Zinc Stable Isotope Research Articles

Zinc absorption from micronutrient powder is low but is not affected by iron in Kenyan infants.

Interference with zinc absorption is a proposed explanation for adverse effects of supplemental iron in iron-replete children in malaria endemic settings. We examined the effects of iron in micronutrient powder (MNP) on zinc absorption after three months of home fortification with MNP in maize-based diets in rural Kenyan infants. In a double blind design, six-month-old, non-anemic infants were randomized to MNP containing 5 mg zinc, with or without 12.5 mg of iron (MNP + Fe and MNP − Fe, respectively); a control (C) group received placebo powder. After three months, duplicate diet collections and zinc stable isotopes were used to measure intake from MNP + non-breast milk foods and fractional absorption of zinc (FAZ) by dual isotope ratio method; total absorbed zinc (TAZ, mg/day) was calculated from intake × FAZ. Mean (SEM) TAZ was not different between MNP + Fe (n = 10) and MNP − Fe (n = 9) groups: 0.85 (0.22) and 0.72 (0.19), respectively, but both were higher than C (n = 9): 0.24 (0.03) (p = 0.04). Iron in MNP did not significantly alter zinc absorption, but despite intakes over double estimated dietary requirement, both MNP groups’ mean TAZ barely approximated the physiologic requirement for age. Impaired zinc absorption may dictate need for higher zinc doses in vulnerable populations.

The zinc stable isotope signature of waste rock drainage in the Canadian permafrost region

Leachate from a well-instrumented experimental-scale waste-rock pile (test pile) at the Diavik Diamond mine, Northwest Territories, was monitored. The well-characterized waste rock consists of granite, pegmatitic granite and biotite schist with an average total sulfur and carbonate carbon concentration of 0.053 and 0.027wt.%, respectively. The leachate emerging from the southern basal drain of the waste rock pile has been monitored since 2007. The zinc stable isotope footprint was characterized alongside standard monitoring parameters during two field seasons, May to November 2011 and 2012. The pH ranged between 4.3 and 6.8 and carbonate alkalinity was low or undetectable (<35mgL−1 CaCO3). The pH was governed by the oxidation of sulfide minerals and the dissolution of primary carbonate minerals and secondary Al and Fe oxyhydroxysulfates and hydroxides. Dissolved Al and Fe concentrations averaged 6.78mgL−1 and 175μgL−1, respectively. The main processes controlling Zn concentrations in the range of 0.4 and 4.7mgL−1 (average=2.2mgL−1) were the oxidative dissolution of sphalerite (ZnS) and the attenuation by secondary Fe and Al hydroxides. Zinc isotopes were fractionated mass dependently. Zinc isotope ratios, ranging between −0.16 and +0.18‰ (average=+0.05‰, n=43) were consistent with values reported for sphalerite from other deposits. The deviations in isotope ratios (Δ=0.36‰) were significant in comparison to analytical uncertainties (0.06‰). Zinc isotope ratios and concentrations were largely uncorrelated, suggesting that the processes affecting Zn mobility had little or no impact on the Zn isotope signature. These data suggest that the Zn isotope ratios of the waste-rock leachate may be used as a fingerprint to track anthropogenic, mine-derived Zn sources in an environment under fluctuating pH, temperature and ionic strength.

Zinc stable isotope fractionation upon accelerated oxidative weathering of sulfidic mine waste

Accelerated oxidative weathering in a reaction cell (ASTM D 5744 standard protocol) was performed over a 33week period on well characterized, sulfidic mine waste from the Kidd Creek Cu–Zn volcanogenic massive sulfide deposit, Canada. The cell leachate was monitored for physicochemical parameters, ion concentrations and stable isotope ratios of zinc. Filtered zinc concentrations (<0.45μm) in the leachate ranged between 4.5mgL−1 and 1.9gL−1—potentially controlled by pH, mineral solubility kinetics and (de)sorption processes. The zinc stable isotope ratios varied mass-dependently within +0.1 and +0.52‰ relative to IRMM 3702, and were strongly dependent on the pH (rpH-d66Zn=0.65, p<0.005, n=31). At a pH below 5, zinc mobilization was governed by sphalerite oxidation and hydroxide dissolution—pointing to the isotope signature of sphalerite (+0.1 to +0.16‰). Desorption processes resulted in enrichment of 66Zn in the leachate reaching a maximum offset of +0.32‰ compared to the proposed sphalerite isotope signature. Over a period characterized by pH=6.1±0.6, isotope ratios were significantly more enriched in 66Zn with an offset of ≈0.23‰ compared to sphalerite, suggesting that zinc release may have been derived from a second zinc source, such as carbonate minerals, which compose 8wt.% of the tailings. This preliminary study confirms the benefit of applying zinc isotopes alongside standard monitoring parameters to track principal zinc sources and weathering processes in complex multi-phase matrices.

