Nitrate [NO3-]and nitrite [NO2-] are naturally occurring ions that are part of the nitrogen cycle. Nitrate is used mainly in inorganic fertilizers, and sodium nitrite is used as a food preservative, especially in cured meats. The nitrate concentration in groundwater and surface water is normally low but can reach high levels as a result of agricultural [activity and] runoff, refuse dump runoff, or contamination with human or animal wastes.