SREL Reprint #2831




Heavy metals

D. C. Adriano1, N. S. Bolan2, J. Vangronsveld3, and W. W. Wenzel4

1University of Georgia, Aiken, SC, USA
2Massey University, Palmerston North, New Zealand
3Limburgs Universitair Centrum, Dlepenbeek, Belgium
4Universität für Bodenkultur, Wien, Austria

Introduction: Certain metals are essential for the normal growth of plants, animals, and humans. In plant nutrition, these are called micronutrients, represented by iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), and molybdenum (Mo). In addition to these micronutrients, arsenic (As), cobalt (Co), chromium (Cr), nickel (Ni), selenium (Se), tin (Sn), and vanadium (V) are essential for animal nutrition. Similarly in human nutrition, the above nutrients are essential, except As and V. They are collectively called micronutrients or trace elements because they are required in only trace amounts (unlike the major nutrients nitrogen, phosphorus, and potassium, required in relatively large amounts) and any excess may result in unfavorable biological response.
Since the advent of the Industrial Age, the environment has been subjected to emission and deposition of anthropogenic chemicals, both organic and inorganic. Consequently, some of these chemicals have accumulated in various ecosystems, both aquatic and terrestrial, to the extent that in numerous instances they have bioaccumulated to exorbitant levels that have the potential to imperil the well-being of biota, including the consumers (i.e., animals and humans). Heavy metals are elements having densities greater than 5 g cm-3. The term refers to metals and metalloids that are associated with pollution and toxicity, but also elements that are required by biota at low concentrations. While some of the most prevalent xenobiotic organics have only been released to the environment during the last 3-4 decades (e.g., polyaromatic hydrocarbons (PAHs), dioxin, trichloroethylene (TCE)), several heavy metals have been produced and subsequently emitted for hundreds of years. For example, lead (Pb) was initially produced even before the rise of the Roman Republic and Empire (approx. 2000 years ago).
The ever-increasing production and demand by society for metals indicate the mounting probability of their dispersal and contact with the environment. A metal may be dispersed from the time its ore is mined to the time it becomes a finished product. In some cases the ultimate disposal of the finished product may also lead to metal dispersion. The growing world population and the importance of metals in growing economies just ensures more production of metals and the likelihood of more dispersal, especially in developing countries.

SREL Reprint #2831

Adriano, D. C., N. S. Bolan, J. Vangronsveld, and W. W. Wenzel. 2005. Heavy Metals. pp. 175-182 In D. Hillel (Ed.). Encyclopedia of Soils in the Environment. Elsevier Academic Press. Amsterdam, The Netherlands.

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