Nitrate and nitrite are naturally occurring ions that are part of the nitrogen cycle.

Naturally occurring nitrate levels in surface and ground water are generally a few miligrams per litre. In many ground waters, an increase of nitrate levels has been observed due to the intensification of farming practice. Concentrations can reach several hundred miligrams per litre. In some countries, up to 10% of the popullation may be exposed to nitrate levels in drinking water of above 50 mg/l.  

In general, for humans vegetables will be the main source of nitrate intake when levels in drinking water are below 10 mg/l. When nitrate levels in drinking water exceed 50 mg/l, drinking water will be the major source of total nitrate intake.  

Extensive epidemiological data support the current guideline value proposed by the World Health Organization (WHO) for nitrate-nitrogen of 10 mg/l. However, this value should not be expressed on the basis of nitrate nitrogen but on the basis of nitrate itself, which is the chemical entity of concern to health, and the guideline value for nitrate is therefore 50 mg/l. Click here for further information about this. 

Nitrification 

Nitrification is the oxidation of an ammonia compound into nitrite, especially by the action of the nitrifying bacteria called Nitrosomas. The nitrites will then be oxidized to nitrates by the bacteria Nitrobacter.

Nitrate is less toxic than nitrite and is used as a food source by live plants.

The process of converting ammonia to nitrate is diagramed in the nitrogen cycle.

Nitrification is most rapid at pH of 7-8 and at temperatures of 25-30^oC. Nitrification causes waters to decrease in pH.

Ecotoxicology of nitrite and nitrate

Nitrite levels above 0.75 ppm in water can cause stress in fish and greater than 5 ppm can be toxic.

Nitrate levels from 0 – 40 ppm are generally safe for fish. Anything greater than 80 can be toxic.  

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