What is Nitrate and why is there concern about its presence in drinking water?

The primary health hazard from drinking water with nitrate-nitrogen occurs when nitrate is transformed to nitrite in the digestive system. The nitrite oxidizes iron in the hemoglobin of the red blood cells to form methemoglobin, which lacks the oxygen-carrying ability of hemoglobin. This creates the condition known as methemoglobinemia (sometimes referred to as "blue baby syndrome"), in which blood lacks the ability to carry sufficient oxygen to the individual body cells causing the veins and skin to appear blue.

Nitrate is one of the most common groundwater contaminants. It is regulated in drinking water primarily because excess levels can cause methemoglobinemia, or "blue baby" syndrome which refers to the bluish color that appears around the mouth, hands, and feet of victims. The disease occurs when hemoglobin in the blood absorbs a nitrate molecule in place of oxygen. The body becomes oxygen deprived leading, if untreated, to form a chemical asphyxiation. Infants are vulnerable because their stomachs lack sufficient quantities of an enzyme that normally neutralizes nitrates.

Although nitrate levels that effect infants do not pose a direct threat to older children and adults, they do indicate the possible presence of other more serious residential or agricultural contaminants, such as bacteria or pesticides.

Nitrate in groundwater originates primarily from fertilizers, septic systems, and manure storage or spreading operations. Fertilizer nitrogen that is not taken up by plants, volatilized, or carried away by surface runoff leaches to the groundwater in the form of nitrate. Nitrogen from manure similarly can be lost from fields, barnyards, or storage locations. Septic systems also can elevate groundwater nitrate concentrations because they only typically remove about half of the nitrogen in wastewater, leaving the remaining half to percolate into the groundwater.