A review of available sources identified acute toxicity data (LD50, LC50) for various species and 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 exposure data, a 4-hour rat LC50, was selected as the TEEL-3 basis and was scaled to a 60-minute equivalent using the ten Berge equation (Section 3.3.4). TEEL-1 and TEEL-2 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 (>6280 mg/m3/4H)
This review generated PAC values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a rat oral LD50, while the current basis is based on higher priority rat LC50 data (Table 3.1). The Rev. 29A and current TEEL-2 and TEEL-1 methodology remain consistent, with differences in values due to the change of the TEEL-3 basis.