User Guide to Thresholds and Classification - Environmental ...

428User Guide for Thresholds and Classifications22.3. Classification of substancesTo make use of all available data for classifying the hazards of the mixture to terrestrial invertebrates, thefollowing assumption has been made and is applied where appropriate.The ‗relevant components‘ of a mixture are those that are present in a concentration of 1% (by weight – w/w)or greater, unless there is a presumption (for example, in the case of highly toxic components) that acomponent present at less than 1% can still be relevant for classifying the mixture for hazards to terrestrialinvertebrates.The approach for classifying hazards to terrestrial invertebrates is tiered, and depends on the type ofinformation available for the mixture itself and for its components. Elements of the tiered approach includeclassification based on:tested mixtures (see section 22.3.1);bridging principles (see section 22.3.2); anda summation approach using the classifications of components (see section 22.3.3).22.3.1. Tested mixturesFor hazard classification to terrestrial invertebrates, the test data on the mixture can be used directly toassign a classification to a substance as indicated in the examples below (see Table 22.2).Where components of the mixture are toxic, the concentrations of components with these properties aresummed to determine the classification of the mixture. Where the sum of these components is ≥ 25%, thenthe more conservative classification applies.Table 22.2: Classification of terrestrial invertebrates of tested mixturesAcute LD 50 of the tested mixtureClassification of mixture< 2 g/terrestrial invertebrate 9.4A2 LD 50 < 11 g/terrestrial invertebrate 9.4B11 LD 50 25 g/terrestrial invertebrate 9.4C>25 g/terrestrial invertebrate Not classified as hazardousIf the mixture is used as a biocide and does not trigger classification under subclass 9.4, see chapter 23.22.3.2. Bridging principlesGuidance on the bridging principles for classifying mixtures without test data is in chapter 18.22.3.3. Classification of a mixture based on the classifications of components: thesummation approachWhen test data on the mixture are not available and the bridging principles are not applicable, thesummation approach is used to derive terrestrial invertebrate classification for the mixture.January 2012 EPA0109