A review of available sources identified the following: mouse and rat LD50 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. The most preferred species and route, a rat oral LD50, was selected as the TEEL-3 basis. The TEEL-2 and TEEL-1 values were derived accorded to Table 3.5
• TEEL-1 = TEEL-2 11
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat oral LD50 (350 mg/kg)
This review generated TEEL values that are inconsistent with those found in Rev 29A. The Rev. 29A values were derived from a molecular weight adjusted TLV-TWA for nickel (CASRN: 7440-02-0), with TEEL-2 and TEEL-3 derived from this basis. The current TEEL-3 basis is animal toxicity data for Nickel(II) acetate tetrahydrate, with TEEL-2 and TEEL-1 derived from this basis. When the Rev. 29A and current methodologies are compared, the relative preference of TEEL derivation (Section 3.4.2) indicates the preferred method is to derive a TEEL-2 from a TEEL-3.