Trace element chemical speciation

Trace Elements, Chemical Species and Speciation Analysis... 

Andreae, M. O. (1979). Arsenic speciation in seawater and interstitial waters the role of biological-chemical interactions on the chemistry of a trace element. Limnol. Oceanog. 24,440-452. 

Fraser CA, Gardner GJ, Maxwell PS, Kubwabo C, Guevremont R, Siu KWM, Berman SS (1995) Preparation and certification of a biological reference material (CARP-i) for polychlorinated dibenzo-p-dioxin and dibenzofliran congeners. Fresenius J Anal Chem 352 143-147. Gardiner PE (1993) Consideration in the preparation of biological and environmental reference materials for use in the study of the chemical speciation of trace elements. Fresenius J Anal Chem 345 287-190. 

Today it has become clear that the effect of trace elements in living systems, in food, and in the environment depends on the chemical form in which the element enters the system and the final form in which it is present. The form, or species, clearly governs its biochemical and geochemical behaviour. lUPAC (the International Union for Pure and Applied Chemistry) has recently set guidelines for terms related to chemical speciation of trace elements (Templeton et al. 2000). Speciation, or the analytical activity of measuring the chemical species, is a relatively new scientific field. The procedures usually consist of two consecutive steps (i) the separation of the species, and (2) their measurement An evident handicap in speciation analysis is that the concentration of the individual species is far lower than the total elemental concentration so that an enrichment step is indispensable in many cases. Such a proliferation of steps in analytical procedure not only increases the danger of losses due to incomplete recovery, chemical instability of the species and adsorption to laboratory ware, but may also enhance the risk of contamination from reagents and equipment. 

The list of elements and their species listed above is not exhaustive. It is limited to the relatively simple compounds that have been determined by an important number of laboratories specializing in speciation analysis. Considering the economic importance of the results, time has come to invest in adequate CRMs. There is a steadily increasing interest in trace element species in food and in the gastrointestinal tract where the chemical form is the determinant factor for their bioavailability (Crews 1998). In clinical chemistry the relevance of trace elements will only be fully elucidated when the species and transformation of species in the living system have been measured (ComeUs 1996 Cornelis et al. 1998). Ultimately there will be a need for adequate RMs certified for the trace element species bound to large molecules, such as proteins. 

Numerous and disparate copper criteria are proposed for protecting the health of agricultural crops, aquatic life, terrestrial invertebrates, poultry, laboratory white rats, and humans (Table 3.8) however, no copper criteria are now available for protection of avian and mammalian wildlife, and this needs to be rectified. Several of the proposed criteria do not adequately protect sensitive species of plants and animals and need to be reexamined. Other research areas that merit additional effort include biomarkers of early copper stress copper interactions with interrelated trace elements in cases of deficiency and excess copper status effects on disease resistance, cancer, mutagenicity, and birth defects mechanisms of copper tolerance or acclimatization and chemical speciation of copper, including measurement of flux rates of ionic copper from metallic copper. 

Soil geochemistry is widely applied in mineral exploration, and with advancing knowledge of speciation and residence phases of trace elements in soils, a variety of partial and selective extractions for chemical analysis have been developed over the past decades. Each of these methods has been designed to target and dissolve only those elements that are adsorbed onto labile phases in soil, from carrier fluids and gases that transported them from a deposit to the surface (e.g. Hall etal. 1996). 

The trace metals listed in Table 11.2 (with the inclusion of Sn) are of particular concern as they are toxic at low concentrations. For historical reasons, these elements are commonly referred to as the heavy metals. The degree to which the heavy metals cause toxic effects is dependent on their concentration, chemical speciation, and other environmental conditions, such as temperature. As illustrated in Table 28.6, the type and physiological state of the target organism are also important as these fectors determine the degree to which internal metabolic processes can detoxify or eliminate the pollutant. 

