Batch experiments were performed using mixed liquors from an activated sludge process receiving mainly residential wastewater and another activated sludge process receiving municipal wastewater which contained a significant portion of industrial wastewater. The experiments were conducted over a range of pH values, and the mixed liquor was maintained at constant pH and temperature. The mixed liquor was dosed with a solution containing six heavy metals, and the soluble and total concentrations of the metals were determined for a range of nominal concentrations. The concentration data were used to estimate the sorption partition coefficients and solubility limits of the heavy metals in mixed liquor for each pH value. The solubilities and partition coefficients (Kp) for the metals were dependent on pH. Kp for cadmium, nickel and zinc increased with increasing pH and decreased for chromium with increasing pH. Solubility limits were higher and Kp values lower for the mixed liquor receiving sewage with a high proportion of industrial contribution, than for the mixed liquor receiving mainly residential wastewater. This may limit the global application of fate models for metals and require site specific calibration.