Metal bioavailability: How does its significance change in the time?

The significance of terms metal bioavailability and bioavailable metal fraction is evolved in the time. passing from a very simple concept to a complex concept bound to abiotic and biotic aspects. At the beginning metal toxicity was related to metal fraction present in water phase, than only free metal ion activity was considered and the free ion activity model (FIAM) was proposed. Successively, due to the exceptions observed and to the consciousness that metal bioavailability could be considered as dynamic characteristic the concept of metal bioavailability became very complex. depending on physical, chemical and biological factors.