Zinc

Physical properties Zinc is a bluish-white, lustrous, diamagnetic metal, It is somewhat less dense than iron and has a hexagonal crystal structure, with a distorted form of hexagonal close packing, in which each atom has six nearest neighbors (at 265.9 pm) in its own plane and six others at a greater distance of 290.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Zinc is a fair conductor of electricity. This melting point is the lowest of all the d-block metals aside from mercury and cadmium. For this reason among others, zinc, cadmium, and mercury are often not considered to be transition metals like the rest of the d-block metals. Although neither zinc nor zirconium is ferromagnetic, their alloy, , exhibits ferromagnetism below 35 K. It also makes up 312 ppm of the Solar System, where it is the 22nd most abundant element. Typical background concentrations of zinc do not exceed: 1 μg/m3 in atmosphere, 300 mg/kg in soil, 100 mg/kg in vegetation, 20 μg/L in freshwater, and 5 μg/L in seawater. The element is normally found in association with other base metals such as copper and lead in the form of ores. Sphalerite, a crystalline form of zinc sulfide, is the most heavily mined zinc-containing ore as it contains 60–62% zinc by mass. Large deposits are in Australia, China, Canada, and the United States, with the largest potential reserves in Iran. The most recent estimate of reserve base for zinc (meets specified minimum physical criteria related to current mining and production practices) was made in 2009 and was calculated to be roughly 480 Mt. Zinc reserves, on the other hand, are geologically identified ore bodies whose suitability for recovery is economically practical (based on variables such as location, grade, quality, and quantity) at the time of determination. Since exploration and mine development is an ongoing process, the amount and number of zinc reserves is not a fixed number, and sustainability of zinc ore supplies cannot be judged by simply extrapolating the combined mine life of today's zinc mines. This concept is well supported by data from the United States Geological Survey (USGS), which illustrates that although refined zinc production increased 80% between 1990 and 2010, the reserve lifetime for zinc has remained unchanged, through the discovery of additional zinc deposits. About 346 million tonnes have been extracted throughout history up to 2002, and scholars have estimated that about 109–305 million tonnes are presently in use. (ZnS)|alt=A black shiny lump of solid with uneven surface Isotopes Five stable isotopes of zinc occur in nature, with 64Zn being the most abundant isotope (49.17% natural abundance). The other isotopes found in nature are (27.73%), (4.04%), (18.45%), and (0.61%). Several dozen radioisotopes have been characterized. , which has a half-life of 243.66 days, is the least active radioisotope, followed by with a half-life of 46.5 hours. Zinc has 10 nuclear isomers, of which 69mZn has the longest half-life, at 13.75 hours. The superscript m indicates a metastable isotope, whose nucleus is in an excited state and which will eventually return to its ground state, through the emission of excess energy in the form of one or more photons (gamma rays), with the nucleus decaying to the ground state by the end of the process. The most common decay mode of a radioisotope of zinc with a mass number lower than 66 is electron capture. The resulting decay product will be an isotope of copper. : + → + The most common decay mode of a radioisotope of zinc with a mass number higher than 66 is beta decay (β−), producing an isotope of gallium. : → + + ==Compounds and chemistry==

Reactivity . The steel is protected from corrosion by a coating of zinc, a process called galvanization. Zinc has an electron configuration of [Ar]4s23d10 and is a member of the group 12 of the periodic table. It is a moderately reactive metal and strong reducing agent; in the reactivity series it is comparable to manganese. The surface of the pure metal tarnishes quickly, eventually forming a protective passivating layer of the basic zinc carbonate, , by reaction with atmospheric carbon dioxide. Zinc burns in air with a bright bluish-green flame, giving off fumes of zinc oxide. Extremely pure zinc reacts only slowly at room temperature with acids. When Zn2+ compounds form, the outer shell s electrons are lost, yielding a bare zinc ion with the electronic configuration [Ar]3d10. The filled interior d shell generally does not participate in bonding, producing diamagnetic and mostly colorless compounds. The ionic radii of zinc and magnesium happen to be nearly identical. Consequently, some of the equivalent salts have the same crystal structure, and in other circumstances where ionic radius is