Environmental metal transport

The role of photocatalysis by transition metal complexes in the environment is reviewed, and its influence on composition of the environmental compartments, transport between them, and activation of the environmental self-cleaning behavior is characterized. In description of atmospheric processes, the attention is paid to coordination compounds as photocatalysts of the transfer and redox reactions of nitrogen oxides. In the case of hydrosphere and soils, various mechanisms of organic pollutant photodegradations are presented in which the iron, copper, and chromium complexes play... 

Photoreactions can change forms and the physicochemical behavior of coordination compoimds and thereby are responsible for transition metal transport between the environmental compartments. Some of these photoreactions are also of significance in natural cleaning to ensime continuity of the processes, catalyst reproducibility should be guaranteed, that is, the relevant photoreactions should belong to the photocatal5rtic family. 

Once the metal has been removed from the environment, it must be transported into the cell for use. In most cases, environmental metal levels are significantly lower than the cellular metal quota (Table 1). This dichotomy requires organisms to concentrate... 

Salomons, W. Baccini, P. (1986) Chemical species and metal transport in lakes. In The Importance of Chemical "Speciation" in Environmental Processes., eds. M. Bernhard et al., pp. 193-216. Berlin Springer-Verlag. 

There is now considerable interest in the area of metal transport in plants because of the implications for phytoremediation -the use of plants to extract, sequester, and/ or detoxify pollutants such as toxic metals. Phytoremediation strategies for radionuclide and heavy metal pollutants focus on hyperaccumulation above ground. Significant progress has been made in recent years in developing native or genetically modified plants for the remediation of environmental contaminants (Meagher 2000). 

If the PBR is less than unity, the oxide will be non-protective and oxidation will follow a linear rate law, governed by surface reaction kinetics. However, if the PBR is greater than unity, then a protective oxide scale may form and oxidation will follow a reaction rate law governed by the speed of transport of metal or environmental species through the scale. Then the degree of conversion of metal to oxide will be dependent upon the time for which the reaction is allowed to proceed. For a diffusion-controlled process, integration of Pick s First Law of Diffusion with respect to time yields the classic Tammann relationship commonly referred to as the Parabolic Rate Law ... 

Finally, some authors have computed metal loading to the enviroranent from specific human activities, such as discharges of waste-water, and compared these with natural release rates. While the details of the computations and conclusions vary, the general observation for many metals is that anthropogenic contributions to metal ion transport rates and environmental burdens are approaching and in many cases have already exceeded natural contributions. A few such comparisons are provided in Tables 15-1-15-4. 

The distribution of metals between dissolved and particulate phases in aquatic systems is governed by a competition between precipitation and adsorption (and transport as particles) versus dissolution and formation of soluble complexes (and transport in the solution phase). A great deal is known about the thermodynamics of these reactions, and in many cases it is possible to explain or predict semi-quantita-tively the equilibrium speciation of a metal in an environmental system. Predictions of complete speciation of the metal are often limited by inadequate information on chemical composition, equilibrium constants, and reaction rates. 

The full appreciation of the overriding importance of metal speciation in evaluating the transport and effects of metals in an environment is a relatively recent event. As more information is gathered on the forms in which metals exist and are transported through various environmental compartments, it will become possible to predict more accurately the response of the biological communities exposed to the metals and hopefully avert or mitigate the adverse effects. 

Heussner S, Cherry RD, Heyraud M (1990) Po-210 and Pb-210 in sediment trap particles on a Mediterranean continental margin. Cont. Shelf Res 10 989-100 Heyraud M, Cherry RD (1983) Correlation of Po-210 and Pb-210 enrichments in the sea-surface microlayer with neuston biomass. Cont Shelf Res 1 283-293 Honeyman BD, Santschi PH (1989)The role of particles and colloids in the transport of radionuclides and trace metals in the oceans. In Environmental particles. Buffle J, van Leewen HP (eds) Lewis Publishers, Boca Raton, p 379-423... 

Metal ions play an important role as catalysts in many autoxidation reactions and have been considered instrumental in regulating natural as well as industrial processes. In these reactive systems, in particular when the reactions occur under environmental or in vivo biochemical conditions, the metal ions are involved in complicated interactions with the substrate(s) and dioxygen, and the properties of the actual matrix as well as the transport processes also have a pronounced impact on the overall reactions. In most cases, handling and analyzing such a complexity is beyond the capacity of currently available experimental, computational and theoretical methods, and researchers in this field are obliged to use simplified sub-systems to mimic the complex phenomena. When the simplified conditions are properly chosen, these studies provide surprisingly accurate predictions for the real systems. In this paper we review the results obtained in kinetic and mechanistic studies on the model systems, but we do not discuss their broad biological or environmental implications. 

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