A review of available sources identified the following toxicity exposures: PEL-TWA, TLV-TWA, LC50 and several LD50 (mouse, rat) toxicity data for oral and intraperitoneal 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 was scaled to a 60-minute equivalent using the ten Berge equation (Section 3.3.4). The LC50 was selected as the TEEL-3 basis because it was the most preferred source. TEEL-2 values derived according to Table 3.5. The TLV-TWA was selected as the TEEL-1 basis.
• TEEL-1 = TLV-TWA (1 ppm/1.9 mg/m3) x 3
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat 6-hr LC50 (>3900 ppm)
This review generated TEEL values that are inconsistent with Rev. 29A. The Rev. 29A basis was a rat oral LD50, a less preferred route than the current basis (LC50>LD50). The methodology of the Rev. 29A and current TEEL derivation are consistent, with different values attributed to changes in TEEL-3. The source of both Rev. 29A and the current TEEL-1 basis are consistent, TLV-TWA, but the current value is based on a more current published value.