Zn Citrate Research Articles

Leaching and vertical distribution of Fe and Zn citrate nanoparticles in Indian red soil

This research aims to address common constraints in the effective utilization of plant nutrients in soil, such as fixation, mobility, leaching, and reactions with soil colloids. To mitigate these issues, Fe and Zn citrate nanoparticles were synthesized and applied as nanochelators in a reconstructed soil profile column. We evaluated the mobility, release, and leaching behaviors of these nanoparticles. Results revealed that, no leaching of Fe and Zn citrate nanoparticles occurred even after a 90-day incubation. The release profiles exhibited a peak at 60 and 90 days for Fe and Zn respectively. In the mobility studies, Fe and Zn availability was highest in the 0–15 cm soil depth. Fe citrate and Zn citrate nanoparticles demonstrated the highest availability at 264.7 mg/kg and 86.26 mg/kg of soil, respectively as compared with commercial samples. The superior performance of Fe and Zn citrate nanoparticles was observed in terms of reduced leaching and improved accessibility, indicating their potential as efficient and environmentally-friendly plant nutrient sources. The study concludes that Fe and Zn citrate nanoparticles are stable nutrient sources that can enhance plant use efficiency with minimal environmental impact.

Structure and complexation mechanism of aqueous Zn(II)-acetate complex studied by XAFS and Raman spectroscopies

In this work, the structure of Zn acetate has been determined by a combination of X-ray absorption fine structure and Raman spectroscopy. We have analyzed the local atomic environment and the main vibrational bands of the acetate and Zn acetate at different pH. The results suggest that Zn acetate complex acquires a bidentate structure that modifies its first coordination shell. Meanwhile, the coordination shell of the hydrated Zn cation is formed by 6 hydroxides at a mean distance of 2.06 Å, the coordination shell of the Zn cation in the complex is formed by 2 hydroxides and 2 oxygens from the carboxyl group of the acetate, at a mean Zn–O distance of 1.96 Å. The structure of the Zn acetate complex is compared to those of Zn malonate and Zn citrate, none of which present a reduction in the coordination shell neither a shrinkage of the Zn–O shell distance.Graphical abstract

Exploring zinc deficiency using serum Zn levels: consequences and potential solutions in suckling pigs.

Three trials were undertaken to provide an answer to different questions: 1) Are suckling pigs able to maintain physiological serum Zn levels throughout lactation and do these levels vary between high and low body weight (BW) pigs?, 2) Are serum Zn levels in pigs soon after weaning a predisposing factor for diarrhea?, and 3) Is it possible to increase serum Zn levels at weaning by supplementing Zn during lactation. In trial 1, blood samples were taken from pigs during lactation. Eight pigs (one piglet per litter) had blood drawn on days 0 (farrowing), 7, 14, 21, and 28 (weaning), and 60 pigs (selected from the whole farrowing batch with 35 sows), categorized as either heavy (8.63 kg) or light (5.50 kg) had blood drawn on day 28. Serum Zn levels at birth were 1.2 mg/L and decreased (P < 0.01) to 0.67 mg/L on day 28. Heavier pigs showed greater (P < 0.01) serum Zn levels (0.98 mg/L) than light BW pigs (0.79 mg/L). In trial 2, blood samples were obtained from 240 pigs at weaning (26.2 ± 2.5 d) with an average initial BW of 6.94 ± 1.87 kg and were distributed into 24 pens (10 pigs/pen) by BW. Diarrhea incidence was recorded daily from days 0 to 35 post-weaning. From the 240 pigs, a group of 110 pigs with uniform BW (6.5 ± 1.9 kg) was selected and separated into two groups based on serum Zn levels at weaning with 55 pigs with low serum Zn (LZn: <0.71 mg/L) and 55 pigs with high serum Zn (HZn: >0.9 mg/L). Pigs with LZn were 2.49 times as likely to have diarrhea as pigs with HZn (P < 0.02). In trial 3, a total of 96 suckling pigs were allotted four treatments that consisted of the daily administration of 0, 6, 18, or 30 mg of Zn as Zn citrate in capsule form during the last 7 d of lactation. Pigs were individually weighed, and blood samples were obtained on days 14, 21 (weaning), and 7 after weaning. Serum Zn levels linearly increased by day as Zn citrate supplementation increased (interaction, P < 0.001). However, only light pigs supplemented with 18 and 30 mg/L of Zn experienced an increase in serum Zn levels during lactation. In conclusion, a decrease in serum Zn levels occurs during lactation and is more severe in low BW pigs. Low Zn status (< 0.7 mg/L) at weaning may be a predisposing factor for diarrhea. However, Zn supplementation during lactation can mitigate this decrease in light pigs.

