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Heavy metal displacement by exchangeable bases (Ca, Mg, K, Na) in soils and sediments

Erik Meers (UGent) , Gijs Du Laing (UGent) , Filip Tack (UGent) and Marc Verloo (UGent)
(2009) SOIL SCIENCE. 174(4). p.202-209
Author
Organization
Abstract
The extractability of heavy metals with exchangeable bases is of particular importance for two reasons: (i) Ca, Mg, K, and Na form the predominant electropositive elements in the soil solution (on molar basis) and can interact with adsorbed fractions of heavy metals; and (ii) single extractions aimed at ascertaining soil mobile or bioavailable fractions of heavy metals in the soils are for a major part based on these interactions. This article assesses metal extractability by Ca(NO3)(2), Mg(NO3)(2), KNO3, and NaNO3, and competitiveness for adsorption to the soil matrix between the exchangeable bases and the metals Cu, Cd, Cr, Ni, and Pb. To this end, experiments were performed in which a moderately contaminated soil was extracted with varying doses of extractant: 0, 0.05, 0.1, 0.25, 0.5 M of NaNO3, 0, 0.05, 0.1, 0.2, 0.4 M of KNO3, 0, 0.05, 0.1, 0.2 M of Ca(NO3)(2), and 0, 0.05, 0.1, 0.2 M of Mg(NO3)(2). In addition, differences in metal extractability between 0.01 M of Ca(NO3)(2) and 0.01 M of CaCl2 and between 1 M Of MgCl2 and 1 M of Mg(NO3)(2) were evaluated in six soils with varying soil composition and pollution level to assess the effect of the counter ion (Cl- vs. NO3-). Finally, in a third experiment, heavy metal desorption in the presence of increasing concentrations of Ca(NO3)(2) (0-0.1 M) was evaluated in four polluted soils. Total, soil content of a given metal does not suffice to assess its environmental impact and bioavailability. Therefore, the study of metal exchangeability with Ca 21 is proposed to grant additional and complementary insight for soil metal analysis. Extraction with sufficiently high ionic strength, such as 0.1 M of Ca(NO3)(2), can be used to give an estimate of the total exchangeable pool, whereas weaker extractions at around the ionic strength of the soil solution (similar to 0.0 1 M of CaCl2) allow for the estimation of the quantitative "responsiveness" of metal release as a function of increasing Ca2+ in the extractant solution at around relevant soil solution conditions.
Keywords
Heavy metals, exchangeable bases, adsorption, single extraction, SEQUENTIAL EXTRACTION PROCEDURE, CONTAMINATED SOILS, SINGLE EXTRACTIONS, POLLUTED SOILS, TRACE-METALS, SPECIATION, ZN, CD, BIOAVAILABILITY, EXTRACTABILITY

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Chicago
Meers, Erik, Gijs Du Laing, Filip Tack, and Marc Verloo. 2009. “Heavy Metal Displacement by Exchangeable Bases (Ca, Mg, K, Na) in Soils and Sediments.” Soil Science 174 (4): 202–209.
APA
Meers, Erik, Du Laing, G., Tack, F., & Verloo, M. (2009). Heavy metal displacement by exchangeable bases (Ca, Mg, K, Na) in soils and sediments. SOIL SCIENCE, 174(4), 202–209.
Vancouver
1.
Meers E, Du Laing G, Tack F, Verloo M. Heavy metal displacement by exchangeable bases (Ca, Mg, K, Na) in soils and sediments. SOIL SCIENCE. 2009;174(4):202–9.
MLA
Meers, Erik, Gijs Du Laing, Filip Tack, et al. “Heavy Metal Displacement by Exchangeable Bases (Ca, Mg, K, Na) in Soils and Sediments.” SOIL SCIENCE 174.4 (2009): 202–209. Print.
@article{853416,
  abstract     = {The extractability of heavy metals with exchangeable bases is of particular importance for two reasons: (i) Ca, Mg, K, and Na form the predominant electropositive elements in the soil solution (on molar basis) and can interact with adsorbed fractions of heavy metals; and (ii) single extractions aimed at ascertaining soil mobile or bioavailable fractions of heavy metals in the soils are for a major part based on these interactions. This article assesses metal extractability by Ca(NO3)(2), Mg(NO3)(2), KNO3, and NaNO3, and competitiveness for adsorption to the soil matrix between the exchangeable bases and the metals Cu, Cd, Cr, Ni, and Pb. To this end, experiments were performed in which a moderately contaminated soil was extracted with varying doses of extractant: 0, 0.05, 0.1, 0.25, 0.5 M of NaNO3, 0, 0.05, 0.1, 0.2, 0.4 M of KNO3, 0, 0.05, 0.1, 0.2 M of Ca(NO3)(2), and 0, 0.05, 0.1, 0.2 M of Mg(NO3)(2). In addition, differences in metal extractability between 0.01 M of Ca(NO3)(2) and 0.01 M of CaCl2 and between 1 M Of MgCl2 and 1 M of Mg(NO3)(2) were evaluated in six soils with varying soil composition and pollution level to assess the effect of the counter ion (Cl- vs. NO3-). Finally, in a third experiment, heavy metal desorption in the presence of increasing concentrations of Ca(NO3)(2) (0-0.1 M) was evaluated in four polluted soils. Total, soil content of a given metal does not suffice to assess its environmental impact and bioavailability. Therefore, the study of metal exchangeability with Ca 21 is proposed to grant additional and complementary insight for soil metal analysis. Extraction with sufficiently high ionic strength, such as 0.1 M of Ca(NO3)(2), can be used to give an estimate of the total exchangeable pool, whereas weaker extractions at around the ionic strength of the soil solution (similar to 0.0 1 M of CaCl2) allow for the estimation of the quantitative {\textacutedbl}responsiveness{\textacutedbl} of metal release as a function of increasing Ca2+ in the extractant solution at around relevant soil solution conditions.},
  author       = {Meers, Erik and Du Laing, Gijs and Tack, Filip and Verloo, Marc},
  issn         = {0038-075X},
  journal      = {SOIL SCIENCE},
  keyword      = {Heavy metals,exchangeable bases,adsorption,single extraction,SEQUENTIAL EXTRACTION PROCEDURE,CONTAMINATED SOILS,SINGLE EXTRACTIONS,POLLUTED SOILS,TRACE-METALS,SPECIATION,ZN,CD,BIOAVAILABILITY,EXTRACTABILITY},
  language     = {eng},
  number       = {4},
  pages        = {202--209},
  title        = {Heavy metal displacement by exchangeable bases (Ca, Mg, K, Na) in soils and sediments},
  url          = {http://dx.doi.org/10.1097/SS.0b013e31819f601a},
  volume       = {174},
  year         = {2009},
}

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