Preface.- Contributors.- List of Abbreviations.- Section 1: Basic Principles: Introduction.-Sources of Heavy Metals and Metalloids in Soils.- Chemistry of Heavy Metals and Metalloids in Soils.- Methods for the Determination of Heavy Metals and Metalloids in Soils.- Effects of Heavy Metals and Metalloids on Soil Organisms.- Soil-Plant Relationships of Heavy Metals and Metalloids.- Heavy Metals and Metalloids as Micronutrients for Plants and Animals.-Critical Loads of Heavy Metals for Soils.- Section 2: Key Heavy Metals And Metalloids: Arsenic.- Cadmium.- Chromium and Nickel.- Cobalt and Manganese.- Copper.-Lead.- Mercury.- Selenium.- Zinc.- Section 3: Other Heavy Metals And Metalloids Of Potential Environmental Significance: Antimony.- Barium.- Gold.- Molybdenum.- Silver.- Thallium.- Tin.- Tungsten.- Uranium.- Vanadium.- Glossary of Specialized Terms.- Index.

Heavy metals in soils : trace metals and metalloids in soils and their bioavailability

Microbes play key geoactive roles in the biosphere, particularly in the areas of element biotransformations and biogeochemical cycling, metal and mineral transformations, decomposition, bioweathering, and soil and sediment formation. All kinds of microbes, including prokaryotes and eukaryotes and their symbiotic associations with each other and 'higher organisms', can contribute actively to geological phenomena, and central to many such geomicrobial processes are transformations of metals and minerals. Microbes have a variety of properties that can effect changes in metal speciation, toxicity and mobility, as well as mineral formation or mineral dissolution or deterioration. Such mechanisms are important components of natural biogeochemical cycles for metals as well as associated elements in biomass, soil, rocks and minerals, e.g. sulfur and phosphorus, and metalloids, actinides and metal radionuclides. Apart from being important in natural biosphere processes, metal and mineral transformations can have beneficial or detrimental consequences in a human context. Bioremediation is the application of biological systems to the clean-up of organic and inorganic pollution, with bacteria and fungi being the most important organisms for reclamation, immobilization or detoxification of metallic and radionuclide pollutants. Some biominerals or metallic elements deposited by microbes have catalytic and other properties in nanoparticle, crystalline or colloidal forms, and these are relevant to the development of novel biomaterials for technological and antimicrobial purposes. On the negative side, metal and mineral transformations by microbes may result in spoilage and destruction of natural and synthetic materials, rock and mineral-based building materials (e.g. concrete), acid mine drainage and associated metal pollution, biocorrosion of metals, alloys and related substances, and adverse effects on radionuclide speciation, mobility and containment, all with immense social and economic consequences. The ubiquity and importance of microbes in biosphere processes make geomicrobiology one of the most important concepts within microbiology, and one requiring an interdisciplinary approach to define environmental and applied significance and underpin exploitation in biotechnology.

http://dzumenvis.nic.in/Physiology/pdf/Metals,%20minerals%20and%20microbes.pdf

Metals, minerals and microbes: geomicrobiology and bioremediation

Remediation of heavy metal(loid)s contaminated soils - To mobilize or to immobilize?

Understanding the origin of the carbon (C) stabilised in soils is crucial in order to device management practices that will foster Caccumulation in soils. The relative contributions to soilC pools of roots vs. shoots is one aspect that has been mostly overlooked, although it appears a key factor that drives the fate of plant tissueC either as mineralized CO2 or as stabilized soil organic matter (SOM). Available studies on the subject consistently indicate that rootC has a longer residence time in soil than shootC. From the few studies with complete datasets, we estimated that the mean residence time in soils of root-derived C is 2.4times that of shoot-derived C. Our analyses indicate that this value is biased neither by an underestimation of root contributions, as exudation was considered in the analysis, nor by a priming effect of shoot litter on SOM. Here, we discuss the main SOM stabilisation mechanisms with respect to their ability to specifically protect root-derived SOM. Comparing in situ and incubation experiments suggests that the higher chemical recalcitrance of root tissues as compared to that of shoots is responsible for only a small portion, i.e. about one fourth, of the difference in mean residence time in soils of root-derived vs. shoot-derivedC. This suggests that SOM protection mechanisms other than chemical recalcitrance are also enhanced by root activities: (1)physico-chemical protection, especially in deeper horizons, (2)micrometer-scale physical protection through myccorhiza and root-hair activities, and (3)chemical interactions with metal ions. The impact of environmental conditions within deeper soil layers on rootC stabilisation appear difficult to assess, but is likely, if anything, to further increase the ratio between the mean residence time of root vs. shootC in soils. Future advances are expected from isotopic studies conducted at the molecular level, which will help unravel the fate of individual shoot and root compounds, such as cutins and suberins, throughout soil profiles.

