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Molybdenum (soluble compounds, as Mo)

May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)

CAS number: Varies

NIOSH REL: The 1989 OSHA PEL may not be protective to workers.

Current OSHA PEL: 5 mg/m3 TWA

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 5 mg/m3 TWA

Description of substance: Varies

Original (SCP) IDLH*: No Evidence [*Note: “Effective” IDLH = 2,500 mg Mo/m3 — see discussion below.]

Basis for original (SCP) IDLH: The available toxicological data contain no data that an acute exposure to the soluble compounds of molybdenum could impede escape or cause irreversible health effects in 30 minutes. For this draft technical standard, therefore, respirators have been selected on the basis of the assigned protection factor afforded by each device up to 500 ´ the OSHA PEL of 5 mg Mo/m3 (i.e., 2,500 mg Mo/m3); only the “most protective” respirators are permitted for use in concentrations exceeding 2,500 mg Mo/m3.

Short-term exposure guidelines: None developed


Lethal concentration data:

Species Reference LC50 LCLo Time Adjusted 0.5-hr LC (CF) Derived value
Na2MoO4Rat Barltrop 1991 >2,080 mg/m3 —– 4 hr >1,939 mg Mo/m3
>194 mg Mo/m3
MoO3Rat Barltrop 1991 >5,840 mg/m3 —– 4 hr >7,784 mg Mo/m3 >778 mg Mo/m3

Lethal dose data:

Species Reference Route LD50 (mg/kg) LDLo (mg/kg) Adjusted LD Derived value
Na2MoO4Rat Barltrop 1991 oral 4,000 —– 13,048 mg Mo/m3 1,305 mg Mo/m3
MoO3Rat Barltrop 1991 oral 2,689 —– 12,541 mg Mo/m3 1,254 mg Mo/m3
MoO3, CaMoO4, (NH4)2MoO4Rat Fairhall et al. 1945 oral —– 120 mg Mo/kg 840 mg Mo/m3 84 mg Mo/m3
MoO3, CaMoO4, (NH4)2MoO4G pig Fairhall et al. 1945 oral —– 120 mg Mo/kg 840 mg Mo/m3 84 mg Mo/m3
CaMoO4Rat Browning 1961 oral 101 —– 339 mg Mo/m3 34 mg Mo/m3
(NH4)2MoO4Rabbit Coulston & Korte 1975 oral 1,870 —– 6,371 mg Mo/m3 637 mg Mo/m3
(NH4)2MoO4G. pig Coulston & Korte 1975 oral 2,200 —– 7,546 mg Mo/m3 755 mg Mo/m3
(NH4)2MoO4Cat Coulston & Korte 1975 oral 1,600 —– 5,488 mg Mo/m3 549 mg Mo/m3

Other animal data: No changes were observed in rats over a 4-week period following inhalation exposures to molybdenum trioxide at 12,000 to 15,000 mg/m3 or to ammonium paramolybdate at 3,000 to 5,000 mg/m3 for 1 hour [Fairhall et al. 1945]; however, irritation of the upper respiratory passages occurred after exposure to the ammonium paramolybdate dust [FDA 1975].

Human data: Mining and metallurgy workers chronically exposed to 60 to 600 mg Mo/m3 reported an increased incidence of nonspecific symptoms that included weakness, fatigue, headache, anorexia, and joint and muscle pain [Lener and Bibr 1984].


1. Barltrop D [1991]. The acute toxicity of certain compounds of molybdenum. Report to the International Molybdenum Association, London, April 1991. London, England: Department of Child Health, Charing Cross and Westminster Medical School.

2. Browning E [1961]. Toxicity of industrial metals. London, England: Butterworths, p. 214.

3. Coulston F, Korte F, eds. [1975]. Heavy metal toxicity, safety and hormology. In: Environmental Quality & Safety, Supplement 1. New York, NY: Georg Thieme Publishers, pp. 1-120.

4. Fairhall LT, Dunn RC, Sharpless NE, Pritchard EA [1945]. The toxicity of molybdenum. Public Health Bulletin 293:1-36, 40-41.

5 FDA [1975]. Toxicity of essential minerals. Information pertinent to establishing appropriate levels of single-mineral dietary supplements. Washington, DC: U.S. Food and Drug Administration.

6. Lener J, Bibr B [1984]. Effects of molybdenum on the organism: a review. J Hyg Epidemiol Microbiol Immunol 29:405-419.