TRACE ELEMENTS AS CONTAMINANTS AND NUTRIENTS Consequences in Ecosystems and Human Health docx

1 The Biological System of Elements: Trace Element Concentration andAbundance in Plants Give Hints on Biochemical Reasons of Stefan Fra¨nzle, Bernd Markert, Otto Fra¨nzle and Helmut Liet

TRACE ELEMENTS AS CONTAMINANTS AND NUTRIENTS

TRACE ELEMENTS AS CONTAMINANTS AND NUTRIENTS

Consequences in Ecosystems and Human Health

Edited by

M N V Prasad

Copyright # 2008 by John Wiley & Sons, Inc All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Prasad, M N V (Majeti Narasimha Vara), 1953 –

Trace Elements as Contaminants and Nutrients: Consequences in Ecosystems and Human Health / M.N.V Prasad.

10 9 8 7 6 5 4 3 2 1

1 The Biological System of Elements: Trace Element Concentration and

Abundance in Plants Give Hints on Biochemical Reasons of

Stefan Fra¨nzle, Bernd Markert, Otto Fra¨nzle and Helmut Lieth

Electrochemical Ligand Parameters and BCF-Defined

2 Health Implications of Trace Elements in the Environment

Nelson Marmiroli and Elena Maestri

v

Shuhe Wei and Qixing Zhou

3.3 Soil Environmental Quality Standards and Background

Abdul R Memon, Yasemin Yildizhan and Eda Kaplan

5 Trace Elements and Plant Secondary Metabolism: Quality

Charlotte Poschenrieder, Josep Allue´, Roser Tolra`,

Merce` Llugany and Juan Barcelo´

4 Vegetables, Fruit, and Berries 125

viii CONTENTS

9 Essentiality of Zinc for Human Health and Sustainable Development 183

M N V Prasad

Fatemeh Alaei Yazdi and Farhad Khorsandi

11 Iron Bioavailability, Homeostasis through Phytoferritins and

Fortification Strategies: Implications for Human

N Nirupa and M N V Prasad

13 Floristic Composition at Kazakhstan’s Semipalatinsk Nuclear

Test Site: Relevance to the Containment of Radionuclides to

K S Sagyndyk, S S Aidossova and M N V Prasad

x CONTENTS

3.1 Accumulation of Uranium and Thorium

15 Exposure to Mercury: A Critical Assessment of Adverse Ecological

Sergi Dı´ez, Carlos Barata and Demetrio Raldu´a

Sources of Mercury in Aquatic Environments—The Case of

16 Cadmium as an Environmental Contaminant: Consequences to

Saritha V Kuriakose and M N V Prasad

3.4 Induction of Oxidative Stress as a Fall-Out of

Danuta Maria Antosiewicz, Agnieszka Sirko and Paweł Sowin´ski

Sonia Plaza and Lucien Bovet

19 Iron: A Major Disease Modifier in Thalassemia 471 Sujata Sinha

Rafael Borra´s Avin˜o´, Jose´ Rafael Lo´pez-Moya and Juan Pedro Navarro-Avin˜o

22 Input and Transfer of Trace Metals from Food via

Simone Wuenschmann, Stefan Fra¨nzle, Bernd Markert and

Neisse and Woivodship Małopolska with Respect to

in Colostrum and Mature Milk Sampled

(Specific Ones) in the Food/Milk System and Extent

xiv CONTENTS

6 Discussion 577

Simona Di Gregorio

24 Environmental Contamination Control of Water

Carlos Paulo and Joa˜o Pratas

4 Case Study: Water Drainage from Uranium Mines Control by

25 Copper as an Environmental Contaminant: Phytotoxicity

Myriam Kanoun-Boule´, Manoel Bandeira De Albuquerque,

Cristina Nabais and Helena Freitas

26 Forms of Copper, Manganese, Zinc, and Iron in Soils

of Slovakia: System of Fertilizer Recommendation

Bohdan Jurani and Pavel Dlapa

xvi CONTENTS

9 Remarks to the System used for Copper, Manganese, Zinc, and

10 New Priorities in Research of Trace Elements in Soils of

Munir Ozturk, Ersin Yucel, Salih Gucel,

Serdal Sakc¸ali and Ahmet Aksoy

29 Bioindication and Biomonitoring as Innovative

Biotechniques for Controlling Trace Metal

Bernd Markert

3 Comparision of Instrumental Measurements and the Use of

From the very beginning, metals such as gold, silver, copper, and iron have played amajor role in the development and history of human societies and civilizations.Metals are dispersed on and in the Earthís crust, and methods for obtaining themfrom natural deposits have evolved over time The distribution of metals is notuniform, and localized deposits serve as ores for metals, usually found as compounds,combined with other minerals and inorganic anions If the concentration of thedesired metal is high enough in the deposit for an economical extraction, then theore can be exploited for a short or long period, depending on the state of the artand technology of mining Most metals have to be puriÝed or reÝned and thenreduced to the metallic state before use For example, the production of steel fromiron requires the elimination of impurities present in the rocks, followed by theaddition of other metals to obtain steel with the desired properties, such as hardnessand resistance to corrosion The science and technology of metals is precisely calledìmetallurgy.î Our post-modern society is still based on the use of metals, and somemajor applications are brieÐy mentioned below:

