Register      Login
Environmental Chemistry Environmental Chemistry Society
Environmental problems - Chemical approaches
RESEARCH ARTICLE

Interpretation of heavy metal speciation in sequential extraction using geochemical modelling

Yanshan Cui A B and Liping Weng B C
+ Author Affiliations
- Author Affiliations

A University of Chinese Academy of Sciences, Beijing 100049, China.

B Department of Soil Quality, Wageningen University, PO Box 47, 6700 AA, Wageningen, the Netherlands.

C Corresponding author. Email: liping.weng@wur.nl

Environmental Chemistry 12(2) 163-173 https://doi.org/10.1071/EN13216
Submitted: 27 November 2013  Accepted: 30 August 2014   Published: 7 January 2015

Environmental context. Heavy metal pollution is a worldwide environmental concern, and the risk depends not only on their total concentration, but also on their chemical speciation. Based on state-of-the-art geochemical modelling, we pinpoint the heavy metal pools approached by the widely used sequential extraction method. The finding of this paper can help users of sequential extraction methods to better interpret their results.

Abstract. In this study, the metal (Cd, Cu, Zn and Pb) fractionation determined by selective sequential extraction (SSE) was compared with metal speciation calculated using a geochemical model, the Multi-Surface Model (MSM). In addition, the sources of Cd, Cu and Zn extracted in the SSE were identified with the help of the modelling. The results showed that the SSE-based Cd fractionation contradicted the modelled results, with the organic-bound Cd as respectively the least and the most important species. This contradiction was explained by the model and was attributed to the weak specific adsorption of Cd to organic matter; For Cu, a good agreement was found between SSE and model fractionation, both recognising organic-bound Cu as the most dominant fraction. The high affinity of organic matter for Cu reduced the degree of Cu extracted in steps preceding the oxidation step. The SSE measured a larger exchangeable Zn fraction than the model predicted, which could be explained by Zn extracted from organic-bound, oxide-bound forms, and certain rapidly dissolvable Zn-minerals if present. Zinc in the micropores of minerals was probably not extracted in 0.43 M HNO3, thus was not included in the modelling for adsorption calculation, which could explain to a certain extent the larger amount of oxide-bound Zn determined in the SSE than calculated in the model. The modelling results for Pb were less reliable than for other metals because of a poor accuracy of Pb concentration in solution predicted. The findings of this paper can help users of the sequential extraction methods to better interpret their results.


References

[1]  J. J. D’Amore, S. R. Al-Abed, K. G. Scheckel, J. A. Ryan, Methods for speciation of metals in soils: a review. J. Environ. Qual. 2005, 34, 1707.
Methods for speciation of metals in soils: a review.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXhtVygs7zE&md5=450854e489c23d5db8b8f141c2d83cbaCAS | 16151225PubMed |

[2]  A. Tessier, P. G. C. Campbell, M. Bisson, Sequential extraction procedure for the speciation of particulate trace-metals. Anal. Chem. 1979, 51, 844.
Sequential extraction procedure for the speciation of particulate trace-metals.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaE1MXitV2rtr4%3D&md5=5260e8479e4492cf2e1dbb36b04f8b7fCAS |

[3]  A. M. Ure, P. Quevauviller, H. Muntau, B. Griepink, Speciation of heavy-metals in soils and sediments – an account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the Commission-of-the-European-Communities. Int. J. Environ. Anal. Chem. 1993, 51, 135.
Speciation of heavy-metals in soils and sediments – an account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the Commission-of-the-European-Communities.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2cXpsVWmsw%3D%3D&md5=37034749a7c08cf738bb044c62aa3b92CAS |

[4]  J. R. Bacon, C. M. Davidson, Is there a future for sequential chemical extraction? Analyst 2008, 133, 25.
Is there a future for sequential chemical extraction?Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXhsVehsrrJ&md5=c662ddeb89f18db9ac0badcbd09dbe9dCAS | 18087610PubMed |

