Zn Stable Isotope Research Articles

Mineral bioavailability and metabolism determined by using stable isotope tracers1

Definitive data on mineral bioavailability in humans and animals can be obtained by using isotopic tracers. The use of stable isotope tracers to study important issues in mineral nutrition has expanded rapidly in the past two decades, particularly in human nutrition studies. Stable isotopes have a number of advantages over radioisotopes. There is no exposure to radiation with stable isotopes, and some minerals have no radioisotope that can be used satisfactorily as a tracer. Multiple stable isotopes of one mineral and isotopes of multiple minerals can be administered simultaneously or sequentially. The analytical methods of choice for stable isotopes are thermal ionization mass spectrometry and inductively coupled plasma mass spectrometry (ICPMS). Thermal ionization mass spectrometry offers the greatest precision and accuracy, but it is slower, more labor intensive, and more costly than ICPMS. Bioavailability data are critical to establishing reliable dietary mineral requirements and recommendations. Combined with a computer program for compartmental modeling, mineral kinetics can be studied, including mineral turnover, pool sizes, and transfer rates between compartments. Our laboratory conducts studies using stable isotopes of Zn, Cu, Fe, Ca, Mg, and Mo. We have studied the effect of the amount of dietary intake of minerals on bioavailability and use, pregnancy and aging, and interactions among minerals. The research resulted in establishing new dietary recommendations for Cu and Mo and developing compartmental models for these minerals. Although stable isotopes have been used more extensively to date in humans than in animals, the techniques applied to humans can be used to study a number of issues important to optimizing feeding strategies for animal production.

Zinc (Zn) absorption during the third trimester in pregnant rural Southern Ethiopian women

The objective of this research was to compare the quantity of zinc absorbed by pregnant (>24 wks gestation) rural Southern Ethiopian women of the Sidama linguistic/ethnic population at the beginning of the rainy season with calculated physiologic requirements. The 17 subjects, a subgroup of a larger study population (n = 99), were studied in their homes whilst on their habitual diets based on maize and fermented enset with no flesh foods and phytate:Zn molar ratio of 30:1. Weighed food records were obtained for either 1 or 2 days. Representative samples of foods consumed by the larger study population were analyzed and the mean Zn concentration for these foods used in calculating dietary Zn intake for each subject. For this subgroup, an extrinsic Zn stable isotope tracer was administered with all meals for one day with a 2nd Zn stable isotope administered IV on the same day. Fractional absorption of Zn (FAZ) was measured by a dual isotope ratio technique based on enrichment measures in morning urine samples collected 4-8 days post-administration. Mean (± SD) FAZ = 0.36 ± 0.11; mean ingested Zn = 4.68 ± 1.96 mg Zn/d; mean absorption (FAZ*ingested Zn) = 1.65 ± 0.77 mg Zn/d. In conclusion, average absorption of Zn by this population is extremely low compared with estimated physiologic requirements. Supported by “Brain Disorders in the Developing World: Research across the Lifespan,” Fogarty International Center/NIH R21 TW006729.

Uptake and Elimination of Lead, Zinc, and Copper by Caddisfly Larvae (Trichoptera: Hydropsychidae) Using Stable Isotope Tracers

Stable isotopes of Pb, Zn, and Cu were used in laboratory experiments to determine the uptake and elimination of these metals by stream-dwelling caddisfly (Trichoptera: Hydropsychidae) larvae. For Pb and Cu, larvae were exposed to environmentally realistic levels (2.5 and 4.5 microg x L(-1), respectively) of one isotope for 9 days followed by a 9-day exposure to either the same isotope, to a second stable isotope of the same metal, or to RW containing no added isotope (two phases in total). For zinc, the exposure concentration was 15 microg x L(-1), and the experiment lasted for a total of 27 (i.e., three phases) rather than 18 days to see if uptake and elimination changed during the extended time period. The uptake clearances (k(u)) determined for the various metals averaged 7.8, 1.4, and 0.6 L x g dw(-1) x d(-1) for Pb, Zn, and Cu, respectively, if the total metal concentration in the water was used in the calculations. The clearance rate constants (k(e)) were less variable, averaging 0.15 d(-1) for Pb, 0.22 d(-1) for Zn, and approximately 0.1 d(-1) for Cu and were similar in both the presence (i.e., elimination) and absence (i.e., depuration) of metal in the water. These values are also comparable with those reported in the literature for other aquatic invertebrates. The use of stable isotopes thus allowed simultaneous measurement of uptake and clearance (elimination and depuration) of these metals at environmentally realistic concentrations and could be of great benefit for determining partitioning, assimilation efficiency, and pathways of these and other metals in the environment.

