A review of available sources identified the following: LDLo and LC50 toxicity data. 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 LC50 was scaled to a 60-minute equivalent using the ten Berge equation (Section 3.3.4). The LC50 reported both male and female rat doses, of which the lowest (female) was selected as the TEEL-3 basis. TEEL-2 and TEEL-1 values were calculated according to Table 3.5.
• TEEL-1 = TEEL-2/11  
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat LC50 (390 mg/m3/4H)
This review generated TEEL values that are significantly more conservative than those in Rev. 29A. The Rev. 29A TEEL-3 basis, a 60-minute rat LC50, was not found during the current review. Instead, the current TEEL-3 basis is a 4-hour rat LC50, with a significantly more conservative dose. The Rev. 29A and current TEEL-2 and TEEL-1 values were derived with the same methodology (Table 3.5).