Radiation & Health
See also the detailed paper by Nuclear Radiologist Dr Peter Karamoskos, 2010, 'Nuclear power & public health', choosenuclearfree.net/health
RADIATION AND HEALTH
Anti-nuclear & Clean Energy (ACE) Campaign
Friends of the Earth, Australia, foe.org.au/anti-nuclear
The weight of scientific opinion holds that there is no threshold below which ionising radiation poses no risk of inducing fatal cancers.
Radiation protection agencies establish dose limits for radiation exposure from nuclear facilities but there is no pretence (from radiation protection agencies, at least) that radiation doses below these levels are without risk.
Moreover, as scientific understanding of the effects of ionising radiation has advanced, permitted dose limits have been dramatically reduced. For workers, the permitted dose has decreased by a factor of 25:
* 500 millisieverts (mSv) p.a. in 1934
* 150 mSv in 1950
* 50 mSv in 1956
* 20 mSv (averaged over five years) in 1991.
In 2009 the International Commission on Radiological Protection concluded that radon gas delivers almost twice the radiation dose to humans as originally thought. Previous dose estimates to miners need to be approximately doubled to accurately reflect the lung cancer hazard.
In Australia, the maximum permitted dose is 1 mSv for members of the public (in addition to background radiation which is typically of the order of 2 mSv p.a.)
Linear no-threshold risk model
Radiation protection agencies around the world, including the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), all base regulations on the linear no-threshold model which assumes that there is no threshold below which radiation exposure is safe.
Uncertainties will always persist because of methodological difficulties. In circumstances where people are exposed to low-level radiation, epidemiological studies are unlikely to be able to demonstrate increased cancer rates because of the 'statistical noise' in the form of widespread cancer incidence from many causes, as well as other methodological difficulties. A report by the US Committee on the Biological Effects of Ionising Radiation (BEIR 2005) illustrates the point − it estimated that one out of 100 people exposed to 100 mSv of radiation over a lifetime would probably develop cancer as a result of that exposure, but that 42 cancers can be expected in the same group from causes other than radiation exposure.
"Firstly, health effects such as cancer due to radiation exposure often take decades to develop. Secondly, cancers due to radiation exposure are indistinguishable from any other cancer. Thirdly, radioisotopes can travel great distances. Therefore epidemiological studies investigating the effects of a particular radiation exposure are necessarily very long, they may involve many countries if not continents, and they are extraordinarily complex.
"Add to this the fact that cancer is a common disease in any event, and the result is that a small percentage increase in cancer rates due to radiation exposure can readily be overlooked, even when the absolute number of cancers caused by radiation exposure may be very large.
"A further source of misleading research results is the mixing, inadvertently or knowingly, of data for populations exposed to quite different levels of radiation, for example after a nuclear accident. The results for heavily exposed populations may then be 'diluted' by results for much less exposed populations and the results overall will appear reassuringly low."
Committee on the Biological Effects of Ionising Radiation
Notwithstanding the methodological problems, there is growing scientific confidence in the linear no-threshold model. An important study was the 2005 report of the Committee on the Biological Effects of Ionising Radiation of the US National Academy of Sciences (BEIR 2005). The BEIR report comprehensively reviewed available data and supports the linear no-threshold risk model.
The BEIR Committee states:
"The Committee judges that the balance of evidence from epidemiologic, animal and mechanistic studies tend to favor a simple proportionate relationship at low doses between radiation dose and cancer risk."
"... the risk of cancer proceeds in a linear fashion at lower doses without a threshold and ... the smallest dose has the potential to cause a small increase in risk to humans."
Richard Monson, Chair of the BEIR Committee and professor of epidemiology at the Harvard School of Public Health, said: "The scientific research base shows that there is no threshold of exposure below which low levels of ionizing radiation can be demonstrated to be harmless or beneficial. The health risks − particularly the development of solid cancers in organs − rise proportionally with exposure. At low doses of radiation, the risk of inducing solid cancers is very small. As the overall lifetime exposure increases, so does the risk."