Seed priming with different levels and sources of zinc on the seed germination and seedling growth of barnyard millet (Echinocola frumentacea)

Seed priming with zinc increases the seed germination and seedling growth of many crops. The present study aimed to investigate the effect of seed priming with different levels and sources of zinc on seed germination and seedling growth of barnyard millet variety MDU1. A germination experiment was conducted with various Zn sources and concentrations viz., T1- Non-primed seeds (control); T2-water priming; T3-GA3 priming; T4-T6: seed priming with 0.10%, 0.25% &amp; 0.50% ZnSO4 ; T7- T9: seed priming with 0.10%, 0.25% &amp; 0.50% Zn EDTA; T10-T12: seed priming with 0.10%, 0.25% &amp; 0.50% Zn citrate and the experimental design was a completely randomized design (CRD) which were replicated five times. The seeds of MDU1 variety were treated with different sources and levels of Zn for 12h and the seed germination study was carried out for 15 days. After 15 days, the germination percentage, speed of germination, germination energy, germination index and the seedling growth parameters such as, root length, shoot length, vigour index and seedling dry weight were recorded. Seed priming with 0.50% ZnSO4 performed better in increasing the germination percentage (99%), speed of germination (76.2%), germination energy (69.4%), germination index (3.91) and seedlings growth parameters like shoot length (14.7cm), root length (16.5cm), seedlings dry weight (0.44g), vigour index I (3099) and II (44.6), Zn content (21.9 mg kg-1) &amp; its uptake (5.54 mg g-1). This was closely followed by seed priming of Zn EDTA at 0.25% and Zn citrate at 0.50%. From this study, it can be concluded that seed priming with 0.50% ZnSO4 could be used to improve the germination and seedling growth of barnyard millet which was also economical.

Role of plant growth promoting bacteria in driving speciation gradients across soil-rhizosphere-plant interfaces in zinc-contaminated soils.

Inoculation of soil or seeds with plant growth promoting bacteria ameliorates metal toxicity to plants by changing metal speciation in plant tissues but the exact location of these changes remains unknown. Knowing where the changes occur is a critical first step to establish whether metal speciation changes are driven by microbial metabolism or by plant responses. Since bacteria concentrate in the rhizosphere, we hypothesised steep changes in metal speciation across the rhizosphere. We tested this by comparing speciation of zinc (Zn) in roots of Brassica juncea plants grown in soil contaminated with 600mgkg-1 of Zn with that of bulk and rhizospheric soil using synchrotron X-ray absorption spectroscopy (XAS). Seeds were either uninoculated or inoculated with Rhizobium leguminosarum bv. trifolii and Zn was supplied in the form of sulfide (ZnS nanoparticles) and sulfate (ZnSO4). Consistent with previous studies, Zn toxicity, as assessed by plant growth parameters, was alleviated in B.juncea inoculated with Rhizobium leguminosarum. XAS results showed that in both ZnS and ZnSO4 treatments, the most significant changes in speciation occurred between the rhizosphere and the root, and involved an increase in the proportion of organic acids and thiol complexes. In ZnS treatments, Zn phytate and Zn citrate were the dominant organic acid complexes, whilst Zn histidine also appeared in roots exposed to ZnSO4. Inoculation with bacteria was associated with the appearance of Zn cysteine and Zn formate in roots, suggesting that these two forms are driven by bacterial metabolism. In contrast, Zn complexation with phytate, citrate and histidine is attributed to plant responses, perhaps in the form of exudates, some with long range influence into the bulk soil, leading to shallower speciation gradients.