A stable‐isotope methodology for measurement of soil‐applied zinc‐fertilizer recovery in durum wheat (Triticum durum)

AbstractA growth‐chamber study was used to develop a zinc stable‐isotope (67Zn) tracing technique to directly measure the amount of soil‐applied zinc (Zn) granular fertilizer taken up by durum wheat (Triticum durum L.) in four different soil types. The 67Zn‐tracer technique was then applied under field conditions at one site to test the ability of the method to measure the crop recovery of soil‐applied Zn granular fertilizer (67Zn). The technique was developed by comparing plants treated with nil Zn fertilizer to natural‐abundance‐Zn‐coated fertilizer and 67Zn‐coated fertilizer with plant parts analyzed for Zn isotopic composition using inductively coupled plasma–mass spectrometry. Zinc‐fertilizer recovery under growth‐chamber conditions was inversely related to the concentration of labile Zn in soils, with the plants on the most Zn‐deficient soils having the greatest amount of Zn derived from the added fertilizer. Zinc derived from fertilizer ranged from 0.3% (Luvisol) to 0.6% (Solonetz) to 13% (Calcisol) and 18% (Lixisol) for soils with DTPA‐extractable Zn of 3.5–0.21 mg kg–1. Across the experiments, fertilizer recovery was measurable but very low (&lt; 1% of added fertilizer being recovered by durum wheat). The recovery of Zn added to the Luvisol was slightly higher in the field than in the glasshouse (but all &lt; 0.1%). Using this stable‐isotope technique, it was possible to directly assess the supply of soil‐applied Zn fertilizers to crop plants.

Iron, copper and zinc isotopic fractionation up mammal trophic chains

There is a growing body of evidence that some non-traditional elements exhibit stable isotope compositions that are distinct in botanical and animal products, providing potential new tracers for diet reconstructions. Here, we present data for iron (Fe), copper (Cu) and zinc (Zn) stable isotope compositions in plants and bones of herbivores and carnivores. The samples come from trophic chains located in the Western Cape area and in the Kruger National Park in South Africa. The Fe, Cu and Zn isotope systematics are similar in both parks. However, local Cu, and possibly Zn, isotopic values of soils influence that of plants and of higher trophic levels. Between plants and bones of herbivores, the Zn isotope compositions are 66Zn-enriched by about 0.8‰ whereas no significant trophic enrichment is observed for Fe and Cu. Between bones of herbivores and bones of carnivores, the Fe isotope compositions are 56Fe-depleted by about 0.6‰, the Cu isotope compositions are 65Cu-enriched by about 1.0‰, and the Zn isotope compositions are slightly 66Zn-depleted by about 0.2‰. The isotopic distributions of the metals in the body partly explain the observed trophic isotopic systematics. However, it is also necessary to invoke differential intestinal metal absorption between herbivores and carnivores to account for the observed results. Further studies are necessary to fully understand how the Fe, Cu and Zn isotope values are regulated within the ecosystem's trophic levels, but the data already suggests significant potential as new paleodietary and paleoecological proxies.

Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth

The zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation.The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰<δ66Zn<0.36‰; δ66Zn defined as the per mille deviation of a sample's 66Zn/64Zn compositional ratio from the JMC-Lyon standard), with the most differentiated lithologies exhibiting more positive δ66Zn values. This fractionation is likely a result of the crystallization of olivine and/or Fe–Ti oxides, which can both host Zn in their crystal structures. Samples from Hekla have a similar range of isotopic variation (0.22‰<δ66Zn<0.33‰), however, the degree of fractionation caused by magmatic differentiation is less significant (only 0.07‰) and no correlation between isotope composition and degree of differentiation is seen. We conclude that high temperature magmatic differentiation can cause Zn isotope fractionation that is resolvable at current levels of precision, but only in compositionally-evolved lithologies. With regards to primitive (ultramafic and basaltic) material, this signifies that the terrestrial mantle is essentially homogeneous with respect to Zn isotopes. Utilizing basaltic and ultramafic sample analyses, from different geologic settings, we estimate that the average Zn isotopic composition of Bulk Silicate Earth is δ66Zn=0.28±0.05‰ (2s.d.).

Zinc isotope ratio imaging of rat brain thin sections from stable isotope tracer studies by LA-MC-ICP-MS

Zinc stable isotope tracers (⁶⁷Zn and ⁷⁰Zn) were injected into rats at two different time points to investigate the feasibility of using tracers to study zinc kinetics at the microscale within distinct tissue features. Laser ablation coupled to multi-collector ICP-MS was used to analyse average isotope ratios in liver thin sections and to generate bio-images showing zinc isotope ratio distribution in brain thin sections. Average isotope ratios of all samples from treated animals were found to be statistically different (P < 0.05) from samples from untreated control animals. Furthermore, differing isotope ratios in physiological features of the brain, namely hippocampus, amygdala, cortex and hypothalamus, were identified. This indicates that these regions differ in their zinc metabolism kinetics. While cortex and hypothalamus contain more tracer two days after injection than 14 days after injection, the opposite is true for hippocampus and amygdala. This study showed that stable isotope tracer experiments can be combined with laser ablation MC-ICP-MS to measure trace element kinetics in tissues at a microscale level.

Microanalytical isotope ratio measurements and elemental mapping using laser ablation ICP-MS for tissue thin sections: zinc tracer studies in rats

The kinetics of zinc absorption, metabolism and excretion is extensively studied by nutritionists. Stable isotopes of zinc can be used to identify body zinc compartments that have different turnover kinetics. Since the compartments might belong to physiological subsections of different organs, there is a need for microsampling analysis to determine isotope ratios of the trace element zinc in tissue samples. Here, we study the feasibility to use laser ablation coupled to quadrupole ICP-MS for the determination of zinc tracers given to rats at different time points with the aim to generate isotope ratio bioimages of heart tissue. A double tracer ((70)Zn and (67)Zn) experiment with rats was designed to label the exchangeable zinc pool as well as the stable zinc pool. The isotope ratios determined by laser ablation ICP-MS were evaluated by additional measurements of tissue digests. Accumulated tracers which made up more than 0.1% of total zinc could be identified in the tissues of the treated rats. It was established that at least 50 measurements from the microsampling were necessary to distinguish between controls and a tracer treated rat resulting in reduced resolution of the bioimage. With the parameters used, features in the tissue thin sections of at least 250 μm(2) in size are necessary to detect the incorporation of a tracer. When different time points have to be measured, higher precisions are required and therefore a larger area needs to be ablated (1 mm(2)). Using the bioimages and pool measurements from one physiological feature, it was possible to show that the aorta cell walls incorporate the zinc tracer at the different time points.

Erratum: Measurement of zinc stable isotope ratios in biogeochemical matrices by double-spike MC-ICPMS and determination of the isotope ratio pool available for plants from soil

Erratum: Measurement of zinc stable isotope ratios in biogeochemical matrices by double-spike MC-ICPMS and determination of the isotope ratio pool available for plants from soil

Measurement of zinc stable isotope ratios in biogeochemical matrices by double-spike MC-ICPMS and determination of the isotope ratio pool available for plants from soil.

