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Research article - Peer-reviewed, 2018

Metal sorption to Spodosol Bs horizons: Organic matter complexes predominate

Tiberg, Charlotta; Sjostedt, Carin; Gustafsson, Jon Petter


While metal sorption mechanisms have been studied extensively for soil surface horizons, little information exists for subsoils, for example Spodosol Bs horizons. Here the sorption of cadmium(10, copper(II) and lead(II) to seven Bs horizons from five sites was studied. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that cadmium(II) and lead(II) were bound as inner-sphere complexes to organic matter. Addition of o-phosphate (to 1 mu mol l(-1)) did not result in any significant enhancement of metal sorption, nor did it influence EXAFS speciation. An assemblage model using the SHM and CD-MUSIC models overestimated metal sorption for six out of seven soil samples. To agree with experimental results, substantial decreases (up to 8-fold) had to be made for the fraction 'active organic matter', f(Hs), while the point-of-zero charge (PZC) of ferrihydrite had to be increased. The largest decreases of f(HS) were found for the soils with the lowest ratio of pyrophosphate-to oxalate-extractable Al (Al-pyp/Al-ox), suggesting that in these soils, humic and fulvic acids were to a large extent inaccessible for metal sorption. The low reactivity of ferrihydrite towards lead(II) can be explained by potential spillover effects from co-existing allophane, but other factors such as ferrihydrite crystallisation could not be ruled out. In conclusion, organic matter was the predominant sorbent for cadmium(II), copper(II) and lead(II). However, for lead(II) the optimised model suggests additional, but minor, contributions from Fe (hydr) oxide surface complexes. These results will be important to correctly model metal sorption in spodic materials. (C) 2018 The Authors. Published by Elsevier Ltd.


Cadmium; Copper; Lead; Soil; EXAFS; Assemblage model

Published in

2018, volume: 196, pages: 556-565

Authors' information

Tiberg, Charlotta
Swedish University of Agricultural Sciences, Department of Soil and Environment
Tiberg, Charlotta
Swedish Geotechnical Institute (SGI)
Swedish University of Agricultural Sciences, Department of Soil and Environment
Swedish University of Agricultural Sciences, Department of Soil and Environment
Gustafsson, Jon Petter (Gustafsson, Jon-Petter)
Royal Institute of Technology (KTH)

UKÄ Subject classification

Soil Science

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