Trace elements, definitions

Templeton D, Ariese F, Coenelis R, Danielsson LG, Muntau H, van Leeuwen H, and Lobinski R (2000) lUPAC guidelines for terms related to speciation of trace elements Definitions, structural aspects and methodological approaches. Analyst, in preparation. 

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. 

The unusual physical complaints and findings in workers overexposed to teUurium include somnolence, anorexia, nausea, perspiration, a metallic taste in the mouth and garlic-like odor on the breath (48). The unpleasant odor, attributed to the formation of dimethyl teUuride, has not been associated with any adverse health symptoms. Tellurium compounds and metaboUc products have been identified in exhaled breath, sweat, urine, and feces. Elimination is relatively slow and continuous exposure may result in some accumulation. No definite pathological effects have been observed beyond the physical complaints outlined. Unlike selenium, teUurium has not been proved to be an essential biological trace element. 

Trace elements include heavy metals, some of which have recently received particular attention. Many definitions of heavy metals have been put forward. The simplest and most precise describes heavy metals as all metal compounds of atomic weight over 20. Other definitions are based on the specific weight, and give the lower limits for heavy metals as 4.5, 5, or even 6 g per cm. Due to toxicity of some heavy metals and the possibility of environmental contamination, the potential for high risk is linked to Hg, Cd, As, Pb, as well as Cu, Zn, Sn, Cr, Ni. 

Although this equation reduces to an identity whenever solute-solvent interactions are embodied in the definition of the Henry s law standard state (cf section 10.2), it must be noted that K[ is the molar ratio of trace element i in the two phases and not the weight concentration ratio usually adopted in trace element geochemistry. As we will see later in this section, this double conversion (from activity ratio to molar ratio, and from molar ratio to weight concentration ratio) complicates the interpretation of natural evidence in some cases. To avoid ambiguity, we define here as conventional partition coefficients (with the same symbol K ) all mass concentration ratios, to distinguish them from molar ratios and equilibrium constants. 

The goals of protecting public health and establishing a scientifically irrefutable definition of the tolerance limits of trace element exposure are conflicting to a degree since the latter presupposes injury as an endpoint. Therefore, of necessity, errors in setting standards must always be made on the side of overestimating the threat. Since the success of standards enforcement is a function of the soundness of its scientific bases (18), it behooves the scientific community to reduce the error of overestimation. 

The boundaries of trace analysis are described by the definition of trace element in the IUPAC Compendium of Chemical Terminology, 2nd edition Any element having an average concentration of less than about 100 parts per million atoms and less than 100pg g As analytical techniques have become more sophisticated and detection capabilities have improved, this upper boundary of the definition of trace is now so far away from the capabilities of analysis in a number of fields that new terms such as ultratrace analysis have entered common parlance. There is no agreement, however, on the range of ultratrace analysis, and this term has no rigorous definition. In the literature, the term is used to define the presence of elements at mass fractions less than 10 6 and 10 8 (1 pg g 1 and 0.01 pg g ) ... 

Even a cursory perusal of any analytical journal will demonstrate the increasing importance of trace and ultra-trace analysis. And as instrumentation continues to develop, the definition of the term "trace element" will undoubtedly continue to change. Covering the composition and underlying properties of freshwater and marine systems, Analytical Measurements in Aquatic Environments provides the basis for understanding both. It discusses all aspects of analytical protocols from the handling of representative samples to the metrological evaluation of specific steps and whole procedures.The book covers ... 

Nickel, atomic number 28, is a transition metal with a variety of essential uses in alloys, catalysts, and other applications. It is strongly suspected of being an essential trace element for human nutrition, although definitive evidence has not yet established its essentiality to humans. A nickel-containing urease metalloenzyme has been found in the jack bean. 

In the coal treated by molten caustic in Run 2, the Cr and Ni levels are significantly higher than in Run 1, suggesting a more severe attack in the second test. If the attack were more severe, then levels of Fe, Al, Si, and ash would be anticipated to be somewhat lower than in Run 1. As can be seen from these data, this is indeed the case. However, because of the numerous variables involved, no definitive conclusions can be drawn. Overall trace element reductions did not seem to be significantly improved in Run 2. 

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