A review of available sources identified exposure limits (STELs, TWAs, ceilings) and acute toxicity data (LD50, LDLo, LC50, TCLo) for various 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. The inhalation exposure was scaled to a 60-minute equivalent using the ten Berge equation (Section 3.3.4). The LC50 was evaluated as a TEEL-3; the resultant TEEL-3 (8.6 mg/m3) was less than reported exposure limits and the source could not be verified (Section 3.3.1). Instead, a rat oral LD50 was selected as the TEEL-3 basis. The TLV-C was selected as the TEEL-2. The TLV-STEL was selected as the TEEL-1.
• PAC-1 = TEEL-1 = TLV-STEL (inhalable fraction, 10 mg/m3)
• PAC-2 = TEEL-2 = TLV-C (25 ppm, 125 mg/m3)
• PAC-3 = TEEL-3 = Rat oral LD50 (3700 mg/kg)
This review generated PAC-3 value consistent with Rev. 29A and inconsistent PAC-2 and PAC-1 values. The Rev. 29A and current TEEL-3 source, and methodology are consistent. The Rev. 29A and current TEEL-2 source are consistent; differences in value may be due to conversion and rounding of the source value, instead of using the reported value (Section 3.4.7.2). The Rev. 29A TEEL-1 was derived from the TEEL-2, while the current TEEL-1 is an exposure limit (TLV-STEL).