[5]  L. P. Weng, E. J. M. Temminghoff, S. Lofts, E. Tipping, W. H. Van Riemsdijk, Complexation with dissolved organic matter and solubility control of heavy metals in a sandy soil. Environ. Sci. Technol. 2002, 36, 4804.
Complexation with dissolved organic matter and solubility control of heavy metals in a sandy soil.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38Xnsl2iu7w%3D&md5=09106d0f538968f5cf1f28146d66d63cCAS |

[6]  L. P. Weng, E. J. M. Temminghoff, W. H. Van Riemsdijk, Contribution of individual sorbents to the control of heavy metal activity in sandy soil. Environ. Sci. Technol. 2001, 35, 4436.
Contribution of individual sorbents to the control of heavy metal activity in sandy soil.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXntlGru74%3D&md5=a97262df8f1ce8fd073b8f23406437edCAS |

[7]  T. J. Schröder, T. Hiemstra, J. P. M. Vink, S. E. A. T. M. Van der Zee, Modeling of the solid-solution partitioning of heavy metals and arsenic in embanked flood plain soils of the rivers Rhine and Meuse. Environ. Sci. Technol. 2005, 39, 7176.
Modeling of the solid-solution partitioning of heavy metals and arsenic in embanked flood plain soils of the rivers Rhine and Meuse.Crossref | GoogleScholarGoogle Scholar | 16201646PubMed |

[8]  S. Lofts, E. Tipping, An assemblage model for cation binding by natural particulate matter. Geochim. Cosmochim. Acta 1998, 62, 2609.
An assemblage model for cation binding by natural particulate matter.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXnsFamsbc%3D&md5=b886aadf15e3c4c3e058fa277e092accCAS |

[9]  D. G. Lumsdon, Partitioning of organic carbon, aluminium and cadmium between solid and solution in soils: application of a mineral–humic particle additivity model. Eur. J. Soil Sci. 2004, 55, 271.
Partitioning of organic carbon, aluminium and cadmium between solid and solution in soils: application of a mineral–humic particle additivity model.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXlsFCks7o%3D&md5=e7841ff119edcdc3ea54eefb938c92eaCAS |

[10]  E. Tipping, D. Berggren, J. Mulder, C. Woof, Modeling the solid-solution distributions of protons, aluminium, base cations and humic substances in acid soils. Eur. J. Soil Sci. 1995, 46, 77.
Modeling the solid-solution distributions of protons, aluminium, base cations and humic substances in acid soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXmtlGgtLw%3D&md5=785f3bd45142b39b2ae1a63e843d005aCAS |

[11]  J. J. Dijkstra, J. C. L. Meeussen, R. N. J. Comans, Evaluation of a generic multisurface sorption model for inorganic soil contaminants. Environ. Sci. Technol. 2009, 43, 6196.
Evaluation of a generic multisurface sorption model for inorganic soil contaminants.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXosFSltrc%3D&md5=447db9b113eb5046fa5987ab8497d885CAS | 19746713PubMed |

[12]  P. M. V. Nirel, F. M. M. Morel, Pitfalls of sequential extractions. Water Res. 1990, 24, 1055.
Pitfalls of sequential extractions.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3cXlsFygs7s%3D&md5=b13487f279112ff39737fbef7b1051cbCAS |

[13]  J. D. Ostergren, G. E. Brown, G. A. Parks, T. N. Tingle, Quantitative speciation of lead in selected mine tailings from Leadville, CO. Environ. Sci. Technol. 1999, 33, 1627.
Quantitative speciation of lead in selected mine tailings from Leadville, CO.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXitFegsLk%3D&md5=3fce8c21035745872b92e90dd853b0e8CAS |

[14]  W. Calmano, S. Mangold, E. Welter, An XAFS investigation of the artefacts caused by sequential extraction analyses of Pb-contaminated soils. Fresenius J. Anal. Chem. 2001, 371, 823.
An XAFS investigation of the artefacts caused by sequential extraction analyses of Pb-contaminated soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXot1OrsL8%3D&md5=c68b87fc83885eb9a2f6bd253dee5746CAS | 11768472PubMed |

