Behaviour of trace metals in soils depends upon complex reactions among microand
macro cations and anions, and different components of various soil phases:
solid, aqueous and gaseous. The main features of the soil biogeochemical system
governing the behaviour of trace elements are: (1) heterogeneous distribution of
compounds and components; (2) seasonal and spatial alteration of major soil variables;
(3) transformation of element species; (4) transfer between phases; and (5)
bioaccumulation.