In accordance with this, the current paper presents the results of investigations referring to the speciation of heavy metals in selected sewage sludge.

It was found that there were differences among metals in the preferential formation of bonds, but also such phenomena occurred in the individual sludge samples for the same element. This was mainly observed for cadmium and nickel.

Especially important are the amounts of metals associated with water soluble plus exchangeable fraction (1 mol.L-1 NH4NO3) as well as fraction of metals extracted by 1 mol.L-1 NH4OAc (pH = 6.0), corresponding to weakly adsorbed and bound with carbonates and labile organic compounds. With reference to this, it was stated that the percentage share of such combinations decreased in the order: Cu < Cr < Zn < Cd < Ni, reaching values of 2.9, 7.2, 8.8, 19.5 and 21.6% respectively. It shows those copper forms the lowest number of fast released combinations, whereas Ni and Cd - the highest.