Uranium (insoluble compounds, as U)

CAS number: 7440–61–1 (Metal)

NIOSH REL: 0.2 mg/m³ TWA, 0.6 mg/m³ STEL; NIOSH considers insoluble uranium compounds to be a potential occupational carcinogens as defined by the OSHA carcinogen policy [29 CFR 1990].

Current OSHA PEL: 0.25 mg/m³ TWA

1989 OSHA PEL: 0.2 mg/m³ TWA, 0.6 mg/m³ STEL

1993-1994 ACGIH TLV: 0.2 mg/m³ TWA, 0.6 mg/m³ STEL

Description of substance: Varies

Original (SCP) IDLH: 30 mg U/m³

Basis for original (SCP) IDLH: ILO [1972] stated that "insoluble compounds tend to be deposited and retained in tissues and organs for long periods. Prolonged irradiation of the thorax, at sites of uranium accumulation, may eventually result in osteosarcoma and pulmonary cancer. Experimental inhalations of uranium oxide (31 to 91 mg/m³) for 5 days led to the appearance of pneumosclerosis 16 months later at points where alpha-tracks were concentrated. After 22 to 23 months, there was hyperplasia of the bronchial epithelium, and, after 56 months, lung cancer was diagnosed." Both the chemical and radioactive properties of the metal must be considered.

Short-term exposure guidelines: None developed

ACUTE TOXICITY DATA:

Animal data: Inhalation of 31 to 91 mg/m³ of uranium oxide for 5 days led to the appearance of pneumosclerosis 16 months later at points where alpha-tracks were concentrated; after 22 to 23 months, there was hyperplasia of the bronchial epithelium, and, after 56 months, lung cancer was diagnosed [ILO 1972].

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

Revised IDLH: 10 mg U/m3 Basis for revised IDLH: The revised IDLH for insoluble uranium compounds is 10 mg U/m3 based on subchronic inhalation toxicity data in animals [ILO 1972] and to be consistent with soluble uranium compounds which have a revised IDLH of 10 mg U/m3. [Note: NIOSH recommends as part of its carcinogen policy that the "most protective" respirators be worn for insoluble uranium compounds at concentrations above 0.2 mg/m3.]

REFERENCE:

1. ILO [1972]. Uranium, alloys, compounds. In: Encyclopaedia of occupational health and safety. 2nd ed. Vol. II (L-Z). Geneva, Switzerland: International Labour Office, pp. 1452-1454.