A review of available sources identified an exposure limit (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 4-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). The LOC was considered as a TEEL-2, but it was not selected because it resulted in a TEEL-2 > TEEL-3. Instead, the 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 (3100 ppb/4H)
This review generated PAC values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was a weight adjusted IDLH (1990) for cyanide compounds, while the current TEEL-3 is a rat LC50 for cyanuric fluoride. The Rev. 29A and current TEEL-2 use the same methodology, with differences due to the change in TEEL-3. The Rev. 29A TEEL-1 basis was a weight adjusted MAK-TWA for cyanides, while the current TEEL-1 was derived from the TEEL-2.