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18 pages, 2422 KiB

Open AccessArticle

Microbial Population Dynamics and the Role of Sulfate Reducing Bacteria Genes in Stabilizing Pb, Zn, and Cd in the Terrestrial Subsurface

by Ranju R. Karna, Ganga M. Hettiarachchi, Joy Van Nostrand, Tong Yuan, Charles W. Rice, Yared Assefa and Jizhong Zhou

Soil Syst. 2018, 2(4), 60; https://doi.org/10.3390/soilsystems2040060 - 3 Nov 2018

Cited by 4 | Viewed by 3113

Abstract

Milling and mining metal ores are major sources of toxic metals contamination. The Spring River and its tributaries in southeast Kansas are contaminated with Pb, Zn, and Cd because of 120 years of mining activities. Trace metal transformations and cycling in mine waste [...] Read more.

Milling and mining metal ores are major sources of toxic metals contamination. The Spring River and its tributaries in southeast Kansas are contaminated with Pb, Zn, and Cd because of 120 years of mining activities. Trace metal transformations and cycling in mine waste materials greatly influence their mobility and toxicity and they affect both plant productivity and human health. It has been hypothesized that under reduced conditions in sulfate-rich environments, these metals can be transformed into their sulfide forms, thus limiting mobility and toxicity. We studied biogeochemical transformations of Pb, Zn, and Cd in flooded subsurface mine waste materials, natural or treated with organic carbon (OC), and/or sulfur (S), by combining advanced microbiological and X-ray spectroscopic techniques to determine the effects of treatments on the microbial community structure and identify the dominant functional genes that are involved in the biogeochemical transformations, especially metal sulfide formation over time. Samples collected from medium-, and long-term submerged columns were used for microarray analysis via functional gene array (GeoChip 4.2). The total number of detected gene abundance decreased under long-term submergence, but major functional genes abundance was enhanced with OC-plus-S treatment. The microbial community exhibited a substantial change in structure in response to OC and S addition. Sulfate-reducing bacteria genes dsrA/B were identified as key players in metal sulfide formation via dissimilatory sulfate reduction. Uniqueness of this study is that microbial analyses presented here in detail are in agreement with molecular-scale synchrotron-based X-ray data, supporting that OC-plus-S treatment would be a promising strategy for reducing metal toxicity in mine waste materials in the subsurface environment. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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19 pages, 2362 KiB

Open AccessArticle

Sources and Pathways of Formation of Recalcitrant and Residual Phosphorus in an Agricultural Soil

by Sunendra R. Joshi, Wei Li, Mark Bowden and Deb P. Jaisi

Soil Syst. 2018, 2(3), 45; https://doi.org/10.3390/soilsystems2030045 - 1 Aug 2018

Cited by 20 | Viewed by 4746

Abstract

Phosphorus (P) is an essential nutrient for sustaining life and agricultural production. Transformation of readily available P into forms that are unavailable to plants adds costs to P replenishment, which eventually translates into lower agronomic benefits and potential loss of soil P into [...] Read more.

Phosphorus (P) is an essential nutrient for sustaining life and agricultural production. Transformation of readily available P into forms that are unavailable to plants adds costs to P replenishment, which eventually translates into lower agronomic benefits and potential loss of soil P into runoff may degrade water quality. Therefore, understanding the sources and pathways of the formation of residual P pools in soils is useful information needed for the development of any technological or management efforts to minimize or inhibit the formation of such P pool and thus maximize availability to plants. In this research, we paired phosphate oxygen isotope ratios (δ¹⁸O_P) with solid-state ³¹P NMR and quantitative XRD techniques along with general soil chemistry methods to identify the precipitation pathways of acid-extracted inorganic P (P_i) pools in an agricultural soil. Based on the comparison of isotope values of 0.5 mol L⁻¹ NaOH-P_i, 1 mol L⁻¹ HCl-P_i, and 10 mol L⁻¹ HNO₃-P_i pools and correlations of associated elements (Ca, Fe, and Al) in these pools, the HNO₃-P_i pool appears most likely to be transformed from the NaOH-P_i pool. A narrow range of isotope values of acid-P_i pools in shallow (tilling depth) and below (where physical mixing is absent) is intriguing but likely suggests leaching of particle-bound P in deeper soils. Overall, these findings provide an improved understanding of the sources, transport, and transformation of acid-P_i pools in agricultural soils and further insights into the buildup of legacy P in soils. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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22 pages, 1962 KiB