The 2005 BEIR report noted that uncertainty remains because of the unavoidable methodological difficulties: "It should be noted however, that even with the increased sensitivity the combined analyses are compatible with a range of possibilities, from a reduction of risk at low doses to risks twice those upon which current radiation protection recommendations are based."
The BEIR Committee explicitly rejected claims that ionising radiation can be beneficial to health: "The assumption that any stimulatory hormetic effects from low doses of ionizing radiation will have a significant health benefit to humans that exceeds potential detrimental effects from the radiation exposure is unwarranted."
Other scientists and scientific bodies have reached similar conclusions. A 2010 report by the United Nations Scientific Committee on the Effects of Atomic Radiation states that "the current balance of available evidence tends to favour a non-threshold response for the mutational component of radiation-associated cancer induction at low doses and low dose rates."
Likewise, a study published in the Proceedings of the National Academy of Sciences (US) in 2003 concluded that: "Given that it is supported by experimentally grounded, quantifiable, biophysical arguments, a linear extrapolation of cancer risks from intermediate to very low doses currently appears to be the most appropriate methodology."
And to give one more example (there are many), the OECD's Nuclear Energy Agency states: "There is a threshold level of radiation exposure (or dose) below which no acute damage is observed. However, there is now a substantial body of evidence which shows that cancers can be caused by radiation even at dose levels that are below this threshold. " (1997, 'Radiation in Perspective: Applications, Risks and Protection')
Misinformation arising from methodological problems
The difficulty of demonstrating health impacts from low-level radiation exposure is used by nuclear proponents as the basis for an endless stream of self-serving, disingenuous and scientifically-indefensible statements.
The industry-funded Uranium Information Centre (UIC) ignored predicted deaths from low-level radiation to claim that nuclear power is far safer than alternative energy sources including hydro. Yet the United Nations Scientific Committee on the Effects of Atomic Radiation estimated the collective effective dose to the world population over a 50-year period of operation of nuclear power reactors and associated nuclear facilities to be two million person-Sieverts. Applying the standard risk estimate to that level of radiation exposure gives a total of 80,000 fatal cancers. Of course, applying risk estimates (with their uncertainties) to dose estimates (with their margin of error) is less than precise. But the nuclear industry's solution − to pretend that its emissions have no impact whatsoever − is dishonest.
To give one further example, the UIC states: "According to authoritative UN figures, the Chernobyl death toll is 56 (31 workers at the time, more since and 9 from thyroid cancer)." However, detailed UN reports in 2005-06 estimated 9,000 cancer deaths due to Chernobyl among the people who worked on the clean-up operations, evacuees and residents of the highly and lower-contaminated regions in Belarus, the Russian Federation and Ukraine. Other, credible scientific studies (listed here) estimate a long-term cancer death toll across Europe ranging from 16,000 to 93,000. Using a standard risk estimate (0.05 cancer deaths per person-Sievert of low-dose exposure to ionising radiation) and the International Atomic Energy Agency's estimate of total exposure (600,000 person-Sieverts) gives an estimated 30,000 cancer deaths from Chernobyl.
Uranium mining and cancer
Uranium mine workers are exposed to radiation from the ore itself and from the inhalation of radon gas. The waste ore and tailings from uranium mining pose a public health hazard well into the future.
There is a well established link between uranium mining and lung cancer. The BEIR VI report reviewed eleven studies of 60,000 underground uranium miners. It reported 2,600 deaths from lung cancer, eight of which were uranium mines in Europe, North America, Asia and Australia. The report found an increasing frequency of lung cancer in miners. This was directly proportional to the cumulative amount of radon the miners had been exposed to.
In addition to exposure to radon gas, uranium miners are also exposed to gamma radiation directly from the radioactive ore. At the Olympic Dam underground uranium and copper mine, the total annual dose per miner is approximately 6 mSv, of which 2−4 mSv are due to radon gas (allowing for the new ICRP risk estimate for radon) and the balance due to gamma radiation. Workers at the smelter at the Olympic Dam mine receive annual doses that may exceed 12mSv.
