Organohalogens in coniferous forest soil

Sammanfattning: This thesis is focused on naturally produced organohalogens in soil. It was long assumed that organohalogens found in the environment were mainly of anthropogenic origin, but recent research has shown that large amounts of naturally produced organohalogens are stored in terrestrial environments. The present study show that halogens are natural constituents of soil organic matter and that an in situ production takes place in soil. Moreover, it is strongly indicated that this production is related to decomposition of organic matter and that fungi generally produce organohalogens during degradation of organic matter. Together, these findings infer that degradation of organic matter is a key process in the formation of organically bound halogens in terrestrial ecosystems. Evidence is also presented that supports the hypothesis that halometabolite production is a source of the organohalogens found in soil, but the relative contribution from this and other potential sources remains to be elucidated.The investigations of the present thesis were limited to coniferous forest soil, and the intention was to examine soil under natural conditions, thus emphasis was placed on field studies. However, since soil in itself is a complex system, laboratory studies were performed to examine aspects not easily observed in the field. The distribution of organohalogens and organic matter at different depths in a soil profile was investigated. The results indicated that organohalogens were produced in the top soil, hence subsequent studies were focused on top soils, in particular the litter layer.Changes in the total amount of organohalogens during decomposition of organic matter in top soil was studied by employing the conventional litter bag technique. Furthermore, experiments were conducted that focused on organisms that degrade organic matter. The fungus Lepista nuda was used as a representative of litter degrading fungi, and investigations were conducted both as field studies of a fairy ring formed by this fungus and as laboratory studies under controlled conditions. Furthermore, the ability of white-rot fungi to produce organohalogens while decomposing wood was examined under laboratory conditions. The chemical analytical methods primarily used were GC-MS (gas chromatography-mass spectrometry ) and GC-AED (gas chromatography-atomic emission detection).