Open AccessFeature PaperArticle

Speciation and Mobility of Mercury in Soils Contaminated by Legacy Emissions from a Chemical Factory in the Rhône Valley in Canton of Valais, Switzerland

by Robin Sue Gilli, Claudine Karlen, Mischa Weber, Johanna Rüegg, Kurt Barmettler, Harald Biester, Pascal Boivin and Ruben Kretzschmar

Soil Syst. 2018, 2(3), 44; https://doi.org/10.3390/soilsystems2030044 - 30 Jul 2018

Cited by 27 | Viewed by 5752

Abstract

Legacy contamination of soils and sediments with mercury (Hg) can pose serious threats to the environment and to human health. Assessing risks and possible remediation strategies must consider the chemical forms of Hg, as different Hg species exhibit vastly different environmental behaviors and [...] Read more.

Legacy contamination of soils and sediments with mercury (Hg) can pose serious threats to the environment and to human health. Assessing risks and possible remediation strategies must consider the chemical forms of Hg, as different Hg species exhibit vastly different environmental behaviors and toxicities. Here, we present a study on Hg speciation and potential mobility in sediments from a chemical factory site, and soils from nearby settlement areas in the canton of Valais, Switzerland. Total Hg ranged from 0.5 to 28.4 mg/kg in the soils, and 3.5 to 174.7 mg/kg in the sediments, respectively. Elemental Hg(0) was not detectable in the soils by thermal desorption analysis. Methylmercury, the most toxic form of Hg, was present at low levels in all soils (<0.010 mg/kg; <0.8% of total Hg). Sequential extractions and thermal desorption analyses suggested that most of the Hg in the soils was present as “matrix-bound Hg(II)”, most likely associated with soil organic matter. For factory sediments, which contained less organic matter, the results suggested a higher fraction of sulfide-bound Hg. Batch extractions in different CaCl₂ solutions revealed that Hg solubility was low overall, and there was no Hg-mobilizing effects of Ca²⁺ or Cl⁻ in solution. Only in some of the factory sediments did high CaCl₂ concentrations result in increased extractability of Hg, due to the formation of Hg-chloride complexes. Additional experiments with soil redox reactors showed that even mildly reducing conditions led to a sharp release of Hg into solution, which may be highly relevant in soils that are prone to periodic water saturation of flooding. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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17 pages, 1434 KiB

Open AccessArticle

Release and Biomethylation of Antimony in Shooting Range Soils upon Flooding

by Matthias Grob, Wolfgang Wilcke and Adrien Mestrot

Soil Syst. 2018, 2(2), 34; https://doi.org/10.3390/soilsystems2020034 - 5 Jun 2018

Cited by 22 | Viewed by 4823

Abstract

Antimony (Sb) is an understudied pollutant with potentially toxic effects at particularly low concentrations. The fate of Sb in the environment is complicated because of its many chemical forms at varying oxidation states. Here, we validated an extraction method and an analytical technique [...] Read more.

Antimony (Sb) is an understudied pollutant with potentially toxic effects at particularly low concentrations. The fate of Sb in the environment is complicated because of its many chemical forms at varying oxidation states. Here, we validated an extraction method and an analytical technique to quantify inorganic and methylated Sb in bulk soil and soil solution. We identified and quantified trimethylantimony (TMSb) in shooting range soils for the first time, up to a concentration of 1.35 mg kg⁻¹. Then, we evaluated the release of Sb species from soil to soil solution as well as the influence of manure addition upon flooding in an incubation experiment with fresh soils from shooting ranges. This incubation experiment showed an immediate and exhaustive Sb release into the soil solution (within 6 h), reaching over 3000 μg L⁻¹ for one site, followed by a sharp decline and again a slow increase at the end of the incubation in Sb concentrations in the soil solution for two of the three sites. TMSb was also formed in the soil solution after 4 to 10 days. High dissolved organic carbon (DOC) concentrations and the dissolution of Fe- and Mn-(oxy-)hydroxides were the main drivers of Sb release, while the addition of organic matter (OM) drove TMSb formation. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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14 pages, 1963 KiB