Toro Energy promotes dangerous radiation junk science
In May, 45 medical doctors working in Australia released a statement calling on would-be uranium miner Toro Energy to stop promoting the dangerous and scientifically-indefensible claim that low-level radiation is beneficial to human health. Not a single doctor or radiation expert spoke up in defence of Toro Energy.
In a media interview, Toro Energy claimed that "we've actually supported different views, scientific views, about the health effects of radiation" and that Doug Boreham (a radiation junk scientist) "is not the only scientist that we support or have supported in the past in terms of sponsorship to conferences". However there is no evidence for those claims and Toro Energy ignored repeated requests to supply evidence − perhaps the company was simply lying to cover up its promotion of dangerous radiation junk science.
Dr Peter Karamoskos, 2010, 'Nuclear power & public health', choosenuclearfree.net/health
Medical Association for Prevention of War: mapw.org.au/nuclear-chain/radiation
A 100 mSv threshold for radiation effects?
One of the lies peddled by nuclear apologists - including James Hansen - is that radiation doses below 100 millisieverts are harmless. This paper by Dr Ian Fairlie gives the lie to those lies ...
A 100 mSv threshold for radiation effects?
November 27, 2012
In recent years, some scientists have promoted the view that there are no observable effects from radiation below 100 mSv, usually in their criticisms of the Linear No Threshold theory. However, many studies show radiation effects well below 100 mSv.
Some useful papers:
PowerPoint presentation on uranium mining, radiation and health by Clive Rosewarne from the Public Health Association of Australia (NT)
Science says ...
The National Council on Radiation Protection says, “every increment of radiation exposure produces an incremental increase in the risk of cancer.”
The US Environmental Protection Agency says, “any exposure to radiation poses some risk, i.e. there is no level below which we can say an exposure poses no risk.”
The US Department of Energy says about “low levels of radiation” that “… the major effect is a very slight increase in cancer risk.”
The US Nuclear Regulatory Commission says, “any amount of radiation may pose some risk for causing cancer ... any increase in dose, no matter how small, results in an incremental increase in risk.”
The National Academy of Sciences, in its “Biological Effects of Ionizing Radiation VII,” says, “it is unlikely that a threshold exists for the induction of cancers ….”
Even Low-Level Radioactivity Is Damaging, Scientists Conclude
University of South Carolina, 13 Nov 2012, 'Even low-level radioactivity is damaging, scientists conclude. ScienceDaily', www.sciencedaily.com /releases/2012/11/121113134224.htm
Even the very lowest levels of radiation are harmful to life, scientists have concluded in the Cambridge Philosophical Society's journal Biological Reviews. Reporting the results of a wide-ranging analysis of 46 peer-reviewed studies published over the past 40 years, researchers from the University of South Carolina and the University of Paris-Sud found that variation in low-level, natural background radiation was found to have small, but highly statistically significant, negative effects on DNA as well as several measures of health.
The review is a meta-analysis of studies of locations around the globe that have very high natural background radiation as a result of the minerals in the ground there, including Ramsar, Iran, Mombasa, Kenya, Lodeve, France, and Yangjiang, China. These, and a few other geographic locations with natural background radiation that greatly exceeds normal amounts, have long drawn scientists intent on understanding the effects of radiation on life. Individual studies by themselves, however, have often only shown small effects on small populations from which conclusive statistical conclusions were difficult to draw.
"When you're looking at such small effect sizes, the size of the population you need to study is huge," said co-author Timothy Mousseau, a biologist in the College of Arts and Sciences at the University of South Carolina. "Pooling across multiple studies, in multiple areas, and in a rigorous statistical manner provides a tool to really get at these questions about low-level radiation."
Mousseau and co-author Anders Møller of the University of Paris-Sud combed the scientific literature, examining more than 5,000 papers involving natural background radiation that were narrowed to 46 for quantitative comparison. The selected studies all examined both a control group and a more highly irradiated population and quantified the size of the radiation levels for each. Each paper also reported test statistics that allowed direct comparison between the studies.
