As the nuclear crisis continues in northeastern Japan, the government is telling people near the damaged Fukushima-Daiichi reactors to stay indoors. The US government is warning Americans already in Japan to stay at least 80 kilometers away from the reactor site. Many people in the U.S., China and Russia are reportedly stocking up on potassium iodide pills to protect themselves against any wind-borne radiation. While there are many uncertainties about the public health situation in Japan, much is known about the health effects of radiation.
Tens of thousands of people in Japan have been scanned for radiation exposure by medical teams wearing white suits and carrying Geiger counters. When radioactive iodine enters the body, it settles in the thyroid. Children are especially vulnerable.
What are the immediate health effects of exposure to radiation?
Exposure to moderate levels of radiation – above one gray (the standard measure of absorbed radiation) – can result in radiation sickness, which produces a range of symptoms.
Nausea and vomiting often begin within hours of exposure, followed by diarrhoea, headaches and fever.
After the first round of symptoms, there may be a brief period with no apparent illness, but this may be followed within weeks by new, more serious symptoms.
At higher levels of radiation, all of these symptoms may be immediately apparent, along with widespread – and potentially fatal – damage to internal organs.
Exposure to a radiation dose of four gray will typically kill about half of all healthy adults.
For comparison, radiation therapy for cancer typically involves several doses of between one and seven gray at a time – but these doses are highly controlled, and usually specifically targeted at small areas of the body.
A sievert is essentially equivalent to a gray, but tends to be used to measure lower levels of radiation, and for assessing long-term risk, rather than the short-term acute impact of exposure. There are 1,000 millisieverts in a sievert.
Radiation and cancer
- Most experts agree even small doses of ionising radiation – as low as 100 millisieverts – can increase the risk of cancer, but by a very small amount.
- In general, the risk of cancer increases as the dose of radiation increases. Exposure to one sievert of radiation is estimated to increase the lifetime risk of fatal cancer by around 5%.
- The thyroid gland and bone marrow are particularly sensitive to ionising radiation.
- Leukemia, a type of cancer that arises in the bone marrow, is the most common radiation-induced cancer. Leukemias may appear as early as a few years after radiation exposure.
- Other cancer can also result from exposure to radiation, but may not develop for at least a decade. These include cancers of the lung, skin, thyroid, breast and stomach.
What are the most likely long-term health effects?
Cancer is the biggest long-term risk. Usually when the body’s cells reach their “sell-by date” they commit suicide. Cancer results when cells lose this ability, and effectively become immortal, continuing to divide and divide in an uncontrolled fashion.
The body has various processes for ensuring that cells do not become cancerous, and for replacing damaged tissue.
But the damage caused by exposure to radiation can completely disrupt these control processes, making it much more likely that cancer will result.
Failure to properly repair the damage caused by radiation can also result in changes – or mutations – to the body’s genetic material, which are not only associated with cancer, but may also be potentially passed down to offspring, leading to deformities in future generations. These can include smaller head or brain size, poorly formed eyes, slow growth and severe learning difficulties.
What risk does Fukushima pose currently?
The Japanese authorities have recorded a radiation level of up 400 millisieverts per hour at the nuclear plant itself.
Professor Richard Wakeford, an expert in radiation exposure at the University of Manchester, said exposure to a dose of 400 millisieverts was unlikely to cause radiation sickness – that would require a dose of around twice that level (one sievert/one gray).
However, it could start to depress the production of blood cells in the bone marrow, and was likely to raise the lifetime risk of fatal cancer by 2-4%. Typically, a Japanese person has a lifetime risk of fatal cancer of 20-25%.
A dose of 400 millisieverts is equivalent to the dose from 50 -100 CT scans.
Prof Wakeford stressed only emergency workers at the plant were at risk of exposure to such a dose – but it was likely that they would only be exposed for short periods of time to minimise their risk.
He suggested the upper limit of their exposure would be 250 millisieverts – around 12 times the normal permitted annual exposure limit in the workplace.
However, even a dose of 100 millisieverts over a year is enough to raise the risk of cancer, and a dose of 250 millisieverts could raise lifetime risk by around 1%.
The level of exposure for the general population, even those living close to the plant, was unlikely to be anywhere near as high. There should be no risk to people living further afield.
What if the situation deteriorates?
If there were to be a meltdown or a fire at the nuclear plant, and unfavourable winds, then experts say radioactive material could reach as far as Toyko, 150 miles (241km) away.
However, even in that situation, the level of radiation is likely to be such that simple measures, such as staying indoors with windows closed, should neutralise the risk.
How can the Japanese authorities minimise the cost to human health?
Prof Wakeford said that provided the Japanese authorities acted quickly, most of the general population should be spared significant health problems.
He said in those circumstances the only people likely to be at risk of serious health effects were nuclear workers at the plant or emergency workers exposed to high levels of radiation.
He said the top priority would be to evacuate people from the area and to make sure they did not eat contaminated food. The biggest risk was that radioactive iodine could get into their system, raising the risk of thyroid cancer.
To counter that risk, people – in particular children – could be given tablets containing stable iodine which would prevent the body absorbing the radioactive version.
The Japanese already have a lot of iodine in their natural diet, so that should help too.
some content via Â bbc.co.uk
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