Effects of soil properties on copper speciation in soil solution

The numerical speciation analysis relies on quantitative assessment of concentrations of different forms of an element in soil solution (free ions, complex ions, neutral complexes), which have different abilities to react (ion activity). The reactivity affects the element’s mobility and bioavailability. This method can be employed to estimate potential bioavailability and toxicity of a given element. This study was undertaken to evaluaate effects of selected soil properties on changes in the total concentration of copper (Cu) and percentages of particular forms of this element in soil solution. The study was based on a microplot experiment. The investigated factors were the soil texture, pH, organic carbon content and degree of soil copper contamination. Soil solutions were obtained with the vacuum displacement method. The concentration of copper in soil solution was determined with the ICP method, and the percentages of particular copper forms in the total copper concentration were calculated with the MINTEQA 2 software. It was found that copper in the analysed soil solutions occurred mainly in the form of metalorganic complexes. The increasing soil acidity was correlated with an increased percentage of free copper ions and copper complexes with organic matter. Simultaneously, the share of bonds with carbonates, sulfates and hydroxyl groups decreased. A decrease in the percentage of Cu2+ free ions in the soil solution was observed in response to an increasing organic carbon content, while the percentage of copper complexes with organic matter rose. The degree of soil copper contamination and soil texture had no influence on the percentages of different copper forms in the soil solution.