The metal-organic complex-bound

In general, TEs in exchangeable and acid-soluble forms are considered to be easily bioavailable (see Table 12.1). The metal-organic complex-bound form is also relatively mobile (Krishnamurti et al., 1995). The reducible and oxidizable forms are relatively stable under standard soil conditions, yet easily reducible and oxidizable fractions may be readily mobilized, as detailed in the ensuing sections. 

Compared with bulk soils, solid-phase speciation of Cd differs substantially in phosphate fertilizer-treated rhizosphere soils (Krishnamurti et al., 1996). The amounts of carbonate-bound Cd and metal-organic complex-bound Cd species of the rhizosphere soils at 2-week plant growth stage, particularly in the soils treated with Idaho phosphate fertilizer, are appreciably higher than those of the corresponding bulk soils (Fig. 4). In comparison to the corresponding bulk soils, the amount of carbonate-bound Cd species of the rhizosphere soils increased by 15-18% in the control soils and by 79-92% in the soils treated with Idaho phosphate fertilizer, whereas the metal-organic complex-bound Cd species increased by 4-7% in the control soils and by 2-3 times in the soils treated with Idaho phosphate fertilizer. The increase in the carbonate-bound Cd... 

As reported above, one fundamental characteristic of DPASV with respect to the speciation problem is the ability to differentiate the total dissolved metals in two fractions on the basis of electrochemical properties of chemical forms in which the metals are present. When the methodology is applied to analyze an untreated (undigested) sample, the measurement is sensitive to the so-called electroactive fraction of total dissolved metal concentration, which, under carefully controlled conditions (especially as regards the deposition potential and the rotation speed of the electrode), is practically composed of the ionic and the inorganically complexed fractions of metal. The metal aliquot strongly bound to organic ligands remains undetected (59, 67, 68). 

Type I A metal ion, metal complex or metal is bound to a chain of a linear or cross-linked organic or inorganic macromolecule via a covalent (at the metal), a coordinative (at the metal), a complex (at the ligand of a complex), an ionic or a 7i-bond (so-called Macromolecular Metal Complexes , Fig. 1-4). Additional possibilities exist for different kinds of binding at the surface of a carrier or the end group of a macromolecule. Examples are described in Chapters 4 and 5. 

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