Nitrates and Nitrites

Nitrates

Nitrates are natural components of vegetables such as spinach and rhubarb, and are also found in preservatives used in many processed meats such as sausages.

Nitrates occur naturally in drinking water as a result of the breakdown of vegetation, but levels can be increased by animal or human pollution and through the use of chemical fertilisers in agriculture.  Levels can also be increased during prolonged periods of drought.

The chief sources of nitrate intake are from vegetables and water with a high nitrate content.  For adults, the World Health Organisation recommends nitrate intakes of between 0-5mg per kg per day.

Regular intake of levels in excess of this have shown to cause methaemoglobinaemia (Blue Baby Syndrome) in babies and infants of up to 12 months of age.  Elderly people and those with poor kidney function may also experience toxic effects.  It has been suggested that prolonged exposure to high levels of nitrate in drinking water is associated with a higher than normal risk of cancer, but epidemiological studies have not supported this and there are no grounds for undue concern.

Whilst most cases of methaemoglobinaemia have occurred with water supplies which had a nitrate concentration in excess of 100 mg/l, 2.3% of cases the level was between 50-100 mg/l.  Clinically insignificant elevation of the levels in methaemoglobinaemia have been reported in bottle fed babies who have had feeds prepared with water which has a nitrate level of 45 mg/l.

Nitrites

The adverse effects of nitrate invariably involve its reduction to nitrite. Hence the ingestion of much lower levels of nitrite may lead to a more rapid onset if clinical effects.

In view of the above, the Council recommends that the action detailed overleaf is taken with regard to high levels of nitrates and/or nitrites in drinking water.

Nitrates

Nitrites