'Nitrogen, total'(organic and inorganic) is not a single chemical substance but a wide range of compounds of nitrogen which can be used directly by plants as a source of nitrogen required for their nutrition directly, or else may be converted into forms that plants can use in the environment.
Nitrogen gas makes up about 80% of the atmosphere and is fairly non-reactive. Before living organisms can make use of nitrogen as a nutrient element, it has to be in a soluble form, such as nitrate or ammonia (inorganic forms) or in organic forms such as proteins which are readily converted into inorganic forms. The key inorganic form of nitrogen is ammonia, a highly reactive gas in its pure form, but which is usually found as ammonium ions when dissolved in water. Ammonium ions are the form of nitrogen used by plants and animals to make amino acids which are then built up into the structural proteins and enzymes that are the key components of all living organisms. The other main inorganic form of nitrogen is the nitrate ion (derived from nitric acid). Nitrate and ammonia are inter-converted in the water and soil by micro-organisms. These inorganic forms are taken up by plants and converted to proteins. Higher animals could not use inorganic forms of nitrogen for their nutrition but instead depend on organic forms already made by the plants and other animals that they eat. Proteins in the animal diet are first broken down into their constituent amino acids and are then reassembled into the required animal proteins and other cell constituents. Waste organic nitrogen compounds in animals are converted into ammonia, and then excreted in the urine as urea and other simple organic forms. These substances then enter the environment where they are converted into nitrate, ammonium ions and nitrogen gas. Some specialised bacteria can also 'fix' nitrogen gas from the atmosphere into ammonium ions. The above process is called the nitrogen cycle. In addition to ammonium and nitrate ions, traces of unstable inorganic nitrogen compounds such as nitrite ions may occasionally be found.
The major use of substances that contribute to total nitrogen in soil and waters is as fertilisers and manure. Synthetic nitrogen fertilisers include substances such as ammonium nitrate, ammonium sulphate, urea, nitro-lime etc.
Major releases to the atmosphere occur as a result of combustion processes, which form oxides of nitrogen that eventually contribute to nitrate formation. Major sources are power stations and road vehicles. Oxides of nitrogen are also formed naturally in thunderstorms and forest fires. Ammonia is also released from animal manure, vehicles equipped with catalytic converters, human breath and babies nappies. Nitrogen released to land and water comes mainly from the application of fertilisers and manure, industrial effluents and atmospheric deposition.
Impacts on human health and environment
Excessive exposure to some chemicals in this diverse group may affect health, with the possible effects depending on the particular chemical.
Releases of nitrogen compounds give rise to concern for two reasons firstly, from their action as plant nutrients, causing eutrophication, and secondly, due to their contribution to acidification of sensitive ecosystems. Nitrogen is usually the key nutrient in shortest supply in natural ecosystems. This means that when the supply of nitrogen in a usable form is increased through the addition of fertiliser or through pollution, the amount of plant biomass that can be s
Emission to water reporting threshold: 50000 kg/year
Data source: European Pollutant Emission Register