Nitrate

Nitrate

Nitrate is a negatively charged ion (anion) of one nitrogen and three oxygen atoms. Potassium nitrate (Saltpeter) is found naturally as a contaminant of salt and was noted in early history as enhancing the preservative effect of salting meat.

Nitrogen is one of the nutrient elements that plants need to grow, plants can only absorb nitrogen in the form of nitrate. Since ancient times farmers have known that the harvests of crops can be significantly increased by fertilizing with composted plant and animal waste or wood ash. In the 19th century a global trade in nitrate rich guano developed with large quantities being shipped from south America to Europe. In the early 20th century German chemists solved the problem of how to fix nitrogen from the air into fertilizers and created artificial fertilizers that todays modern agricultural process depends on. Since the advent of artificial fertilizers nitrates have grown steadily as contaminants of water.

Nitrates are oxidising agents and are used in the production of explosives, the combination of ammonium nitrate and fuel oil create the industrial explosive known as ANFO, used widely as a blasting agent. In 1993 the IRA detonated an ANFO truck bomb on Bishopsgate, London killing a man and causing £350m of damage.

Agency Limit (ppm)
UK - DEFRA 50
US - EPA 10
EU - EEA 50
WHO 50

Nitrate and our health

Nitrate is relatively stable and unreactive and as such its toxicity is low. However, the action of the bacterial microflora of the mouth and the gut can reduce nitrates to highly toxic nitrites. Health concerns for nitrite focus on its propensity to reduce the ability of blood to carry oxygen particularly in the young where it is a cause of blue baby syndrome. Additionally, nitrites have been classified as probable carcinogens as they react to form nitrosamine compounds that are known to damage DNA.

Nitrate in our drinking water

The majority of nitrate in groundwater in the UK is due to pollution from agriculture, other sources of nitrates are from sewage sludge disposal to land and from atmospheric deposition. Nitrate contamination moves slowly through the ground until it reaches the water table. A major study by the British Geological survey found that Nitrate moves at between 0.7 and 2 meters a year.

The current UK regulatory standard for nitrate in drinking water is 50ppm this standard may be breached at times of the year in agricultural areas as nitrate levels are seasonal.

Tests

Nitrates in your drinking water can be detected by the following tests.

Removing Nitrate

Nitrate can be reduced or removed from your drinking water using the following methods.

  • Reverse Osmosis
  • Anion Exchange Columns
  • Activated Carbon Filters

Further reading