NITRATE

Agricultural fields form the main diffuse sources of the NO₃⁻ that is leached to groundwater. However, NO₃⁻ is also released from exercise yards and manure storage facilities, which represent important potential point sources of contamination. The problem of groundwater contamination by nitrates appears to be worsening at the end of the 20th century. Elevated concentrations of nitrate (greater than 2 mg/L) in drinking water have been associated with adverse health effects. Ingestion of nitrate by infants can cause low oxygen levels in the blood, a potentially fatal condition known as methemoglobinemia or “blue baby” disorder. High nitrate and nitrite levels can also cause methemoglobinemia in livestock and other animals. If excessive amounts of phosphorus and nitrates are added to the water, algae and aquatic plants can be produced in large quantities. When these algae die, bacteria decompose them, and use up oxygen. This process is called eutrophication. Dissolved oxygen concentrations can drop too low for fish to breathe, leading to fish kills.