DIFFERENTIATION OF ERIONITE FROM OTHER FIBROUS ZEOLITES BY CENTRAL STOP DISPERSION STAINING: A PRELIMINARY PLM INVESTIGATION

Erionite is a fibrous zeolite which is difficult to differentiate from other fibrous zeolites by Polarized Light Microscopy (PLM) and other routine environmental laboratory techniques. Mesothelioma-like disease is associated with erionite based on epidemiologic studies conducted in the Cappadocian region of Turkey during the 1970s. These studies are important because they initiated a growing awareness that fibrous mineral carcinogeneity is a function of asbestiform habit not restricted to the six minerals currently classified as asbestos. IARC classifies erionite as Group I carcinogen which includes asbestos, but erionite is currently not regulated by the United States Environmental Protection (USEPA) in the same manner. Erionite has never been used in the manufacture of commercial products to a large extent, and its use is prohibited. The potential risk of exposure to erionite, however, exists in the mining and excavation of volcanic rock deposits containing zeolites used for aggregate, crushed stone applications and disturbance of soils derived from erosion of such deposits during road construction. The USEPA has indicated that erionite causes lung cancer in lab rats, and is actively performing risk assessment studies on roadway gravel dust containing erionite with the North Dakota Department of Health. These exposure assessment studies may lead to inclusion of erionite into the regulated asbestos mineral classification. This PLM investigation was initiated in order to assess the viability of development of an analytical protocol for identification of fibrous zeolites using Central Stop Dispersion Staining (CSDS) similar to the EPA 600 Method for asbestos identification. Analyses performed on fibrous zeolite specimens from documented localities, potential misclassification errors based on traditional methods of analysis, and preliminary observations obtained from CSDS with a 1.48 “high dispersion” (HD) refractive index liquid for fibrous zeolite differentiation will be discussed.