A review of available sources did not identify exposure limits, acute toxicity, or health hazard ratings for cesium oxide. Analysts determined that cesium oxide reacts with air to form cesium carbonate (CASRN: 534-178-8), therefore available sources of acute toxicity data (LD50) for several species and routes of cesium carbonate (CASRN: 534-178-8) were evaluated for TEEL development (Section 3.4.6). 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. The most preferred species and route toxicity data, a rat oral LD50, was selected as the TEEL-3 basis. TEEL-2 and TEEL-1 values were derived according to Table 3.5.
• PAC-1 = TEEL-1 = TEEL-2/11
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat oral LD50 (cesium carbonate, CASRN: 534-17-8; 2333 mg/kg)
This review generated PAC values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a rat LDLo for the chemical of interest that could not be found during the review; instead, analysts selected a rat oral LD50 for cesium carbonate, an expected byproduct of cesium oxide exposure to air. The Rev. 29A and current TEEL-2 and TEEL-1 use the same methodology, with differences due to the change in TEEL-3.