URANIUM (SOLUBLE)

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 7440-61-1; Chemical Formula: U

The current OSHA limit for soluble uranium compounds is 0.05 mg/m³ TWA, measured as uranium. NIOSH has no REL for soluble uranium compounds. Since 1968, the ACGIH has increased its TLV for soluble uranium from 0.05 mg/m³ to 0.2 mg/m³, with a 0.6 mg/m³ STEL. The previous TLV of 0.05 mg/m³ was based on animal studies relating exposure level and duration to the resulting tissue concentration of uranium and on other chronic animal studies showing the kidney to be the most sensitive target organ. In 1968, the ACGIH’s List of Intended Changes included a TLV of 0.2 mg/m³ for all forms of uranium, and this value was adopted by the ACGIH in 1969. The basis for adopting the 0.2 mg/m³ TLV for soluble uranium compounds was a study by Wing, Heatherton, and Quigley (1963, as cited in ACGIH 1986/Ex. 1-3, p. 617) reporting no adverse effects from radiation exposure over a 25-year period. Although no data were discussed in the ACGIH (1986/Ex. 1-3) Documentation regarding typical exposure levels at the plants studied, the documentation does mention that seven accidental, brief exposures to soluble uranium compounds at levels two- to fivefold the former TLV of 0.05 mg/m³ did not result in physiologic changes or significant body burden.

Allied Signal, Inc. (Ex. 3-1084) is of the opinion that OSHA’s limit for the soluble compounds of uranium is “unrealistically low based on NRC (Nuclear Regulatory Commission) and industry experience.” This company states that the fact that soluble uranium “exits the body quite rapidly” means that it does not produce radiation-induced cancer. OSHA finds that this evidence is not sufficiently detailed to use as a basis for raising its limit for these compounds, and NIOSH (Ex. 8-47, Table N1) concurs.

OSHA does not find this evidence adequate to meet the Agency’s more stringent standard of proof for relaxing an existing exposure limit. In addition, OSHA notes that the 25-year period of observation in the Wing et al. (1963, as cited in ACGIH 1986/Ex. 1-3, p. 617) study is not long enough to rule out the occurrence of some forms of radiation-induced cancer and, further, that the power of this study to detect health effects occurring in a small percentage of the population was very limited. OSHA is accordingly not raising its current PEL for the soluble uranium compounds.