A review of available sources identified rat acute toxicity data (LCLo, LD50, LDLo) for several routes. 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 route toxicity, a 4-hour rat LCLo, was selected as the TEEL-3 and it was scaled to 60-minute equivalent using the ten Berge equation (Section 3.3.4). 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 LCLo (61 mg/m3/4H)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a weight adjusted 1990 IDLH, while the current TEEL-3 is inhalation acute toxicity data for zinc cyanide. The Rev. 29A and current TEEL-2 use the same methodology, with differences due to the change in TEEL-3. The Rev. 29A TEEL-1 basis was a weight adjusted MAK-TWA, while the current TEEL-1 was derived from the TEEL-2 (Table 3.5).