Naturally occurring asbestos: Validation of PCOM quantitative determination

The quantitative determination of the content of asbestos in rock matrices is a complex operation that is susceptible to significant errors. The principal instruments used for the analysis are the Scanning Electron Microscope (SEM) and the Phase Contrast Optical Microscope (PCOM). Although the PCOM resolution is inferior than that of SEM (0.5 µm VS 1 nm), PCOM analysis has several advantages, including more representativity of the analyzed sample, more effective recognition of chrysotile and a lower cost. The PCOM error evaluation generally provided by analysis laboratories varies between 50% and 150%. There are not, however, enough specific studies that discuss every error in addition to the instrumental error or that link them to the asbestos content in rock samples. Our work aims to provide a validation of a methodology for the determination of the total content of asbestos using PCOM. The threshold for asbestos concentration in soils is 1000 mg/kg, as defined by Italian law in force. (D. Lgs. 152, 2006). •The asbestos content assessment in rock sample is necessary for the planning of excavation work in green stones.•There are not well-defined procedures for asbestos quantification in massive sample.•A methodology for the determination of asbestos concentration using PCOM is provided and validated.