Zinc

Zinc (pronounced /ˈzɪŋk/, from German: Zink) is a metallic chemical element with the symbol Zn and atomic number 30. In nonscientific context it is sometimes called spelter.^[1] Commercially pure zinc is known as Special High Grade, often abbreviated SHG, and is 99.995% pure.^[2]

Notable characteristics

Zinc is a moderately reactive bluish grey metal that tarnishes in moist air and burns in air with a bright bluish-green flame, giving off fumes of zinc oxide. It reacts with acids, alkalis and other non-metals. If not completely pure, zinc reacts with dilute acids to release hydrogen. The one common oxidation state of zinc is +2. From 100 °C to 210 °C (212 °F to 410 °F) zinc metal is malleable and can easily be beaten into various shapes. Above 210 °C (410 °F), the metal becomes brittle and will be pulverized by beating. Zinc is nonmagnetic.

Applications

Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper in annual production

Popular misconceptions

The highly characteristic metal counters of traditional French bars are often referred to as zinc bars or vaguely zinc, but actually zinc has never been used for this purpose and the counters are really made of an alloy of lead and tin.^{citation needed}

History

The name of the metal zinc is unusual and, while vague in origin, was probably first used by Paracelsus, a Swiss-born German chemist, who referred to the metal as "Zincum", in the 16th century.^[4] These words in German apparently mean "tooth-like, pointed or jagged part" and, as zinc metallic crystals are needle-like, the derivation appears plausible.

In ancient India the production of zinc metal was very common. Many mine sites of Zawar Mines, near Udaipur, Rajasthan, were active even during 1300–1000 BC. There are references of medicinal uses of zinc in the Charaka Samhita (300 BC). The Rasaratna Samuccaya (800 AD) explains the existence of two types of ores for zinc metal, one of which is ideal for metal extraction while the other is used for medicinal purpose.^{citation needed} Zinc alloys have been used for centuries, as brass goods dating to 1400–1000 BC have been found in Israel and zinc objects with 87% zinc have been found in prehistoric Transylvania. Because of the low boiling point and high chemical reactivity of this metal (isolated zinc would tend to go up the chimney rather than be captured), the true nature of this metal was not understood in ancient times.

The manufacture of brass was known to the Ebi by about 30 BC, using a technique where calamine and copper were heated together in a crucible. The zinc oxides in calamine were reduced, and the free zinc metal was trapped by the copper, forming an alloy. The resulting calamine brass was either cast or hammered into shape.

Smelting and extraction of impure forms of zinc was accomplished around 1200 AD in India.^[4] China did not learn of the technique until 17th Century AD.^[4] In the West, impure zinc as a remnant in melting ovens was known since antiquity, but usually discarded as worthless. Strabo mentions it as pseudo-arguros — "mock silver". The Berne zinc tablet is a votive plaque dating to Roman Gaul, probably made from such zinc remnants.

Pure zinc in the West

The metallurgist Andreas Libavius received in 1597 a quantity of zinc metal in its pure form, which was unknown in the West before then. Libavius identified it as Indian/Malabar lead. It was regularly imported to Europe from the orient in the 17th and first half of the 18th century,^[4] but was at times very expensive.^{citation needed}

The isolation of metallic zinc in the West may have been achieved independently by several people:

In 1758, William's brother, John, developed a new process for calcining zinc sulfide into an oxide for use in the retort process. Prior to this only calamine could be used to produce zinc. This process was then used into the 20th century. In 1798, Johann Ruberg built the first horizontal retort smelter in Upper Silesia. This was much more fuel efficient and less labor intensive than the vertical retort process. Jean-Jacques Daniel Dony built a different kind of horizontal zinc smelter in Belgium, which processes more.^[4]

Biological role

Zinc is an essential element, necessary for sustaining all life. It is estimated that 3,000 of the hundreds of thousands of proteins in the human body contain zinc prosthetic groups, one type of which is the so-called zinc finger. In addition, there are over a dozen types of cells in the human body that secrete zinc ions, and the roles of these secreted zinc signals in medicine and health are now being actively studied. Zinc ions are now considered to be neurotransmitters. Cells in the salivary gland, prostate, immune system and intestine use zinc signalling.^[8]