Experimental justification of the efficacy of Zn and Ag citrates in bird bacterioses

Experimental justification of the efficacy of Zn and Ag citrates in bird bacterioses

Nano zinc carriers influences release kinetics of zinc and iron in a laboratory incubation experiment under Inceptisol and Alfisol

Zinc (Zn) deficiency is a widespread phenomenon globally. Conventional Zn fertilizers viz zinc sulfate (ZnSO4· 7H2O) reported to have very low use efficiency (1–5%). Hence, technological interventions in increasing Zn use efficiency are of utmost important. Keeping this in view, a laboratory incubation study was undertaken to evaluate the effect of various Zn carriers on release kinetics of zinc and iron under Inceptisol and Alfisol. Zincated nanoclay polymer composite (ZNCPC), nano zinc oxide (n-ZnO), Zn-citrate were compared with conventional one i.e., zinc sulfate. ZNCPC attributed highest DTPA-Zn content at 45 days of incubation in Inceptisol (2.99 mg kg−1) and at 60 days of incubation in Alfisol (2.36 mg kg −1). Zn citrate was found another efficient Zn carrier followed by ZNCPC but superior over n-ZnO as per as the Zn availability and control release behavior is concern. Thus, ZNCPC was found to be the most efficient Zn carrier as compared to conventional zinc sulfate and other nano Zn carriers. High aspect ratio of n-ZnO curbs its soil application.

The influence of different amounts of zinc citrate on blood biochemical indices and productivity of rabbit organism

Deficiency of micro- and macronutrients in the organism of young rabbits causes disorders of metabolism and decreased productivity. Inclusion of essential micronutrients made by nanotechnology to the rabbit diet can eliminate this problem. Therefore, the purpose of our research was to investigate the influence of different amounts of zinc citrate in combination with cobalt and chromium citrates on the biochemical processes in the organism and the productivity of rabbits from 62 to 86 days of age. Researches were performed on rabbits 40 days of age, weighing 1.2–1.4 kg. The animals of the experimental groups were fed with fodder ration of the control group and during the day were fed with cobalt citrate in the amount of 40 μg Co/kg of body weight, chromium citrate – 40 mcg Cr/kg of body weight and zinc citrate, calculated respectively in I, II and III of experimental groups 0.25; 0.50 and 0.75 mg Zn/kg of body weight. In the preparatory period – on the 10th day and in the experimental on the 12th, 24th and 36th days of drinking the supplements in 4 animals from the group blood samples were taken for biochemical researches. Body weight gain was also determined by weighing. It was found that in the blood of animals of the first experimental group on the 12th day of drinking mineral additives increased the cholesterol content on 28.8%, on 24th day – decrease by 39.1% and increase – creatinine by 11.6%, and on 36th day – increase in blood of total protein on 12.3%, increase of alkaline phosphatase activity by 23.0%, creatinine content by 15.5% and average daily growth by 9.4%. A similar additive containing zinc citrate of 0.50 mg Zn/kg of body weight in the blood of rabbits of the second experimental group increased the activity of ACAT by 12 and 24 days, respectively, by 37.3 and 22.1%, respectively, and reduced their cholesterol content by 33.9 and 63.1% compared to the control. Whereas in the same group the growth of ALT activity was noted by 23.7%, and the average daily increase was higher than the control indicator by 7.9% 36 days of the research in comparison with the control group. The high content of zinc citrate in the mineral supplement (0.75 mg Zn/kg) in the blood of rabbits of the third experimental group contributed to the increase of the total protein concentration in all periods of the research, AST activity increased by 26.1% on the 24th day, AAT by 34.9% and the content of triacylglycerols and cholesterol was decreased, while on the 36th day the AAT activity increased by 20.3%, under these conditions, the average daily weight gain of rabbits was the highest and amounted to 38.4 g, which was 12.9% higher than the control. Therefore, the additive in the content of citrates of Co and Cr in the amount of 40 μg/kg of body weight and Zn citrate in the amount of 0.75 mg Zn/kg of body weight contributed to the improvement of metabolic processes and increase of growth indices, which may indicate the dose-dependent influence of the additives used in the rabbit young body.

