A review of available sources identified numerous animal toxicity sources, from which the oral LD50 of the most preferred species (guinea pig, mouse, and rat,) were evaluated. Data sources were selected according to the hierarchy listed in Table 3.1. Toxicity data were selected based on the 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. Of these, the rat oral LD50 (206 µg/kg) was the most preferred route and species, and it was selected as the TEEL-3 basis. TEEL-2 and TEEL-1 values were derived from this TEEL-3 value. The TEELs were determined to be:
• TEEL-1 = 0.00062 mg/m3
• TEEL-2 = 0.0068 mg/m3
• TEEL-3 = 0.041 mg/m3
However, since the late 1980s, the Environmental Protection Agency (EPA) has implemented a Toxicity Equivalency Factor (TEF) to evaluate the acute toxicity of dioxin and DLCs relative to a reference chemical. 1,2,3,7,8-PentaCDD has a TEF=1, and is also one of two reference compounds identified by the EPA. Of these two chemicals, lower TEEL values for a comparable route and species (rat LD50) were reported for the other reference chemical, 2,3,7,8-TCDD (CASRN: 1746-01-6). As such, analysts recommend that 1,2,3,7,8-PentaCDD use the more conservative TEEL values of 2,3,7,8-TCDD due to its similarity.
• TEEL-1 = TEEL-12,3,7,8-TCDD
• TEEL-2 = TEEL-22,3,7,8-TCDD
• TEEL-3 = TEEL-32,3,7,8-TCDD
This review generated TEEL values consistent with those in Rev. 29A.