MOLYBDENUM (INSOLUBLE)

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: 7439-98-7; Chemical Formula: Insoluble compounds (as Mo)

OSHA formerly had a limit of 15 mg/m³ TWA for the insoluble compounds of molybdenum, which include molybdenum metal dust and the dioxide; this was the Agency’s generic limit for all particulates. The ACGIH recommends a TLV-TWA of 10 mg/m³, measured as molybdenum, for these substances. The proposed PEL was 10 mg/m³ TWA (total particulate), measured as molybdenum, and these are the limits established in the final rule. Molybdenum is a silver-white metal or a dark gray or black powder.

Mogilvskaya (1950, as cited in ACGIH 1986/Ex. 1-3, p. 415) reported that the dust of molybdenum metal and molybdenum dioxide caused irritation of mucosal surfaces in white mice after an intensive dusting for one hour; in a similar 30-day exposure, the metal and the dioxide proved minimally poisonous.

NIOSH (Ex. 8-47, Table N4) notes that reviews of molybdenum’s toxicity have been published by Browning (1961b), Friberg and Lener (1986), and Stokinger (1981d). NIOSH states that, although these reviewers generally agree that the insoluble compounds of molybdenum have a low order of toxicity, there is some evidence that respiratory effects have been caused by exposure to these compounds. NIOSH recommends that the toxicological literature on molybdenum be evaluated on a continuing basis. No other comments on this substance were received by OSHA.

OSHA is establishing PELs for the insoluble compounds of molybdenum of 10 mg/m³ TWA (total particulate) and 5 mg/m³ TWA (respirable particulate), measured as molybdenum. The Agency concludes that these limits will protect workers from the significant health risks of exposure to the insoluble compounds of molybdenum, which include eye, nose, and skin irritation, and, perhaps, chronic respiratory effects. OSHA finds that these effects constitute material health impairments.