Comparative study of Cu–Zn coatings electrodeposited from sulphate and chloride baths

In this work, the effect of the nature of the salt anion (chloride and sulphate) in the Cu–Zn citrate bath was investigated, using cyclic voltammetry (CV) and chronoamperometry (CA). Experimental electrodeposition parameters (switching potential and imposed potential) were varied in order to examine their influence on the deposits. The coating microstructures were observed by scanning electron microscope (SEM-EDS), the coating phases were characterized by X-ray diffraction (XRD) analysis and the surface composition was assessed by XPS. Higher current efficiency was obtained in chloride baths compared to sulphate baths and best deposits were obtained at −1.4Vvs.(Ag/AgCl/KCl) compared to −1.2 and −1.5Vvs.(Ag/AgCl/KCl). Corrosion test results in 0.5 M NaCl solution show that Cu–Zn deposit produced from chloride bath exhibited the highest corrosion resistance.

Speciation and localization of Zn in the hyperaccumulator Sedum alfredii by extended X-ray absorption fine structure and micro-X-ray fluorescence

Differences in metal homeostasis among related plant species can give important information of metal hyperaccumulation mechanisms. Speciation and distribution of Zn were investigated in a hyperaccumulating population of Sedum alfredii by using extended X-ray absorption fine structure and micro-synchrotron X-ray fluorescence (μ-XRF), respectively. The hyperaccumulator uses complexation with oxygen donor ligands for Zn storage in leaves and stems, and variations in the Zn speciation was noted in different tissues. The dominant chemical form of Zn in leaves was most probably a complex with malate, the most prevalent organic acid in S. alfredii leaves. In stems, Zn was mainly associated with malate and cell walls, while Zn–citrate and Zn–cell wall complexes dominated in the roots. Two-dimensional μ-XRF images revealed age-dependent differences in Zn localization in S. alfredii stems and leaves. In old leaves of S. alfredii, Zn was high in the midrib, margin regions and the petiole, whereas distribution of Zn was essentially uniform in young leaves. Zinc was preferentially sequestered by cells near vascular bundles in young stems, but was highly localized to vascular bundles and the outer cortex layer of old stems. The results suggest that tissue- and age-dependent variations of Zn speciation and distribution occurred in the hyperaccumulator S. alfredii, with most of the Zn complexed with malate in the leaves, but a shift to cell wall– and citric acid–Zn complexes during transportation and storage in stems and roots. This implies that biotransformation in Zn complexation occurred during transportation and storage processes in the plants of S. alfredii.

Availability of Zinc and the Ligands Citrate and Histidine to Wheat: Does Uptake of Entire Complexes Play a Role?

Organic ligands in soils affect the availability of trace metals such as Zn to plants. This study investigated the effects of two of these ligands, citrate and histidine, on Zn uptake by wheat under hydroponic conditions. Uptake of (65)Zn in the presence of these ligands was compared to uptake in the presence of EDTA at the same free Zn concentration (Zn(2+) ~ 50 nM). In the presence of citrate Zn root uptake was enhanced ~3.5 times and in the presence of histidine, by a factor of ~9, compared to the EDTA treatments. Citrate uptake was slightly reduced in the treatment containing ligands and Zn compared to the treatment containing the same ligand concentration but no Zn. In addition, a higher uptake of Zn than of citrate was observed. This suggests that the enhanced Zn uptake was primarily due to increased supply of Zn(2+) by diffusion and dissociation of Zn-citrate complexes at the root surface. Histidine uptake was much higher than citrate uptake and not influenced by the presence of Zn. As histidine forms stronger complexes with Zn than citrate, the results suggest that the enhancement of Zn uptake in the presence of histidine was in part due to the uptake of undissociated Zn-histidine complexes.

