Five soils differently contaminated by emissions from copper smelters were treated with the organic materials lignite, compost, and sewage sludge. The concentrations of Cu, Zn, and Pb in soil solutions were measured after different incubation times within 30 days. Speciation of metals in soil solution was determined via modeling with Visual MinteQ. Soil amendment with all organic materials led to a temporary increase of Cu concentrations in soil solutions. Those effects and metal speciation in solutions were highly dependent on the kind of organic amendment that in particular affected pH and dissolved organic carbon concentrations in soils. Applying acidic lignite resulted in the release of free metal ions into the solution, while the application of immature compost led to the formation of metal complexes with soluble organic compounds. Soil amendment with limed, alkaline sewage sludge resulted in a strong increase in Cu concentrations in solutions due to the formation of ammine-Cu complexes. Principal component analysis confirmed that the main factors that determined solubility of metals in the experiment were pH and dissolved organic carbon concentrations in soil solutions. The strongest increase in metal solubility was observed directly after the application of amendments, and afterward the concentrations of metals in soil solutions started to decrease over time.