## 4 Discussion and Conclusions  
Among the minerals that form airborne particulates, the most hazardous ones display a fibrous-asbestiform crystal habit [18], such as chrysotile. The presence and the structural coordination of surface Fe are considered the main factors of fibre toxicity, together with bio-persistence and the aspect ratio [19; 20; 21; 22; 23]. Toxic effects on human health, due to exposure to high doses (essentially of the occupational type) to asbestos, have been recognised for a very long time [24]. However, the toxic effect due to environmental exposure at low doses of asbestos has also received a great deal of attention [25; 26]. In recent research, attention has turned to the potential deleterious effects of naturally occurring asbestos (NOA) exposure. The airborne presence of asbestos fibres has been ascribed to their release from anthropic sources (e.g., from the structural and ornamental stones used in buildings), as well as from natural sources (e.g., from outcropping rocks), caused by a combination of atmospheric agents and anthropogenic activities. Pulmonary pathologies, verified in many different parts of the world, have been attributed to the rocks normally used in local buildings--for example, chrysotile and tremolite asbestos in outcropping ophiolitic rocks and soils in several regions of Italy and Spain [27; 28; 29; 30]. The quantities of chrysotile detected in both samples after laser ablation are not negligible. The global scientific community has also acknowledged the lack of evidence of a threshold level of exposure to asbestos fibres, below which there is no risk of mesothelioma [28]. Rock scientists (petrographers and mineralogists) can provide detailed characterisations of asbestos minerals and determine the type of work environment exposure by analysing the powder left on HEPA filters and hygienic facemasks. Another aspect to consider is that the presence of trace elements, especially heavy metals, in asbestos minerals' structures contributes to their toxic potential [29] due to the capability of these elements to induce lung cancer, if released into the body once the asbestos is inhaled. Figure 12: Transmission electron micrographs of samples M-17 (**a**,**b**) and M-12 (**c**,**d**). (**a**) The classic tube morphology of chrysotile can be observed. (**b**) Magnification of (**a**) indicated in the empty red square. The red arrows indicate the chrysotile core, which always runs empty longitudinally along the fibre’s axis. The blue arrow indicates a chrysotile fibre section perpendicular to its direction of elongation. Top right chrysotile SAED and chemical analysis (EDS/TEM) both acquired at the point indicated by the solid red square. (**c**) Chrysotile and lizardite magnification indicated in the empty blue square. The red arrows indicate the chrysotile core. (**d**) lizardite showing plate-like morphology. The authors of this paper believe that a continuation of the research is needed, using samples containing a much greater number of fibrous minerals, but, at present, there are some conclusions that can be considered, as chrysotile (asbestos) was detected in both powder samples coming from the ablation laser of M-12 and M-17:  
* Asbestos exhaled during laser ablation processes (e.g., cleaning, texturizing, etc.) could represent a serious hazard for the environment and for occupational safety. * HEPA filters and hygienic face masks retain particles of different nature, expelled through laser cleaning. It is easier to investigate this using hygienic face masks, due to their texture. * Either the use of masks by workers or the implementation of a filtering method in the ablation equipment can reduce the risk of fibre inhalation during cleaning activities to protect and restore monuments and historical buildings. * Communicating these results to workers during outreach activities will encourage self-protection measures, which will protect their health from these hazardous materials.