Image analysis method (IAM) for measurement of particle size distribution and mass availability on carpet fibers

Exposure to particles that have deposited on surfaces is common in occupational and residential environments. Lack of an accurate tool for assessing particle size distribution and loading (mass per unit area) on carpet fibers available for exposure contributes to the uncertainty associated with current risk assessment models. This research presents a new, direct image analysis method (IAM) for measuring particle size distribution and loading on carpet fibers. New and old carpet fibers loaded with Arizona Test Dust were used to test the method. Carpet fibers were removed from the bulk carpet, mounted on substrates, and scanning electron microscopy (SEM) images were collected. Particle size distribution and total mass were calculated from the processed images. The Arizona Test Dust (ATD) size distribution on fibers from two different carpets had mass median diameters of 3.6 (+/- 1.2) and 4.1 (+/- 0.7) mu m, similar to that for bulk ATD, 4.0 (+/- 0.5) mu m. Total ATD mass available on new carpet fibers calculated by IAM were statistically correlated with the mass collected on micro-vacuum samples (R-2 = 0.95). Direct comparison of the aerodynamic diameters measured by IAM with those measured automatically by the SEM showed a slight negative bias due to image resolution problems for the smallest particles.