Zinc is an activator of certain enzymes, such as carbonic anhydrase. Carbonic anhydrase is important in the transport of carbon dioxide in vertebrate blood. It is also required in plants for leaf formation, the synthesis of indole acetic acid (auxin) and anaerobic respiration (alcoholic fermentation).^{citation needed}

Food sources

Zinc is found in oysters, and to a far lesser degree in most animal proteins, beans, nuts, almonds, whole grains, pumpkin seeds and sunflower seeds.^[9] A turkey's neck and beef's chuck or shank also contain good amounts of zinc. Phytates, which are found in whole grain breads, cereals, legumes and other products, have been known to decrease zinc absorption. Clinical studies have found that zinc, combined with antioxidants, may delay progression of age-related macular degeneration.^[10] Significant dietary intake of zinc has also recently been shown to impede the onset of flu.^{citation needed} Soil conservation analyzes the vegetative uptake of naturally occurring zinc in many soil types.

The (US) recommended dietary allowance of zinc from puberty on is 11mg for males and 8mg for females, with higher amounts recommended during pregnancy and lactation.

Zinc deficiency

Zinc deficiency is typically the result of inadequate dietary intake of zinc, disease states that promote zinc losses, or physiological states that require increased zinc. Populations that consume primarily plant based diets that are low in bioavailable zinc often have zinc deficiencies ^[11] ^[12] Diseases or conditions that involve intestinal malabsorption promote zinc losses. Fecal losses of zinc caused by diarrhea are one contributing factor ^[13], often common in developing countries. Changes in intestinal tract absorbability and permeability due, in part, to viral, protozoal, and bacteria pathogens may also encourage fecal losses of zinc ^[14]. Physiological states that require increased zinc include periods of growth in infants and children as well as in mothers during pregnancy ^[15].

Signs of zinc deficiency include hair loss, skin lesions, diarrhea, and wasting of body tissues. Eyesight, taste,^[16]^[17]^[18]^[19]^[20] smell and memory are also connected with zinc. A deficiency in zinc can cause malfunctions of these organs and functions. Congenital abnormalities causing zinc deficiency may lead to a disease called Acrodermatitis enteropathica. Conservative estimates suggest that 25% of the world's population is at risk of zinc deficiency.^[21]

Zinc supplementation has been shown to reduce diarrhea prevalence and mortality in children <5 years of age.^[22]

Zinc deficiency during pregnancy can negatively affect both the mother and fetus. Animal studies indicate that maternal zinc deficiency can upset both the sequencing and efficiency of the birth process. An increased incidence of difficult and prolonged labor, hemorrhage, uterine dystocia and placental abruption has been documented in zinc deficient animals ^[23]. These effects may be mediated by the defective functioning of estrogen via the estrogen receptor, which contains a zinc finger protein ^[23]. A review of pregnancy outcomes in women with acrodermatitis enteropathica, reported that out of every seven pregnancies, there was one abortion and two malfunctions, suggesting the human fetus is also susceptible to the teratogenic effects of severe zinc deficiency. However, a review on zinc supplementation trials during pregnancy did not report a significant effect of zinc supplementation on neonatal survival ^[23].

Cognitive and motor function may also be impaired in zinc deficient children. Zinc deficiency can interfere with many organ systems especially when it occurs during a time of rapid growth and development when nutritional needs are high, such as during infancy ^[24]. In animal studies, rats who were deprived of zinc during early fetal development exhibited increased emotionality, poor memory, and abnormal response to stress which interfered with performance in learning situations ^[25]. Zinc deprivation in monkeys showed that zinc deficient animals were emotionally less mature, and also had cognitive deficits indicated by their difficulty in retaining previously learned problems and in learning new problems ^[25]. Human observational studies show weaker results. Low maternal zinc status has been associated with less attention during the neonatal period and worse motor functioning.^[26] In some studies, supplementation has been associated with motor development in very low birth weight infants and more vigorous and functional activity in infants and toddlers.^[26]

It is rarely recognised that lack of zinc can contribute to acne. Leukonychia, white spots on the fingernails, are often seen as an indication of zinc deficiency.

