[1]Dr Geraldine Thomas has extensive experience in studying health risks of radiation accidents. For 13 years, she has been running the Chernobyl Tissue Bank, a unique research project that has investigated the health consequences of the Chernobyl nuclear disaster, particularly with respect to the molecular pathology of the thyroid cancers associated with radiation exposure. She holds the position of professor of molecular oncology at the University of Wales and professor of molecular pathology at Imperial College London.
Q: What are the immediate symptoms of radiation sickness?
A. Very high doses of 1000 mSv are likely to result in transient nausea, and a decreased white blood cell count. 5-10 x or higher can result in death.
Nothing even approaching this has so far been seen — the highest amount which was within the confines of one of the reactors was 400mSv.
When measured at the next reactor in line this was 10x lower. Radioactivity levels fall off very quickly the further you move away from the source. The only health concerns at present are for those working in the plant, but this is minimised by ensuring a turn round of staff so radiation exposure levels to an individual remain within safe limits.
Q: What is the difference between surface and internal absorption?
A. Surface contamination is just that — particles landing on the skin. The skin acts as a good barrier (the top layer of the skin is already dead, which is why we shed skin cells all the time) and radiation from some radioisotopes will not penetrate deep into the skin. Internal absorption is from inhaling radioactive particles or ingesting them — e.g. Sucking a finger that is contaminated on the surface with radiation, or eating contaminated food.
Q: Can the radiation spread into soil, water, milk, meat, cloud etc.? How long will it then linger on?
A. Surface contamination can spread into soil, water etc. In this particular instance, there is little local produce being grown (the tsunami effectively washed away large amounts of rice fields etc) and it is winter. The Japanese drink very little milk — and milk production is likely to be away from the nuclear plant due to the evacuation. Also, the milk would be transported for sterilisation prior to being given to the population. Each radioactive isotope has a half life — the time it takes for the level of radiation to halve. For 131-I the isotope of iodine we are most concerned about in terms of heath consequences for the general population, the half life is 8 days, so within 100 days nearly all of the radiation due to this isotope has gone from the environment.
Q: What is the physiology of radiation “contamination” in an individual? How does it actually harm our body?
A. Radiation damages cells by breaking strands of DNA and by causing changes in the DNA sequence, called mutations.
If mutations accumulate over time in daughters of the damaged cells, this may result in cancer. High levels of radiation cause so many changes in the DNA that the cells effectively commit suicide, which is why we use radiation to kill cancer cells.
If this happens in the normal tissues in our bodies that have a high growth rate e.g. those of the skin, gut and bone marrow, it gives rise to acute radiation sickness, and is potentially lethal
Q: How much radiation are we naturally exposed to? How does this level compare to the radiation at Fukushima?
A. Normal rates of background radiation vary — usually of the order of 2 mSv per year. Some areas of the world (e.g. Areas of Kerala) have much higher background rates up to 10 to 15 times average background rates. A CT scan equates to about 7-8 mSv.
The recommended yearly exposure for the nuclear power industry workers is 20 mSv per year. The levels outside the exclusion zone are not much higher than background — we do not have accurate readings for inside the plant, but they are likely to be substantially higher.
Q: Can you confirm that there is no significant public health risk at this stage?
A. There is no significant risk to public health from radiation at the present time.
Q: How does this event compare to the Chernobyl disaster?
A. This does not remotely compare to the Chernobyl disaster. Chernobyl was the result of human error that resulted in a steam explosion and a fire in the graphite core of the reactor that burnt for a week. This shot large amounts of volatile isotopes such as 131-I high into the atmosphere, and this was then distributed by the prevailing wind and rainfall.
The population around Chernobyl was mildly iodide deficient, was a rural economy which relied on home grown food and milk from a cow kept in the backyard.
In Fukushima there has not been a significant release of radiation outside the plant boundary, the reactors are all still with containment intact, although pressure within this needs to be vented occasionally — hence the puffs of steam. There must be some damage to the reactors themselves as we have slight leaks of radiation in the vented steam. There has been no other significant release.
The Japanese have an iodine-rich diet, do not each much dairy and have nowhere to grow crops locally due to the tsunami. Please note that even if there was a Chernobyl-style accident, the only health consequence is likely to be thyroid cancer from radioiodine in those who are very young at exposure.
Thyroid cancer is treatable. However, the measures put in place by the Japanese should protect the population even against this.
They have learnt from Chernobyl.
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