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Heavy Metals in Soils

Trace Metals and Metalloids in Soils and their Bioavailability

herausgegeben von: Brian J. Alloway

Verlag: Springer Netherlands

Buchreihe : Environmental Pollution

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

This third edition of the book has been completely re-written, providing a wider scope and enhanced coverage. It covers the general principles of the natural occurrence, pollution sources, chemical analysis, soil chemical behaviour and soil-plant-animal relationships of heavy metals and metalloids, followed by a detailed coverage of 21 individual elements, including: antimony, arsenic, barium, cadmium, chromium, cobalt, copper, gold, lead, manganese, mercury, molybdenum, nickel, selenium, silver, thallium, tin, tungsten, uranium, vanadium and zinc. The book is highly relevant for those involved in environmental science, soil science, geochemistry, agronomy, environmental health, and environmental engineering, including specialists responsible for the management and clean-up of contaminated land.

Inhaltsverzeichnis

Frontmatter

BASIC PRINCIPLES

Chapter 1. Introduction

Abstract

This new (third) edition of ‘Heavy Metals in Soils’ provides an up to date and in-depth coverage of analytical methods, concentrations in soils, soil chemistry and effects on plants, animals and humans of the 21 most environmentally important heavy metals and metalloids. Although retaining a similar structure to the two earlier editions (1990 and 1995) it has been completely re-written by a team of mainly new authors. Its scope has been expanded by the inclusion of 4 new chapters in Part I (Basic Principles) dealing with soil organisms, soil-plant relationships, heavy metal(loid)s as micronutrients and critical loads. Part II, (Key Heavy Metals and Metalloids) covers the 11 most important elements and Part III (Other Heavy Metals and Metalloids of Potential Environmental Significance) deals with a further 10 less well known, but nonetheless important elements. Figures are given for total world mining production of most of these heavy metal(loid)s over the period from 1973 to 2010. Opinions differ on the appropriateness of the term ‘heavy metals’ and these are discussed together with a brief consideration of significant developments in the study and management of heavy metal(loid)s in soils over the 22 years since the first edition.

Brian J. Alloway

Chapter 2. Sources of Heavy Metals and Metalloids in Soils

Abstract

Heavy metals and metalloids in soils are derived from the soil parent material (lithogenic source) and various anthropogenic sources, most of which involve several metal(loid)s. There are many different anthropogenic sources of heavy metal(loid) contamination affecting both agricultural and urban soils. However, localised contamination from a predominant single source, such as a metal smelter can have a marked effect on soils, vegetation and possibly also on the health of the local population, especially in countries where there are inadequate emission controls and soil quality standards. In general, soils at industrial sites can have distinct groups of heavy metal(loid) contaminants, which depend on the respective industries and their raw materials and products. Soils in all urban areas are generally contaminated with lead (Pb), zinc (Zn), cadmium (Cd) and copper (Cu) from traffic, paint and many other non-specific urban sources. Although the heavy metal(loid) composition of agricultural soils tends to be more closely governed by the parent material, inputs from sources such as deposition of long-distance, atmospherically-transported aerosol particles from fossil fuel combustion and other sources, organic material applications and contaminants in fertilisers can also be significant. Removal of Pb from petrol and paints, changes in the type and structure of industries and strict regulations on atmospheric emissions and waste water discharges have resulted in a general reduction in the loads of heavy metal(loid)s reaching soils in many countries. However, historic contamination still affects soils in many areas and may have impacts for decades or even centuries afterwards.

