A review of available sources identified the following exposures: REL-STEL, LCLo, LD50, and TCLo for inhalation and oral 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 based on the hierarchies stated in Sections 3.3.1, 3.3.2, and evaluated using factors in Tables 3.2, 3.3, and 3.4. Concentration exposures were adjusted to 60-minute concentration equivalents with the ten Berge equation (Section 3.3.5). The TCLo was not selected because it did not exhibit relevant toxicity endpoints (Section 3.3.2.). Although concentration-based data is preferred, the LD50 has a higher statistical relevance (See A-3), therefore the rat oral LD50 was selected as the TEEL-3 basis. A TEEL-2 estimate was calculated from this TEEL-3 value, according to guidance in the handbook (Table 3.5). The REL-STEL was selected as the TEEL-1 value as the most preferred source (Table 3.1).
• TEEL-1 = TLV-STEL (45 mg/m3)
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat Oral LD50 (2600 mg/kg)
This review generated TEEL values consistent with those of Rev. 29A because they have the same basis.