Tantalum (metal and oxide dust, as Ta)

CAS number: 7440–25–7 (Metal)

NIOSH REL: 5 mg/m³ TWA, 10 mg/m³ STEL

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 Ta/m³ -- see discussion below.]

Basis for original (SCP) IDLH: Because no evidence of an IDLH is shown in the available toxicological data, respirators have been assigned on the basis of the assigned protection factor afforded by each device up to 500 ´ the OSHA PEL of 5 mg Ta/m³ (i.e., 2,500 mg Ta/m³); only the "most protective" respirators are permitted for use in concentrations exceeding 2,500 mg Ta/m³.

Short-term exposure guidelines: None developed

ACUTE TOXICITY DATA:

Lethal dose data:

Species	Reference	Route	LD50 (mg/kg)	LDLo (mg/kg)	Adjusted LD	Derived value
Ta2O5 Rat	Coulston &Korte 1975	oral	8,000	-----	45,862 mg Ta/m3	4,586 mg Ta/m3

Human data: None relevant for use in determining the revised IDLH.

Revised IDLH: 2,500 mg Ta/m3 Basis for revised IDLH: No inhalation toxicity data are available on which to base an IDLH for tantalum metal and oxide dust. Therefore, based on acute oral toxicity data in animals [Coulston and Korte 1975], a value of about 4,500 mg Ta/m3 would have been appropriate. However, the revised IDLH for tantalum metal and oxide dust is 2,500 mg Ta/m3 based on being 500 times the NIOSH REL and OSHA PEL of 5 mg Ta/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).

REFERENCE:

1. 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.