[15]  C. Kheboian, C. F. Bauer, Accuracy of selective extraction procedures for metal speciation in model aquatic sediments. Anal. Chem. 1987, 59, 1417.
Accuracy of selective extraction procedures for metal speciation in model aquatic sediments.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL2sXhs1Oqs7g%3D&md5=30c85957171feceb736ca10748ec94b8CAS |

[16]  N. D. Kim, J. E. Fergusson, Effectiveness of a commonly used sequential extraction technique in determining the speciation of carmium in soils. Sci. Total Environ. 1991, 105, 191.
Effectiveness of a commonly used sequential extraction technique in determining the speciation of carmium in soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3MXltFSiu74%3D&md5=ecb0e1ae3bb9c7245a35568141728f12CAS |

[17]  C. Whalley, A. Grant, Assessment of the phase selectivity of the European Community Bureau of Reference (BCR) sequential extraction procedure for metals in sediment. Anal. Chim. Acta 1994, 291, 287.
Assessment of the phase selectivity of the European Community Bureau of Reference (BCR) sequential extraction procedure for metals in sediment.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2cXks1GjtLs%3D&md5=50a180e514c7b8272fca26ea6bca82f3CAS |

[18]  M. Raksasataya, A. G. Langdon, N. D. Kim, Assessment of the extent of lead redistribution during sequential extraction by two different methods. Anal. Chim. Acta 1996, 332, 1.
Assessment of the extent of lead redistribution during sequential extraction by two different methods.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28XlvFKnsL4%3D&md5=b3ddc3666dfaa0e914aa134926082087CAS |

[19]  X. Q. Shan, C. Bin, Evaluation of sequential extraction for speciation of trace-metals in model soil containing natural minerals and humic acid. Anal. Chem. 1993, 65, 802.
Evaluation of sequential extraction for speciation of trace-metals in model soil containing natural minerals and humic acid.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3sXhtVWjt74%3D&md5=74ab540fd72bcf9c63069ab3b0429364CAS |

[20]  A. C. Scheinost, R. Kretzschmar, S. Pfister, D. R. Roberts, Combining selective sequential extractions, X-ray absorption spectroscopy, and principal component analysis for quantitative zinc speciation in soil. Environ. Sci. Technol. 2002, 36, 5021.
Combining selective sequential extractions, X-ray absorption spectroscopy, and principal component analysis for quantitative zinc speciation in soil.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38XotlCjs7g%3D&md5=bfb9bb9d1985a4bd19d4aac3c3bc90dfCAS | 12523415PubMed |

[21]  F. Degryse, A. Voegelin, O. Jacquat, R. Kretzschmar, E. Smolders, Characterization of zinc in contaminated soils: complementary insights from isotopic exchange, batch extractions and XAFS spectroscopy. Eur. J. Soil Sci. 2011, 62, 318.
Characterization of zinc in contaminated soils: complementary insights from isotopic exchange, batch extractions and XAFS spectroscopy.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXltleqt7g%3D&md5=6842ed31180d29be54d40c6e4e56d5b7CAS |

[22]  T. A. Kirpichtchikova, A. Manceau, L. Spadini, F. Panfili, S. Marcu, M. A. Marcus, T. Jacquet, Speciation and solubility of heavy metals in contaminated soil using X-ray microfluorescence, EXAFS spectroscopy, chemical extraction, and thermodynamic modeling. Geochim. Cosmochim. Acta 2006, 70, 2163.
Speciation and solubility of heavy metals in contaminated soil using X-ray microfluorescence, EXAFS spectroscopy, chemical extraction, and thermodynamic modeling.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xjslyht7k%3D&md5=2e20142d8a2ce6243034871b268ed91bCAS |

