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Photodegradation of contaminants of emerging concern in environmental matrices : a new holistic perspective to complete the laboratory modeling approach

Abstract : Contaminants of emerging concern (CECs) show great environmental concern due to their potential toxic effect and persistence. More and more detected every year; they became ubiquitous as anthropogenic activities increase and their harmful effects were shown on aquatic organisms and human health. Conventional wastewater treatment plans do not fully remove CECs, as they were not designed to remove these pollutants. Developing and understanding novel water treatment approaches is essential to improve water quality and protect the environment. Processes based on light irradiation are very promising in this way. It is of high interest to evaluate the formation of potential photoproducts and their related toxicity; it also aims at understanding sunlight-induced transformation mechanisms of contaminants in the environment.The aim of this project was to apply different approaches to study the photodegradation of contaminants. Firstly, a laboratory modeling approach was applied to five contaminants: benzisothiazolinone, naproxen, perfluorooctanoic acid, maprotiline, and enrofloxacin. Direct photolysis and advanced oxidation processes, such as peroxide/UV, photocatalysis, photosensitizers, and Fenton reactions, were employed. They were either carried out under laboratory conditions in ultrapure water or on a pilot plant scale in secondary treated wastewater to model realistic conditions and study the matrix effect. The photodegradation efficiencies were studied using LC-MS analysis and UV-Vis spectroscopy. As mineralization is rarely achieved, LC-MS measurements were performed for the untargeted detection of photoproducts on an ultra-high-resolution FT-ICR mass spectrometer. This made the accurate identification of molecular formulas possible; structural elucidation of numerous photoproducts was achieved owing to MS2 experiments. Based on these structures, in silico toxicity calculations were performed to obtain information on their potential toxic effects. In parallel, in vitro bioassays were used to study the mixture's toxicity at each step of the photodegradation reaction. Through this approach, the scientific achievements include assessing the fate of contaminants, proposing and optimizing viable photodegradation processes, and elucidating photochemical reaction pathways.In parallel with the modeling approach, a non-targeted analytical approach was used to study complex mixtures. Direct infusion mass spectrometry was used to detect thousands of molecular ions and assess their formulas accurately. To better process these datafiles, the SPIX software was developed. One of its features is to find all the ions that undergo changes between two conditions. The other feature includes comparing a series of conditions, proposing kinetic models for each of them individually. The exportation of statistically relevant changes and further data processing was carried out. The software's application and mathematical background are presented through the analysis of contaminants in complex matrices, such as secondary treated wastewater and natural organic matter. The extension of the software to process 3D LC-MS datasets represents the latest developments. This software helped with rapid data processing and is innovative and unique in studying molecules' kinetics in complex samples. The holistic approach provided by SPIX constitutes a complementary tool to modeling approaches; it allows to detect and monitor relevant reactions in very complex media and contributes to reducing operator subjectivity during results interpretation.
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Submitted on : Thursday, November 25, 2021 - 8:01:27 PM
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Zsuzsanna Varga. Photodegradation of contaminants of emerging concern in environmental matrices : a new holistic perspective to complete the laboratory modeling approach. Analytical chemistry. Institut Polytechnique de Paris, 2021. English. ⟨NNT : 2021IPPAX036⟩. ⟨tel-03450185⟩

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