CASITILE, THE NEW ASBESTOS (Revised) Page 4: Experimental Evidence and Examples
EXPERIMENTAL EVIDENCE AND EXAMPLES:
In 1980, a paper on the ‘Characterization and properties of cement dust’ (Deruyterre A, Baetten J, Helsen J, 1980) looked at how chrysotile fibres are changed during manufacture, discovering that when chrysotile is added into a cement mix in the manufacture of AC products, the composition of supposedly ‘pure’ chrysotile actually changes through incorporation of calcium, a metal which is absent from raw chrysotile.
This study echoed the findings of a paper written even earlier by N. Smirnov in 1962, ‘The petrography of asbestos-cement’. Smirnov’s study immersed asbestos fibres in the hydration products of Portland cement. After extensive analysis, he also noticed that a chemical reaction occurred between the two, creating chrysotile fibres that had altered their appearance.
The current implications of these papers are considerably more profound than they might have appeared to be in the 1960s and 1970s. Now that it has been shown that pure chrysotile fibres are cleared very rapidly from the lung (they have low biopersistence) (Bernstein DM, Rogers R, Smith P (2004). It also emerges that the fibres undergo chemical alteration and in most cases have cement particles adhering to them so changing their aerodynamic diameter that they are no longer respirable. The altered chrysotile fibres have very little chance of making it past the upper airways, let alone into the lung, as will be documented below.
Another study which found these alterations to chrysotile was a paper written by L Elovskaya in 1992 entitled, “Modification of chrysotile asbestos under the influence of environment and cement hydration products in asbestos cement”.
In a series of original experiments, using electron microscopy and energy dispersion tests, Elovskaya also explored the existence of a chemical reaction between hydration products in Portland cement and the surface of chrysotile fibres.
The conclusions drawn in Elovskaya’s paper were that:
- fibres emitted from asbestos cement products in the course of their exploitation are significantly different from those emitted by raw chrysotile. Their surface characteristics, composition and crystal structure all change
- such chemical changes lead to a marked decrease in the biological penetrability of chrysotile fibres. Therefore any risk posed by asbestos cement becomes significantly less
In echo of these findings, Professor Pooley in 2004 wrote a paper, entitled “Report on the examination of asbestos cement products to investigate changes in character of its asbestos content”. This investigated Elovskaya’s and all previous findings, and found definitively that chrysotile fibres included in a Portland cement based matrix are chemically and structurally altered.
Samples prepared from the AC products and a control sample of pure chrysotile were subjected to, before and after dispersal in distilled water, X-ray diffraction in an electron microscope (EM). Samples of respirable AC dust were also generated and examined in a similar manner.
The conclusions which emerged from Professor Pooley’s report were unequivocal. They confirmed that mixing with cement induces chemical and structural changes in the chrysotile fibres. These show increased levels of calcium and silicon and an increased tendency to aggregate.
This report provided clear images of the altered fibres, confirming the results from the papers previously published.