2-METHYLCYCLOPE

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: 12108-13-3; Chemical Formula: CH₃C₅H₄Mn(CO)₃

OSHA formerly had no limit for 2-methylcyclopentadienyl manganese tricarbonyl (Cl-2). The ACGIH has a TLV-TWA of 0.2 mg/m³, measured as manganese, with a skin notation. The proposed PEL was 0.2 mg/m³ as an 8-hour TWA, with a skin notation; NIOSH (Ex. 8-47, Table N1) concurs. This limit, measured as manganese, is established in the final rule, along with a skin notation. Cl-2 is a dark orange liquid with a faintly pleasant odor; it is a complex organic compound containing about 25 percent manganese by weight.

2-Methylcyclopentadienyl Mn tricarbonyl is highly toxic in its concentrated form, causing adverse effects primarily on the central nervous system. It is somewhat irritating to the eyes but skin contact does not produce irritation or sensitization; however, Cl-2 is readily absorbed through the skin (ACGIH 1986/Ex. 1-3, p. 387). Animal studies indicate that Cl-2 has a toxicity similar to that of tetraethyl lead and is highly toxic by all routes of exposure (U.S. Navy Smoke Abatement Additive, as cited in ACGIH 1986/Ex. 1-3, p. 387).

The single-dose oral LD(50) for rats is 23 or 39 mg/kg, depending on sex. The skin LD(50) for rabbits is 1692 + 145 mg/kg, and the 1-hour inhalation LC(50) for rats is about 350 mg/m 3 (The Ethyl Corporation, as cited in ACGIH 1986/Ex. 1-3, p. 387). Toxic exposures by all routes produce rapidly appearing symptoms of mild excitement, hyperactivity, tremors, severe clonic spasms, weakness, respiratory distress, and occasional clonic convulsions, followed by terminal coma (U.S. Navy Smoke Abatement Additive, as cited in ACGIH 1986/Ex. 1-3, p. 387).

Acute exposure causes damage to the liver, kidneys, and cerebral cortex, as well as changes in lung tissue (ACGIH 1986/Ex. 1-3, p. 387). Browning (1966/Ex. 1-1018) observed chronic bronchitis, peribronchitis, interstitial pneumonia, and lung abscesses in animals that subsequently died from long-term inhalation exposure to Cl-2; exposure to Cl-2 concentrations of approximately 12 mg/m³ for 100 days produced no deviation in weight gain patterns and no gross or microscopic changes in two dogs (Browning 1966/Ex. 1-1018). The liver and kidneys are the principal target organs associated with acute overexposures; the lungs of overexposed animals were hemorrhagic (Browning 1966/Ex. 1-1018).

In humans, skin contact should be entirely avoided. A 5 to 15-ml spill on one worker’s hand and wrist was reported to have caused “thick tongue,” nausea, giddiness, and headache within 3 to 5 minutes (U.S. Navy Smoke Abatement Additive, as cited in ACGIH 1986/Ex. 1-3, p. 387). NIOSH submitted the only comment on this substance.

In the final rule, OSHA establishes a PEL of 0.2 mg/m³ TWA, measured as manganese, with a skin notation, for 2-methylcyclopentadienyl manganese tricarbonyl. The Agency concludes that this limit will protect workers against the significant risk of CNS effects and systemic damage, which constitute material health impairments and are associated with exposure to Cl-2 at levels higher than the new PEL. A skin notation is established because of Cl-2’s demonstrated ability to penetrate human skin rapidly and to cause systemic effects.