Molybdenum (insoluble compounds, as Mo)

CAS number: 7439–98–7 (Metal)

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

Current OSHA PEL: 15 mg/m³ TWA

1989 OSHA PEL: 10 mg/m³ TWA

1993-1994 ACGIH TLV: 10 mg/m³ TWA

Description of substance: Varies

Original (SCP) IDLH*: No Evidence [*Note: "Effective" IDLH = 7,500 mg Mo/m³ -- see discussion below.]

Basis for original (SCP) IDLH: The available toxicological data contain no evidence that an acute exposure to a high concentration of insoluble molybdenum compounds would impede escape or cause any irreversible health effects within 30 minutes. For this draft technical standard, therefore, respirators have been selected on the basis of the assigned protection factor afforded by each device. However, for some particulate substances for which no evidence of an IDLH exists, the determination of allowable respiratory protection based on protection factors may result in the assignment of respirators for concentrations that are not likely to be encountered in the occupational environment. Therefore, for all such particulate substances it has been arbitrarily determined that only the "most protective" respirators are permitted for use in concentrations exceeding 500 ´ the OSHA PEL (500 ´ 15 mg Mo/m³ is 7,500 mg Mo/m³).

Short-term exposure guidelines: None developed

ACUTE TOXICITY DATA:

Animal data: No fatalities were reported among animals that ingested amounts of molybdenum disulfide in doses as great as 6,000 mg Mo/kg [Fairhall et al. 1945]. No changes were observed in rats over a 4-week period following inhalation exposures to metallic molybdenum at 25,000 to 30,000 mg/m³ or to molybdenum dioxide at 10,000 to 12,000 mg/m³ for 1 hour [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].

Revised IDLH: 5,000 mg Mo/m3 Basis for revised IDLH: The available toxicological data contain no evidence that an acute exposure to a high concentration of insoluble molybdenum compounds would impede escape or cause any irreversible health effects within 30 minutes. However, the revised IDLH for insoluble molybdenum compounds is 5,000 mg Mo/m3 based on being 500 times the OSHA PEL of 10 mg Mo/m3 (500 is an assigned protection factor for respirators and was used arbitrarily during the Standards Completion Program for deciding when the "most protective" respirators should be used for particulates).

REFERENCES:

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

2. 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.

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