Brian J. Alloway

Chapter 3. Chemistry of Heavy Metals and Metalloids in Soils

Abstract

It is a simple matter to conceptually classify trace metal fractions in soil in terms of their relative ‘availability’. However, the challenge has always been to translate this qualitative understanding into predictive models of metal solubility, ideally based on proven mechanistic processes of specific adsorption, ion exchange, precipitation, colloidal flocculation, reduction, intra-aggregate diffusion etc. This chapter starts with a brief examination of the surface properties of the main metal adsorbents in soil, including humus, and the colloidal minerals Fe/Mn oxides, alumino-silicate clays, zeolites and sparingly soluble Ca salts. The interaction of these phases with the transient soil variables (e.g., pH, redox potential, temperature) in controlling metal solubility is discussed alongside the overarching influence of time. The sheer complexity of these co-dependencies still confounds our efforts to resolve an exact description of metal solubility and speciation and the range of modelling approaches which has emerged from this ‘confrontation’ is outlined. Currently the literature still presents an uneasy co-existence of relatively simple descriptions of metal solid ↔ solution equilibrium along with thermodynamically consistent mechanistic models. To compensate for their limited predictive power in the face of soil heterogeneity, the empirical equations are often extended to incorporate key soil properties (soil organic carbon content, pH etc.) as determinants of the model parameters – with surprising success. The principal challenge for mechanistic models is to resolve a meaningful basis for their description of metal dynamics which can be confirmed experimentally. However, an equally important goal is to reconcile the demanding requirements for their operation with the paucity of such data in geochemical studies and datasets. With much wider use in recent years the remaining shortcomings of the mechanistic models are becoming more apparent and this has created new experimental imperatives. These include characterising the small proportions of high affinity sites on adsorbents and developing descriptions of mixed adsorbents beyond a purely additive approach. The future promises continued improvement of models describing trace metal dynamics in soils and their increasing incorporation into human and environmental risk assessment tools.

Scott D. Young

Chapter 4. Methods for the Determination of Heavy Metals and Metalloids in Soils

Abstract

This chapter explores the analytical methods currently available for the measurement of heavy metal content in soils, ranging from well-established techniques routinely applied in laboratories worldwide, to newly emerging approaches, and with emphasis on the need to select strategies that are ‘fit-for-purpose’ in terms of the information required. Included are guidelines for field sampling and for the storage of samples and avoidance of contamination. Brief information is provided on analytical techniques directly applicable to solid samples including neutron activation analysis, laser-induced breakdown spectrometry and X-ray-based methods. Suitable approaches to sample extraction for different situations are summarised (total digestion, pseudototal digestion, single and sequential extraction) together with examples of procedures involving hot-plate, block, bomb, and microwave apparatus. The use of extractants to assess (plant) bioavailability or (human) bioaccessibility of heavy metals in soils is discussed. Details are provided of the various types of atomic spectrometry that nowadays serve as ‘workhorses’ for trace metal determination in environmental chemistry, with particular emphasis on their principles, strengths, limitations and applicability. Included are flame and electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. The chapter also provides a brief introduction to the vast topic of speciation analysis, an area of particular interest for metals that can occur in different oxidation states e.g. Cr, or that have environmentally important organometallic forms e.g. Hg. Finally, some recommendations are given on strategies that researchers should adopt whenever possible to improve the quality of their analytical data.

Christine M. Davidson

Chapter 5. Effects of Heavy Metals and Metalloids on Soil Organisms

Abstract

At the molecular level metals and metalloids cause organisms to produce chemicals such as metallothioneins to bind metals and reduce their toxicity and/or chemicals such as heat shock proteins that repair any damage done. On a cellular scale metal-rich P and S “granules” are often produced, particularly in cells that line the digestive organs, which concentrate and detoxify the contaminants. Granules either accumulate or are excreted. If metals accumulate, the location of accumulation varies between species though is often either in an organ analogous to the liver or at sites which are shed during moulting. Countless studies document effects on weight, reproduction and mortality of organisms. Variation in results are due to a complex combination of contaminant bioavailability, uptake pathways, exposure duration and soil properties. At the field scale metal and metalloid contaminants usually result in either population decline due to toxic effects/loss of prey or population growth due to the removal of predators or competition. Populations of different species are affected in different ways, modifying community structure and ecosystems. Organisms found in contaminated soils in which naïve introduced individuals of the same species can not survive exhibit either acclimation/tolerance (reversible changes in physiology) or adaptation/resistance (a change in genetic structure). A large number of toxicity tests exist to investigate and demonstrate the impact of metals and metalloids on organisms. Omic technologies offer great potential to help develop our level of understanding of these effects but are not yet a mature technology.

