PARIS – The risk from radioactive contamination of food depends on several factors but the duration of the problem depends especially on which type of radioactive element is to blame, say experts.
Japan on Saturday said that it had discovered abnormal levels of radiation in milk and spinach from areas near Fukushima, and in tap water in Tokyo and five central prefectures, but there was no threat to health.
In historical cases of contamination, the main source has been wind-borne dust which is deposited on fruit or vegetables or which falls on the soil, where it is absorbed by grass and leafy plants.
Radioactive particles are then transmitted through the food chain, which explains why cattle can have higher-than-normal levels of radioactivity in their milk and meat.
Ingested, these particles are hazardous because they release energy that can slice through molecular bonds in DNA, thus increasing the risk of cancer.
The problem can be short-term or long-term, depending on the nature of the radioactive source and the amount of contamination in the local environment, which in turn is also influenced by the weather.
Iodine 131, for instance, has a “half life”—a measure of decay—of only eight days, which means it is likely to break down in the environment in a few weeks.
“There is a short-term risk to human health if radioactive iodine in food is absorbed into the human body,” the International Atomic Energy Agency (IAEA) said on Saturday.
“If ingested, it can accumulate in and cause damage to the thyroid. Children and young people are particularly at risk.”
Taking “stable” forms of iodine, such as potassium iodide tablets, can block radioactive iodine in the thyroid, the IAEA said.
The longer-term problem comes from enduring elements such as caesium 137, whose “half life” is measured in 30 years and may even take several centuries before it breaks down totally.
Caesium fallout from the Chernobyl nuclear disaster in April 1986 caused long-term contamination problems in many European countries, leading to restrictions on the sale of milk or dairy beef as far as Scotland.
According to a 1993 study by the IAEA, more than six years after Chernobyl, farmers in some mountain areas of southern Norway, more than 1,000 kilometres (600 miles) from the disaster, were raising reindeer with up to 20,000 becquerel per kilogram (Bq/kg) of radiation, and sheep with up to 10,000 Bq/kg.
Strontium 90 is another dangerous long-term contaminant, as is plutonium 239.
Plutonium is one of the most toxic substances for man, but through direct contact rather than through food.
“Plutonium 239 is absorbed to a negligible extent from soil by plants and is very poorly absorbed from the gastrointestinal tract of animals and man,” says the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).
The maximum dose for radioactive iodine, according to Euratom guidelines, is 150 Bq/kg or becquerels per litre (Bq/l) for infant food; 500 Bq/kg or Bq/l for dairy products; 2,000 Bq/kg or Bq/l for other foods and 500 Bq/l for liquids intended for consumption.
The maximum dose of radioactive elements lasting beyond 10 days—thus including caesium—is 400 Bq/kg or Bq/l for infant food; 1,000 Bq/kg or Bq/l for dairy products; 1,250 Bq/kg or Bq/l for other foods; and 1,000 Bq/l for liquids intended for consumption.
Radioactivity also exists in the natural environment, for instance as a background source that comes from certain kinds of rocks. In addition, many countries permit safe irradiation of food products to kill or prevent bacteria in order to prolong shelf life.
(AFP)