Stoney David A, Bowen Andrew M, Ausdemore Madeline, Stoney Paul L, Neumann Cedric, Stoney Frederick P
Stoney Forensic, Inc., 14101-G Willard Road, Chantilly, VA, 20151-2934 USA.
Department of Mathematics and Statistics, South Dakota State University, Brookings, SD 57007 USA.
Forensic Sci Int. 2019 May;298:106-114. doi: 10.1016/j.forsciint.2019.02.032. Epub 2019 Feb 26.
Prior work has shown that the contact surfaces of footwear rapidly lose very small particles (VSP) when walking on dry soil. Other research, with more general sampling from shoe soles, has shown that particles can persist much longer. Given rapid losses from contact surfaces, we hypothesize that non-contact, recessed areas of footwear retain particles from prior exposures. Here we conduct differential analysis of VSP recovered separately from contact and recessed surfaces, following a controlled series of environmental exposures. Work boots and tennis shoes were exposed by walking distances of 250 m, sequentially, in three environmental sites. VSP were harvested separately from contact and recessed surfaces using a moist swabbing procedure. VSP were analyzed by microscopy and the proportions attributable to each site were determined using a newly developed statistical model. The principal findings are (1) contact surfaces of footwear are dominated by VSP attributable to the most recent site of exposure, (2) recessed surfaces of footwear retain VSP from prior exposures, (3) sole type appears to be a source of major differences in the amount of VSP from prior exposures remaining in recessed areas, and (4) when VSP attributable to prior exposures are found, there is no clear trend for dominance between earlier exposures. The significance of these findings is considerable. In cases where the last site visited is of interest, VSP from contact surfaces of footwear will give a nearly pure sample of that site. In cases where prior sites visited are of interest, the VSP from the contact surfaces can be used as a background signal, providing a means for differential analysis of VSP mixtures found in the recessed areas of the sole. The strong influence of shoe sole type on the retention of VSP from prior exposures indicates that efforts to explore the rates of VSP loss from recessed areas will need to take characteristics of the sole type into account. The absence of a clear trend for dominance between earlier exposures suggests that once traces are lodged within the recessed areas of footwear soles they can be retained for long periods of time. These findings support prior research on the retention of particles on footwear that shows periods of long retention following rapid initial losses of trace materials. The differential analysis of VSP is a significant contribution to the methods available for the deconvolution of particle mixtures into fractions that are characteristic of their contributing sources.
先前的研究表明，鞋子的接触表面在干燥土壤上行走时会迅速丢失非常小的颗粒（VSP）。其他从鞋底进行更广泛采样的研究表明，颗粒可以留存更长时间。鉴于接触表面的快速损失，我们推测鞋子的非接触、凹陷区域会留存先前接触的颗粒。在此，我们在一系列受控的环境暴露后，对分别从接触表面和凹陷表面回收的VSP进行差异分析。工作靴和网球鞋依次在三个环境场地行走250米的距离进行暴露。使用湿拭子程序分别从接触表面和凹陷表面采集VSP。通过显微镜对VSP进行分析，并使用新开发的统计模型确定每个场地的VSP所占比例。主要发现如下：（1）鞋子的接触表面主要是归因于最近暴露场地的VSP；（2）鞋子的凹陷表面留存先前接触的VSP；（3）鞋底类型似乎是凹陷区域留存的先前暴露的VSP数量存在重大差异的一个来源；（4）当发现归因于先前暴露的VSP时，早期暴露之间没有明显的主导趋势。这些发现的意义重大。在对最后访问的场地感兴趣的情况下，鞋子接触表面的VSP将给出该场地几乎纯净的样本。在对先前访问的场地感兴趣的情况下，接触表面的VSP可作为背景信号，为分析鞋底凹陷区域中发现的VSP混合物提供差异分析方法。鞋底类型对先前暴露的VSP留存的强烈影响表明，探索凹陷区域VSP损失率的研究需要考虑鞋底类型的特征。早期暴露之间没有明显的主导趋势表明，一旦痕迹留在鞋底凹陷区域，它们可以长时间留存。这些发现支持了先前关于颗粒在鞋子上留存的研究，该研究表明在痕量物质最初快速损失后会有长时间的留存。VSP的差异分析对将颗粒混合物解卷积为其来源特征部分的现有方法做出了重大贡献。