Zinc deficiency as a cause of anorexia nervosa

Zinc deficiency causes a decrease in appetite -- which could degenerate in anorexia nervosa (AN). Appetite disorders, in turn, cause malnutrition and, notably, inadequate zinc intake. The use of zinc in the treatment of anorexia nervosa has been advocated since 1979 by Bakan. At least 15 trials showed that zinc improved weight gain in anorexia. A 1994 randomized, double-blind, placebo-controlled trial showed that zinc (14 mg per day) doubled the rate of body mass increase in the treatment of anorexia nervosa (AN). Deficiency of other nutrients such as tyrosine and tryptophan (precursors of the monoamine neurotransmitters norepinephrine and serotonin, respectively), as well as vitamin B1 (thiamine) could contribute to this phenomenon of malnutrition-induced malnutrition.^[28]

Zinc toxicity

Even though zinc is an essential requirement for a healthy body, too much zinc can be harmful. Excessive absorption of zinc can also suppress copper and iron absorption. The free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish. The Free Ion Activity Model (FIAM) is well-established in the literature, and shows that just micromolar amounts of the free ion kills some organisms. A recent example showed 6 micromolar killing 93% of all daphnia in water.^[29]

The free zinc ion is also a powerful Lewis acid up to the point of being corrosive. Stomach acid contains hydrochloric acid, in which metallic zinc dissolves readily to give corrosive zinc chloride. Swallowing a post 1982 American one cent piece (97.5% zinc) can cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach.^[30] Zinc toxicity, mostly in the form of the ingestion of US pennies minted after 1982, is commonly fatal in dogs where it causes a severe hemolytic anemia.^[31] In pet parrots zinc is highly toxic and poisoning can often be fatal^[32].

There is evidence of induced copper deficiency at low intakes of 100–300 mg Zn/d. The USDA RDA is 15 mg Zn/d. Even lower levels, closer to the RDA, may interfere with the utilization of copper and iron or to adversely affect cholesterol.^[33].

Immune system

Zinc salts are effective against pathogens in direct application. Gastroenteritis is strongly attenuated by ingestion of zinc, and this effect could be due to direct antimicrobial action of the zinc ions in the GI tract, or to absorption of the zinc and re-release from immune cells (all granulocytes secrete zinc), or both.^[34]^[35]

In clinical trials, both zinc gluconate and zinc gluconate glycine (the formulation used in lozenges) have been shown to shorten the duration of symptoms of the common cold.^[36] The amount of glycine can vary from two to twenty moles per mole of zinc gluconate.

It should be known that there have been clinical trials that both support the use of zinc for the common cold, and are inconclusive of its effectiveness. All clinical trials have their critics, including the dosage amount used, and the highly subjective format of patient self-reporting the results of their trials.^[37]

Abundance

Zinc is the 23rd most abundant element in the Earth's crust. The most heavily mined ores (sphalerite) tend to contain roughly 10% iron as well as 40–50% zinc. Minerals from which zinc is extracted include sphalerite (zinc sulfide), smithsonite (zinc carbonate), hemimorphite (zinc silicate), and franklinite (a zinc spinel).

The earth has been estimated to have 46 years supply of zinc.^[38] A chemist estimated in 2007 that at the current rate of usage, the worlds supply of zinc would be exhausted by about the year 2037.^[39]

Zinc mining and processing

Alloys

The most widely used alloy of zinc is brass, in which copper is alloyed with anywhere from 9% to 45% zinc, depending upon the type of brass, along with much smaller amounts of lead and tin. Alloys of 85–88% zinc, 4–10% copper, and 2–8% aluminium find limited use in certain types of machine bearings. Alloys of primarily zinc with small amounts of copper, aluminium, and magnesium are useful in die casting as well as spin casting. An example of this is zinc aluminium. Similar alloys with the addition of a small amount of lead can be cold-rolled into sheets. An alloy of 96% zinc and 4% aluminium is used to make stamping dies for low production run applications where ferrous metal dies would be too expensive.^[40]

Compounds

Zinc oxide is perhaps the best known and most widely used zinc compound, as it makes a good base for white pigments in paint. It also finds industrial use in the rubber industry, and is sold as opaque sunscreen. A variety of other zinc compounds find use industrially, such as zinc chloride (in deodorants), zinc pyrithione (anti-dandruff shampoos), zinc sulfide (in luminescent paints), and zinc methyl or zinc diethyl in the organic laboratory. Roughly one quarter of all zinc output is consumed in the form of zinc compounds.

