What are Generic cut-offs/ lower limits of concentration?
In GHS, and regional versions of it, there is a concept of relevance in relation to which components of a mixture ‘count’ when applying GHS mixture calculations. Effectively, you can ignore components below the generic cut-off limit when you calculate the hazards of a mixture. However there are circumstances which modify the generic situations.
An example in CLP is the generic cut off for ingredients which are classified as Hazardous to the Aquatic Environment Acute Category 1 is 0.1%. This means, when considering which ingredients ‘count’ look at ingredients at 0.1% or more. However, if an ingredient has an m-factor (multiplying factor) or specific concentration limit, then this overrides the generic cut-off. For example, alpha cedrene found in cedarwood oil, has an m-factor of 10. This m-factor means the contribution of alpha cedrene is 10 times higher in a mixture calculation and the ingredient is relevant at 10 times lower – therefore the cut-off limit for alpha cedrene is 0.01%.
A different scenario is when considering the effect of corrosive ingredients on an irritant end point for eyes or skin.
Here is what Article 184.108.40.206.1 of CLP legislation says about skin corrosion/irritation:
220.127.116.11.1. In order to make use of all available data for purposes of classifying the skin corrosion/irritation hazards of mixtures, the following assumption has been made and is applied where appropriate in the tiered approach: The ‘relevant ingredients’ of a mixture are those which are present in concentrations ? 1 % (w/w for solids, liquids, dusts, mists and vapours and v/v for gases), unless there is a presumption (e.g., in the case of skin corrosive ingredients) that an ingredient present at a concentration < 1 % can still be relevant for classifying the mixture for skin corrosion/irritation.
OSHA GHS has the same approach, shown in A.18.104.22.168 worded as follows for eye damage/irritation:
A.22.214.171.124 In general, the approach to classification of mixtures as seriously damaging to the eye or eye irritant when data are available on the ingredients, but not on the mixture as a whole, is based on the theory of additivity, such that each corrosive or irritant ingredient contributes to the overall irritant or corrosive properties of the mixture in proportion to its potency and concentration. A weighting factor of 10 is used for corrosive ingredients when they are present at a concentration below the concentration limit for classification with Category 1, but are at a concentration that will contribute to the classification of the mixture as an irritant. The mixture is classified as seriously damaging to the eye or eye irritant when the sum of the concentrations of such ingredients exceeds a threshold cut-off value/concentration limit.