With respect to metal performances, the dissolved organic matter (DOM) in the soil solution represents the most active fraction of the total organic matter in a soil. Originating primarily from litter leachates and root exudates, it contains two important fractions: simple organic acids as well as polyvalent macromolecules. Low molecular weight ligands are responsible for the dissolution of surface bound metals. Polyvalent macromolecules, in contrast, tend to be adsorbed at the mineral surface, inhibiting the mineral weathering. Due to the continous dissolution of the "bridging" metals by strong organic chelators, the adsorbed humic material can be redissolved. Depending on the relative proportion of the two fractions, enhanced or inhibited mineral dissolution occurs. DOM is affected by microorganisms, which modify the chemical properties of it. The role of DOM in determining metal performances is therefore governed by its chemical properties, and by all site factors affecting microbial activity.