A review of available sources identified the following: TWA exposure limits and acute toxicity data (LD50, LC50, LDLo) for numerous 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. Inhalation exposures were scaled to 60-minute equivalents using the ten Berge equation (Section 3.3.4). Although inhalation is the most preferred route, the LC50 was not selected as the TEEL-3 basis because it was based on a less preferred species (rat). Instead, a woman oral LDLo was selected as the TEEL-3 basis since human exposures are given primary consideration over other species. The TEEL-2 value was derived according to Table 3.5, and the TLV-TWA was selected as the TEEL-1- basis.
• TEEL-1 = TLV-TWA (0.5 mg/m3) x 3
• TEEL-2 = TEEL-3/6
• TEEL-3 = Human (female) oral LDLo (24 mg/kg)
This review generated TEEL-2 and TEEL-3 values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was based on rat LC50 toxicity data (1440 mg/m3/1H), however the recommended TEEL-3 is based on woman oral LDLo data, which is more preferred (human > rat) (Section 3.3.2). The TEEL-2 methodology remains consistent with the difference in values due to the change of the TEEL-3 basis. Additionally, the TEEL-1 value and methodology remain consistent.