National Drinking Water Database

Nitrate (measured as Nitrogen)

Nitrate is a naturally occurring chemical that is an important plant nutrient often used in fertilizers. Most human exposure arises from food, but drinking water is an important source of exposure in contaminated areas. Nitrate ends up in drinking water due to agricultural runoff from fertilizer use, erosion of natural deposits, or from animal and human waste via septic tanks and sewage systems. Rural water supplies of mid-western farming states, whose sources are often untreated groundwater, are most susceptible to high levels of nitrate. Nitrate is also used in chemical, petrochemical and metal industries; metal-finishing plants are the primary industrial emitters of nitrate into surface waters (Gabaldon 2007).

Bacteria in the gut convert nitrate to nitrite, which is mostly responsible for any toxic effects observed. One of the most well known signs of nitrate/nitrite poisoning is oxygen deprivation due to methemoglobinemia. In the blood, nitrite changes hemoglobin (which carries oxygen), to methemoglobin (which is unable to carry oxygen). This causes blood to carry less oxygen, and can be fatal if too much methemoglobin is produced. Symptoms include rapid breathing, muscle tremors, lack of coordination, weakness, diarrhea and frequent urination.

Drinking water is a more important source of exposure in bottle-fed infants as compared to adults (California Environmental Protection Agency 1997g). Infants are especially susceptible to methemoglobinemia, which can cause "blue baby syndrome." Pound for pound, infants drink more water than adults, resulting in higher nitrate exposure. Infants also tend to have higher levels of bacteria in the gut that can convert nitrate to nitrite. In addition, hemoglobin is converted more easily to methemoglobin in infants. Finally, infants are less capable of metabolizing methemoglobin. Over 2,000 causes of "blue baby syndrome" have been reported from around the world since the mid-1950s, mostly from contaminated drinking water used to make infant formula (California Environmental Protection Agency 1997g). Several studies have reported an association between high maternal drinking water nitrate levels and risk of birth defects, including incomplete brain development (Arbuckle 1988; Croen 2001; Cedergren 2002).

Inside the body, nitrite can react with amines to form N-nitroso compounds, many of which are known animal carcinogens (California Environmental Protection Agency 1997g, National Toxicology Program (NTP) 2002a). Some but not all human cancer studies have found associations between high drinking water levels of nitrate and cancer, such as non-Hodgkin's lymphoma and cancers of the bladder and stomach (California Environmental Protection Agency 1997g; Ward 1996). Exposure to nitrate, nitrite and N-nitroso compounds have been associated with increased risk of type 1 diabetes in approximately half of the studies that have looked at this issue (Longnecker and Daniels 2001). Other possible health effects in people include low blood pressure (California Environmental Protection Agency 1997g) and altered immune function (Ustyugova 2002).