Open AccessArticle

Deciphering and Predicting Microscale Controls on Radon Production in Soils, Sediments and Rock

by Neha Mehta and Benjamin D. Kocar

Soil Syst. 2018, 2(2), 30; https://doi.org/10.3390/soilsystems2020030 - 9 May 2018

Cited by 8 | Viewed by 3632

Abstract

Soils, sediments and rock are natural sources of radon (Rn), which poses an ongoing threat to human health. Numerous studies have measured Rn release from bulk earth materials, yet few have examined microscale controls on Rn flux from solids (emanation), which is required [...] Read more.

Soils, sediments and rock are natural sources of radon (Rn), which poses an ongoing threat to human health. Numerous studies have measured Rn release from bulk earth materials, yet few have examined microscale controls on Rn flux from solids (emanation), which is required to develop a process-based framework for predicting the rate and extent of production. Here, we use a novel closed loop flow-through system to measure Rn emanation from two crushed rock types with disparate physical and geochemical characteristics, shale and granitic pegmatite. We relate the extent of Rn emanation from each sample to microscale characteristics examined using conventional and synchrotron-based techniques, such as Rn parent radionuclide distribution within mineral grains, porosity, and surface area. Our results illustrate that the extent of Rn release from solids is primarily dependent on the position of parent radionuclides within host mineral grains relative to the “recoil range”—the maximum distance a daughter product (such as Rn) may traverse within a solid and into an adjacent pore owing to alpha-recoil—and is less dependent on the bulk parent radionuclide (e.g., radium) activity. We also present a simple model for predicting the emanation coefficient for pure solids based on mineralogical and physical parameters, which is an initial step toward developing a framework for predicting Rn efflux (exhalation) from soils. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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13 pages, 596 KiB

Open AccessArticle

Arsenic Speciation of Contaminated Soils/Solid Wastes and Relative Oral Bioavailability in Swine and Mice

by Brooke N. Stevens, Aaron R. Betts, Bradley W. Miller, Kirk G. Scheckel, Richard H. Anderson, Karen D. Bradham, Stan W. Casteel, David J. Thomas and Nicholas T. Basta

Soil Syst. 2018, 2(2), 27; https://doi.org/10.3390/soilsystems2020027 - 1 May 2018

Cited by 20 | Viewed by 3969

Abstract

Arsenic (As) is one of the most widespread, toxic elements in the environment, and human activities have resulted in a large number of contaminated areas. However abundant, the potential of As toxicity from exposure to contaminated soils is limited to the fraction that [...] Read more.

Arsenic (As) is one of the most widespread, toxic elements in the environment, and human activities have resulted in a large number of contaminated areas. However abundant, the potential of As toxicity from exposure to contaminated soils is limited to the fraction that will dissolve in the gastrointestinal system and be absorbed into systemic circulation or bioavailable species. In part, the release of As from contaminated soil to gastrointestinal fluid depends on the form of solid phase As, also termed “As speciation”. In this study, 27 As-contaminated soils and solid wastes were analyzed using X-ray absorption spectroscopy (XAS) and results were compared to in vivo bioavailability values determined using the adult mouse and juvenile swine bioassays. Arsenic bioavailability was lowest for soils that contained large amounts of arsenopyrite and highest for materials that contained large amounts of ferric arsenates. Soil and solid waste type and properties rather than the contamination source had the greatest influence on As speciation. Principal component analysis determined that As(V) adsorbed and ferric arsenates were the dominant species that control As speciation in the selected materials. Multiple linear regression (MLR) was used to determine the ability of As speciation to predict bioavailability. Arsenic speciation was predictive of 27% and 16% of Relative Bioavailable (RBA) As determined using the juvenile swine and adult mouse models, respectively. Arsenic speciation can provide a conservative estimate of RBA As using MLR for the juvenile swine and adult mouse bioassays at 55% and 53%, respectively. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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20 pages, 3621 KiB

