OSHA previously had no limit for the soluble iron salts and proposed establishing the ACGIH-recommended limit of 1 mg/m3, measured as iron, for these substances. NIOSH (Ex. 8-47, Table N1) concurred with OSHA's proposed limit for the soluble salts of iron, and the final rule establishes an 8-hour TWA PEL of 1 mg/m3.
When injected into the bloodstream of experimental animals, iron salts (especially the ferric salts) are highly toxic (ACGIH 1986/Ex. 1-3, p. 328). The acute intravenous dose of ferric chloride that is lethal to rabbits is about 7.2 mg/kg (Drinker, Warren, and Page 1935/Ex. 1-315). The ACGIH (1986/Ex. 1-3, p. 328) considers the salts to be irritants to the respiratory tract when inhaled as dusts and mists. Stewart and Faulds (1934/Ex. 1-764) described the ferric salts as skin irritants. The oral toxicities of iron salts are considered to be moderate to low, although marked gastrointestinal irritation results from ingestion (U.S. Department of Labor 1941, as cited in ACGIH 1986/Ex. 1-3, p. 328); 30 grams is the estimated fatal dose for humans (Smyth 1956/Ex. 1-759).
NIOSH was the only commenter on OSHA's proposed 8-hour TWA PEL of 1 mg/m3, measured as iron, for the soluble salts of iron. The Agency concludes that, in the absence of any limit, employees are at risk of skin and mucous membrane irritation associated with exposure to high concentrations of these salts. OSHA considers these effects to be material impairments of health and deems this risk to be significant. Therefore, OSHA is establishing a 1-mg/m3 8-hour TWA PEL for the soluble iron salts.