Speciation of metals in water

LIMITS (mg l 1) FOR METAL LEVELS IN SURFACE WATER INTENDED FOR THE ABSTRACTION OF DRINKING WATER 

Simple physical, Normal physical, Intensive physical and 

Metal Guideline Mandatory Guideline Mandatory Guideline Mandatory 

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Lauder, L. (1987) Speciation of Metals in Water, Sediment and Soil Systems (Proceedings of the International Workshop). Springer-Verlag, Berlin. 

The availability of the analytes for uptake by plants, for transport through the soil, and for dissolution into water can be estimated from a well-studied speciation scheme. Risk assessment for disposal of wastes in landfills or for land disposal of dredge spoils or sewage sludges requires knowledge not only of the total metal content but also of the content in each separate fraction to begin to understand how the metals will act in the environment. Table 5.7 summarizes the methods available for speciation of metals in samples. 

This chapter presents information on (1) the partitioning of iron, aluminum, manganese, copper, cadmium, and lead between dissolved and particulate phases (2) molecular size characteristics and stability relationships of metals and organic matter and (3) the speciation of metals in the particulate phase. The importance of organic-metal and particulate-metal interactions in river water is discussed also. 

To date, our understanding of the speciation of metals in hydrothermal fluids and on mineral surfaces has been based largely on the classical Born model. It is clear that we can now go wed beyond this approach and develop an atomistic picture of aqueous solutions based on either quantum mechanics or classical simulations. Classical simulations using simple pair potentials appear to give a reliable picture of of alkali and alkaline earth halide solutions. Some transition metals (such as Zn, Cu and Mn ) can also be treated at this level. Systems where there is hydrolysis and proton transfer, however will require either dissociatable water models or must be done using quantum mechanical calculations. Quantum mechanical calculations are also needed to understand... 

A number of speciation schemes have been devised whereby a range of analytical techniques is applied to a single sample in order to provide as much information as possible about the different species. The first reasonably comprehensive scheme was developed by Batley and Florence [32]. The scheme has been applied mainly to the speciation of metals in sea water. The broad conclusion of their studies is that lead is associated largely with colloidal inorganic particles [33]. 

Lawson, P.S., Sterritt, R.M. Lester, J.N. (1983) The speciation of metals in sewage and activated sludge effluent. Water, Air, Soil Pollution, 21, 387-402. 

In rivers and streams heavy metals are distributed between the water, colloidal material, suspended matter, and the sedimented phases. The assessment of the mechanisms of deposition and remobilization of heavy metals into and from the sediment is one task for research on the behavior of metals in river systems [IRGOLIC and MARTELL, 1985]. It was hitherto, usual to calculate enrichment factors, for instance the geoaccumulation index for sediments [MULLER, 1979 1981], to compare the properties of elements. Distribution coefficients of the metal in water and in sediment fractions were calculated for some rivers to find general aspects of the enrichment behavior of metals [FOR-STNER and MULLER, 1974]. In-situ analyses or laboratory experiments with natural material in combination with speciation techniques are another means of investigation [LANDNER, 1987 CALMANO et al., 1992], Such experiments manifest univariate dependencies for the metals and other components, for instance between different metals and nitrilotriacetic acid [FORSTNER and SALOMONS, 1991], but the interactions in natural systems are often more complex. 

Anodic stripping voltammetry (ASV) is a very sensitive instrumental technique for the measurement of metals in solution. Of particular importance are determinations of reactive or ASV-labile metal concentrations. ASV-labile metal is defined as the fraction of the total metal concentration that is measured under a defined set of ASV and solution conditions. Labilities of metal species in natural water have been related to toxicities. Thus, one objective of speciation analysis carried out by ASV is to find conditions where the ASV-labile fraction is a close approximation to the toxic fraction of a metal. In experimental terms, the ASV-labile metal should be equal to the electroactive fraction of the metal. The latter... 

Parthasarathy, N., J. Buffle, N. Gassama, and F. Cuenod. 1999. Speciation of trace metals in waters Direct selective separation and preconcentration of free metal ion by supported liquid membrane. Chem. Anal. 44 455 170. 

Figure 14.1 Pathways of key processes controlling trace metal speciation in aquatic systems, as they relate to the interchange of metals between water and sediments. (Modified from Santschi et al., 1997.)...

Transport of metals in the environment is critically dependent on speciation. Often metals are associated with colloidal materials, fulvic acid, or humic acid. Extensive research is ongoing to study the uptake capacity of these materials as well as minerals, the distribution of elements in natural water samples, and species-dependent means of remediation. Speciation of yttrium and lanthanides in natural water has been reported [415] using size exclusion chromatography and ICP-MS. Multistage filtration has also been used with ICP-MS measurement of the separated fractions [416]. Kinetic studies of metal uptake rate as a function of EDTA, NTA, and fulvic acid concentrations in the water have been described [417]. 

In Chapter 1 the broad statement is made that the rates of metal complexation reactions are generally high. A more refined conclusion can be drawn from Table 2.3, which lists the time scales over which a number of complex formation and dissociation reactions occur that are important in soil solutions and other natural waters.7 Perusal of these data makes clear the point that although they are usually very rapid, complexation reactions do span a time scale ranging over at least 10 orders of magnitude. Thus the kinetics of these reactions can be very important to understanding the aqueous speciation of metals and ligands in detail. 

Bourg, A.C.M. and Vedy, J.C., Expected speciation of dissolved trace metals in water of acid profiles, Geoderma, 38, 279, 1986. 

Use of solute speciation models to help predict metal availability to organisms in natural systems has not been attempted to date. Statistical comparisons of calculated Cu activities in various natural waters with concentrations of Cu in resident phytoplankton populations would provide a relatively simple test of the laboratory-based models of Cu availability. For organisms other than phytoplankton, however, the problem of modeling the bioavailability of metals in natural systems will be more complex. 

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