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March 16, 2011

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Doses of iodine medication not helpful

THE fear of wind-carried radiation from Japan's crippled nuclear power station has alarmed citizens and prompted many residents to buy respirators and iodine pills that taken correctly can protect the thyroid from radioactive iodine.

The third explosion yesterday at a nuclear reactor building and a fire at a fourth in the Fukushima station have sent alarms around the world.

On Monday night radiation level readings at the plant were five times that of a standard abdominal X-ray. One X-ray is 600 μSv, while the reading outside the reactor station was 3,130 μSv per hour.

A lethal exposure is considered to be 4,000 mSv at one time, and below 100 μSv is safe. (1 mSv=1,000 μSv)

Iodine 131 and caesium 137 are found around nuclear power plants. When inhaled iodine 131 can damage the thyroid bland, caesium 137 damages the nervous system and the system that forms blood cells.

Taking iodine pills can help prevent absorption of radioactive iodine, but there is no need for such medicine at this time, says Professor Zhu Guoying, a researcher at the Radiomedicine Institute of Fudan University.

Doses with unnecessary medication will not be helpful, she says. Radiation can cause damage to organs and systems when they are exposed to a great amount of radioactive elements.


"But damage depends on the amount of radiation, the length of exposure and the different toxic elements," says Professor Zhu.

Gray (Gy) is a standard unit widely used to describe the absorbed radiation dose of ionizing radiation. It is defined as the absorption of one joule of ionizing radiation by 1kg of matter, usually human tissue.

On exposure to radiation of 4Gy, half of the healthy adults will die, most experts say. People will live for only an hour when exposed to radiation of 5Gy.

Radiation of 1-7 Gy is used in radiotherapy, but only targeted at particular parts of the body in treating cancers.

"Being exposed to radiation over 1Gy can cause instant reactions such as feeling sick and vomiting," says Zhu. It may be accompanied by diarrhea, headache and fever, since the digestive and nervous systems are most vulnerable to radiation.

And radiation can have long-term impact, though symptoms are not immediately visible.

"Problems can conceal themselves for months or even years, but damage to the organs will eventually occur," says Zhu.

Some damage can be repaired, some cannot. The biggest concern is that radiation can cause cell abnormalities and eventually cancer.

Radiation can strike DNA and the energy changes can easily damage structure, causing mutations that lead to cancer as the damaged cells keep copying themselves.

The government is monitoring the situation and will make an announcement if there is any cause for alarm.


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