Is soil carbon mostly root carbon? Mechanisms for a specific stabilisation

http://andrewsforest.oregonstate.edu/pubs/pdf/pub1374.pdf

Stabilization and destabilization of soil organic matter: mechanisms and controls

In soil environments, sorption/desorption reactions as well as chemical complexation with inorganic and organic ligands and redox reactions, both biotic and abiotic, are of great importance in controlling their bioavailability, leaching and toxicity. These reactions are affected by many factors such as pH, nature of the sorbents, presence and concentration of organic and inorganic ligands, including humic and fulvic acid, root exudates, microbial metabolites and nutrients. In this review, we highlight the impact of physical, chemical, and biological interfacial interactions on bioavailability and mobility of metals and metalloids in soil. Special attention is devoted to: i) the sorption/desorption processes of metals and metalloids on/from soil components and soils; ii) their precipitation and reduction-oxidation reactions in solution and onto surfaces of soil components; iii) their chemical speciation, fractionation and bioavailability.

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Mobility and bioavailability of heavy metals and metalloids in soil environments

Sorption and desorption of AsO 4 on or from different soil components may have a dominant role in regulating As mobility in soils. The objectives of this work were to provide information on the factors that influence the competitive sorption of AsO 4 and PO 4 in soil. We studied the competitive sorption of PO 4 and AsO 4 on selected phyllosilicates, metal oxides, synthetic organo-mineral complexes, and soil samples as affected by pH (4.0-8.0), ligands concentration, surface coverage of the oxyanions on the samples and the residence time. We found that Mn, Fe, and Ti oxides and phyllosilicates particularly rich in Fe (nontronite, ferruginous smectites) were more effective in sorbing AsO 4 than PO 4 . In fact, by adding AsO 4 and PO 4 as a mixture (AsO 4 /PO 4 molar ratio of 1) more AsO 4 , than PO 4 was usually sorbed on birnessite, pyrolusite, goethite, nontronite, and ferruginous smectite, but more PO 4 than AsO 4 was sorbed on noncrystalline Al precipitation products, gibbsite, boehmite, allophane, and kaolinite. For example, at pH 5.0 the sorbed AsO 4 /sorbed PO 4 molar ratio (rf) was 1.81 for bimessite, 1.05 for nontronite, but was only 0.45 for kaolinite and 0.14 for allophane. For montmorillonite, illite, and vermiculite the rf values were slightly <1. For soil samples, particularly rich in kaolinite, halloysite, allophane, and containing relatively large amounts of organic C, the rf values were usually much <1. For all the samples, the rf values increased by decreasing the pH and with the residence time of the oxyanions. The sorption of AsO 4 (or PO 4 ) on goethite and gibbsite decreased by increasing the initial PO 4 /AsO 4 (or ASO 4 / PO 4 molar ratio) up to 2.0. However, PO 4 inhibited AsO 4 sorption more on gibbsite than on goethite, whereas AsO 4 prevented PO 4 sorption more on goethite than on gibbsite. The data reported in this paper suggest that the mobility, the bioavailability, and the toxicity of As in soil environments may be greatly affected by the nature of soil components, pH, presence of anions (PO 4 ), and residence time.

