Determination of the Size Distribution of Amphibole Asbestos and Amphibole Non-Asbestos Mineral Particles
THE MICROSCOPE
2016, Volume 64:1, pp. 13–25
DOI
https://doi.org/10.59082/IALY2074
AUTHORS
D.R. Van Orden, R.J. Lee, C.M. Hefferan, S. Schlaegle, and M. Sanchez
ABSTRACT
Over the last few years, there have been a number of investigations into the presence of amphibole minerals in soil or bedrock throughout the U.S., resulting in remediation of school grounds or highway right-of-ways, or delayed construction of needed dams. A review of available data suggests that the identified amphibole minerals were called “asbestos” simply based on being elongated particles and may not have been asbestos fibers. To clarify the characteristics of amphibole minerals, a study was conducted to characterize the size distributions of amphibole asbestos fibers and non-asbestos amphibole particles to determine differences and similarities between the populations. Ten mineral samples that could be visually characterized as asbestos or non-asbestos were obtained (five of each). Each sample was ground, suspended in water and deposited onto a 0.2 μm pore-size polyester filter. The filters were imaged in a field emission scanning electron microscope at magnifications up to 18,000×. The images were processed to obtain the length and width of particles that were at least 2 μm long and less than 3 μm wide (no minimum aspect ratio was applied). The data show there are clear differences in the dimensions of populations of asbestos and non-asbestos amphiboles, with asbestos being thinner and having a higher aspect ratio than non-asbestos. In addition, there is a set of particles in the asbestos samples that were not observed in the non-asbestos samples: fibers longer than 10 μm, thinner than 0.5 μm, and that have aspect ratios in excess of 30:1.