Mark E. Hodson

Chapter 6. Soil-Plant Relationships of Heavy Metals and Metalloids

Abstract

Nutrient uptake by plants is essential for their development and for the passage of minerals into the food chain, but it also faces several limitations. Whereas soil physicochemical characteristics impose limiting factors on element availability for plants, excess of non-essential metals and metalloids pose a threat for plant health and the environment. To improve nutrient uptake, the plant possesses several mechanisms to explore the soil for minerals such as root development, but the symbiosis with microorganisms clearly improves the ability of plants to overcome these limitations. After metal uptake by the plants, plants make use of different strategies to maintain the metal homeostasis and to limit the metal-induced cellular damage. Also in the research on metal phytotoxicity, microorganisms are shown to be important players in the protection of the plant to excess metal exposure.

Ann Cuypers, Tony Remans, Nele Weyens, Jan Colpaert, Andon Vassilev, Jaco Vangronsveld

Chapter 7. Heavy Metals and Metalloids as Micronutrients for Plants and Animals

Abstract

Much of the emphasis of the chapters in this book is on heavy metal(loid)s as soil contaminants, their bioavailability and possible toxicity to plants, ecosystems, animals and humans. However, many of the heavy metal(loid)s are actually micronutrients, that is they are essential (in small quantities) for the normal growth of plants and/or animals. Copper (Cu), manganese (Mn), molybdenum (Mo), nickel (Ni) and zinc (Zn) are the heavy metals that are essential for higher plants. For animals and humans, chromium (Cr), Cu, cobalt (Co), Mn, Mo, selenium (Se), vanadium (V) and Zn are the micronutrient heavy metal(loid)s. Iron (Fe), not usually considered a heavy metal is essential for both plants and animals. Several other elements, including arsenic (As), cadmium (Cd), lead (Pb) and tin (Sn) may possibly have an essential role at very low concentrations. This chapter briefly covers the essential functions of these heavy metal(loid)s in plants and/or animals and the significance of relatively low and high available concentrations in soils. Deficiencies and toxicities of micronutrients adversely affect plant and animal health, cause reductions in growth rate (and yield), overt symptoms of physiological stress and, in extreme cases, the death of the plant or animal. In many parts of the world, the adverse effects of deficiencies of essential heavy metal(loid)s are more important economically than toxicities arising from soil contamination.

Brian J. Alloway

Chapter 8. Critical Loads of Heavy Metals for Soils

Abstract

To enable a precautionary risk assessment for future inputs of metals, steady-state methods have been developed to assess critical loads of metals avoiding long-term risks to food quality and eco-toxicological effects on organisms in soils and surface waters. A critical load for metals equals the load resulting at steady state in a concentration in a compartment (e.g. soil solution, plant, fish) that equals the critical limit for that compartment. This chapter presents an overview of methods to assess critical limits and critical loads of metals, with a focus on cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) in soils in relation to impacts on: (i) agriculture (food quality and crop health) and (ii) ecology (plants, invertebrates and soil organisms involved in nutrient cycling processes). Results are presented using generic input data. Furthermore, examples of national and European applications are shown. Results are discussed in view of the uncertainty and applicability of the critical load concept for heavy metals in future agreements on the reduction of metal emissions. It is concluded that for policy applications, dynamic models are also needed to estimate the times involved in attaining a certain chemical state in response to input (deposition, fertilisers or manure) scenarios.