soft soaps, pottery, and glass Potassium hydroxide is an electrolyte in alkaline

is mainly used to make glass, but is also required to prepare chemicals, paper,

as well as to provide the Ýzz and neutralize excess stomach acid in analgesicdrugs

aluminum, Mg produces a strong structural metal Another use of Mg is in

pro-duces plaster of Paris

brass, bronze, and steel Chromium is also needed to produce alloys such asstainless steel or nichrome; the latter is often used as the wire heating element

in various devices such as toasters Compounds of Cr have many practical

xix

applications, such as for pigments production and leather tanning The main use

of manganese is as an additive to steel and in the preparation of different alloys

uses than any other metal Nickel is one of our most useful metals; in its purestate, it resists corrosion, and it is thus frequently layered on iron and steel as

a protective coating by electrolysis When alloyed with iron or with copper,

Ni makes the metal more ductile and resistant to corrosion and to impact

electrical wiring It is also resistant to corrosion and thus appropriate to carry hot

present, its surface becomes coated with a green Ýlm

also used in various alloys, like brass (Cu and Zn) and bronze (Cu, Sn, and Zn).Zinc is important in the manufacture of zinc ñ carbon dry cells and other bat-teries Zinc oxide is used in sunscreens and to make quick-setting dentalcements Zinc sulÝde is suitable to prepare phosphors that glow when submitted

to UV light or high-energy electrons of cathode rays, like the inner surface of

TV picture tubes and the displays of computer monitors Cadmium is useful

as a protective coating on other metals and for making Ni ñ Cd batteries

Woodís metal consists of an alloy of Bi, Pb, Sn, and Cd, melting at 708C only,used to seal the heads of overhead sprinkler systems: A Ýre triggers the systemautomatically by melting the alloy Different lead oxides are also needed inmaking pottery glazes and Ýne lead crystal; in corrosion-inhibiting coatingsapplied to structural steel; and as the cathode in lead storage batteries.However, metals not only play an essential role in our daily life, but also arereleased into the environment in an uncontrolled way and become contaminants, oreven pollutants A contaminant is present where it would not normally occur, or atconcentrations above natural background, whereas a pollutant is a contaminant thatcause adverse biological effects to ecosystems and/or human health In such acontext, green plants play a key role in the availability and mobility of metals.Plants can remove metals from contaminated soils and water for cleanup purposes.Several plant species, hyperaccumulating elements like nickel, gold, or thallium,can be used for phytomining On the other hand, crops with a reduced capacity toaccumulate toxic metals in edible parts should be valuable to improve food safety

In contrast, crop plants with an enhanced capacity to accumulate essential minerals

in an easily assimilated form can help to feed the rapidly increasing world populationand improve human health through balanced mineral nutrition Because many metalshyperaccumulated by plants are also essential nutrients, food fortiÝcation and phyto-remediation are thus two sides of the same coin The different chapters of this book

xx FOREWORD

do address the dual role of trace elements as nutrients and contaminants and reviewthe consequences for ecosystems and health.

DR JEAN-PAULSCHWITZGUE ¥BEL

Chairman of COST Action 859

Laboratory for Environmental Biotechnology (LBE)

Swiss Federal Institute of Technology Lausanne (EPFL),

Station 6, CH 1015, Lausanne, Switzerland

It is a general belief that the fruits and vegetables that our parents ate when they weregrowing up were more nutritious and enriched with essential mineral nutrients andwere less contaminated with toxic trace elements than the ones that are being con-sumed by us currently A study of the mineral content of fruits and vegetablesgrown in Great Britain between 1930 and 1980 has added weight to that beliefwith findings of such decreases in nutrient density The study, conducted by scientists

in Great Britain, found significantly lower levels of calcium, magnesium, copper, andsodium in vegetables, as well as significantly lower levels of magnesium, iron, copperand potassium in fruits Research studies are showing that the reducing nutritionalvalue and the problem of contamination associated with food quality is increasing

at an alarming rate The decline in quality of agricultural produce has corresponded

to the period of increased industrialization of our farming systems, where emphasishas been on cash crop cultivation that demands high doses of agrochemicals—that

is, fertilizers and pesticides

Several of the trace elements are essential for human as well as animal health.However, nutritionally important trace elements are deficient in soils in manyregions of the world and the health problems associated with an excess, deficiency,

or uneven distribution of these essential trace elements in soils are now a majorpublic health issue in many developing countries Therefore, the development of

