A review of available sources identified exposure limits (TWAs, STELs) and acute toxicity data (LC50, LD50, LDLo, TCLo) for several 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). Two rat LC50 were evaluated; analysts considered that the more conservative dose (300 mg/m3/2H) was closest in duration to 60 minutes and that the 4-hour duration dose (8.16 mg/L/4H) is more current (1985 vs. 1982). Additionally, analysts compared resultant TEEL-3 values to available rat oral LD50 toxicity, which yielded TEEL-3 values ranging from 240-290 mg/m3. Considering this, analysts selected to more current rat LC50 as the TEEL-3 basis. The human TCLo was evaluated as a source, however it was not selected because it did not list either the sex or duration of the dose (Section 3.3.1). Instead, the TEEL-2 value was derived according to Table 3.5. The PEL-STEL was selected as the TEEL-1.
• PAC-1 = TEEL-1 = PEL-STEL (3 mg/m3, dust)
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat LC50 (8.16 mg/L/4H)
This review generated PAC-3 and PAC-2 values inconsistent with Rev. 29A and a consistent PAC-1 value. The Rev. 29A TEEL-3 basis was a rat oral LD50, while the current basis is a rat LC50, a more preferred route (inhalation > oral, Section 3.3.2). The Rev. 29A and current TEEL-2 use the same methodology, with the differences due to the change in the TEEL-3. Although the Rev. 29A and current TEEL-1 values are consistent, the Rev. 29A TEEL-1 was an REL-STEL while the current TEEL-1 is a PEL-STEL (Table 3.5).