Feasibility study for the formulation of asbestos bulk sample calibration standards

Abstract

An examination of analysis results from bulk asbestos proficiency testing programs has revealed a pervasive tendency for laboratories to overestimate the amount of asbestos in test samples. In response, a series of weight percent calibration standards was formulated, verified by in-house analysis to be suitable for use, and distributed to two dozen laboratories for independent analysis. Results of those analyses yielded several quantitation tendencies, including the following: a) overestimation was the rule, increasing as the asbestos weight percentage decreased; b) stereomicroscopic quantitation showed the greatest overestimation and variability while point-counting showed the least; c) overestimation was greater in samples containing amphiboles than chrysotile; d) overestimation was high in samples with perlite or vermiculite matrices; and e) underestimation was common in chrysotile/cellulose combinations. This overestimation may preclude a laboratory from correctly determining whether a sample contains greater that 1% asbestos; it may likewise make difficult the decision of whether a sample falls under the jurisdication of the NESHAP point-counting amendment. Findings from the study relative to formulation of standards, interpretation of analytical data, and weight/volume/area percentage relationships, are being incorporated into a bulk materials analytical methodology currently in preparation for the Environmental Protection Agency.