The former OSHA standard for sodium fluoroacetate was 0.05 mg/m3 as an 8-hour TWA, with a skin notation. The ACGIH has established exposure limits of 0.05 mg/m3 TLV-TWA and 0.15 mg/m3 TLV-STEL, with a skin notation. The proposal retained the former 8-hour TWA PEL and added a STEL of 0.15 mg/m3 with a skin notation; NIOSH (Ex. 8-47) concurred with this proposal, and these limits are established in the final rule. The skin notation is retained. Sodium fluoroacetate is a fine white powder, which is sometimes dyed black for commercial use.
Sodium fluoroacetate causes vomiting, convulsions, and ventricular fibrillation. It is highly toxic by inhalation, ingestion, or via absorption through the skin (Occupational Health Guidelines for Chemical Hazards, NIOSH/OSHA 1981). The ACGIH calculated and set the threshold limit of 0.05 mg/m3 based on studies of rats indicating an oral LD(50) of 1.7 mg/kg (Lehman 1951/Ex. 1-790). Tissue changes in rats were noted in a later study by the same author in which the animals were fed 0.25 mg sodium fluoroacetate/kg/day (Lehman 1952, as cited in ACGIH 1986/Ex. 1-3, p. 534); the equivalent level in humans would be 17 mg/person/day. A further study by Miller and Phillips (1955, as cited in ACGIH 1986/Ex. 1-3, p. 534) examined growth rates in rats fed various dosages of sodium fluoroacetate. Rats who received 10 ppm in their diet experienced a transient fluctuation in growth rate. At 20 ppm (approximately 2 mg/kg in young rats), the growth rate declined markedly the first week; the rats survived and resumed growth at the normal rate in three to four weeks. Tolerance for the chemical lasted less than two weeks, and those rats who had adjusted to sodium fluoroacetate showed a second retardation of growth when returned to a dietary level of 20 ppm after a two-week interval of eating a normal diet. Miller and Phillips (1955, as cited in ACGIH 1986/Ex. 1-3, p. 534) noted that rats conditioned to a dietary level of 20 ppm were then able to adjust to a level of 40 ppm (a dose that is greater than the single LD(50) dose per day). The comment from NIOSH (Ex. 8-47) was the only one made to the record on sodium fluoroacetate.
In the final rule, OSHA is retaining the 8-hour TWA of 0.05 mg/m3 and adding a STEL of 0.15 mg/m3 for sodium fluoroacetate; the skin notation is also retained. The Agency concludes that the 8-hour TWA and short-term exposure limits, with a skin notation, will reduce the risk of systemic effects possible as a result of short-term exposures above the 8-hour TWA of 0.05 mg/m3.