| 1. |
- Cao, Feifei, et al.
(author)
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Large-scale arsenic mobilization from legacy sources in anoxic aquifers : Multiple methods and multi-decadal perspectives
- 2023
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In: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 892
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Journal article (peer-reviewed)abstract
- While geogenic arsenic (As) contamination of aquifers have been intensively investigated across the world, the mobilization and transport of As from anthropogenic sources have received less scientific attention, despite emerging evidence of poor performance of widely used risk assessment models. In this study we hypothesize that such poor model performance is largely due to insufficient attention to heterogeneous subsurface properties, including the hydraulic conductivity K and the solid-liquid partition (Kd), as well as neglect of laboratory-to-field scaling effects. Our multi-method investigation includes i) inverse transport modelling, ii) in-situ measurements of As concentrations in paired samples of soil and groundwater, and iii) batch equilibrium experiments combined with (iv) geochemical modelling. As case study we use a unique 20-year series of spatially distributed monitoring data, capturing an expanding As plume in a Chromated Copper Arsenate (CCA)-contaminated anoxic aquifer in southern Sweden. The in-situ results showed a high variability in local Kd values of As (1 to 107 L kg−1), implying that over-reliance of data from only one or few locations can lead to interpretations that are inconsistent with field-scale As transport. However, the geometric mean of the local Kd values (14.4 L kg−1) showed high consistency with the independently estimated field-scale “effective Kd” derived from inverse transport modelling (13.6 L kg−1). This provides empirical evidence for the relevance of using geometric averaging when estimating large-scale “effective Kd” values from local measurements within highly heterogenous, isotropic aquifers. Overall, the considered As plume is prolonged by about 0.7 m year−1, now starting to extend beyond the borders of the industrial source area, a problem likely shared with many of the world's As-polluted sites. In this context, geochemical modelling assessments, as presented here, provided a unique understanding of the processes governing As retention, including local variability in, e.g., Fe/Al-(hydr)oxides contents, redox potential and pH.
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| 2. |
- Gustafsson, Jon Petter, 1964-, et al.
(author)
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Fosfors betydelse för metallers mobilitet i mark
- 2013
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Reports (other academic/artistic)abstract
- The aim with this project was to investigate the role of dissolved phosphate for the adsorption of lead(II), copper(II), cadmium(II) and uranium(VI) onto ferrihydrite and to soils. The methods involved batch studies, EXAFS spectroscopy, and equilibrium modelling. Phosphate was found to significantly enhance the adsorption of all investigated metals onto ferrihydrite. Results obtained so far show that the results are consistent with the formation of ternary surface complexes at low pH, but additional research is required to understand the processes in more detail. Similar enhancements were not observed in soil samples to which phosphate is added, and the reasons for this remain to be fully elucidated. In any case, this research shows that the presence of phosphate may restrict the mobility of many trace metals in environments that contain iron(III) (hydr)oxides.
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| 3. |
- Gustafsson, Jon Petter, et al.
(author)
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Modelling lead(II) sorption to ferrihydrite and soil organic matter
- 2011
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In: Environmental Chemistry. - : CSIRO Publishing. - 1448-2517 .- 1449-8979. ; 8:5, s. 485-492
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Journal article (peer-reviewed)abstract
- Lead(II) adsorption to soil organic matter and iron (hydr)oxides is strong, and may control the geochemical behaviour of this metal. Here, we report the adsorption of Pb(2+) (i) to 2-line ferrihydrite, and (ii) to a mor layer. The results showed that ferrihydrite has heterogeneous Pb(2+) binding. Use of a surface complexation model indicated that similar to 1% of the surface sites adsorbed Pb(2+) more strongly than the remaining 99 %. Although only one surface complexation reaction was used (a bidentate complex of the composition (equivalent to FeOH)(2)Pb(+)), three classes of sites with different affinity for Pb(2+) were needed to simulate Pb(2+) binding correctly over all Pb/Fe ratios analysed. For the mor layer, Pb(2+) sorption was much stronger than current models for organic complexation suggest. The results could be described by the Stockholm Humic Model when the binding heterogeneity was increased, and when it was assumed that 0.2% of the binding sites were specific for Pb. Use of revised model parameters for nine Vietnamese soils suggest that lead(II) binding was more correctly simulated than before. Thus, underestimation of lead(II) sorption to both (hydr) oxide surfaces and organic matter may explain the failure of previous geochemical modelling attempts for lead(II).
