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 NO3 value 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.


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).