Open AccessArticle

Centennial Fertilization-Induced Soil Processes Control Trace Metal Dynamics. Lessons from a Long-Term Bare Fallow Experiment

by Folkert Van Oort, Remigio Paradelo, Nicolas Proix, Ghislaine Delarue, Denis Baize and Fabrice Monna

Soil Syst. 2018, 2(2), 23; https://doi.org/10.3390/soilsystems2020023 - 19 Apr 2018

Cited by 8 | Viewed by 3844

Abstract

Long-term bare fallow (LTBF) experiments with historical sample archives offer unique opportunities to study long-term impacts of anthropogenic activities on mineral soil fractions. In natural agro- and ecosystems, such impacts are often masked by organic matter due to its buffering action and rapid [...] Read more.

Long-term bare fallow (LTBF) experiments with historical sample archives offer unique opportunities to study long-term impacts of anthropogenic activities on mineral soil fractions. In natural agro- and ecosystems, such impacts are often masked by organic matter due to its buffering action and rapid turnover. The 42-plot LTBF trial of INRA (Institut National de la Recherche Agronomique) started in Versailles (France) in 1928 to assess the impacts of prolonged application of fertilizers and amendments on the composition and properties of loamy soils. Here, we established geochemical budgets of major and trace elements on surface samples from 1929 and 2014 for four groups of treatments relevant for developed soil processes. We considered accompanying effects of soil compaction or decompaction due to changing physicochemical conditions over 85 years. Element losses from the surface horizon were quantified via fertilization-induced or -amplified soil processes: clay leaching favored by Na- or K-based fertilization, and lixiviation of major and trace elements in acidic or alkaline soil conditions. Enhanced mineral weathering was shown for acidified and nonamended plots. Conclusions on trace metal migration were confirmed by selected analyses on subsurface horizons. Additional information was provided on specific element inputs via fertilizers and/or diffuse inputs via atmospheric deposition. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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19 pages, 4462 KiB

Open AccessArticle

Point of Zero Charge: Role in Pyromorphite Formation and Bioaccessibility of Lead and Arsenic in Phosphate-Amended Soils

by Ranju R. Karna, Matthew R. Noerpel, Todd P. Luxton and Kirk G. Scheckel

Soil Syst. 2018, 2(2), 22; https://doi.org/10.3390/soilsystems2020022 - 14 Apr 2018

Cited by 24 | Viewed by 5892

Abstract

Soluble lead (Pb) can be immobilized in pure systems as pyromorphite through the addition of phosphorus (P) sources; however, uncertainties remain in natural systems. Knowledge of point zero charge (PZC) is important to predict the ionization of functional groups and their interaction with [...] Read more.

Soluble lead (Pb) can be immobilized in pure systems as pyromorphite through the addition of phosphorus (P) sources; however, uncertainties remain in natural systems. Knowledge of point zero charge (PZC) is important to predict the ionization of functional groups and their interaction with metal species in solution. This study utilized Pb- and As-contaminated soils to determine the combined effect of pH with respect to PZC and different rates of P-application on pyromorphite formation as well as Pb and arsenic (As) bioaccessibility as impacted by speciation changes. Solution chemistry analysis along with synchrotron-based Pb- and As-speciation as well as bioaccessibility treatment effect ratios (TERs) were conducted. Results indicated no significant effect of PZC on pyromorphite formation in P-amended soils; however, the TER_Pb appeared significantly lower at pH > pH_PZC and higher at pH < pH_PZC (α = 0.05). In contrast, the TER_As was significantly higher at pH > pH_PZC compared to the other two treatments for the tested soils. The lack of conversion of soil Pb to pyromorphite may be attributed to several reasons including the presence of highly stable minerals, such as plumbojarosite, limiting soluble Pb availability to react with phosphates, high Fe and S content in IKS, high organic matter in BO, and high Ca content in NW. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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15 pages, 2909 KiB

Open AccessArticle

A Comparison of the Solubility Products of Layered Me(II)–Al(III) Hydroxides Based on Sorption Studies with Ni(II), Zn(II), Co(II), Fe(II), and Mn(II)

by Lasita Bhattacharya and Evert J. Elzinga

Soil Syst. 2018, 2(2), 20; https://doi.org/10.3390/soilsystems2020020 - 10 Apr 2018

Cited by 22 | Viewed by 5806

Abstract

The precipitation of mixed metal–aluminum-layered double hydroxides (Me(II)–Al(III)-LDH)) may be an important control of the solubility of Mn(II), Fe(II), Ni(II), Zn(II), and Co(II) in soils, but assessment of this process is hindered by a lack of thermodynamic data. Here, we determined the solubility [...] Read more.