a determining factor, the chemistry of zinc has much in common with that of magnesium. Compared to the transition metals, zinc tends to form bonds with a greater degree of covalency. Complexes with N- and S- donors are much more stable. Complexes of zinc are mostly 4- or 6- coordinate, although 5-coordinate complexes are known. Zn(III) is predicted to exist in the presence of strongly electronegative trianions; however, there exists some doubt around this possibility. Zinc(I) compounds Zinc(I) compounds are very rare. The [Zn2]2+ ion is implicated by the formation of a yellow diamagnetic glass by dissolving metallic zinc in molten ZnCl2. The [Zn2]2+ core would be analogous to the [Hg2]2+ cation present in mercury(I) compounds. The diamagnetic nature of the ion confirms its dimeric structure. The first zinc(I) compound containing the Zn–Zn bond, (η5-C5Me5)2Zn2 has been reported in 2004. Zinc(II) compounds , |alt=Sheets of zinc acetate formed by slow evaporation Binary compounds of zinc are known for most of the metalloids and all the nonmetals except the noble gases. The oxide ZnO is a white powder that is nearly insoluble in neutral aqueous solutions, but is amphoteric, dissolving in both strong basic and acidic solutions. Pnictogenides (Zinc nitride|, zinc phosphide|, zinc arsenide| and zinc antimonide|), the peroxide (zinc peroxide|), the hydride (zinc hydride|), and the carbide () are also known. Of the four halides, zinc fluoride| has the most ionic character, while the others (zinc chloride|, zinc bromide|, and zinc iodide|) have relatively low melting points and are considered to have more covalent character. In weak basic solutions containing ions, the hydroxide Zinc hydroxide| forms as a white precipitate. In stronger alkaline solutions, this hydroxide is dissolved to form zincates (zincate|). Organozinc compounds are those that contain zinc–carbon covalent bonds. Diethylzinc (Diethylzinc|) is a reagent in synthetic chemistry. It was first reported in 1848 from the reaction of zinc and ethyl iodide, and was the first compound known to contain a metal–carbon sigma bond. Test for zinc Cobalticyanide paper (Rinnmann's test for Zn) can be used as a chemical indicator for zinc. 4 g of K3Co(CN)6 and 1 g of KClO3 is dissolved on 100 ml of water. Paper is dipped in the solution and dried at 100 °C. One drop of the sample is dropped onto the dry paper and heated. A green disc indicates the presence of zinc. ==History==

Ancient use Various isolated examples of the use of impure zinc in ancient times have been discovered. Zinc ores were used to make the zinc–copper alloy brass thousands of years prior to the discovery of zinc as a separate element. Judean brass from the 14th to 10th centuries BC contains 23% zinc. Knowledge of how to produce brass spread to Ancient Greece by the 7th century BC, but few varieties were made. Ornaments made of alloys containing 80–90% zinc, with lead, iron, antimony, and other metals making up the remainder, have been found that are 2,500 years old. A possibly prehistoric statuette containing 87.5% zinc was found in a Dacian archaeological site. Strabo writing in the 1st century BC (but quoting a now lost work of the 4th century BC historian Theopompus) mentions "drops of false silver" which when mixed with copper make brass. This may refer to small quantities of zinc that is a by-product of smelting sulfide ores. Zinc in such remnants in smelting ovens was usually discarded as it was thought to be worthless. The manufacture of brass was known to the Romans by about 30 BC. The resulting calamine brass was then either cast or hammered into shape for use in weaponry. Some coins struck by Romans in the Christian era are made of what is probably calamine brass. er Eimer from Warstade, Germany, second to third century AD|alt=Large black bowl-shaped bucket on a stand. The bucket has incrustation around its top. The oldest known pills were made of the zinc carbonates hydrozincite and smithsonite. The pills were used for sore eyes and were found aboard the Roman ship Relitto del Pozzino, wrecked in 140 BC. The Berne zinc tablet is a votive plaque dating to Roman Gaul made of an alloy that is mostly zinc. The Charaka Samhita, thought to have been written between 300 and 500 AD, mentions a metal which, when oxidized, produces pushpanjan, thought to be zinc oxide. Zinc mines at Zawar, near Udaipur in India, have been active since the Mauryan period ( and 187 BC). The smelting of metallic zinc here, however, appears to have begun around the 12th century AD. Smelting and extraction of impure zinc by reducing calamine with wool and other organic substances was accomplished in the 13th century in India. The Chinese did not learn of the technique until the 17th century. The name of