Complexation with Dissolved Organic Matter and Solubility Control of Heavy Metals in a Sandy Soil

Abstract

The complexation of heavy metals with dissolved organic matter (DOM) in the environment influences the solubility and mobility of these metals. In this paper, we measured the complexation of Cu, Cd, Zn, Ni, and Pb with DOM in the soil solution at pH 3.7-6.1 using a Donnan membrane technique. The results show that the DOM-complexed species is generally more significant for Cu and Pb than for Cd, Zn, and Ni. The ability of two advanced models for ion binding to humic substances, e.g., model VI and NICA-Donnan, in the simulation of metal binding to natural DOM was assessed by comparing the model predictions with the measurements. Using the default parameters of fulvic and humic acid, the predicted concentrations of free metal ions from the solution speciation calculation using the two models are mostly within 1 order of magnitude difference from the measured concentrations, except for Ni and Pb in a few samples. Furthermore, the solid-solution partitioning of the metals was simulated using a multisurface model, in which metal binding to soil organic matter, dissolved organic matter, clay, and iron hydroxides was accounted for using adsorption and cation exchange models (NICA-Donnan, Donnan, DDL, CD-MUSIC). The model estimation of the dissolved concentration of the metals is mostly within 1 order of magnitude difference from those measured except for Ni in some samples and Pb. The solubility of the metals depends mainly on the metal loading over soil sorbents, pH, and the concentration of inorganic ligands and DOM in the soil solution.

Validation of Transfer Functions Predicting Cd and Pb Free Metal Ion Activity in Soil Solution as a Function of Soil Characteristics and Reactive Metal Content

“…The deviations between predicted and measured Cd 2+ and Pb 2+ activities were as approximately equal to the deviations observed by Weng et al (2002) …”

“…Free ion activities of Cd and Pb in BSE, CaCl 2 -extracts and lysimetric waters were calculated from total metal concentrations in solution, concentrations of major cations, anions, DOC, and pH using the speciation model WHAM/Model VI (Tipping, 1998). We assumed that dissolved organic matter (DOM) can be modelled as 65% active fulvic acid, which is an average value found by optimizing the model for binding of Cu to natural DOM in surface waters (Bryan et al, 2002) and is a reasonable estimate for the binding of several metals including Cd and Pb to DOM in soil solutions (Weng et al, 2002). DOM was calculated by assuming it to comprise 50% C by weight.…”

Assessment of the content of heavy metals and potential pathogenic microorganisms in soil under illegal dumping sites

“…In the publication, there is a lot of information stating that the solubility of metal sorbent depends primarily on the soil, pH, the concentration of the inorganic ligands and soluble humic acids in soil solution. The solubility of the metals depends mainly on the metal loading over soil sorbents, pH, and the concentration of inorganic ligands and dissolved organic matter (DOM) in the soil solution (Krosshavn et al 1993;Dube et al 2001;Weng et al 2002;Ashworth and Alloway 2008). The contamination coefficient (CF) allowed for the classification of the examined soils to the appropriate group, depending on the geochemical background factor.…”

Effects of rice straw on the speciation of cadmium (Cd) and copper (Cu) in soils

“…This 30% fraction of fulvic acids is relatively lower than found in other studies. For example, Weng et al (2002b) have assumed that 60% of DOM is humics. The soil solution speciation calculations suggests that most of the complexed Cu and Cd in the soil solution is organic complex with DOM.…”