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Differential Sampling of Footwear To Separate Relevant Evidentiary Particles From Background Noise

NCJ Number
Date Published
February 2017
35 pages
This project tested the ability to separate particle signals on the contact surfaces of footwear soles using differential analysis of loosely held, moderately held, and strongly held particle fractions by 1) designing and conducting a series of realistic environmental exposures suitable for testing very small particle (VSP) transfer retention and fractionation; 2) designing, developing, and testing a differential sampling protocol suitable for testing the physical fractionation of VSP signals; and 3) testing the ability to use differential sampling to separate specific VSP signals of interest.

Prior research that has used comparable studies involving a generalized sampling of particles on footwear soles from both contact and recessed areas shows the retention of particles from earlier contacts. The current study determined that although particles on the contact surfaces of footwear were removed and replaced, particles on the more recessed areas of the sole were not. Three environmental exposure sites were chosen to have different characteristic particle types (soil minerals). Shoes of two types (work boots and tennis shoes) were tested, accumulating particles by walking 250 m in each environment. Some shoes were exposed to only one environment, and others were exposed to all three in one of six sequences. Sampling methods were developed to separate particles from the contact surface of the shoe based on how tightly they were held to the sole. Project findings have important implications for guiding further research. Research on differential sampling of footwear should continue, focusing on the difference between particle populations found on contact surfaces and those found on recessed areas of the sole; and research on related computational and statistical methods for objectively interpreting mixtures of particles should continue. 16 figures, 6 tables, and 52 references

Date Published: February 1, 2017