A review of available sources identified exposure limits (TWAs, OEL-STEL, IDLH) and acute toxicity data (TDLo, LDLo, LD50) 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. The original IDLH (1990, 450 mg/m3) and revised IDLH (1994, 50 mg/m3) were developed from the same sources; therefore, it’s unclear why they differ in magnitude. Further, the human toxicity cited is stated to be estimated (EDLo= 65 mg/kg, Deichmann and Gerarde, 1969). This dose is also reported by the National Center for Biotechnology Information; however, it is not cited as an estimated value. Considering this, analysts determined a dog oral LD50 was a more reliable source, and it was selected as the TEEL-3 basis. The TEEL-2 was derived according to Table 3.5. An OEL-STEL (Austria, Denmark) was selected as the TEEL-1.
• TEEL-1 = OEL-STEL (Austria/Denmark, 0.5 mg/m3)
• TEEL-2 = TEEL-3/6
• TEEL-3 = Dog oral LD50 (65 mg/kg)
This review generated TEEL values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was the 1990 IDLH that cites an estimated human oral toxicity dose as its primary basis. Instead, the current TEEL-3 basis is a dog oral LD50, a more reliable source (Section 3.2.2.). The Rev. 29A TEEL-2 basis was a rat oral TDLo. In review, there were no available toxicity sources with appropriate endpoints from which to develop a TEEL-2; therefore, the current TEEL-2 was derived from the TEEL-3. The Rev. 29A TEEL-1 was derived from a TWA, while the current TEEL-1 is an OEL-STEL, a more preferred source (STEL > TWA).