Wim de Vries, Jan Engelbert Groenenberg, Steve Lofts, Ed Tipping, Maximilian Posch

KEY HEAVY METALS AND METALLOIDS

Chapter 9. Arsenic

Abstract

Arsenic (As), an ubiquitous element known for its toxicity to biota naturally occurs in several oxidation states between –III and +V. Total As concentrations in the soil solid phase range between 0.1 and 55 mg kg⁻¹ in uncontaminated soils but may be as high as several percent in soils contaminated by mining, smelter and other industrial activities. In aerobic mineral soils, As is primarily associated with iron (Fe) (oxy)hydroxides whereas As sulphide minerals may precipitate in anaerobic conditions. In the presence of Fe (oxy)hydroxides only minor amounts of As are associated with (oxy)hydroxides of aluminium (Al) or manganese (Mn), clay minerals or organic matter. There is no evidence for significant association of As with calcium (Ca) minerals below pH 9.5. Binding of As to organic matter appears to be important in organic soils such as forest floors of peat, but the nature of this association is largely unknown. The main control of both As(III) and As(V) solubility in soils is sorption to Fe (oxy)hydroxides, mainly as inner-sphere bidentate (mononuclear and binuclear) and monodentate surface complexes, with a greater share of monodentate complexes at low As loads and increasing pH (at pH values >8), and predominance of binuclear bidentate complexes at highest As loads. The main As species in soil pore water are arsenate in aerobic soil and undissociated arsenous acid in anaerobic conditions, with little contribution of organic forms. Soil pore water in organic soils may also contain substantial amounts of organic As, primarily in methylated forms. Biological transformations of As include oxidation – reduction and methylation – demethylation reactions triggered by soil bacteria and fungi. Plant roots take up As(V) via phosphate transporters and As(III) by aquaporins and release As(III) back into their rhizospheres after internal reduction of As(V) to As(III). Arsenic pollution is a global phenomenon with a major contribution of anthropogenic emissions to the global As cycle. Large-scale risks to ecosystems and human health arise not only from (ancient) mining and smelter activities, but more recently also from of the use of As-contaminated water as a source of drinking water and for irrigation of crops, in particular paddy rice.

Walter W. Wenzel

Chapter 10. Cadmium

Abstract

Cadmium (Cd) is naturally present in soils at concentrations 0.1–1 mg Cd kg⁻¹. Cadmium is readily available for uptake by food crops and food chain contamination with Cd from contaminated soil has led to effects on kidney functioning in humans, even reaching fatal levels in subsistence farmers who consumed rice from a contaminated area in Japan. Diffuse Cd sources, notably P-fertilisers and atmospheric depositions have increased soil Cd concentrations by about 0.1–0.3 mg Cd kg⁻¹ above pre-industrial levels and actions have been taken worldwide to limit Cd emissions or Cd exposure to humans. Emissions of Zn–Cd smelters have been cut in numerous places but residual soil Cd contamination is still present. Cadmium retention in soil is controlled by sorption reactions and soil pH is the main determinant. Soil Cd availability for crop uptake varies by about a factor 10 among soils and generally increases 1.5-fold by decreasing soil pH with one unit. Crops differ in Cd uptake and hard wheat and potatoes have a considerable impact on the dietary Cd intake. Contrasting views exist on the food chain risk of Cd as both soil Cd and food Cd bioavailability may have been larger in the Japanese case study than in the general environment. In Europe, a generic Cd risk assessment in 2007 led to the conclusion that risk cannot be excluded for the general population environmentally exposed to Cd. However, limits on P fertilisers, as main determinants of Cd emissions, are not yet in place.