Analysis of naturally occurring isotopic variations is a promising tool for investigating Zn transport and cycling in geological and biological settings. Here, we present the recently installed double-spike (DS) technique at the MAGIC laboratories at Imperial College London. The procedure improves on previous published DS methods in terms of ease of measurement and precisions obtained. The analytical method involves addition of a 64Zn–67Zn double-spike to the samples prior to digestion, separation of Zn from the sample matrix by ion exchange chromatography, and isotopic analysis by multiple-collector inductively coupled plasma mass spectrometry. The accuracy and reproducibility of the method were validated by analyses of several in-house and international elemental reference materials. Multiple analyses of pure Zn standard solutions consistently yielded a reproducibility of about ±0.05‰ (2 SD) for δ66Zn, and comparable precisions were obtained for analyses of geological and biological materials. Highly fractionated Zn standards analyzed by DS and standard sample bracketing yield slightly varying results, which probably originate from repetitive fractionation events during manufacture of the standards. However, the δ66Zn values (all reported relative to JMC Lyon Zn) for two less fractionated in-house Zn standard solutions, Imperial Zn (0.10 ± 0.08‰: 2 SD) and London Zn (0.08 ± 0.04‰), are within uncertainties to data reported with different mass spectrometric techniques and instruments. Two standard reference materials, blend ore BCR 027 and ryegrass BCR 281, were also measured, and the δ66Zn were found to be 0.25 ± 0.06‰ (2 SD) and 0.40 ± 0.09‰, respectively. Taken together, these standard measurements ascertain that the double-spike methodology is suitable for accurate and precise Zn isotope analyses of a wide range of natural samples. The newly installed technique was consequently applied to soil samples and soil leachates to investigate the isotopic signature of plant available Zn. We find that the isotopic composition is heavier than the residual, indicating the presence of loosely bound Zn deposited by atmospheric pollution, which is readily available to plants. FigureZinc isotope ratio pools of bulk soil and the associated acid leach (estimated plant available pool) as measured by double-spike MC-ICPMS. δxZnLyon-JMC=(Rsample/RJMC-Lyon -1)x103, where Rsample and RJMC-Lyon denote the xZn/64Zn isotope ratio of the sample and standard (JMC-Lyon), respectively, and where x denotes either 66 or 68.

Bodily variability of zinc natural isotope abundances in sheep

Evidence is growing that the range of zinc stable isotope compositions, represented by the deviation of (66)Zn in permil units relative to a standard and expressed as delta(66)Zn, is larger in organic matter than in inorganic material. This study reports the variations of delta(66)Zn in various organs of sheep raised on a controlled diet. Zinc was purified by anion-exchange chromatography. The Zn concentrations and Zn stable isotope compositions were determined by quadrupole inductively coupled plasma mass spectrometry and multi-collector inductively coupled plasma mass spectrometry, respectively. The data show that delta(66)Zn variability exceeds 1 per thousand, with bone, muscle, serum and urine enriched in the heavy isotopes, and feces, red blood cells, kidney and liver enriched in light isotopes, all relative to the diet value. The (66)Zn enrichment of the circulating serum reservoir is likely to take place in the digestive tract, probably through the preferential binding of lighter isotopes with phytic acid, which is known to control the uptake of metallic elements. Mass balance calculations suggest that the (66)Zn depletion between diet and feces, which is not balanced by any other outward flux, leads to a secular isotopic drift in serum. A simple time-dependent two-box model, involving the gastro-intestinal tract on the one hand and the muscle and bone on the other, predicts that the maximum (66)Zn enrichment, which equals the difference in delta(66)Zn between diet and bulk (approximately 0.25 per thousand), is reached after about ten years. Therefore, a better understanding of the variations of natural abundance of Zn isotopes in animals and humans will probably bring new perspectives for the assessment of their Zn status.

Measurement of total Zn and Zn isotope ratios by quadrupole ICP-MS for evaluation of Zn uptake in gills of brown trout ( Salmo trutta) and rainbow trout ( Oncorhynchus mykiss)

This study evaluates the potential use of stable zinc isotopes in toxicity studies measuring zinc uptake by the gills of brown trout ( Salmo trutta) and rainbow trout ( Oncorhynchus mykiss). The use of stable isotopes in such studies has several advantages over the use of radioisotopes, including cost, ease of handling, elimination of permit requirements, and waste disposal. A pilot study using brown trout was performed to evaluate sample preparation methods and the ability of a quadrupole inductively coupled plasma mass spectrometer (ICP-MS) system to successfully measure changes in the 67Zn/ 66Zn ratios for planned exposure levels and duration. After completion of the pilot study, a full-scale zinc exposure study using rainbow trout was performed. The results of these studies indicate that there are several factors that affect the precision of the measured 67Zn/ 66Zn ratios in the sample digests, including variations in sample size, endogenous zinc levels, and zinc uptake rates by individual fish. However, since these factors were incorporated in the calculation of the total zinc accumulated by the gills during the exposures, the data obtained were adequate for their intended use in calculating zinc binding and evaluating the influences of differences in water quality parameters.

