A review of available sources identified the following: PEL-STEL, LD50 (dog, rat,) and LDLo, TDLo toxicity data for oral routes. 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. Although the dog is the most preferred species, and LDLo is less statistically relevant (see Appendix A), the LD50 TEEL-3 values were an order of magnitude higher than others calculated, therefore these toxicity data were not selected. Instead, the rat oral LD50 was selected as the TEEL-3 basis, as the next most preferred species and route. The Human (male) TDLo was selected as the TEEL-2 basis because it was the most preferred species basis. A TEEL-3 was calculated from this TEEL-2, according to guidance in the handbook. The TLV-STEL was the most preferred and selected as the TEEL-1.
• TEEL-1 = PEL-STEL (0.1 ppm)
• TEEL-2 = Estimated from human (male) TDLo (8420 µg/kg)
• TEEL-3 = Rat oral LD50 (517 mg/kg)
This review generated more conservative TEEL-2 and TEEL-3 values than those published in Rev. 29A. The current TEEL-1 values are consistent with Rev. 29A. The recommended TEEL-2 basis is consistent with the preference for human toxicity with appropriate endpoints discussed in Section 3.3.2. The recommended TEEL-3 relies on a more statistically significant type of toxicity exposure (LD50 > LDLo) that results more conservative TEEL-3 values.