A review of available sources identified the following: a Level of Concern (LOC) exposure limit (1989,) a human male 10-minute TCLo, and a rat 10-minute LC50. 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. The 10-minute TCLo and LC50 toxicity exposures were scaled to 60-minute equivalents using the ten Berge equation (Section 3.3.4). The rat LC50 was selected as the TEEL-3 basis. For the TEEL-2 basis, the LOC was considered but was determined to be significantly less conservative than the TEEL derived from human toxicity data (human male 10 min. TCLo). The chemical hazard summary states, “…cholinesterase inhibitor that is highly toxic by skin absorption and inhalation; Symptoms of heavy exposure could include convulsions, cyanosis, pulmonary edema, and coma.”. This chemical was also a basis for "nerve gases" in Germany, as mentioned in the description. With this, the more conservative TEEL-2 basis was determined to be appropriate. TEEL-1 values were derived according to Table 3.5.
• TEEL-1 = TEEL-2/11
• TEEL-2 = Human (male) 10-min TCLo (8.2 mg/m3. Toxicity endpoints: pupillary constriction (miosis) / headache)
• TEEL-3 = rat 10-min LC50 (360 mg/m3)
This review generated TEEL values more conservative than Rev. 29A. In Rev. 29A, a Level of Concern was selected as the TEEL-2 basis, with TEEL-3 and TEEL-1 values derived according to Table 3.5. The LOC derived TEELs are significantly less conservative than the TEELs derived from the toxicity data. With this, the current, more conservative TEELs are more appropriate, considering the hazard summary and previous chemical use.