the metal was probably first documented by Paracelsus, a Swiss-born German alchemist, who referred to the metal as "zincum" or "zinken" in his book Liber Mineralium II, in the 16th century. The word is probably derived from the German , and supposedly meant "tooth-like, pointed or jagged" (metallic zinc crystals have a needle-like appearance). Zink could also imply "tin-like" because of its relation to German zinn meaning tin. Yet another possibility is that the word is derived from the Persian word seng meaning stone. The metal was also called Indian tin, tutanego, calamine, and spinter. Libavius described the properties of the sample, which may have been zinc. Zinc was regularly imported to Europe from the Orient in the 17th and early 18th centuries, Before it was isolated in Europe, it was imported from India in about AD 1600. Flemish metallurgist and alchemist P. M. de Respour reported that he had extracted metallic zinc from zinc oxide in 1668. In 1738 in Great Britain, William Champion patented a process to extract zinc from calamine in a vertical retort-style smelter. His technique resembled that used at Zawar zinc mines in Rajasthan, but no evidence suggests he visited the Orient. Champion's process was used through 1851. Later work was named after Luigi Galvani.|alt=Painting of a middle-aged man sitting by the table, wearing a wig, black jacket, white shirt and white scarf. William Champion's brother, John, patented a process in 1758 for calcining zinc sulfide into an oxide usable in the retort process. Jean-Jacques Daniel Dony built a different kind of horizontal zinc smelter in Belgium that processed even more zinc. --> Italian doctor Luigi Galvani discovered in 1780 that connecting the spinal cord of a freshly dissected frog to an iron rail attached by a brass hook caused the frog's leg to twitch. He incorrectly thought he had discovered an ability of nerves and muscles to create electricity and called the effect "animal electricity". The galvanic cell and the process of galvanization were both named after Luigi Galvani, and his discoveries paved the way for electrical batteries, galvanization, and cathodic protection. ==Production==

Mining and processing Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper with an annual production of about 13 million tonnes. About 70% of the world's zinc originates from mining, while the remaining 30% comes from recycling secondary zinc. Commercially pure zinc is known as Special High Grade, often abbreviated SHG, and is 99.995% pure. Worldwide, 95% of new zinc is mined from sulfidic ore deposits, in which sphalerite (ZnS) is nearly always mixed with the sulfides of copper, lead and iron. The ore is finely ground, then put through froth flotation to separate minerals from gangue (on the property of hydrophobicity), to get a zinc sulfide ore concentrate :2ZnS + 3O2 ->[t^o] 2ZnO + 2SO2 The sulfur dioxide is used for the production of sulfuric acid, which is necessary for the leaching process. If deposits of zinc carbonate, zinc silicate, or zinc-spinel (like the Skorpion Deposit in Namibia) are used for zinc production, the roasting can be omitted. For further processing two basic methods are used: pyrometallurgy or electrowinning. Pyrometallurgy reduces zinc oxide with carbon or carbon monoxide at into the metal, which is distilled as zinc vapor to separate it from other metals, which are not volatile at those temperatures. The zinc vapor is collected in a condenser. :ZnO + H2SO4 -> ZnSO4 + H2O Finally, the zinc is reduced by electrolysis. Environmental impact Refinement of sulfidic zinc ores produces large volumes of sulfur dioxide and cadmium vapor. Smelter slag and other residues contain significant quantities of metals. About 1.1 million tonnes of metallic zinc and 130 thousand tonnes of lead were mined and smelted in the Belgian towns of La Calamine and Plombières between 1806 and 1882. The dumps of the past mining operations leach zinc and cadmium, and the sediments of the Geul River contain non-trivial amounts of metals. Effective sewage treatment greatly reduces this; treatment along the Rhine, for example, has decreased zinc levels to 50 ppb. Soils contaminated with zinc from mining, refining, or fertilizing with zinc-bearing sludge can contain several grams of zinc per kilogram of dry soil. Levels of zinc in excess of 500 ppm in soil interfere with the ability of plants to absorb other essential metals, such as iron and manganese. Zinc levels of 2000 ppm to 180,000 ppm (18%) have been recorded in some soil samples. ==Applications==

