A review of available sources did not identify exposure limits or acute toxicity data for ammonium molybdate(VI) tetrahydrate. Analysts did identify exposure limits for soluble molybdenum compounds (as molybdenum, CASRN: 7439-98-7; TWAs, IDLH). In addition, analysts evaluated the toxicity of molybdenum trioxide (MoO3) to inform TEEL development (the ratio of O:Mo in ammonium molybdate(VI) tetrahydrate is 3.4). The 1990 (2500 mg/m3) and 1994 (1000 mg/m3) IDLHs were evaluated; the 1990 IDLH is based on a PEL-TWA (5 mg/m3 x 250), while the 1994 IDLH is based on acute toxicity for a wide range of soluble molybdenum compounds, including those with MoO3 and MoO4. Analysts calculated molybdenum trioxide TEELs based on inhalation (rat LC50, TEEL-3 =260 mg/m3) and other routes (LD50, TEEL-3 = 31 mg/m3, 210 mg/m3, 530 mg/m3). Considering that the specific toxicity of MoO3 indicates a more conservative TEEL-3, analysts did not select either IDLH. Instead, analysts selected the most preferred TWA, the TLV-TWA 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.
• TEEL-1 = MW-adjusted TLV-TWA (molybdenum and compounds, soluble; CASRN: 7439-98-7, 0.5 mg/m3) x 3
• TEEL-2 = TEEL-1 x 11
• TEEL-3 = TEEL-2 x 6
This review generated TEEL values consistent with Rev. 29A.