Metal speciation, effect

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. 

Mercury provides an excellent example of the importance of metal speciation in understanding biogeochemical cycling and the impact of human activities on these cycles. Mercury exists in solid, aqueous, and gaseous phases, and is transported among reservoirs in all these forms. It undergoes precipitation-dissolution, volatilization, complexation, sorption, and biological reactions, all of which alter its mobility and its effect on exposed populations. The effect of all... 

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. 

Effect of Medium Composition on Metal Speciation and Toxicity. 417... 

The interpretation of previous attempts at measuring the impact of metals on microbially mediated processes has been hindered by the use of a wide range of experimental conditions and measurements. Already, a shift from studies based on total metal concentration to those based on bioavailable metal concentrations has occurred. The next step will entail accurately predicting and measuring metal speciation patterns in order to identify microbial responses to metal speciation. Only then will it be possible to develop more effective methods to quantify and mitigate deleterious effects of metals on the myriad processes that microbes mediate in the environment. 

The environmental standards based on total heavy metal concentration in the soil solution seem the most important criterion for the exposition of further compartments of the environment. The additional effects connected with metal speciation and complexations were not considered in the study. 

Pinheiro, J. P. and van Leeuwen, H. P. (2001). Metal speciation dynamics and bioavailability. 2. Radial diffusion effects in the microorganism range, Environ. Sci. Technol., 35, 894-900. 

Weber G, Messerschmidt J, von Bohlen A, Alt F. Effect of extraction pH on metal speciation in plant root extracts. Fresenius. J. Anal. Chem. 2001 371 921-926. 

An important aspect of metal-microbe interactions, but one that is rarely addressed, is metal speciation and metal bioavailability. It is the metal species present and their relative bioavailability rather than total metal concentration in the environment that determines the overall physiological and toxic effects on biological systems (Bernhard, Brinckman Sadler, 1986 Hughes Poole, 1989 Morrison, Batley Florence, 1989). 

The chemical pathways for the decomposition of H202 appear to play a minor role in the overall decay processes. Direct-sunlight photolysis is not important in natural waters (I). The effect of H202 on metal speciation, and therefore on H202 decomposition, has been demonstrated in marine systems but not in lakes. Additional studies are required to better understand these processes in lake waters. 

Gunn, AM., Hunt, D.T.E. and Winnard, DA. (1989) The effect of heavy metal speciation in sediment on bioavailability to tubificid worms, in M. Munawar, G. Dixon, C.I. Mayfield, T. Reynoldson and M.H. Sadar (eds.), Environmental Bioassay Techniques and their Application Proceedings of the Is International Conference held in Lancaster, England, 11-14 July 1988, Kluwer Academic Publishers, Dordrecht, Netherlands, pp. 487 196). 

Voelker, B.M. and Kogut, B. (2001) Interpretation of metal speciation data in coastal waters the effects of humic substances on copper binding as a test case, Marine Chemistry 74, 303-318. 

Simpson, S.L., Apte, S.C. and Batley, G.E. (1998) Effect of short-term resuspension events on trace metal speciation in polluted anoxic sediments. Environ. Sci. Technol., 32, 620. 

Metal speciation procedures, which have been verified under controlled laboratory conditions and evaluated by means of bioassays, will require further verification in order to determine their ecological effects. For example, how does the response of the bioassay test species to a toxic metal fraction relate to the toxicity to larger organisms such as fish in the natural environment Bioaccumulation of metals in populations has been very difficult to relate to metal speciation measurements. There is a challenge for analytical chemists to develop metal speciation procedures that are relevant to ecotoxicology (Morrison and Wei, 1991). 

To some extent, every metal investigated shows the general biological responses reported. The intensity of its impact is a function of its chemical characteristics, especially its redox properties on one hand and of metal speciation at the cellular level on the other hand. Further research is required to specify the biological effect, typical for every metal studied. 

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