A contribution to environmental risk assessment for transport of cadmium through groundwater layers. Case study of the Sava river (near Zagreb, Croatia) region

Adsorption capacities of cadmium on aquifer material of the Sava River allu vial sediment were determined as a function of flow rate, pH and presence o f organic coating using laboratory column technique. In a permeameter with constant hydrostatic pressure, a laboratory coefficient of permeability, K- l, and a specific coefficient of permeability, K-s, have been determined. T he value Of 28.6 Darcy for specific permeability shows that the sediment be longs to a good aquifer (permeability > 1 Darcy). The adsorption capacity o f cadmium at the bottom of the breakthrough curve, C-sb, of a fresh sedimen t at pH 5.8 varied from 0.40 to 0.45 mg g(-1) at axial flow rate between 98 and 501 cm h(-1) Capacity values of maximum adsorption, C-s, were in the r ange from 0.67 to 0.72 mg g(-1). This implied a significance of C-sb values in risk assessment studies concerning a discharge of cadmium into rivers a nd lakes and its input to groundwater layers. Distribution coefficients, K- d, were between 26.3 and 28.2 ml g(-1). In order to create a more reproduci ble column, a fraction between 125 and 250 mu m was used. In that case C-s values varied from 0.25 mg g(-1) at pH 2.5 (organic coating present) to 1.1 2 mg g(-1) at pH 5.8 (organic coating removed). (C) 1998 Elsevier Science L td. All rights reserved.