Systemic translocation of 70Zinc: Kinetics following intratracheal instillation in rats

Mechanisms of particulate matter (PM)-induced cardiotoxicity are not fully understood. Direct translocation of PM-associated metals, including zinc, may mediate this effect. We hypothesized that following a single intratracheal instillation (IT), zinc directly translocates outside of the lungs, reaching the heart. To test this, we used high resolution magnetic sector field inductively coupled plasma mass spectrometry to measure levels of five stable isotopes of zinc ( 64Zn, 66Zn, 67Zn, 68Zn, 70Zn), and copper in lungs, plasma, heart, liver, spleen, and kidney of male Wistar Kyoto rats (13 weeks old, 250–300 g), 1, 4, 24, and 48 h following a single IT or oral gavage of saline or 0.7 μmol/rat 70Zn, using a solution enriched with 76.6% 70Zn. Natural abundance of 70Zn is 0.62%, making it an easily detectable tracer following exposure. In IT rats, lung 70Zn was highest 1 h post IT and declined by 48 h. Liver endogenous zinc was increased 24 and 48 h post IT. 70Zn was detected in all extrapulmonary organs, with levels higher following IT than following gavage. Heart 70Zn was highest 48 h post IT. Liver, spleen and kidney 70Zn peaked 4 h following gavage, and 24 h following IT. 70Zn IT exposure elicited changes in copper homeostasis in all tissues. IT instilled 70Zn translocates from lungs into systemic circulation. Route of exposure affects 70Zn translocation kinetics. Our data suggests that following pulmonary exposure, zinc accumulation and subsequent changes in normal metal homeostasis in the heart and other organs could induce cardiovascular injury.

Current dietary zinc intake has a greater effect on fractional zinc absorption than does longer term zinc consumption in healthy adult men

BackgroundNo studies have examined the independent effects of current and longer-term dietary zinc intakes on zinc absorption. ObjectiveWe determined the effects of current compared with longer-term zinc intake on fractional zinc absorption (FZA). DesignWe studied 9 men whose usual zinc intakes were >11 mg/d. FZA was measured at baseline, depletion (0.6 mg Zn/d for 1 wk and 4 mg Zn/d for 5 wk), and repletion (11 mg Zn/d for 4 wk with 20 mg supplemental Zn/d for first 7 d). During 2 successive days after each dietary period, subjects consumed either adequate-zinc meals (11 mg Zn/d) with a zinc stable isotope tracer for 1 d, followed by low-zinc meals (4 mg Zn/d) with zinc tracer, or vice versa. Five days after oral dosing, a zinc tracer was infused intravenously. FZA was measured with the use of a modified double isotope tracer ratio method with urine samples collected on days 5–7 and 10–12 of absorption studies. ResultsPlasma and urinary zinc did not vary by dietary period. Mean FZA was greater from low-zinc meals than from adequate-zinc meals (60.9% ± 13.8% compared with 36.1% ± 8.9%; P < 0.0001), whereas mean total absorbed zinc was greater from adequate-zinc meals than from low-zinc meals (3.60 ± 0.91 compared with 2.48 ± 0.56; P < 0.0001), regardless of the longer-term dietary period. ConclusionsFZA was inversely related to current zinc intake, but there was no detectable effect of longer-term dietary zinc. If longer- term zinc intake does modify FZA, such changes are smaller than those caused by current zinc intake, or they occur only after more severe zinc depletion.

