The effects of season and soil type on microbial degradation of gasoline residues from incendiary devices

Abstract

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.