Ab initio study of local vibrational modes in II–VI semiconductors: ZnS : Se and ZnSe : N

A parameter-free (with a single exception) method to calculate local vibrational modes from first principles is presented. It is applied to point defects in II–VI semiconductors: SeS in ZnS shows a very pronounced fine structure, because there are six stable Se isotopes and five stable Zn isotopes. The calculated results agree very well with recent experiments. For NSe in ZnSe, a recent assignment of FTIR absorption bands at 537 and 553cm−1 is verified. The fine structure of the mode, which to our knowledge has not yet been observed, is calculated.

Zinc absorption, distribution, excretion, and retention by healthy preterm infants.

Zinc (Zn) is an essential nutrient for growth, but little is known about Zn absorption, distribution, excretion, and retention in preterm infants. Nine infants with gestational age 32+/-1 wk (mean+/-SE), birth weight 1.44+/-0.08 kg, postnatal age 14+/-3 d, on Zn intake of 23+/-3 micromol/kg per d via enteral feeding of preterm formula were studied. A stable Zn isotope (70Zn) was administered orally or i.v., and plasma, red blood cells, urine, and feces were sampled for up to 30 d. Samples were analyzed for Zn by inductively coupled plasma atomic emission spectrometry and for isotope enrichment by inductively coupled plasma mass spectrometry. Data were analyzed by compartmental analysis using the Simulation Analysis and Modeling program, and absorption, distribution, excretion, and retention were calculated. Absorption was 36+/-5% or 7+/-1 micromol/kg per d; distribution in plasma was 15+/-1 micromol Zn/L and in RBC was 41+/-4 micromol Zn/L; excretion in urine was 0.55+/-0.03 micromol Zn/kg per d and in feces was 17+/-3 micromol Zn/kg per d and retention was 5+/-1 microl/kg per d. Results show that healthy preterm infants with Zn intake of 23 micromol/kg per d and expected growth rates (> 15 g/kg per d) absorb and retain Zn at rates comparable to in utero accretion. The values for absorption, distribution, and excretion by this population of healthy preterm infants provide a normal range for future studies, although further studies are required to determine endogenous excretion rates in healthy preterm infants. We speculate that these values can be used to determine whether Zn kinetics are abnormal in sick infants or in infants with slow growth.

Preliminary study of metals in proteins by high-performance liquid chromatography-inductively coupled plasma mass spectrometry using multi-element time-resolved analysis.

The feasibility of multi-element and multi-isotope determinations during the on-line chromatographic separation of protein matrices was investigated using time-resolved software with inductively coupled plasma mass spectrometry. Size-exclusion chromatography was used to separate a mixture of known proteins and the behaviour of associated elements was monitored. It was possible to scan either the entire mass range or a selected number of isotopes. Reversed-phase chromatography was used to separate Zn-containing species in chicken meat that had been intrinsically and extrinsically labelled with stable isotopes of Zn. The ratio obtained for the intrinsic label agreed with that obtained by other workers using thermal ionization mass spectrometry. Time-resolved analysis permitted rapid data acquisition, thus reducing the number of chromatographic runs required. However, at present, data handling can be time consuming. Further software developments will add to the advantages that this technique offers.

