title: Using isotopic dilution to assess chemical extraction of labile Ni, Cu, Zn, Cd and Pb in soils.
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.
authors.affiliation: Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster, LA1 4AP, England, United Kingdom; The University of Nottingham, School of Biosciences, Sutton Bonington Campus, LE12 5RD, England, United Kingdom.
authors.forename: J M
authors.initials: JM
authors.lastname: Garforth
authors.affiliation: The University of Nottingham, School of Biosciences, Sutton Bonington Campus, LE12 5RD, England, United Kingdom. Electronic address: liz.bailey@nottingham.ac.uk.
authors.forename: E H
authors.initials: EH
authors.lastname: Bailey
authors.affiliation: British Geological Survey, Environmental Science Centre, Keyworth, Nottingham, NG12 5GG, England, United Kingdom.
authors.forename: A M
authors.initials: AM
authors.lastname: Tye
authors.affiliation: The University of Nottingham, School of Biosciences, Sutton Bonington Campus, LE12 5RD, England, United Kingdom.
authors.forename: S D
authors.initials: SD
authors.lastname: Young
authors.affiliation: Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster, LA1 4AP, England, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Lofts
mesh_terms: D019342:Acetic Acid / Q000737:chemistry; D002104:Cadmium / Q000032:analysis; D002122:Calcium Chloride / Q000737:chemistry; D003300:Copper / Q000032:analysis; D004492:Edetic Acid / Q000737:chemistry; D004787:Environmental Pollution / Q000032:analysis*; D007854:Lead / Q000032:analysis; D019216:Metals, Heavy / Q000032:analysis*; D009532:Nickel / Q000032:analysis; D017942:Nitric Acid / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D052616:Solid Phase Extraction / Q000379:methods*; D006113:United Kingdom; D015032:Zinc / Q000032:analysis
chemical_list: D019216:Metals, Heavy; D012987:Soil; D012989:Soil Pollutants; D002104:Cadmium; D007854:Lead; D017942:Nitric Acid; D003300:Copper; D009532:Nickel; D004492:Edetic Acid; D015032:Zinc; D002122:Calcium Chloride; D019342:Acetic Acid
keywords: Soil chemical extraction; Stable isotope dilution