Health

Published: Sunday March 20, 2011 MYT 12:00:00 AM
Updated: Friday September 27, 2013 MYT 12:22:47 PM

The dangers of radiation exposure

A nuclear meltdown will primarily affect the areas around its site, although the effects can linger on for generations.

I RECEIVED an sms from a friend on Monday, purporting to be a BBC news flash. It read (sic): “Japan govt confirms radiation leak at fukushima nuclear plants. Asian countries should take necessary precautions.

“Remain indoors first 24 hrs. Close doors n windows. Swab neck skin with betadine where thyroid area is, radiation hits thyroid first.

“Take extra precaution, radiation may hit phil at startng 4pm 2day.”

I knew it was a hoax straight away.

Firstly, because based on the latest news reports from Japan, it seemed highly unlikely that the leaked radiation particles had reached a high enough level to pose a danger to the Philippines.

As of Friday, the levels have not yet reached hazardous levels even in Tokyo, located 240km south of the Fukushima Dai-Ichi nuclear power plant.

And secondly, because swabbing betadine – an antiseptic containing iodine – over the thyroid area does nothing whatsoever to prevent radiation poisoning.

However, I can see how many people would believe in the message as most people would be unlikely to know much about radiation in general.

Effects of radiation

The Oxford Advanced Learners Dictionary (7th edition) gives one of the definitions of radiation as “powerful and very dangerous rays that are sent out from radioactive substances”.

Radioactive substances are elements that have unstable nuclei. The instability of these nuclei causes them to naturally decay, or deteriorate, over time. During this process, radiation is produced and released from the substance.

The more potentially harmful types of radiation include X-rays, high frequency ultraviolet rays, beta (ß) rays and gamma (γ) rays, among others. Their danger lies in the fact that they can penetrate through our body – and for some rays, even through concrete – and affect our cells.

According to Universiti Malaya Professor of Medical Physics Dr Ng Kwan Hoong, radiation has two effects on the DNA in our cells.

“The rays can break the double-helix of DNA directly, or indirectly produce free radicals that affect our DNA to create cancer cells,” he says. He adds that this damage results in two consequences.

The first one occurs when someone is exposed to high levels of radiation for a short time, and develops acute radiation syndrome. An example of this would be the workers at the Chernobyl Nuclear Power Plant, Ukraine, when the infamous nuclear accident occurred in 1986.

The high levels of radiation these workers were exposed to caused their cells to die, and resulted in their deaths, within hours or days.

The second one happens when someone is chronically exposed to radiation, like the inhabitants of the areas around Chernobyl, who continued to receive lower, but still dangerous, levels of radiation over a long period of time.

In such cases, radiation causes genetic mutations that increase the chances of developing cancers, or causes physical or mental defects that are inheritable.

According to Bergonie and Tribondeau’s law of radiosensitivity, undifferentiated cells that reproduce themselves rapidly are the most radiosensitive, or vulnerable to these effects. (See Radiosensitive cells)

The effects of radiation on these cells result in the symptoms of radiation sickness. For example, the effect on embryonic cells results in birth defects, the effect on epithelial cells (that line most of our organs) results in nausea, vomiting and diarrhoea, and the effect on white blood cells decreases our ability to fight off infections.

There is no cure for radiation sickness. As Prof Ng says: “Once ingested, the (radioactive) particle remains inside the body. There is no way to neutralise it.”

Although the radioactive substance will decay over time and disappear from the body, its effects will continue to affect the body throughout that entire time, and beyond.

Away from the actual source of the nuclear explosion, radioactive particles need to be swallowed or breathed in to affect the body.

That is why in cases of exposure, people are advised to remove their clothes and bathe themselves, as this will remove most of the particles from their bodies.

The medical management for the condition is supportive, meaning that doctors treat the symptoms of the sickness to make the patient more comfortable and allow the body time to recover itself, not the cause of it.

Nuclear meltdown

The main worry now for the Fukushima nuclear power plant is the ability of the emergency workers there to keep the overheating reactors cool enough.

Failure to do so could result in either the rods containing the radioactive materials overheating and melting, or exposure of the rods to the atmosphere, where they can catch fire and explode.

In the event of a nuclear meltdown, the key concern would be whether the containment structure would be able to hold the radioactive substances within it, or leak them into the surrounding environment.

An explosion caused by exposure of radioactive substances to the atmosphere would throw out those substances into the atmosphere and surrounding environment.

