Speciation controlling factors

Mattigod, S. V. 1983. Chemical composition of aqueous extracts of fly ash Ionic speciation as a controlling factor. Environmental Technology Letters, 4, 485-490. 

Meili M, Iverfeldt A, Hakanson L. 1991. Mercury in the surface-water of Swedish forest lakes -concentrations, speciation and controlling factors. Water, Air, Soil Pollution 56 439-453. 

Meili M, Iveeeeldt a and Hakanson L (1991) Mercury in the Surface Water of Swedish Forest Lakes - Concentrations, Speciation and Controlling Factors. Water Air Soil Pollut 56 439-453. 

Soil pH is the most important factor controlling solution speciation of trace elements in soil solution. The hydrolysis process of trace elements is an essential reaction in aqueous solution (Table 3.6). As a function of pH, trace metals undergo a series of protonation reactions to form metal hydroxide complexes. For a divalent metal cation, Me(OH)+, Me(OH)2° and Me(OH)3 are the most common species in arid soil solution with high pH. Increasing pH increases the proportion of metal hydroxide ions. Table 3.6 lists the first hydrolysis reaction constant (Kl). Metals with lower pKl may form the metal hydroxide species (Me(OH)+) at lower pH. pK serves as an indicator for examining the tendency to form metal hydroxide ions. 

In this case, permeability depends only on factors that are outside the organism. Such a scenario might occur in an eutrophic lake where metal speciation is controlled by natural organic ligands forming inert complexes. 

The factors which control the distribution of trace elements [defined arbitrarily in geochemistry as those elements present at less than 0.1 weight percent (wt %)] can be discussed under a number of headings - structural, thermodynamic, kinetic and, in the sedimentary environment, solubility and speciation. 

We wish to stress that comparison of the isotopic effects in biologic and abiologic systems will be most meaningful if experimental conditions are identical, where the only difference is the presence or absence of bacteria. The wide variety of buffers, growth media, and others conditions that are involved in biological experiments raise the possibihty that spurious results may be obtained if these factors are not carefully controlled. Because speciation may exert a strong control on Fe isotope fractionations (Schauble et al. 2001), even small differences across experimental studies may be significant. 

Measurements of S cycling in Little Rock Lake, Wisconsin, and Lake Sempach, Switzerland, are used together with literature data to show the major factors regulating S retention and speciation in sediments. Retention of S in sediments is controlled by rates of seston (planktonic S) deposition, sulfate diffusion, and S recycling. Data from 80 lakes suggest that seston deposition is the major source of sedimentary S for approximately 50% of the lakes sulfate diffusion and subsequent reduction dominate in the remainder. Concentrations of sulfate in lake water and carbon deposition rates are important controls on diffusive fluxes. Diffusive fluxes are much lower than rates of sulfate reduction, however. Rates of sulfate reduction in many lakes appear to be limited by rates of sulfide oxidation. Much sulfide oxidation occurs anaerobically, but the pathways and electron acceptors remain unknown. The intrasediment cycle of sulfate reduction and sulfide oxidation is rapid relative to rates of S accumulation in sediments. Concentrations and speciation of sulfur in sediments are shown to be sensitive indicators of paleolimnological conditions of salinity, aeration, and eutrophication. 

Factors Controlling Speciation of S. Speciation of S in sediments is influenced by many of the same factors that control S retention. However, S speciation may be a more sensitive indicator of many of these variables. 

Sulfur content has been reported in the literature for approximately 80 lakes speciation has been reported for only about half of them. These data point to some important factors controlling S speciation, but generally are inadequate to test hypotheses rigorously. 

Smith, J.V.S., Jankowski, J. and Sammut, J. (2003) Vertical distribution of As(III) and As(V) in a coastal sandy aquifer Factors controlling the concentration and speciation of arsenic in the Stuarts Point groundwater system, northern New South Wales, Australia. Applied Geochemistry, 18(9), 1479-96. 

The number of analytical methods developed for the study of the distribution of metal- and metalloid-containing species in the last decade has been impressive. However, a majority of these are as yet to be applied to real biological materials. With the greater appreciation of the pre- and post-sampling factors that influence chemical speciation, and the development of appropriate quality control materials the results of these studies will become more reliable. Consequently, the use of chemical speciation data will become indispensable to accurate environmental impact assessment, and to our understanding of the roles that metals and metalloids play in biological systems. 

Chemical models of metal speciation have been used to assess the biological availability of different solute metal forms. Pagenkopf and Andrew (l ) used equilibrium models to suggest that the availability of Cu to fishes was controlled by the concentration of the free Cu ion. Equilibrium models were also used to show that the toxicity of Cu to phytoplankton followed the activity of metals rather than total metal concentrations l8) and that the concentration of free Zn ion plus additional factors (e.g. competition from Ca and Mg) may affect the availability of solute Zn to fishes (19>20). 

Separation of species by factor analysis is limited in several ways. In order of decreasing Importance the separability is controlled by speciation behavior over the ranges of parameters used, experimental point distribution over the ranges of parameters, number of species involved in the calculation, and number of factors determined. 

GC) of organic species, ICP-MS, and HG-ICP-AES. Of these, HG-AFS and ICP-MS are probably the most widely used methods. Like arsenic, there are no generally accepted ways of preserving selenium speciation in water samples, and even fewer studies of the factors controlling the stability of the various species. Many of the precautions for arsenic-preserved species (Section 9.02.2.2.3) are also likely to apply to the preservation of selenium species. 

Experience with bioleaching of arsenic-rich gold ores has shown that the ratio of pyrite to FeAsS is an important factor controlling the speciation of the arsenic released (Nyashanu et al., 1999). In the absence of pyrite, —72% of the arsenic released was As(III), whereas in the presence of pyrite and Fe(III), 99% of the arsenic was As(V). It appears that pyrite catalyzed the oxidation of As(III) by Fe(III), since Fe(III) alone did not oxidize the arsenic (Nyashanu et al., 1999). 

Although geology is the primary control on the selenium concentration of sod, the bioavailability of selenium to plants and animals is determined by other factors including pH and redox conditions, speciation, soil texture and mineralogy, organic matter content, and the... 

---