3-24-11
Fukushima radioactive fallout nears Chernobyl levels
Austrian researchers have used a worldwide network of radiation detectors – designed to spot clandestine nuclear bomb tests – to show that iodine-131 is being released at daily levels 73 per cent of those seen after the 1986 disaster. The daily amount of caesium-137 released from Fukushima Daiichi is around 60 per cent of the amount released from Chernobyl....
The Chernobyl accident emitted much more radioactivity and a wider diversity of radioactive elements than Fukushima Daiichi has so far, but it was iodine and caesium that caused most of the health risk – especially outside the immediate area of the Chernobyl plant, says Malcolm Crick, secretary of a United Nations body that has just reviewed the health effects of Chernobyl. Unlike other elements, he says, they were carried far and wide by the wind.
Moreover the human body absorbs iodine and caesium readily. "Essentially all the iodine or caesium inhaled or swallowed crosses into the blood," says Keith Baverstock, former head of radiation protection for the World Health Organization's European office, who has studied Chernobyl's health effects.
Iodine is rapidly absorbed by the thyroid, and leaves only as it decays radioactively, with a half-life of eight days. Caesium is absorbed by muscles, where its half-life of 30 years means that it remains until it is excreted by the body. It takes between 10 and 100 days to excrete half of what has been consumed.
While in the body the isotopes' radioactive emissions can do significant damage, mainly to DNA. Children who ingest iodine-131 can develop thyroid cancer 10 or more years later; adults seem relatively resistant. A study published in the US last week found that iodine-131 from Chernobyl is still causing new cases of thyroid cancer to appear at an undiminished rate in the most heavily affected regions of Ukraine, Belarus and Russia.
Caesium-137 lingers in the environment because of its long half-life. Researchers are divided over how much damage environmental exposure to low doses has done since Chernobyl. Some researchers think it could still cause thousands of new cases of cancer across Europe.
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3-29-11 After the 1986 Chernobyl accident, the most highly contaminated areas were defined as those with over 1490 kilobecquerels (kBq) of caesium per square metre. Produce from soil with 550 kBq/m2 was destroyed.
People living within 30 kilometres of the plant have evacuated or been advised to stay indoors. Since 18 March, MEXT has repeatedly found caesium levels above 550 kBq/m2 in an area some 45 kilometres wide lying 30 to 50 kilometres north-west of the (Fukushima) plant. The highest was 6400 kBq/m2, about 35 kilometres away, while caesium reached 1816 kBq/m2 in Nihonmatsu City and 1752 kBq/m2 in the town of Kawamata.
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