Presence of Fe3+ and Zn2+ promoted biotransformation of Cd–citrate complex and removal of metals from solutions

The promotion to Cd–citrate complex biotransformation via addition of Fe3+ and Zn2+ was investigated. Single Fe(III)– or Zn–citrate complex was completely degraded by Pseudomonas sp. MBR, Cd–citrate complex was not. In the Cd–citrate media with molar ratio of 1:2 and 1:3, pH increase obtained from the metabolism of excess citrate slightly promoted the biotransformation of Cd–citrate complex, Cd remained in solutions. The presence of Fe3+ and Zn2+ resulted in complete biotransformation of Cd–citrate complex in the 1:1:2 Fe:Cd:citrate and Zn:Cd:citrate and 1:1:1:3 Fe:Zn:Cd:citrate media. Alkaline pH obtained from biotransformation of metal–citrate complexes caused almost complete removal of metals (>98%) through precipitation and co-precipitation. Pseudomonas sp. MBR potentially could be used to treat wastewater containing mixed citrate complexes of Fe(III), Zn and Cd.

Zinc induced damage to kidney proximal tubular cells: Studies on chemical speciation leading to a mechanism of damage

This study was carried out to investigate whether zinc can potentiate renal toxicity using monolayer cultures of kidney proximal tubular cells and if so to establish the chemical species and the mechanism involved. MethodsZinc was prepared as the citrate complex at pH 7.4 in phosphate buffered saline. Monolayers of kidney proximal tubular cells under standard cell culture conditions were exposed to zinc concentrations of 0, 5 10, 20, 50 and 100μmol/L. To assess cellular damage, thiazol blue (MTT) uptake, NAG and LDH release, DAPI staining and Tunel assay were used. Cytoprotective agents: trolox, cysteine, glutathione, ascorbic acid and sodium selenite were used to investigate if the damage was reversible. ResultsIncubation of kidney cells with zinc citrate showed a dose related reduction in cell viability (p<0.005) associated with cellular uptake of zinc ions. After 24h incubation with 100μmol/L Zn citrate, NAG release was not significantly different compared to the control whereas LDH increased 3 fold. DAPI staining showed apoptotic bodies within the cells confirmed by Tunel assay using flow cytometry. Electron microscopy showed significant morphological changes including loss of brush border, vacuolated cytoplasm and condensed nuclei. Trolox almost completely (>85±5%) and sodium selenite partially recovered (40±4%) the viability of cells exposed to Zn but no protection was observed with other cytoprotectants, e.g. glutathione, cysteine or ascorbic acid.In conclusion zinc can induce damage to kidney cells by a mechanism dependent on zinc ions entering the cell, binding to the cell organelles and disrupting cellular processes rather than damage initiated by free radical and ROS production.

AMELIORATION OF ZINC DEFICIENCY OF CORN IN CALCAREOUS SOILS OF THAILAND: ZINC SOURCES AND APPLICATION METHODS

A variety of zinc (Zn) fertilizer sources are applied with varied responses on calcareous soils in Thailand. Seed treatment is an alternative method to deliver Zn to corn and alleviate Zn deficiency. To address this Zn delivery methods we conducted greenhouse studies on corn grown in three calcareous soils of Thailand to three Zn fertilizer sources [zinc sulfate (ZnSO4), Zn-ethylenediaminetetraacetic acid (EDTA) and Zn citrate]. We also evaluated effectiveness of soaking corn seed in three concentrations of ZnSO4 (0.4, 0.8 and 1.6%) prior to planting compared to soil applied methods. Applications of zinc increased the growth, dry matter yield and zinc uptake of corn with few differences observed among the types of fertilizers. Seed soaking with ZnSO4 solution also increased Zn uptake, growth rate and yield comparable to soil-applied Zn. Seed soaking prior to planting is an effective and efficient method to supply Zn to corn grown in Zn deficient calcareous soils of Thailand.

