A review of available sources did not identify exposure limits or acute toxicity data for rhodium(IV) oxide. Rhodium(IV) oxide is highly insoluble, therefore exposure limits for insoluble rhodium metal and fumes (Rh, CASRN: 7440-16-6) were evaluated for TEEL development. A review of available sources for rhodium identified IDLH (1990) and TWA (PEL, REL, TLV) exposure limits for metal, fume, and insoluble compounds (as Rh). Data sources were selected according to the hierarchy listed in Table 3.1. The IDLH (1990) (200 mg/m3) for insoluble rhodium metal and fumes was evaluated as the TEEL-3 basis, however it was not selected because the IDLH had no evidence and was based on a lower priority exposure limit, a PEL-TWA (0.1 mg/m3) x 2000. Instead, the TLV-TWA was selected as the TEEL-1 basis and a compound adjustment factor was applied (Section 3.2.2). TEEL-2 and TEEL-3 values were derived according to Table 3.5. (Note that, prior to molecular weight adjustment, this approach resulted in a IDLH (1990) = TEEL-1 derived TEEL-3 [200 mg/m3]).
• TEEL-1 = MW-adjusted TLV-TWA (insoluble rhodium and fumes; CASRN: 7440-16-6; 1 mg/m3) x 3
• TEEL-2 = TEEL-1 x 11
• TEEL-3 = TEEL-2 x 6
This review generated TEEL values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-1 basis was the TLV-TWA for soluble rhodium compounds; the current review determined that rhodium(IV) oxide is insoluble, therefore the current TEEL-1 basis is the TLV-TWA for insoluble rhodium. The Rev. 29A and current TEEL-2/TEEL-3 values used the same methodology, with differences due to the change in TEEL-1.