An investigation into the recovery of ignitable liquid residues from entomological samples using solid-phase microextraction

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The analysis of fire debris can indicate the presence of an ignitable liquid, but the volatility of these substances means that the likelihood of detecting them diminishes over time. It is proposed in this thesis that when a scene contains burnt human remains, entomological samples can be analysed for the detection of ignitable liquids, as an alternative to fire debris. It is hypothesised that a larva’s ability to invade areas protected from the external environment, such as the natural body openings of cadavers, and accumulate substances present in the tissue in which they are feeding, will extend the period in which ignitable liquids can be detected. In small-scale experiments conducted under controlled laboratory conditions, petrol and kerosene were detected in larvae of the blow fly Lucilia cuprina, (Wiedemann) (Diptera: Calliphoridae) that had been fed on meat burnt using these ignitable liquids. Four sample sets of meat, each with six replicates (24 meat samples in total) were prepared. The first and second sets were burnt using petrol and kerosene, respectively. The final two sets were control groups. Six larvae were collected daily from each of the 24 meat samples for a period of five days. Once the adults had emerged, six adults and six puparia were also collected from each meat sample. All of the entomological samples collected were analysed using solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). It was found that larvae of the blow fly Lucilia cuprina can be used in a small-scale setting to detect both petrol and kerosene from burnt substrates for at least five days. Positive results for the ignitable liquids of interest were also obtained for a limited number of adult flies and puparia. Given these findings, further research was conducted using a more realistic experiment (conducted in duplicate) that mirrored a casework scenario more closely. Sample sets identical to those in the small-scale experiments were prepared using 24 piglets, each approximately 1.39 kg in weight, instead of the meat samples. These piglets were placed a minimum of 51 m apart at the Holsworthy Military Area in New South Wales, Australia, for three days. After this time, the piglets were transferred to a controlled laboratory. It was found during these fieldwork experiments that petrol and kerosene could be successfully detected in larvae for as long as eight days, and in the adult and puparia samples for at least one month. These findings confirm the significant advantage of using entomological samples as an alternative to fire debris, in that they extend the period available for sampling volatile ignitable liquids by at least one month. In particular, puparia can withstand changing climatic conditions, and unlike the larvae and adults, are immobile and hence could be found close to human remains even after considerable time has elapsed.
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