A review of available sources identified exposure limits (LOC) and acute toxicity data (LCLo, LD50) for several 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. Analysts selected the most preferred species and route, a 3-hour rat LCLo, as the TEEL-3 basis and it were scaled to 60-minute equivalent using the ten Berge equation (Section 3.3.4). Other available toxicity data supports this level of conservatism. The LOC was evaluated as a TEEL-2, however this resulted in a TEEL-2 > TEEL-3. Instead, the TEEL-2 and TEEL-1 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 (316 mg/m3/3H)
This review generated PAC values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was a rat oral LD50, while the current TEEL-3 basis is a rat LCLo, a more preferred route (Section 3.3.2). The Rev. 29A TEEL-2 was an LOC; this was evaluated, but instead the TEEL-2 was derived from the TEEL-3. The Rev. 29A and current TEEL-1 use the same methodology, with differences due to the change in TEEL-2.