A review of available sources identified exposure limits (OEL-TWAs) and acute toxicity data (LC50, 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 LC50 studies identified do not report mortalities; as such, analysts instead selected the lowest dose, most preferred species and route toxicity data, a rat oral LD50, as the TEEL-3 basis. The TEEL-2 value was derived according to Table 3.5. The OEL-TWA (Canada) was selected as the TEEL-1 basis.
• PAC-1 = TEEL-1 = OEL-TWA (1ppm/4.6 mg/m3) x 3
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat oral LD50 (700 mg/kg)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a rat oral LD50; the current TEEL-3 basis is also a rat oral LD50, but the current review identified a study with a lower dose (Section 3.3.1). The Rev. 29A and current TEEL-2 use the same methodology, with differences due to the change in TEEL-3. The Rev. 29A TEEL-1 was derived from the TEEL-2, while the current TEEL-1 basis is an exposure limit (OEL-TWA).