Diatomaceous Earth Toxicology
By Edouard Bastarache
Synonyms :
Diatomite, diatomaceous silica,
infusorial earth.
Uses
:
In the production of filters, polishes,
absorbents, insulators.
Toxicity
:
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. Altough 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.
Quebec's exposure limit
:
VEMP (Valeur d'Exposition Moyenne
Pondérée) =3D 6mg/m³ (Total dust), if the
crystalline silica content is < 1%
References :
1-Occupational Medicine,Carl Zenz,
last edition.
2-Clinical Environmental Health and
Toxic Exposures, Sullivan & Krieger; last edition.
3-Sax's Dangerous Properties of
Industrial Materials, Lewis C., last edition.
4-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R.R. last
edition.
5-Chemical Hazards of the Workplace,
Proctor & Hughes, 4th edition
Edouard Bastarache M.D.
Occupational & Environmental Medicine
Author of "Substitutions for Raw Ceramic Materials"
Tracy, Québec, CANADA
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
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