The identification of ignitable liquid residues in fire debris is a key finding for determining the cause and origin of a suspicious fire. However, the complex mixtures of organic compounds that comprise ignitable liquids are susceptible to microbiological attack following collection of the sample. Biodegradation can result in selective removal of many of the compounds required for identification of an ignitable liquid. Such degradation has been found to occur rapidly in substrates such as soil, rotting wood, or other organic matter. Furthermore, fire debris evidence must often be stored for extended periods at room temperature prior to analysis due to case backlogs and available evidence storage. Hence, extensive damage to ignitable liquid residues by microbes poses a significant threat to subsequent laboratory work. In this work, the effects of microbial degradation of ignitable liquids in soil have been evaluated as a function of time. Key findings include the loss of n-alkanes, particularly C(9)-C(16), which showed the most dramatic decrease in gasoline as well as the petroleum distillates, while branched alkanes remained unchanged. Monosubstituted benzenes also showed the most dramatic loss in gasoline. In the heavy petroleum distillates, n-alkanes with even carbon numbers were degraded more than n-alkanes with odd carbon numbers.

Ignitable liquid residues recovered from a fire scene will often show signs of weathering as a result of exposure to the heat of the fire. In addition, when the substrate is rich in organic matter, both weathering and microbial degradation may be observed. In this study, 20 μL aliquots of fresh gasoline samples were intentionally weathered and also subjected to microbial degradation in potting soil. These samples were then analyzed using a passive adsorption-elution recovery method and gas chromatography/mass spectrometry. Peak areas from compounds of interest were normalized and autoscaled and then subjected to principal components analysis. This analysis showed that while lower boiling compounds are subject to weathering, a different set of compounds are subject to microbial degradation. Of the compounds studied, heptane, octane, toluene, and ethylbenzene were the most vulnerable to both weathering and microbial degradation. In contrast, 1,3,5-trimethylbenzene and 2-ethyltoluene were the most resistant to both phenomena.

In cases where fire debris contains soil, microorganisms can rapidly and irreversibly alter the chemical composition of any ignitable liquid residue that may be present. In this study, differences in microbial degradation due to the season in which the sample is collected was examined. Soil samples were collected from the same site during Fall, Winter, Spring and Summer and the degradation of gasoline was monitored over 30 days. Predominant viable bacterial populations enumerated using real-time PCR and reverse transcriptase polymerase chain reaction (RT-PCR) enumeration revealed the predominant viable bacterial genera to be Alcaligenes, Bacillus, and Flavobacterium. Overall, the compounds most vulnerable to microbial degradation are the n-alkanes, followed by the mono-substituted alkylbenzenes (e.g., toluene, ethylbenzene, propylbenzene and isopropylbenzene). Benzaldehyde (a degradation product of toluene) was also identified as a marker for the extent of biodegradation.Ultimately, it was determined that soil collected during an unusually hot and dry summer exhibited the least degradation with little to no change in gasoline for up to 4 days, readily detectable n-alkanes for up to 7 days and relatively high levels of resilient compounds such as

Biodegradation can result in selective removal of many of the compounds required for the identification of an ignitable liquid. In this study, the effects of microbial degradation on tiki torch fuel, lamp oil, and turpentine are reported. Samples of soil spiked with 20 μL of the liquids were stored at room temperature for up to 7 days. The ignitable liquids were then recovered using passive headspace concentration onto charcoal strips followed by solvent elution using pentane. Microbial degradation of tiki torch fuel resulted in the loss of the n-alkanes relative to the branched alkanes. Changes in the profile of the lamp oil were minor due to the highly branched nature of its alkanes. Microbial degradation of turpentine resulted in the selective loss of limonene and o-cymene. Overall, significant degradation by microbial action could result in the inability to identify the presence of an ignitable liquid or misclassify the ignitable liquid found.

The primary task of a fire debris chemist is to determine if there is an ignitable liquid present in a fire debris sample and, if so, to classify it according to its boiling point and carbon number range. However, in organic-rich substrates such as soil, the ignitable liquid residue is subject to microbial degradation due to the ease with which bacteria can metabolize the various hydrocarbons present. This is a rapid process which is problematic in many forensic laboratories as fire debris is often stored for extended periods of time due to case backlog. Although microbial degradation has been studied in laboratory samples, it has not been well-studied in "real-world" samples, which have not only been exposed to microbial degradation but have also suffered the effects of weathering due to the intense heat of the fire. In this work, the effects of microbial degradation of gasoline from an incendiary device have been evaluated over time. In addition to visually monitoring chromatographic changes, this work also utilizes multivariate statistical techniques to simplify the complex data set and elucidate trends that might not otherwise be observed. Results indicate a clear difference between glass samples, which suffered the loss of low boiling compounds, and soil, which suffered the loss of the normal alkanes and lesser substituted aromatics. Also, devices deployed on lawn soil and in the winter season appear to show the most extensive degradation of gasoline. Finally, while the ratio of the C(3)-alkylbenzenes is significantly altered in soil samples recovered from large devices, the overall chromatographic profile of gasoline recovered from smaller incendiary devices is significantly lower.