Iron is a plentiful element, making up at least 5 percent of the Earth's crust. Surface erosion from water dissolves iron, which seeps into soil and becomes part of virtually all natural water sources, including well water. Iron is required by animals for producing hemoglobin, which is responsible for carrying oxygen in the blood and the reason why blood is red. Iron levels in public drinking water are established more for taste and aesthetic reasons than health, although some people are more sensitive to its effects.
Origins of Iron in Water
Iron is plentiful in the Earth's core and crust and is brought to the surface primarily via volcanic eruptions. The main naturally occurring iron minerals are magnetite, hematite and goethite. Weathering processes, such as wind, rain and tidal waters, release iron into oceans, rivers and lakes. By the time iron seeps into aquifers that serve as sources of drinking water, it's in the form of iron carbonate. Iron can exist in water as soluble ferrous iron or insoluble ferric iron. Water containing ferrous iron is clear and colorless because the iron is dissolved, although when exposed to air, it will precipitate out of solution into a reddish-brown compound. This compound is oxidized ferric iron that will not dissolve back in water again.
Iron Levels in Water
Seawater naturally contains between 1 and 3 parts per billion of iron. Rivers usually contain between 0.5 and 1 part per million of iron, whereas groundwater is seldom found at concentrations greater than 10 parts per million. According to the U.S. Environmental Protection Agency, the present recommended limit for iron is 0.3 parts per million, although this level is based on taste and appearance rather than on any detrimental health effect. When iron exceeds 0.3 parts per million, bathtubs and sinks can become stained a reddish-brown color, and the water may have a metallic taste.
Health Effects of Iron
The body contains about 4 g total iron, of which 70 percent is in blood and the rest is mainly in bone marrow. Men require about 7 mg iron daily, although women require up to 11 mg because of menstruation. Iron is an essential component of hemoglobin, which binds and transports both oxygen and carbon dioxide. Iron is also a component of many enzymes and is involved in DNA synthesis.
Dangers of Iron
Iron can accumulate and reach dangerous levels within people, especially those who suffer from hemochromatosis, which is a genetic disease that increases iron absorption from the intestines. Normal individuals absorb about 25 percent of dietary iron, although this is significantly increased in those with hemochromatosis. When high levels of iron are absorbed, it is stored and accumulates in vital organs, such as the pancreas, liver and heart. Stored iron produces free radicals, which can cause tissue damage, inflammation and organ failure. According to a 1994 study published in "Annals of Neurology," excessive iron plays a role in degenerative brain diseases, such as Parkinson's and Alzheimer's disease. Iron compounds can form in water, such as FeCl2 and FeSO4, and may have more negative impact upon health than iron does by itself. Healthy people are only rarely affected by iron overdose, although the risks are increased with excessive supplementation and drinking private well water exceptionally high in iron.
References
- "Fluids and Electrolytes with Clinical Application"; Joyce LeFever Kee; 2010
- U.S. Environmental Protection Agency: Iron Levels in Water
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Professional Guide to Diseases: Ninth Edition"; Springhouse Publishing; 2009
- "Annals of Neurology"; Complex 1, Iron and Ferritin in Parkinson's Disease Substantia Nigra; V. Mann, et al; July 1994
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