The pH dependence of free ionic activities and total dissolved concentrations of copper and cadmium in soil solution

Abstract Concentrations of total dissolved Cu and Cd and activities of their free ions in soil solution are suggested to be influenced by soil pH. The objective of this research was to study the relationships between free ionic activities and total dissolved concentrations of Cu and Cd and soil pH. Soil samples from Elkhorn, WI, USA (Typic Argiudoll), were used as a model. Free ions Cu 2+ and Cd 2+ were determined in the soil saturation extracts by using Donnan analysis with graphite furnace AAS. The values of soil pH beyond their indigenous values were obtained by additions of dilute nitric acid to the soil-water mixtures. The results showed that logarithmic concentrations of total dissolved Cu and Cd showed curve-linear relationships with soil pH. Free ionic Cu 2+ and Cd 2+ activities were negatively correlated with soil pH. The slopes of log (Cu 2+ ) vs. pH plots were − 0.10 and − 0.30 and those of log (Cd 2+ ) vs. pH plots were − 0.60 and − 0.70 for the control soil and the sewage-sludge-treated soil, respectively.