A review of available sources identified exposure limits (STELs, TWAs) and acute toxicity data (LC50, LD50) for several 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 toxicity data, a 4-hour rat LC50, was selected as the TEEL-3; a duration of 240 minutes was assumed (Section 3.3.2) and it was scaled to 60-minute equivalent using the ten Berge equation (Section 3.3.4). The TEEL-2 value was derived according to Table 3.5. The lowest reported OEL-STEL (South Africa, 15-minute) was selected as the TEEL-1.
• PAC-1 = TEEL-1 = OEL-STEL (South Africa Mining. 70 mg/m3)
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = LC50 rat inhalation (14 g/m3 with 4H assumed)
This generated PAC-3 and PAC-2 values consistent with Rev.29A and an inconsistent PAC-1 value. The Rev. 29A and current TEEL-3 and TEEL-2 use the same source and methodologies. The Rev. 29A TEEL-1 basis was a TLV-TWA, while the current TEEL-1 is an OEL-STEL (Table 3.5, see Note).