Artificial formation of medium and long chain 1-haloalkanes during pyrolysis of polar geomacromolecules

Dominant C12 to C30 1-chloro-, 1-bromo- and 1-iodo-n-alkanes were observed during off line and on line pyrolysis at relatively low temperatures (300 and 358 °C) of polar fractions of extracts from contemporary marine sediments. The nature of the halogens in the original polar lipid fractions was further studied using X-ray photoelectron spectroscopy (XPS), which showed the presence of significant proportions of halogenated (especially chlorinated) inorganic salts and no evidence for the presence of organic halogens. Washing the original polar lipid fractions resulted in the disappearance of halogen signals during XPS analysis and the (quasi) absence of haloalkanes from the pyrolysates. Off line pyrolysis of different individual model compounds in the presence of an inorganic halide (CaCl2) under the same conditions as those used for the analysis of the polar lipid fractions showed artificial formation of chloroalkanes from fatty acids. Overall, the results clearly demonstrate that haloalkanes can be formed artificially during the pyrolysis of polar extracts containing inorganic halogenated salts and suggest that free and/or esterified fatty acids are possible precursors of these artefacts. In spite of the growing evidence that halogenation reactions can induce the formation of aliphatic halogenated compounds during diagenesis in sediments and soils, the question as to whether medium and long chain (> C12) 1-haloalkanes are truly present in sediments remains speculative.