Major applications of zinc include, with percentages given for the US and galvanization (coating of iron or steel) is the most familiar form. In 2009 in the United States, 55% or 893,000 tons of the zinc metal was used for galvanization. Zinc is more reactive than iron or steel and thus will attract almost all local oxidation until it completely corrodes away. A protective surface layer of oxide and carbonate ( forms as the zinc corrodes. This protection lasts even after the zinc layer is scratched but degrades through time as the zinc corrodes away. The relative reactivity of zinc and its ability to attract oxidation to itself makes it an efficient sacrificial anode in cathodic protection (CP). For example, cathodic protection of a buried pipeline can be achieved by connecting anodes made from zinc to the pipe. A zinc disc attached to a ship's iron rudder will slowly corrode while the rudder stays intact. There are also efforts to use zinc as anode material in secondary cells with a comparable cell chemistry, for example by advanced electrolytes. Zinc is used as the anode or fuel of the zinc–air battery/fuel cell. The zinc-cerium redox flow battery also relies on a zinc-based negative half-cell. Alloys A widely used zinc alloy is brass, in which copper is alloyed with anywhere from 3% to 45% zinc, depending upon the type of brass. Alloys of 85–88% zinc, 4–10% copper, and 2–8% aluminium find limited use in certain types of machine bearings. Zinc has been the primary metal in American one cent coins (pennies) since 1982. The zinc core is coated with a thin layer of copper to give the appearance of a copper coin. In 1994, of zinc were used to produce 13.6 billion pennies in the United States. Alloys of zinc with small amounts of copper, aluminium, and magnesium are useful in die casting as well as spin casting, especially in the automotive, electrical, and hardware industries. An example of this is zinc aluminium. The low melting point together with the low viscosity of the alloy makes possible the production of small and intricate shapes. The low working temperature leads to rapid cooling of the cast products and fast production for assembly. Another alloy, marketed under the brand name Prestal, contains 78% zinc and 22% aluminium, and is reported to be nearly as strong as steel but as malleable as plastic. This superplasticity of the alloy allows it to be molded using die casts made of ceramics and cement. For building facades, roofing, and other applications for sheet metal formed by deep drawing, roll forming, or bending, zinc alloys with titanium and copper are used. Unalloyed zinc is too brittle for these manufacturing processes. to tire balances and flywheels. Cadmium zinc telluride (CZT) is a semiconductive alloy that can be divided into an array of small sensing devices. Other industrial uses in paints.|alt=White powder on a glass plate Roughly one quarter of all zinc output in the United States in 2009 was consumed in zinc compounds; The zinc zinc-oxide cycle is a two step thermochemical process based on zinc and zinc oxide for hydrogen production. Zinc chloride is often added to lumber as a fire retardant and sometimes as a wood preservative. It is used in the manufacture of other chemicals. Zinc sulfide (ZnS) is used in luminescent pigments such as on the hands of clocks, X-ray and television screens, and luminous paints. Crystals of ZnS are used in lasers that operate in the mid-infrared part of the spectrum. Zinc sulfate is a chemical in dyes and pigments. Zinc powder is sometimes used as a propellant in model rockets. Zinc sheet metal is used as a durable covering for roofs, walls, and countertops, the last often seen in bistros and oyster bars, and is known for the rustic look imparted by its surface oxidation in use to a blue-gray patina and susceptibility to scratching. , the most abundant isotope of zinc, is very susceptible to neutron activation, being transmuted into the highly radioactive , which has a half-life of 244 days and produces intense gamma radiation. Because of this, zinc oxide used in nuclear reactors as an anti-corrosion agent is depleted of before use, this is called depleted zinc oxide. For the same reason, zinc has been proposed as a salting material for nuclear weapons (cobalt is another, better-known salting material). is used as a tracer to study how alloys that contain zinc wear out, or the path and the role of zinc in organisms. Zinc dithiocarbamate complexes are used as agricultural fungicides; these include Zineb, Metiram, Propineb and Ziram. Zinc naphthenate is used as wood preservative. Zinc in the form of ZDDP, is used as an anti-wear additive for metal parts in engine oil. Organic chemistry Organozinc chemistry is the science of compounds that contain carbon-zinc bonds, describing the physical properties, synthesis, and chemical reactions. Many organozinc compounds are commercially important. Among important applications are: • The Frankland-Duppa Reaction