Erik Smolders, Jelle Mertens

Chapter 11. Chromium and Nickel

Abstract

Nickel (Ni) and chromium (Cr) are elements naturally present in all rock types and present in the pedosphere in a range from trace amounts to relatively high concentrations, as compared to other trace elements. Particularly high Ni and Cr concentrations are found in serpentine rocks and soils, originating from this rock type and colonized by a specialized flora that may present some curious species capable of hyperaccumulating extraordinary high concentrations of Ni in their above-ground parts. In recent decades, the large release of Cr and Ni by industrial activities, mainly the manufacture of stainless steel, as well as the use of sewage sludge as soil amendment in agricultural soils, have caused an impressive increase in the levels of these two metals in the pedosphere and other environmental matrices. This has led to increasing environmental concern as, while relatively low concentrations of Ni and Cr are essential for plants and other living organisms including humans, both the elements are toxic for all living organisms if present in excessive concentrations. This chapter reviews the distribution and the geochemical behaviour of Ni and Cr, their main dynamics in the soil environment, with regards to the natural and anthropogenic sources. The relationships of Ni and Cr with the plants, in particular with some Ni hyperaccumulator species are also discussed.

Cristina Gonnelli, Giancarlo Renella

Chapter 12. Cobalt and Manganese

Abstract

Cobalt (Co) and manganese (Mn) are closely associated in soils because they have similar chemical properties. The main forms of Mn in soil are the water-soluble and exchangeable forms of Mn(II) and the insoluble Mn oxides, mainly Mn(IV) and to a lesser and more uncertain extent as Mn(III). The concentration of water-soluble plus exchangeable Mn(II) (WS+Exch Mn) is determined by the relative rates of the chemically independent and physically separate reactions, the microbial oxidation of Mn(II) and the chemical reduction of the Mn oxides (by organic matter). The solubility and availability of Co to plants is influenced greatly by the activity of the Mn oxides and the reactions which affect Mn. The Mn oxides also participate in sorption and oxidation reactions which impact on soil health in that the former affects the availability of trace metals and the latter oxidises organic moieties, of which some are phytotoxic.

Nicholas C. Uren

Chapter 13. Copper

Abstract

Background copper (Cu) concentrations in soil depend on geology and typically vary between 2 and 50 mg Cu kg⁻¹. The widespread use of Cu has resulted in significant anthropogenic inputs to topsoils through atmospheric deposition and agricultural practices (fertilisers, pesticides, sewage sludge etc.). Copper mainly occurs in its divalent state (Cu²⁺) and has high affinity for binding to organic matter. Sorption processes control the solubility of Cu under most environmental conditions, but Cu precipitates can form in alkaline soils. The solid-liquid partitioning of Cu in soil is largely controlled by the soil pH and organic matter content, with higher solubility at low pH and low organic matter content. Except for acidic soils, most (>90%) of the dissolved Cu in soil is complexed with dissolved organic matter. Copper is an important essential element for all living organisms and deficiency in plants and ruminants occur in soils with low available Cu. Copper concentrations in plant shoots typically range between 4 and 15 mg Cu kg⁻¹ dry matter (DM) and are well regulated over a wide soil Cu concentration range. Elevated soil Cu concentrations cause toxic effects in all terrestrial organisms (plants, invertebrates and micro-organisms). The toxicity of Cu largely depends on soil properties, which control the bioavailability of Cu in soil through their effect on precipitation, sorption and complexation processes. Predicted no effect concentrations (PNECs), protecting 95% of all species or microbial processes, vary between approximately 10 and 200 mg Cu kg⁻¹ soil and increase with increasing cation exchange capacity, clay and organic matter content.

Koen Oorts

Chapter 14. Lead

Abstract

Lead (Pb) is among the elements that have been most extensively used by man over time. This has led to extensive pollution of surface soils on the local scale, mainly associated with mining and smelting of the metal and addition of organic Pb compounds to petrol. Other sources of soil Pb pollution are shooting ranges and sewage sludges. Release of Pb to the atmosphere from various high-temperature processes has led to surface contamination on the regional and even global scale. Lead is particularly strongly bound to humic matter in organic-rich soil and to iron oxides in mineral soil, and is rather immobile in the soil unless present at very high concentrations. Transfer of Pb from the soil to green parts of plants is generally small, except in cases with extensive surface soil concentration. Concerns about health effects due to Pb pollution particularly in urban areas and to Pb uptake in agricultural crops have led to development of a variety of soil remediation techniques.

