A review of available sources did not identify exposure limits or acute toxicity data for arsenous acid. Analysts evaluated exposure limits (IDLH, REL-C, PEL-TWA) for inorganic arsenic compounds (CASRN: 7440-38-2) and acute toxicity data (LD50, LDLo) for a similar chemical, trisodium arsenate (AsNaO3, CASRN: 13464-37-4) for TEEL development (Section 3.4.6). 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 arsenic 1990 IDLH was evaluated, however acute toxicity data for trisodium arsenate and arsenic acid (AsH3O4, CASRN: 7778-39-4) indicated the IDLH is not sufficiently conservative. Considering this, analysts selected the rat intraperitoneal LDLo for trisodium arsenate as the TEEL-3 basis (Section 3.4.6). The REL-C for inorganic arsenic compounds (CASRN: 7440-38-2) was evaluated for the TEEL-2 but it was not selected because it resulted in a TEEL-2 < TEEL-1. Instead, the TEEL-2 was derived according to Table 3.5. The PEL-TWA for inorganic arsenic compounds (CASRN: 7440-38-2) was selected as the TEEL-1 basis and a compound adjustment factor was applied (Section 3.2.2).
• PAC-1 = TEEL-1 = MW-adjusted PEL-TWA (inorganic arsenic compounds, CASRN: 7440-38-2; 0.01 mg/m3) x 3
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = Rat intraperitoneal LDLo (9 mg/kg)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 basis was a weight adjusted arsenic IDLH, while the current TEEL-3 basis is a chemical specific rat intraperitoneal LDLo. 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 derived from the TEEL-2, while the current TEEL-1 basis is a weight adjusted PEL-TWA (Section 3.4.2).