A review of available sources identified rat acute toxicity data (LC50, LD50) for various routes (oral, inhalation). 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 exposure data, a 4-hour rat LC50, was selected as the TEEL-3 basis and scaled to a 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 LC50 (3151 ppm/4H)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a rat oral LD50, while the current basis is a more preferred route, rat LC50 (inhalation > oral, Section 3.3.2). The Rev. 29A and current TEEL-2 and TEEL-1 methodology remains consistent, with differences in values due to the change of the TEEL-3 basis.