Using isotopic dilution to assess chemical extraction of labile Ni, Cu, Zn, Cd and Pb in soils

Garforth, Judith M.; Bailey, Elizabeth H.; Tye, Andrew M.; Young, Scott D.; Lofts, Stephen

Abstract

Chemical extractants used to measure labile soil metal must ideally select for and solubilise the labile fraction, with minimal solubilisation of non-labile metal. We assessed four extractants (0.43 M HNO3, 0.43 M CH3COOH, 0.05 M Na2H2EDTA and 1 M CaCl2) against these requirements. For soils contaminated by contrasting sources, we compared isotopically exchangeable Ni, Cu, Zn, Cd and Pb (EValue, mg kg-1), with the concentrations of metal solubilised by the chemical extractants (MExt, mg kg-1). Crucially, we also determined isotopically exchangeable metal in the soil–extractant systems (EExt, mg kg-1). Thus ‘EExt - EValue’ quantifies the concentration of mobilised non-labile metal, while ‘EExt - MExt’ represents adsorbed labile metal in the presence of the extractant. Extraction with CaCl2 consistently underestimated EValue for Ni, Cu, Zn and Pb, while providing a reasonable estimate of EValue for Cd. In contrast, extraction with HNO3 both consistently mobilised non-labile metal and overestimated the EValue. Extraction with CH3COOH appeared to provide a good estimate of EValue for Cd; however, this was the net outcome of incomplete solubilisation of labile metal, and concurrent mobilisation of non-labile metal by the extractant (MExt < EExt > EValue). The Na2H2EDTA extractant mobilised some non-labile metal in three of the four soils, but consistently solubilised the entire labile fraction for all soil-metal combinations (MExt ≈ EExt). Comparison of EValue, MExt and EExt provides a rigorous means of assessing the underlying action of soil chemical extraction methods and could be used to refine long-standing soil extraction methodologies.

Citation

Garforth, J. M., Bailey, E. H., Tye, A. M., Young, S. D., & Lofts, S. (2016). Using isotopic dilution to assess chemical extraction of labile Ni, Cu, Zn, Cd and Pb in soils. Chemosphere, 155, https://doi.org/10.1016/j.chemosphere.2016.04.096

• Journal Article Type: Article
• Acceptance Date: Apr 24, 2016
• Online Publication Date: May 3, 2016
• Publication Date: Jul 1, 2016
• Deposit Date: Jul 20, 2016
• Publicly Available Date: Jul 20, 2016
• Journal: Chemosphere
• Print ISSN: 0045-6535
• Electronic ISSN: 1879-1298
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 155
• DOI: https://doi.org/10.1016/j.chemosphere.2016.04.096
• Public URL: https://nottingham-repository.worktribe.com/output/975918
• Publisher URL: http://www.sciencedirect.com/science/article/pii/S0045653516305860
• Contract Date: Jul 20, 2016