The organisms studied included plants and animals, but had a large preponderance of human subjects. Each study examined one or more possible effects of radiation, such as DNA damage measured in the lab, prevalence of a disease such as Down's Syndrome, or the sex ratio produced in offspring. For each effect, a statistical algorithm was used to generate a single value, the effect size, which could be compared across all the studies.
The scientists reported significant negative effects in a range of categories, including immunology, physiology, mutation and disease occurrence. The frequency of negative effects was beyond that of random chance.
"There's been a sentiment in the community that because we don't see obvious effects in some of these places, or that what we see tends to be small and localized, that maybe there aren't any negative effects from low levels of radiation," said Mousseau. "But when you do the meta-analysis, you do see significant negative effects."
"It also provides evidence that there is no threshold below which there are no effects of radiation," he added. "A theory that has been batted around a lot over the last couple of decades is the idea that is there a threshold of exposure below which there are no negative consequences. These data provide fairly strong evidence that there is no threshold -- radiation effects are measurable as far down as you can go, given the statistical power you have at hand."
Mousseau hopes their results, which are consistent with the "linear-no-threshold" model for radiation effects, will better inform the debate about exposure risks. "With the levels of contamination that we have seen as a result of nuclear power plants, especially in the past, and even as a result of Chernobyl and Fukushima and related accidents, there's an attempt in the industry to downplay the doses that the populations are getting, because maybe it's only one or two times beyond what is thought to be the natural background level," he said. "But they're assuming the natural background levels are fine."
"And the truth is, if we see effects at these low levels, then we have to be thinking differently about how we develop regulations for exposures, and especially intentional exposures to populations, like the emissions from nuclear power plants, medical procedures, and even some x-ray machines at airports."
Anders P. Møller, Timothy A. Mousseau. The effects of natural variation in background radioactivity on humans, animals and other organisms. Biological Reviews, 2012; DOI: 10.1111/j.1469-185X.2012.00249.x
No safe dose
By Dr Bill Williams, 12 December 2006, www.onlineopinion.com.au/view.asp?article=5249&page=0
The recent zeal among conservative politicians for expanding Australia’s nuclear industry should raise questions about its potential impact on the health of humans and their habitat. Unfortunately, the recently released Switkowski Report on Uranium Mining Processing and Nuclear Energy brings little serious critical analysis to bear on the subject.
We exist in a naturally radioactive environment: the rocks and mountains, the sun in particular, produce a “background” level. Average exposure to “background” ionizing radiation worldwide is measured at 2.4 millisievert (mSv) a year. About half of this is from radon gas and its decay products.
However, human activities in the past century have greatly increased our exposure to ionizing radiation, through atomic weapons development, testing and use, as well as uranium-mining and nuclear electricity generation. The ongoing atmospheric fallout from the nuclear weapons testing in the 50s and 60s adds an average extra dose to us all of 0.02mSv per year.
These doses are estimated to have already resulted in 430,000 additional fatal cancers worldwide by the year 2000, and a total of 2.4 million extra cancer deaths long-term.
Unfortunately there is no level of radiation exposure below which we are at zero risk: even low-level medical exposures such as chest X-rays (0.04mSv per test) carry a quantifiable risk of harm. While high doses of ionizing radiation will cause greater health damage, even low doses are associated with adverse environmental and human consequences.
Using the “linear no-threshold” risk model, the 2005 US National Academy of Sciences Committee on the Biological Effects of Ionizing Radiation (BEIR VII) estimated:
- over a lifetime, a dose of 1mSv creates an excess risk of cancer of approximately 1 in 10,000. Higher doses are associated with proportionately higher risk, for example a dose of 100mSv would cause 1 in 100 people to develop cancer;
- approximately 1 individual in 100 persons would be expected to develop cancer from a lifetime (70 years) exposure just to background x and gamma rays (excluding radon and other high LET radiations)
It should be noted that while these are average risks, the risks in vulnerable groups of the population may be considerably higher. BEIR VII assessed women as having about twice the radiation risk for solid cancer incidence as men, and 38 per cent higher cancer mortality risk than men.
