The facts on iron

What is iron?

Pure iron is a soft, silvery metal often covered by a thin layer of reddish dust. It is highly abundant in our environment from core to crust. It is rare to find pure iron in nature, and it is most common to find the metal bound to other elements such as oxygen.

Elemental iron is highly chemically reactive. In warm, moist air, iron will quickly oxidize to form rust or iron oxide. The presence of rust makes it easy to identify iron in geological formations, from the red clays of the southern United States, to the iron-rich rocks of Mars which are red to the naked eye from millions of miles away.

Where is iron found?

Most of the iron in the universe has come from the exploding centers of dying stars. These “supernovae” expel hot gasses that settle and cool into stars and planets. As our planet formed, most of the Earth’s iron sunk to the molten core. The rest resides in the crust — in large deposits mined as ore, or smaller, finer deposits such as red clay or sand. The largest known iron deposits are found in the former Soviet republics, which contain 33 percent of the world’s iron ore, and Canada, which contains about 14 percent.

Hubble Space Telescope observations of a pair of very distant exploding stars, called Type Ia supernovae

Not all the iron on Earth was here when the planet formed. Some was delivered to the planet from the heavens by shooting stars or meteors, which are dubbed meteorites when they strike Earth’s surface. Iron meteorites can be distinguished from regular iron rocks by the criss-cross pattern that emerges on the inner surfaces when polished. This makes meteoritic iron a rare commodity, sought after throughout antiquity as a gemstone.

The ancients thought that all iron had a heavenly origin. The Greek name for iron is sideros denoting a relationship to the stars, and one of the oldest words for the metal, anbar, means sky and fire. The ancient Romans valued iron as a heavenly gift from the god of war, Mars, and appropriately used iron to arm their military forces. Ancient Egyptian jewelry often contained polished beads of meteoritic iron. Today meteoric iron is most readily found in museums.

Living things contain much smaller amounts of iron. Iron has an affinity for binding to oxygen and it is used by blood cells to carry oxygen through the body. The body also uses iron in a reaction that allows cells to create their own fuel and as part of an enzyme in the immune system that helps fight infections.

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What are the uses of iron?

Natural iron — iron that is not completely pure, but has very few contaminants — can be hammered cold to form crude shapes, or heated to a temperature that allows it to assume any form a smith has time and inclination to make. The first forged, or “wrought iron” tools date to at least 4000 B.C. in Africa and Asia with experts quibbling over which culture invented the process. Cultures dating from this period up through 500 B.C. were characterized by their iron craftsmanship and became part of the Iron Age.

Iron gained newfound significance during the Industrial Revolution as steel changed the face of industry. Steel is an iron alloy with about 1 percent carbon and some other metal additives such as chromium that assumes the best properties of other iron alloys. Steel has the rigidity of cast-iron — so it stays sharp — while retaining just enough elasticity to sustain blows without cracking. Early iron smelters could not accurately control the temperature of their ovens or the precise amount of carbon inclusion needed to create steel, but increasing research and experimentation during the 1800s allowed for a materials revolution that paved the way for technologies like the railroad, the automobile, skyscrapers, steel-hulled ships, and countless other modern marvels. Despite an increased use of plastics and more exotic materials in our computer-driven society, steel still plays a crucial role in literally holding up the infrastructure of buildings, roadways, bridges, industry, and mass transportation that we take for granted every day.

The world’s largest producers of iron include China, Japan, Russia, and the United States. Total world production averages about 1 billion gross tons per year. Explosive industrial growth in China in recent years has led to increased importation of iron ore so that China is now both the top producer and consumer of iron.

Aside from its crucial employment in heavy industry, people also commonly use iron as a dietary supplement by taking iron-fortified vitamins.

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Do we need iron for health?

