estrogenic properties [3]).
Liquid chromatography combined with mass spectrometry (LC-MS) and related techniques, such as ultra-performance LC-MS (UPLC-MS), have become robust, sensitive techniques for detecting parent compounds and TPs at ultra-trace levels in environmental samples [4], [5]. Unlike gas chromatography (GC)-MS, LC-MS can determine polar analytes without the need for previous derivatization. This advantage of LC-MS is particularly attractive when simultaneously analyzing compounds belonging to structurally distinct groups whose determination by GC-MS would involve more than one derivatization reaction.
With the advent and availability of recent analytical instrumentation that aids compound identification [e.g., LC coupled to ion-trap (IT)-MS or time-of-flight (ToF)-MS], more degradates and metabolites are being identified. These two MS techniques provide complementary data that facilitate structural elucidation of unknown compounds. For example, the ability to conduct multiple stages of fragmentation in an IT-MS system can generate MSn spectra with considerable amounts of structural information that identifies an unknown degradate. Further confirmation of the proposed identity or chemical formula of new degradation products can be achieved by accurate-mass measurements using a ToF-MS system or other high-resolution mass analyzers. Current bench-top ToF-MS instruments can now achieve a low-femtomole (fmol)-level sensitivity, high resolving power and mass accuracy. Even more powerful in terms of confirmatory analysis are hybrid triple-quadrupole ToF-MS (QqToF-MS) systems that acquire product-ion spectra with accurate-mass measurements of product ions (precision in the low-ppm range) [6], [7], [8], [9]. An alternative to ToF instruments is the recently launched LTQ Orbitrap that combines a conventional linear IT (LIT-MS) with an Orbitrap mass analyzer. This system provides outstanding mass accuracy, mass resolution and reliable high-sensitivity MSn performance.
Using LC-MS, there has been a vast number of analytical methods for determination of emerging pollutants and studies of their occurrence in the environment published (e.g., pharmaceuticals [9], [10], [11], hormones [12], [13], [14], endocrine-disrupting compounds [7], [15], PFCs [16], [17], [18], [3], drinking-water DBPs [3], [19], [20], sunscreens and ultraviolet (UV) filters [21], [22], brominated flame retardants [23], [24], [25], [26], [27], [28] and benzotriazoles [29], [30], [31]).
Recently, several articles focused on degradation products of emerging products and their toxicological effects. In this sense, in recent years, different review papers have been published on analytical methods for emerging contaminants [10], [11], [12], [13], and the occurrence of these compounds in the environment. However, this is the first review article devoted to the fate and the ecotoxicology of emerging pollutants and especially focusing on their metabolites and TPs in the aquatic environment.
Section snippets
Occurrence and fate of emerging pollutants
Emerging pollutants can reach the environment by being transported and distributed via different routes. The physico-chemical properties of chemicals (e.g., water solubility, vapor pressure and polarity) determine their behavior in the environment. The major sources of environmentally-relevant emerging contaminants are primarily WWTP effluents and secondarily terrestrial run-offs (from roofs, pavements, roads and agricultural land), including atmospheric deposition.
Veterinary drugs used for
Transformation of emerging pollutants
Emerging pollutants undergo various degrees of transformation in engineered surroundings and the environment. Some relatively inert molecules persist in the environment and are difficult to degrade. These compounds can be toxic and accumulate in food chains to present additional human and ecological risks. Others can be degraded to TPs. Degradation processes for synthetic chemicals in natural and engineered surroundings can attenuate the environmental burden of these xenobiotics. Various
Toxicity
There has recently been a great deal of research focused on investigating biological effects of new emerging pollutants residues in the environment.
Conclusions
Surveys of contaminants in the environmental samples have shown a cocktail of synthetic contaminants in the environment. However, not only the compound in its unalterated form has to be monitored, but also TPs formed in natural or engineered settings need to be taken into consideration. There is a lack of ecotoxicological information about some groups of emerging pollutants, but there is particularly a lack of knowledge of the effects that can be produced in the receiving environments by their
Acknowledgements
The work described in this article was supported by the Spanish Ministerio de Educación y Ciencia Project CEMAGUA, and by the European Union through project NORMAN (Contract No. 018486). Marinel la Farré thanks the Ministerio de Educación y Ciencia for support through the I3 P program. This work reflects only the authors’ views, and the European Community is not liable for any use that may be made of the information contained therein.
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