“foods and animal feeds” fortified with essential nutrients is now one of the mostattractive research fields globally In order to achieve this, knowledge of thetraditional forms of agriculture, along with conservation, greater use of nativebio-geo-diversity, and genetic diversity analysis of the cultivable crops, is a must

A number of trace elements serve as cofactors for various enzymes and in a variety

of metabolic functions Trace elements accumulated in medicinal plants have thehealing power for numerous ailments and disorders Trace elements are implicated

in healing function and neurochemical transmission (Zn on synaptic transmission);

Cr and Mn can be correlated with therapeutic properties against diabetic and vascular diseases Certain transition group elements regulate hepatic synthesis ofcholesterol Nutrinogenomics, pharmacogenomics, and metallomics are now emerging

cardio-as new arecardio-as of research with challenging tcardio-asks ahead

Soil, sediment, and urban dust, which originate primarily from the Earth’s crust, isthe most pervasive and important factor affecting human health and well-being Traceelement contamination is a major concern because of toxicity and the threat to humanlife and the environment A variety of elements commonly found in the urbanenvironment originate technogenically In an urban environment, exposure of

xxiii

human beings to trace elements takes place from multiple sources, namely, watertransported material from surrounding soils and slopes, dry and wet atmosphericdeposition, biological inputs, road surface wear, road paint degradation, vehiclewear (tyres, body, brake lining, etc.), and vehicular fluid and particulate emissions.Lead and cadmium are the two elements that are frequently studied in street dust,but very little attention has been given to other trace elements such as Cr, Cu, Zn,and Ni, which are frequently encountered in the urban environment.

Street dusts often contain elevated concentrations of a range of toxic elements, andconcerns have been expressed about the consequences for both environmental qualityand human health, especially of young children because of their greater susceptibility

to a given dose of toxin and the likelihood to ingest inadvertently significant tities of dust Sediment and dust transported and stored in the urban environmenthave the potential to provide considerable loadings of heavy metals to receivingwater and water bodies, particularly with changing environmental conditions Onland, vegetables and fruits may be contaminated with surficial deposits of dusts.Environmental and health effects of trace metal contaminants in dust are dependent,

quan-at least initially, on the mobility and availability of the elements, and mobility andavailability is a function of their chemical speciation and partitioning within or ondust matrices The identification of the main binding sites and phase associations

of trace metals in soils and sediments help in understanding geochemical processesand would be helpful to assess the potential for remobilization with changes insurrounding chemistry (especially pH and Eh) Sophisticated analytical and specia-tion techniques and synchrotron research are being applied to this field of research

in developed nations

This book covers both the benefits of trace elements and potential toxicity andimpact of trace elements in the environment in the chosen topics by leaders of theworld in this area

University of Hyderabad

Hyderabad, India

I am thankful to Padmasri Professor Seyed Ehtesham Hasnain, Vice-Chancellor,University of Hyderabad for inspiring me to focus research in the area of healthand nutritional science which gained considerable momentum under his dynamicleadership I am grateful to all authors for cogent reviews which culminated in thepresent form

Thanks are due to Anita Lekhwani, Senior Acquisitions Editor, Chemistry andBiotechnology for laying the foundation for this fascinating subject in 2005

I wish to place on record my appreciation for Rebekah Amos, Senior EditorialAssistant; Kellsee Chu, Senior Production Editor at John Wiley and Sons forsuperb and skillful technical assistance in production of this work punctually

Dr K Jayaram and Mr H Lalhruaitluanga helped in the preparation of the Indexand their assistance is greatly appreciated Last, but not least, I must acknowledge theexcellent cooperation of my wife, Savithri

xxv

University, Almaty 050040, Republic of Kazakhstan

38039 Kayseri, Turkey

University of Barcelona, E-08193 Bellaterra, Spain

DANUTA MARIA ANTOSIEWICZ, Department of Ecotoxicology, Faculty of Biology,The University of Warsaw, 02-096 Warsaw, Poland

SALAHA ATTIA-ISMAIL, Desert Research Center, Matareya, 11753 Cairo, Egypt

RAFAELBORRA ¥SAVIN ò O¥, ABBA Chlorobia S.L., Citriculture Department, School ofAgronomists, Polytechnic University of Valencia, 46022 Valencia, Spain

