Health implications of natural fibrous zeolites for the intermountain west

Abstract

INTRODUCTION Fibrous zeolites have recently been implicated in an endemic outbreak of malignant pleural mesothelioma in several villages in Cappadocia in central Tur- key (Baris et al., 1979; Lilis, 1981). The possible association between fibrous zeolites and mesothelioma and the potential biological activity of fibrous erionite from the United States are under active investigation. The zeolite minerals com- prise a group of over forty hydrated aluminum silicates. More than 300 probable deposits of the various natural zeolites are located in 25 states in the United States. Reserves of perhaps 10 trillion tons are present in the western United States; about 120 million tons are deposited near the surface (Sheppard, 1975). Several zeolites, including erionite and mordenite, may occur with a fibrous habit. Fibrous erionite is found in several well-defined deposits in Arizona, Nevada, Oregon, and Utah, where it occurs as thin, pure beds within sedimentary tuff sequences, or as outcrops in desert valleys of the Intermountain region. MINERALOGY Zeolites were first recognized as a new group of minerals by Baron Cronstedt with the discovery of stilbite in 1756 (Papke, 1972). Because of the unique quality of intumescence, zeolites were aptly named from the Greek zein and lithos mean- ing “boiling stones.” Zeolites are a group of crystalline sedimentary minerals’ that contain alkali or alkaline-earth elements in a hydrated aluminum silicate structure. They have an open, three-dimensional framework composed of silicon and aluminum tetrahedra (Flanigan, 1959). The central silicon or aluminum in each tetrahedron is sur- rounded by four oxygen atoms each of which is shared by two tetrahedra in a honeycombed, crystalline lattice with cavities and apertures characteristic of each