A review of available sources identified a LOC and acute toxicity data (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 most preferred species and route toxicity data, a human (male) oral LDLo was selected as the TEEL-3 basis. Several rat oral LD50 doses were also considered but resulted in TEELs that were not sufficiently conservative. The LOC was considered as a TEEL-2; however, it was not selected because 1) the resultant TEEL-2 was approximately equivalent to the TEEL-3 (0.18 mg/m3 and 0.20 mg/m3), and 2) available human (male) TDLo data was available, and selected, as a TEEL-2 basis. The TEEL-1 value was derived according to Table 3.5.
• TEEL-1 = TEEL-2/11
• TEEL-2 = Human (male) oral TDLo (71 µg/kg; arrhythmia)
• TEEL-3 = Human (male) oral LDLo (286 µg/kg)
This review generated a TEEL-3 value inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a rat oral LD50; instead, the current TEEL-3 basis is a human (male) oral LDLo, in accordance with primacy for human data (Section 3.3.2). The Rev. 29A TEEL-2 was based on the 0.18 mg/m3 LOC, but this approach was not used because human toxicity data (LDLo, TDLo) indicate more conservative values are appropriate. The Rev. 29A and current TEEL-1 use the same methodology, with differences due to the change in TEEL-2.