Studied and used for more than 50 years now, irradiation is nothing new, but then neither is the debate about it.

Irradiation has been used to sterilize medical and hospital supplies, food packaging materials and cosmetics ingredients for years, but it hasn’t been used widely in food

The World Health Organization says more than 30 countries have granted approval for the irradiation of dozens of foods, but the industry has been slow to expand its use because of fears of consumer backlash.

Here’s a closer look at this controversial food preservation method.

What is irradiation?

Irradiation involves passing foods are through a machine that sends out low doses of ionizing radiation, typically gamma rays, to kill off unwanted organisms. The rays pass through food like microwaves in a microwave oven, but do not heat the food significantly. The process is enough though to disrupt the DNA and kill insects and bacteria that can make people ill.

Like food heated in a microwave, irradiation energy disappears from the food immediately. The food does not become radioactive in any way.

What are its benefits?

Irradiation can significantly reduce bacteria levels on food and kill off parasites. In fact, the Canadian Cattlemen's Association has been calling for the approval of irradiation in ground beef, saying that, when combined with other food safety interventions, "irradiation could essentially eliminate E.coli-related illness" from ground beef.

Irradiation can also help slow spoilage by destroying moulds and yeast that cause food to spoil. As well, it can slow the ripening of fresh fruits, and prevent sprouting in root vegetables, allowing for longer shelf life.

The World Health Organization says irradiation offers a residue-free alternative to pesticides for preventing the importation of harmful insects on tropical fruits and foods, saying the process can even kill the weevils that lodge inside mango seeds.

How much energy is used?

The amount of radiation energy absorbed by a food is measured in Grays (named after 20th century British physicist Louis Harold Gray) The World Health Organization has determined that irradiation up to 10 kilograys (kGy) "introduces no special nutritional or microbiological problems."

Ten kGy is the amount of heat required to raise the temperature of water by 2.4 degrees Celsius. The amount of irradiation used to delay sprouting of vegetables and fruit ripening is less than 2 kGy, while the amount used to kill off pathogens ranges from 1 to 7 kGy.

High dose irradiation over 10 kGy can completely sterilize a food, but is only used for products intended for those with severely compromised immune systems.

In Canada, Food and Drug Regulations place upper limits on the energy levels that can be used on foods.

Are irradiated foods free of all pathogens?

Irradiation doesn’t sterilize a food, so the process does not guarantee food safety. But it does significantly reduce the levels of microorganisms that may be present on or in food, such as E.coli, Salmonella and Campylobacter bacteria.

The foods must still be handled safely after they are irradiated, says Health Canada. Consumers must refrigerate irradiated foods and cook them well, to fully destroy organisms.

Does it change the food?

Food irradiation kills off living cells and organisms, but Health Canada says it does not diminish the nutritional value of the food.

The WHO says irradiation can lower the content of some vitamins, but “storing food at room temperature for a few hours after harvesting does the same thing.”

Irradiation has little effect on the flavour of most fruits and vegetables but can change the flavour of some foods. Milk and dairy products have an odd flavour after irradiation, for example, and leaner cuts of meat can also have a different flavour, says the WHO.

Is irradiation safe?

The WHO, the UN’s Food and Agricultural Organization, and the International Atomic Energy Agency have reviewed about 50 years of research and conclude the process is safe.

They found that irradiated foods are as safe as food preserved with other techniques, such as canning, pasteurizing and fermenting.

“Studies in animals, many of which continued for periods of years, have not disclosed any reason to be concerned about long-term health effects of irradiated food or about risks from eating such food,” the WHO says. “These studies have been conducted in many different countries and by reputable international organizations.”

The WHO says irradiation is a cost-effective way of controlling harmful organisms and extending shelf-life, particularly in tropical countries, where foods can spoil quickly.

Which foods are irradiated in Canada?

Health Canada says so far, the main use of irradiation in Canada has been on spices, but onions, potatoes, wheat, white and whole wheat flour have all been approved for irradiation and sale in Canada. It’s not clear how much of those foods are currently regularly irradiated.

Health Canada has completed the scientific review of four proposed new uses of the food irradiation: mangoes, poultry, shrimp and ground beef. Reports suggest Health Canada will propose changes next month to allow the sale of irradiated ground beef in Canada.