Speciation cadmium species

In addition to soil solution, speciation of trace elements in water of the Nahr-Ibrahim river valley of Lebanon was studied with the AQUACHEM model. The results indicate that a high percentage of Pb and Zn is present as carbonate species, but in low percentages in free hydrated ion species. Cadmium exhibits as a high percentage of a free hydrated Cd2+. 

Stolzberg [143] has reviewed the potential inaccuracies of anodic stripping voltammetry and differential pulse polarography in determining trace metal speciation, and thereby bio-availability and transport properties of trace metals in natural waters. In particular it is stressed that nonuniform distribution of metal-ligand species within the polarographic cell represents another limitation inherent in electrochemical measurement of speciation. Examples relate to the differential pulse polarographic behaviour of cadmium complexes of NTA and EDTA in seawater. 

Florence, T.M. (1977) Trace metal species in fresh waters. Water Res., 11, 681-687. Florence, T.M. (1982) Development of physicochemical speciation procedures to investigate the toxicity of copper, lead, cadmium and zinc towards aquatic biota. Anal. Chim. Acta, 141, 73-94. 

A combination of IPC and inductively coupled plasma (ICP) MS was extensively explored for the speciation of phosphorus, arsenic, selenium, cadmium, mercury, and chromium compounds [108-118] because it provides specific and sensitive element detection. Selenium IPC speciation was joined to atomic fluorescent spectrometry via an interface in which all selenium species were reduced by thiourea before conventional hydride generation [119], Coupling IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes with cold vapor generation and atomic fluorescence detection was successfully validated [120]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of Cr(III) and Cr(VI) [121] and arsenic compounds employing hydride generation [122]. 

IPC-ICP-MS was extensively explored for the speciation of phosphorus, arsenic, selenium, cadmium, mercury, and chromium compounds [4-17] because it provides specific and sensitive element detection. Selenium IPC speciation took also advantage of coupling with atomic fluorescent spectrometry via an interface in which all selenium species are reduced by thiourea before conventional hydride generation... 

Both the amounts and proportion of organic compounds of root exudates vary substantially with plant species and cultivars. Further, the same plant culti-var grown in different soils shows variations with respect to the kind and amount of LMWOAs present in the rhizosphere (Table 9). More recent data show that the kind and amount of root exudates vary with the level of Cd in contaminated soils (Chou et al, 2003 Wang et al, 2003), as illustrated in Table 10. Further, the amount of LMWOAs correlates significantly with the Cd concentration in the rhizosphere soils (Table 11). Cadmium speciation in relation to its bioavailability in the rhizosphere merits increased attention. 

Figure 8 New trends in speciation Separation of Cd-metallothionein isoforms by (A) SEC with UV and ICP-MS detection, (B) reversed-phase-LC-ICP-MS of the main Cd containing species eluted by SEC, (C) ES-MS of the peaks labeled as 1 and 2 in the RP-LC-ICP-MS chromatogram. (Reproduced from Polec K, Garcfa-Arribas O, Perez-Calvo M, etal. (2000) Identification of cadmium-bioinduced ligands in rat liver using parallel HPLC-ICP-MS and HPLC-electrospray MS. Journal of Analytical Atomic Spectrometry 15 1363-1368.)...

The environmental impact and the biological activity of cadmium, as well as other metals, organometals, and radionuclides, are strictly dependent on their speciation, unambiguously defined by lUPAC as the distribution of an element amongst defined chemical species in a system [1]. 

The atmospheric pollution by cadmium is a result both of natural and man-made activities, such as the combustion processes based on fossil fuels (in particular coal and oil) and the emission from processes in the pyro-metallurigical non-ferrous metal industries. The deposition, transport, and inhalation processes are controlled predominantly by the size of the atmospheric aerosols, so that the primary type of speciation of interest to atmospheric chemists is the metal size distribution. However, chemical speciation (in terms of the distribution of both the dissolved/ particulate species and the inorganic/organic complexes) is important in governing... 

In the atmosphere, cadmium is present as a result of both namral and man-made activities, mainly in finer particles. It mainly occurs in various inorganic forms, though organic complexation may play important roles in some cases. In the natural waters, cadmium is mainly present as chloride and/or carbonate species, though the presence of organic ligands may influence its speciation. In soils and sediments, including soil solutions, cadmium speciation is deeply affected by the characteristic of the matrix. 

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