Project

Discipline

DOM; oxidation; phenoxyl radicals; NOM; phenols; organic contaminants; photosensitizers

Lead
Das in Oberflächengewässern natürlich vorkommende gelöste organische Material ist unter Einwirkung des Sonnenlichts eine Quelle von reaktiven chemischen Spezies. Diese können verschiedene Schadstoffe abbauen und sind somit an der Selbstreinigung der Gewässer beteiligt. Unter diesen reaktiven Spezies befinden sich organische Radikale, deren Wirkung auf im Wasser gelöste Schadstoffe bisher noch wenig bekannt ist. Für den Abbau von gewissen Klassen von Schadstoffen, die zur oxidativen Transformation neigen, könnten oxidierende organische Radikale (OOR) eine entscheidende Rolle spielen.
Lay summary
Inhalt und Ziel desForschungsprojekts Dieses Projekt soll dazu dienen, die Bedeutung von OOR in sonnenbelichteten Gewässern besser zu verstehen, vor allem in Bezug auf den Abbau von im Wasser gelösten Schadstoffen. Die Hauptziele bestehen darin, (i) wichtige Klassen von Schadstoffen zu identifizieren, deren Abbau massgeblich von OOR bestimmt wird, (ii) chemische Eigenschaften der OOR zucharakterisieren, und (iii) die Hypothese zu überprüfen, dass chemisch genau definierte Phenoxyradikale als Modelle für OOR dienen können. Wir konnten während den letzten zehn Jahren zeigen, dass phenolische Bestandteile des organischen Materials für die Hemmung von Licht-induzierten Transformationsprozessen bestimmter Schadstoffe verantwortlich sind. Dieses Projekt soll das Gegenstück aufzeigen, nämlich dass eine Gruppe solcher phenolischen Bestandteile unter Lichteinwirkung den Abbau von Schadstoffen beschleunigen kann. Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts Unser Projekt wird neue wichtige Erkenntnisse im wissenschaftlichen Gebiet der Umwelt-Photochemie liefern. Diese können von Behörden und interessierten Kreisen dazu verwendet werden, um die Abbauwege und Abbauraten von verschiedenen Mikroverunreinigungen besser als nach heutigem Stand zu beurteilen, und so einen verbesserten Schutz von aquatischer Umwelt und Bevölkerung zu erreichen.

Direct link to Lay Summary

Last update: 19.07.2017

Active participation

Number	Title	Start	Funding scheme

The ubiquitous and in its chemical composition extremely complex dissolved organic matter (DOM) is a source of various reactive intermediates when exposed to ultraviolet (UV) light. Such intermediates induce the transformation of many aquatic contaminants in sunlit surface waters or UV-based water treatment systems. The reactive intermediates produced from photoirradiated DOM comprise well-defined chemical entities, such as the hydroxyl radical, carbonate radical or singlet oxygen, as well as excited states or radical species that are often elusive to precise chemical identification because derived from and still attached to the DOM backbone. Excited triplet states of the DOM (3DOM*) have been recognized (with decisive contributions by the applicants) as pivotal photooxidants affecting the fate of organic contaminants in surface waters. Besides 3DOM*, the existence of DOM-derived photooxidants having longer lifetimes than 3DOM* and therefore termed "long-lived photooxidants" (LLPOs) was demonstrated based on the transformation kinetics of probe compounds. Although there has been little research about these photooxidants, for the the phototransformation of certain contaminant classes, such as electron-rich phenols and anilines, the contribution of LLPOs is expected to be high and even override the effect of 3DOM*. Based on the fact that DOM carries many phenolic groups which, when oxidized (e.g. by 3DOM*), lead to the formation of phenoxyl radicals, we hypothesize that DOM-attached phenoxyl radicals are substantial components of LLPOs. With the present proposal we intend to characterize the reactivity of LLPOs with various classes of contaminants and identify their chemical nature.The main objectives of the project are: (1) To identify the classes and types of contaminants prone to transformation induced by LLPOs with the goal of a broader evaluation of the role and relevance of LLPOs in the fate of aquatic contaminants in surface waters; (2) To characterize the chemical nature of LLPOs by means of diagnostic chemical kinetic methods; (3) To verify the hypothesis that photochemically produced phenoxyl radicals are able to mimic the phototransformation of organic contaminants induced by LLPOs.To pursue these objectives, a kinetic methodology developed by the applicants will be used and further improved to measure the effect of LLPOs on the transformation of selected contaminants. The reactivity of phenoxyl radicals will be mainly studied using laser flash photolysis.Besides clarifying the questions of the objectives, the present project is expected to provide an improved understanding of the role of phenolic moieties in the photochemistry and redox chemistry of DOM. It also offers stimulating links to the topic of DOM as an antioxidant, which was addressed in two preceding SNF proposals. The part of the study regarding the reactivity of phenoxyl radicals, which will be performed using model phenols, is expected to fill a gap in the aqueous chemical kinetics of these radicals, which might, in addition to aquatic environments, also be of interest for biochemical systems.The present project will also achieve the education of a PhD student and offer the opportunity for a continued international collaboration and exchange in the fields of photochemistry and kinetics of transient intermediates (Prof. Petr Klan and Prof. Dominik Heger, Masaryk University, Brno, Czech Republic).