A review of available sources identified the following: a TLV-TWA and animal toxicity data (LD50, LC50, and LCLo). 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. Although the LC50 is the most preferred route, analysts selected a rat LCLo toxicity dose as the TEEL-3 basis because 1) it was determined to be a more reliable source (Section 3.3.1,) 2) it was the most preferred species (rat > mouse,) and 3) it resulted in a more conservative TEEL value. This 2-hour rat LCLo was scaled to 60-minute equivalent using the ten Berge equation (Section 3.3.4). The TEEL-2 was derived according to Table 3.5. The TLV-TWA was selected as the TEEL-1 basis.
• TEEL-1 = TLV-TWA x 3 (1 ppm)
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat LCLo (1000 ppm/2H)
This review generated TEEL values that are inconsistent with those in Rev 29A. The Rev. 29A and current TEEL-1 sources and methodology are the same. The Rev. 29A TEEL-3 basis was the mouse LC50, while the current TEEL-3 basis is an inhalation toxicity dose (LCLo) of a preferred species (rat > mouse) and a more reliable source (peer reviewed medical journal). The Rev. 29A and current TEEL-2 methodology are consistent (Table 3.5,) with differences due to changes in TEEL-3 values.