HEAVY METALS
D C Adriano, University of Georgia, Aiken, SC, USA
N S Bolan, Massey University, Palmerston North, New Zealand
J Vangronsveld,Limburgs Universitair Centrum, Dlepenbeek,
Belgium
W W Wenzel, Universität 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., aniamls 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 prod- uct 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. p. 175-182. In Encyclopedia of Soils in the Environment, edited by D. Hillel. Elsevier Academic Press. Amsterdam, The Netherlands.
