Contaminant Focus

Chromium-6
Nitrate/Nitrite
Iron & Manganese
Arsenic


Chromium-6
Tap water has an average of 0.4 to 8 ppb of chromium.

What it is:
• Chromium is a metallic element that occurs naturally in association with iron.
• The odorless, tasteless, malleable metal takes a high polish and has a high melting point.
• Acting as a chemical cation, chromium freely surrenders its outer electrons to anions willing to receive them. This process leaves the chromium with three positive charges (Cr⁺³ or trivalent) or six positive charges (Cr⁺⁶ or hexavalent).

Occurrence:
• Trivalent chromium occurs naturally in the environment and can be found in rocks and soil as well as fruits, vegetables and meat.
• Hexavalent chromium is a by-product of industrial processes — forging stainless steel, chrome plating, manufacturing dyes and pigments, tanning leather, producing photographic materials and staining wood.
• Particles of Cr⁺⁶ are scattered through the air within and surrounding industrial plants, settling on land and water. While most of these particles cling to the soil, some sink into underground aquifers.
• Workers can be exposed to chromium dust in the air of industrial plants using dichromate salts by breathing in the materials or by skin contact.
• Persons living in the vicinity of such industrial facilities or uncontrolled waste sites may also be exposed via airborne dust and water contamination.

Health effects:
• Cr⁺³ is not considered a health risk. It is a mineral nutrient essential to cell membrane receptor sites stimulated by insulin. In the absence of trivalent chromium, tissues resist insulin's influence. Blood sugar cannot enter cells to be metabolized and signs of Type II diabetes may appear. The federal government has established a minimum daily requirement of 50 to 200 milligrams of chromium for dietary ingestion.
• Cr⁺⁶ is considered toxic. Exposure to hexavalent chromium may cause the following symptoms: Nausea; kidney and liver damage; thick muco-pus from respiratory membranes; punched-out, penetrating ulcers on mucous membranes; holes in the nasal septum and small bones defining the nasal and oral cavities; nosebleeds; reproductive problems; and body pains.
• Industrial workers exposed to chromate dust have a lung cancer rate 20 times that of the general population.

Regulation:
• The U.S. Environmental Protection Agency (EPA) has set a maximum contaminant level (MC.L) for total chromium of 0.1 ppm (100 ppb) in drinking water.
• Tap water has an average of 0.4 to 8 ppb of chromium.

Water treatment:
• Reverse osmosis and distillation will reduce all types of chromium found in water.
• Cr⁺³ can be removed from water with a strong acid cation ion exchange resin in the sodium form. An acid strip will normally be required periodically to strip Cr⁺³ from the resin, followed by a normal salt regenera.tion to convert the resin to the sodium form. A second regenera.tion may be necessary if the pH of the service cycle is too low.
• Reverse osmosis, deionization and distillation are considered effective in removing Cr⁺⁶.  top of page

Nitrate/Nitrite

What it is:
• Nitrate, with a single negative charge, is an ion (or salt) of nitric acid (HNO₃) or other organic or inorganic substances, such as potassium nitrate (KNO₃). Nitrite, also with a single negative charge, is an ion (or salt) of nitrous acid (HNO₂) or other substances.
• Nitrate is colorless, odorless, tasteless, very stable and easily dissolves in water. It moves with water and can migrate for miles from its source.
• Nitrite is unstable and quickly reacts with other compounds.
• Levels of nitrate can be expressed in either of two ways: “Nitrate as nitrogen” (symbol: NO₃-N) or simply as nitrate (NO₃). To convert NO₃-N to NO₃ in parts per million (ppm, or mg/L), multiply NO₃-N by 4.42.
• In ion exchange treatment, to convert NO₃ to the calcium carbonate (CaCO₃) equivalent in ppm, multiply the NO₃value by 0.81.

Occurrence:
• Nitrates occur naturally in water at low levels. Plants use nitrates as a nutrient. Most nitrates consumed by humans come from dietary raw or cooked vegetables, with few known health effects.
• High nitrate levels occur in areas where microorganisms break down fertilizers, animal waste, wastewater or septic seepage, urban drainage or decaying plants. Due to agricultural runoff or animal feedlots, rural waters may be high in nitrates.
• Nitrate and nitrite levels in the body are the result of internal nitrate production and external sources. Intake of some amount of nitrates is a normal part of the nitrogen cycle in humans.