Iron is essential to proper nutrition. The metal is important in many key functions in the human body from the transport of oxygen in the blood to helpful enzymes in the immune system that help fight infection. In fact, it was the first trace element identified as a necessary part of the human diet early in the seventeenth century. The first attempts at producing dietary iron supplements involved dissolving iron filings in wine as a treatment for a condition known as chlorosis (an iron deficiency causing a greenish-yellow discoloration of the skin). Today iron supplements take the form of vitamin tablets that we take orally.

A lack of iron in the diet can have serious consequences. Iron deficiency anemia is one of the most common forms of malnutrition in the world today. This disease is characterized by a low concentration of red blood cells or low levels of hemoglobin, a protein in red blood cells where 70 percent of the body’s iron is stored. When the body recognizes that there is not enough stored iron for normal function, it cuts down on the production of hemoglobin leaving the blood with a lower oxygen-carrying capacity. This very slowly suffocates tissues. Over time, a person with iron deficiency anemia might develop symptoms such as fatigue, dizziness, weakness, irritability, pallor, rapid heartbeat and shortness of breath. Iron deficiency anemia has been identified in a large percentage of the world’s population with pregnant women, children, and teens at greatest risk for developing the disease. Women of childbearing age are at particular risk since they regularly lose iron through blood discharged in menstruation.

Still another form of iron deficiency is sickle-cell anemia, a notorious genetic disorder. This disease is genetically recessive, meaning that one must have inherited a defective copy of the gene from both parents to develop the disorder. This disease is caused by an abnormality in the way hemoglobin proteins form. Instead of the saucer-like shape of normal red blood cells, these cells are crescent- or sickle-shaped. Sickle-shaped red blood cells are unable to carry oxygen as well as normal cells, leading to a condition that causes many of the symptoms of acquired iron deficiency anemia. However, this disease carries the added risk of blood clots since the abnormally shaped cells are more likely to stick to each other and the walls of the blood vessels. Unfortunately, simply increasing the dietary iron intake will not help individuals with this disease.

There is currently no cure, but there is hope that through persistent research, a cure can be found. Currently, people with sickle-cell disease can be treated with a host of drugs that alleviate symptoms and prevent opportunistic infections that arise as a result of a weakened immune system. A 1999 report in the Journal of the American Medical Association (JAMA) described in vitro fertilization techniques can prevent the disease from being handed down to offspring.

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Can too much iron harm living things?

While iron is essential for health, too much iron can be harmful — even deadly. As with iron deficiencies, there are two conditions that overload the body with iron, one genetic and one acquired. Both conditions relate to iron in the bloodstream. This time, however, the ill effects have nothing to with the amount of oxygen reaching organ tissues. Iron overload exerts its toxic effects through the amount of iron deposited in the liver, heart, pancreas, joints, and pituitary gland.

Hemochromatosis is a recessive genetic disorder affecting an estimated one out of every two hundred individuals of Caucasian descent. One person in ten carries a single defective gene, and about 1 in 300 carries two copies (they are said to be homozygous for the gene). The proportion of these people who have disease symptoms is not clear. Hemochromotosis makes the body prone to absorbing large amounts of iron from the diet, leading to accumulation of iron deposits in their organs. This iron excess can lead to darkening of the skin, liver cancer, cirrhosis of the liver, enlargement of the heart, congestive heart failure, infertility, impotence, joint pains and diabetes. In most cases, the disease is identified because of symptoms of fatigue, lethargy, arthritis or impotence. Blood tests and a liver biopsy with quantitative iron testing are accepted as the best means of confirming the disease. Since the condition is caused by an excess of iron in the blood, this is one of the few diseases for which the medieval treatment of draining blood is the most effective treatment. This is done through a medical procedure called therapeutic phlebotomy.

Occasionally, people acquire iron overload. This can result from multiple blood transfusions, for example as treatment for inherited blood disorders such as thalassemias. Iron is common in tobacco products, so heavy smokers are at elevated risk for acquiring iron overload. Welders can also inhale excessive amounts of iron, though the problem remains confined to the lung. Those who consume large quantities of red meat and use tobacco products are at increased risk of developing the condition. An excess of vitamin C in the diet is also known to promote the absorption of dietary iron. Acquired iron overload in these cases is generally mild, and can be treated by simply avoiding or reducing the main sources of iron ingestion.

