The magnitude 9.0 earthquake and subsequent tsunami that struck Japan on March 11, killing more than 26,000 people and damaging or destroying more than 125,000 buildings, has also threatened the nation’s food production system and tested emergency quality assurance procedures.
Damage at four reactors at the Fukushima 1 Nuclear Power Plant, located in the Futaba District of Fukushima Prefecture, led to the release of radioactivity and the discovery of radioactive isotopes in some foods, including spinach and milk. Although the crisis has caused international alarm, the scope of the problem is considered limited to Japan and well under control there.
Japan’s government responded to the disaster by issuing a set of limits for radiation content in food and a program of inspection. The radionuclides of particular concern are iodine-131, cesium-134, and cesium-137, but authorities are also monitoring for the presence of uranium and plutonium isotopes.
Radiation can enter the food chain when isotopes from the plume are deposited on plant or soil surfaces, or released into water. The surface contamination can lead to tissue contamination if the substances are consumed or inhaled. In some cases, radioactive material can concentrate in tissue. Contaminated produce or meats could result in illness even for those living far from the site of the disaster.
“In general, the risk to the food supply after a nuclear accident depends on a variety of factors, which can include the amount and type of radioactive emission; wind speed, its direction, and whether or not there is precipitation, which affects dispersion of material; and the type of food being produced, as some foods absorb radioactive materials differently,” said Aphaluck Bhatiasevi, Communications Officer, Global Alert and Response Department for the World Health Organization.
Japan has set limits of 300 becquerels (Bq) per kilogram radioactive iodine in drinking water and milk, and 2,000 for vegetables (excluding root vegetables). Milk used in baby formula must contain less than 100 Bq/kg. With regard to radioactive cesium, drinking water and milk must fall below 200 Bq/kg, and most other foods are limited to 500. Limits are much lower for uranium, alpha-emitting nuclides of plutonium, and transuranic elements.
A becquerel is the amount of radioactive material in which one decay occurs per second.
Early in the unfolding disaster, Japanese food safety inspectors found iodine-131 in milk at levels five times the allowable limit and in spinach at seven times the limit.
The ongoing discharge of radioactive water into the ocean has also caused concerns about contamination of seafood. The ocean dilutes the radioactivity, mitigating the problem, and the most common contaminant, iodine-131, with a half-life of eight days, will rapidly disappear from the environment.
According to Bhatiasevi, tests have found radioactive cesium and iodine in some fish samples. “In the longer term,” she said, “bioaccumulation can occur in seafood. It is therefore important to continue to monitor seafood for a long period of time. WHO and its partners are researching the potential contamination of seafood and implications for other countries and areas, if any.”
Nearby nations, including South Korea, Hong Kong, China, and Australia, have been testing imported foods from Japan or have banned them.
Japan imports more food than it exports, but some foods are shipped to other countries. Australia has restricted imports of milk and milk products, fresh fruit, vegetables, seaweed, and seafood from Japanese prefectures affected by the nuclear disaster.