The precipitation of mixed metal–aluminum-layered double hydroxides (Me(II)–Al(III)-LDH)) may be an important control of the solubility of Mn(II), Fe(II), Ni(II), Zn(II), and Co(II) in soils, but assessment of this process is hindered by a lack of thermodynamic data. Here, we determined the solubility products (Ksp) of the Me(II)–Al(III)-LDHs formed by these metals based on long-term Me(II)–γAl₂O₃ sorption studies complemented with X-ray absorption spectroscopy (XAS) measurements. The LDH phases had the chemical formula Me(II)_2/3Al_1/3(OH)₂Cl_1/3. Solubility products were derived as Ksp = (Me²⁺)_aq^2/3(Al³⁺)_aq^1/3(OH⁻)_aq²(Cl⁻)_aq^1/3, where brackets represent aqueous activity values determined from the equilibrium solution chemistry of the sorption samples. The Ksps are metal-dependent, with values increasing by two orders of magnitude in the order Ni(II) < Zn(II) < Co(II) < Fe(II) < Mn(II). Comparison to the solubility of β-Me(OH)₂ suggests considerable thermodynamic preference of Me(II)–Al(III)-LDH over β-Me(OH)₂ in soil environments and reveals a linear relation between the log-transformed Ksp values of Me(II)–Al(III)-LDH and β-Me(OH)₂. Solubility plots suggest that Ni(II)–, Zn(II)–, and Co(II)–Al(III)-LDH may form in metal-polluted soils. Fe(II)–Al(III)-LDH may occur in riparian soils undergoing reduction, but precipitation of Mn(II)–Al(III)-LDH appears unlikely as it requires [Mn²⁺]_aq much higher than commonly encountered in reducing soils. Additional thermodynamic and field studies are needed to further assess the importance of Me(II)–Al(III)-LDHs in soils and related geochemical systems. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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13 pages, 2563 KiB

Open AccessArticle

Zinc Presence during Mineral Formation Affects the Sorptive Reactivity of Manganese Oxide

by Shiliang Zhao, Chenning Li, Pan Liu, Rixiang Huang, Emily M. Saad and Yuanzhi Tang

Soil Syst. 2018, 2(2), 19; https://doi.org/10.3390/soilsystems2020019 - 2 Apr 2018

Cited by 6 | Viewed by 3261

Abstract

The sorptive reactivity of layered manganese (Mn) oxides is controlled by their layer and interlayer structure, which can be affected by processes such as metal coprecipitation. This study investigated the effects of Zn coprecipitation on the sorptive reactivity of δ-MnO₂, a [...] Read more.

The sorptive reactivity of layered manganese (Mn) oxides is controlled by their layer and interlayer structure, which can be affected by processes such as metal coprecipitation. This study investigated the effects of Zn coprecipitation on the sorptive reactivity of δ-MnO₂, a common layered Mn oxide mineral. Selected cation (i.e., Cd) and anion (i.e., phosphate and arsenate) species were used to probe the changes in δ-MnO₂ sorptive reactivity. Cd uptake by δ-MnO₂ was suppressed by Zn coprecipitation but total metal uptake (Cd and Zn) was enhanced, indicating more available vacancy sites (e.g., smaller particle size and higher vacancy site density) in Zn-coprecipitated δ-MnO₂. Phosphate and arsenate sorption on δ-MnO₂ was significantly enhanced by Zn-coprecipitation, and the enhancement was more effective compared to Zn sorption on pure δ-MnO₂. X-ray diffraction and X-ray adsorption spectroscopy analysis did not detect the formation of surface precipitations and/or ternary complexes. The enhanced anion sorption on Zn-coprecipitated δ-MnO₂ was likely due to the compensation of negative surface charge by sorbed Zn, as well as the structural modifications introduced by Zn coprecipitation. Results from this study can provide a better understanding on the interactions between metal-coprecipitated Mn oxides and other species in natural environments. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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21 pages, 19841 KiB

