A review of available sources identified exposure limits (OEL-TWA) and rat and mouse acute toxicity data (LD50). In addition, exposure limits (IDLH, TWAs) for soluble barium (CASRN: 7440-39-3) were evaluated for TEEL development. 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 IDLH was considered as a TEEL-3 basis; however, it was several orders greater than TEELs derived from toxicity data. The source of the rat LD50 could not be verified (Section 3.3.1); instead, analysts selected the mouse intraperitoneal LD50 as the TEEL-3 basis. The TEEL-2 was derived according to Table 3.5. The OEL-TWA was selected as the TEEL-1.
• TEEL-1 = OEL-TWA (Finland, 0.5 mg/m3) x 3
• TEEL-2 = TEEL-3/6
• TEEL-3 = Mouse intraperitoneal LD50 (146 mg/kg)
This review generated TEEL values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a MW-adjusted 1990 IDLH; the current basis is acute toxicity data for barium oxide. The Rev.29A and current TEEL-2 use the same methodology, with differences due to the change in TEEL-3. The Rev. 29A TEEL-1 basis was a MW-adjusted soluble barium TLV-TWA, while the current basis is an OEL-TWA for barium oxide.