A review of available sources identified a LOC and acute toxicity data (LC50, LD50) for various 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. Although the rat LC50 was the highest priority toxicity data, it was not selected for TEEL development since the duration was not reported. Instead, a dog oral LD50 was selected as the TEEL-3 basis. The LOC was evaluated as the TEEL-2; however, it was not selected because TEEL-2 values derived from the TEEL-3 (Table 3.5) using available acute toxicity data generated values (0.23 to 0.83 mg/m3) that indicate the LOC is not sufficiently conservative. 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 = Dog oral LD50 (12 mg/kg)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was the rat LC50 found in this review, which had a reported duration of 240-minutes; however, it is unclear if this duration was the default time of 240 minutes for rat acute exposures with unspecified exposure times, or if this was the actual reported duration (Section 3.3.2). Given the uncertainty and the availability of other acute toxicity data, a dog oral LD50 was selected as the TEEL-3 basis. The Rev. 29A TEEL-2 was the LOC, while the current value was derived from the TEEL-3 (Table 3.5). The Rev. 29A and current TEEL-1 methodology remains consistent, with the differences due to the change in TEEL-2.