Isotopes

Naturally occurring zinc is composed of the 5 stable isotopes ⁶⁴Zn, ⁶⁶Zn, ⁶⁷Zn, ⁶⁸Zn, and ⁷⁰Zn with ⁶⁴Zn being the most abundant (48.6% natural abundance). Twenty-one radioisotopes have been characterised with the most abundant and stable being ⁶⁵Zn with a half-life of 244.26 days, and ⁷²Zn with a half-life of 46.5 hours. All of the remaining radioactive isotopes have half-lives that are less than 14 hours and the majority of these have half lives that are less than 1 second. This element also has 4 meta states.

Zinc has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of isotopically enriched ⁶⁴Zn, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope Zn-65 with a half-life of 244 days and produce approximately 2.27 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several days. Such a weapon is not known to have ever been built, tested, or used.

Precautions

Metallic zinc is not considered to be toxic, but free zinc ions in solution (like copper or iron ions) are highly toxic. There is also a condition called zinc shakes or zinc chills (see metal fume fever) that can be induced by the inhalation of freshly formed zinc oxide formed during the welding of galvanized materials. Excessive intake of zinc can promote deficiency in other dietary minerals.

References

^ spelter. The American Heritage® Dictionary of the English Language: Fourth Edition. 2000
^ Special High Grade Zinc (SHG) 99.995%, <http://nyrstar.com/nyrstar/en/products/zinccongalvanising/techdownloads/shg_budel.pdf>. Retrieved on 04-23-2008 .
^ Ananda S. Prasad, MD, PhD; James T. Fitzgerald, PhD; Bin Bao, MD, PhD; Frances W.J. Beck, PhD; and Pranatharthi H. Chandrasekar, MD. "Duration of Symptoms and Plasma Cytokine Levels in Patients with the Common Cold Treated with Zinc Acetate: A Randomized, Double-Blind, Placebo-Controlled Trial." Annals of Internal Medicine [1]
^ ^a ^b ^c ^d ^e ^f ^g ^h Habashi, Fathi, Discovering the 8th Metal, International Zinc Association (IZA), <http://www.iza.com/Documents/Communications/Publications/History.pdf> .
^ Metals Reference and Encyclopedia (Atlas Publishing Co, 1968).
^ R. O. Roberts, 'Dr John Lane and the foundation of the non-ferrous metal industry in the Swansea valley' Gower 4 (1951), 19-24; F. V. Emery, 'Further light on Dr John Lane' Gower 20 (1969), 8-13; R. O. Roberts, 'Further note on Dr John Lane' Gower 22 (1972), 23-5.
^ Rhys Jenkins, 'The Zinc Industry in England: the early years up to 1850' Transactions of the Newcomen Society 25 (1945-7), 41-52.
^ Hershfinkel Michal, Silverman William F, and Sekler Israel (2007). "The Zinc Sensing Receptor, a Link Between Zinc and Cell Signaling". Mol Med 13 (7-8): 331-336. doi:10.2119/2006-00038.Hershfinkel. PMID 17728842.
^ Zinc content of selected foods per common measure (pdf). USDA National Nutrient Database for Standard Reference, Release 20. USDA. Retrieved on 2007-12-06.
^ Age-Related Eye Disease Study Research Group. www.pubmed.gov. Retrieved on 2007-11-13.
^ Solomons, N.W. (2001) Dietary Sources of zinc and factors affecting its bioavailability. Food Nutr. Bull. 22: 138-154
^ Sandstead, H. H. (1996) Zinc deficiency: a public health problem? Am. J. Dis. Children. 145: 853-859
^ Castillo-Duran, C., Vial, P. & Vauy, R. (1988) Trace mineral balance during acute diarrhea in infants. Journal of Pediatrics. 113: 452-457
^ Manary, M.J., et al, (2000). Dietary phytate reduction improves zinc absorption in Malawian children recovering from tuberculosis but not in well children. Journal of Nutrition, 130: 2959-2964
