Volume 8, Issue 5 (May 2011)
Evaluation of Asbestos in Dust on Surfaces by Micro-Vacuum and Wipe Sampling
Micro-vacuum and wipe sampling methods are routinely used to measure surface dust contamination in both occupational and environmental settings. Both methods are subject to variability in their efficiency of dust collection resulting primarily from textural surface characteristics and dust loading. As part of a study to determine contamination levels of asbestos and other World Trade Center related contaminants in the wall cavity of a high-rise office building, paired samples were collected from 15 locations. The surface type of 14 locations was concrete-masonry block; the remaining surface type was a polyvinyl chloride coating. Micro-vacuum wipe pairs were obtained from the same wall component at contiguous locations. A template was used to ensure that equal 100-cm2 areas were consistently sampled. Micro-vacuum and wipe samples were collected and analyzed for asbestos using ASTM Methods D5756 and D6480, respectively. The average surface concentration reported by the micro-vacuum samples was numerically higher than the wipe samples, but the difference was not statistically significant (P=0.195). Both methods yielded an equal number of samples below the analytical sensitivity; the false-negative rates were the same for each method. Micro-vacuum and wipe sample concentrations were not correlated (R2=0.207). The length and width of asbestos structures collected by wipe samples was significantly larger than by micro-vacuum samples (P=<0.001). Micro-vacuum sampling for asbestos in dust on rough surfaces yields numerically higher concentrations of asbestos. Despite variations in the relative efficiency of particle collection by these methods, the data pairs demonstrate that micro-vacuum and wipe samples produced statistically equivalent results, with micro-vacuum samples being more efficient on the rough surface tested.