Fluoro-mobilization of metals in a Slovak forest soil affected by the emissions of an aluminum smelter

Depositions originating from a central Slovak Al smelter may increase metal solubility in adjacent soils because they contain F (mainly HF). The reaso n for fluoro-mobilization of metals may be the formation of soluble fluoro- metal complexes or the mobilization of organic matter and subsequent format ion of organo-metal complexes. The objectives of our work were (1) to asses s the extent of metal mobilization by fluoride in a Slovak Lithic Eutrochre pt affected by the emissions of an Al smelter and (2) to model the dissolve d metal species with the help of a chemical equilibrium model (MINEQL+). Th e O (Moder), A, and B horizons were equilibrated with solutions at F concen trations of 0, 0.9, 2.7, and 9.0 mmol l(-1). In the extracts, the concentra tions of Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Zn, dissolved organic c arbon (DOC), free and complexed F, and the pH and electrical conductivity ( EC) were determined. The heavy metal concentrations in the O horizon (Cd: 0 .99, Cr: 18.0, Cu: 44, Ni: 26, Pb: 110, and Zn: 84 mg kg(-1)) were 2.5 to 9 times larger than those in the A and B horizons. The concentrations of H2O -soluble F decreased from the O (261 mg kg(-1)) to the A (103 mg kg(-1)) an d B horizon (92 mg kg(-1)). In batch experiments increasing addition of F i ncreased the equilibrium concentrations of Al, Cr, Cu, Fe, Ni, Pb, and DOC in all samples, of Cd in the A, and of K in the B horizon. At the same time the concentrations of complexed F and pH increased whereas EC decreased. C hemical equilibrium modelling indicated that the mobilizing effect of F res ulted from the formation of fluoro-Al complexes and organo-complexes of all other metals.