in which an oxalate ester (ROCOCOOR) reacts with an alkyl halide R'X, zinc and hydrochloric acid to form α-hydroxycarboxylic esters RR'COHCOOR • Organozincs have similar reactivity to Grignard reagents but are much less nucleophilic, and they are expensive and difficult to handle. Organozincs typically perform nucleophilic addition on electrophiles such as aldehydes, which are then reduced to alcohols. Commercially available diorganozinc compounds include dimethylzinc, diethylzinc and diphenylzinc. Like Grignard reagents, organozincs are commonly produced from organobromine precursors. Zinc has found many uses in catalysis in organic synthesis including enantioselective synthesis, being a cheap and readily available alternative to precious metal complexes. Quantitative results (yield and enantiomeric excess) obtained with chiral zinc catalysts can be comparable to those achieved with palladium, ruthenium, iridium and others. Dietary supplement supplement pills is one compound used for the delivery of zinc as a dietary supplement.|alt=Skeletal chemical formula of a planar compound featuring a Zn atom in the center, symmetrically bonded to four oxygens. Those oxygens are further connected to linear COH chains. In most single-tablet, over-the-counter, daily vitamin and mineral supplements, zinc is included in such forms as zinc oxide, zinc acetate, zinc gluconate, or zinc amino acid chelate. Generally, zinc supplement is recommended where there is high risk of zinc deficiency (such as low and middle income countries) as a preventive measure. Although zinc sulfate is a commonly used zinc form, zinc citrate, gluconate and picolinate may be valid options as well. These forms are better absorbed than zinc oxide. Gastroenteritis Zinc is an inexpensive and effective part of treatment of diarrhea among children in the developing world. Zinc becomes depleted in the body during diarrhea and replenishing zinc with a 10- to 14-day course of treatment can reduce the duration and severity of diarrheal episodes and may also prevent future episodes for as long as three months. Gastroenteritis is strongly attenuated by ingestion of zinc, possibly by direct antimicrobial action of the ions in the gastrointestinal tract, or by the absorption of the zinc and re-release from immune cells (all granulocytes secrete zinc), or both. Common cold Weight gain Zinc deficiency may lead to loss of appetite. The use of zinc in the treatment of anorexia has been advocated since 1979. At least 15 clinical trials have shown that zinc improved weight gain in anorexia. A 1994 trial showed that zinc doubled the rate of body mass increase in the treatment of anorexia nervosa. Deficiency of other nutrients such as tyrosine, tryptophan and thiamine could contribute to this phenomenon of "malnutrition-induced malnutrition". A meta-analysis of 33 prospective intervention trials regarding zinc supplementation and its effects on the growth of children in many countries showed that zinc supplementation alone had a statistically significant effect on linear growth and body weight gain, indicating that other deficiencies that may have been present were not responsible for growth retardation. Other People taking zinc supplements may slow down the progress to age-related macular degeneration. Zinc supplement is an effective treatment for acrodermatitis enteropathica, a genetic disorder affecting zinc absorption that was previously fatal to affected infants. Zinc may help individuals sleep more. and is considered very photo-stable. Zinc oxide is one of the most common active ingredients formulated into a sunscreen to mitigate sunburn. Zinc pyrithione is widely included in shampoos to prevent dandruff. Topical zinc has also been shown to effectively treat, as well as prolong remission in genital herpes. ==Biological role==

Zinc is an essential trace element for humans for plants and for microorganisms. Zinc is required for the function of over 300 enzymes and 1000 transcription factors, and is stored and transferred in metallothioneins. It is the second most abundant trace metal in humans after iron and it is the only metal which appears in all enzyme classes. Roughly  grams of zinc are distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye. Semen is particularly rich in zinc, a key factor in prostate gland function and reproductive organ growth. Zinc homeostasis of the body is mainly controlled by the intestine. Here, ZIP4 and especially TRPM7 were linked to intestinal zinc uptake essential for postnatal survival. In humans, the biological roles of zinc are ubiquitous. in addition to hundreds more that transport and traffic zinc; a similar in silico study in the plant Arabidopsis thaliana found 2367 zinc-related proteins. It plays a key role in synaptic plasticity and so in learning. Zinc homeostasis also plays a critical role in the functional regulation of the central nervous system. L- and D-histidine facilitate brain zinc uptake. SLC30A3 is the primary zinc transporter involved in cerebral zinc homeostasis. Enzymes of human carbonic anhydrase II, with zinc atom visible in the center|alt=Interconnected stripes, mostly of yellow and blue color with a few red segments. help read DNA sequences.