[23]  M. P. Isaure, A. Laboudigue, A. Manceau, G. Sarret, C. Tiffreau, P. Trocellier, G. Lamble, J. L. Hazemann, D. Chateigner, Quantitative Zn speciation in a contaminated dredged sediment by µ-PIXE, µ-SXRF, EXAFS spectroscopy and principal component analysis. Geochim. Cosmochim. Acta 2002, 66, 1549.
Quantitative Zn speciation in a contaminated dredged sediment by µ-PIXE, µ-SXRF, EXAFS spectroscopy and principal component analysis.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38XivFOhs7o%3D&md5=e78fc087f7151c914c970a213039e40fCAS |

[24]  K. G. Scheckel, J. A. Ryan, D. Allen, N. V. Lescano, Determining speciation of Pb in phosphate-amended soils: method limitations. Sci. Total Environ. 2005, 350, 261.
Determining speciation of Pb in phosphate-amended soils: method limitations.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXhtFegsL7L&md5=30539cacd1c58e9a9a5d222b13144b4fCAS | 16227085PubMed |

[25]  G. L. Guo, Q. X. Zhou, P. V. Koval, G. A. Belogolova, Speciation distribution of Cd, Pb, Cu, and Zn in contaminated Phaeozem in north-east China using single and sequential extraction procedures. Aust. J. Soil Res. 2006, 44, 135.
Speciation distribution of Cd, Pb, Cu, and Zn in contaminated Phaeozem in north-east China using single and sequential extraction procedures.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XivVSmtro%3D&md5=a47363b1e066b935a5e0c0161af3c45aCAS |

[26]  R. Terzano, M. Spagnuolo, B. Vekemans, W. De Nolf, K. Janssens, G. Falkenberg, S. Flore, P. Ruggiero, Assessing the origin and fate of Cr, Ni, Cu, Zn, Pb, and V in industrial polluted soil by combined microspectroscopic techniques and bulk extraction methods. Environ. Sci. Technol. 2007, 41, 6762.
Assessing the origin and fate of Cr, Ni, Cu, Zn, Pb, and V in industrial polluted soil by combined microspectroscopic techniques and bulk extraction methods.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXpsFyiu70%3D&md5=85368d33e5a1e9c18fd27b14dca799b5CAS | 17969692PubMed |

[27]  F. Degryse, K. Broos, E. Smolders, R. Merckx, Soil solution concentration of Cd and Zn can be predicted with a CaCl2 soil extract. Eur. J. Soil Sci. 2003, 54, 149.
Soil solution concentration of Cd and Zn can be predicted with a CaCl2 soil extract.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXit1KjtLo%3D&md5=a138381ec400c34b31bbd4f5de49ccc9CAS |

[28]  E. J. M. Temminghoff, S. E. A. T. M. Van der Zee, F. A. M. De Haan, Copper mobility in a copper-contaminated sandy soil as affected by pH and solid and dissolved organic matter. Environ. Sci. Technol. 1997, 31, 1109.
Copper mobility in a copper-contaminated sandy soil as affected by pH and solid and dissolved organic matter.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXhvFGgtr8%3D&md5=f73e19b8e875c238b1b69d5c1de94a02CAS |

[29]  L. P. Weng, A. Wolthoorn, T. M. Lexmond, E. J. M. Temminghoff, W. H. Van Riemsdijk, Understanding the effects of soil characteristics on phytotoxicity and bioavailability of nickel using speciation models. Environ. Sci. Technol. 2004, 38, 156.
Understanding the effects of soil characteristics on phytotoxicity and bioavailability of nickel using speciation models.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXpt1aktro%3D&md5=d00846c17d906052aebc4950f23ccbc1CAS | 14740731PubMed |

[30]  L. T. C. Bonten, J. E. Groenenberg, L. P. Weng, W. H. Van Riemsdijk, Use of speciation and complexation models to estimate heavy metal sorption in soils. Geoderma 2008, 146, 303.
Use of speciation and complexation models to estimate heavy metal sorption in soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXpsVKqurw%3D&md5=fc25ea091f939d027838daad2dacb496CAS |