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| 4. |
- Gustafsson, Jon Petter, et al.
(author)
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Molybdenum binding to soil constituents in acid soils : An XAS and modelling study
- 2015
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In: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 417, s. 279-288
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Journal article (peer-reviewed)abstract
- Despite its importance as a trace element, the binding mechanisms of molybdenum in soils are not well known. In this study, we studied the binding of molybdenum onto selected soil samples, and we used X-ray absorption spectroscopy (XAS) to characterize the coordination of molybdenum on three important environmental sorbents: ferrihydrite (Fh), amorphous aluminium hydroxide (Al(OH)(3)) and fulvic acid. The X-ray near-edge structure (XANES) data showed that the added molybdenum(VI) was not reduced, although for the organic samples the coordination shifted from tetrahedral to octahedral. The EXAFS (extended X-ray absorption fine structure) analysis showed that molybdenum(VI) on Fh and Al(OH)(3) was dominated by edge-sharing bidentate complexes with Mo center dot center dot center dot Fe and Mo center dot center dot center dot Al distances of 2.80 and 2.62 angstrom, respectively. For ferrihydrite, there was a minor contribution from a corner-sharing bidentate complex at 3.55 angstrom. Further, geochemical modelling suggested an additional role of an outer-sphere complex at high pH. A sample from a spodic Bs horizon had XANES and EXAFS features similar to those of Mo sorbed to Al(OH)(3), highlighting the importance of Al(OH)(3)-type sorbents in this soil. However, in the studied organic samples molybdenum(VI) was present in a distorted octahedral configuration as an organic complex. The results were used to improve molybdenum binding reaction equilibrium constants in the CD-MUSIC model for ferrihydrite and in the Stockholm Humic Model. Collectively the results show that acid soils may contain sorbents able to bind molybdenum efficiently, and thus prevent its leaching to waters.
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| 5. |
- Gustafsson, Jon Petter, et al.
(author)
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Predicting sulphate adsorption/desorption in forest soils : Evaluation of an extended Freundlich equation
- 2015
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In: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 119, s. 83-89
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Journal article (peer-reviewed)abstract
- Sulphate adsorption and desorption can delay the response in soil acidity against changes in acid input. Here we evaluate the use of an extended Freundlich equation for predictions of pH-dependent SO4 adsorption and desorption in low-ionic strength soil systems. Five B horizons from Spodosols were subjected to batch equilibrations at low ionic strength at different pHs and dissolved SO4 concentrations. The proton coadsorption stoichiometry (eta), i.e. the number of H+ ions co-adsorbed for every adsorbed SO42- ion, was close to 2 in four of five soils. This enabled the use of a Freundlich equation that involved only two adjustable parameters (the Freundlich coefficient K-F and the non-ideality parameter m). With this model a satisfactory fit was obtained when only two data points were used for calibration. The root-mean square errors of log adsorbed SO4 ranged from 0.006 to 0.052. The model improves the possibility to consider SO4 adsorption/desorption processes correctly in dynamic soil chemistry models.
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| 6. |
- Rijk, Ingrid, 1985-, et al.
