A review of available sources identified human and animal toxicity data. 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. Of the available toxicity sources, the lowest rat LC50 was selected as the TEEL-3 basis. The 4-hr exposure was scaled to a 60-minute equivalent using the ten Berge equation (Section 3.3.4). The lowest human TDLo with applicable toxicity endpoints was selected as the TEEL-2 basis. The TEEL-1 value was derived according to Table 3.5.
• TEEL-1 = TEEL-2/11
• TEEL-2 = man TDLo oral 286 mg/kg (headache, nausea, loss of muscle coordination)
• TEEL-3 = Rat 4-hr LC50 (> 7,000 mg/m3)
This review generated TEEL values which are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a rat oral LD50 (1,200 mg/kg), while the current recommendation is a higher priority route (LC50 > LD50). The Rev. 29A TEEL-2 was derived from Rev. 29A TEEL-3, while the current TEEL-2 basis is based on human toxicity data with the toxic endpoint methemoglobinemia (headache, nausea, loss of muscle coordination), which would be hazardous to first responders.