A review of available sources identified exposure limits (LOC) and acute toxicity data (LD50, LDLo) for several species and routes. Analysts also evaluated exposure limits for cyanides (CN, CASRN: 57-12-5; IDLH, ceiling limits, STELs, TWAs) for TEEL development. 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. Analysts evaluated the original (1990) and revised (1994) IDLH sources and determined that the inclusion of acute inhalation toxicity data is relevant to TEEL development; as such, the 1994 IDLH for cyanides was selected as the TEEL-3 basis. The LOC was evaluated as the TEEL-2, however this resulted in a TEEL-2 > TEEL-3; as such, analysts instead selected the TLV-C for cyanides as the TEEL-2 basis (note that the TLV-C = REL-C). A compound adjustment factor was applied to these exposure limits (IDLH, TLV-C) according to Section 3.2.2. The TEEL-1 value was derived according to Table 3.5.
• PAC-1 = TEEL-1 = TEEL-2/11
• PAC-2 = TEEL-2 = MW-adjusted TLV-C (Cyanide; CASRN: 57-12-5; 5 mg/m3)
• PAC-3 = TEEL-3 = MW-adjusted IDLH (1994; Cyanide; CASRN: 57-12-5; 25 mg/m3)
This review generated PAC values inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was a weight adjusted 1990 IDLH, while the current TEEL-3 is a weight adjusted 1994 IDLH; analysts determined that the 1994 was an appropriate TEEL-3 source due to its inclusion of acute human toxicity data. The 1994 IDLH was used according to Handbook guidelines (Section 4.2-4.3). The Rev. 29A TEEL-2 was derived from the TEEL-3, while the current TEEL-2 is an exposure limit (Table 3.1). The Rev. 29A TEEL-1 was a MAK-TWA, while the current TEEL-1 was derived from the TEEL-2 (Section 3.4.2).