Showing papers on "Zinc toxicity published in 1993"

Accumulation, regulation and toxicity of copper, zinc, lead and mercury in Hyalella azteca

Abstract: Zinc, lead and mercury accumulation in the amphipod Hyalella azteca increases with increasing exposure to metals. During 10 week chronic toxicity tests, metal accumulated at the highest non-toxic/lowest toxic concentration was 126/136 µg Zn g−1, 7.1/16 µg Pb g−1 and 56/90 µg Hg g−1 dry weight. Concentrations of lead and mercyry in control animals were substantially lower (1.3 µg Pb g−1 and 0.4 µg Hg g−1), but concentrations of zinc in controls (74 µg g−1) were about one half those of the lowest toxic concentration. Copper was completely regulated. Accumulated copper concentrations after 10 weeks exposure to all waterborne copper concentrations resulting in less than 100% mortality were not significantly different from controls (79 µg g−1). Lead and mercury concentrations in wild H. azteca should be useful indicators of potential toxicity. Zinc accumulation may also be a useful indicator of zinc toxicity, but careful comparison with control or reference animals is necessary because of the small differences between toxic and control concentrations. Copper is not accumulated by H. azteca under chronic exposure conditions and body burdens of field animals cannot be used as an indicator of exposure or potential toxic effects. Short term exposures to copper, however, result in elevated copper concentrations in H. azteca, even at concentrations below those causing chronic toxicity. Short term bioaccumulation studies might, therefore, provide a useful indication of potential chronic copper toxicity.

Effect of zinc supplementation on resistance of cultured human skin fibroblasts toward oxidant stress.

Abstract: In purified system zinc has been shown to have an antioxidant role. Its effects on the resistance of cultured cells towards oxidative stress in vitro were examined. Diploid human skin fibroblasts were grown for 21 d in culture media (RPMI 1640 containing 15% fetal calf serum) added with different zinc (Zn) concentrations (100, 125, and 150 microM as Zinc chlorur ZnCl2). In comparison, cell controls were grown in standard culture media (6.5 microM Zn). The intracellular zinc levels of treated fibroblasts increased from 3- to 7-fold (2330 +/- 120 ng/mg protein in 150-microM Zn-treated cells versus 331 +/- 21 ng/mg protein in control cells). The intracellular copper increased 3- fold whereas the iron content slightly but not significantly decreased. The index of basal lipid peroxidation measured as thiobarbituric acid reactants (TBARs) of zinc-supplemented cells was lower than that of non zinc supplemented controls (0.89 mumol/g protein in 150 microM Zn-treated cells versus 1.59 mumol/g protein in controls). At these high doses of zinc, fibroblasts expressed lower antioxidant metalloenzymes activities. Diminished TBARs in Zn treated cells tends to support that Zn acts protectively against free radical mediated damage. However when the cells were challenged with extracellular oxidant stresses mediated by hypoxanthine/xanthine oxidase or hydrogen peroxide (H2O2), an increased toxicity in Zn-supplemented cells was observed. When we applied an intracellular oxidative stress as UV-B or UV-A radiation, Zn-treated fibroblasts were more resistant than cells grown in normal medium. If Zn has shown antioxidant effect in some in vitro or in vivo systems our observations clearly demonstrate that this role is not mediated by antioxidant metalloenzymes.

Radish as an indicator plant for derelict land: Uptake of zinc at toxic concentrations

Abstract: Radish was grown in glasshouse experiments. Two experiments involved mixing varying ratios of calcareous zinc (Zn) mine waste with soil and in the third, radish was grown in culture solution supplemented with Zn. Zinc toxicity was seen at higher treatment concentrations. From curves for substrate Zn versus % yield the toxic threshold was estimated as 343 μg Zn/g soil which compares favourably with the British “trigger concentration” of 300 μg Zn/g. Small yields of hypocotyls were obtained at 1000 μg Zn/g. A 50% yield reduction occurred at tissue Zn concentrations from 36.1–1013 μg/g. The shape of Zn uptake curves suggested that hypocotyls were “indicators” of Zn uptake but leaves were “excluders”. The relative ease with which radish is grown in terms of climate and supervision together with its growth properties on contaminated soil suggest it is suitable as a monitor crop for derelict land.