One of the most serious forms of iron overload is acute iron poisoning. While iron-fortified vitamin tablets may be a convenient way to round out a diet, they can be harmful to small children and infants if consumed in high amounts. Acute iron poisoning resulting from overdoses on iron-fortified vitamin tablets and iron-containing drugs is the leading cause of poisoning death of children under the age of six in the United States, according to the United States Food and Drug Administration (FDA). Since 1986, over 110,000 incidents of iron poisoning resulting from accidental ingestion of iron tablets by children under the age of six have been reported to poison control centers. Of those cases, 35 resulted in death.

In 1994, the FDA released guidelines to help curb the tide of iron poisoning cases. New labels must be stamped on iron-containing drugs and dietary supplements. The message to consumers reads: "WARNING: Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under six. Keep this product out of reach of children. In case of accidental overdose, call a doctor or poison control center immediately." The FDA has also instituted an education campaign to inform parents about the dangers of iron poisoning in children .

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Can iron harm the environment?

Iron overdoses can be severe in human beings, especially children, but its effects within ecosystems can be far more widespread and circuitous. As with humans, iron is essential to most living organisms. Animals, plants, and even bacteria require the metal for proper metabolism. However, when human activities alter the geochemistry within an ecosystem and allow for chemical interactions with iron that would not normally occur in nature, iron quickly becomes an accomplice in many insidious environmental problems.

Take the mining industry, for example, and a problem known as acid mine drainage (AMD). When companies mine metals such as copper, gold, lead, uranium, and zinc, they often seek metal deposits near the earth’s crust and dig what are known as open pit mines. Metal ores that have been sheltered from the earth’s weather for millions of years may suddenly be exposed to air and rain water. This new mixture of air, water, and heavy metal compounds makes for a series of new and environmentally harmful chemical reactions collectively known as AMD.

Sulfur and iron are the key components that allow the reactions to proceed. Heavy metal compounds containing sulfur can dissolve in the lightly acidic rain water, releasing sulfur into the rain water runoff. One common waste mineral in the mining industry known as pyrite, iron disulfide (FeS2), or “fool’s gold” reacts with the air and water to form sulfuric acid (H2SO4). This makes for extremely acidic water conditions that can lower the pH of streams and rivers to levels that are hazardous to aquatic life.

Iron does not simply come along for the ride in the AMD process. Iron can be a useful tracer for AMD as well as an environmental menace itself. Bright orange water and rocks in a mine’s effluent stream are a tell-tale sign of AMD. Ferric hydroxide (Fe(OH)3) or “yellow-boy” is a bright orange, rusty-colored compound that forms during the series of reactions that lead to AMD runoff. When “yellow-boy” begins to cloud the water near a mine, it is a sign that sulfuric acid is also present.

Not only does “yellow-boy” clearly mark the AMD process, but it can harm aquatic life directly when if precipitates out of runoff. As mining runoff moves downstream, chemical reactions in the stream can act to buffer or neutralize the effluent. However, as the pH of the water returns to neutral levels, “yellow-boy” becomes less soluble and precipitates out of the mixture in bright orange, rusty-colored clouds. The undissolved particles can harm the aquatic ecosystem by blocking light and blanketing stream beds, which obscures food sources for bottom dwellers.

AMD is a severe environmental and economic problem in the United States. It is estimated that AMD in combination with other toxins from abandoned mines in the U.S. have polluted 180,000 acres of reservoirs and lakes as well as 12,000 miles of streams and rivers. The cost to taxpayers of cleaning up this pollution is estimated to be between $32 and $72 billion.

Iron can damage aquatic communities in more subtle ways. Aquatic organisms such as algae and bacteria can thrive in iron-rich environments, such as effluent from iron ore mining plants. When this mineral-rich effluent is pumped into an established and stable aquatic ecosystem, growth of algae and iron-metabolizing bacteria is stimulated.