Open AccessArticle

Cu, Pb, and Zn Sorption to Biogenic Iron (Oxyhydr)Oxides Formed in Circumneutral Environments

by Andrew H. Whitaker and Owen W. Duckworth

Soil Syst. 2018, 2(2), 18; https://doi.org/10.3390/soilsystems2020018 - 31 Mar 2018

Cited by 17 | Viewed by 5335

Abstract

The transportation and immobilization of potentially toxic metals in near-surface environments may be partially controlled by sorption processes at the solid-water interface. Myriad studies have shown that iron (oxyhydr)oxides have large sorption capacities and form strong surface complexes with metal ions. Biogenic iron [...] Read more.

The transportation and immobilization of potentially toxic metals in near-surface environments may be partially controlled by sorption processes at the solid-water interface. Myriad studies have shown that iron (oxyhydr)oxides have large sorption capacities and form strong surface complexes with metal ions. Biogenic iron (oxyhydr)oxides (BIOS) form at redox gradients where dissolved ferrous iron encounters oxygenated conditions, allowing bacteria to outcompete abiotic Fe oxidation. This process produces biominerals with distinct surface and structural properties (incorporation of cell-derived organic matter, poor crystallinity, and small particle sizes) that may alter their metal-binding affinity and sorption processes. To better understand metal binding by BIOS, Cu, Pb, and Zn, sorption rate and isotherm studies were conducted with synthetic two-line ferrihydrite and BIOS. Additionally, X-ray absorption spectroscopy and total scattering were used to elucidate the BIOS mineral structure and metal ion surface structures. On a mass normalization basis, BIOS sorbed approximately 8, 4, and 2 times more Cu, Pb, and Zn, respectively, than 2LFh over similar dissolved concentrations. Spectroscopic analyses revealed poorly crystalline structures and small coherent scattering domain sizes for BIOS. Additionally, extended X-ray absorption fine-structure spectroscopy revealed Cu, Pb, and Zn sorbed to BIOS via inner-sphere complexes, similar to 2LFh. These results suggest that, in metal contaminated environments, BIOS are more efficient in metal binding than their synthetic counterparts. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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22 pages, 10268 KiB

Open AccessArticle

Soil Processes, Pedofeatures and Microscale Metal Distributions: Relevant Study of Contaminant-Dynamics Calls for Pedology-Based Soil-Depth Sampling Strategies

by Folkert Van OORT, Eddy Foy, Jérôme Labanowski, Sophie Leguédois and Toine Jongmans

Soil Syst. 2018, 2(1), 17; https://doi.org/10.3390/soilsystems2010017 - 14 Mar 2018

Cited by 4 | Viewed by 4689

Abstract

Short-term variations of soil conditions affect the form, mobility and bioavailability of metal pollutants. Released metals migrate toward depth where they are intercepted or precipitate, leading to variable spatial metal distribution patterns, at a macro-, meso- and microscale. Studies at a mesoscale give [...] Read more.

Short-term variations of soil conditions affect the form, mobility and bioavailability of metal pollutants. Released metals migrate toward depth where they are intercepted or precipitate, leading to variable spatial metal distribution patterns, at a macro-, meso- and microscale. Studies at a mesoscale give access to trace metal (TM) associations induced by pedological processes. Although scarcely documented, such meso-scale studies represent an essential step for relevant environmental risk assessment, halfway between field- and molecular-scale investigations. We argued for such approach by performing optical microscopy and micro-X-ray fluorescence on thin sections from two soils, contaminated either by industrial zinc-smelter waste or by urban wastewater. Consistent correlation between key indicators of pedological processes (Fe, Mn, and Ca) and trace metals (Zn, Pb, and Cu) on some 20 elemental maps of TM-hosting soil constituents and pedofeatures reveal distinct coinciding localizations, illustrating TM-accumulation via interception or (co)-precipitation processes. Micromorphological interpretation of characteristic pedofeatures in subsurface horizons (crystals, argillans, ferrans, and mangans) containing significant amounts of TM provide valuable insight into the contaminant dynamics in terms of lixiviation, colloidal transport, redox conditions, or fungal activity. Our mesoscale approach stresses the importance of pedology-based sampling strategies, instead of systematic soil-depth sampling, for soil contamination research in natural ecosystems. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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15 pages, 1734 KiB

