Organic matter-metal complexes

Schnitzer, M. and Khan, S. "Humic Substances in the Environment," 327 p. Marcel Dekker, New York, 1972. Broadbent, F. and Lewis, T. Soil organic matter-metal Complexes 4. Nature and properties of exchange sites. Soil Sci. 91, 393-399 (1961). 

Examples are organic-matter metal complexing phenolic polymers ... 

Buffle, J., Tessier, A., and Haerdi, W., Interpretation of trace metal complexation by aquatic organic matter, in Complexation of Trace Metals in Natural Waters, Kramer, C.J.M. and Duinker, J.C., Eds., Martinus Nijhoff/Dr. W. Junk Publishers, The Hague, 1984, pp. 301-316. 

Generally for sedimentary rocks substitution in silicate lattices of primary minerals is of lesser importance. As the primary minerals decompose during weathering the alkaline earths and alkali metals tend to remain in solution and some of the metallic micronutrients pass into the lattices of the secondary or clay minerals. Others become adsorbed onto clay sized particles, are incorporated into humified organic matter by complexation or separate as precipitates following changes in redox potential. 

In aquatic systems, in addition to the complexation of metal ions by natural organic matter, metal bioavailability, bioaccumulation, and toxicity are highly affected by water hardness and alkalinity (Banks et al. 2003). This is also applicable to metal mixtures where complexation of metals can occur even at higher rates than when single chemical compounds are present. 

MacCarthy, P., An interpretation of stability constants for soil organic matter-metal ion complexes under Schubert conditions. J. Environ. Sci. Health A12, 43-59 (1977). 

Much emphasis has been placed in recent years on the use of chelates in supplying plants with iron, zinc, copper and manganese. Since chelation reactions are believed to be involved in the reaction of humus with these metal ions it is appropriate to consider what is meant by chelation and to compare the status of metals held in this manner with that of those held in the organic matter exchange complex. Incidentally, the formation of soluble metal—organic complexes has long been known although emphasized only comparatively recently (Horner et al., 1934). 

In this work ion-exchange and gel-permeation chromatography coupled with membrane filtration, photochemical oxidation of organic metal complexes and CL detection were applied to the study of the speciation of cobalt, copper, iron and vanadium in water from the Dnieper reservoirs and some rivers of Ukraine. The role of various groups of organic matters in the complexation of metals is established. 

In addition to the interactions discussed above, which all depend in part on the ioniz-ability, or at least polarizability, of the surface and the adsorbates, hydrophobic parts of ligands may bind to corresponding parts of surfaces. Thus, if a metal ion is complexed or irreversibly bonded to a hydrophobic molecule, the metal may be incorporated into the bulk or surface of a particle via hydrophobic interaction between the molecule and the solid phase. Such interactions may be quantitatively significant in systems with high concentrations of dissolved and particulate organic matter. 

Transport in solution or aqueous suspension is the major mechanism for metal movement from the land to the oceans and ultimately to burial in ocean sediments. In solution, the hydrated metal ion and inorganic and organic complexes can all account for major portions of the total metal load. Relatively pure metal ores exist in many places, and metals from these ores may enter an aquatic system as a result of weathering. For most metals a more common sequence is for a small amount of the ore to dissolve, for the metal ions to adsorb onto other particulate matter suspended in flowing water, and for the metal to be carried as part of the particulate load of a stream in this fashion. The very insoluble oxides of Fe, Si, and A1 (including clays), and particulate organic matter, are the most important solid adsorbents on which metals are "carried."... 

Davis, ]. A. (1984). Complexation of trace metals by adsorbed natural organic matter. Geochim. Acta 48, 679-691. 

Upon formation of a metal chelate or complex, the next rate-limiting step in delivering iron to the cell is the diffusion of iron complexes through the. soil in response to diffusion gradients. In the vicinity of plant roots, metal chelates and complexes may also move by bulk flow in the transpiration stream as water moves from the soil into the plant. However, depending on their charge characteristics and hydrophobicity, metal chelators and complexes can become adsorbed to clay and organic matter, which may then decrease their mobility and bioavail-... 

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