^ Gibson, R.S. (2006) Zinc: the missing link in combating micronutrient malnutrition in developing countries. Proceedings of the Nutrition Society, 65: 51-60
^ Ikeda M, Ikui A, Komiyama A, Kobayashi D, Tanaka M (2008). "Causative factors of taste disorders in the elderly, and therapeutic effects of zinc". J Laryngol Otol 122 (2): 155–60. doi:10.1017/S0022215107008833. PMID 17592661.
^ Stewart-Knox BJ, Simpson EE, Parr H, et al (2008). "Taste acuity in response to zinc supplementation in older Europeans". Br. J. Nutr. 99 (1): 129–36. doi:10.1017/S0007114507781485. PMID 17651517.
^ Stewart-Knox BJ, Simpson EE, Parr H, et al (2005). "Zinc status and taste acuity in older Europeans: the ZENITH study". Eur J Clin Nutr 59 Suppl 2: S31–6. doi:10.1038/sj.ejcn.1602295. PMID 16254578.
^ McDaid O, Stewart-Knox B, Parr H, Simpson E (2007). "Dietary zinc intake and sex differences in taste acuity in healthy young adults". J Hum Nutr Diet 20 (2): 103–10. doi:10.1111/j.1365-277X.2007.00756.x. PMID 17374022.
^ Nin T, Umemoto M, Miuchi S, Negoro A, Sakagami M (2006). "[Treatment outcome in patients with taste disturbance]" (in Japanese). Nippon Jibiinkoka Gakkai Kaiho 109 (5): 440–6. PMID 16768159.
^ Maret W, Sandstead HH (2006). "Zinc requirements and the risks and benefits of zinc supplementation". J Trace Elem Med Biol 20 (1): 3–18. doi:10.1016/j.jtemb.2006.01.006. PMID 16632171.
^ Fischer Walker CL, Black RE (2007). "Micronutrients and diarrheal disease". Clin. Infect. Dis. 45 Suppl 1: S73–7. doi:10.1086/518152. PMID 17582575.
^ ^a ^b ^c Shah, D. & Sachdev, H.P.S. (2006) Zinc deficiency in pregnancy and fetal outcome. Nutrition Reviews, 64: 15-30
^ Sanstead, H. H. et al, (2000) Zinc nutriture as related to brain. J. Nutr. 130: 140S-146S
^ ^a ^b Black, M.M. (2003) The evidence linking zinc deficiency with children’s cognitive and motor functioning. J. Nutr. 133: 1473S-1476S
^ ^a ^b Black, M. (1998) Zinc deficiency and child development. Am. J. Clin. Nutr. 68: 464S-9S
^ Eby GA (2007). "Zinc treatment prevents dysmenorrhea". Med. Hypotheses 69 (2): 297–301. doi:10.1016/j.mehy.2006.12.009. PMID 17289285.
^ Neurobiology of Zinc-Influenced Eating Behavior. Retrieved on 2007-07-19.
^ Muyssen et al., (Aquat Toxicol. 2006)
^ Bothwell and Mair, PEDIATRICS 2003
^ Stowe CM, Nelson R, Werdin R, et al: Zinc phosphide poisoning in dogs. JAVMA 173:270, 1978
^ See, for example, this list of common parrot illnesses and their causes.
^ Zinc toxicity by GJ Fosmire, American Journal of Clinical Nutrition.
^ Aydemir, T, B.; Blanchard, R.K.; Cousins, R.J (2006). "Zinc Supplementation of Young Men Alters Metallothionein, Zinc Transporter, and Cytokine Gene Expression in Leucocyte Populations". PNS 103 (3): 1699-1704.
^ Valko, M; Morris, H.; Cronin, MTD (2005). "Metals, Toxicity and Oxidative stress". Current Medicinal Chemistry 12 (12): 1161-1208. doi:10.2174/0929867053764635.
^ Godfrey JC, Godfrey NJ, Novick SG. (1996). "Zinc for treating the common cold: Review of all clinical trials since 1984.". PMID 8942045.
^ US Pharmacist, "Zinc and the Common Cold: What Pharmacists Need to Know",Darrell T. Hulisz, Pharm.D.
^ New Scientist, 26 May 2007.
^ Augsberg University Calculate When Our Materials Run Out retrieved May 4, 2008
^ Samans, Carl H.: Engineering Metals and their Alloys MacMillan 1949

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