The analysis of trace evidence in forensic geoscience can contribute valuable information to a criminal investigation, especially in the search to exclude a suspect from a crime scene or in the attempt to profile an unknown forensic environment. The examination of microscopic components of soils and sedi- ments can provide useful circumstantial evidence in a range of experimental and case work scenarios. Relatively established techniques, including quartz grain surface texture analysis , palynology , and soil geochemistry; are increasingly complemented by new methods in the examination of both the organic and inorganic components of a trace geoforensic sample. More recent research is now considering the importance of new geoforensic methods including microbial DNA profiling, mycology,and alkane signatures. In comparison, however, diatom analysis has been relatively limited in its forensic application to date.
The value of diatom evidence to geoforensic enquiry lies in the multiple environmental characteristics that can be inferred. Diatoms are unicellular microscopic algal organisms which are widely distributed and naturally abundant in a range of aquatic and terrestrial environments. Individual diatom species and population assemblages are diverse and environmentally specific due to their sensitivity to multiple variables including light, nutrient availability, pH, and salinity. The hardened silica cell wall (SiO2) is resistant to decay and retains diagnostic features enabling species identification and forensic comparison. Furthermore, the microscopic nature of diatoms increases their potential for use in a forensic capacity. It is highly unlikely that the transfer of diatom traces from a crime scene will be recognised by a perpetrator, enhancing the potential for diatoms to be recovered as evidence.
Diatoms have been established as reliable and naturally abundant environmental indicators in a broad range of applica- tions including palaeoecological reconstruction, water quality management, and climate change research. The main application of diatoms in forensic science is currently pathological, assisting in the diagnosis of drowning as a cause of death. Further research has been directed towards the use of algae, and particularly diatoms, in the estimation of the post mortem submersion interval (PMSI) of an item or cadaver recovered from water. Fossil diatoms have also been recognised as important tracers in soils and anthropogenic materials including paints, pesticides, and safe ballasts.
While diatom analysis has been used in various case work examples, little experimental research is currently observed within the forensic geoscience literature. This echoes the forensic palynology literature which included very little experimental research until 2005 in contrast to extensive case work examples. Forensic palynology is now a well established field of enquiry with such experimental studies crucial in providing a sound evidence base for the collection and interpretation of pollen evidence in order to provide valuable intelligence. A similar research focus in forensic diatom analysis is essential to provide reliable data towards developing this independent technique for the ecological assess- ment of geological materials in criminal investigation. Experimen- tal consideration of diatoms in pertinent contexts such as the transfer of diatoms from various source habitats to recipient surfaces, and the recoverability of particulates from those items for forensic analysis contributes to the appropriate interpretation and presentation of evidence in a court of law.
This paper aims to examine the transfer of diatoms to clothing in a range of aquatic and terrestrial environments, and determine an effective technique for the collection of diatom evidence for forensic comparison. Clothing was determined an appropriate recipient surface to examine diatom transfer due to its frequent presence at a range of crime scenes. The optimal recovery and analysis of trace evidence from clothing is therefore imperative for the reliable comparison and exclusion of samples in forensic geoscience.
In this study, three methods were tested on cotton t-shirts in contact with multiple water and soil sites. The traditional method of rinsing with water (RW) was compared to rinsing with ethanol (RE) (suggested as most efficient in previous research by Uitdehaag), and hydrogen peroxide extraction (H2O2) (adapted from ecological diatom investigation). The efficacy of each extraction method was assessed through consideration of the total diatom valve count yielded in each experimental sample, the species richness of each experimental sample when compared to a control, and the similarity of sample composition as determined by correspondence analysis. The impact of submersion time upon the transfer of diatom evidence was also examined. In aquatic contexts, t-shirt samples were submerged for 3 min, 30 min, 3 h, and 24 h; in order to replicate different forensic transfer scenarios. Residual clothing samples were later examined under scanning electron microscopy (S.E.M.) to assess the number of diatoms still adhered to clothing following each treatment.