Eiliv Steinnes

Chapter 15. Mercury

Abstract

In spite of its low abundance in the Earth’s crust, mercury (Hg) has aroused substantial attention, first because of its numerous applications and more recently because of its toxicity. The extensive use of Hg has resulted in significant contamination of soils locally and regionally and sometimes to human and animal exposure at toxic levels. Human use of Hg started already in antiquity and reached a maximum around 1975. Since then the major applications have been strongly reduced in many countries. All chemical forms of Hg are toxic to humans and animals, methyl Hg in particular. In soils Hg may originate from Hg minerals, diffuse air pollution, and local pollution sources such as chlor-alkali factories and the use of sewage sludge and organic Hg compounds in agriculture. Elemental Hg from the atmosphere mainly due to previous human emissions is a dominant source of soil pollution worldwide. In soils, Hg occurs as various forms of Hg(II), generally strongly bound to organic matter and sulphides. The Hg content is generally higher in organic-rich soils than in mineral soils. Root uptake of Hg in plants is generally low, and Hg in above-ground plant material is mostly derived from atmospheric deposition. Under reducing conditions in soils methyl Hg may be formed and subsequently transported to lakes and rivers and accumulated in aquatic food chains.

Eiliv Steinnes

Chapter 16. Selenium

Abstract

Selenium (Se) is both an essential micronutrient for animals and humans and potentially toxic at relatively low intakes. Total soil Se is usually low (0.01–2 mg/kg), but parts of China, India and the USA have toxic soil Se levels. Available soil Se is poorly correlated with total soil Se and is highly variable, both locally and globally. The plant availability of Se in soil depends on the major Se species present and on soil characteristics, including the quantity of sorption components (aluminium and iron oxide/hydroxides), pH and redox status. Also, the presence of anions competing for the same sorption surfaces (including sulphate, phosphate and organic anions) affects root uptake and retention of Se in soil, and microbial activity is important for Se interactions with organic matter. Depletion of Se and S is common in soils of Sub-Saharan Africa, due to soil erosion, leaching and volatilisation through burning. The only viable long-term solution, especially for farmers who cannot afford commercial fertilisers, is to re-establish agricultural ecosystems that are closer to the natural ecosystems they replaced. Selenium is not considered to be essential for higher plants; however, it has numerous health roles in humans and animals, mostly mediated by Se-dependent enzymes. Although diseases associated with profound Se deficiency (Keshan disease, Kaschin-Beck disease and myxoedema) are rare, suboptimal intake is widespread and may increase risk of heavy metal toxicity, certain cancers, cardiovascular diseases and HIV disease. It is possible to biofortify food crops using selenate, but a high proportion is retained in the soil, and more targeted supplementation may be preferable to conserve this scarce micronutrient.

Olav Albert Christophersen, Graham Lyons, Anna Haug, Eiliv Steinnes

Chapter 17. Zinc

Abstract

Zinc (Zn) is naturally present in all soils in typical background concentrations 10–100 mg Zn kg^–1. Human activities have enriched topsoils with Zn through atmospheric depositions, fertilization and sewage sludge application. Zinc contaminated soils with negative impact on the soil ecosystem are found around Zn smelters, near Zn mining sites and under galvanized structures. The solubility of Zn in soils is almost invariably controlled by sorption reactions. Pure Zn minerals (carbonates, silicates, hydroxides) have been detected at high total soil Zn concentrations (>1,000 mg Zn kg⁻¹) but are rarely controlling Zn solubility. Zinc is specifically sorbed as Zn²⁺ on pH-dependent binding sites of oxyhydroxides and organic matter and, at high concentrations, by ion exchange reactions on clay minerals. In general, soil solution Zn concentrations increase fivefold per unit pH decrease. Zinc deficiency for agricultural crops is found in about 1/3 of worldwide soils due to low total Zn concentrations and/or high pH. Soils containing less than 0.5 mg Zn kg⁻¹ diethylenetriaminepentaacetic acid (DTPA) extractable Zn are potentially Zn deficient. Dietary Zn deficiency in humans is often associated with Zn deficient soils and crop Zn biofortification is now a global initiative through selection for Zn-efficient crops or judicious fertilisation. Zinc toxic soils are less widespread than deficient ones. Risk of Zn toxicity is manifested by effects on soil dwelling organisms, i.e. plants, invertebrates and soil microorganisms. Toxic effects are identified at total Zn concentrations 100 to >1,000 mg kg⁻¹ and toxicity decreases with increasing soil CEC. Risk assessments of Zn have proposed maximal additions as low as 26 mg added Zn kg⁻¹ in the EU to maintain soil ecosystem structure and function.