Open AccessArticle

Influence of Soil Moisture Status on Soil Cadmium Phytoavailability and Accumulation in Plantain (Plantago lanceolata)

by Aaron Stafford, Paramsothy Jeyakumar, Michael Hedley and Christopher Anderson

Soil Syst. 2018, 2(1), 9; https://doi.org/10.3390/soils2010009 - 12 Feb 2018

Cited by 16 | Viewed by 4757

Abstract

The effect of fluctuating soil moisture cycles on soil cadmium (Cd) phytoavailability was investigated in a pot trial with two contrasting soils (Kereone (Allophanic), total Cd 0.79 mg kg⁻¹; and Topehaehae (Gley), total Cd 0.61 mg kg⁻¹) that were [...] Read more.

The effect of fluctuating soil moisture cycles on soil cadmium (Cd) phytoavailability was investigated in a pot trial with two contrasting soils (Kereone (Allophanic), total Cd 0.79 mg kg⁻¹; and Topehaehae (Gley), total Cd 0.61 mg kg⁻¹) that were either sown with plantain (Plantago lanceolata) or left unseeded. Varying soil moisture contents were established using contrasting irrigation regimes: “flooded” (3 days flooded and then 11 days drained); or “non-flooded” (irrigation to 70% of potted field capacity every 7 days). Overall, there was no significant difference in mean 0.05 M CaCl₂ soil extractable Cd concentrations or plant tissue Cd concentrations between flooded and non-flooded irrigation. However, there was a consistent trend for an increase in soil extractable Cd concentrations following irrigation, regardless of the irrigation regime. Mean soil extractable Cd and plant tissue Cd concentrations were significantly greater (approximately 325% and 183%, respectively) for the Topehaehae soil than the Kereone soil, despite the lower soil total Cd concentration of the Topehaehae soil. These results indicate that Cd solubility is sensitive to increases in soil moisture following periods of soil drainage, but insensitive to short-term periods of soil saturation. Plant tissue Cd concentrations in Cd-sensitive forage crops such as plantain are likely to be greater following large rainfall events over summer and autumn. This has the potential to increase animal dietary Cd exposure and rate of liver/kidney Cd accumulation. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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13 pages, 5648 KiB

Open AccessArticle

Altered Bacterial Communities in Long-Term No-Till Soils Associated with Stratification of Soluble Aluminum and Soil pH

by Ricky W. Lewis, Victoria P. Barth, Todd Coffey, Carol McFarland, David R. Huggins and Tarah S. Sullivan

Soil Syst. 2018, 2(1), 7; https://doi.org/10.3390/soils2010007 - 5 Feb 2018

Cited by 20 | Viewed by 5191

Abstract

Soil acidification is a global issue that often results in increased aluminum (Al) toxicity. While no-till (NT) management has many benefits regarding sustainability, a discrete zone of acidification often occurs when ammoniacal fertilizers are banded below the seed. The full agroecological consequences of [...] Read more.

