Abstracts: ISEE 20th Annual Conference, Pasadena, California, October 12–16, 2008: Contributed Abstracts
Direct dermal contact is a primary exposure route and significant contributor to a person's overall dose of a contaminant. Such exposure to environmental contaminants has been a priority research focus for pesticides, toxic metals, and biocontaminants. Most of this research has focused on transfer of these particles and residues from common surfaces to a person's skin or clothing. This research investigated transfer in the opposite direction. Our goal was to determine the transfer rate of contaminant particles from a person's skin or clothing to common indoor surfaces. Once deposited on the new surface, subsequent dermal contact by another person will contribute to that individual's total exposure. This mechanism of contaminant transport may be a significant contributor to the exposure of additional people who may not normally come into direct contact with the contaminant. The findings of this research may have implications for children's and adult's health as well as homeland security.
A volunteer wearing normal clothing was uniformly exposed to a high concentration of a fluorescent aerosol inside a wind tunnel. After exposure, the volunteer immediately entered an exposure chamber where a series of scripted activities were performed. The activities were designed to insure equal contact with a variety of rigid and upholstered furniture surfaces. Fluorometric analysis of skin, clothing, and surface samples collected before and after the volunteer conducted the activities quantified the particle mass transferred to a unit area of the surface (ng/cm2). The mass transferred was normalized by the aerosol concentration (ng/cm3) and exposure time (min) inside the wind tunnel during the experiment to yield a transfer velocity (cm/min). Independent variables included in the linear multivariate analysis of the transfer velocities included volunteer identification, surface type contacted, clothing type, and the corresponding second and third level interactions.
The linear multivariate regression model was statistically significant (P-value < 0.0001) with a correlation coefficient of 0.84. The median transfer velocity was 0.047 cm/min with quartiles of 0.008 and 0.209 cm/min. The largest fraction of particles was transferred from clothing to upholstered surfaces. Direct contact of skin to a hard surface transferred one fifth fewer particles. Clothing contact with a hard surface transferred the lowest percentage of particles.
The experimental findings highlight the importance of particle transfer from a person to other surfaces on subsequent exposures and contaminant transport routes. Upholstered surfaces may receive the most particles during contact but the three dimensional nature of the surface may not easily release the particles for transfer to another person. Transfer of particles from a person to a hard surface is substantially lower; indicating secondary exposure of an unexposed person may not contribute significantly to their overall dose. However, a child or adult unknowingly exposed to a contaminant may inadvertently transport the contaminant to a previously clean room within a building or to a completely different microenvironment. This accidental transport and transfer to surfaces may subsequently increase the exposure risk of additional children and adults who are unaware of the contamination threat.