MANOELBANDEIRADEALBUQUERQUE, Center for Functional Ecology, Department ofBotany, University of Coimbra, 3001-455 Coimbra, Portugal

JUANBARCELO¥, Department of Plant Physiology, Bioscience Faculty, AutonomousUniversity of Barcelona, E-08193 Bellaterra, Spain

CARLOS BARATA, Environmental Chemistry Department, IIQAB-CSIC, 08034Barcelona, Spain

LUCIENBOVET, Philip Morris International R & D, Philip Morris Products SA, 2000Neuchaàtel, Switzerland

SIMONADIGREGORIO, Department of Biology, University of Pisa, 56126 Pisa, Italy

Barcelona, Spain

University, 842 15 Bratislava, Slovak Republic

OTTOFRA ® NZLE, Christian-Albrechts-University Kiel, Ecology Centre, Olshausenstr

40, D-24089 Kiel, Germany

STEFAN FRA ® NZLE, International Graduate School (IHI) Zittau, Department ofEnvironmental High Technology, D-02763 Zittau, Germany

xxvii

HELENAFREITAS, Center for Functional Ecology, Department of Botany, University

of Coimbra, 3001-455 Coimbra, Portugal

MARIAGREGER, Department of Botany, Stockholm University, 106 91 Stockholm,Sweden

HELMUTLIETH, Wipperfu®rther Strasse 147, D-51515 Ku®rten, Germany

MERCE` LLUGANY, Department of Plant Physiology, Bioscience Faculty,Autonomous University of Barcelona, E-08193 Bellaterra, Spain

JOSE¥RAFAELLO ¥PEZ-MOYA, ABBA Chlorobia S.L., Citriculture Department, School

of Agronomists, Polytechnic University of Valencia, 46022 Valencia, Spain

ELENA MAESTRI, Division of Genetics and Environmental Biotechnologies,Department of Environmental Sciences, University of Parma, Parma 43100, Italy

BERND MARKERT, International Graduate School (IHI) Zittau, Department ofEnvironmental High Technology, D-02763 Zittau, Germany

NELSON MARMIROLI, Division of Genetics and Environmental Biotechnologies,Department of Environmental Sciences, University of Parma, Parma 43100, Italy

Gebze, Kocaeli, Turkey

CRISTINANABAIS, Center for Functional Ecology, Department of Botany, University

of Coimbra, 3001-455 Coimbra, Portugal

JUAN PEDRO NAVARRO-AVIN ò O, ABBA Chlorobia S.L., Citriculture Department,School of Agronomists, Polytechnic University of Valencia, 46022 Valencia,Spain; and Department of Agrarian Sciences and of the Natural Environment,

School of Technology and Experimental Sciences, University ìJaume I,î 12071Castello¥n, Spain

N NIRUPA, Department of Plant Sciences, University of Hyderabad, Hyderabad

CHARLOTTE POSCHENRIEDER, Department of Plant Physiology, Bioscience Faculty,Autonomous University of Barcelona, E-08193 Bellaterra, Spain

Universiy, Almaty 050040, Republic of Kazakhstan

SERDALSAKC š ALI, Biology Department, Faculty of Science & Arts, Fatih University,

34500 Hadimkoy, Istanbul, Turkey

ARUN K SHANKER, Central Research Institute for Dryland Agriculture (CRIDA),Indian Council of Agricultural Research (ICAR), Santoshnagar, Hyderabad,

Biochemistry and Physiology Department, Plant Breeding and AcclimatizationInstitute, 05-870 B onie, Radziko¥w, Poland

University of Barcelona, E-08193 Bellaterra, Spain

SHUHE WEI, Key Laboratory of Terrestrial Ecological Process, Institute ofApplied Ecology, Chinese Academy of Sciences, Shenyang 110016, PeopleísRepublic of China

SIMONEWUENSCHMANN, Fliederweg 17, D-49733 Haren, Germany

FATEMEH ALAEIYAZDI, Department of Agronomy, Yadz Agricultural and NaturalResources Research Center, Yazd, Yazd Province, I.R of Iran

YASEMIN YILDIZHAN, Institute of Genetic Engineering and Biotechnology, 41470Gebze, Kocaeli, Turkey

Eskisehir, Turkey

HARALDZECHMEISTER, University of Vienna, Faculty of Life Sciences, Department

of Conservation Biology, Vegetation, and Landscape Ecology, A-1090,Vienna, Austria

QIXINGZHOU, Key Laboratory of Terrestrial Ecological Process, Institute of AppliedEcology, Chinese Academy of Sciences, Shenyang 110016, Peopleís Republic

of China; and College of Environmental Science and Engineering, NankaiUniversity, Tianjin 300071, Peopleís Republic of China

xxx CONTRIBUTORS

1 The Biological System of Elements:

Trace Element Concentration and Abundance in Plants Give Hints

on Biochemical Reasons of

Sequestration and Essentiality

Department of Environmental High Technology, International Graduate School (IHI) Zittau, D-02763 Zittau, Germany