(author)
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Biochar and peat amendments affect nitrogen retention, microbial capacity and nitrogen cycling microbial communities in a metal and polycyclic aromatic hydrocarbon contaminated urban soil
- 2024
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In: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 936
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Journal article (peer-reviewed)abstract
- Soil contaminants may restrict soil functions. A promising soil remediation method is amendment with biochar, which has the potential to both adsorb contaminants and improve soil health. However, effects of biochar amendment on soil-plant nitrogen (N) dynamics and N cycling microbial guilds in contaminated soils are still poorly understood. Here, a metal- and polycyclic aromatic hydrocarbon (PAH) contaminated soil was amended with either biochar (0, 3, 6 % w/w) and/or peat (0, 1.5, 3 % w/w) in a full-factorial design and sown with perennial ryegrass in an outdoor field trial. After three months, N and the stable isotopic ratio δ15N was measured in soil, roots and leaves, along with microbial responses. Aboveground grass biomass decreased by 30 % and leaf N content by 20 % with biochar, while peat alone had no effect. Peat in particular, but also biochar, stimulated the abundance of microorganisms (measured as 16S rRNA gene copy number) and basal respiration. Microbial substrate utilization (MicroResp™) was altered differentially, as peat increased respiration of all carbon sources, while for biochar, respiration of carboxylic acids increased, sugars decreased, and was unaffected for amino acids. Biochar increased the abundance of ammonia oxidizing archaea, while peat stimulated ammonia oxidizing bacteria, Nitrobacter-type nitrite oxidizers and comB-type complete ammonia oxidizers. Biochar and peat also increased nitrous oxide reducing communities (nosZI and nosZII), while peat alone or combined with biochar also increased abundance of nirK-type denitrifiers. However, biochar and peat lowered leaf δ15N by 2-4 ‰, indicating that processes causing gaseous N losses, like denitrification and ammonia volatilization, were reduced compared to the untreated contaminated soil, probably an effect of biotic N immobilization. Overall, this study shows that in addition to contaminant stabilization, amendment with biochar and peat can increase N retention while improving microbial capacity to perform important soil functions.
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| 7. |
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| 8. |
- Tiberg, Charlotta, et al.
(author)
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Evaluating solubility of Zn, Pb, Cu and Cd in pyrite cinder using leaching tests and geochemical modelling
- 2017
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In: Applied Geochemistry. - : Elsevier BV. - 0883-2927. ; 85, s. 106-117
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Journal article (peer-reviewed)abstract
- Production of sulfuric acid by roasting of pyrite (Fe sulfide) produces a Fe rich waste product, pyrite cinder (or pyrite ash), which often contains high levels of trace metals such as Zn and Pb. The chemical forms of the metals and their solubility in these materials are poorly known. To evaluate the risks associated with pyrite cinder and manage cinder contaminated sites efficiently more knowledge on the chemical processes in pyrite cinder is needed. In this study the solubility of Zn, Pb, Cu and Cd in a pyrite cinder from Bergvik, Sweden, was investigated. The objectives were to (i) identify the solubility controlling processes for Zn, Pb, Cu, and Cd in the pH range 3-9, (ii) characterize the Fe (hydr) oxides present in these materials and (iii) to identify implications for management strategies of pyrite cinder contaminated sites. This was done using a combination of batch experiments, selective extractions, X-ray absorption spectroscopy and geochemical modelling. Hematite was identified as the dominating Fe mineral in the cinder. A geochemical model using generic binding parameters could describe the solubility of Zn, Cu and Cd in the cinder well, while Pb concentrations were generally underestimated. The modelling indicated that adsorption to Fe (hydr) oxides was the most important solubility controlling mechanism for all metals, except for Zn at pH > 6, where Zn minerals seemed to control the concentrations of Zn. To minimize leaching of Zn, Pb, Cu and Cd from cinder materials, remediation strategies should be focused on keeping the pH > 6. (C) 2017 The Authors. Published by Elsevier Ltd.
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| 9. |
- Tiberg, Charlotta, et al.
