A review of available sources identified exposure limits (STEL, TWA) and acute toxicity data (LD50, LDLo, TDLo) for several species and routes. 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. A 4-hour rat LC50 for a similar chemical, potassium dichromate (CASRN: 7778-50-9) was selected as the TEEL-3 basis (Section 3.4.6) and it was scaled to a 60-minute equivalent using the ten Berge equation (Section 3.3.4). The dose was reported as a range; therefore, analysts used the lower limit of the range for calculations. The TEEL-2 value was derived according to Table 3.5. The lowest reported 15-minute inhalable fraction OEL-STEL (Sweden) was selected as the TEEL-1.
• PAC-1 = TEEL-1 = OEL-STEL (Sweden, 0.015 mg/m3)
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat LC50 (potassium dichromate, CASRN: 7778-50-9; 83-99 mg/m3/4H)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a weight adjusted 1990 IDLH for chromates (CASRN: 1333-82), while the current TEEL-3 basis is a rat LC50 for a similar chemical, potassium dichromate (Section 3.4.6). 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 weight adjusted TLV-TWA for soluble chromium (VI) (CASRN: 744-47-3), while the current TEEL-1 is an exposure limit for sodium dichromate (STEL), a more preferred source (see note, Table 3.5).