GEOLOGIC, ENVIRONMENTAL AND NORMATIVE ISSUES IN THE NATURAL OCCURRENCES OF ASBESTOS (NOA) MANAGEMENT

The term “asbestos” refers to a group of silicate minerals with a fibrous habit, which belong to the serpentine and amphibole families. The fibrous minerals defined asbestos by the Legislative Decree of 15 August 1991 are six: chrysotile, amosite (fibrous variety of grunerite), crocidolite (fibrous variety of riebeckite), anthophyllite, tremolite and actinolite. The chemical-physical properties of asbestos have made them, in the past, one of the most important inorganic materials for industrial purposes and technological applications. However, the extraction, use and marketing of these minerals have been prohibited, due to the proven harmful effects, mainly affecting the respiratory system, that asbestos fibres can cause. Italy was among the first countries to ban the use of asbestos through Law 27/03/1992 n.257. In addition to the known six minerals classified as asbestos, in nature exist also amphiboles and antigorite and lizardite (polymorphs of serpentine), which have the same composition of asbestos groups but not the same morphology. These minerals in fact are chemically and geometrically (length > 5 µm, width < 3 µm and length: diameter > 3:1) but not morphologically analogous to regulated asbestos. The debate about their potential hazardous properties is open and ongoing, therefore, their morphological characterization has a key role in establishing a reliable asbestos hazard scenario. During these 3 years of PhD studies, multi-instrumental and multidisciplinary approaches have been implemented, starting from the study of the influence of textural constraints and the subsequent origin of asbestiform/non-asbestiform minerals in the massive rock. Secondly, it was established whether asbestos fibres homogeneously distributed in the different fractions ground from asbestos-bearing lithotypes and was calculated the contribution of fibres from each fraction to the overall concentration in the sample. The Italian decree (M.D. 06/09/94), which regulates the counting criteria of asbestos fibres potentially present in excavated soil and rocks, suggests a method of sample preparation. This provides for the division of the sample into particle size classes before reaching the particle size fraction on which it will then be performed the fibre count. The powdered fractions were characterised using a Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy (SEM-EDS). The still in use (in some cases), Italian normative M.D. 161/2012, specifies that analyses must be performed on the < 2 mm fraction and the concentration (mg/kg) correlated with the weight of the whole sample < 20 mm. However, the fibre counts yielded asbestos concentrations 50–60% lower compared with total asbestos analyses according to the new R.P.D. 120/2017. Consequently, there is a need to standardize the normative worldwide regulations to manage asbestos-containing materials by re-evaluation of sample preparation and quantification of asbestos. A subsequent part of the project focused on the SEM-EDS analysis of amphiboles with asbestiform and non-asbestiform habit, subject to mechanical stress by grinding for three different time intervals, in order to assess how different time lengths of comminution control geometry and morphology of the particles. The mode of comminution is fundamental for the following quantitative determination of fibres. It is a critical step because it can affect the morphology and geometric ratios of fibres, inducing positive or negative false. When mechanical stress is applied to rocks containing pristine prismatic or acicular amphiboles, these mineral phases can break, originating particles with dimensions and geometrical ratios that would label them as asbestos. Therefore, a normative and scientific gap arise in the classification criteria of a particle as a real asbestiform mineral or as a “cleavage fragment”. In the third and final part of the thesis work, the same samples previously used were prepared to perform biological assays. The capacity of several asbestiform and non-asbestiform powders to cause both cytotoxic effects and carcinogenic potential in BALB/c 3T3 cells was then monitored and evaluated.