2. Relevance to Public Health 2.1 Background and Environmental Exposures to Nitrate and Nitrite in the United States

Nitrate and nitrite can be organic or inorganic chemicals depending on their chemical structures. This profile pertains to inorganic nitrate and nitrite, specifically the nitrate anion and the nitrite anion. Nitrate and nitrite occur naturally in the environment as part of the nitrogen cycle, and are produced both endogenously and exogenously. Ammonia-oxidizing bacteria convert ammonia into nitrite; nitriteoxidizing bacteria convert nitrite into nitrate in aerobic environments. This two-stage process is known as nitrification. Main sources of ammonia in the environment are decaying organic matter and human and animal wastes. Nitrification, atmospheric fixation, and nitrogen fertilizers contribute to nitrite and nitrate concentrations in the environment. In nature, salts of nitrate and nitrite completely dissociate and these anions typically exist as ionic species. In the environment, nitrite is readily oxidized to nitrate. Nitrate is generally stable in the environment; however, it may be reduced through biotic (living systems; plants, microbes, etc.) processes to nitrite under anerobic conditions.