title: Natürliche Bildung von halogenierten Essigsäuren und Iodalkanen
creator: Fahimi, Isabelle Jasmine
subject: ddc-540
subject: 540 Chemistry and allied sciences
description: ABSTRACT This thesis deals with organohalogen compounds and their formation by natural abiotic soil processes, providing a framework in which a literature survey and a resume of the multitude of laboratory experiments are integrated. In the first chapter the literature on the sources, occurrence and sinks of halogenated acetic acids (HAAs), which are phytotoxic, and probably related to forest dieback, is summarized. They are ubiquitous in precipitations and are accumulated in coniferous needles. Next to anthropogenic sources there have also been indications of a natural biotic formation of HAAs in soil. In the following main segment experiments on the abiotic formation of HAAs in soils are presented. This process is probably due to a coupled oxidation/halogenation of organic matter. Experiments with soils, humic acid and phenolic model compounds show that HAAs are generated abiotically. In the case of ethoxyphenol, this occurs through the oxidation of a C2-unit, and in the case of the other model substances probably through the breakdown of the aromatic ring system. More dichloroacetic acid (DCA) than trichloroacetic acid (TCA) is formed. The addition of iron and H2O2 leads to a further increase in formation of HAAs. Probably a Fenton reaction (Fe(II) + H2O2 -> Fe(III) + OH. + OH-) occurs between the iron and the H2O2, forming OH radicals which oxidize the Cl-, leading to the chlorination of organic matter. In the forth chapter the formation of OH radicals, measured by the 2-deoxy-D-ribose method, in aquatic systems with humic acid or soil is investigated; neither sunlight, nor the addition of H2O2 or iron is required. The in vitro formation of OH radicals increases linearly with the amount of soil or humic acid employed. In the fifth chapter the abiotic formation of alkyl iodides in soil is studied. Soils, humic acid and model substances were employed. Similar to the formation of HAAs, two reaction pathways are possible: either, in the case of guiacol, the splitting off of a methyl group and/or the fragmentation of an aromatic system. Probably an oxidation of organic matter with iron is induced. An addition of iron leads to an increase of the production of homologous alkyl iodides from C1 to C4; this confirms the redox-induced mechanism of this reaction. In summary the results of this study indicate that organohalogen compounds are produced abiotically in soil. Their formation is dependent on environmental conditions, e.g. iron content, pH and organic carbon (Corg). 
date: 2003
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/3407/1/DISSERTATIONxxx.PDF
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/3407/2/HeidocAnfg1.PDF
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/3407/3/Heidocanfg2.PDF
identifier: DOI:10.11588/heidok.00003407
identifier: urn:nbn:de:bsz:16-opus-34078
identifier:   Fahimi, Isabelle Jasmine  (2003) Natürliche Bildung von halogenierten Essigsäuren und Iodalkanen.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/3407/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng