U.S. flag

An official website of the United States government, Department of Justice.

Rates of Loss and Replacement of Very Small Particles (VSP) on the Contact Surfaces of Footwear During Successive Exposures

NCJ Number
Date Published
March 2019
9 pages
It has previously been shown that a walk of 250 m (approximately 175 steps/shoe) in a new environment is sufficient to remove and replace particles present on the contact surfaces of footwear; however, it is unknown how quickly this replacement occurs, so this article describes experiments that measured how quickly (in terms of steps) this loss and replacement of VSP occurs.

The principal findings of this study are (1) that the contact surfaces of footwear are dominated by VSP attributable to the most recent site of exposure; (2) that walking in a new location rapidly removes and replaces VSP from the contact surfaces of footwear; (3) major replacement occurs in 5 to 10 steps, and nearly complete replacement occurs by 25 steps; (4) the character of the loading site may influence the initial rate of loss and replacement of VSP (during the first five steps); and (5) overall, the loss and replacement of VSP on footwear in these experiments can be reasonably described by the relationship 1/(Steps plus 2.68). Three sites were chosen to have different, characteristic particle types (soil minerals). Footwear of two types (work boots and tennis shoes) were tested, accumulating particles by walking 250 m in one site, followed by walking a designated number of steps (per shoe) in a second site. Very small particles (VSP) were harvested from contact surfaces of the footwear (those surfaces in direct contact with the ground when walking) using a moist swabbing procedure. (Publisher abstract modified)

Date Published: March 1, 2019