Christian-Albrechts-University Kiel, Ecology Centre, Olshausenstr 40, D-24089 Kiel, Germany

HELMUT LIETH

Wipperfu¨rther Strasse 147, D-51515 Ku¨rten, Osnabrueck, Lower Saxony, Germany

With ongoing improvement of analytic gear, it has already become commonplace todetect the vast majority of (stable) elements in biological samples [Garten, 1976;Markert, 1996, Lieth and Markert, 1990] as well as in soils [Kabata-Pendiasand Pendias, 1984; Fra¨nzle, 1990] or seawater [Nozaki, 1997] The concentrationsthere may be considerably lower than in environmental compartments, down to thepico- or even femtomolar levels, because metal ions may not undergo bioaccumula-tion in plants or fungi [Lepp et al., 1987; Fra¨nzle, 1993; Markert et al., 2003] in

 Bernd Markert’s present address: Fliederweg 17, D-49733 Haren-Erika, Germany.

Trace Elements as Contaminants and Nutrients: Consequences in Ecosystems and

Human Health, Edited by M N V Prasad

Copyright # 2008 John Wiley & Sons, Inc.

1

the same manner as unpolar organics As a rule, there is “genuine” soil/plantbioconcentration (i.e., BCF [Biological Concentration Factor] 1) for only a fewmetals (Mg, Zn, K) in green plants, with that of others being rare.

The presence of some chemical element in biomass, be it in substantial amounts,does by no means imply that it exerts some biochemical function Several elementsthat are very abundant in the environment (particularly in soils) are not known to beessential for any kind of organism (e.g., Al, Ti) [Fra¨nzle and Markert, 2007a,b] Yet,besides the principal nonmetals C, H, O, N, S, and P, metals and other copious ortrace elements were involved in biology quite apparently from the very beginnings

of biological evolution [Beck and Ling, 1977; Kobayashi and Ponnamperuma,1985a,b; Williams and da Silva, 1996; Frausto and Williams, 2001]—that is, frombiogenesis itself—whereas during chemical evolution metal ions are (were) rarelyrequired to afford crucial intermediates or catalyze transformations providing import-ant structural features [Fra¨nzle, 2007; Fra¨nzle and Markert, 2002] All living beings,even those that appear least advanced with respect to biological or biochemical com-plexity, share the requirement for at least seven metals (namely, K, Mg, Mn, Fe, Cu,

Zn, Mo [or W in hyperthermophilic creatures]) These metals obviously differ siderably in their chemical properties; the latter is to be anticipated because metals inbiology serve to effect or catalyze rather different transformations, causing them orjust increasing selectivities of transformations Nevertheless, the exact function is not

species, irrespective of full genetic sequencing such as with Arabidopsis thaliana).Moreover, there are fairly many cases of metals acting in bioinorganic chemistrywhich differ from the optimum catalysts as defined by all the experiences in inorganicand metal – organic catalytic chemistry [Fra¨nzle, 2007] In addition, there are bio-chemical processes transforming substantial amounts of matter in the biospherewhich rely upon combinations of various metals The most prominent example ofthis is photosynthesis: Mn (þ Ca) ions are located in the center of photosystem II,affording oxidation of water, with the electrons thus liberated being shuttled to

to restore chlorophyll as a neutral molecule, respectively Hence, photosynthesiswill occur in an efficient manner only if some stoichiometric relationship between

Mg and Mn is kept within a green plant; the empirical value for green leavesMg/Mn is close to 5 (stoichiometric, not mass, ratio), with conifer needles differingsomewhat from this value

The same reasoning on mandatory metal ratios holds for animal metabolism, too,here concerning, for example, the Mo/Mg and Cu/Mg ratios for combinations ofoxidizing substrates (Mo, Cu in redox enzymes) and for storing energy from thisprocess (Mg in kinases, NTPases) For the sake of efficient metabolism, living organ-isms must keep these ratios in their bodies rather constant throughout lifetimes Inthose parts of their corresponding environments from which they retrieve metals(soil, ambient water, food organisms), the respective interelemental ratios mostlikely will differ from the demands of the organism under consideration and possiblyeven vary with time Hence the organism need not just obtain several different metals

by complexation but also has to achieve some fractionation among them Because

2 THE BIOLOGICAL SYSTEM OF ELEMENTS

metal – biomass interactions, starting with sequestration from food or environment,depend on complexation of the metal ions to biomass or some carrier within or(with root exudate) outside the organism, this fractionation will be accomplisheddue to either unequal complex formation equilibria or selective transport across mem-branes Moreover, the number of different sequestration agents in/around roots,fungal mycelia, or the guts of some animals is considerably smaller than that ofdifferent metal ions; accordingly, different metals are transported by the same carriersand compete for their binding sites [Duffield and Taylor, 1987].

