A review of available sources identified the following: exposure limits (MAK-TWA, MAK-STEL) and acute toxicity data for mixtures of 5-chloro-2-methyl-4-isothazoli-3-one (CMIT) and 2-methyl-2H-isothazol-3-one (MIT, CASRN: 55965-82-9). 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. Inhalation exposures were scaled to 60-minute equivalents using the ten Berge equation (Section 3.3.4). The most preferred route and species, a rat LC50 a.i. (0.33 mg/L/4H) was available for Kathon886F a mixture of CMIT (10.4%), MIT (3.7%), and inert material used as a biocide. The percent CMIT to total active ingredients (CMIT + MIT) was calculated to be 73.76%, which was used to scale the final TEEL value:
TEEL-3Kathon866F x 73.76% = 14.551 mg/m3 x 73.76% = 10.7 mg/m3
A similar scaling was performed for the most preferred TEEL-1 source, a MAK-STEL for a Kathon mixture of a 3:1 CMIT to MIT mixture (75% CMIT). The TEEL-2 value was derived according to Table 3.5.
• TEEL-1 = MAK-STEL (3:1 mixture of CMIT to MIT, 0.40 mg/m3) x 75% (proportion that is CMIT)
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat LC50 (Kathon886F, a.i. 0.33 mg/L/4H) x 73.76% (proportion of Kathon886F active ingredients that is CMIT)
This review generated TEEL values that are more conservative than Rev. 29A. The Rev. 29A TEEL-1 basis was the MAK-TWA for a Kathon 3:1 CMIT to MIT mixture that did not account for the ratio of compounds. The Rev. 29A TEEL-2 and TEEL-3 values were derived from this TEEL-1. The current TEEL-3 basis is a more preferred source, and accounts for the ratio of active ingredients. The TEEL-2 was derived from this TEEL-3. The current TEEL-1 basis is a more preferred source, a MAK-STEL, which also accounts for the ratio of active ingredients.