Anyone unfortunate enough to be on or near the site of the explosion will be directly exposed to the radiation rays that can penetrate the body.

However, for those further away, the potential damage will be caused by radioactive particulates thrown into the atmosphere and surrounding environment.

Prof Ng says that in the case of a nuclear fallout, there are two main radioisotopes that people will be exposed to – caesium-137 (Cs-137) and iodine-131 (I-131).

These are the two radioactive elements that will spread the furthest because of their volatility, or ability to change from solid or liquid to gas easily.

The danger from these two substances comes not so much from direct exposure (unless you are on or near the plant itself), but through consuming food and drinks that are contaminated with them across a period of time.

For example, the substances can settle on grass consumed by cows, which produce contaminated milk for human consumption, or are themselves eaten as beef. This chain of events results in the radioactive particles ending up in the human body, where it stays until it decays.

Prof Ng explains: “Caesium-137 is water-soluble and chemically toxic in small amounts. It has a long half-life of about 30 years.

“After entering the body, caesium is quite uniformly distributed throughout the body, with higher concentrations in muscles and lower in bones.

“The biological half-life of caesium is rather short at about 70 days.”

The half-life of a radioactive substance is the amount of time taken for half of the amount of the substance to decay.

Meanwhile, he explains that non-radioactive iodine in our daily food is absorbed by the body and concentrated in the thyroid glands for its proper functioning.

“When radioactive I-131 is present in high levels in the environment from radioactive fallout, it can be absorbed through contaminated food, and will also accumulate in the thyroid glands.

“As it decays, the radiation emitted may cause damage to the thyroid. The main risk from exposure to high levels of I-131 is the induction of radiogenic thyroid cancer in one’s later life,” he says.

That is why the Japanese government has supplied potassium iodide pills to the inhabitants nearest to the Fukushima plant as a preventive measure.

The idea is to saturate the thyroid gland with the non-radioactive iodine in the pills, so that the gland will not be able to take up the radioactive iodine if the person consumes or inhales it.

However, Prof Ng adds that as iodine is continually being excreted by the body, the pills need to be taken regularly as long as the risk of exposure to radioactive iodine is present.

Constant exposure

The million-ringgit question is, of course, will Malaysia be affected in the worst case scenario of a nuclear meltdown at the Fukushima plant?

Prof Ng says no. “Based on the dilution principle, by the time any radioactive particles get here, they will not pose a danger to the population.”

The fact is, we are being exposed to radiation all the time.

We receive an average of two to three millisieverts (mSv) of radiation a year from natural sources like the sun, granite rock, natural radon gas and others. (A sievert is the SI unit measuring the biological effect of radiation exposure by an ionising radiation source undergoing an energy loss of one joule per kilogram of body tissue.)

Many medical imaging procedures, like X-rays and CT scans, also involve the necessary exposure of patients to radiation.

However, the risk of being negatively affected by these procedures is far outweighed by the benefits of being able to visualise the body parts necessary for diagnostic and therapeutic purposes. (See Regular radiation risks)

Prof Ng quoted Medical University of South Carolina Professor of Radiology Dr G. Donald Frey, who once said: “It would be a tragedy if someone did not have a medical imaging procedure that might save his or her life, or alter the course of treatment, solely because of concern over the effects of radiation.”

He adds that current radiation protection recommendations are based on the Linear No Threshold (NLT) hypothesis.

This hypothesis assumes that even the lowest, near-zero dose of radiation can be detrimental, that the risk per unit dose is constant and incremental, and that the risk can only increase with dose; thus, erring on the side of caution.

For example, while the maximum allowed limit for radiation exposure for those working with radioactive materials is 20mSv per year, an investigation will be launched once a worker’s dose badge shows signs of being exposed to one-third of that amount.

Prof Ng also points out that the chances of radiation workers dying from exposure is about one in 20,000, as compared to one in 200 for those who smoke 10 cigarettes a day and one in 10,000 from road accidents.

He says that while the effects of high doses of radiation are known through studies on those exposed to such levels by nuclear accidents and atom bomb survivors, among others, the effects of low doses of radiation are only extrapolations from the known data on high doses.

“We usually assume that all doses of radiation, no matter how small, increase the risk of stochastic effects such as cancer; however, it is very difficult, perhaps impossible, to prove this,” he says.

Tags / Keywords: Health, Lifestyle, Health, radiation, effects, exposure

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