User Guide to Thresholds and Classification - Environmental ...

153User Guide for Thresholds and ClassificationsAppendix 10B: Calculating acute toxicity – examples10B.1 Example 1A mixture contains 10% of component A with an oral median lethal dose (LD 50 ) of 2,000 milligrams perkilogram of bodyweight (mg/kg bw) and 30% of component B with an oral LD 50 of 1,500 mg/kg bw.The toxicity of the substance as a mixture expressed as an LD 50 would be as follows.C a /ATE a + C b /ATE b + ...+ C z /ATE z = 100/ATE mixWhere:C a = percentage of the component in the substance as a mixtureATE a = acute toxicity estimate of componentATE mix = estimated LD 50 of the mixtureTherefore, example 1:10/2,000 + 30/1,500 = 100/LD 50 (mixture)LD 50 (mixture) = 4,000 mg/kg bwThe calculated LD 50 of the mixture of 4000 mg/kg bw is less than the acute oral toxicity threshold of 5000mg/kg bw and so triggers the threshold. The mixture would be classified as 6.1E.10B.1 Example 2A mixture contains 10% of component A, which is classified as a category 6.1C toxicant, and 30% ofcomponent B with an oral LD 50 of 1,500 mg/kg bw. Using the formula in example 1, the toxicity of thesubstance as a mixture, expressed as an LD 50 , would be as follows.Using the range conversion table (see Table 10.2), a category 6.1C classification is equivalent to an LD 50 of100 mg/kg bw.C A /T A + C B /T B = 100/T M10/100 + 30/1,500 = 100/LD 50 (mixture)LD 50 (mixture) = 833 mg/kg bwThe calculated LD 50 of the mixture of 833 mg/kg bw is less than the acute oral toxicity threshold of 5,000mg/kg bw, so triggers the threshold. The mixture would be classified as a 6.1D.January 2012 EPA0109