ASBESTOS HAZARD IN WESTERN ALPS PETROLOGY, CHARACTERIZATION AND QUANTITATIVE DETERMINATION OF FIBROUS MINERALS IN THE ASBESTOS-BEARING SERPENTINITES OF THE PIEMONTE ZONE (SUSA AND LANZO VALLEYS) ; LE RISQUE ASBESTE DANS LES ALPES OCCIDENTALES CARTOGRAPHIE, PETROGRAPHIE, QUANTIFICATION DES MINERAUX FIBREUX DANS LES SERPENTINITES ASBESTIPHERES DE LA ZONE PIEMONTAISE. APPLICATION A LES VALLEES DE SUSA ET DE LANZO

Abstract

The word "asbestos", that means unquenchable, is used for a group of silicate minerals occurring with a fibrous habit, belonging to the serpentine and amphibole families. According to the Italian Legislation (D.L. 15/08/91) the six fibrous silicates defined as asbestos are: chrysotile, amosite and crocidolite (fibrous varieties of grunerite and riebeckite, respectively), anthophyllite, tremolite and actinolite. These minerals are made up of incombustible, chemically stable, inert, phono-absorbing, flexible and tensile fibers. The chemical and physical properties of asbestos made it, in past decades, one of the most important inorganic materials for industrial uses and technological applications. At the end of the 1950s the correlation between exposure to asbestos and development of pleural mesothelioma and bronchogenic carcinoma was established. Since the last decades, asbestos health hazard is considered not only an occupational problem, but also a potential environmental hazard. As a consequence, in most western countries, the current legislation imposed severe laws to regulate the use of potentially asbestos-bearing rocks and soils. The pathogenicity of the asbestos fibers has been considered to be due to one or more of the following factors: i) the fibrous habit (a mineral is defined as fibrous when its length/diameter ratio is greater than 3:1); ii) chemical-mineralogical factors (fiber type, chemical composition, surface reactivity); iii) the biopersistence. These factors are interconnected: in fact, the fiber dimensions influence its surface reactivity, fiber composition controls its biopersistence and biopersistence is associated to the fiber habit. Though the six asbestos minerals are considered as equally dangerous for the human health, recent epidemiological studies have demonstrated that crocidolite, amosite and tremolite are clearly more dangerous than chrysotile. In the Western Alps fibrous minerals mainly occur in the Piemonte Zone of Calcschists with meta-ophiolites. This work is part of a ...