The involvement of aluminium in biological systems is very slight. The chemistry of this element indicates that it and in fact all simple trivalent cations with no redox properties are avoided since they are too powerful as Lewis acids and their reactions are in slow exchange relative to those of the divalent ions such as magnesium and zinc. There is also an interactive chemistry with silicon and this could limit aluminium availability in some waters and even protect within organisms. The toxicity of aluminium in cellular systems is well documented but its involvement in specific diseases such as Alzheimer's, remains uncertain.