Lead, metabolic isotopic tracer studies

Advances in instrumentation may also fill a niche in isotope tracer studies of lead exposure and metabolism in organisms. In those studies, the inherent isotopic abundances are altered by 50% to > 200% with the addition of a lead tracer enriched in one of the four stable lead isotopes, and those changes may be readily detected with ICPMS. It is also especially suited for such studies because it can be used to analyze samples relatively rapidly. 

These advances in stable istopic tracer measurements are important because of the limitations in lead radiotracer measurements. Tracer studies of lead metabolism using radioisotopes ( Pb, Pb, and Pb) have been hindered by the relatively poor precision of the measurements, their relatively short ( Pb tin = 51.88 hr and "Pb tm = 10.64 hr) or long ( Pb tin 22.3 yr) half-lives, and the relatively weak gamma energy of Pb. Additionally, concerns about the radiation hazard of these isotopes have severely restricted their utilization in many laboratory and clinical studies. 

Rabinowitz M, Wetherill GW, Kopple JD. 1974. Studies of human lead metabolism by use of stable isotope tracers. Environ Health Perspect 7 145-153. 

The first ever application of a radiotracer in a biological experiment dates back to 1923 when George de Hevesy used Pb to study plant uptake of lead from solution [5]. His seminal work was honored by the Nobel Prize in Chemistry in 1943 and made him the father of isotope tracing, a tool that is still indispensable in virtually any area of scientific research. The first use of a stable isotope to study mineral metabolism was reported in 1963, when Lowman and Krivit injected stable Fe together with radioactive Fe into a human subject to compare the plasma clearance of the two isotopes [6]. However, it was not until the 1980s that stable isotope techniques were explored systematically to study mineral and trace element metabolism in humans. This was not only due to the increasing recognition of health hazards associated with the use of radioisotopes. Mass spectro-metric techniques had to be refined to measure isotope ratios of the heavier elements at a precision suitable for the exploitation of isotopically enriched elements as tracers. Stable isotopic labels are made up from the same isotopes as the natural element, from which they differ only in terms of composition, that is, in the relative abundances of their isotopes. 

B. Stable Lead Isotopic Tracers in Metabolic Studies... 

Trace levels of inorganic chemical species, e.g. lead, arsenic, cadmium, are aiso monitored in food stuffs, often using ICP-MS. The advantage of MS over AAS is that severai eiements may be measured simultaneously and the concentrations of individual isotopes may be measured, facilitating metabolism/ nutrient studies with stable isotope materials. Precise determination of isotope ratios (e.g. C, N and O) by IRMS is also important in agricultural and food authenticity studies. Accelerator mass spectrometry is used in tracer studies, for the determination of extremely low levels of carbon-14 (and other) isotopes. 

Stable isotopes of each of these elements have played important roles in elucidation of their chemistries. Specifically, and have been used as stable tracers for research on N-chemistry dealing with food and fiber production, metabolic pathways, and environmental control. Their value is ultimately limited because macroscopic amounts of carrier often exceed in situ concentrations (and therefore influence the biochemistry), and natural nitrogen isotope fractionation leads to variances in natural abundance. Nevertheless, stable tracers have been used effectively in many studies, including foflowing N-cycle processes in soils (1) and unraveling metabolic pathways (2,3). 

Radioactive P serves as an excellent marker for general phosphorus metabolism studies in plants and animals. Isotope P occupies a leading position in biochanical tracer woik, where it is particularly useful because of its short half-life and relatively harmless emitted radiation. 

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