Historical variations in the isotopic composition of atmospheric zinc deposition from a zinc smelter

In order to test the usefulness of stable zinc isotopes as an atmospheric source tracer, we analyzed the zinc isotopic composition of two sediment cores, taken at 1 km distance of the former zinc smelter in Lommel, Belgium. The peat bog lake sediments accumulate mainly atmospheric particles, have high organic matter contents (12–60 wt.%), are anoxic and highly contaminated with heavy metals (up to 4.7 wt.% Zn, and 1.1 wt.% Pb) with a sulfide mineralogical control on mobility. Down core variations in δ 66Zn (relative to the JMC 3-0749L standard) were small, ranging from + 0.07‰ to + 0.39‰, but are nevertheless eight times the external reproducibility of 0.04‰. Good agreement was found between the two cores, and despite 30% Zn mobilization to deeper layers, no evidence of associated diagenetic Zn isotope fractionation was found. Sediments deposited in the early 20th century have δ 66Zn of + 0.30‰ ± 0.05‰ (2SD, n = 5) and a shift takes place between 1945 and 1950 to δ 66Zn values of + 0.14‰ ± 0.09‰ (2SD, n = 7) in the 2nd half of the century. In order to understand this shift in δ 66Zn we analyzed 32 ore-grade sphalerite (ZnS) samples from African, Australian and European origin. Together with 29 published δ 66Zn values for ore-grade ZnS, we find remarkably homogeneous isotopic compositions, which when averaged for mining location gives δ 66Zn of + 0.16‰ ± 0.20‰ (2SD, n = 10 mines, n = 61 analyses). Early 20th century Zn deposition with δ 66Zn of +0.30‰ is significantly different (p < 0.001) from average ZnS δ 66Zn of +0.16‰. We suggest that this reflects the presence of an atmospheric smelting residue (slag) component, enriched in the heavy Zn isotopes due to Rayleigh type fractionation during Zn refining.

New Evaluation of Neutron Nuclear Data for Zinc Isotopes

New evaluation of neutron-induced nuclear data for five stable isotopes of zinc (mass numbers A = 64, 66, 67, 68, and 70) was consistently carried out in the incident neutron energy range from 10−5 eV up to 20MeV. In the low energy region up to about 100keV, the resonance parameters were evaluated by taking account of the available measured data. In the fast neutron region, the comprehensive calculations with nuclear reaction models, in which compound, preequilibrium, and direct processes are taken into account, were performed to estimate cross sections for various reactions and double differential cross sections of emitted neutrons and γ-rays. The comparisons of the evaluated cross sections with the experimental data and existing evaluated nuclear data libraries are made and show a good agreement with the measurements.

Zinc absorption during late pregnancy in rural southern Ethiopia

Little is yet known about zinc absorption in late pregnancy, and no information on absorption from the total diet is available. The objective was to measure the fractional absorption of zinc (FAZ) and to estimate the total quantity of absorbed zinc (TAZ) each day during the third trimester of pregnancy in poor rural southern Ethiopian women. The participants (n = 17) were a convenience sample from a larger study population. The third stage of pregnancy was estimated from fundal height by the Bushulo Health Center prenatal outreach program. FAZ was determined with a dual-isotope tracer ratio technique that uses measurements of urine enrichment with zinc stable isotopes administered intravenously and orally, as an extrinsic label, with all meals in 1 d. Total dietary zinc (TDZ) was calculated from weighed diet records and Ethiopian food-composition tables supported by zinc and phytate analyses of major food items for individual meals. Plasma zinc and exchangeable zinc pool size were also estimated. Mean (+/-SD) FAZ was 0.35 +/- 0.11, TDZ was 6.0 +/- 3.2 mg/d, TAZ was 2.1 +/- 1.0 mg/d, phytate intake was 1033 +/- 843 mg/d, plasma zinc was 44.1 +/- 6.0 microg/dL, and the exchangeable zinc pool size was 142 +/- 39 mg. The molar ratio of phytate to zinc was 17:1. Women from a poor rural population who were dependent on a moderately high-phytate diet had low TDZ and low plasma zinc concentrations in the third trimester of pregnancy. TAZ was modestly higher than that predicted but did not meet physiologic requirements.

