Divided opinions have emerged in Japan over food irradiation, an internationally accepted practice of exposing food to minor doses of radiation to destroy bacteria, viruses, microorganisms and insects.

Opponents of the process say that it is hazardous to people's health because of the way it alters chemicals in certain foods, while advocates argue it is an effective way to sterilize food.

In June this year, members of the civic consumer association "Shoku no Communication Entakukaigi," (Roundtable communication on food) submitted a petition to the Ministry of Health, Labor and Welfare to consider irradiation as a possible method of food sterilization. In addition to making the request, the association irradiated frozen and defrosted raw beef liver in an experiment with the help of the Japan Atomic Energy Agency (JAEA)'s Takasaki Advanced Radiation Research Institute.

The experiment consisted of exposing frozen and defrosted chunks of raw beef liver to 1.5 kilograys and 3 kilograys of gamma radiation -- the same type used in X-rays. In terms of dosage, one kilogray (kGy) is the equivalent of about one sievert. In the experiment, 17 people examined the smell and color of the irradiated liver. They found that with liver that had been irradiated while still frozen, there was almost no difference in smell and color from that of non-irradiated liver, regardless of the radiation dose. However, liver exposed to radiation after being defrosted became white on the surface, and its smell deteriorated. The subjects did not taste the samples.

Mariko Ichikawa, the head of the consumer association and a consumer affairs consultant, is calling on the central government to start irradiation tests.

"Radiation can exterminate germs inside liver," she says. "If there are no other food sterilization methods, irradiation could surely be one option."

More than 50 countries, including the United States, China and Britain, back food irradiation, which eliminates the need for pesticides or heat to kill bacteria and insects. Irradiation is also used as a way of stopping vegetables from sprouting. In 1980, a panel including World Health Organization officials concluded that food would not become toxic even if it were irradiated up to a level of 10 kilograys.

In Japan, however, food irradiation and imports of irradiated foods are banned under the Food Sanitation Act. The exception is when irradiation is used to stop potatoes from sprouting. Irradiated potatoes, however, account for only about 0.2 percent of all domestic potato produce, meaning that they are hardly seen on the market in Japan.

People opposing food irradiation, however, have raised concerns about the effect of the process on certain substances. Although radiation does not remain in irradiated foods, opponents have pointed out that certain elements in the food may be transformed into toxic substances as a result of irradiation.

In food containing fat, for example, irradiation alters the fatty acids, leading to the formation of chemicals known as "alkylcyclobutanones." An experiment on rats overseas concluded that although alkylcyclobutanones are not carcinogenic, if given in large quantities along with carcinogens, the combination can boost the potency of cancer.

In an experiment by the Osaka Prefectural Institute of Public Health in which chunks of beef thigh, minced meat, liver, as well as pork and chicken thigh were hit with 1 to 7 kilograys of radiation, it became clear that the higher the radiation levels were, the more alkylcyclobutanones increased. Though the chemical amounts that remained in the meat after the experiment were extremely small, officials say that alkylcyclobutanones can be detected even after the meat is heated.

One particularly contentious issue regarding food irradiation in Japan is that of spices. Given that irradiated spices are distributed across the world, in 2000 the All Nippon Spice Association submitted a petition to the Ministry of Health, Labor and Welfare, requesting permission to irradiate spices. However, the Japan Liaison Against Food Irradiation, an association comprising 54 civic groups, including the Japan Housewives' Association, opposed the initiative, arguing that the dearth of food poisoning caused by spices indicates that there is no need for their irradiation.

The health ministry's Pharmaceutical Affairs and Food Sanitation Council, meanwhile, has continued deliberations on the potential risks and amounts of alkylcyclobutanones generated by irradiation, after concluding in May 2010 that "there is not enough sufficient data" to make an official decision on the issue.

An official with the health ministry's Standards and Evaluation Division commented, "We are currently asking related industries to provide data on the safety of food irradiation. At this stage, we cannot say that consumers are open to food irradiation."

The debate between residents opposing food irradiation and those who support it, however, continues at full speed.

"Peroxide and other toxic substances are produced in foods that have been irradiated," says Hiroshi Satomi, the head of "Shokuhin Shosha Network" (Food Irradiation Network), a civic group questioning the safety of the method. "We need to conduct experiments on animals that have been given alkylcyclobutanones, and observe any long-term toxicity."

Yasuhiko Kobayashi, the chief of JAEA's Quantum Beam Science Directorate, however, argues: "Food irradiation is a very practical method, because it can exterminate germs inside foods in their packaged state. Just as food irradiation is used on meat in the United States, there is value in considering its application to foods besides potatoes in Japan."

While food irradiation seems to be considered safe in many parts of the world, there is strong resistance against it in Japan, for reasons including the Fukushima No. 1 nuclear power plant disaster.

Yuriko Inubushi, a member of the board of trustees of civic group Consumption Science Center, commented: "It's not that I'm completely against food irradiation, but I just don't feel there is a dire need to consume irradiated raw liver at a time when people still lack an understanding of it."