What it is:

• The second most abundant metal found on Earth, Iron makes up at least 5 percent of the Earth’s crust.
• Iron is seldom found in drinking water at concentrations greater than 10 milligrams per liter (mg/L). However, as little as 0.3 mg/L can cause water to turn a reddish brown color.
• Iron is used to construct drinking water pipes and iron oxides are used as pigments in paints and plastics. Various iron salts are used as coagulants in water treatment.
• Iron occurs mainly in two forms: Ferrous iron, which is soluble, and ferric iron, which is insoluble.
• Manganese is a tasteless, odorless, silver-colored metal that occurs naturally, often in combination with iron, oxygen, sulfur and chlorine.
• Metallic manganese is used to strengthen steel. Manganese compounds are used in the production of dry-cell batteries, matches, fireworks, animal feed, varnish and other products. Potassium permanganate (KMnO₄), usually in purple crystal form, is a powerful oxidant used in water disinfection.

Occurrence:

• Elemental iron is rarely found in nature, as the iron ions Fe²⁺ and Fe³⁺ readily combine with oxygen- and sulfur-containing compounds to form oxides, hydroxides, carbonates and sulfides.
• The most common sources in groundwater are the weathering of iron-bearing minerals and rocks, plus some man-made sources such as industrial effluents, acid-mine drainage, sewage and landfill leachate.
• Manganese is commonly found in soil in South Africa, Russia, Ukraine, Georgia, Gabon and Australia.
• Low levels of manganese are present in surface water and groundwater, often in groundwater with iron. The average amount of manganese in drinking water is 0.004 parts per million. Excess amounts enter water through human sources such as landfills and industrial runoff.
• Sponges, algae, plankton and mollusks accumulate manganese. Low levels of manganese are essential for human life.

Health effects:

• Iron is not hazardous to health, but it is considered a secondary contaminant.
• Iron is an essential element for human nutrition.
• Manganese is a toxic essential trace element, but is essential at low levels for normal functioning of humans and animals.
• Chronic exposure to high levels of manganese in water has been shown in some limited studies to cause lower intelligence and poor coordination in children.
• Manganism can occur from the frequent inhalation of manganese. Symptoms include: Psychological problems resembling dementia, diminished motor skills, tremors, weakness and speech difficulties. It is not known if manganism can occur from the frequent ingestion of water with elevated levels of manganese, as all studies have been limited and inconclusive.

Regulation:

• The U.S. Environmental Protection Agency’s (EPA) Secondary Maximum Contaminant Level (for aesthetic/cosmetic effects) for iron is 0.3 mg/L. Levels above this can cause a rusty color, sediment, metallic taste and reddish or orange staining.
• The Secondary Maximum Contaminant Level for manganese in drinking water is 0.05 mg/L. Levels above this can cause black staining of laundry and plumbing, bitter taste of water.