Sauve S, Parker DR (2000) Chemical speciation of trace elements in soil solution. In Tabatabai MA and Sparks DL (eds) Chemical processes in soils. Soil Sci Soc Am Book Series no 8, Madison, Wisconsin... 

This chapter discusses the chemical mechanisms influencing the fate of trace elements (arsenic, chromium, and zinc) in a small eutrophic lake with a seasonally anoxic hypolimnion (Lake Greifen). Arsenic and chromium are redox-sensitive trace elements that may be directly involved in redox cycles, whereas zinc is indirectly influenced by the redox conditions. We will illustrate how the seasonal cycles and the variations between oxic and anoxic conditions affect the concentrations and speciation of iron, manganese, arsenic, chromium, and zinc in the water column. The redox processes occurring in the anoxic hypolimnion are discussed in detail. Interactions between major redox species and trace elements are demonstrated. 

Interest in trace element speciation studies in natural waters has increased considerably during the last decade. It has become apparent that data on total concentrations of any element rather than on individual well defined chemical entities, are often inadequate to identify transport mechanisms, ultimate fate and toxicity of particular elements to organisms. A study of the different trace metal species and their relative distribution will assist in understanding the chemical processes that take place in the highly reactive estuarine zone and in the open sea. These processes include the rate at which chemical processes take place, the participation in geochemical processes (precipitation/dissolution, adsorption/desorption). 

Recent reviews on chemical speciation are published by e.g. Stumm and Brauner (1975), Florence and Batley (1980) and Leppard (1983) sometimes, with special reference to metal-organic interactions (Mantoura, 1982) or complexation in natural waters (Kramer and Duinker, 1984b). Bruland (1983) summarized the distribution and behaviour of trace elements in ocean waters. The occurrence of certain species is largely dependent on the environmental conditions. There exists a strong competition of trace metals with H+ or major cations like Ca2+ and Mg2+ in seawater, but also with other trace metals which might form more stable complexes with the ligand in question on the other side, many potential ligands or chelators compete for one trace element. 

In many experiments chemical equilibrium is assumed, however dynamic nonequilibrium processes in seawater may result in products different from those expected under equilibrium conditions. Equilibria can be complex and may involve several types of reactions simultaneously. Kinetics can therefore affect speciation of trace elements and should be taken into account. 

Niirnberg, H.W., 1983. Voltammetric studies on trace metal speciation in natural waters. Part II Application and conclusions for chemical oceanography and chemical limnology. In G.G. Leppard (ed.), Trace Element Speciation in Surface Waters. Plenum, New York, pp. 211-230. 

Not only do microorganisms have a profound influence on the concentration of elements in the atmospheric, aquatic and terrestrial environments (Lovelock, 1979), but the concentration and chemical speciation of these elements predicates which organisms can compete and survive within a given environment. Therefore, the cycling and mobility of trace elements will be linked to the cycling of bulk elements and correlations to the various bulk element cycles can be postulated. 

Templeton, D., Ariese, M.F., Cornelis, R., Danielsson, L.-G., Muntau, H. and van Leeuwen, H.P. (2000) IUPAC guidelines for terms related to chemical speciation and fractionation of trace elements definitions, structural aspects and methodological approaches. Pure Appl. Chem., 74, 1453-1470. 

Development of chemical speciation schemes which can be directly related to measures of bioavailability - This would allow the determination of which active trace element species merit the most intensive research from the standpoint of environmental perturbation. Some studies have attempted to correlate metal fractions determined by a particular technique (operationally defined speciation) with those that are bioavailable (functionally defined speciation) (Larsen and Svensmark, 1991 Buckley, 1994 Deaver and Rodgers, 1996). However, any correlation is only empirical and more research is required to achieve an understanding of the mechanisms involved in bioavailability and to develop rational predictive models. 

Tanizaki, Y., Shimokawa, T. and Yimazaki, M. (1992a) Physico-chemical speciation of trace elements in urban streams by size fractionation. Water Res., 26, 55-63. 

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