Apparent zinc absorption by rats from foods labelled intrinsically and extrinsically with 67Zn

A variety of foods (peas (Pisum sativum), chicken meat, eggs, goat's milk, human milk) enriched with the stable isotope 67Zn were prepared by means of intrinsic- and extrinsic-labelling procedures. They were fed to rats and apparent absorption of 67Zn determined from faecal excretion measurements using thermal ionization mass spectrometry. There were significant differences in the absorption of the extrinsic and intrinsic label which differed in magnitude between the foods tested. The extrinsic 67Zn was less well absorbed in peas, chicken meat, eggs, and human milk than intrinsic 67Zn, but in goat's milk the extrinsic 67Zn was better absorbed than the intrinsic label. These results demonstrate that extrinsically-added stable Zn isotopes do not fully exchange with endogenous Zn in many foods, and illustrate the need for caution when using extrinsic labels for Zn bioavailability studies.

Comparison of fast‐atom bombardment, thermal ionization and inductively coupled plasma mass spectrometry for the measurement of 64Zn/67Zn stable isotopes in human nutrition studies

Fast-atom bombardment, thermal ionization and inductively coupled plasma mass spectrometry are contrasted in comparative measurements of 64Zn/67Zn isotope ratios on samples isolated in the course of a human mineral-nutrition experiment. The data are evaluated with reference to the precision normally required in enriched stable-isotope mineral-nutrition studies, and the convenience of the mass spectrometric techniques is also compared.

The Oligocene and Miocene Outliers of West Cornwall and their Bearing on the Geomorphological Evolution of Oldland Britain

The Tertiary sediments preserved at St Agnes, Crousa Downs and Polcrebo Downs, Cornwall, are described in detail. The deposits at St Agnes have yielded two contrasting floras, one mid-Oligocene, the other Miocene in age. The latter appears to be the first recorded proven Miocene extant in the British landscape. Accordingly, it has become necessary to distinguish two discrete outliers at St Agnes: that termed the St Agnes Formation sensu stricto (Miocene) and the Beacon Cottage Farm Formation (Oligocene, the local equivalent of the Bovey Formation). A tripartite stratigraphy is proposed for the former, the upper and lower Members comprising wind-blown sands and the middle Member a colluvial slope-wash deposit; all were apparently formed under warm-temperate conditions. The sediments at Crousa and Polcrebo remain undated; both preserve deep weathering profiles of tropical or subtropical type in the Palaeozoic floor below and are themselves much affected by in situ deep weathering. Structurally, all four outliers appear to be simple erosional relics of once more widespread and, possibly, thicker sheets. No secondary structures have been identified. All four apparently survived as a result of their locations on prominent watersheds originating in at least mid- or even early Tertiary times. The geomorphological relations of the four outliers are considered in detail. The sub-St Agnes Surface is shown to be the homologue of a planation surface that is widely developed in west Cornwall at an elevation of between ca. 75-131 m above sea level (ASL). The latter is redefined and termed the Reskajeage Surface. Its age is shown to be pre-Upper Miocene rather than Pleistocene, as was previously widely held. There is indirect evidence that it formed subaerially over a long period during mid-Tertiary times; essentially, it appears to be an etchplain of tropical and subtropical origins, now largely stripped of its former saprolitic cover. It is demonstrated that the grosser physiography of west Cornwall was established by the end of the Palaeogene at the latest and, also, that the area has probably never been inundated by Tertiary seas, except shallowly near to the end of that period (i.e. by the St Erth transgression). The prolonged morphodynamic stability of the region, as established in this paper, has important consequences for the interpretation of landscape evolution elsewhere in areas of Oldland (i.e. post-Armorican) western Europe, especially where datable Tertiary deposits have yet to be recognized.

Elastic Electron Scattering from Zn Isotopes

Elastic electron scattering from the stable even-even Zn isotopes was measured in the region of the first diffraction minimum ($0.3\ensuremath{\le}q\ensuremath{\le}1.1$ ${\mathrm{fm}}^{\ensuremath{-}\mathrm{t}}$). The cross-section ratios for each pair of isotopes were used to determine the change in the rms radius. The rms radius follows an ${A}^{\frac{1}{3}}$ law between $^{64}\mathrm{Zn}$ and $^{66}\mathrm{Zn}$ and between $^{68}\mathrm{Zn}$ and $^{70}\mathrm{Zn}$: whereas, between $^{66}\mathrm{Zn}$ and $^{68}\mathrm{Zn}$ the rms radius decreases significantly.