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Persistence of diatoms as trace evidence in clothing fabrics: The effects of active removal (machine washing) and passive removal (time and environment)

Flynn, Ross Christopher (2021) Persistence of diatoms as trace evidence in clothing fabrics: The effects of active removal (machine washing) and passive removal (time and environment). Masters by Research thesis, Murdoch University.

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Literature available in the field of forensics covering terrestrial-based evidence is comprehensive; however, many aspects of aquatic environmental evidence have yet to be well researched. One such developing area of aquatic evidence is that of diatoms, a major group of unicellular algae that exist in natural bodies of both fresh and marine waters. Due to their unique qualities and characteristics, diatoms have the potential to be used as evidence of contact with specific water sources. While initially used in forensics to aid drowning diagnoses, more recent case studies and research have investigated diatoms in the context of their use as a form of trace evidence, as well as factors affecting initial transfer and subsequent extraction. This research was the first to investigate factors affecting the persistence of diatoms in fabrics in both passive and active removal pressure contexts. The pressure environments selected represent realistic case circumstances, in which someone may discard (passively affect), or machine wash (actively affect) their clothing after its exposure to diatoms. Additionally, this study investigated whether cross contamination of diatoms could occur between diatom enriched fabrics and blank fabrics within a washing machine environment.

Both experiments' test fabrics were immersed in diatom enriched waters containing equal parts C. Muelleri and Navicula sp. species at 2,000,000 dv/mL. The passive removal experiment tested the influence of exposure (indoor and outdoor environments) and time (week 1/2/3/4/8/12) on the concentration of diatoms across three various fabrics (cotton knit/denim weave/polyester knit). The active removal experiment tested the machine type (front loader/top loader), wash temperature (warm ~40°C/cold) and the number of washes (1/2/3) on concentrations within DEFs, in addition to testing for cross contamination using blank fabrics within the washing load. Diatoms were extracted from fabrics using the established H2O2 method and quantified under a compound light microscope (CLM) at 400x magnification.

The passive experiment (PE) showed that exposure environment and time both played an important role in diatom persistence, with concentration reductions occurring much quicker initially outdoors compared to indoors, but still featuring notable loss for the indoor group during experiment. Rainfall was noted as heavier on average when the outdoor group lost the majority of its diatom concentrations. The active experiment (AE) showed that the number of washes most greatly impacted the concentration, followed by machine type, followed by wash temperature and these trends were consistent across all tested fabrics. By the first wash all groups still contained diatoms, however at a much lower concentration, and by the second, mostly the top loader washes still contained quantifiable diatoms and by the third wash none of the groups contained quantifiable diatoms. Front loader washes removed diatoms from clothing more effectively than top loaders, and within these machine groups, warm washes were more effective at removal than cold washes. Trends observed in the PE and AE were mostly consistent across all varieties of fabrics tested. Additionally, the AE showed that cross contamination between DEFs and blank fabrics was possible, however at relatively low levels. Across both the passive and active experiments, it is consistently shown that time is of the utmost importance when it comes to retrieving DEF evidence as diatoms appear to be lost passively over time even when left alone in different environments in addition to being vulnerable to machine washing removal.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): Medical, Molecular and Forensic Sciences
Supervisor(s): Magni, Paola, Vadiveloo, Ashiwin, Moheimani, Navid and Pitts, Kari
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