Now, correlations among element abundances were produced for a number ofplant species some time ago [Markert, 1996; see Section 2.1] Here, abundances ofelement pairs were compared in 13 different plant species and correlated to eachother Conspicuously, abundances of chemically similar elements like P and As or

Ca and Ba are not correlated, whereas the REE (rare earth elements) abundancesare closely correlated once again From the correlation analysis a so-called BSEhas been established (Fig 1, see also Section 2.1)

between adjacent dots refer to abundance correlations among elements investigated in earlier works The respective biological functions of the elements are given in different shadowings Although after chemical evolution, its biological counterpart and successor acted to introduce a considerable number of metals into biomass where they behave e.g as biocatalyst components, generally speaking the concentrations of the latter metals (even Ca, Mg or Fe, Zn) are low, far lower than in the Earth’s crust which gives rise to a more prominent role for non-metals in biology/biochemistry which are gathered in the very left tip of the triangle This latter fact cor- responds to the fact that non-metals form the back-bones of biological materials, both in bulk and membranes.

Accordingly, abundances of essential elements may but need not be positivelycorrelated In addition, there is a need for definition of binding properties of metalions toward (different kinds of) biological material which can account forenrichments in certain samples For this purpose, a general relationship that links con-centrations or, more precisely, bioconcentration factors (BCF [values]) to complexstabilities of metals taken up by some organism must be constructed (and expressed

chains There are several reasons for this particular approach in biochemistry:

essential nor considerably toxic), hence can be expected just to follow chemicalequilibria by speciation into biological material rather than being selectivelyenriched or expelled/retained/linked to certain “controlling” sites/molecules

closely similar stabilities

physio-logical conditions and can be described by perturbation theory because there areonly small effects on metal ions brought about by electronic properties andenergies

Any living being thus must cope with the endeavor to

corre-sponding organism while being constantly connected to an environment (e.g.,soil, surrounding water) that usually does not match the respective demandsdirectly (cf Liebig´ minimum principle),

catalyz-ing the same biochemical transformation (e.g., Mn and Mg in photosynthesis).There are several matters that render this a complicated endeavor: The relativestabilities of (chelate) complexes of (divalent) metal ions usually change according

to a certain sequence, referred to as Irving – Williams sequence [Irving andWilliams, 1953], which itself is not related to the specific amounts required by anorganism, nor to the abundances of metals in soil or fresh water (or the inverse beha-vior, thereby permitting organisms to retrieve similar amounts of Mn, Cu, Zn, and so

on in spite of their highly different complex stabilities) Yet, the Irving – Williamssequence rather is something like a rule-of-thumb With ligands other than dicarbox-ylates, amino acids, or phenol(-ic) carboxylates, there are (often several) “inversions”

of the stability series Accordingly, living beings might select appropriate metals byproducing and delivering suitable ligands, with the above ones not being the onlyones that could be produced in substantial amounts and given away, for example,

by roots or mycelia On the other hand, soil organic matter (SOM) or aquatic organics

4 THE BIOLOGICAL SYSTEM OF ELEMENTS

(DOM) contain certain ligand functions capable of retaining metals from transfer intoliving beings Thus there is some competition for the metals between plant or fungusand soil The data that are derived from analyses of (plant) biomass (e.g., Markert[1996]) thus correspond to some superposition of effects.

Therefore, organisms have to change concentrations of the metal ions encountered

(basidiomycete) fungi need much more Fe and Cu, sometimes also V, to accomplishoxidative degradation of lignin than green plants require for sustaining their unlikebiochemistry The latter in turn have larger demands for Mg and Mn owing to photo-synthesis Plants and fungi might—and do—deliver different ligands to cope withthis: citric, malic, and oxalic acids in green plants and peptides; hydroxamates andsometimes amino acids in fungi (and also in soil bacteria) [Kaim and Schwederski,1993; Farago, 1986; Haas and Purvis, 2006] How, then, do these ligands comparewith respect to metal binding affinities and selectivities to the former ones?Complex stabilities depend on the extent of metal ion – ligand interactions; at thesame time, due to orbital interactions, the more the energy levels of the central metalions are changed, the stronger the interactions become In metal ions that are suscep-tible to redox reactions, the shift of orbital energies can be detected directly by change

of redox potential of the altered complex Hence there should be a relationshipbetween complex stability and the potential shift caused by some ligand in a standard

latter providing a measure for binding capability [Fra¨nzle, 2007] This argument fromperturbation theory can be represented in the following equation, with complex stabi-lities at a given metal ion taken from experiment or literature (aqueous medium, 258C,

linear regression analysis:

Here, x is the slope parameter of the correlation between (logarithmic) complexformation constant (taken, e.g., from Furia [1972] and Moeller et al [1965]) and theelectrochemical ligand parameter [Lever, 1990; Fra¨nzle, 2007; Fra¨nzle and Markert,2007a] for a given metal ion—say, in a series of Zn(II) complexes with bidentateligands (e.g., glycinate, oxalate, lactate, ethylene diamine, and aminomethanepho-

ions were published elsewhere, e.g., Fra¨nzle and Markert [2007a]) while c gives the

to define fractionation behavior via an effective electrochemical ligand parameter.Thus a large, if not comprehensive, set of parameters were produced by the first

1

This is not to suggest involvement of active transport in any case but might also refer to processes that rely upon metabolic energy—for example, associated with biosynthesis and eventual oxidative destruction of sequestrants connected with the Krebs tricarboxylate cycle, with destruction of these primary ligands being necessary to “hand over” the metal ions to other (cytosol) ligands in the root itself.

author (e.g., Fra¨nzle and Markert [2007a]) which permit to estimate hydrolytic

moiety When different ligands are present, speciation or distribution/partition mayalso be inferred from the above equation In soil, kinds and properties of ligands(SOM) change upon humification, and so do the ligand affinities of the metal ions.Then soil composition (C/N ratios, etc.) and speciation of N-free versus nitrogeneousligands control which metals will be passed into green plants or fungi, respectively

Studies: Environmental Analyses

The first data on element (abundance) correlations among green plant species later on

to be used in this study were obtained at Grasmoor (literally, “grassy bog”) naturalreserve near Osnabru¨ck, Lower Saxony, Germany around 1990 (Figs 2a and 2b).The original abundance correlations were derived from these data for a total of 13plant species [Markert, 1996] and called the Biological System of Elements (Figs 1and 3), with the name “Biological System of Elements” alluding to the chemical per-iodic system of elements (cf Railsback [2003]) From these data already the clear-cutlimits of that analogy become apparent: There is nothing like (some) “biological/biochemical group[s] of elements” which could directly be related/compared tothe chemical groupings of the PSE While abundances of most REEs among eachother and with Al correlate strongly, there are almost no relationships, for example,for distributions of P and As or of Ca and Ba Recently, when converting thesedata from mere correlations of abundances into a kind of parameter which describesboth (a) the general binding features of some kind of bioorganic ligand system/tissue

to retain and accumulate metals and (b) their capacity of fractionation among thelatter, comparative data for the same species at other sites (Betula pendula) and forquite different (including aquatic) plants were calculated (Table 2) For essentialelements, this is expected to correspond to the demands that relatively differamong different plant species, with distributions/BCF values of certain nonessentialelements to be used as a benchmark for this The focus of interest thus shifted frommere comparison to producing a scale for the underlying biochemistry; for the latter

of bioavailability of metals in certain soils) are used to get an idea on bioinorganic

2

The question for binding stabilities of metals or some fractions of the latter to soil [Tyler, 2004] need not

be considered here; it suffices to use the overall soil concentrations (produced, e.g., by aqua regia tion or nitric acid/HF digestion of some soil sample) for this purpose: As plants partly use the same ligands

extrac-in retrieval of heavy metals (e.g., citric acid) as extrac-in this procedure, correspondextrac-ing barriers—which will, moreover, hold to most of chemically similar metals like the REEs and Al—blocking some part of soil heavy metal content from the plants will just provide a constant correction term As comparisons and analy- sis of data are based on clusters of elements displaying equal BCF likewise, the effects from but partial bioavailability cancel out in this approach.

6 THE BIOLOGICAL SYSTEM OF ELEMENTS

Figure 2 (a, b) The “primary study site”: Grasmoor bog area near Osnabru¨ck/FGR

Ku¨sten- und Naturschutz)].

(metal ion) concentration processes and eventually characterize fractionation inside

The distribution of the essential metal Mg among the 13 species is highly correlated

and Sr (0.63), but not Mn (20.13; in spite of the coupling between Mn [PS II]and Mg [chlorophyll, rubisco] in photosynthesis), Zn (20.09), V (20.73), or Ba(þ0.27) [Markert, 1996] There are positive abundance correlations between Mg

correlation coefficients partly reported (numbers on lines connecting elements noted next to each other) There are both clusters of essential elements and highly correlated metals which

do not resemble each other very mcuh in chemical terms (AI, V Y) besides REE intercorrelations.