[31]  E. Tipping, Humic ion-binding model VI: an improved description of the interactions of protons and metal ions with humic substances. Aquat. Geochem. 1998, 4, 3.
Humic ion-binding model VI: an improved description of the interactions of protons and metal ions with humic substances.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXntlSjuro%3D&md5=cf0c6c40511e5000b173c62e5266b947CAS |

[32]  D. G. Kinniburgh, W. H. Van Riemsdijk, L. K. Koopal, M. Borkovec, M. F. Benedetti, M. J. Avena, Ion binding to natural organic matter: competition, heterogeneity, stoichiometry and thermodynamic consistency. Colloids Surf. A Physicochem. Eng. Asp. 1999, 151, 147.
Ion binding to natural organic matter: competition, heterogeneity, stoichiometry and thermodynamic consistency.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXhvV2ns7g%3D&md5=ece005c69fc7baa21a80e238cc1312daCAS |

[33]  C. J. Milne, D. G. Kinniburgh, E. Tipping, Generic NICA–Donnan model parameters far proton binding by humic substances. Environ. Sci. Technol. 2001, 35, 2049.
Generic NICA–Donnan model parameters far proton binding by humic substances.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXis1GrsLY%3D&md5=e2dcf5f560efcfa3a363bce0afeaeb37CAS | 11393987PubMed |

[34]  C. J. Milne, D. G. Kinniburgh, W. H. Van Riemsdijk, E. Tipping, Generic NICA–Donnan model parameters for metal-ion binding by humic substances. Environ. Sci. Technol. 2003, 37, 958.
Generic NICA–Donnan model parameters for metal-ion binding by humic substances.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXosVWgsQ%3D%3D&md5=2eda2310a7221ae42b73f399e3b9e8b5CAS | 12666927PubMed |

[35]  F. A. Vega, L. P. Weng, Speciation of heavy metals in River Rhine. Water Res. 2013, 47, 363.
Speciation of heavy metals in River Rhine.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38Xhs1Wms7jN&md5=1bb53324ffd089f0de07067438bbc156CAS | 23127623PubMed |

[36]  T. Hiemstra, W. H. Van Riemsdijk, A surface structural approach to ion adsorption: the charge distribution (CD) model. J. Colloid Interface Sci. 1996, 179, 488.
A surface structural approach to ion adsorption: the charge distribution (CD) model.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28XjtFOjur0%3D&md5=3068f658fd08e212a711fe0c6f659bd8CAS |

[37]  T. Hiemstra, W. H. Van Riemsdijk, Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides. J. Colloid Interface Sci. 1999, 210, 182.
Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXoslSrtA%3D%3D&md5=86d1069481664521e01fda95b573c859CAS | 9924122PubMed |

[38]  A. Violante, R. Ricciardella, M. Pigna, Adsorption of heavy metals on mixed Fe–Al oxides in the absence or presence of organic ligands. Water Air Soil Pollut. 2003, 145, 289.
Adsorption of heavy metals on mixed Fe–Al oxides in the absence or presence of organic ligands.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXjsFWitbs%3D&md5=fd974d904ef70f29451c0ae7fe315952CAS |

[39]  T. Hiemstra, J. Antelo, R. Rahnemaie, W. H. Van Riemsdijk, Nanoparticles in natural systems I: the effective reactive surface area of the natural oxide fraction in field samples. Geochim. Cosmochim. Acta 2010, 74, 41.
Nanoparticles in natural systems I: the effective reactive surface area of the natural oxide fraction in field samples.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXhsVCqsLzJ&md5=c5ba8d9acc3ca438ade128f72be3ddeeCAS |

[40]  O. Jacquat, A. Voegelin, A. Villard, M. A. Marcus, R. Kretzschmar, Formation of Zn-rich phyllosilicate, Zn-layered double hydroxide and hydrozincite in contaminated calcareous soils. Geochim. Cosmochim. Acta 2008, 72, 5037.
Formation of Zn-rich phyllosilicate, Zn-layered double hydroxide and hydrozincite in contaminated calcareous soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXhtFOjtbfL&md5=2d47a6f12bed0420231c9b34bebf8919CAS |

