An organic-rich substrate such as soil is an excellent source of carbon for bacteria. Since ignitable liquids are comprised of various hydrocarbons, soil bacteria can also utilize these fuels as a carbon source. Previous work completed in our laboratory on the biodegradation of ignitable liquids has shown a significant loss of normal alkanes fromC9 to C16 as well as lower substituted aromatic compounds. Branched alkanes appear to be more resistant to degradation than normal alkanes. In addition, the degree of degradation was positively correlated to the length of the alkyl chain on the mono-substituted alkylbenzenes. This can be problematic for fire debris analysis as samples may sit for many weeks before they are analyzed due to case backlog. As a result, selective loss of key components due to bacterial metabolism can make identifying and classifying ignitable liquid residues by their chemical composition and boiling point range very difficult. Of particular interest in this study is monitoring degradation of various ignitable liquids in all ASTM classes in order to expand existing knowledge of this phenomenon.In this study, ignitable liquids from each class were spiked onto potting soil and allowed to age. The samples were then analyzed using passive headspace adsorption followed by solvent desorption and then analyzed by GC-MS. This study will show that gasoline and petroleum distillates, which predominantly contain aromatic and n-alkane hydrocarbons respectively, suffer significantly from microbial degradation in just a few days while naphthenic-paraffinic liquids, which contain branched and cyclic alkanes, generally suffer the least. Oxygenated and isoparaffinic liquids also suffer from microbial degradation. The changes in the chromatographic profile of various ignitable liquids described herein are a result of the selectivity of the bacteria to metabolize the hydrocarbons found in these liquids, which is solely based on the chemical structure of the compound.

Trends in microbial degradation of various ignitable liquids in soil

246th National Meeting (2013)

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