The human toxicity category aggregates all toxic emissions potentially affecting human health into units of m3 water. This im¬pact category contains the largest savings, after normalisation. The reduction in impact is due to substitution of virgin aluminium production. Fig. 3 shows how a ±15% change in each component of the waste in Case 1 will either give a result equal to the impact of the reference composition or provide a 20% increase in savings. The 20% increase in total avoided impact is due to a change in alu¬minium content from 0.5% to 0.6%. The human toxicity category is therefore very sensitive to the content of aluminium in the waste, and most importantly to how much of the available aluminium is recycled. The changes in total impact are much smaller for Case 2. This is because the quantity of aluminium recycled is approxi¬mately the same in all scenarios. However, due to the level of accu¬racy in the model used, there are some small differences in the quantity of aluminium recycled, even in Case 2. Although these dif¬ferences are less than 10 kg recycled aluminium per tonne total waste, they are nevertheless the reason for the variation in the Case 2 results.