A review of available sources identified a LOC and acute toxicity data (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 route and species, a rat LD50, was selected as the TEEL-3 basis. Analysts considered the LOC as a TEEL-2; however, this value was a magnitude greater than a TEEL-2 would be, if derived from acute toxicity. As such, the LOC was not selected; instead, the TEEL-2 and TEEL-1 values were derived according to Table 3.5.
• TEEL-1 = TEEL-2/11
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat oral LD50 (3500 µg/kg)
This review generated TEEL values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was derived from the TEEL-2, while the current TEEL-3 basis is a rat oral LD50. The Rev. 29A TEEL-2 was the LOC, which analysts considered during this review, but not selected because available acute toxicity data indicate a more conservative value was appropriate. The Rev. 29A and current TEEL-1 use the same methodology (Table 3.5), with differences due to the change in TEEL-2.