NO3nitrogen

NO3 nitrogen, commonly referred to as nitrate-nitrogen, denotes the portion of nitrogen contained in the nitrate ion (NO3−). In this form, nitrogen is in the +5 oxidation state. Nitrate is a highly soluble inorganic anion found in soils, water, and various biological systems, and it forms salts with cations such as sodium or potassium.

Natural and human sources supply nitrate to the environment. Nitrification by soil bacteria converts ammonium to nitrate, while mineral weathering and the decomposition of organic matter also release nitrate. Anthropogenic inputs include agricultural fertilizers, animal waste, municipal sewage, and industrial emissions. Because nitrate is highly soluble, it readily moves with water and can accumulate in groundwater and surface waters under favorable conditions.

Biologically, plants absorb nitrate through their roots and reduce it to nitrite and then to ammonium for incorporation into amino acids and other organic molecules. Nitrate is a key component of the global nitrogen cycle, linking fixation, mineralization, and denitrification processes that regulate nitrogen availability in ecosystems.

Environmental and health considerations center on elevated nitrate levels. Excess nitrate in water can promote eutrophication and algal blooms, leading to hypoxic conditions that harm aquatic life. For drinking water, high nitrate levels pose health risks, particularly methemoglobinemia in infants. Regulatory standards commonly specify limits such as 10 mg/L as nitrate-nitrogen (NO3-N) or 45 mg/L as nitrate (NO3−).

Measurement and units: nitrate content is reported as nitrate-nitrogen (NO3-N) or nitrate (NO3−). Conversions: NO3− to NO3-N involves multiplying by about 0.226; NO3-N to NO3− involves multiplying by about 4.43. Analytical methods include ion chromatography, spectrophotometry, and chemiluminescence.