A review of available sources identified acute toxicity data (LD50) for various species and routes, and exposure limits (OEL-STELs, TWAs, IDLH 1990 & 1994). 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 1990 and 1994 IDLH were evaluated for the TEEL-3 basis; the 1994 value includes additional toxicity data that support a more conservative value (1500 mg/m3 vs. 5000 mg/m3). In addition, available toxicity data (rat/mouse LD50) indicate that a more conservative TEEL-3 is appropriate (~350-400 mg/m3). As such, the 1994 IDLH was selected as the TEEL-3 basis. The TEEL-2 was derived according to Table 3.5. The most reported OEL-STEL value (Finland/UK/Denmark/South Africa Mining, 15-min average) was selected as the TEEL-1.
• PAC-1 = TEEL-1 = OEL-STEL (Finland/UK/Denmark/South Africa Mining)
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = IDLH (1994)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was the IDLH (1990), while the current basis is the IDLH (1994) due on its inclusion of additional toxicity data. The 1994 IDLH was used according to Handbook guidelines (Section 4.2-4.3). The Rev. 29A TEEL-2 basis was a rat oral TDLo that was not found in this review and instead was derived from the TEEL-3 (Table 3.5). The Rev. 29A TEEL-1 was derived from the TEEL-2 (Table 3.5), while the current TEEL-1 is an exposure limit (OEL-STEL).