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Microbial Degradation of Petroleum Hydrocarbons: Implications for Arson Residue Analysis

NCJ Number
Journal of Forensic Sciences Volume: 37 Issue: 6 Dated: (November 1992) Pages: 1585-1599
K P Kirkbride; S M Yap; S Andrews; P E Pigou; A C Dinan; F L Peddie; G Klass
Date Published
This article describes a method and results of an analysis of microbial activity on hydrocarbon accelerants and discusses some implications and recommendations for arson investigation.
The study examined the effects of micro-organisms on common hydrocarbon accelerants such as gasoline both in vitro and in matrices similar to those encountered as arson residues. The sources of microorganisms for the study were two genuine arson residues that were found to give anomalous gas chromatograms. Samples of soil were taken from these residues and inoculated into enrichment cultures that contained Stanier's mineral salts medium and an aliquot of the putative hydrocarbon accelerant. The activity of each of seven microorganisms was examined by culturing each with samples of unleaded gasoline in either minimal medium or nutrient medium. A control prepared without inoculation was also used. The testing shows that certain species of pseudomonas microorganisms metabolize aromatic and simple aliphatic hydrocarbons that are important compounds in the identification of common accelerants. Complete metabolism of benzene and mono-substituted aromatic substances was found to occur within 48 hours, and simple aliphatic substances degraded more slowly. Accelerants exposed to these microorganisms can be degraded almost beyond recognition, certainly beyond conclusive identification for forensic purposes. Degradation may be prevented by adding a nonvolatile bactericide to arson residues or by keeping the items under refrigeration from the time they are collected until they are analyzed. Another approach is to demonstrate to fact-finders that an anomalous residue does contain microorganisms that are capable of metabolizing hydrocarbons. The tests described are appropriate for such a demonstration. 11 figures and 7 references