EDTA disodium zinc has superior bioavailability compared to common inorganic or chelated zinc compounds in rats fed a high phytic acid diet

Different zinc (Zn) compounds have unique properties that may influence the amount of Zn absorbed particularly in the presence of phytic acid (PA), a common food component that binds Zn and decreases its bioavailability. In this study, 30-day-old male rats (n=12/diet group) were fed diets supplemented with PA (0.8%) and low levels (8mg Zn/kg diet) of inorganic (Zn oxide, Zn sulphate) or chelated (Zn gluconate, Zn acetate, Zn citrate, EDTA disodium Zn, Zn orotate) Zn compounds for 5 weeks. Two control groups were fed diets supplemented with low or normal (30mg Zn/kg diet) Zn (as Zn oxide) without added PA. Control rats fed the low Zn oxide diet showed depressed Zn status. Addition of PA to this diet exacerbated the Zn deficiency in rats. Growth (body weight gain and femur length) and Zn concentrations in plasma and tissues were similar in rats fed Zn oxide, Zn sulphate, Zn gluconate, Zn acetate, Zn citrate or Zn orotate. Rats fed EDTA disodium Zn showed enhanced growth compared to rats fed Zn oxide or Zn gluconate and had higher Zn concentrations in plasma and femur compared to rats fed all other Zn compounds. Only the haematological profile of rats fed EDTA disodium Zn did not differ from control rats fed normal Zn. These data indicate that in rats fed a high PA diet, bioavailability of commonly used inorganic or chelated Zn compounds does not differ appreciably, but Zn supplied as an EDTA disodium salt has superior bioavailability.

Effect of a single brushing with two Zn-containing toothpastes on VSC in morning breath: a 12 h, randomized, double-blind, cross-over clinical study

This randomized, double-blind, 12 h clinical study tested the effect of a single brushing with two Zn-containing toothpastes on volatile sulfur compound (VSC) levels in morning breath. The following toothpastes were each tested by all 28 participants: A—Zn toothpaste, B–-experimental toothpaste (Zn citrate + PVM/MA copolymer) and C–-control toothpaste without Zn. The evening prior to test days participants brushed their teeth for 2 min with 1 g toothpaste. 12 h later and prior to eating or performing oral hygiene, morning breath levels of VSC (H2S, CH3SH) were analysed by gas chromatography. Subjects then rinsed for 30 s with 5 ml cysteine and breath samples were analysed for H2S (H2Scys). Median VSC (area under the curve) values were compared for A, B and C and the effects of A and B on VSC were compared with C. Toothpaste B was more effective than both toothpastes A and C in reducing H2S, CH3SH and H2Scys (p < 0.05). Compared with toothpaste C, toothpastes A and B reduced H2S by 35% and 68%, respectively (p = 0.003), and CH3SH by 12% and 47%, respectively (p = 0.002). Toothpaste B reduced H2Scys by 48% compared with toothpaste C (p = 0.001). It is suggested that the superior effect of the experimental toothpaste was most likely due to a higher Zn concentration combined with longer retention of Zn due to the PVM/MA copolymer.

Cadmium, lead and zinc leaching from smelter fly ash in simple organic acids—Simulators of rhizospheric soil solutions

Emissions from base-metal smelters are responsible for high contamination of the surrounding soils. Fly ash from a secondary Pb smelter was submitted to a batch leaching procedure (0.5–168 h) in 500 μM solutions of acetic, citric, or oxalic acids to simulate the release of toxic metals (Cd, Pb, Zn) in rhizosphere-like environments. Organic acids increased dissolution of fly ash by a factor of 1.3. Cadmium and Pb formed mobile chloro- and sulphate-complexes, whereas Zn partly present in a citrate (Zn–citrate −) complex is expected to be less mobile due to sorption onto the positively charged surfaces of hydrous ferric oxides (HFO) and organic matter (OM) in acidic soil.

