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- Introduction
:
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- Molybdenum trioxide (MoO3) is used in
ceramics as a colorant to produce yellowish and yellow green
colors.
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- Sources :
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- Molybdenum is obtained from such ores as
:
- -molybdenite (MoS2);
- -wulfenite (PbMoO4);
- -powellite (-Ca(MoW)O4).
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- Occupational and
Environmental Exposure :
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- Common uses of molybdenum include
:
- -metallurgy, such as its use in
alloys;
- -as a catalyst for the chemical
industry;
- -as a pigment.
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- 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.
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- Clinical Toxicology
:
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- I-Solubility Factor :
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- A - Insoluble
molybdenum compounds include :
- -metallic molybdenum;
- -molybdenum disulfide (MoS2);
- -lead molybdate (PbMoO4).
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- B - Soluble compounds
include :
- -molybdenum trioxide (MoO3);
- -ammonium molybdate;
- -ammonium paramolybdate
((NH4)6Mo7O24-4H2O);
- -calcium molybdate (CaMoO4);
- -sodium molybdate dihydrate
(Na2MoO4-2H2O).
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- II-Routes of Exposure :
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- 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.
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- III-Distribution, Metabolism, and
Elimination :
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- 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.
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- More than 50% of molybdenum is excreted
primarely through the kidneys. Approximately 6% is excreted
through the bile when excess molybdenum is present.
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- IV-Signs, Symptoms, and Syndromes
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- A-Acute Toxicity :
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- 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.
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- B-Chronic Toxicity :
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- 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.
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- V-Management of Toxicity or Exposure
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- 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.
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- 1-Medical and Biological Monitoring
:
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- 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.
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- 2-Exposure Controls :
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- 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.
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- 3-Exposure Limits :
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- 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).
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- Summary :
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- 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.
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- 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/
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- References :
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- 1-Clinical Environmental Health and
Toxic Exposures, Sullivan & Krieger; last edition.
- 2-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R. last
edition.