Tuesday, 5 April, 2011
The Japanese authorities have announced that radiation levels surrounding the Fukushima Daiichi nuclear power plant are increasing to potentially harmful levels. New Scientist investigates the health risks associated with nuclear power plant explosions.
How do nuclear accidents impact health?
Apart from the damage caused by fires and explosions, accidents also release radioactive materials which can cause radiation sickness. Radiation exposure above a certain threshold, usually only received by workers and emergency teams in a stricken plant, causes acute radiation syndrome within hours of exposure. Depending on the dose of radiation this ranges from skin rashes, vomiting and diarrhoea, to coma and death.
Radiation damages DNA, especially as it assembles in dividing cells. That means tissues which contain many dividing cells, such as the gut lining, skin and bone marrow, are most at risk of damage. High enough doses also damage brain cells and such doses are invariably fatal.
Less severe damage can be treated, however. Gut damage disturbs fluid balance and can lead to blood infection; marrow damage means no blood cells are produced for clotting and fighting infection. If those problems can be managed, people can be kept alive long enough for gut and marrow to regenerate. A cloned human hormone that boosts white blood cell production sometimes helps; there is little else.
Fears of nuclear terrorism have recently inspired more funding for research into new treatments, most aiming to limit cell death in damaged tissues.
What radioactive elements are being released at the Fukushima Daiichi nuclear power plant?
As nuclear cores melt down, reacting nuclear fuel creates many different radioactive elements, all with different toxic effects. Results from previous accidents at nuclear power plants suggest that inert gases such as xenon and krypton are likely to be released, together with iodine-131, two isotopes of caesium, and possibly strontium, tellurium and rubidium.
What effect do these elements have on the body?
Exposure to any radioactive material is bad: the US Nuclear Regulatory Commission assumes that exposure to anything higher than normal background levels increases health risks.
Xenon and krypton are not retained by the body so they have little effect.
Iodine-131 and caesium are more damaging, however. Iodine is actively taken up by the thyroid gland to make hormones. If iodine-131, which emits beta particles, is taken up, this can damage DNA and cause thyroid cancer.
Following the Chernobyl nuclear reactor explosion in Ukraine in 1986, more than 6000 people developed thyroid cancer, probably after drinking contaminated milk as children, according to an investigation by the UN released in February. For unknown reasons iodine-131 does not seem to affect adults.
These cancers can be prevented if children are given pills containing the non-radioactive isotope of iodine soon after exposure. These saturate the thyroid with safe iodine and stop it taking up the radioactive kind. Most children did not get these pills after Chernobyl. They are now being distributed in Japan.
Vast amounts of caesium-137 were distributed across 40 per cent of Europe's surface after Chernobyl. Environmental levels remain elevated in wildlife, with restrictions still in place on eating some sheep farmed in the UK, and game and mushrooms from elsewhere. However, exposure to environmental caesium-137 from Chernobyl has never been linked conclusively to any direct health effects in people, although researchers are divided over whether there is no effect, or just not enough data to say.
How do the nuclear reactor explosions happening in Japan compare to previous nuclear disasters?
The crisis at the Fukushima Daiichi nuclear power plant is the worst nuclear accident since Chernobyl in Ukraine in 1986. However, so far it seems more likely to resemble the Three Mile Island (TMI) accident in Pennsylvania in 1979 which, like Fukushima, lost coolant and had a partial meltdown.
So far, the release of radioactivity at Fukushima appears to be closer to what happened at TMI than at Chernobyl. The huge plume of smoke from Chernobyl spread radiation over most of Europe and forced evacuation within a 30-kilometre radius. The gases that escaped TMI, in contrast, might have travelled as far as New York state, but most stayed within 15 kilometres of the plant.
US authorities have found little evidence of any health damage after TMI. But Joseph Mangano of the Radiation and Public Health Project, a pressure group, claims that deaths from disease have been 26 to 54 per cent higher among young people who were fetuses or babies living downwind of the accident than among local but less exposed people.
He blames the absence of a solid conclusion on poor data on where radionuclides went, and who was exposed to how much. The same arguments will dog Fukushima, unless the data collection is better this time.