Methods for the analysis of asbestos in incoherent soils

Soils contaminated with asbestos, whether of natural origin or deriving from anthropogenic pollution, can have very different dimensional, chemical and humidity characteristics.

The legal limit that allows to define an asbestos contaminated soil is a concentration of 1000 mg / kg of asbestos fibers, as per DLGS 152/2006. The analytical methods suggested in Italy by regulation (DM 6/09/94) for the determination of asbestos content are Diffrattometry (XRD) and  Fourier Transform Infrared (FTIR), methods that do not allow to distinguish the fibrous material and secondly Scanning Electron Microscopy (SEM). The Phase Contrast Optical Microscopy (PCOM) is considered a methodology only useful for a qualitative analysis for it low rilevability index (0,1 mm in respect of   for SEM and    for XRD and FTIR).

The goal of this study is to describe the cheap and quick soil analysis methodology used in the Asbestos laboratory of DIATI Politecnico di Torino where also the representativeness of the analysed quantity of material is considered.

When the sample is an incoherent soil, sieving (at 0.6 - 0.3 – 0.150-0.075 mm) after drying is carried out. The asbestos fibers eventually present in the classes >0.6 mm and 0.6-0.3 mm, that are visible with a low magnification (5-10 x), can be recovered by flotation and weighted after drying. The quantitative analysis of the classes 0.3-0.075 is perfomed by means of PCOM, measuring the dimensions of the fibers, hipotyzing the third dimension equal to the width and calculating the weight knowing the density of the asbestos fiber observed.  .The presence of asbestos in the finer particle size class can be verified by SEM, but is the asbestos content in the other particle size classes is high the value obtained for the finer class is generally found to be irrelevant to the final result.If the initial sample has a very fine particle size, it is homogenized by grinding and is prepared for reading under the SEM by depositing a known quantity on a polycarbonate membrane. The results thus obtained are referred to the analysis of at least 100 g of material.

The reliability of the technique has been verified by participating in interlaboratory circuits.