Digging up the dirt on crime: The dynamics of soil chemistry and its microbiome indecomposition

Despite its forensic importance as trace evidence, soil is under-utilised by forensicscientists, due to a lack of research into the suitability of analytical approaches anda subsequent lack of understanding of the soil. This project aimed to address this issue byexamining both the chemical and microbial methods used for the discrimination of soilsamples. A comprehensive chemical analysis approach, focusing on high performance liquidchromatography, UV-visible spectroscopy and Mass Spectrometry was used to develop adirectly-translatable method for the modern forensic testing laboratory, coupled withmodern genomic approaches to correlate the chemical and microbial data.Both high and ultra-high performance liquid chromatography was used to analyseacetonitrile extractions from 210 soil samples taken from four locations across the Geelongand Surf Coast Shire area from March 2020 to January 2021. A further 60 samples were storedin a dark cupboard in standard laboratory conditions over the same period to examine theeffects of storage and thereby inform best practice sample handling. Importantly, throughprincipal coordinates analysis of the UV-visible chromatograms, it was found that this methodcould discriminate between locations, timepoints, and age points, and therefore, for the firsttime, shows that the method may offer a quick and reliable method for forensic soil analysis.Soil microbiome changes were investigated through the burial of 192 5 cm2 pork skins,wrapped with different fabrics (synthetic and natural) or without fabric, buried at the fourlocations, and excavated at 5, 19, and 54 days after burial. It was found that fabrics directlyimpact the biomass growth on pork skins including relative presence of biofilm and variablemould and staining patterns. The data generated here highlighted the importance of both thesoil chemistry and soil microbiome for forensic analysis.