Zinc selenide is a chemical compound of zinc and selenium. It occurs naturally as the mineral stilleite. Zinc selenide is a semiconductor and is used in light-emitting diodes, diode lasers, x-ray and gamma ray detectors, and as as infrared optical material. Zinc is a metallic element with the atomic number 30. It is found in nature most often as the mineral sphalerite. Though excess zinc in harmful, in smaller amounts it is an essential element for life, as it is a cofactor for over 300 enzymes and is found in just as many transcription factors. Selenium is a nonmetal element with the atomic number 34 and the chemical symbol Se. Selenium rarely occurs in its elemental state in nature and is usually found in sulfide ores such as pyrite, partially replacing the sulfur in the ore matrix. It may also be found in silver, copper, lead, and nickel minerals. Though selenium salts are toxic in large amounts, trace amounts of the element are necessary for cellular function in most animals, forming the active center of the enzymes glutathione peroxidase, thioredoxin reductase, and three known deiodinase enzymes. (9, 2, 3, 4)
belongs to the class of inorganic compounds known as miscellaneous mixed metal/non-metals. These are inorganic compounds containing non-metal as well as metal atoms but not belonging to afore mentioned classes.
Anaemia results from the excessive absorption of zinc suppressing copper and iron absorption, most likely through competitive binding of intestinal mucosal cells. Unbalanced levels of copper and zinc binding to Cu,Zn-superoxide dismutase has been linked to amyotrophic lateral sclerosis (ALS). Stomach acid dissolves metallic zinc to give corrosive zinc chloride, which can cause damage to the stomach lining. Metal fume fever is thought to be an immune response to inhaled zinc. Selenium readily substitutes for sulfur in biomolecules and in many biochemical reactions, especially when the concentration of selenium is high and the concentration of sulfur is low. Inactivation of the sulfhydryl enzymes necessary for oxidative reactions in cellular respiration, through effects on mitochondrial and microsomal electron transport, might contribute to acute selenium toxicity. Selenomethionine (a common organic selenium compound) also appears to randomly substitute for methionine in protein synthesis. This substitution may affect the structure and functionability of the protein, for example, by altering disulfide bridges. Inorganic forms of selenium appear to react with tissue thiols by redox catalysis, resulting in formation of reactive oxygen species and causing damage by oxidative stress. (8, 2, 3, 1)
Metabolism
Zinc can enter the body through the lungs, skin, and gastrointestinal tract. Intestinal absorption of zinc is controlled by zinc carrier protein CRIP. Zinc also binds to metallothioneins, which help prevent absorption of excess zinc. Zinc is widely distributed and found in all tissues and tissues fluids, concentrating in the liver, gastrointestinal tract, kidney, skin, lung, brain, heart, and pancreas. In the bloodstream zinc is found bound to carbonic anhydrase in erythrocytes, as well as bound to albumin, _2-macroglobulin, and amino acids in the the plasma. Albumin and amino acid bound zinc can diffuse across tissue membranes. Zinc is excreted in the urine and faeces. Selenium may be absorbed through inhalation and ingestion, while some selenium compounds may also be absorbed dermally. Once in the body, selenium is distributed mainly to the liver and kidney. Selenium is an essential micronutrient and is a component of glutathione peroxidase, iodothyronine 5'-deiodinases, and thioredoxin reductase. Organic selenium is first metabolized into inorganic selenium. Inorganic selenium is reduced stepwise to the intermediate hydrogen selenide, which is either incorporated into selenoproteins after being transformed to selenophosphate and selenocysteinyl tRNA or excreted into the urine after being transformed into methylated metabolites of selenide. Elemental selenium is also methylated before excretion. Selenium is primarily eliminated in the urine and feces, but certain selenium compounds may also be exhaled. (8, 3)
3, not classifiable as to its carcinogenicity to humans. (7)
Uses/Sources
Zinc selenide is a semiconductor and is used in light-emitting diodes, diode lasers, x-ray and gamma ray detectors, and as as infrared optical material. (4)
Chronic exposure to zinc causes anemia, atazia, lethargy, and decreases the level of good cholesterol in the body. It is also believed to cause pancreatic and reproductive damage. Chronic oral exposure to high concentrations of selenium compounds can produce a disease called selenosis. The major signs of selenosis are hair loss, nail brittleness, and neurological abnormalities (such as numbness and other odd sensations in the extremities). Animal studies have shown that selenium may also affect sperm production and the female reproductive cycle. (8, 3)
Symptoms
Ingestion of large doses of zinc causes stomach cramps, nausea, and vomiting. Acute inhalation of large amounts of zinc causes metal fume fever, which is characterized by chills, fever, headache, weakness, dryness of the nose and throat, chest pain, and coughing. Dermal contact with zinc results in skin irritation. Short-term oral exposure to high concentrations of selenium may cause nausea, vomiting, and diarrhea. Brief exposures to high levels of elemental selenium or selenium dioxide in air can result in respiratory tract irritation, bronchitis, difficulty breathing, and stomach pains. Longer-term exposure to either of these air-borne forms can cause respiratory irritation, bronchial spasms, and coughing. (8, 3)
Treatment
Zinc poisoning is treated symptomatically, often by administering fluids such as water or milk, or with gastric lavage. (3)