|alt=A twisted band, with one side painted blue and another gray. Its two ends are connected through some chemical species to a green atom (zinc). Zinc is an efficient Lewis acid, making it a useful catalytic agent in hydroxylation and other enzymatic reactions. Two examples of zinc-containing enzymes are carbonic anhydrase and carboxypeptidase, which are vital to the processes of carbon dioxide () regulation and digestion of proteins, respectively. In vertebrate blood, carbonic anhydrase converts into bicarbonate and the same enzyme transforms the bicarbonate back into for exhalation through the lungs. Without this enzyme, this conversion would occur about one million times slower at the normal blood pH of 7 or would require a pH of 10 or more. The non-related β-carbonic anhydrase is required in plants for leaf formation, the synthesis of indole acetic acid (auxin) and alcoholic fermentation. Carboxypeptidase cleaves peptide linkages during digestion of proteins. A coordinate covalent bond is formed between the terminal peptide and a C=O group attached to zinc, which gives the carbon a positive charge. This helps to create a hydrophobic pocket on the enzyme near the zinc, which attracts the non-polar part of the protein being digested. Other proteins Zinc serves a purely structural role in zinc fingers, twists and clusters. Zinc fingers form parts of some transcription factors, which are proteins that recognize DNA base sequences during the replication and transcription of DNA. Each of the nine or ten ions in a zinc finger helps maintain the finger's structure by coordinately binding to four amino acids in the transcription factor. The concentration of zinc in blood plasma stays relatively constant regardless of zinc intake. Zinc may be held in metallothionein reserves within microorganisms or in the intestines or liver of animals. Metallothionein in intestinal cells is capable of adjusting absorption of zinc by 15–40%. However, inadequate or excessive zinc intake can be harmful; excess zinc particularly impairs copper absorption because metallothionein absorbs both metals. The human serotonin transporter and norepinephrine transporter do not contain zinc binding sites. Nutrition Dietary recommendations The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for zinc in 2001. The current EARs for zinc for women and men ages 14 and up is 6.8 and 9.4 mg/day, respectively. The RDAs are 8 and 11 mg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 11 mg/day. RDA for lactation is 12 mg/day. For infants up to 12 months the RDA is 3 mg/day. For children ages 1–13 years the RDA increases with age from 3 to 8 mg/day. As for safety, the IOM sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of zinc the adult UL is 40 mg/day including both food and supplements combined (lower for children). Collectively the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes (DRIs). The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL are defined the same as in the United States. For people ages 18 and older the PRI calculations are complex, as the EFSA has set higher and higher values as the phytate content of the diet increases. For women, PRIs increase from 7.5 to 12.7 mg/day as phytate intake increases from 300 to 1200 mg/day; for men the range is 9.4 to 16.3 mg/day. These PRIs are higher than the U.S. RDAs. The EFSA reviewed the same safety question and set its UL at 25 mg/day, which is much lower than the U.S. value. For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For zinc labeling purposes 100% of the Daily Value was 15 mg, but on May 27, 2016, it was revised to 11 mg. A table of the old and new adult daily values is provided at Reference Daily Intake. Dietary intake containing zinc|alt=Several plates full of various cereals, fruits and vegetables on a table. Animal products such as meat, fish, shellfish, fowl, eggs, and dairy contain zinc. The concentration of zinc in plants varies with the level in the soil. With adequate zinc in the soil, the food plants that contain the most zinc are wheat (germ and bran) and various seeds, including sesame, poppy, alfalfa, celery, and mustard. Zinc is also found in beans, nuts, almonds, whole grains, pumpkin seeds, sunflower seeds, and blackcurrant. Other sources include fortified food and dietary supplements