Natural organic matter metal ions complexation

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. 

Divalent cations, particularly calcium, have been shown to enhance fouling of membranes with natural organic matter (NOM).3 Because is it s acidic nature, NOM can form complexes with dissolved metal ions. The strongest bonds occur with calcium. This is a function of the size of the metal ion, it s electronic charge, and the... 

Huber C., Filella M., and Town R. M. (2002) Computer modelling of trace metal ion speciation practical implementation of a linear continuous function for complexation by natural organic matter. Comput. Geosci. 28, 587-596. 

Cu, have shown toxic effects on a diverse assortment of aquatic biota (6 8). The very same metal ions, on the other hand, portray a reduction or complete eradication of toxic effects when complexed with natural organic matter. Fate and transport of metal ions in the environment are also governed by associations with fulvic acid material. Therefore, determination of stability constants between FA ligand sites and potentially hazardous metal ions should be considered fundamentally important. 

Finally, the concentration of dissolved organic matter and amount of humic acids are required in order to take into account the interaction of free metallic ions with the dissolved organic matter, especially humic substances. This part of the model has not been fully validated for natural conditions (high diversity and complexity of natural organic matter). Furthermore, dissolved organic matter may interact directly with biological material. 

One problem with trying to ascertain the relative radionuclide-complexing ability of different environmental surfaces is a lack of consistency in the framework that is used for evaluating sorption (complexation) among surface types. Metal oxides (including clays) have been the subject of a vast amount of experimental research and modeling. While both natural organic matter and microbial surfaces have received attention for their ability to accumulate metal ion (bacteria and viruses much less so), there has been relatively little work done on the simulation of metal-NOM and metal-bacteria interactions in a manner that is consistent with the surface complexation (SC) approach used for metal oxides. Examples of the application of SC to NOM and bacteria are Westall et al. (1995), and Fein et al. (1997), respectively. As a consequence, it is difficult to predict competition between environmental surface types for radionuclides. 

Past studies have shown a decrease in the toxicity of metals in the presence of organic matter, due to the binding of natural ligands that are believed to bind metals and reduce the concentration of free ionic species. The free ion activity model proposes that the free metal ion (as opposed to total metal ion concentration) is the dominant species available for organisms, and assumes that the colloidally complexed species should be less available. 

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