BORON OXIDE

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: 1303-86-2; Chemical Formula: B₂O₃

OSHA formerly regulated boron oxide under its generic total particulate limit of 15 mg/m³ (5 mg/m³ for the respirable fraction), and the ACGIH recommends a total dust TLV-TWA of 10 mg/m³. The proposed total particulate PEL was 10 mg/m³, and this limit is established in the final rule; the 5-mg/m³ PEL for the respirable fraction is retained. NIOSH (Ex. 8-47, Table N4) concurs with these limits. Boron oxide occurs as either a white powder or a granular solid, and it has a bitter taste.

Animal studies indicate that eye and skin irritation were caused by the ocular instillation and the topical application, respectively, of boron oxide to the skin and eyes of rabbits. Aerosol administration at various exposure levels for varying time periods caused mild nasal irritation and an increase in urine acidity and creatinine coefficient in dogs and rats (Wilding, Smith, Yevich et al. 1959/Ex. 1-599). Young rats that were force-fed a 10-percent slurry of boron oxide in water for three weeks showed no growth retardation or other effects (Wilding, Smith, Yevich et al. 1959/Ex. 1-599).

Garabrant and co-workers (1984/Ex. 1-555) determined the prevalence of eye and respiratory irritation among boron oxide-exposed workers; those exposed to boron oxide concentrations ranging from 1.2 to 8.5 mg/m³ were then compared with controls. Workers exposed at an average concentration of 4.1 mg/m³ reported significant increases in productive cough; eye, nose, and throat irritation; dryness of the mouth; and sore throats (Garabrant, Bernstein, Peters, and Smith 1984/Ex. 1-555).

The ACGIH believes that a total dust TLV-TWA of 10 mg/m³ will provide protection against boron oxide’s irritant effects (ACGIH 1986/Ex. 1-3). However, OSHA specifically noted in the preamble to the proposed rule that irritation of the upper respiratory tract and eyes occurs among occupationally exposed workers at levels below 10 mg/m³, and the Agency solicited additional information on the boron oxide exposure levels associated with adverse health effects in workers.

U.S. Borax (Exs. 120, 3-744, and 8-49; Tr. pp. 9-11 to 9-120) submitted comments to the record on the health effects of exposure to the borates and boron oxide. John C. Middleton, Manager of Product Safety for U.S. Borax Research Corporation, opposed the reduction in the PEL for boron oxide from 15 mg/m³ to 10 mg/m³ on the grounds that such a reduction was not “supportable” (Tr. p. 9-112). Mr. Middleton urged OSHA to “delay action” on boron oxide until a large epidemiological study being sponsored by U.S. Borax is completed; the American Mining Congress (Ex. 3-876) supported U.S. Borax’s request for a delay.

In response to these commenters, OSHA notes that boron oxide dust is not an inert substance; it causes eye and upper respiratory tract irritation as well as skin irritation. Although OSHA will follow the progress of the U.S. Borax study with great interest, the Agency does not find it appropriate to delay further in reducing the PEL for boron oxide.

Accordingly, the final rule establishes permissible exposure limits of 10 mg/m³ TWA, as total particulate for boron oxide. The Agency concludes that these limits will protect workers against the significant risk of upper-respiratory-tract and eye irritation associated with exposure to this substance. OSHA finds that these health effects constitute material impairments of health.