[41]  O. Jacquat, A. Voegelin, R. Kretzschmar, Soil properties controlling Zn speciation and fractionation in contaminated soils. Geochim. Cosmochim. Acta 2009, 73, 5256.
Soil properties controlling Zn speciation and fractionation in contaminated soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXpsFGmsL0%3D&md5=ed3e9a372c773712399f156fbd15b945CAS |

[42]  M. G. Keizer, W. H. Van Riemsdijk, ECOSAT: Equilibrium Calculation of Speciation and Transport; Manual Program 1994 (Agricultural University of Wageningen: Wageningen).

[43]  H. S. Harned, B. B. Owen, The Physical Chemistry of Electrolyte Solutions 1958 (Reinhold Book Corp: New York).

[44]  Z. Abbas, E. Ahlberg, S. Nordholm, From restricted towards realistic models of salt solutions: Corrected Debye–Huckel theory and Monte Carlo simulations. Fluid Phase Equilib. 2007, 260, 233.
From restricted towards realistic models of salt solutions: Corrected Debye–Huckel theory and Monte Carlo simulations.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXhtFGksbnP&md5=70977ff81e43b2a7b14329277a75cbfbCAS |

[45]  E. Tipping, J. Rieuwerts, G. Pan, M. R. Ashmore, S. Lofts, M. T. R. Hill, M. E. Farago, I. Thornton, The solid-solution partitioning of heavy metals (Cu, Zn, Cd, Pb) in upland soils of England and Wales. Environ. Pollut. 2003, 125, 213.
The solid-solution partitioning of heavy metals (Cu, Zn, Cd, Pb) in upland soils of England and Wales.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXksF2gsrw%3D&md5=87da10c3f40a03738a3613465a8ca129CAS | 12810315PubMed |

[46]  J. D. MacDonald, W. H. Hendershot, Modelling trace metal partitioning in forest floors of northern soils near metal smelters. Environ. Pollut. 2006, 143, 228.
Modelling trace metal partitioning in forest floors of northern soils near metal smelters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xks1Ols7w%3D&md5=32c0e0c205b43ad234efb35d9177aa23CAS | 16448733PubMed |

[47]  J. P. Gustafsson, C. Tiberg, A. Edkymish, D. B. Kleja, Modelling lead(II) sorption to ferrihydrite and soil organic matter. Environ. Chem. 2011, 8, 485.
Modelling lead(II) sorption to ferrihydrite and soil organic matter.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhtlykt73N&md5=e464383d4c0d55eea3b6429c564f51f0CAS |

[48]  S. Lofts, E. Tipping, Assessing WHAM/Model VII against field measurements of free metal ion concentrations: model performance and the role of uncertainty in parameters and inputs. Environ. Chem. 2011, 8, 501.
Assessing WHAM/Model VII against field measurements of free metal ion concentrations: model performance and the role of uncertainty in parameters and inputs.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhtlykt73J&md5=6d5203022a7c53649a5ef04da5785dcbCAS |

[49]  J. E. Groenenberg, G. F. Koopmans, R. N. J. Comans, Uncertainty analysis of the Nonideal Competitive Adsorption–Donnan model: effects of dissolved organic matter variability on predicted metal speciation in soil solution. Environ. Sci. Technol. 2010, 44, 1340.
Uncertainty analysis of the Nonideal Competitive Adsorption–Donnan model: effects of dissolved organic matter variability on predicted metal speciation in soil solution.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXnvVyh&md5=83e6aebafab2414378002f4cd40db980CAS | 20047312PubMed |

[50]  C. Hanahan, Dissolution of hydroxide minerals in the 1 M sodium acetate, pH 5, extracting solution in sequential extraction schemes. Environ Geol 2004, 45, 864.
Dissolution of hydroxide minerals in the 1 M sodium acetate, pH 5, extracting solution in sequential extraction schemes.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXislOhtLw%3D&md5=d84d95b07a9d047db3d535a94e72eb62CAS |