Organic profiling of Western Australia soils for provenance determination

Bethany Morey

In Western Australia, the Swan Coastal Plain encompasses the majority of the Perth metropolitan region and hence is often the site of forensic investigations. Due to the similarity in the geology and associated mineralogical profiles of the area, analysis of organic components of soil recovered from items of interest may provide greater discriminatory power when attempting to determine provenance. Identification of plant waxes has been used previously in the United Kingdom to discriminate between soils derived from garden beds; however, the wider applicability of the technique, particularly for soils low in organic matter, such as those present within the Swan Coastal Plain in Perth, Western Australia, has not been demonstrated. The efficiencies of two methods were compared to assess their suitability for the extraction of plant wax compounds in Perth Metropolitan soils. Soxhlet extraction was found as the more accurate method when compared with the alternative liquid-liquid extraction. The development of the Soxhlet methodology enabled the extraction of alkanes and fatty acids from a 2.5 g soil sample. Soil samples were collected within a series of North-South and East-West lines within the Bassendean and Spearwood Dune systems of the Swan Coastal Plain (n=19) to represent a small sample of differing soils provenances and enabled the investigation of the between-site variation. Samples were subjected to Soxhlet extraction for 24h, and the alkanes and fatty acids present in the extracts were analysed using GC-MS. Qualitative analysis (n=8) of combined alkane and fatty acid profiles provided a preliminary understanding of the differences that may occur between sample sites as a result of the surrounding botanical influences. Quantitative analysis (n=11) revealed that the combined alkane and fatty acid profiles enabled the discrimination between the soil sites (R = 0.873 p = 0.001). The results of this study indicate the potential for the organic profiling of soils with low organic content at a scale relevant to forensic investigations.

Organic profiling of Western Australia soils for provenance determination

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