Leachates have been monitored over a period of two years by sampling the leachates from six different areas (cells) a two different lots with different composition and age. More than 250 samples have been analysed by three different techniques (PCOM, SEM and TEM), with the aim of quantifying the actual content of asbestos fibre together with their sizes. During these analysis fibrils (microfibres with sizes lower than the standard one) and nanoparticles have also been evaluated.

Asbestos fibres concentrations
As shown by the figure, the average concentrations of asbestos fibres with standard sizes (length >5 µm, diameter <3 µm, aspect ratio 3:1) measured by SEM varies between 40.000 ff/L and 250.000 ff/L.

Even if the error bars are taken into account, such values are much lower than those encountered in the preliminary study carried out in 2002 (around one million ff/L). The gathered data does not seem to indicate a correlation with the amount of conferred asbestos, but rather with the stage of maturation of the cells: in 2002 the analysed cells were still in the cultivation phase.

As shown by the pie chart, only 6% of the observed fibres (n=2656) have been classified as “asbestos fibres” (chrysotile 78%, 22% anphiboles). Among the “other fibres” (n=1319), 82% is made of inorganic mineral fibres of various nature (mainly alumino-silicates, sodium and calcium sulphates, silicates and iron oxide), while the remaining 18% (n=243) is made by titanium oxide. Fibrils represent more than 40% of the total number of fibres observed by SEM.

Hovever, if one looks at the data in their temporal development (without distinguishing between cells), one finds large fluctuations in the concentrations, with some values around the 1 milion fibres per liter, similar to the values observed in 2002 during the preliminary sampling campaign. Comparing these data with precipitations, we found that a direct correlation is present only when the cell is still under coltivation.

On the other hand, we can say that in 92% of the observed samples (n=50) asbestos concentrations values below 800.000 fibres/Liter and 87% below 600.000 fibres/Liter.

Sizes
The large majority of the asbestos fibres have dimensions close to the minimum to be classified as standard fibres (see figure), and only 13% of the fibres have lengths larger than 10 µm. In particular, 48% of the asbestos fibres have a length between 5 and 6 µm, whereas 41% have diameters between 1,5 and 2 µm.

Remarks
The analysis made by using the optical microscope PCOM are in line with the SEM results, but it was shown that discerning between asbestos fibres and other fibres may become problematic for PCOM when many different kind of interferents are present. Furthermore, the number of fibrils observed by PCOM is always largely under-estimated. By TEM analysis a large number of potentially dangerous nanoparticles have been observed, which are not visible by SEM (see the image of a titanium oxide fibres surrounded by tin oxide nanoparticels and their magnification).