Naturally produced volatile and polar organohalogens in soils

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The present knowledge of the natural (biotic and abiotic) formation and degradation of halogenated organic compounds in soils is very limited. It is not clear whether, and under which environmental conditions soils can act as a sink or source of these compounds. In terms of atmospheric abundance and environmental significance the most important halogenated compounds formed in nature are undoubtedly the gaseous halomethanes. Recently it has become apparent that most atmospheric CH3Cl and CH3Br have a terrestrial rather than a marine origin. Besides monohalogenated organohalogens, polyhalogenated compounds such as volatile (e.g. CH2Cl2, CHCl3) and polar (e.g. halophenols, haloanisols, haloacetic acids, halobenzoic acids, halophenylacetic acids) compounds are produced in the terrestrial environment. The central hypothesis of the Research Unit project NAFOSA is that most of the known reaction schemes for the abiotic halogenation in the terrestrial environment are linked to radical chemistry by three essential redox-sensitive soil constituents - organic matter, iron, and oxygen. It seems to be by chance that halides are involved in these soil reactions. To address the hot spots of halogenation processes it is necessary to quantify the reaction turnover numbers of reduced organic material delivered by biotic processes in contact with reactive surfaces of secondary oxidic minerals (Fe, Mn). While NAFOSA is heading mainly for volatile compounds, the project NAVOPOS is additionally intending to unravel the flip side of the coin: Identification and quantitation analysis of polar halogenated compounds from abiotic degradation processes.