A review of available sources identified exposure limits (LOC) and acute toxicity data (LD50) for several species and routes. Data sources were evaluated 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 rat oral LD50 (1986), was selected as the TEEL-3 basis. The LOC was considered as a TEEL-2, but it was not selected because 1) it would have resulted in a TEEL-2 > TEEL-3, 2) other TEEL-3 values calculated from acute toxicity data ranged from 3-10 mg/m3, supporting a more conservative approach, and 3) the rat oral LD50 data is the most current (Section 3.3.1). Instead, the TEEL-2 and TEEL-1 values were derived according to Table 3.5.
• PAC-1 = TEEL-1 = TEEL-2/11
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat oral LD50 (19 mg/kg)
This generated PAC values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a rat intraperitoneal LD50 (1981) while the current TEEL-3 basis is a rat oral LD50 (1986), a more preferred route, more current source, resulting in a more conservative TEEL value (Sections 3.3.1 and 3.3.2). The Rev. 29A TEEL-2 was the LOC; instead, the current TEEL-2 was derived from the TEEL-3. The Rev. 29A and current TEEL-1 use the same methodology, with differences due to the change in TEEL-2.