Abiotic Formation of Organohalo- gens in the Terrestrial Environment

To date more than 3650 organohalogen compounds are known to be naturally produced by biogeochemical processes [1]. The current understanding of the abiotic formation of organohalogens during early diagenetic processes in soils and sediments are reviewed. Next to volatile alkyl halides and polar organohalogens such as haloacetates there is evidence that even semivolatile organohalogens (e.g. polychlorinated dibenzodioxins) and halogenated humic substances are naturally formed by geochemical processes. The abiotic formation of halocarbons during diagenetic processes can be structured in three branches (see Fig. 14). Biomass burning means radical chemistry of organic material in the presence of halides at elevated temperatures resulting in methyl halides [2–4]. Volcanoes are producing a whole bunch of volatile organohalogens including fluoro compounds via radical chemistry starting from methane, ethene and ethyne in the presence of halides on very hot mineral surfaces [5][6]. Early diagenetic processes in soils and sediments comprise radical chemistry of organic material in the presence of halides at ambient temperatures driven by redox-sensitive elements such as iron [7–13].