|Monthly Tech-Tip |
Diatomite, diatomaceous silica, infusorial earth.
In the production of filters, polishes, absorbents, insulators.
Amorphous silica, natural diatomaceous earth, is usually considered to be of low toxicity; however, pure amorphous silica is rarely found. Depending on the source, it may contain a low percentage of contaminating quartz, rarely over 2%; characteristically, natural diatomite contains no measurable cristobalite.
Processing of amorphous silica by high-temperature calcining, with or without the concomitant use of fluxing agents, alters the silica from the benign amorphous to the pathogenic form (cristobalite), which causes lung fibrosis.
Non-flux-calcined diatomite may contain from 20% to 30% cristobalite, flux-calcined diatomite may contain as much as 60% cristobalite. Calcined diatomite can produce a severe and disabling pneumoconiose, which is attributed to its cristobalite content. Although a form of silicosis, it characteristically produces pathologic and radiographic changes, which are different from classical quartz silicosis. Diffuse rather than nodular changes are more common.
There is no evidence to associate any form of diatomaceous earth with human cancer.
The IARC concluded that evidence is inadequate to describe amorphous silica as carcinogenic in either experimental animals or humans. The IARC concluded that crystalline silica is a probable human carcinogen.
VEMP (Valeur d'Exposition Moyenne Pondérée) =3D 6mg/m³ (Total dust), if the crystalline silica content is < 1%.
By Edouard Bastarache
Article by Edouard Bastarache
Edouard Bastarache is a well known doctor that has written many articles on the subject of toxicity of ceramic materials and books on technical aspects of ceramics. He writes in both English and French.