The transferability of diatoms to clothing and the methods appropriate for their collection and analysis in forensic geoscience

Abstract

Forensic geoscience is concerned with the analysis of geological materials in order to compare and exclude environmental samples from a common source, or to identify an unknown provenance in a criminal investigation. Diatom analysis is currently an underused technique within the forensic geoscience approach, which has the potential to provide an independent ecological assessment of trace evidence. This study presents empirical data to provide a preliminary evidence base in order to be able to understand the nature of diatom transfers to items of clothing, and the collection of transferred diatom trace evidence from a range of environments under experimental conditions. Three diatom extraction methods were tested on clothing that had been in contact with soil and water sites: rinsing in water (RW), rinsing in ethanol (RE), and submersion in H2O2 solution (H). Scanning electron microscopy (S.E.M.) analysis was undertaken in order to examine the degree of diatom retention on treated clothing samples. The total diatom yield and species richness data was recorded from each experimental sample in order to compare the efficacy of each method in collecting a representative sample for analysis. Similarity was explored using correspondence analysis. The results highlight the efficiency of H2O2 submersion in consistently extracting high diatom counts with representative species from clothing exposed to both aquatic and terrestrial sites. This is corroborated by S.E.M. analysis. This paper provides an important empirical evidence base for both establishing that diatoms do indeed transfer to clothing under forensic conditions in a range of environments, and in identifying that H2O2 extraction is the most efficient technique for the optimal collection of comparative samples. There is therefore potentially great value in collecting and analysing diatom components of geoforensic samples in order to aid in forensic investigation.

Research advances in forensic diatom testing

“…Several studies have provided methodologies to extract more diatoms from different items. Scott et al [23] used three methods to extract diatoms from cotton t-shirts that had been in contact with diatom-rich water and soil. They performed a correlation study on the diatom species and abundance in water samples, and investigated the effects of soaking duration on diatoms.…”

The Value of an Empirical Approach for the Assessment of Diatoms as Environmental Trace Evidence in Forensic Limnology

“…The individual properties of a soil sample have traditionally been observed using light and electron microscopy methods (Dawson and Hillier 2010). Optical analyses allow for the examination and identification of individual particulates such as quartz grain surface textures (Bull and Morgan 2006), pollen grains (Wiltshire 2015), and diatom valves (Scott et al 2014). A growing area of research is directed towards improving the range and efficiency of those techniques available for the analysis of geoforensic evidence types.…”

“…Given the variability of environments (even those with similar underlying geology and land use), analysis of the microscopic characteristics of a trace soil or water sample can be used effectively in a range of forensic investigations. Examples within the literature include homicide (Smith et al 2002), serious assault (Siver et al 1994), poaching and wildlife crime (Morgan et al 2006), burglary (Mildenhall 2006), and the reconstruction of international war crimes (Brown 2006).…”

“…When recognized and appropriately recovered as evidence, botanical material offers a valuable biological technique for the comparison and exclusion of samples and in the profiling of an unknown environment (Wiltshire, 2009). This has primarily been observed through pollen analysis which has been widely used in casework across the U.S. and Europe (Smith et al 2002;Brown, 2006;Wiltshire 2006). Concurrent empirical research considers the transfer and persistence dynamics of pollen evidence in various forensic scenarios (Riding and Rawlins, 2007;Morgan et al 2014aMorgan et al , 2014b, and generates knowledge of the diverse range of circumstances in which pollen may be recovered during an investigation.…”

“…Several case examples within the literature consider the successful application of freshwater algae as trace evidence in various investigative scenarios (Siver et al 1994;Cameron 2004), however empirical research studies generating additional intelligence within the field are relatively recent (Scott et al 2014). Growing calls within the forensic science community, from both academics and policy makers, increasingly identify the need for research to establish empirical evidence bases for forensic application (Mnookin et al 2011; Annual Report of the Government Chief Scientific Adviser 2015).…”