Children are at even greater risk - radiation during infancy for boys results in three to four times the cancer risk as between 20 to 50 years of age, and female infants have double the risk of boys.
Ionizing radiation causes damage to the DNA in living cells. Atoms and molecules become ionized or excited, which can produce free radicals, break chemical bonds, produce new chemical bonds and cross-linkage between macromolecules and damage molecules that regulate vital cell processes such as DNA, RNA and proteins.
In recent years biologists have identified specific radiation-induced damage at the molecular level to nucleotide sequences on chromosomal DNA, including double-strand breaks, large deletions and sister chromatid exchange.
The cell can repair certain levels of damage in its chromosomal DNA: at low doses cellular damage is usually repaired. However, faulty repairs may lead to cell death or to proliferation of abnormal cells which form a cancer.
At higher levels, cell death results. At extremely high doses, cells cannot be replaced quickly enough, and tissues fail to function; this can result in massive cell death, organ (particularly bone marrow and gut) damage and death to the individual.
Radiation effects are often categorised by when they appear.
The prompt effects include radiation sickness and radiation burns. High doses delivered to the whole body within short periods of time can produce effects such as blood component changes, fatigue, diarrhoea, nausea and death. These effects will develop within hours, days or weeks, depending on the size of the dose. The larger the dose, the sooner a given effect will occur.
When radiation effects are delayed, DNA abnormalities are passed on to subsequent generations of cells, where the abnormal coding can lead to tissue abnormalities, including cancers.
Cancer development is a multistage process, and is similar for radiation-associated cancers as for spontaneous cancers or those associated with exposure to other carcinogens.
Low dose radiation appears to act principally on the early stages of cancer initiation, whereas for higher doses, effects on later stages of cancer promotion and progression are also likely. Genetic disorders associated with deficiencies in the ability to repair DNA damage and in tumour-suppressor type genes (which normally suppress cancer development) increase the radiation cancer risk.
Mutational events at key points such as “proto-oncogene” or “suppressor gene” sites provide a credible mechanism for radiation-induced malignant (cancerous) transformation.
Such cancers will take many cell generations to develop, so it may be several decades before they are detected.
The delay enables polluters to avoid responsibility for the disease-promoting properties of radiation. This avoidance is amplified by the fact that leukemia and other cancers induced by radiation are indistinguishable from those that result from other causes.
Ionising radiation is also responsible for serious reproductive effects through prenatal exposure. Rapidly proliferating and differentiating tissues are most sensitive to radiation damage, so radiation exposure can produce developmental problems, particularly in the developing brain, when the fetus is exposed in the womb.
The developmental conditions most commonly associated with prenatal radiation exposure include low birth weight, microcephaly, mental retardation, and other neurological problems.
Long-term, inter-generational genetic effects are also possible if the damage to the DNA code occurs in a reproductive cell (egg or sperm) whereby the coding error may be passed on to offspring … resulting potentially in birth defects and cancers in the children.
While many plant and animal experiments leave no doubt that radiation exposure can alter genetic material and cause disease, and human data also show DNA and chromosomal damage associated with exposure to ionizing radiation, a resultant effect on genetic diseases has not yet been observed in the case of the Hiroshima and Nagasaki survivors.
This does not mean that there is no such effect in humans. It may be that there were genetic abnormalities produced that were incompatible with life and those pregnancies therefore ended in miscarriage. It may also be that an increased rate of genetic abnormalities will be found in future generations, that is, the changes will skip one or more generations. Radiation-induced genetic damage is likely to manifest mainly as multi-system developmental abnormalities.
Evidence has emerged recently that the cell may also exhibit the phenomenon of “genomic instability”, where the progeny of an irradiated cell may unexpectedly become highly susceptible to general mutation and damage is detected only after several cell divisions. This may also occur in the progeny of cells close to the cell which is traversed by the radiation track but which themselves are not directly hit (“bystander effect”).
This phenomenon has been reproduced several times in laboratory studies of human cells but has not been confirmed in living humans. Such studies would necessarily need to be extraordinarily long. However if the theory of induced genetic instability is correct, then the human gene pool could be permanently altered.