Soil acidification is a global issue that often results in increased aluminum (Al) toxicity. While no-till (NT) management has many benefits regarding sustainability, a discrete zone of acidification often occurs when ammoniacal fertilizers are banded below the seed. The full agroecological consequences of NT stratification and impacts on bacterial communities are largely unknown. Using next-generation sequencing (NGS) and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt), we characterized the influence of liming amendment and soil stratification on bacterial community composition and predicted function in 2-cm depth increments. Soil depth, pH, DTPA extractable aluminum (DTPA-Al), and KCl extractable Al (KCl-Al) were all significantly correlated with bacterial community structure and function. In soils with the lowest pH and greatest extractable Al, bacterial community was distinct, with highest relative abundance of the Koribacteraceae family, an indicator of soil degradation. Additionally, aspects of bacterial metabolism and nutrient turnover were impacted in the lowest pH zones, including secondary metabolite, carbohydrate, and energy metabolism. These results suggest that soil stratification (Al and pH) in NT systems has direct impacts on microbial community structure and function, potentially influencing ecosystem services at a highly resolved spatial scale within surface depths relevant to seed germination and emergence. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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13 pages, 2078 KiB

Open AccessArticle

Effects of Ionic Strength on Arsenate Adsorption at Aluminum Hydroxide–Water Interfaces

by Tingying Xu and Jeffrey G. Catalano

Soil Syst. 2018, 2(1), 1; https://doi.org/10.3390/soils2010001 - 1 Jan 2018

Cited by 11 | Viewed by 4856

Abstract

Adsorption processes at mineral–water interfaces control the fate and transport of arsenic in soils and aquatic systems. Mechanistic and thermodynamic models to describe this phenomenon only consider inner-sphere complexes but recent observation of the simultaneous adsorption of inner- and outer-sphere arsenate on single [...] Read more.

Adsorption processes at mineral–water interfaces control the fate and transport of arsenic in soils and aquatic systems. Mechanistic and thermodynamic models to describe this phenomenon only consider inner-sphere complexes but recent observation of the simultaneous adsorption of inner- and outer-sphere arsenate on single crystal surfaces complicates this picture. In this study, we investigate the ionic strength-dependence of the macroscopic adsorption behavior and molecular-scale surface speciation of arsenate bound to gibbsite and bayerite. Arsenate adsorption decreases with increasing ionic strength on both minerals, with a larger effect at pH 4 than pH 7. The observed pH-dependence corresponds with a substantial decrease in surface charge at pH 7, as indicated by ζ-potential measurements. Extended X-ray absorption fine structure (EXAFS) spectroscopy finds that the number of second shell Al neighbors around arsenate is lower than that required for arsenate to occur solely as an inner-sphere surface complex. Together, these observations demonstrate that arsenate displays macroscopic and molecular-scale behavior consistent with the co-occurrence of inner- and outer-sphere surface complexes. This demonstrated that outer-sphere species can be responsible for strong adsorption of ions and suggests that environments experiencing an increase in salt content may induce arsenic release to water, especially under weakly acidic conditions. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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Review

Jump to: Research

20 pages, 4172 KiB

Open AccessReview

The Fate of Chemical Pollutants with Soil Properties and Processes in the Climate Change Paradigm—A Review

by Bhabananda Biswas, Fangjie Qi, Jayanta Kumar Biswas, Ayanka Wijayawardena, Muhammad Atikul Islam Khan and Ravi Naidu

Soil Syst. 2018, 2(3), 51; https://doi.org/10.3390/soilsystems2030051 - 1 Sep 2018

Cited by 98 | Viewed by 16848

Abstract

Heavy metal(loid)s and organic contaminants are two major groups of pollutants in soils. The fate and exposure of such pollutants in soil depends on their chemical properties, speciation, and soil properties. Soil properties and processes that control the toxicological aspects of pollutants include [...] Read more.

Heavy metal(loid)s and organic contaminants are two major groups of pollutants in soils. The fate and exposure of such pollutants in soil depends on their chemical properties, speciation, and soil properties. Soil properties and processes that control the toxicological aspects of pollutants include temperature, moisture, organic matter, mineral fractions, and microbial activities. These processes are vulnerable to climate change associated with global warming, including increased incidences of extreme rainfall, extended dry periods, soil erosion, and a rise in sea level. Here we explain evidence that relates to the effects of climate change-driven soil processes on the mobility, transport, and storage of pollutants in soil. The review found that changes in climate could increase human exposure to soil contaminants mainly due to processes involving soil organic carbon (SOC), surface runoff, redox state, and microbial community. However, uncertainties remain in relation to the extent of contaminant toxicity to human health, which is linked to global change drivers. Full article

(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)

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