Jelle Mertens, Erik Smolders

OTHER HEAVY METALS AND METALLOIDS OF POTENTIAL ENVIRONMENTAL SIGNIFICANCE

Chapter 18. Antimony

Abstract

Antimony (Sb) is a naturally occurring metalloid that has a wide range of industrial applications. There exists an increasing interest in this metalloid as it is likely to be a pollutant in industrialised environments. It is now known that Sb has fewer geochemical and toxicological similarities with As than previously believed. It has low mobility and bioavailability in soils, and presents low toxicity to plants, although where Sb is present in more mobile forms in the soil it can be accumulated by plants and affect their growth.

Rafael Clemente

Chapter 19. Barium

Abstract

Barium (Ba) is a common element in the Earth’s crust and is present at higher concentrations than most other trace elements, and naturally occurs in one oxidaton state (+II). Industrial uses of Ba are wide and variable including: oil and gas drilling muds. The most common minerals of Ba are barite and hollandite and in geochemical processes it is usually associated with K⁺. Barium is not very mobile in most soils although plants may take up Ba easily from acid soils, but there are few reports of toxic concentrations of Ba in plants.

Paula Madejón

Chapter 20. Gold

Abstract

Gold (Au) is a noble, relatively scarce metal, highly valuable for its beauty, resistance to corrosion and as a long-term investment. Demand for it has increased steadily and it has become vital in different technological fields. Gold nanoparticles have also attracted broad interest. Despite being chemically inert towards most naturally occurring substances Au may be subject to biological interactions in soils. The impact of Au concentrations in different environmental compartments is not known with certainty.

Rafael Clemente

Chapter 21. Molybdenum

Abstract

Molybdenum (Mo) occurs at relatively low concentrations in most rocks and soils, but in relatively high concentrations in soils developed on black shales. It is present as an oxyanion in soil solution and, unlike most other heavy metals, is most mobile and plant available in alkaline conditions. Its main ore mineral is molybdenite, but it is also produced as a by-product from the processing of copper (Cu) ores. It is used mainly for making alloys and stainless steels. It is essential for plants and deficiencies can occur in brassicas, legumes, wheat, sunflowers and some other crops in many parts of the world, mainly on acid and sandy soils. It was recently proved to be essential for animals and humans, but deficiencies are rare. Molybdenum-induced copper deficiency (molybdenosis) in cattle and sheep is a serious problem on Mo-rich pasture soils in several countries.

Brian J. Alloway

Chapter 22. Silver

Abstract

Silver (Ag) is a precious metal that has recently become a valuable industrial metal and Ag nanoparticles are being increasingly used in a wide range of applications. In soils, Ag is strongly sorbed but may cause environmental concern. Both monovalent Ag ion and Ag nanoparticles have antimicrobial properties that have found different uses, but could also provoke adverse effects in soil beneficial bacteria. Silver toxicity to plant species varies from highly toxic to easily inactivated by the plant.