3

Si is essential for certain (fairly many) terrestrial plants, algae.

8 THE BIOLOGICAL SYSTEM OF ELEMENTS

with Eu, and negative correlations of Mg abundances with those of Y, Gd, Tb, and Hothrough Yb, whereas occurrences of Pr, Nd, and Lu (which latter, strictly speaking, is

certain coordination effects) in the 13 plant species investigated by Markert are not atall correlated to the abundances of Mg

So, most of these data suggest that there are some biochemistry” plants in which essential elements (almost) altogether are present inelevated levels besides others which contain appreciably less of all theseelements—metals and nonmetals alike Yet, Mn and Zn deviate from this pattern

Zn usually), must be decoupled from the general tration “antipodal” relationship However, if either essential or highly toxic elementsare considered, it may well be that these are either enriched (essential trace elements)

high-concentration/low-concen-or rejected by specific chemical means, such as chaperons [Rosenzweig, 2001], some

of which also control metal distribution in plants, supporting rejection of As, Cd, and

Pb there while controlling transport and allocation of Cu or Zn [Tottey et al., 2005].Though also some major essential elements make their way through biologicalmaterials/tissues without any such contributions from chaperons (Mg, Mn, mostlyalso Ni), it is advisable for understanding the consecutive chemical steps inelement transport (Fig 4, Fra¨nzle [2007]) to focus on such elements (i.e., metalions) which are neither essential nor prominently toxic

A large group of such elements which fulfill this condition are rare earth elements(lanthanoids, REE), including yttrium (cf Jakubowski et al [1999]) Unlikeconventional chemical “wisdom” has it, REE chemical properties differ sufficientlyfrom each other—especially concerning complex formation [Moeller et al.,1965]—also to undergo substantial fractionation in biomass [Emsley, 2001] andalso bring about distinct differences in toxicities As the data set [Markert, 1996]includes all Y and the two La – Nd and Sm – Lu series, REEs and some other elements(Sr, Al) can be used for benchmarking metal fractionation in a plant For all theseelements, c and x values for mono- and bidentate binding are available [Fra¨nzle,2007; Fra¨nzle and Markert, 2007a,b] Thus Eq (2) can be applied for calculatingeffective electrochemical ligand parameters for biomass (assuming bidentatecoordination as corresponding to average interaction constants of numerous metalions with biological material [data from Williams and Silva, 1996]) from REEdistributions, with their large number of 15 elements (omitting promethium)allowing for construction of meaningful clusters of identical BCF These in turn

accumulation of weakly binding elements like the heavier alkaline earths beyond

Mg within a plant (Section 3.3)

The electrochemical ligand parameters as introduced in this chapter are now knownfor hundreds of donor compounds or ions [Lever, 1990], mainly from direct

electrochemical studies and an additivity assumption; others are derived from

species) More recently, data were added by Fra¨nzle using Eq (1) to calculate

Ru(II/III) redox ligands involving biorelevant ligands were done, producing a

The list includes including many ligands that are involved in biological processes, be

it amino acids, their side chains (e.g., imidazole [histidine], dialkyl sulfide ine]), heterocycles (purines, flavines), salicylic acid (some kind of prototype of tanninderivatives), or phosphorylated species For orientation, a couple of data for speciesinvolved in soil chemistry and general biochemistry is given in (Table 1)

com-ponents are taken from the tricarboxylate cycle (citrate, malate; a comprehensive list of exuded ligands can be found in Dakora and Phillips [2002]), with the original ligands removed by oxidation after resorption and replaced by carrier proteins in xylem and histosol, with the ions eventually ending up in leaf proteins Swift brackets denote catalysts (matalloen- zymes containing the corresponding metal) Owing to oxidative cleavage of the original ligand, metals may be transported and accumulated efficiently further on even when forming weak complexes (Ba, REEs in certain nutforming trees) but likewise reside in the roots without any further vertical transport (Cd in corn).

10 THE BIOLOGICAL SYSTEM OF ELEMENTS

3 RESULTS

investi-gations whether this is a result of an abundant biochemical setting in terms of port and metal retention in photosynthetic organs merely or can be interpreted as anadaption to the plants (frequent) requirement to maintain certain ratios of essentialelements for proper biochemical interconnections among reactions promoted byunlike elements Yet there is some hint concerning this: The CEP (competitive exclu-sion principle) theorem states that different biological species must “tap” resources inunlike ways in order to be able to coexist in the same habitat (see below) This

trans-TABLE 1 Ligands Involved in Soil and Biochemistry

Denticity n

Biologically Relevant Ligand (Example)

and caffeic acids, humic acids Chelating