(author)
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Immobilization of Cu and As in two contaminated soils with zero-valent iron - Long-term performance and mechanisms
- 2016
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In: Applied Geochemistry. - : Elsevier. - 0883-2927 .- 1872-9134. ; 67, s. 144-152
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Journal article (peer-reviewed)abstract
- Immobilization of trace elements in contaminated soils by zero-valent iron (ZVI) is a promising remediation method, but questions about its long-term performance remain unanswered. To quantify immobilization and predict possible contaminant remobilization on long timescales detailed knowledge about immobilization mechanisms is needed. This study aimed at assessing the long-term effect of ZVI amendments on dissolved copper and arsenic in contaminated soils, at exploring the immobilization mechanism(s), and at setting up a geochemical model able to estimate dissolved copper and arsenic under different scenarios. Samples from untreated and ZVI-treated plots in two field experiments where ZVI had been added 6 and 15 years ago were investigated by a combination of batch experiments, geochemical modeling and extended X-ray absorption fine structure (EXAFS) spectroscopy. Dissolved copper and arsenic concentrations were described by a multisurface geochemical model with surface complexation reactions, verified by EXAFS. The ZVI remained "reactive" after 6-15 years, i. e. the dissolved concentrations of copper and arsenic were lower in the ZVI-treated than in the untreated soils. There was a shift in copper speciation from organic matter complexes in the untreated soil to surface complexes with iron (hydr)oxides in the ZVI-treated soil. The pH value was important for copper immobilization and ZVI did not have a stabilizing effect if pH was lower than about 6. Immobilization of arsenic was slightly pH-dependent and sensitive to the competition with phosphate. If phosphate was ignored in the modeling, the dissolution of arsenate was greatly underestimated. (C) 2016 Elsevier Ltd. All rights reserved.
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| 10. |
- Tiberg, Charlotta
(author)
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Metal sorption to ferrihydrite : phosphate effects, X-ray absorption spectroscopy and surface complexation modelling
- 2016
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Doctoral thesis (other academic/artistic)abstract
- Phosphorus affects the sorption of many metals and arsenate to iron (hydr)oxides. This may influence the mobility and bioavailability of metals and arsenate. Phosphorus therefore plays an important role in, e.g., determining the ecotoxicological risk of contaminants in soils. The overall aim of this thesis was to improve the understanding of lead(II), copper(II), cadmium(II) and arsenate binding to iron (hydr)oxides. The focus was on how phosphate affects the sorption on ferrihydrite and soils in which ferrihydrite is an important constituent. The effect of phosphate on the sorption of lead(II), copper(II), cadmium(II) and arsenate was determined by batch experiments. X-ray absorption spectroscopy (XAS) was performed to identify the binding mechanisms. Geochemical models were developed based on the XAS results and knowledge about the mineral or soil properties. Phosphate enhanced the sorption of lead(II), copper(II) and cadmium(II) to ferrihydrite. The increased sorption was best explained by the formation of ternary complexes including the ferrihydrite surface, the metal and the phosphate ion. Phosphate competed strongly with arsenate for sorption sites on ferrihydrite. The competition was even stronger on poorly crystalline aluminium hydroxide. Zero-valent iron that is mixed into soil rapidly oxidises to ferrihydrite that can adsorb contaminants. It was shown that the immobilisation of copper and arsenic in soils that had been stabilised by zero-valent iron is long-lasting. Copper immobilisation was most effective at high pH (>6) and at low organic matter content. Competition with phosphate needs to be taken into account when modelling arsenate sorption in soils. Otherwise the latter may be greatly overestimated. Metal sorption to some podzolised soils was investigated in batch experiments. Despite the large influence on metal sorption in the pure ferrihydrite systems the addition of phosphate did not affect lead(II), copper(II) or cadmium(II) sorption to the B and C horizons of podzolised soils. The reasons may be strong metal binding to organic matter combined with a relatively small addition of phosphorus in the experiments. In conclusion this thesis shows that phosphate greatly affects the sorption of lead(II), copper(II), cadmium(II) and arsenate to iron (hydr)oxides. To determine the impact of this effect in more complex matrices such as soils, more research is needed.
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