A review of available sources identified acute toxicity data (TDLo, TCLo, LDLo) for various species and routes, and exposure limits (TWAs, STELs, IDLH). 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. Analysts evaluated a rat intraperitoneal LDLo (Pb) and dog oral LDLo (PbO, lead monoxide, CASRN: 1317-36-8) to determine an appropriate magnitude for the TEEL-3 value; the rat LDLo (1 g/kg) yielded a TEEL-3 of 520 mg/m3, while the dog LDLo (765 mg/kg) yielded a TEEL-3 of 770 mg/m3. Considering this, analysts determined that the 1994 IDLH was overly conservative and selected the 1990 IDLH as the TEEL-3. A human (female) oral TDLo and human TCLo were considered for the TEEL-2 basis; however, the TDLo data was for a chronic exposure (6 years), and the TCLo data did not have a duration listed. As such, the TEEL-2 was derived according to Table 3.5. The MAK-STEL (Germany DGF, inhalable fraction, 15-minute) was selected as the TEEL-1.
• PAC-1 = TEEL-1 = MAK-STEL (0.032 mg/m3)
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = IDLH (1990, 700 mg/m3)
This review 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 a MAK-STEL (Table 3.1).