The potential for geochemical discrimination of single- and mixed-source soil samples from close proximity urban parkland locations

K Cheshire,R.M Morgan,J Holmes

doi:10.1080/00450618.2016.1144789

K Cheshire, R.M Morgan + Show 1 more

Open Access

https://doi.org/10.1080/00450618.2016.1144789

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Abstract

This initial study assessed the feasibility of geochemical analysis to discriminate single- and mixed-source soil/sediment samples from close proximity sites, a key attribute for forensic comparison and crime reconstruction. Key techniques including ICP-MS, ICP-AES and XRF were able to discriminate between the sites used in this study. The findings of this experimental study provide empirical evidence that highlights the difficulties associated with interpreting data from the elemental analysis of soil samples from geographically similar locations, and demonstrates the issues associated with samples of mixed provenance. Statistical analysis of mixed-provenance samples in comparison with the single-source control sites revealed no significant difference between the mixed and single source samples illustrating that, in this particular case, the samples could not be excluded from having a similar source in direct contrast to previously published findings. This study underlines the necessity to understand further the degree of complexity that exists for the analysis and interpretation of both single- and mixed-source forensic soil/sediment samples and confirms the need for multiple independent methods to be used in order to begin to draw meaningful conclusions of forensically relevant provenance.

Highlights

Five single-source samples from each site (20 samples for each collection time) and a further 11 samples composed of artificial mixtures of materials from these sites were analysed using Inductively Coupled Plasma - Mass Spectroscopy (ICP-MS), Inductively Coupled Plasma - Atomic Emission Spectroscopy (ICP-AES) and X-ray Fluorescence (XRF)
With regards to comparing single-source with mixed-source samples, XRF and ICP-AES appear to potentially be more able to infer a relationship between the mixed-source sample and the single source that has contributed to it based on the Principal Component Analysis (PCA) statistical assessment (Figures 3 and 4), but this is clearly a highly complex issue and further research is needed to establish the reproducibility of this finding at other sites and scenarios
XRF, ICP-MS and ICP-AES identified a clear distinction between sites A–D, similar findings have been found by Morrisson et al.[33] through other independent forms of analysis, which highlights the benefit of adopting multiple techniques to provide reliable and Collection Axis 1 Axis 2 Total variance (%)

Summary

Introduction

Forensic geoscience Forensic geoscience refers to the assessment of earth materials, be they physical, biological or chemical (see Table 1), in order to be able to indicate a potential provenance and/or establish a relationship between the suspect(s), victim(s) or artefact(s)[1−3]. The use of multiple independent methods of analysis is required to ensure meaningful inferences can be made concerning the source of that material and to enable the comparison between samples to be undertaken[3]. DiatomsBacterial DNA Pollen Mycology Organic matter Plant wax signatures ICP-MS, ICP-AES, XRF, AAS and SEM-EDX (elemental analysis) FTIR and Loss-on-Ignition (organic analysis) Binocular microscopy and XRD (mineralogy). Particle size analysis by Laser granulometry QemSCAN Quartz grain surface texture analysis by SEM Colour Magnetic susceptibility Reference. Hawksworth and Wiltshire[7] Carvalho et al.[8]

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Discussion

Conclusion