Health effects:
• Water high in nitrates that is ingested by infants, pregnant women, adults with low stomach acidity or people with a certain enzyme deficiency can cause methemoglobinemia, or “blue baby syndrome,” as the ingested nitrates are converted to nitrites in the body. This reduces the oxygen-carrying capacity of the blood, and severe cases result in brain damage or death.
• Infants younger than 4 months of age who are fed formula diluted with water from rural domestic wells are especially prone to developing health effects from nitrate exposure. The high pH of the infant gastrointestinal system favors the growth of nitrate-reducing bacteria, particularly in the stomach and especially after ingestion of contaminated waters. Adult stomachs are typically too acidic to allow for significant bacterial growth and the resulting conversion of nitrate to nitrite.
• Prolonged intake of high nitrates can result in gastric distress in humans and has been shown to cause cancer in test animals.

In the news:
• In January 2011, East Oregonian reported that nitrate levels are still too high in the groundwater of Oregon’s lower Umatilla basin despite efforts to reduce them. The main sources of nitrates in the area include irrigated agriculture, confined animal feeding operations, septic systems, land application of food processing water and the Umatilla Chemical Depot’s bomb washout lagoons. The Oregon Department of Environmental Quality (DEQ) formed a task force in 1997 to deal with the problem, but nitrates in the groundwater remain high and are actually increasing in many wells in DEQ’s management area.

Regulation:
• The U.S. Environmental Protection Agency (EPA) has set a maximum contaminant level (MCL) for nitrates at 10 ppm, and for nitrites at 1 ppm.
• About 1 to 2 percent of the U.S. population that uses drinking water from public water systems might be exposed to nitrates in excess of the EPA-recommended maximum concentration.
• EPA estimates that 1.2 percent of community water wells and 2.4 percent of private wells exceed the nitrate standard.

Water treatment:
• Ion exchange, reverse osmosis and distillation are effective methods for reducing nitrates/nitrites.
• Ion exchange media for nitrates/nitrites can include standard strong base anion exchange resins or nitrate-selective resins.  top of page

Iron & Manganese

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.  top of page

Arsenic

What it is:
• Chemical symbol: As
• Atomic number: 33
• Arse.nic is an odorless, tasteless semi-metal element that can enter drinking water naturally through the erosion of natural deposits in the earth.
• Arse.nic also enters drinking water through agricultural and industrial runoff.

Occurrence:
• In groundwater, arse.nic generally occurs in two forms: Trivalent arse.nic (As+3, or arsenite) or pentavalent arse.nic (As+5, or arsenate). Although both forms are harmful to human health, trivalent arse.nic is more harmful and more difficult to remove from water. Trivalent arse.nic can be converted into pentavalent arse.nic in the presence of an effective oxidant such as free chlorine. Treatment with chloramines will not ensure a complete conversion of trivalent arse.nic to pentavalent arse.nic.
• Arse.nic is abundant in the Earth's crust. It is present in many different minerals, the most common of which is arsenopyrite.
• Arse.nic is also found in the atmosphere. One-third has entered naturally, most from volcanic eruption. The rest is from industrial emissions.
• Geological inorganic arse.nic is especially present in Taiwan, Bangladesh and India.
• Organic arse.nic is mainly found in sea-dwelling creatures.

Health effects:
• Arse.nic poisoning may cause the following effects: Stomach pain, nausea, vomiting, diarrhea, partial paralysis, numbness in hands and feet, blindness, thickening and discoloration of the skin.
• Arse.nic has also been linked to cancers of the bladder, lungs, skin, kidneys, nasal passages, liver and prostate.

Regulation:
• The U.S. Environmental Protection Agency (EPA) maximum contaminant level (MC.L) for arse.nic is 10 parts per billion (ppb). This enforceable MC.L became effective Jan. 23, 2006, for both organic and inorganic forms.

Water treatment:
• Ion exchange
• Reverse osmosis
• Distillation
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Authors: Water Technology editorial staff
Sources: Agency for Toxic Substances & Disease Registry (ATSDR), Colorado State Cooperative Extension, East Oregonian, Minnesota Department of Health, U.S. Environmental Protection Agency (EPA), Water Quality Association (WQA).