Speciation of Cadmium in the Environment

Kim, N.D. and Fergusson, J.E., Effectiveness of a commonly used sequential extraction techniques in determining the speciation of cadmium in soils. Sci Total Environ 1991 105 191-209. 

Raspoe B (1980) Distribution and speciation of cadmium in natural waters. In Nriagu JO, ed. Cadmium in the environment. Part I, Chapter 6, pp.147-236. John Wiley Sons, New York. 

Abstract This chapter reports an analysis of literature dedicated to the speciation of cadmium in various environmental compartments, i.e., atmosphere, natural waters, soils and sediments. The difficulty of the cadmium speciation studies, due to the variability of composition of different natural systems and to the low cadmium concentration in the environment, is highlighted. As an alternative approach, cadmium behavior is assessed by modelling its reactivity towards the main classes of ligands usually present in natural systems. The stability of cadmium complexes with... 

Luten, J.B., W. Bouquet, M.M. Burggraaf, and J. Rus. 1986. Accumulation, elimination, and speciation of cadmium and zinc in mussels, Mytilus edulis, in the natural environment. Bull. Environ. Contam. Toxicol. 37 579-586. 

Cadmium is a silver-white, blue-tinged, lustrous metal that melts at 321 °C and boils at 767°C. This divalent element has an atomic weight of 112.4, an atomic number of 48, and a density of 8.642 g/cm. It is insoluble in water, although its chloride and sulfate salts are freely soluble. The availability of cadmium to living organisms from their immediate physical and chemical environments depends on numerous factors, including adsorption and desorption rates of cadmium from terrigenous materials, pH, Eh, chemical speciation, and many other modifiers. The few selected examples that follow demonstrate the complex behavior of cadmium in aquatic systems. 

In the following sections, the original speciation of metals released during various industrial activities are reviewed, and possible changes in speciation in the environment outlined. The spatial location of metallic compounds at specific types of site is not discussed in detail the reader is referred to the Department of the Environment s Industry Profiles (Department of the Environment 995a-o). The present review is focused on cadmium, arsenic, chromium, mercury, lead, copper, nickel and zinc because they are conunon at industrially contaminated sites in forms which are considered hazardous. Cadmium, arsenic, chromium, mercury and lead were identified as groundwater contaminants representing threats to human health in a comprehensive US survey (Knox Canter 1996). 

As already discussed in previous chapters, speciation plays an important role in cadmium toxicity and exposure to living organisms, influences its availability, accumulation, bio-modification, as well as its transport inside the organisms, and within and between environmental compartments too. That is why speciation studies are of fundamental importance to fully appreciate how this element behaves in the environment. Unfortunately, a careful analysis of literature dedicated to the speciation of cadmium reveals that this term is often abused and erroneously used, resulting in a consistent reduction of the papers really matching lUPAC recommendations and being effectively dedicated to cadmium speciation. 

Berggren, D. (1989) Speciation of aluminium, cadmium, copper, and lead in humic soil solutions - a comparison of the ion exchange column procedure and equilibrium dialysis. Int.J. Environ. Anal. Chem., 35, 1-15. 

Sunda, W. G., D. W. Engel, and R. M. Thuotte (1978). Effect of chemical speciation on toxicity of cadmium to grass shrimp. Palaemonetes pugio Importance of free cadmium ion. Environ. Sci. Technol. 12, 409- 13. Takamatsu, T., M. Kawashima, andM. Koyama(1985). The role of Mn-rich hydrous manganese oxide in the accumulation of arsenic in lake sediments. Water Res. 19, 1029-1032. 

Hirsch, D., and Banin, A. J. (1990). Cadmium speciation in soil solutions the residual effect of sewage sludge on heavy metal content of tobacco and peanut. J. Environ. Qual. 19, 366-372. 

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