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26. IronName: Iron
Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Iron nuclei are very stable. Iron is a vital constituent of plant and animal life, and is the key component of haemoglobin. The pure metal is not often encountered in commerce, but is usually alloyed with carbon or other metals. The pure metal is very reactive chemically, and rapidly corrodes, especially in moist air or at elevated temperatures. Any car owner knows this. Iron metal is a silvery, lustrous metal which has important magnetic properties. Iron is essential to all organisms, except for a few bacteria. Animals incorporate iron into the heme complex, an essential component of proteins involved in redox reactions, including respiration. Inorganic iron is also found in the iron-sulfur clusters of many enzymes, such as nitrogenase (Synthesis of ammonia from nitrogen and hydrogen) and hydogenase. A class of non-heme-iron enzymes is responsible for a wide range of functions within several life forms, such as methane monooxygenase (oxidizes methane to methanol), ribonucleotide reductase (reduces ribose to desoxyribose; DNA biosynthesis), hemerythrins (oxygen transport and fixation in marine invertebrae) and purple acid phosphatase (hydrolysis of phosphate esters). Iron distribution is heavily regulated in mammals. For example, when the body is fighting a bacterial infection, the body "hides" iron so it cannot be used by the bacteria (see transferrin). Good sources of dietary iron include meat, fish, poultry, lentils, beans, spinach, tofu, chickpeas, black-eyed pea, strawberries and farina. Iron provided by dietary supplements is often found as Iron (II) fumarate. The RDA for iron varies considerably based on the age, gender, and source of dietary iron (heme-based iron has higher bioavailability) The first signs of use of iron come from the Sumerians and the Egyptians, where around 4000 BC, small items, such as the tips of spears and ornaments, were being fashioned from iron recovered from meteorites. Because meteorites fall from the sky some linguists have conjectured that the English word iron, which has cognates in many northern and western European languages, derives from the Etruscan aisar which means "the gods". By 1600 BC to 1200 BC, iron was used increasingly in the Middle East, but did not supplant the dominant use of bronze. In the period from the 12th to 10th century BC, there was a rapid transition in the Middle East from bronze to iron tools and weapons. The critical factor in this transition does not appear to be the sudden onset of a superior ironworking technology, but instead the disruption of the supply of tin. This period of transition, which occurred at different times in different parts of the world, is the ushering in of an age of civilization called the Iron Age. Cast iron development lagged in Europe, as the smelters could only achieve temperatures of about 1000 K. Through a good portion of the Middle Ages, in Western Europe, iron was still being made by the working of sponge iron into wrought iron. Some of the earliest casting of iron in Europe occurred in Sweden, in two sites, Lapphyttan and Vinarhyttan, between 1150 and 1350 AD. There are suggestions by scholars that the practice may have followed the Mongols across Russia to these sites, but there is no clear proof of this hypothesis. In any event, by the late fourteenth century, a market for cast iron goods began to form, as a demand developed for cast iron cannonballs. Early iron smelting (as the process is called) used charcoal as both the heat source and the reducing agent. In 18th century England, wood supplies ran down and coke, a fossil fuel, was used as an alternative. This innovation by Abraham Darby supplied the energy for the Industrial Revolution. Excessive dietary iron is toxic, because excess ferrous iron reacts with peroxides in the body, producing free radicals. When iron is in normal quantity, the body's own antioxidant mechanisms can control this process. In excess, uncontrollable quantities of free radicals are produced. The lethal dose of iron in a 2 year old is about 3 grams of iron. One gram can induce severe poisoning. There are reported cases of children being poisoned by consuming between 10-50 tablets of ferrous sulfate over a few hour period. Overconsumption of iron is the single highest cause of death in children by unintentional ingestion of pharmaceuticals. The DRI lists the Tolerable Upper Intake Level (UL) for adults as 45 mg/day. For children under 14 years old the UL is 40 mg/day. If iron intake is excessive a number of iron overload disorders can result, such as hemochromatosis. For this reason, people shouldn't take iron supplements unless they suffer from iron deficiency and have consulted a doctor. Blood donors are at special risk of low iron levels and are often recommended to supplement their iron intake. Quick links
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