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Abstract
Volatile halogenated organic compounds (VOX) contribute to ozone depletion and global
warming. There is evidence of natural VOX formation in many environments ranging from
forest soils to salt lakes. Laboratory studies have suggested that VOX formation can
be chemically stimulated by reactive Fe species while field studies have provided
evidence for direct biological (enzymatic) VOX formation. However, the relative contribution
of abiotic and biotic processes to global VOX budgets is still unclear. The goals
of this study were to quantify VOX release from sediments from a hypersaline lake
in Western Australia (Lake Strawbridge) and to distinguish between the relative contributions
of biotic and abiotic VOX formation in microbially active and sterilized microcosms.
Our experiments demonstrated that the release of organochlorines from Lake Strawbridge
sediments was mainly biotic. Among the organochlorines detected were monochlorinated,
e.g., chloromethane (CH3Cl), and higher chlorinated VOX compounds such as trichloromethane
(CHCl3). Amendment of sediments with either Fe(III) oxyhydroxide (ferrihydrite) or
a mixture of lactate/acetate or both ferrihydrite and lactate/acetate did not stimulate
VOX formation. This suggests that although microbial Fe(III) reduction took place,
there was no stimulation of VOX formation via Fe redox transformations or the formation
of reactive Fe species under our experimental conditions.