A review of available sources identified mouse and rat acute toxicity data (LD50) for the oral route. Data sources were selected according to the hierarchy listed in Table 3.1. Toxicity data were selected according to type of exposure, species, and route according to the hierarchies stated in Sections 3.3.1, 3.3.2, and evaluated using factors in Tables 3.2, 3.3, and 3.4. The most preferred species data, a rat oral LD50, was selected as the TEEL-3 basis. TEEL-2 and TEEL-1 values were derived according to Table 3.5.
• PAC-1 = TEEL-1 = TEEL-2/11
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat oral LD50 (6400 mg/kg)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a weight adjusted 1990 IDLH for cyanides (CASRN: 57-12-5), while the current TEEL-3 is based on acute toxicity data for potassium ferrocyanide. The Rev. 29A and current TEEL-2 use the same methodology, with differences due to the change in TEEL-1. The Rev. 29A TEEL-1 basis was a weight adjusted MAK-TWA for cyanides (CASRN: 57-12-5), while the current TEEL-1 was derived from the TEEL-2. The reduced level of conservatism is in the TEELs, specifically TEEL-2 and TEEL-3, is supported by World Health Organization statements that ferrocyanides (calcium, potassium, and sodium) have low toxicity because” the strong chemical bond between iron and the cyanide groups.”