The controversial technique of irradiation to increase the shelf life of food is safe, the World Health Organization (WHO) has proclaimed.

The WHO's findings could now lead to widespread use of the procedure, which is currently being used on a limited commercial basis in about 30 countries.

Many feared that the procedure could transform mutated microorganisms in food into superbugs resistant to radiation. But the WHO, which began its investigations because of these concerns, concluded that the superbug is theoretically possible, but had not been detected in any scientific research so far.

Environmentalists and consumer groups are also worried about irradiation because it can kill up to a fifth of some vitamins in food, in particular thiamine and the tocopherols (vitamin E). This can be offset to some extent if the irradiation takes place in a vacuum at low temperature.

Food such as meat, poultry, seafood, spices, fruit and vegetables is most suitable for irradiation. The procedure is very difficult to detect once completed, although inspectors monitor the levels of radiation while the process is taking place.

In defending its position, the WHO points out that up to 70 per cent of diarrheal diseases, which cause a quarter of all deaths in developing countries, are due to infected food.

Two babies were recently treated in Wisconsin, US, for seizure after drinking bottled drinking water. The mothers had given their babies up to three bottles a day as an inexpensive supplement to formula, and had thought it safe because it was marketed as being especially prepared for infants. However, the increased water raised the total body water of the infants by 8 per cent, and so reduced serum sodium levels. Doctors say that babies get all the liquids they need from breast milk or supplements. JAMA, 5 October 1994.

Shellfish should be purified before serving, even if they have been boiled, microbiologists at the University of Barcelona, Spain have recommended. Experiments with mussels, comtaminated with the polio and two other viruses, still had traces of them after five minutes boiling. Often, shellfish are eaten raw, and are grown and harvested in polluted waters.