Metal Speciation, Chelation and Complexing Ligands in Plants
Most transition metal ions and some main group metal ions form complexes with small (Cl−, carboxylic acids, amino acids) and macromolecular organic substances (proteins, DNA, polysaccharides) present in the xylem and phloem of plants (Lobinski and Potin-G
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Springer-V erlag Berlin Heidelberg GmbH
M N V Prasad (Ed.)
Heavy Metal Stress in Plants From Biomolecules to Ecosystems Second Edition
With 76 Figures, two in Color, and 56 Tables
,
Springer
M N V Prasad Department of Plant Sciences University of Hyderabad Hyderabad, Andhra Pradesh India
First Edition 1999 © Springer-Verlag Berlin Heidelberg 2004 Originally published by Springer-Verlag Berlin Heidelberg New York in 2004
springeronline.com ISBN 978-3-642-07268-0
ISBN 978-3-662-07743-6 (eBook)
DOI 10.1007/978-3-662-07743-6
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Preface
Biogeochemical cycling of essential and non-essential elements in ecosystem is a complex problem. AI, Ca, Fe, Na, P, K, S, Si, Ti, Mg; bioelements, viz. C, H, Nand 0, constitute about 99% of the elemental composition of the environment. Elements such as As, Cd, Co, Cu, Cr, Hg, Mo, Mn, Ni, Pb, Se, Zn etc constitute about 1% of the total elemental content of the soil al}d hence are called trace elements. We use the term 'heavy metal' for those weighing more than 5 g cm-3 e.g. Zn (7.1), Cr (7.2), Cd (8.6), Ni (8.7), Co (8.9), Cu (8.9), Mo (10.2), Pb (11.4), and Hg (13.5); Al (2.7) is a light metal; 'As and Sn' half-metals and 'Se' non-metal. Some metals can occur in different valence states rendering more or less toxic in different states. One example is less toxic Cr(III) and the more toxic Cr(VI). A few metals are precious, like gold or platinum. Cd and As are poisonous and others like Cs, Hg and Ga are liquids at room temperature. Elements viz., As, B, Cd, Cr, Cu, Hg, Ni, Pb, Se, U, V, and Zn are present naturally in soils in low concentrations but may be elevated because of human activities, fossil fuel combustion, mining, smelting, sludge amendment to soil, fertilizer and agrochemical application. At low concentrations some trace elements (e.g. Cu, Cr, Mo, Ni, Se and Zn etc.) are essential for healthy functioning and reproduction of microorganisms, plants and animals including man. However, at high concentrations, the same essential elements may pose toxicity. Some trace elements are also non-essential e.g. As, Cd, Pb and Hg e
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