Copper species in aqueous sewage sludge extract

The Cu in the saturation extract of dried Davis sewage sludge was mainly in a complexed form. A Cu²⁺ specific ion electrode was used to determine the extent of complexation. The adsorption coefficient for the complexed Cu on Yolo silt loam was 4 while for Cu added as CUSO₄ it was 90 L kg^?1 at relevant Cu concentrations in solution. Paper electrophoresis was used to define the Cu complexes according to their mobility in an electric field. Six fractions of positive, negative and neutral charge were isolated. The portion of Cu in the sludge which was water soluble increased significantly upon drying. The large percentage of complexed Cu and its relatively low adsorption on soil suggested that sewage sludge may, under certain conditions, be a source of Cu contamination of plant systems and, in extreme cases, of ground water.