A review of available sources did not identify exposure limits and acute toxicity data for sodium butyl butylphosphonate. This chemical is a sodium salt of dibutyl phosphate, or phosphoric acid, dibutyl ester (CASRN: 107-66-3). As such, analysts evaluated exposure limits (IDLH, STELs, TWAs) and acute toxicity data (LD50) for dibutyl phosphate 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. The IDLH was evaluated as a TEEL-3, however it was developed from chronic data for tributyl phosphate, so it was determined unsuitable for TEEL development. Instead, analysts selected the rat oral LD50 for the TEEL-3 basis. The TLV-STEL was selected as the TEEL-1 and a molecular weight adjustment was applied according to Section 3.4.3.2.
• TEEL-1 = MW-adjusted TLV-STEL (dibutyl phosphate, CASRN: 107-66-4, 17 mg/m3)
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat oral LD50 (dibutyl phosphate, CASRN: 107-66-4, 3200 mg/kg)

This review generated TEEL values inconsistent with Rev 29A. The Rev. 29A basis were the TEELs for a dibutyl butylphosphonate (CASRN: 78-46-6). Analysts determined that dibutyl phosphate is a more structurally similar compound to sodium butyl butylphosphonate. The current TEEL-1 is a weight adjusted exposure limit (TLV-STEL, Section 3.4.3.2) and the TEEL-3 basis is a rat oral LD50 (Section 3.4.6). The Rev. 29A and current TEEL-2 use the same methodology, with differences due to the TEEL-3.