Competitive Sorption of Arsenate and Phosphate on Different Clay Minerals and Soils

The mobility, bioavailability, and toxicity of metal(loid)s are influenced by their interactions with phyllosilicates, organic matter, variable charge minerals, and microorganisms. Physicochemical processes influencing the chemistry of metal(loid)s in soil environments include sorption/desorption, solution complexation, oxidation-reduction, and precipitation-dissolution reactions. In particular, the sorption/desorption reactions of metal(loid)s on/from soil sorbents are influenced by pH, nature of soil components, and presence and concentrations of cations and inorganic anions. In recent years, many extraction tests have been used for assessing trace elements mobility and phytoavailability. Chemical speciation of toxic elements may be achieved by spectroscopic analyses (XAS), which provide information about oxidation state, symmetry, and identity of the coordinating ligand environment, and possible solid phases.

/pdf/chemical-processes-affecting-the-mobility-of-heavy-metals-4xa708lhg9.pdf

Chemical Processes Affecting the Mobility of Heavy Metals and Metalloids in Soil Environments

A. Fundamentals on Biotic and Abiotic Interactions of Metals and Metalloids with Soil Components. A.1 Impacts of Physicochemical-Biological Interactions on Metal and Metalloid Transformations in Soils: An Overview (P.M. Huang). A.2 Transformation and Mobilization of Metals, Metalloids and Radionuclides by Microorganisms (G.M. Gadd). A.3 Kinetics and Mechanisms of Sorption/Desorption in Soils: A Multi-Scale Assessment (M.J. Borda and D.L. Sparks). A.4 Spectroscopic Techniques for Studying Metal-Humic Complexes in Soil (N. Senesi and E. Loffredo). A.5 Factors Affecting the Sorption-Desorption of Trace Elements in Soil Environments (A.Violante, G.S.R. Krishnamurti and M. Pigna). A.6 Modeling Adsorption of Metals and Metalloids by Soil Components (S. Goldberg and L. J. Criscenti). B. Transformations and Dynamics of Metals and Metalloids as Influenced by Soil-Root-Microbe Interactions. B.1 Biogeochemistry of Metals and Metalloids at the Soil-Root Interface (F. Hinsinger and F. Courchesne). B.2 Biogeochemical Processes Controlling the Cycling of Arsenic in Soils and Sediments (S. Fendorf, M. Herbel, K. J. Tufano, and B. D. Kocar). B.3 Microbial Oxidation and Reduction of Iron in the Root Zone and Influences on Metal Mobility (S. C. Neubauer, D. Emerson, and J. P. Megonigal). B.4 The Complexity of Aqueous Complexation: The Case of Aluminum- and Iron(III)-Citrate (M.E. Essington). C. Speciation, Mobility and Bioavailability of Metals and Metalloids and Restoration of Contaminated Soils. C.1 Chemical Speciation and Bioavailability of Trace Metals (G.S.R. Krishnamurti and R. Naidu). C.2 Fractionation and Mobility of Trace Elements in Soils and Sediments (P. S. Fedotov and M. Miro). C.3 Sources and Mobility of Metallic Radionuclides in Soil Systems ( S. Staunton , C-S. Haudin, G. Wang and G. Shaw). C.4 Remediation of Metal Contaminated Soils: An Overview (M. Grafe and R. Naidu). C.5 Phosphate-Induced Lead Immobilization in Contaminated Soils: Mechanisms, Assessment and Field Applications (R. Melamed and L.Q. Ma).

/pdf/biophysico-chemical-processes-of-heavy-metals-and-metalloids-2wa99rkscv.pdf

Biophysico-Chemical Processes of Heavy Metals and Metalloids in Soil Environments

We studied (i) the competitive adsorption of arsenate and phosphate on goethite as affected by pH, anion concentration, and order of anion addition; (ii) the effect of increasing amounts of arsenate or phosphate on the desorption of phosphate or arsenate from the surfaces of goethite; and (iii) the

Antonio Violante

Papers

Mobility and bioavailability of heavy metals and metalloids in soil environments

Competitive Sorption of Arsenate and Phosphate on Different Clay Minerals and Soils

Chemical Processes Affecting the Mobility of Heavy Metals and Metalloids in Soil Environments

Biophysico-Chemical Processes of Heavy Metals and Metalloids in Soil Environments

EFFECT OF pH, PHOSPHATE AND OXALATE ON THE ADSORPTION/DESORPTION OF ARSENATE ON/FROM GOETHITE