The effects of pH and soil type on concentrations of zinc, copper and nickel extracted by calcium chloride from sewage sludge-treated soils

Abstract

The effects of pH on concentrations of zinc, copper and nickel extracted by calcium chloride from a clay loam and two sandy loam soils that had been treated with sewage sludge were studied. Concentrations of all the metals increased rapidly as pH decreased below a threshold value ranging from 6·2 to 7·0 for Zn, 6·2 to 7·2 for Ni and 4·7 to 5·7 for Cu. Both the total concentrations and the threshold pH values were influenced by differences in soil texture and (between the two light-textured soils) by differences in soil cation exchange capacity. The amount of zinc and copper extracted from the mixtures was considerably less than that extracted from the same quantity of sludge alone.