Surface or adsorbed species

In addition to the soluble chemical species and possible solid phase species described in the previous sections no discussion on speciation can be complete without the consideration of surface species. These include the inorganic and organic ions adsorbed on the surface of particles. Natural systems such as soils, sediments and waters abound with colloids such as the hydrous oxides of iron, aluminium, manganese and silicon which have the potential to form surface complexes with the various cationic and anionic dissolved species (Evans, 1989). 

In recent years the understanding of colloid surfaces and soils constituents has increased tremendously. Surface coordinating functional groups on particulate inorganic and humic materials are viewed as complexant ligands (Stumm, 1992). 

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