Variation In Zn Concentration Research Articles

Assessing element-specific patterns of bioaccumulation across New England lakes

Little is known about differences among trace elements in patterns of bioaccumulation in freshwater food webs. Our goal was to identify patterns in bioaccumulation of different elements that are large and consistent enough to discern despite variation across lakes. We measured methylmercury (MeHg) and trace element (As, Cd, Hg, Pb, and Zn) concentrations in food web components of seven New England lakes on 3–5 dates per lake, and contrasted patterns of bioaccumulation across lakes, metals and seasons. In each lake, trace element concentrations were compared across trophic levels, including three size fractions of zooplankton, planktivorous fish, and piscivorous fish. The trophic position of each food web component was estimated from N isotope analysis. Trace element concentrations varied widely among taxa, lakes and sampling dates. Yet, we identified four consistent patterns of bioaccumulation that were consistent across lakes: (1) MeHg concentration increased (i.e., was biomagnified) and Pb concentration decreased (i.e., was biodiminished) with increased trophic position. (2) Zinc concentration (as with MeHg) was higher in fish than in zooplankton, but overall variation in Zn concentration (unlike MeHg) was low. (3) Arsenic and Cd concentrations (as with Pb) were lower in fish than in zooplankton, but (unlike Pb) were not significantly correlated with trophic position within zooplankton or fish groups. (4) Average summer concentrations of As, Pb, Hg, and MeHg in zooplankton significantly predicted their concentrations in either planktivorous or piscivorous fish. Our secondary goal was to review sampling approaches in forty-five published studies to determine the extent to which current sampling programs facilitate cross-lake and cross-study comparisons of bioaccumulation. We found that studies include different components of the food web and sample too infrequently to enable strong cross-lake and cross-study comparisons. We discuss sampling strategies that would improve our capacity to identify consistent patterns of bioaccumulation and drivers of elevated trace element concentrations under naturally high levels of variability.

Effects of Fe-EDDHA Chelate Application on Evolution of Soil Extractable Iron, Copper, Manganese, and Zinc

Up to date, soil application of synthetic chelates is the most effective mean of controlling iron (Fe) deficiency chlorosis in many crops. The responses of three representative soils (I, II, and III) of a large orchard area (Ribera Alta del Jucar) to the application of three commercial Fe-EDDHA chelates (Sequestrene 138 Fe G-100, Group Carla Val F.E.A 6 Superior and Ferrishell plus) at 100 (D1) and 200 µg Fe/kg of soil (D2) were analyzed. Extractable concentrations of Fe, copper (Cu), manganese (Mn), and zinc (Zn) were determined at 7, 14, 21, 42, and 71 days after the application. Data were subjected to multifactor ANOVA to analyze the effects of time, dose, soil, and chelate type on Fe, Cu, Mn, and Zn concentrations. Soil type affected the recovery percentage of Fe by DTPA extraction. The extractable Fe increased to 40–60 mg Fe/kg of soil by the D1 dose and to 70–100 mg Fe/kg of soil by the D2 dose for soils I and II. However, in the case of soil III, recovery increased to 60–80 mg Fe/kg of soil for D1 and 100–140 mg Fe/kg of soil for D2. As the pH of the three soils was similar, this recovery difference is attributed to the differing textural compositions of the soils. The extractable concentrations of Fe increased in the sandy loam soil in contrast to the clay loam soils. The Fe-EDDHA formula did not affect significantly extractable Fe concentration. Increases in the extractable Cu and Mn were observed after Fe-EDDHA soil application. These increases could be due to changes in the redox potential that alters the form and solubility of some metals, possibly affecting the metal-chelate equilibrium. In the case of Zn, the variation in Zn concentration is hardly appreciable, with Fe preventing effective Zn chelation. No difference in effectiveness has been found between the Fe-EDDHA formula brands used in this experiment.

Equilibrium partial pressures and crystal growth of Cd 1− xZn xTe

The partial pressures, p Cd and p Zn , over Cd 1− x Zn x Te (CZT) and Cd 1− x Zn x melts were estimated based on known thermodynamic data and the partial pressures, p Cd and p Zn , over Cd 0.86Zn 0.14 alloy melt at a temperature of about 980°C could be equilibrium with those over Cd 0.8Zn 0.2Te melt at a melting temperature of 1162°C. The Cd 0.8Zn 0.2Te crystal growth from the melt under controlled constituent partial pressures, provided by Cd 0.86Zn 0.14 alloy instead of only Cd source was carried out in this work. The best result for the resistivity, which has reached up to about 10 10 Ω cm, has been obtained under the equilibrium partial pressures estimated by thermodynamic relationships. The axial variation in Zn concentration, which has been obviously improved due to the Zn replenishment from the reservoir during the whole growth procedure, is within about 4%. EPD on the average was about 2×10 5 and 4×10 4 cm −2 at the middle of the bulk. IR transmissivity in the range of 2 to 42 μm is larger than 60%. In addition, the relationship between resistivities and conducting types of the crystal and different controlled pressures is also discussed.

Identification of an index tissue to predict zinc status of wheat

The critical concentration of Zn in wheat tissues for the prediction of Zn response and diagnosis of Zn deficiency was examined in a glasshouse experiment with wheat (Triticum aestivum, line QT 4118) grown to anthesis in two Vertisols at Zn application rates of 0, 1.25, 2.5, 5, 10, 15 and 30 kg ha-1 equivalent as ZnSO4 7H2O. The wheat tissues examined were the youngest mature leaf blade (YMB), the leaf immediately below the youngest mature leaf blade (YMB-1), the older leaves, the ear, the stem and the whole tops. The minimum Zn concentration required in a tissue at 0.90 relative yield, referred to as the critical Zn concentration, was determined using the Cate-Nelson graphical and statistical models, the Mitscherlich equation and a two-intersecting straight lines model. The Zn status of wheat was best defined by the Zn concentration in the YMB. Although the critical Zn concentration of the YMB did not vary much with the method of estimation, the Cate-Nelson statistical procedure explained a higher percentage of the variation in Zn concentration in the YMB and relative yield than the Mitscherlich and the two intersecting straight lines models. The critical concentration of Zn in the YMB was 16.0 mg kg-1 dry matter. It is concluded that determination of Zn concentration in the YMB is the best procedure for evaluating the Zn status of wheat plants.

The phytate and mineral content of some cereals, cereal products, legumes, legume products, snack bars, and nuts available in New Zealand

Analyses for phytate by an indirect precipitation method and for the minerals calcium (Ca), zinc (Zn), iron (Fe), copper (Cu), and manganese (Mn) by atomic absorption spectrophotometry were carried out on 100 foods available in New Zealand. Foods with 1% phytate (dry weight basis) included untoasted muesli, rolled oats, wheat germ, wheat bran, soybean, and some soy products. Most breads contained between 0.35 and 0.60% phytate; legumes on average had 0.62% phytate, as did snack bars. There was a wide variation in Ca and Zn contents: There was a tenfold variation in Ca content among the legume products, whereas there was a seventyfold variation in Zn content among the cereals. The phytate: Zn molar ratio, which is presumed to indicate the biovailability of Zn, was above 20∶1 for two-thirds of the cereals and almost all of the snack bars; it was above 15∶1 for one-third of the breads, almost all of the legumes, and half of the legume products. These high phytate: Zn molar ratios, as well as some Ca: phytate molar ratios above 6∶1, indicate that there might be a reduced biovailability of Zn in many of the foods analyzed in this study.