A review of available sources identified oral LD50 toxicity data for rat and mouse, and two MAK-TWAs for zinc (CASRN: 7440-66-6) for inhalable and respirable fractions. 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. Of the LD50 data, the mouse data (1260 mg/kg) from the European Chemicals Agency (ECHA) was selected as the TEEL-3 basis because of its source credibility in comparison to the other data, which was obtained from a safety data sheet. The MAK-TWAs for respirable (0.1 mg/m3) and inhalable (2 mg/m3) fractions for zinc were evaluated since the inhalable fraction was used as the TEEL-1 basis for the previous revision. Using the respirable fraction yielded the most conservative TEEL values, but it was determined that the mouse oral LD50 toxicity data from ECHA should be used because it based on zinc bromide, the chemical of interest. TEEL-2 and 3 values were calculated according to Table 3.5.
• TEEL-1 = TEEL-2/11
• TEEL-2 = TEEL-3/6
• TEEL-3 = Mouse oral LD50 (1260 mg/kg)
This review generated values that are more conservative and therefore inconsistent with those in Rev. 29A. In Rev. 29A the TEEL-1 basis was a MAK-TWA inhalable fraction for zinc (7440-66-6) which was then supposed to be molecular weight adjusted but appears not to have been. The TEEL-2 and TEEL-3 were then derived according to Table 3.5. Instead, this review found and used rat oral LD50 toxicity data for the actual chemical of interest, which yielded more conservative TEEL values.