Radiation health authorities use scientific modelling to calculate and set “permissible limits” for ionizing radiation exposure. As the scientific techniques have become more sophisticated, the recommended exposures for the public and the workforce have steadily been reduced: levels once regarded as “safe” are now known to be associated with cancers, bone marrow malignancies and genetic effects.
The dose limits recommended in 1991 by the International Commission on Radiological Protection (ICRP) which are most widely used internationally are more than 12 times lower that those recommended in the early 1950s at the time of the first British nuclear test explosions in Australia.
The growing scientific literature refining our understanding of the pathogenic properties of ionising radiation has dramatically increased pressure on the nuclear industry to reduce radiation exposures.
However, in their rush to give the thumbs-up to nukes, the Prime Minister’s team of “experts”, led by former Telstra chief and ex-nuclear physicist Ziggy Switkowski, make light of the health burden attributable to the nuclear industry.
They are silent on the recent study published in the British Medical Journal which revealed that a cumulative exposure for adult workers in the nuclear industry of 100mSv - the current recommended five-year occupational dose limit - would lead to a 10 per cent increase in mortality from all cancers, and a 19 per cent increased mortality from leukemia (of types other than chronic lymphatic leukemia).
They are silent on multiple reported and controversial clusters of childhood cancers and congenital malformations in the vicinity of nuclear reactors and other nuclear facilities.
They frequently assert a record of “good management” in the Australian nuclear industry to date: a clear misrepresentation in view of hundreds of instances of mismanagement (leaks, spills, contamination, regulatory breaches) at Ranger, Olympic Dam and Beverly and the total failure of either industry or regulators to monitor health impacts in local populations despite known distribution of radio-toxins into habitat and food chain.
The Switkowski Report does not provide either “a factual base” or “an analytical framework” for discussion: it gives a whitewash to a complex and controversial subject. Not only is it likely to exacerbate Australia’s greenhouse emissions by vociferously promoting the nuclear non-solution, but it endangers Australians long-term by threatening to expand an industry whose toxic legacy will continue for many generations.
Dr Bill Williams is a GP in rural Victoria. He is the Vice President of the Medical Association of the Prevention of War and Board Member of the International Campaign to Abolish Nuclear Weapons.
Ionizing radiation, health effects and protective measures
World Health Organisation
Fact sheet No.371, November 2012, http://www.who.int/mediacentre/factsheets/fs371/en/index.html
Ionizing radiation is a type of energy released by atoms in the form of electromagnetic waves or particles.
People are exposed to natural sources of ionizing radiation, such as in soil, water, vegetation, and in human-made sources, such as x-rays and medical devices.
Ionizing radiation has many beneficial applications, including uses in medicine, industry, agriculture and research.
As the use of ionizing radiation increases, so does the potential for health hazards if not properly used or contained.
Acute health effects such as skin burns or acute radiation syndrome can occur when doses of radiation exceed certain levels.
Low doses of ionizing radiation can increase the risk of longer term effects such as cancer.
What is ionizing radiation?
Ionizing radiation is a type of energy released by atoms that travels in the form of electromagnetic waves (gamma or X-rays) or particles (neutrons, beta or alpha). The spontaneous disintegration of atoms is called radioactivity, and the excess energy emitted is a form of ionizing radiation. Unstable elements which disintegrate and emit ionizing radiation are called radionuclides.
All radionuclides are uniquely identified by the type of radiation they emit, the energy of the radiation, and their half-life.
The activity — used as a measure of the amount of a radionuclide present — is expressed in a unit called the becquerel (Bq): one becquerel is one disintegration per second. The half-life is the time required for the activity of a radionuclide to decrease by decay to half of its initial value. The half-life of a radioactive element is the time that it takes for one half of its atoms to disintegrate. This can range from a mere fraction of a second to millions of years (e.g. iodine-131 has a half-life of 8 days while carbon-14 has a half-life of 5730 years).
