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Molybdenum Compounds Toxicology

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 :
-small intestine;
-adrenal glands;

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 :
-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.

References :
1-Clinical Environmental Health and Toxic Exposures, Sullivan & Krieger; last edition.
2-Toxicologie Industrielle et Intoxications Professionnelles, Lauwerys R. last edition.

Out Bound Links

In Bound Links

Edouard Bastarache M.D.
Occupational & Environmental Medicine
Author of "Substitutions for Raw Ceramic Materials"
Tracy, Québec, CANADA


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