Introduction:
Molybdenum
trioxide (MoO3) is used in ceramics as a colorant to produce
yellowish and yellow green colors.
Sources :
Molybdenum
is obtained from such ores as:
-molybdenite
(MoS2);
-wulfenite
(PbMoO4);
-powellite
(-Ca(MoW)O4).
Occupational and
Environmental Exposure:
Common
uses of molybdenum include:
-metallurgy,
such as its use in alloys;
-as
a catalyst for the chemical industry;
-as
a pigment.
Exposure
commonly occurs during the liberation of dust from mining and
the processing of ore, from the grinding of metals or alloys,
from oxyacetylene cutting, and from dust from its various compounds.
Clinical Toxicology:
I-Solubility Factor
:
A-Insoluble molybdenum compounds include:
-metallic
molybdenum;
-molybdenum
disulfide (MoS2);
-lead
molybdate (PbMoO4).
B-Soluble compounds include:
-molybdenum
trioxide (MoO3);
-ammonium
molybdate;
-ammonium
paramolybdate ((NH4)6Mo7O24-4H2O);
-calcium
molybdate (CaMoO4);
-sodium
molybdate dihydrate (Na2MoO4-2H2O).
II-Routes of Exposure:
Exposure
to molybdenum and related compounds usually occurs via inhalation
of dust. If these compounds are water-soluble, absorption is
increased, and toxicity may be greater than that from non-water-soluble
compounds.
Gastrointestinal
absorption is approximately 50% of an ingested amount and depends
on the water solubility of the compound involved.
III-Distribution,
Metabolism, and Elimination:
Molybdenum
is present in humans, with an average adult content of 9 mg.
Human
whole blood levels average approximately 5 ng per ml.
It
is contained principally in:
-liver;
-kidney;-
-small
intestine;
-adrenal
glands;
-fat;
-blood.
More
than 50% of molybdenum is excreted primarely through the kidneys.
Approximately 6% is excreted through the bile when excess molybdenum
is present.
IV-Signs, Symptoms,
and Syndromes:
A-Acute Toxicity:
Molybdenum
products may cause toxicity in humans, but adequate studies
reporting such effects are lacking.
The
high prevalence of articular effects in Armenian villages was
associated with a significant ingestion of molybdenum, which
caused a disorder of the metabolism of uric acid.
Workers
involved in producing molybdenum oxide have demonstrated a higher
rate of:
-headaches;
-backaches;
-aching
joints;
-non-specific
skin and hair changes.
Molybdenum
trioxide may cause irritation to mucous membranes (eyes, nose,
throat).
Exposure
to molybdenum dust causes an increase in serum uric acid and
ceruloplasmin.
B-Chronic Toxicity:
Data
are extremely limited in regard to chronic toxicity from molybdenum
and its compounds. Molybdenum may cause a pneumoconiosis in
susceptible individuals, but definitive data are lacking.
V-Management of Toxicity
or Exposure:
Persons
exposed to hazardous concentrations of molybdenum should be
removed from further exposure. Treatment is symptomatic, and
no specific therapy is available for removal of molybdenum from
tissues. Treatment of joint complaints is supportive.
1-Medical and Biological
Monitoring:
Laboratory
measurements of serum and urinary molybdenum levels may be performed,
but levels do not correlate with signs and symptoms. Serum uric
acid and ceruloplasmin may be elevated.
2-Exposure Controls:
Prevention
of exposure is the mainstay in preventing toxicity, including
good process enclosures with general dilution ventilation and
local exhaust ventilation. NIOSH and OSHA recommend that workers
exposed to insoluble molybdenum compounds wear personal protective
equipment designed to limit dust, mist, or fume inhalation.
Workers
exposed to soluble compounds need impervious clothing, gloves,
face shields, and other appropriate clothing as necessary to
prevent skin contact.
However,
no data are available regarding skin effects or clinical effects
from this route of absorption.
3-Exposure Limits:
In
Quebec, the VEMP (Valeur d’Exposition Moyenne Pondérée)
is:
1-Insoluble
compounds: 10 mg/m3 (as Mo)
2-Soluble
compounds: 5 mg/m3 (as Mo).
Summary:
Good house keeping of your studio is very important; to do so you may, among other things, use wet processes, or even a vacuum
system whose air is exhausted outside of the workshop.
Avoidance of processes generating unnecessary dust is also important.
According
to the severity of exposure, the preventive measures proposed
by NIOSH and OSHA should be applied.
Edouard
Bastarache M.D. (Occupational & Environmental Medicine)
Author
of « Substitutions for Raw Ceramic Materials »
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
References:
1-Clinical
Environmental Health and Toxic Exposures, Sullivan & Krieger;
last edition.
2-Toxicologie
Industrielle et Intoxications Professionnelles, Lauwerys R.
last edition.
