Leaks, explosions and meltdowns at any of Japan's troubled nuclear reactors could expose large numbers of people to radiation. These are some of the potential health risks of radiation exposure and how the condition can be treated.
Humans are exposed to low doses of radiation on a daily basis, including natural sources such as the sun and radon in the soil, medical tests such as CT scans, and from industrial and commercial products such as tobacco and smoke detectors.
The cumulative effect of this low dose of exposure is not clearly understood, said Fiona McNeill, a professor of applied radiation sciences at McMaster University in Hamilton.
But the fear in Japan is that damage to nuclear plants could result in the release of high doses of radiation and those dangers are far more clear.
Dr. McNeill said the health effects of radiation exposure are strongly dose related: The greater and more prolonged the exposure, the sicker a person gets.
Most of what we know about the dangers radiation poses to human health comes from studies of the atomic bombings of Hiroshima and Nagasaki during the Second World War, and large-scale nuclear industrial accidents such as Chernobyl in 1986 and Three Mile Island in 1979.
Radiation dosage is measured in sieverts (Sv). A dose as small as 0.25 Sv can cause detectable changes in blood but signs of radiation sickness do not usually appear below 0.1 Sv.
The first signs of radiation sickness are nausea and vomiting and, by 0.3 Sv, hair loss. Radiation can damage the gastrointestinal tract, the reproductive tract and, in particular, the thyroid.
Radiation also destroys white blood cells, leaving people susceptible to infection. With mass exposure, such as would occur with an explosion at a nuclear plant, the greatest risk in the short term would by the rapid spread of infectious disease.
By 4.5 Sv exposure, about half of people exposed die and 8 Sv or more is invariably fatal.
At Chernobyl, for example, firefighters at the scene were exposed to more than 16 Sv of radiation, while those living in surrounding areas had exposure ranging from 0.5 Sv to 5 Sv.
Over the long term, exposure to radiation, because it damages bone marrow, greatly increases the risk of developing cancer, particularly leukemia and thyroid cancer.
Treatment and prevention
When there is a threat of radioactive material being released, the first action of public health officials is to evacuate citizens from the immediate area of a plant, to minimize exposure.
After a leak occurs, one of the key actions is the simplest: To decontaminate. That means removing clothes and shoes - which capture about 90 per cent of radioactive particles in the air - and washing away residue. It is particularly important to keep radioactive particles away from wounds.
In news reports, you will often hear of plans to distribute "iodine." In fact, the pill that is used is potassium iodide. Iodine is essential to proper function of the thyroid gland and the thyroid will absorb radioactive iodine; iodine is given because it will fill the space in the thyroid and prevent radioactive material from being absorbed.
There's a catch, though: "It only works if you take the potassium iodide tables before being exposed to radioactive iodine," Dr. McNeill said. So the pills need to be distributed and taken before a leak occurs.
People who suffer from radiation sickness, meaning they have ingested or absorbed significant quantities of radioactive material (of which there are several kinds) can be treated with drugs called filgrastim (brand name Neupogen) or pegfilgrastim (Neulasta). These blood-derived medications stimulate the growth of white blood cells and help people fight off infections.
Prussian blue is a dye that binds to the radioactive elements cesium and thallium and helps the body excrete them. Another drug, DTPA (Diethylene Triamine Penta Acetic Acid) acts in a similar manner to help clear the body of the radioactive elements plutonium, americium and curium.