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Copper Solubility in Myersville B Horizon Soil in the Presence of DTPA

Inst. of Terrestrial Ecology (ITÖ), Swiss Federal Inst. of Technology (ETH), Grabenstrasse 3, CH-8952, Schlieren, Switzerland

Alba Torrents

Dep. of Civil Engineering

Bruce R. James

Dep. of Natural Resource Sciences and Landscape Architecture, Univ. of Maryland, College Park, MD 20742

*Corresponding author (vulava{at}ito.umnw.ethz.ch).

ABSTRACT

Organic ligands greatly affect the speciation and solubility of heavy metals in soils, depending on complex interactions of pH, ligand-to-metal ratio, and the order of application of metals and ligands to soils. To understand how these variables influence the fate of metals added to soil, we investigated the solubility of Cu(II) in Myersville B horizon soil (Ultic Hapludalf) in the presence of diethylenetriaminepentaacetic acid (DTPA), a strong complexing agent. Copper solubility was studied as a function of soil pH, individual and relative concentrations of Cu²⁺ and DTPA, and the order of application of these components to the soil. In the presence of DTPA (1.0 and 10 mmol kg^–1 soil), Cu(II) solubility (0.1 and 1.0 mmol kg^–1 soil) increased with an increase in pH (4 to 7). However, this occurred only when DTPA concentration Cu(II) concentration, implying that the relative concentrations of DTPA and Cu(II) were critical in controlling Cu(II) solubility. The order of application of Cu(II) and DTPA to the soil also strongly influenced Cu solubility. The three orders of application of these components were (i) application of premixed stock solutions of Cu(II) and DTPA in specified ratios and concentrations to the soil, (ii) equilibration of Cu(II) with the soil followed by application of DTPA, and (iii) equilibration of DTPA with soil followed by Cu(II) application. Of these three, the highest Cu solubility was observed in the third case when DTPA > Cu(II). This was attributed to surface coordination of DTPA, which prevents Cu from binding with soils. Also, an increase in background electrolyte concentration was accompanied by a decrease in the pH and, therefore, a change in Cu(II) solubility. These results have several implications in the field of contaminant and nutrient management in soils.

This work was performed at the Univ. of Maryland. Joint contribution from the Colleges of Engineering and Natural Resource Sciences, Univ. of Maryland.