Rafael Clemente

Chapter 23. Thallium

Abstract

Thallium (Tl) is widely distributed in the natural environment although at very low concentrations. It mainly occurs in the oxidation state Tl (I), whilst Tl (III) increases under acid and oxidizing conditions. Geochemical behaviour of Tl is analogous to that of potassium. Thallium does not occur in a free state in nature although several minerals contain it as a major constituent. The most common Tl-containing minerals are Lorandite and Crooksite. This element is mobilised by the combustion of fuels and other industrial processes and tends to persist in soils, depending on the soil type. It is considered a non-essential element and highly toxic to living organism. It is relatively easily taken up by plants and enters the food chain and it has been shown to accumulate in fish and other animals, with toxic effects.

Paula Madejón

Chapter 24. Tin

Abstract

Tin (Sn) is one of the metals of antiquity and its use with copper in the alloy bronze was a major development in human history. It is now mainly used in protective coatings on steel, in electrical solders and in the production of organotin compounds which have a wide range of uses including as biocides. Adsorption of inorganic forms of Sn in soils is positively correlated with pH, organic matter content and cation exchange capacity. Plant uptake is greatest in acid soils and in most species Sn accumulates in the roots. Organotin compounds with three organic groups, such as tributyltin, have the highest biocidal activity and constitute the greatest ecotoxicity hazard. Organotins are more ubiquitous sources of Sn in soils than inorganic forms and can reach soils in atmospheric deposition, fungicidal crop sprays and sewage sludges. They behave as enzyme disruptors in many animal species and there is concern about their possible impact on human health.

Brian J. Alloway

Chapter 25. Tungsten

Abstract

Tungsten (W) is a lithophile element that occurs naturally in small concentrations in soils and sediments. Its hardness and resistance to corrosion (alone, alloyed with other metals, or combined with carbon) makes it an important strategic element with a wide range of both common and specialised applications. Concerns over adverse environmental effects of W have recently arisen and its designation as a non-toxic and environmentally benign metal is being reconsidered. Tungsten speciation and the formation of polytungstates in acid conditions may be important in ecotoxicology.

Rafael Clemente, Nicholas W. Lepp

Chapter 26. Uranium

Abstract

Uranium (U) is a naturally radioactive element and one of its radioisotopes (²³⁵U) is the basis for nuclear fission reactions in electricity generation and nuclear weapons. Uranium has both chemotoxic and radiotoxic properties and is a potential hazard to ecosystems and human health. Concentrations in rocks vary with relatively high concentrations occuring in black shales, coal, phosphorites, certain sandstones and some limestone formations and in the soils derived from them. Groundwaters associated with U-rich rocks can contain elevated concentrations of U. Soil contamination can arise from phosphate fertilisers, U mining, nuclear waste processing, nuclear explosions, coal combustion, disposal of coal ash and civil and military uses of depleted uranium (DU). Unlike iron and manganese which also have cations with more than one valency state, the highest valency U(VI) is most mobile and plant-available. High carbonate concentrations can produce soluble complexes, but reducing conditions cause the formation of insoluble ions, and U is strongly adsorbed in soils and sediments rich in iron oxides and organic matter. Plant availability is generally higher in acid conditions.

Brian J. Alloway

Chapter 27. Vanadium

Abstract

Vanadium (V) is widely distributed in nature, and has oxidation states of II, III, IV or V. The content of this element in soil depends upon the parent material. Combustion of coals and oils represents the major source of V enrichment of the biosphere. The most important minerals of V are Vanadite and Roscoelite. Trace concentrations of V have been reported to benefit plant growth, while higher concentrations are toxic. Pentavalent compounds are the most toxic and the toxicity of V compounds usually increases as the valence increases.

Paula Madejón

Backmatter

Titel: Heavy Metals in Soils
herausgegeben von: Brian J. Alloway
Verlag: Springer Netherlands
Electronic ISBN: 978-94-007-4470-7
Print ISBN: 978-94-007-4469-1
DOI: https://doi.org/10.1007/978-94-007-4470-7