AMPHIBOLE VS. AMPHIBOLE ASBESTOS AND THEIR RELATIONSHIP TO ASBESTOS-IN-TALC METHODOLOGY

A significant amount of controversy exists concerning what is and isn’t truly amphibole asbestos. Counting criteria for various methods use aspect ratio to distinguish (3:1, 5:1, or 20:1). The concept of mean aspect ratio of a “population” also does not give adequate definition when applied to trace amounts of contaminant where only one or two particles may be present.

In addition to high aspect ratio, durability of fibers is a characteristic unique to asbestos; although durability is not a feature readily measured in a microscope. Applying the historic principles of asbestos mining and processing can give clues about how to exploit the unique properties of asbestos for the purpose of its analysis. SpecificallyThe use of grinding and sieving is therefore proposed as a step in preparation that will essentially separate asbestos from non-asbestos particles for analysis.

Two samples of tremolite asbestos, one from NIST and another from Lone Pine. CA, were characterized. The NIST tremolite is generally thought to be less asbestiform than the Lone Pine tremolite. Both were subjected to grinding using lab scale milling to simulate full scale commercial grinding facilities and subsequently sieved into separate size fractions. These size fractions were characterized and examined by polarizing light microscopy, scanning electron microscopy, and transmission electron microscopy. This technique may be useful in the study of asbestos vs. elongated mineral fibers proposed in the NIOSH roadmap.

This research will aid in efforts by the United States Pharmacopeia (USP), a non-governmental entity involved in maintaining and improving standards for materials used in the manufacture of pharmaceuticals, to update the current asbestos-in-talc method. Establishing a detection limit for this procedure is of ultimate concern as it was not addressed in historical methodology. Recent studies show that it is possible to achieve a detection level that exceeds that required for regulatory purposes (<0.1%). Samples with extremely low levels of asbestos (as analyzed by alternative microscopy methods) indicated that detection could be achieved at between 100 to 500 for both amphibole and chrysotile.