A review of available sources identified exposure limits (PEL-TWA) and acute toxicity data (LC50, LD50, TDLo) for several routes and species. 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. Inhalation exposures were scaled to 60-minute equivalents using the ten Berge equation (Section 3.3.4). Of the available data, the most preferred data type, three rat LC50 (103 ppm/8H, 98 mg/m3/4H, and 1480 mg/m3/1H) were considered for the TEEL-3 basis. Although data with exposure times closest to 60 minutes should be selected (Section 3.3.2), the 1480 mg/m3/1H dose could not be verified from the source (Section 3.3.1). The 103 ppm/8H source was the oldest and longest duration (1956). Considering this, the lowest dose, most recent study (98 mg/m3/4H, 1990) was selected as the TEEL-3 basis. A rat oral TDLo was considered for the TEEL-2, but resulted in a TEEL-2 > TEEL-3. Instead, the TEEL-2 value was derived according to Table 3.5. The PEL-TWA was selected as the TEEL-1 basis.
• PAC-1 = TEEL-1 = PEL-TWA (0.001 ppm/0.01 mg/m3) x 3
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat LC50 (98 mg/m3/4H)
This review generated PAC values inconsistent with Rev. 29A. In Rev. 29A the TEEL-3 basis was a 1-hour rat LC50 located in this review; however, the current TEEL-3 basis is a more recent study, a 4-hour rat LC50. The Rev. 29A TEEL-2 basis was a rat 24-hour TCLo that was not found in the current review. Instead, the current TEEL-2 was derived from the TEEL-3 (Table 3.5). The Rev. 29A and current TEEL-1 use the same source and methodology; minor difference in values may be due to rounding.