GEOLOGIC SITE ASSESSMENT FOR NATURALLY OCCURRING ASBESTOS

Asbestiform minerals are found in many geologic settings world-wide, and adverse health effects are attributable to them in a wide variety of circumstances. Asbestiform minerals are generally associated with the metamorphism of ultramafic rocks, but the various asbestiform minerals form or can be found in association with a wide variety of geological environments including sedimentary and igneous. Since NOA minerals are not always apparent to the eye, knowledge of the geologic environment on a site is frequently the best indicator of the potential for NOA minerals.

Site-specific identification and assessment methods for NOA for environmental risk assessment have been poorly developed. This is largely because the assessment methods used were developed either for health risk assessment of asbestos in industrial settings, or for the economic assessment of naturally occurring deposits for minerals exploitation. The application of the minerals exploration assessment method runs the risk of underestimating NOA since the method is intended to identify occurrences, which by their nature, have a volume of tens of thousands of tons of geologically concentrated asbestiform material. The use of industrial health risk assessment methods run the risk of overestimating NOA since they look at total asbestos present, but do not factor in geologic occurrence or exposure pathways. The investigation and assessment of NOA for environmental risk assessment has to incorporate site-geology and disturbance scenarios in order to determine the exposure risk. The mere presence of NOA on a site does not pose a risk unless the material can become respirable.