in various forms. A 1998 review concluded that zinc oxide, one of the most common supplements in the United States, and zinc carbonate are nearly insoluble and poorly absorbed in the body. For fortification, however, a 2003 review recommended cereals (containing zinc oxide) as a cheap, stable source that is as easily absorbed as the more expensive forms. A 2005 study found that various compounds of zinc, including oxide and sulfate, did not show statistically significant differences in absorption when added as fortificants to maize tortillas. Deficiency Nearly two billion people in the developing world are deficient in zinc. Groups at risk include children in developing countries and elderly with chronic illnesses. In children, it causes an increase in infection and diarrhea and contributes to the death of about 800,000 children worldwide per year. Zinc supplements help prevent disease and reduce mortality, especially among children with low birth weight or stunted growth. While zinc deficiency is usually due to insufficient dietary intake, it can be associated with malabsorption, acrodermatitis enteropathica, chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses. The most recent published update of the survey (NHANES 2013–2014) reported lower averages – 9.3 and 13.2 mg/day – again with intake decreasing with age. Symptoms of mild zinc deficiency are diverse. but excessive zinc does also. western vegetarians and vegans do not suffer any more from overt zinc deficiency than meat-eaters. Major plant sources of zinc include cooked dried beans, sea vegetables, fortified cereals, soy foods, nuts, peas, and seeds. Soil remediation Species of Calluna, Erica and Vaccinium can grow in zinc-metalliferous soils, because translocation of toxic ions is prevented by the action of ericoid mycorrhizal fungi. Agriculture Zinc deficiency appears to be the most common micronutrient deficiency in crop plants; it is particularly common in high-pH soils. Zinc-deficient soil is cultivated in the cropland of about half of Turkey and India, a third of China, and most of Western Australia. Substantial responses to zinc fertilization have been reported in these areas. Plants that grow in soils that are zinc-deficient are more susceptible to disease. Zinc is added to the soil primarily through the weathering of rocks, but humans have added zinc through fossil fuel combustion, mine waste, phosphate fertilizers, pesticide (zinc phosphide), limestone, manure, sewage sludge, and particles from galvanized surfaces. Excess zinc is toxic to plants, although zinc toxicity is far less widespread. ==Precautions==

Toxicity Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption. The Free Ion Activity Model 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. The free zinc ion is 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 through the high solubility of the zinc ion in the acidic stomach. Evidence shows that people taking 100–300 mg of zinc daily may suffer induced copper deficiency. A 2007 trial observed that elderly men taking 80 mg daily were hospitalized for urinary complications more often than those taking a placebo. Levels of 100–300 mg may interfere with the use of copper and iron or adversely affect cholesterol. Zinc in excess of 500 ppm in soil interferes with the plant absorption of other essential metals, such as iron and manganese. The U.S. Food and Drug Administration (FDA) states that zinc damages nerve receptors in the nose, causing anosmia. Reports of anosmia were also observed in the 1930s when zinc preparations were used in a failed attempt to prevent polio infections. On June 16, 2009, the FDA ordered removal of zinc-based intranasal cold products from store shelves. The FDA said the loss of smell can be life-threatening because people with impaired smell cannot detect leaking gas or smoke, and cannot tell if food has spoiled before they eat it. Recent research suggests that the topical antimicrobial zinc pyrithione is a potent heat shock response inducer that may impair genomic integrity with induction of PARP-dependent energy crisis in cultured human keratinocytes and melanocytes. Poisoning In 1982, the US Mint began minting pennies coated in copper but containing primarily zinc. Zinc pennies pose a risk of zinc toxicosis, which can be fatal. One reported case of chronic ingestion of 425 pennies (over 1 kg of zinc) resulted in death due to gastrointestinal bacterial and fungal sepsis. Another patient who ingested 12 grams of zinc showed only lethargy and ataxia (gross lack of coordination of muscle movements). Zinc is highly toxic in parrots and poisoning can often be fatal. The consumption of fruit juices stored in galvanized cans has resulted in mass parrot poisonings with zinc. ==See also==