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 alluvial sediment were determined as a function of flow rate, pH and presence of organic coating using laboratory column technique. In a permeameter with constant hydrostatic pressure, a laboratory coefficient of permeability, Kl, and a specific coefficient of permeability, Ks, have been determined. The value of 28.6 Darcy for specific permeability shows that the sediment belongs to a good aquifer (permeability >1 Darcy). The adsorption capacity of cadmium at the bottom of the breakthrough curve, Csb, of a fresh sediment 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, Cs, were in the range from 0.67 to 0.72 mg g−1. This implies a significance of Csb values in risk assessment studies concerning a discharge of cadmium into rivers and lakes and its input to groundwater layers. Distribution coefficients, Kd, were between 26.3 and 28.2 ml g−1. In order to create a more reproducible column, a fraction between 125 and 250 μm was used. In that case Cs values varied from 0.25 mg g−1 at pH 2.5 (organic coating present) to 1.12 mg g−1 at pH 5.8 (organic coating removed).