Metals mobilization

Natural mobilization includes chemical, mechanical, and biological weathering and volcanic activity. In chemical weathering, the elements are altered to forms that are more easily transported. For example, when basic rocks are neutralized by acidic fluids (such as rainwater acidified by absorption of CO2), the minerals contained in them dissolve. 

Biological and volcanic activity also have roles in the natural mobilization of elements. Plants can play multiple roles in this process. Root growth breaks down rocks mechanically to expose new surfaces to chemical weathering, while chemical interactions between plants and the soil solution affect solution pH and the concentration of salts, in turn affecting the solution-mineral interactions. Plants also aid in decreasing the rate of mechanical erosion by increasing the stability of the land to erosion. These factors are discussed more fully in Chapters 6 and 7. 

Volcanic activity has a significant effect on the mobilization of metals, particularly the more volatile ones, e.g. Pb, Cd, As, and Hg. The effects of vol-canism are qualitatively different from those of the weathering and other near-surface mobilization processes mentioned above. Volcanism transports materials from much deeper in the crust and may inject elements into the atmospheric reservoir. 

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One of the characteristics of the cycle of metal mobilization and deposition is that the form of the metal is changed. This change in speciation of a metal has a profound effect on its fate. The link between metal speciation and fate is the central theme of this chapter. 

Treatment additives, chelating agents, and clay minerals can be added to a system to bind to metals and reduce metal mobility. Treatment additives, such as carbonates, phosphates, and hydroxides, form insoluble precipitates with metals, thus decreasing their bioavailability. Jonioh et al.141... 

Gadd GM (2000) Bioremediation potential of microbial mechanisms of metal mobilization and immobilization. Curr Opinion Biotechnol 11 271-279... 

C02-philic molecules have been utilized for the design of metal-mobilizing ligands to be used in SCCO2 [67-69,135-137], e.g., as shown in Fig. 7a [55] and for the synthesis of surfactants that form micelles, emulsions, and micro emulsions in CO2, e.g., as shown in Fig. 7b. [70] Polymer solubility in SCCO2 has been studied [71] and utilized for polymer synthesis [72-74]. Recently, DeSimone and co-workers synthesized high-molar-mass fluoropolymers in SCCO2, and studied the polymerization kinetics [75]. 

Mid-depth maxima are produced by mid-depth sources of metals. Some of these maxima are created by remineralization of detrital biogenic particles, such as seen in Figure 11.4f for cadmium. Others are caused by lateral transport of metals mobilized from coastal sediments as illustrated in Figure 11.17(a) for manganese. Mid-depth maxima can also result from hydrothermal emissions as shown in Figure 11.19 for Mn (aq) and He(g) at a site in the Eastern North Pacific Ocean. Hydrothermal fluids are emitted into the ocean from chimneys located atop the East Pacific Rise at water depths of about 2500 m. After entering the ocean, the Mn and He are entrained in subsurfece currents and... 

Three mechanisms have been proposed to explain how particulate metals could be transported within such sediments so as to support the growth of Fe-Mn nodules (1) anoxic microzones, (2) bioturbation, and (3) shifts in the depth of the redox boundary over time. Anoxic microzones are present within fecal pellets and the interiors of radiolarian shells where detrital POM is still present. Metals mobilized within these microzones should be able to diffuse through the sediments for substantial distances... 

Speciation of transition metals by natural organic substances that behave as complexing ligands may occur in the subsurface following waste and sludge disposal. As a result, metal solubility increases, favoring metal mobility with depth. 

Mapping of geochemical systems, including enrichment and depletion zones of metals mobile forms in covered areas, could be a key criterion for assessing a favourable region. 

Acidification of acid-sensitive waters is accompanied by severe changes in biological communities. Effects range from reductions in diversity without changes in total biomass to elimination of all organisms. In many cases the immediate cause of the changes is unknown. Some effects are the result of H" toxicity itself or of the toxicity of metals mobilized from the watershed, others have more indirect causes such as changes in predator-prey interactions or in physical conditions of lakes (ex. transparency). [14]... 

In some cases, the metal-mobilizing effect of a therapeutic chelating agent may not only enhance that metal s excretion—... 

The highly polar ionic character of EDTA limits its oral absorption. Moreover, oral administration may increase lead absorption from the gut. Consequently, EDTA should be administered by intravenous infusion. In patients with normal renal function, EDTA is rapidly excreted by glomerular filtration, with 50% of an injected dose appearing in the urine within 1 hour. EDTA mobilizes lead from soft tissues, causing a marked increase in urinary lead excretion and a corresponding decline in blood lead concentration. In patients with renal insufficiency, excretion of the drug—and its metal-mobilizing effects—may be delayed. 

Penicillamine is used chiefly for treatment of poisoning with copper or to prevent copper accumulation, as in Wilson s disease (hepatolenticular degeneration). It is also used occasionally in the treatment of severe rheumatoid arthritis (see Chapter 36). Its ability to increase urinary excretion of lead and mercury had occasioned its use in outpatient treatment for intoxication with these metals, but succimer, with its stronger metal-mobilizing capacity and lower adverse-effect profile, has generally replaced penicillamine for these purposes. 

Catsch, A. Radioactive Metal Mobilization in Medicine, Springfield, 111., Charles C. Thomas 1964... 

A-acetyl penicillamine, has been used experimentally in mercury poisoning and may have superior metal-mobilizing capacity, but it is not commercially available. 

Fytianos, K., Bovolenta, S. and Muntau, H. (1995) Assessment of metal mobility from sediment of Lake Vcgoritis./. Environ. Sci. Health A, 30, 1169-1190. 

Acetic acid or chelating agents such as EDTA to determine trace metal mobility and availability of metals for plant uptake... 

An approach similar to that in soils can be applied to metal-contaminated sediments, where sulfides, measured as acid-volatile sulfides (AVS), have been demonstrated as being the predominant factor controlling metal mobility and toxicity in anaerobic sediments. The difference or ratio between SEM (simultaneous extracted metals) and AVS (SEM-AVS) is used to predict toxicity. In cases where SEM does not exceed the AVS, this approach has been shown to consistently predict the absence of toxicity (Allen et al. 1993 Ankley et al. 1996 DiToro, Hansen et al. 2001b). When SEM exceeds the AVS, toxicity is predicted, but the appearance and extent of toxicity may be determined by other binding phases (e.g., organic carbon) in the pore water. Luoma and Fisher (1997) stated that the association of metal bioavailability with AVS in sediments is not, however, straightforward in all cases and should be treated with caution. 

The method of soil suspensions extracts is based on metal desorption/dissolution processes, which primarily depend on the physico-chemical characteristics of the metals, selected soil properties and environmental conditions. Metal adsorption/ desorption and solubility studies are important in the characterization of metal mobility and availability in soils. Metals are, in fact, present within the soil system in different pools and can follow either adsorption and precipitation reactions or desorption and dissolution reactions (Selim and Sparks, 2001). The main factors affecting the relationship between the soluble/mobile and immobile metal pools are soil pH, redox potential, adsorption and exchange capacity, the ionic strength of soil pore water, competing ions and kinetic effects (e.g. contact time) (Evans, 1989 Impelhtteri et al., 2001 McBride, 1994 Sparks, 1995). 

Davranche, M., Bollinger, J. C., and Bril, H. (2003). Effect of reductive conditions on metal mobility from wasteland solids An example from the Mortagne-du-Nord site (France). Appl. Geochem. 18(3), 383-394. 

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