Effects of Dietary Phytate and Supplemental Zinc on Exchangeable Zinc Pool Mass in Young and Elderly Korean Women

The exchangeable zinc pool (EZP) has been proposed as a zinc status measure. This study was done to determine the effects of dietary phytate (P) and supplemental Zn on EZP size in young and elderly Korean women. Thirteen young (20–24y) and 12 elderly women (64–75y) were studied for three metabolic periods (MP). In MP 1, the women consumed a high phytate (HP) diet (P: Zn molar ratio=23); in MP 2 a low phytate (LP) diet (P: Zn molar ratio=10) was fed, and in MP 3 the women took a 22 mg/d Zn supplement for 27 days while consuming their usual diets. A zinc stable isotope, 70Zn, was given intravenously on d 5 in MP 1 and 2, and on d 20 in MP 3. Plasma samples were collected after isotope administration for measuring isotopic ratios by Inductively Coupled Plasma (ICP) Mass Spectrometry and PZn concentrations by ICP Emission Spectrometry. EZP was calculated using the method of Miller et al (J Nutr 1994;124:–76). Dietary phytate did not alter PZn or EZP in either group. Supplemental Zn increased PZn and EZP in the young, but had no effect in elderly women. This suggests that PZn and EZP are not sensitive markers of zinc status in older individuals. Supported by Korea Research Foundation and the USDA/ARS WHNRC

Zinc absorption in Guatemalan schoolchildren fed normal or low-phytate maize

Poor bioavailability of zinc from high-phytate diets is an important contributory factor to zinc deficiency in low-income populations. The objective of this study was to determine the effect of low-phytate maize consumption on zinc absorption. The participants were apparently healthy children from the Central Highlands of Guatemala. Sixty children (20 per group) were randomly assigned to be fed only the low-phytate maize or 1 of 2 control maizes, the isohybrid wild-type maize or a local maize, for a 10-wk period. During the final week, the fractional absorption of zinc for all meals was measured during 1 d with the use of zinc stable isotopes and a dual isotope ratio technique based on urine enrichment data. Mean (+/-SD) phytate intakes for the low-phytate, wild-type, and local maize groups were 1536 +/- 563, 2056 +/- 517, and 2253 +/- 687 mg/d, respectively. Corresponding zinc intakes were 8.6 +/- 2.5, 8.1 +/- 2.0, and 9.7 +/- 2.6 mg/d, and the dietary phytate:zinc molar ratios were 18 +/- 5, 26 +/- 6, and 23 +/- 5. Corresponding fractional absorptions of zinc were 0.32 +/- 0.07, 0.28 +/- 0.07, and 0.29 +/- 0.06. The respective values for total absorbed zinc were 2.72 +/- 0.88, 2.30 +/- 0.96, and 2.78 +/- 1.04 mg/d. No significant differences in either the fractional absorption of zinc or total absorbed zinc were seen between the maize groups. Under the conditions of the present study, zinc absorption was not increased by the long-term use of low-phytate maize in children whose major dietary staple is maize.

Studies on zinc bioavailability from a representative diet in Chinese urban women of childbearing age using a double label stable isotope technique

The objectives of the study were to determine dietary zinc bioavailability by using a double label stable isotope technique, and to identify the zinc content and levels of some possible factors which may affect zinc utilization in a typical representative Chinese urban diet. Twenty urban women of childbearing age were fed a diet extrinsically labeled with 67Zn and received intravenous (i.v.) injections of 70Zn. Fecal monitoring, urine monitoring and chemical balance technique were used simultaneously for comparisons. Isotopic enrichment in feces and urine after oral and i.v. administration of stable zinc isotopes was measured to determine the ways of zinc absorption. The mean (±SD) zinc intake from the representative Chinese diet was 10.22±0.80 mg/day, which is lower than the reference nutrient intake (RNI) level (11.5 mg/day), and mainly came from the subsidiary foods (63%). The mean dietary Fe/Zn weight was 1.1±0.1. The phytate/zinc molar ratio in the diet was about 3:1. The phytic acid×Ca/zinc molar ratio in the diet was about 45:1. The apparent and true absorption rates of 67Zn were 36.2±9.7% and 38.2±10.1%, respectively, which were higher than the apparent absorption determined by balance technique (29.7±10.6%). The mean fractional absorption (FA) determined in urine was 35.7±13.3. In conclusion, the subsidiary food is the main source of dietary zinc in this typical diet. The extrinsic labeling technique by use of stable isotopes was more reliable and accurate to determine zinc absorption. Moreover, the double isotopic tracer ratio (DITR) technique applied to urine samples was a more practical and valuable way to evaluate zinc absorption than other methods. It can be speculated that iron and phytic acid might not be the main inhibitors in the representative Chinese diet.