With irradiation, food is placed in a special processing chamber and exposed to a carefully measured level of intense ionising radiation, usually from cobalt-60 or through a process called linear acceleration.

The most commonly treated foods are uncooked meat, poultry, fruit and vegetables.

The process is highly specialised, and food companies often make use of established facilities, essentially small nuclear plants. The 160 signatory nations of the Codex Alimentarius' food standards guidelines are required to label irradiated foods with the radura symbol.

No one seems sure how much irradiated food is available in Hong Kong, but it would seem increasingly common given the number of treatment facilities in the region and the rising prevalence of the process among our trading partners in North America and Europe.

Although irradiation has been in use since the 1950s and has been used widely by the US in its space programme, it has only become popular in the past few years.

Studies have shown it does not cause radioactivity in food. Taste, colour or texture in most food groups - the main exception being dairy products - is not affected. Tests have shown a small loss of vitamin content in some foods, but the most heated debate rages over whether irradiation can harm those who eat it or genetically affect their future children.

Such claims are rejected by Hong Kong food scientist Domas So Chi-him, a senior lecturer at the Vocational Training Council in Chai Wan and the past chairman of the Hong Kong Food Science and Technology Association. 'It is extraordinary in terms of technology,' he said. 'This is the only way to kill disease-carrying micro-organisms in raw meat or poultry.'

The most common of these bacteria - salmonella, E-Coli 0157, listeria, campylobacter and toxoplasma gondi - kill millions of people around the world each year. Even in a highly developed country like the US, they put hundreds of thousands of people in hospital.

Irradiation expert Christine Bruhn, from the University of California's Davis Centre for Consumer Research, said that if half the ground beef, poultry and prepared meat in the US were treated, 352 deaths, 6,000 severe illnesses and 880,000 hospital admissions would be prevented. She said claims that the process was unsafe were unfounded.

'There is not a problem with irradiated food, and this is not just my opinion, but that of the public health community in the United States and many other countries,' Dr Bruhn said.

'The World Health Organisation recommends that people choose irradiated foods for safety wherever it's available. The American Dietetics Association, the American Medical Association, the Centres for Disease Control - every health group that I'm aware of - is recommending and endorsing the safety of irradiated foods.'

Dr Bruhn said studies on animals and humans had failed to show adverse health effects or genetic disorders in offspring.

She suggested that Hong Kong's wet markets would benefit from the technology and cited the example of a street-stall delicacy in Thailand known as nam. Made of raw, minced, preserved pork and chilli shaped into a sausage, it had been notorious for causing stomach upsets until a supermarket chain in the early 1990s started selling an irradiated version which made the dish even more popular.

Other Asian countries with irradiation facilities are China, South Korea, Japan, Indonesia, Vietnam, Bangladesh, Pakistan and India. The California-based firm SureBeam is funding projects in the Philippines to build facilities to improve the life of mangoes so they can be exported to the US by ship.

But other countries, including Australia, have placed a moratorium on food irradiation (although Australia's strict regulations have been modified to allow for the treating of seeds, herbs and nuts).

The Australian government's concerns are shared by Donald Louria, chairman of the University of Medicine and Dentistry of New Jersey's department of preventative medicine and community health.

An HIV/Aids specialist and member of Physicians for Social Responsibility, Dr Louria said that without conclusive evidence of safety, the potential remained that irradiated foods could cause chromosomal damage or genetic harm.

The two most conclusive studies - one in India on malnourished children and another in China on healthy young and middle-aged adults - gave conflicting results. Although the Indian study was not ideal - it was conducted on a small and select group - it showed that some of the wheat eaten had resulted in chromosomal abnormalities. No such damage was noticed in the Chinese study.

As with genetically modified foods, there is also the contentious labelling issue. In the US, food companies are lobbying to have the radura symbol replaced by terms such as 'pasteurised' or 'cold pasteurised'. Added to this is the thorny issue of labelling food in markets and on restaurant menus.

Hong Kong's government has yet to decide on the labelling of genetically modified food, but companies marketing irradiated food have to label it. How can this be done - or even guaranteed - with irradiated produce such as mangoes from China or other produce from elsewhere in the region?

Democratic Party legislator and chairman of the Legislative Council's panel on food safety and environmental hygiene Fred Li Wah-ming said Hong Kong was far behind other countries over labelling. 'In the US, there is compulsory labelling on 13 ingredients, and we don't have any yet,' Mr Li said.

'This is one of the subjects we're looking into this year. We are so far behind because the Hong Kong government is looking after the interests of the trade - the food importers and wholesalers. They always have pressure on the government because labelling will increase the cost. They have a strong lobby and the consumer's right to know is always being sacrificed.'

Andrianna Natsoulas, the international organiser for the Washington-based advocacy group Public Citizen, believes increasing public awareness is crucial. On a grassroots level, contacting stores and requesting they do not stock irradiated food is an effective approach.

'Unfortunately, the pro-irradiation industry has a lot of clout,' she said. 'They have been successful in the past three years, especially in the US, and just pushing forward the legislation without the adequate research being conducted.'

Irradiated foods are available in 40 of America's 50 states, and thousands of supermarkets stock them. As with genetically modified foods, the main government monitoring agencies - the US Department of Agriculture and the Food and Drug Administration - have given their approval. Irradiated foods are expected soon to be approved in school lunch programmes.

Conversely, European countries have shown some concern. In December, the European Parliament voted against expanding the list of foods that could be irradiated until further research is done.

For some, irradiated foods are a matter of healthy choice. But for others, until more testing is carried out, they are a matter of concern.