Factors affecting trace element

FACTORS AFFECTING TRACE ELEMENT SPECIATION IN SOIL SOLUTION... 

There are numerous variables that can affect trace element determinations before the analysis of the sample is undertaken and these require careful control. Guidelines giving details of sample collection procedures, and procedures for limitation of contamination in a range of sample types, are available for essential and toxic trace elements. Age, sex, ethnic origin, time of sampling in relation to food intake, time of day and year, history of medication, tobacco usage, and other factors should be recorded when establishing reference intervals from healthy control populations. 

Radionuclide studies offer an additional method to investigate the factors that affect trace element absorption. Radioactivity emitted by the radionuclide was measured in blood 14 days after the oral ingestion of zinc-65 and compared with the amount of radioactivity emission determined by whole-body counting (Watson et al. 1987). The results indicated that, where whole-body counting facilities were not available, measurement of radioactivity emitted in blood was a reasonable alternative for the prediction of zinc absorption. Recovery for this method was adequate (88%) precision was acceptable (<17% CV). The limit of detection for zinc was not reported. 

Many U-series elements occur in nature at much lower concentrations than the more commonly used trace elements, such as the lanthanides. This fact, coupled with the highly incompatible nature of many U-series elements, means that in some cases factors other than lattice strain may influence the uptake of cations into a mineral, and so affect the partition coefficient. 

Overall, it is not possible to evaluate whether any of these factors have compromised the data included in published studies. More research is required to determine how U-and Th-series nuclides are affected by various well construction methods and sampling procedures, how reliable are data from wells not designed fro trace element monitoring, and if there are any factors that have affected the data collected from past studies. Most importantly, radionuclide studies must incorporate greater awareness of the potential problems, summarize whatever details are available regarding the wells used, and consider potential problems where the relevant information is not available. 

FACTORS AFFECTING CONTENTS OF TRACE ELEMENTS IN ARID AND SEMI-ARID SOILS... 

In summary, we may add that bacterial utilization of quinoline and its derivatives as a rule depends on the availability of traces of molybdate in the culture medium [363], In contrast, growth of the bacterial strains on the first intermediate of each catabolic pathway, namely, the lH-2-oxo or 1 II-4-oxo derivatives of the quinoline compound was not affected by the availability of molybdate. This observation indicated a possible role of the trace element molybdenum in the initial hydroxylation at C2. In enzymes, Mo occurs as part of the redox-active co-factor, and all the Mo-enzymes involved in N-heteroatomic compound metabolism, contain a pterin Mo co-factor. The catalyzed reaction involves the transfer of an oxygen atom to or from a substrate molecule in a two-electron redox reaction. The oxygen is supplied by the aqueous solvent. Certainly, the Mo-enzymes play an important role in the initial steps of N-containing heterocycles degradation. 

Even before an experiment or analysis is carried out, many factors may affect the speciation of trace elements in the sample under investigation. 

Figure 12 Variability of trace element concentrations in MORE, expressed as 100 standard deviation/mean concentration. The data for Global MORE are from the PETDB compilation of (Su, 2002). All segments refers to 250 ridge segments from all oceans. Normal segments refers to 62 ridge segments that are considered not to represent any sort of anomalous ridges, because those might be affected by such factors as vicinity to mantle plumes or subduction of sediments (e.g., back-arc basins and the Southern Chile Ridge). The Atlantic MORE, 40-55° S, from which samples with less than 5% MgO have been removed (source le Roux et al., 2002).

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