To explain the effect of DOM in the metal complex formation, the qualitative aspect of DOM must be also considered.The addition of OFMSW to the soil strongly affected soil-DOM characteristics. In particular the abundance of carboxylic acid observed in the DOM of soil treated with OFMSW, seems to confirm the report on the ability of DOM to mobilize heavy metal by forming metal complexes. Organic complexes have been recognized to have a strong impact on the migration of metals (Pb, Cu, Zn, and Cd) in soilsand organic acids