Zinc toxicity symptom development and partitioning of biomass and zinc in peanut plants 1

Abstract: High soil zinc (Zn) concentrations can cause Zn toxicity in peanuts (Arachis hypogaea L), which decreases productivity and can be fatal to the plants The objectives of this study were 1) to determine the optimal sampling time and plant part for diagnosis of Zn toxicity in peanuts, 2) to relate toxicity symptoms to plant Zn concentrations and calcium:zinc (Ca:Zn) ratios, and 3) to model the distribution of Zn and biomass into plant parts in relation to Zn concentration in the whole plant A greenhouse study utilized four soils (Lakeland sand, Tifton loamy sand, Greenville sandy clay loam, and Greenville sandy clay) with Zn applications of 0, 10, 20, and 40 mg Zn/kg soil Plants were sampled for analysis of nutrient concentrations, and Zn toxicity ratings were recorded biweekly Toxicity symptoms became visible 4–8 weeks after planting, with stunting appearing at four weeks, horizontal leaf growth and leaflet folding at six weeks, and stem splitting at eight weeks Optimal sampling time for diagn

Sequential Changes in the Development of the Pancreatic Lesion of Zinc Toxicosis in Sheep

Abstract: Forty-two 10-month-old castrated male sheep were dosed with zinc oxide to study the pathogenesis of the pancreatic lesion. For 4 weeks, the sheep were dosed three times per week with 240 mg Zn (as ZnO)/kg body weight/dose, and seven groups of six sheep each were necropsied at 4, 7, 14, 21, 28, 56, and 112 days after the start of dosing. Plasma zinc concentrations rose rapidly to 2.0-2.5 micrograms Zn/ml over the dosing period and fell rapidly to less than 1 microgram Zn/ml within 2 weeks after dosing ceased. Organ zinc levels in liver, kidney, and pancreas fell from concentrations above 800 micrograms Zn/g (dry matter basis) to less than 200 micrograms/g within 4 weeks after dosing ceased. Although no animals showed any clinical signs of zinc toxicity, many sheep dosed with zinc oxide developed pancreatic lesions. Pancreatic lesions took up to 4 weeks to develop fully. The early pancreatic lesions involved necrosis of the pancreatic duct epithelium, periductular inflammation, and interlobular fat necrosis, all evident at 7 days but not at 4 days. These early lesions were followed by edema, lobular cystic change, atrophy, fibrosis, and a ductular hyperplasia. The initial lesion of the pancreas was ductular injury, and the subsequent pancreatic lesions may have developed in those lobules whose excretory ducts were obstructed by inflammatory debris.

Effect of sublethal concentration of mercury and zinc on the energetics of a freshwater fish Cyprinus carpio (Linnaeus).

Abstract: Exposure of a freshwater fish Cyprinus carpio to the sublethal concentration of mercury (0.1 mg L-1) and zinc (6.0 mg L-1) resulted in distinct changes in the energy metabolism of gill, liver and muscle at 1, 15 and 30 days. The changes were: (a) The rate of oxygen consumption and SDH activity decreased in the organs of mercury-exposed fish at all the three exposure periods in the order 1 > 15 15 > 30 days. (b) The activity of LDH and the levels of pyruvate and lactate increased in all the three organs of the fish at the three exposure periods studied in both the metal media. But, this increase was also in the order 1 > 15 15 > 30 days in the organs of the fish exposed to mercury and zinc, respectively. (c) The results indicated greater reliance of mercury exposed fish on the energetically less efficient anaerobic glycolysis as the oxidative metabolism suppressed, and the dependency of zinc-exposed fish on both the oxidative and anaerobic glycolytic pathways in order to meet the energy requirements. On prolonged exposure zinc-exposed fish could adapt to sublethal toxic stress, such type of adaptive-response was not observed in mercury-exposed fish.

Effect of intraperitoneal administration of zinc in C57/6J mice.

Abstract: Intraperitoneal administration of zinc chloride to C57/6J mice in vivo at 28 micrograms/g body weight was more lethal to the male mice and induced growth retardation in the male and female survivors. In the group of experimental survivors, the weight of the lungs were significantly decreased compared with the control animals. The inherent dangers of zinc excess is highlighted, especially with regard to the possibility of cumulative zinc toxicity.

Zinc-Binding Peptides as a Function of Zn and S in Soybeans

Abstract: Soybean (Glycine max [L.] Merr. cv. Ransom) plants were grown for two weeks in nutrient solutions at 0.8 and 40 μM Zn and 0.02 and 20 mM S. Zinc toxicity appeared to induce synthesis of low molecular weight Zn-binding peptides in soybean roots and leaves. This binding of Zn-ions seemed to increase in leaves when the S concentration was high in the nutrient solution.