The level of dose is critical in determining the outcome for those affected, writes MUIRIS HOUSTON
EXPOSURE TO radiation, depending on the amount and the source, may be hazardous to human health. One of the pioneers of radiology, Marie Curie, paid the ultimate price from continuous exposure to early X-ray machines. In the 1986 Chernobyl nuclear power plant accident, 32 workers died from radiation-related injuries.
Radiation may affect the person exposed, including possible teratogenic effects on a foetus, or it could manifest itself in the exposed individual’s children through genetic damage.
What are the health risks posed by the damaged reactors at the Fukushima nuclear plant? Some 170,000 people have been evacuated from a 20km area (12.4 miles) around the plant, while latest reports suggest there were up to 260 people within a 10km radius when radiation levels rose and some 22 people are reported to have been contaminated following an explosion and partial reactor meltdown.
In terms of risk to the general public, radioactive iodine and caesium are the two elements of primary concern. Iodine-131 has a half-life of eight days; when it is absorbed by the body it accumulates in the thyroid gland. Located in the neck, the thyroid regulates our metabolism. But when radioactive iodine accumulates in the gland it causes cancer. The risk is greatest in children.
By administering potassium iodide, levels of iodine in the thyroid are topped up, thus preventing the accumulation of the radioactive material.
In the longer term, the greater threat to health is caesium-137, which has a half-life of 30 years. This element still contaminates the area around the Chernobyl plant in Ukraine. It is water-soluble and chemically similar to potassium and therefore mimics how potassium is metabolised. After entering the body, caesium-137 can damage cells, leading to an increased risk of cancer.
The total dose from environmental radiation of natural origin is about 2.2 millisieverts (mSv) per annum. Following an acute whole body exposure of 500 mSv to 2Sv, a risk for nuclear plant workers, nausea and vomiting are likely. At levels of 6Sv or greater, headache and a fever develop, in addition to gastrointestinal symptoms. And when a person is acutely exposed to multiples of 10Sv convulsion and death are inevitable.
Radiation causes inflammation of the lungs (pneumonitis), which in turn leads to fibrosis (scarring). Different parts of the gastrointestinal tract differ in their sensitivity to radiation: the oesophagus (gullet) and rectum are relatively radio-resistant, while the stomach and small intestine are much more sensitive. Radiation damage to the lens in the eye may cause a cataract some years after exposure.
But bone marrow is the main area of concern. White cells, manufactured in the marrow, are especially sensitive to depletion and may drop to 50 per cent of normal levels within 48 hours of exposure. Platelet levels also drop so the person may develop both spontaneous bleeding and infection.