A review of available sources identified exposure limits (LOC) and acute toxicity data (LC50, LD50) for several routes and species. 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 species and route, a 2-hour rat LC50, was selected as the TEEL-3 basis and it was scaled to 60-minute equivalent using the ten Berge equation (Section 3.3.4). Other available toxicity data (LD50) resulted in TEEL-3 in a comparable range (2.5-10 mg/m3), supporting a more conservative value. The LOC was considered as a TEEL-2 source, however this resulted in a TEEL-2 > TEEL-3. 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 (72 mg/m3/2H)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-2 was the LOC, from which the TEEL-3 was derived. Instead, the current TEEL-3 is a 2-hour rat LC50, from which the TEEL-2 was derived. The Rev. 29A and current TEEL-1 use the same methodology (Table 3,5), with differences due to the change in TEEL-2.