COMPOSITION AND SPECIATION OF SOIL SOLUTI ON COLLECTED IN A HEAVY-METAL POLLUTED CALCAREOUS SOIL

Close to a brass foundry, which had emitted heavy metal containing dus ts for over 80 years, soil water was collected in the topsoil (18 cm) and in the subsoil (40 cm) of a severely polluted Calcic Fluvisol by m eans of polyethylen suction cups over a period of 2 years. The total m etal content of the topsoil (extracted with 2M HNO3 at 100-degrees-C f or 2 hours) was 38 nmol g-1, 24 mumol g-1, and 25 mumol g-1 for Cd, Cu , and Zn, respectively. The mean heavy metal concentrations of the soi l solution were 0.5 nmol L-1, 300 nmol L-1, and 200 nmol L-1 in the to psoil and 0.6 nmol L-1, 90 nmol L-1, and 30 nmol L-1 in the subsoil fo r Cd, Cu, and Zn, respectively. Solubility calculations showed that th e soil solutions were undersaturated with respect to heavy metal carbo nates as well as to hydroxides. It seems that the heavy metal concentr ation is determined by sorption processes rather than by precipitation . The composition of the soil solution has been shown to be governed b y the presence of calcite, by the soil temperature and by the partial pressure of CO2 in the soil air. The pCO2 in the soil air (in both dep ths) has been estimated at 2 mbar during the winter term and at 20 mba r during the summer term. A corresponding increase of the concentratio n of macroelements (Ca, Mg, Na) as well as of total dissolved carbonat e and of dissolved organic matter (DOC) has been measured in the summe r half year. No significant seasonal variations of the heavy metal con centrations were detected and no correlations with concentrations of o ther components could be found.