Localization an speciation of Zn in mycorrhized roots by μSXRF and μEXAFS

Mycorrhizae are symbiotic associations between soil fungi and plant roots, which enhance mineral nutrition for the plant, and might play an important role in metals acquisition and accumulation. The processes allowing metals mobilization in the soil, absorption by the root and/or the fungus, transfer or bioaccumulation are still poorly understood. However, the properties of mycorrhizal fungi could be used for phytoremediation, a soft technique using plants for the clean-up of metal polluted soils. In this work, mycorrhized roots of tomato plants grown in a Zn-contaminated soil were investigated. The distribution of metals and the speciation of Zn were studied at the micron scale using micro synchrotron-based X-ray fluorescence (pSXRF) and micro X-ray absorption spectroscopy (μEXAFS). Zn associated to the root was Zn malate and/or Zn citrate, and Zn associated to the fungus was Zn phyllosilicate. This study illustrates the great potential of X-ray microbeams for the study of biological samples containing various amounts of metals.

Forms of zinc accumulated in the hyperaccumulator Arabidopsis halleri.

The chemical forms of zinc (Zn) in the Zn-tolerant and hyperaccumulator Arabidopsis halleri and in the non-tolerant and nonaccumulator Arabidopsis lyrata subsp. petraea were determined at the molecular level by combining chemical analyses, extended x-ray absorption spectroscopy (EXAFS), synchrotron-based x-ray microfluorescence, and muEXAFS. Plants were grown in hydroponics with various Zn concentrations, and A. halleri specimens growing naturally in a contaminated site were also collected. Zn speciation in A. halleri was independent of the origin of the plants (contaminated or non-contaminated) and Zn exposure. In aerial parts, Zn was predominantly octahedrally coordinated and complexed to malate. A secondary organic species was identified in the bases of the trichomes, which contained elevated Zn concentrations, and in which Zn was tetrahedrally coordinated and complexed to carboxyl and/or hydroxyl functional groups. This species was detected thanks to the good resolution and sensitivity of synchrotron-based x-ray microfluorescence and muEXAFS. In the roots of A. halleri grown in hydroponics, Zn phosphate was the only species detected, and is believed to result from chemical precipitation on the root surface. In the roots of A. halleri grown on the contaminated soil, Zn was distributed in Zn malate, Zn citrate, and Zn phosphate. Zn phosphate was present in both the roots and aerial part of A. lyrata subsp. petraea. This study illustrates the complementarity of bulk and spatially resolved techniques, allowing the identification of: (a) the predominant chemical forms of the metal, and (b) the minor forms present in particular cells, both types of information being essential for a better understanding of the bioaccumulation processes.

The oral anti-volatile sulphur compound effects of zinc salts and their stability constants.

Volatile sulphur compounds (VSC) produced in the oral cavity, are a major cause of oral malodour. Zinc (Zn) ions inhibit VSC formation. The objective of this study was to examine whether Zn salts with low stability constants were more suitable as sources of Zn in lozenges than salts with high stability constants. The former provide free Zn ions upon dissolution in water, whereas the latter provide almost no free Zn. Identical lozenges containing Zn-acetate and -gluconate, which have low stability constants, and Zn citrate and amino acid-chelated Zn, which have extremely high stability constants, were tested. All the lozenges contained 0.9% w/w Zn. Ten volunteers sucked the lozenges until dissolved, and oral VSC were measured by gas chromatography. Zn-acetate, -gluconate and -chelate had an impressive anti-VSC effect even 3 h after the lozenges were taken. Zn citrate had significantly less effect than the other lozenges except Zn acetate after 2 and 3 h. It was concluded that the anti-VSC effect was not related to the stability constants of the Zn compounds tested. Alternative ligands. with stronger affinity for Zn than the ligands in the lozenges, must be present in the oral cavity to explain these results. It is suggested that the sulphide ion may serve this function.