Showing papers on "Zinc toxicity published in 1990"

Mechanism of toxicity of zinc to the marine diatomNitzschia closterium

Abstract: The effect of zinc on cell division, photosynthesis, ultrastructure, respiration, ATP levels, mitochondrial electron-transport chain (ETC)-activity, total thiols and glutathione in the marine diatomNitzschia closterium (Ehrenberg) W. Smith was investigated. Although 65µg Zn 1−1 halved the cell division rate, photosynthesis and respiration were unaffected by zinc concentrations up to 500µg Zn 1−1. Most of the zinc associated with the cells was bound at the cell surface, with only 3 to 4% of this extracellular zinc penetrating the cell membrane. Once inside the cell, zinc exerted its toxicity at a number of sites. Increased ATP production and ETC activity were observed in zinc-treated cells. Zinc also enhanced cellular thiols (SH) and total glutathione, and zinc toxicity was reversible by the addition of thiol compounds such as cysteine. Zinc-thiol binding may be a detoxification mechanism for the cell. It is suggested that increased ATP production may provide the energy required for increased glutathione synthesis at the expense of other energy-requiring processes including cell division. The mechanisms of toxicity of ionic zinc and copper toN. closterium were compared.

A review of the biochemical roles, toxicity and interactions of zinc, copper and iron: II. Copper.

Abstract: Copper is an essential nutrient for living matter. Through its cuproenzymes, copper displays a variety of metabolic functions. Atomic absorption spectrophotometry, radioisotope studies and establishment of cell and molecular biology have provided the necessary tools to study copper absorption, metabolism, physiology and biochemistry. The vital role of metallothionein in copper homeostasis is examined. Ceruloplasmin represents the molecular link between copper and iron metabolism. The genetic predisposition of copper toxicity has been attributed to the cause of Wilson's disease in humans. The interrelationships between copper and other dietary factors is addressed.

Zinc toxicity to freshwater algae

Abstract: Studies with natural phytoplankton from Lake Ontario as well as with pure cultures of two green and one diatom freshwater algal species revealed that the International Joint Commission water quality objective of 30 μg Zn/L was toxic to primary productivity and cell multiplication. The toxicity of Zn varied with its anionic forms, with nitrate being the most toxic, followed by chloride, sulphate, and acetate. Experiments with radioactive 65Zn indicated that Zn was rapidly taken up by the algae, and incorporated mainly into polysaccharide and nucleic acid fractions. These results indicate that an objective for Zn of 30 μg/L is too high to protect algae in the Great Lakes. Based on our results and other published data, a new objective of 10 μg Zn/L has been recommended to the International Joint Commission.

Soil zinc and pH effects on leaf zinc and the interaction of leaf calcium and zinc on zinc toxicity of peanuts.

Abstract: Zinc toxicity of peanuts (Arachis hypogaea L.), resulting from excessive amounts of Zn applied to previous crops, has been observed for many years in a limited number of peanut fields in Georgia. A tentative critical value of 12 mg/kg of Mehlich No.1 extractable soil Zn has been reported, but soil pH should be considered in establishing a more precise critical value since availability of soil Zn is affected greatly by soil acidity. A 3‐year study was conducted on a Tifton loamy sand (thermic, Plinthic Paleudults) to evaluate the relationship between soil pH and soil Zn on concentration of Zn in peanut leaves. Factorial treatments were 0, residual, medium, and high rates of Zn and soil pH levels near 5.5, 5.9, 6.2, and 6.8. Pod yields were not affected by treatments and Zn toxicity was not observed. Leaf Zn was affected more by soil pH than by soil Zn, but correlation coefficients were highest where both soil pH and soil Zn were included in the determination. A regression equation, based on soil p...

Effect of lead, zinc, mercury, and copper with and without estrogen on serum vitellogenin level in Magur fish (Clarias batrachus L.).

Abstract: Injection(s) of lead, zinc, and mercuric acetate decreased the serum vitellogenin content in Magur fish, while cupric acetate failed to cause any change in the vitellogenin level. Estrogen injections on 7th, 8th and 9th d increased the serum vitellogenin level in normal and copper salt treated fish, but were totally ineffective in altering the reduced vitellogenin content in lead, zinc, and mercury salts treated fish. Vitellogenin level almost restored to normal level at 6 week in lead, zinc, and mercury treated fish, and estrogen injections on 37th, 38th, and 39th d enhanced the serum vitellogenin content in all groups.