A review of available sources identified exposure limits (OEL-STELs, OEL-TWAs) and acute toxicity data (LC50, LCLo, LD50) for numerous 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. Inhalation exposures were scaled to 60-minute equivalents using the ten Berge equation (Section 3.3.4). Analysts compared inhalation sources; of these, the lowest duration (4H vs. 7H), more current (1949 vs. 1943) and most preferred species (rat > mouse) acute toxicity data, a rat LCLo, was selected as the TEEL-3 basis. Available OEL-STEL (20-50 ppm) and OEL-TWA (10-25 ppm) were evaluated as TEEL-1 sources, however these resulted in TEEL-1 > TEEL-2. Instead, 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 (2000 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 TEEL-3 basis is a more preferred route (inhalation > oral), a 4-hour rat LCLo. The Rev. 29A and current TEEL-2 and TEEL-1 use the same methodology, with differences due to the change in TEEL-3.