User Guide to Thresholds and Classification - Environmental ...

274User Guide for Thresholds and Classificationsa. Dilutioni. If a substance as a mixture is diluted with a diluent that has an equivalent or lower hazardii.b. Batchingclassification than the least ecotoxic original component and is not expected to affect the hazards ofother components, then assign the new mixture the same classification as the original mixture orsubstance.If the mixture is diluted with water or other non-ecotoxic material, calculate the ecotoxicity of themixture from the original mixture or substance.Assume the ecotoxicity hazard classification of one batch of substance as a mixture is substantiallyequivalent to that of another batch of the same commercial product produced by or under the control ofthe same manufacturer. If there is reason to believe significant variation exists, such that the ecotoxicityhazard classification of the batch has changed, consider conducting testing or assessing the hazard usingthe mixture rules.c. Concentration of highly ecotoxic mixturesIf a mixture is classified as very ecotoxic (that is, 9.1A, 9.2A, 9.3A, or 9.4A), and components of themixture that are classified as very ecotoxic in their own right are further concentrated, classify the moreconcentrated mixture as 9.nA without additional testing.d. Interpolation within one ecotoxicity classIf mixtures X and Y are in the same classification category and mixture Z is made in which the ecotoxiccomponents have concentrations intermediate to those in mixtures X and Y, then assume mixture Z is inthe same classification category as mixtures X and Y. Note that this assumes the identity of thecomponents is the same in all three mixtures.Substantially similar mixturesFor example, assume:i. mixture one comprises components A and B; andii. mixture two comprises components C and B.The concentration of component B is the same for both mixtures and the concentration of component Aequals that of component C. If the data on the ecotoxicity of A and C are available and substantiallyequivalent (that is, A and C are from the same hazard class and are not expected to affect the ecotoxicityof B), and mixture one has already been tested, mixture two does not need to be tested. That is, mixtureone and mixture two are classified in the same category.18.3.5. Classification of mixture based on classifications of components: the summationapproachSee the specific ecotoxicity chapters for details about classifying a mixture based on classifications ofcomponents.Aquatic ecotoxicity – chapter 19.Ecotoxicity to the soil environment – chapter 20.January 2012 EPA0109