The Transfer and Persistence of Trace Particulates: Experimental studies using clothing fabrics

Abstract

A series of experiments were conducted using various types of pollen grain, powder and metal particulates to determine their persistence on a range of different types of materials. The decay curves generated in the repeated experiments all broadly conform to those obtained and already presented in the literature for fibres and glass particulates. The experiments presented in this paper were conducted for up to 647 hours for individual runs and it was found that a general rule existed that it was the material type rather than the particulate type that was the major controlling factor in the persistence of particles. For the pollen grain experiments the overall theory is sustained; there is a significant loss initially followed by a slower decay although this is not precise given the varied nature of palynomorph types. The manner by which the particulates were introduced onto the material had an initial immediate effect, however, the persistence of these particulates over longer periods of time was generally unaffected. The inference presented in these published papers (referring to glass, paint, foam, hair etc.) is that in the first instance, particulates are shed from clothing rapidly (minutes) and then subsequently shed more slowly, with varying percentages of particulates remaining after several hours. The overall effect of the decay curve appears to be one of exponential decrease. There are however, a number of factors which have been reported to affect the persistence and decay curves of small particulates and these are well summarised by Houck [6]. He considers that the size and texture of the material being transferred may affect the persistence of such trace materials and links this to the type of surface on which the material is being retained. Further, he considers whether the particulates can be easily removed (and whether a suspect has tried to remove them). Crucially, he identifies the importance of the length of time interval between the offence and recovery of the retained material and links this to the degree of activity undertaken by the suspect or the victim following particulate transfer.The experiments presented in this paper are in response to a series of specific casework requirements in which it was deemed necessary to determine the relevant transfer and persistence of small sedimentary particles (soils, natural clays, silts and 4 sands, pollen and metal particulates), from a number of different types of clothing.Specifically, this paper seeks to identify not only the transfer, persistence and relevant abundance of particulates on clothing over time, but also whether a general rule can be introduced for all such trace particles of generally similar size (less than 100m diameter) and occurrence (glass, paint, fibres, hair, soils, clays, silts, sands, pollen and other anthropogenic materials). There is a need to consider whether geoscientific trace materials act in the same, or different, manner as those anthropogenic particulates already documented in the literature. We need to inve...

The relevance of the evolution of experimental studies for the interpretation and evaluation of some trace physical evidence

“…They also demonstrate the persistence of the transferred glass particulates on clothing over time and after different levels of activity and that glass particulates exhibited the classic decay of trace evidence that has been documented for fibres, foam, hair, pollen and soil (all in accord with the established theory, see above). The recovery of albeit a single glass particulate in each experimental run after the garment had been washed and dried is noteworthy and tends to concur with the preliminary findings of Bull et al [36] for pollen particulates. This is of course only a preliminary experiment and further work needs to be done to ascertain the wider significance of such a finding on clothing that has been washed.…”

“…These figures show that glass particulates are transferred onto the clothing with 12 particulates being recovered from the first taping following the smashing of the first pane, and 34 particulates recovered after the smashing of the second pane. After a five minute walk wearing the same clothing a large number of the particulates had been shed (in accord with the published literature for other trace particulates [21,22,23,36,37]. Further running and walking (tapings 3-5 in Table 1 and Figure 4) shows a more linear and slower reduction in particulates retained on the clothing.…”

“…Pollen has been demonstrated to remain for at least 647 hours (approximately 27 days) on different types of clothing [36]. A similar study on glass particulates observed the persistence of glass particulates on items of clothing eight hours after smashing a window pane [21].…”

“…A wide range of experimental studies have been undertaken to establish the persistence over time of a number of different types of trace particulates on clothing (for fibres: [24][25][26][27][28][29][30][31][32]; foam: [33][34][35]; pollen and soil: [36]; glass: [21,22,23,37]). In general a two-stage decay curve has been demonstrated for each form of particulate evidence following the original study by Pounds and Smalldon [16].…”

The use of grain size distribution analysis of sediments andsoils in forensic enquiry

“…The grain size distribution of a forensic sample must now take into account alteration and mixing of soil from different sources caused by the movement of the material by anthropogenic effects on footwear, clothing and vehicles. Thus, not only is there a complication of mixing to consider in forensic enquiry but there is also the thorny issue of selective transfer, persistence and decay of materials which will alter the grain size distribution curve further [10].…”