Cobaltic-cobaltous oxide exists as a mixture of cobalt(II) oxide (CoO, CASRN: 1307-96-6) and cobalt(III) oxide (C2O3), as indicated in the cobalt(II) oxide identification: “…commercial oxides are usually not definite chemical compounds but mixtures of the cobalt oxides.” A review of available sources identified acute toxicity data (LD50) for cobalt(II) oxide and cobalt(III) oxide. In addition, analysts evaluated exposure limits for cobalt metal dust and fumes (IDLH, TWAs, Co, CASRN: 7440-48-4). 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 lowest dose rat oral LD50 (cobalt(II) oxide), was selected as the TEEL-3 basis. The TEEL-2 value was derived according to Table 3.5. The cobalt TLV-TWA was selected as the TEEL-1 basis and a compound adjustment factor was applied (Section 3.2.2).
• TEEL-1 = MW-adjusted TLV-TWA (cobalt, CASRN: 7440-48-4, 0.02 mg/m3) x 3
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat oral LD50 (cobalt(II) oxide, CASRN: 1307-96-6, 202 mg/kg)
This review generated TEEL-3 and TEEL-2 values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was a molecular weight adjusted IDLH for cobalt, while the current basis is a rat LD50 for a constituent in this chemical mixture (CoO, CASRN: 1307-96-6). The Rev. 29A and current TEEL-2 use the same methodology, with differences due to the change in TEEL-3.