MINERALOGICAL, GEOCHEMICAL, AND TOXICOLOGICAL VARIATIONS OF ASBESTOS TOXICOLOGICAL STANDARDS AND AMPHIBOLE SAMPLES FROM LIBBY, MT

Asbestiform mineral dust exposure is associated with lung diseases such as asbestosis, malignant mesothelioma, and bronchogenic carcinoma. Past focus was primarily on human exposure and health effects of commercial asbestos. Recently, there has been renewed recognition of the potential deleterious health effects of asbestos that may occur as accessory minerals in rocks (e.g. serpentinite) and in some mineral commodities used in consumer products (e.g. vermiculite or talc). Within the past decades, in vitro and in vivo studies have shown asbestos to be cytotoxic and mutagenic, yet the mechanisms responsible have escaped identification. Asbestos-related diseases may be a result of two mechanisms, mechanical and intracellular. Evidence in the literature indicates that the potential for the asbestiform minerals to elicit one, or both, of these mechanisms may be based on mineralogy, size, shape, chemistry, elemental speciation, and electral properties. However, contradictory evidence can also be found in the literature about the specific mechanism of toxicity attributed to specific asbestiform minerals. Thus, the mechanistic questions can be best answered through increased collaborative research between the geochemistry and health-related communities. One key step in the collaborative research process is the mineralogical and geochemical characterization of existing and new asbestos standards for toxicological studies. Thus, the USGS has analyzed 5 sets of asbestos standards (5 amosites, 4 anthophyllites, 6 chrysotiles, 5 crocidolites, 4 tremolites) and samples of Libby asbestos. Chemical analyses indicate that elemental content varies between asbestos standards of the same mineral. Analysis (XRD, SEM, EDS) also indicates differences in asbestos habit (particle shape) and the presence of other minerals as contaminants between different asbestos standards, within the sets of asbestos standards and within the Libby samples. Geochemical solubility studies in simulated lung fluids revealed additional variations with these test samples. The level of toxicological indicators varied within each group as well. These variations between the asbestos standards, or those within the sets of the same asbestiform mineral, may be responsible for conflicting toxicological results, ultimately inhibiting mechanistic identification.