Isotopes, stable, human metal

The Achilles Heel In the use of stable Isotopes for human nutritional studies Is the methodology available for the detection of the enriched stable Isotope Unlike the radioactive studies where one can use a relatively cheap and very accessible technique such as scintillation counting, there appear to be only two methods for the analysis of metal Isotopes mass spectrometry (10-18) and neutron activation analysis (7-9) To date, both methods have proven to be less than desirable because of the time-Intensive nature of the analysis ... 

In the last five years stable isotopes of many metals have proven to be useful in studying mineral absorption and metabolism in human subjects There is growing reluctance to use radioisotopes for such experiments and they are contraindicated in some populations Stable isotopes are beginning to fill this gap ... 

The role of metals and other elements in the health of humans, animals, and plants continues to be of great interest both on a routine basis and in research. Two recent reviews described the important impact of ICP-MS in biomedical research [227, 228]. ICP-MS provides the ability to measure multiple elements at ultratrace levels rapidly and to measure isotope ratios at low enough concentrations so that stable isotope tracers can be used for biomedical research [229]. Much remains unknown about the role of metals and their speciation on biological activity, in large part as a result of inadequate measurement techniques. 

Element uptake from soil and transfer into the edible parts of plants have been addressed in several other studies. Soil-to-plant transfer factors in fruit and vegetables grown in various agricultural conditions have been determined for, for example, Pt [100], T1 [101], and various other metal contaminants [102], In a study on stable isotopes of fission product elements (Ce, Cs, Sr), an in vitro enzy-molysis method has been applied to investigate the solubilization of the analytes from fodder in a simulated ruminant digestion [103], The effect of inhibitors of fission product solubility was also considered and essential elements were determined simultaneously to evaluate potential nutrition problems for the animals from the use of such inhibitors. Selective leaching of individual classes of metal complexes with different ligands and sequential enzymolysis have been recently applied to estimate the potential bioavailability to humans of Cd and Pb in cocoa powder and related products [104]. 

Studies in human adults using radioisotopes or stable isotopes of Zn showed that Zn absorption is higher from human milk (41 percent) than from cow (28 percent) or soy formulas (14 percent) [77]. In any case, it seems that there is no need to fortify cow-based formulas with Zn, since cow milk contains much more Zn than breast milk [77]. However, Zn bioavailavility from breast milk is clearly higher than from formulas, which indicates a different composition in Zn species. Experiments in speciation of Zn in formula milk whey carried out by SEC showed that Zn was mostly found in the LMW (< 10 kDa) fraction, as a complex of citrate and only a small fraction of the metal was bound to whey proteins (435 kDa) [15, 18, 21]. Although such species are detected in human milk, important differences have been found between the distribution patterns of Zn in breast milk and in cow-based formula milks (see Fig. 17.11 and compare with Fig. 17.4). The levels of Zn in formulas are higher than in human milk and in colostrums [18]. 

Stable isotopes of minerals are safe and convenient to use for bioavailability studies in humans Chelation of metals to form volatile complexes makes it possible to use ordinary EI/MS instrumentation for measurement of isotopic enrichment Stable isotopes can be complementary to radioisotopes in some of experiments Observations of fecal isotopic excretion are inherent to bioavailability and absorption studies using stable isotopes and are unlikely to be made in studies employing low level radioiaotopes ... 

CAS 7440-09-7. K. Metallic element of atomic number 19, group IA of the periodic table, an alkali metal, aw 39.098, valence of 1. Potassium-40 is a naturally occurring radioactive isotope. There are also two stable isotopes. The synthetic isotope, po-tassium-42, is used in tracer studies, primarily in medicine. An essential element in plant growth and in animal and human nutrition occurs in all soils. 

Consequently, this review is designed to briefly summarize many of the available techniques for accurate measurements of environmental and human lead contamination. This includes the importance of ultraclean techniques for lead analysis as well as brief descriptions of some current and emerging analytical techniques for measuring lead exposures in humans. The descriptions are preceded by abbreviated discussions of the chemical properties of lead, natural and anthropogenic variations in its stable isotopic composition, and historical records of lead contamination in the environment. The report concludes with a summary of some indirect methods of measuring lead exposure and toxicity in humans. Much of the material in this report is based on reviews written for several recent reports Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations (NRC 1993), Lead in the Biosphere Recent Trends (Smith and Flegal 1995), and In Vivo Measurement and Speciation of Nephrotoxic Metals (Smith and McNeill 1995). 

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