User Guide to Thresholds and Classification - Environmental ...

260User Guide for Thresholds and Classifications17.3.2. Classification of mixtures when data are not available for the complete mixture:bridging principlesWhen the mixture itself has not been tested to determine its specific target organ or systemic toxicity, butthere are sufficient data on the individual ingredients and similar tested mixtures to adequately characterisethe hazards of the mixture, these data can be used in accordance with the following bridging principles. Thisensures the classification process uses the available data to the greatest extent possible in characterisingthe hazards of the mixture without needing additional testing in animals.a. DilutionIf a mixture is diluted with a diluent that has the same or a lower toxicity classification as the least toxicoriginal ingredient and is not expected to affect the toxicity of other ingredients, then the new mixture maybe classified as equivalent to the original mixture.b. BatchingThe toxicity of one production batch of a complex mixture can be assumed to be substantially equivalentto that of another production batch of the same commercial product, where produced by or under thecontrol of the same manufacturer, unless there is reason to believe there is significant variation such thatthe toxicity of the batch has changed. If the latter occurs, a new classification is necessary.c. Concentration of highly toxic mixturesIf, in a mixture classified 6.9A, the concentration of a toxic ingredient is increased, the concentratedmixture should remain classified as 6.9A without additional testing.d. Interpolation within one toxicity categoryFor three mixtures with identical ingredients, where mixtures A and B are in the same toxicity categoryand mixture C has the same toxicologically active ingredients with concentrations intermediate to theconcentrations of those ingredients in mixtures A and B, then mixture C is assumed to be in the sametoxicity category as mixtures A and B.e. Substantially similar mixturesGiven:i. two mixtures: (A + B) and (C + B);ii.iii.iv.the concentration of ingredient B is essentially the same in both mixtures;the concentration of ingredient A in mixture (A + B) equals that of ingredient C in mixture (C + B);anddata on toxicity for ingredients A and C are available and substantially equivalent; that is they are inthe same hazard category and are not expected to affect the toxicity of ingredient B; thenif mixture (A + B) has already been classified by testing, mixture (C + B) can be assigned the samecategory.f. AerosolsA hazard classification may be assigned for specific target organ toxicity (single or repeat exposure) foraerosols. Although in many cases, data are available only from repeat-dose oral studies, classification forJanuary 2012 EPA0109