OSHA had no former permissible exposure limit for bromacil. The Agency proposed an 8-hour TWA PEL of 1 ppm for this substance, which is consistent with the ACGIH's TLV-TWA for bromacil. The final rule establishes a PEL of 1 ppm for this substance; NIOSH concurs with OSHA's determination of a PEL for bromacil (Ex. 8-47, Table N1). Bromacil is a white crystalline solid.
In two-year feeding studies in rats, no-observed-adverse-effect dietary concentrations were determined to be 12.55 mg/kg/day (1.25ppm) for rats and 1250 ppm for dogs; the oral LD(50) for male rats is5200 mg/kg (Sherman and Kaplan 1975/Ex. 1-572). Inhalation studies in rats have shown that all rats tolerate a four-hour exposure to concentrations equivalent to 4800 mg/m3. Studies of guinea pigs showed no skin sensitization but displayed skin irritation after exposures at unspecified levels. Rabbits showed no clinical signs of toxicity when bromacil was applied to the skin at a dose of 5000 mg/kg (ACGIH 1986/Ex. 1-3, p.64).
OSHA received a comment on the proposed limit for bromacil from ConAgra, Inc. (Ex. 3-635), which is of the opinion that bromacil's exposure effects do not warrant the establishment of a PEL. OSHA notes, however, that rats fed 1250 ppm (125 mg/kg/ day) exhibited damage to the thyroid; the Agency finds that this evidence requires the establishment of a PEL at the 1-ppm level to protect workers exposed to this herbicide from experiencing this and other potentially adverse systemic effects.
OSHA is therefore establishing an 8-hour TWA permissible exposure limit of 1 ppm for bromacil. The Agency concludes that this limitwill protect employees against the significant risk of thyroid damage and irritation, which together constitute material health impairments that are potentially associated with exposure to bromacil at levels above the new PEL.