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Predicting trace metal solubility and fractionation in urban soils from isotopic exchangeability

Mao, L.C.; Young, S.D.; Tye, A.M.; Bailey, E.H.


L.C. Mao

S.D. Young

A.M. Tye

Professor of Environmental Geochemistry


Metal-salt amended soils (MA, n = 23), and historically-contaminated urban soils from two English cities (Urban, n = 50), were investigated to assess the effects of soil properties and contaminant source on metal lability and solubility. A stable isotope dilution method, with and without a resin purification step, was used to measure the lability of Cd, Cu, Ni, Pb and Zn. For all five metals in MA soils, lability (%E-values) could be reasonably well predicted from soil pH value with a simple logistic equation. However, there was evidence of continuing time-dependent fixation of Cd and Zn in the MA soils, following more than a decade of storage under air-dried conditions, mainly in high pH soils. All five metals in MA soils remained much more labile than in Urban soils, strongly indicating an effect of contaminant source on metal lability in the latter. Metal solubility was predicted for both sets of soil by the geochemical speciation model WHAM-VII, using E-values as an input variable. For soils with low metal solution concentrations, over-estimation of Cd, Ni and Zn solubility was associated with binding to the Fe oxide fraction while accurate prediction of Cu solubility was dependent on humic acid content. Lead solubility was most poorly described, especially in the Urban soils. Generally, slightly poorer estimation of metal solubility was observed in Urban soils, possibly due to a greater incidence of high pH values. The use of isotopically exchangeable metal to predict solubility is appropriate both for historically contaminated soils and where amendment with soluble forms of metal is used, as in toxicological trials. However, the major limitation to predicting solubility may lie with the accuracy of model input variables such as humic acid and Fe oxide contents where there is often a reliance on relatively crude analytical estimations of these variables.


Mao, L., Young, S., Tye, A., & Bailey, E. (in press). Predicting trace metal solubility and fractionation in urban soils from isotopic exchangeability. Environmental Pollution,

Journal Article Type Article
Acceptance Date Sep 6, 2017
Online Publication Date Sep 22, 2017
Deposit Date Oct 6, 2017
Publicly Available Date Sep 23, 2018
Journal Environmental Pollution
Print ISSN 0269-7491
Electronic ISSN 1873-6424
Publisher Elsevier
Peer Reviewed Peer Reviewed
Public URL
Publisher URL


Mao et al EP 2017.pdf (1.5 Mb)

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