Such was the case in 1956 when the Reserve Mining Company opened shop on Lake Superior’s Silver Bay in Minnesota. The plant at Silver Bay was extracting taconite ore for steel production. The taconite effluent and tailings — the mineral silt that results from ore processing — were procedurally pumped through a pipe into Lake Superior. The effluent contained large amounts of iron and other more harmful metals.

As early as 1956 and 1957, people living in the vicinity of the Silver Bay plant began to notice cloudy green water caused by suspended taconite particles. Fishermen found a peculiar gray slime on their nets. When analyzed in a laboratory, researchers found the sludge to contain heavy amounts of taconite as well as algae and iron-metabolizing bacteria feasting on the heavy iron content in the mineral. Iron-loving bacteria and algae exploded wherever the Reserve Mining Company spread its effluent, disturbing some of the most fundamental nodes in the complex aquatic food web.

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How does iron behave in our bodies?

Iron serves many crucial functions in the body. It is a part of the hemoglobin protein that carries oxygen in the bloodstream, and it plays a role in chemical pathways in cells that help them to release energy from organic molecules. In enzymes, iron acts to facilitate the synthesis of DNA and the fixation of carbon monoxide and nitric oxide.

Iron's versatile role in the body is a result of its unique chemistry. In an aqueous or watery solution, iron can form two stable ions or charged particles. These particles, Fe II and Fe III, have positive charges of +2 and +3 respectively. These large positive charges makes them ideal for making and breaking bonds. For this reason, iron is a key component in numerous enzymes in the body.

When iron enters the body through food or drink, it must be metabolized — chemically processed — and delivered to the blood. But iron cannot simply float through the bloodstream to locations in the body where it is needed. At a pH of 7 (the normal pH of human blood is pH 7.4) iron readily ionizes into the Fe II and Fe III forms and then quickly combines with hydrogen and oxygen. This series of reactions makes the metal biologically unavailable. Some other means is necessary to protect and transport iron throughout the body.

A protein aptly named transferrin serves this purpose. Transferrin's particular chemical configuration grabs iron and safely protects it from any further chemical changes. Its grip is so strong, that only specific target cells with special receptor sites can receive the iron. Iron can then make its way into the liver, into newly synthesized hemoglobin in red blood cells, and other regions of the body that require it for chemical pathways — particularly the bone marrow, spleen and liver.

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What are the government standards and guidelines on iron?

There are a few iron compounds classified as immediately dangerous to life or health (IDLH) by the National Institute for Occupational Safety and Health (NIOSH). One of the deadliest, Ferbam, which used as a pesticide and preservative in food crops, sounds like a stuffed toy. Its longer name, ferric dimethyldithiocarbamate, sounds a little more like the black, odorless solid that is capable of causing depression of the central nervous system (paralysis or death).

Ferrovanadium dust (FeV), used in steel manufacture, causes the same symptoms seen in most iron salt exposures: irritation of the eyes, skin, and mucous membranes; abdominal pain, diarrhea, vomiting; and possible liver damage. These reactions are typical of high doses received from industrial accidents near large stores of these dusts. The IDLH limit for ferbam is 800 milligrams per cubic meter (mg/m3). This amount of ferbam dust — equivalent to 80 percent of the weight of a paperclip in a square box three feet on each side — can cause immediate health defects and possibly death. The IDLH limits for FeV dust is 500 mg/m3 (500 milligrams per cubic meter).

For typical iron salts such as ferrous sulfate (FeS04), ferrous chloride (FeCl2), ferric nitrate (Fe[N03]3), ferric sulfate (Fe[S04]3), or ferric chloride (FeCl3), the IDLH limit is 2500 mg/m3 (2500 milligrams per cubic meter). In industrial settings, exposure to these chemicals can be avoided using protective clothing, masks, and respirators classified as “most protective”.