People are exposed to natural radiation on a daily basis. Natural radiation comes from many sources including more than 60 naturally-occurring radioactive materials found in soil, water and air. Radon, a naturally-occurring gas, emanates from rock and soil and is the main source of natural radiation. Every day, people inhale and ingest radionuclides from air, food and water.
People are also exposed to natural radiation from cosmic rays, particularly at high altitude. On average, 80% of the annual dose that a person receives of background radiation is due to naturally occurring terrestrial and cosmic radiation sources. Background radiation levels vary due to geological differences. Exposure in certain areas can be more than 200 times higher than the global average.
Human exposure to radiation also comes from human-made sources ranging from nuclear power generation to medical uses of radiation diagnosis or treatment. Today, the most common human-made sources of ionizing radiation are X-ray machines and other medical devices.
Type of exposure
Radiation exposure may be internal or external, and can be acquired through various exposure pathways.
Internal exposure to ionizing radiation occurs when a radionuclide is inhaled, ingested or otherwise enters into the bloodstream (e.g. injection, wounds). Internal exposure stops when the radionuclide is eliminated from the body, either spontaneously (e.g. through excreta) or as a result of a treatment.
External contamination may occur when airborne radioactive material (dust, liquid, aerosols) is deposited on skin or clothes. This type of radioactive material can often be removed from the body by simply washing.
Exposure to ionizing radiation can also result from external irradiation (e.g. medical radiation exposure to X-rays). External irradiation stops when the radiation source is shielded or when the person moves outside the radiation field.
Health effects of ionizing radiation
Radiation damage to tissue and/or organs depends on the dose of radiation received, or the absorbed dose which is expressed in a unit called the gray (Gy). The potential damage from an absorbed dose depends on the type of radiation and the sensitivity of different tissues and organs.
The sievert (Sv) is a unit of radiation weighted dose also called the effective dose. It is a way to measure ionizing radiation in terms of the potential for causing harm. The Sv takes into account the type of radiation and sensitivity of tissues and organs. The Sv is a very large unit so it is more practical to use smaller units such as millisieverts (mSv) or microsieverts (Sv). There are one thousand Sv in one mSv, and one thousand mSv in one Sv. In addition to the amount of radiation (dose), it is often useful to express the rate at which this dose is delivered (dose rate) e.g. Sv/hour or mSv/year.
Beyond certain thresholds, radiation can impair the functioning of tissues and/or organs and can produce acute effects such as skin redness, hair loss, radiation burns, or acute radiation syndrome. These effects are more severe at higher doses and higher dose rates. For instance, the dose threshold for acute radiation syndrome is about 1 Sv (1000 mSv).
If the dose is low or delivered over a long period of time (low dose rate), there is greater likelihood for damaged cells to successfully repair themselves. However, long-term effects may still occur if the cell damage is repaired but incorporates errors, transforming an irradiated cell that still retains its capacity for cell division. This transformation may lead to cancer after years or even decades have passed. Effects of this type will not always occur, but their likelihood is proportional to the radiation dose.
This risk is higher for children and adolescents, as they are significantly more sensitive to radiation exposure than adults.
Epidemiological studies on populations exposed to radiation (for example atomic bomb survivors or radiotherapy patients) showed a significant increase of cancer risk at doses above 100 mSv.
Prenatal exposure to ionizing radiation may induce brain damage in foetuses following an acute dose exceeding 100 mSv between weeks 8-15 of pregnancy and 200 mSv between weeks 16-25 of pregnancy. Before week 8 or after week 25 of pregnancy human studies have not shown radiation risk to fetal brain development. Epidemiological studies indicate that cancer risk after fetal exposure to radiation is similar to the risk after exposure in early childhood.
Radiation exposure in nuclear emergencies
Radioactive material may be released into the environment during an emergency in a nuclear power plant (NPP). The radionuclides of greatest concern to human health are iodine and caesium.
Occupational exposure, either internally or externally, of rescuers, first responders, and NPP workers is likely to occur during the emergency response. It may result in radiation doses high enough to cause acute effects such as skin burns or acute radiation syndrome.
Those living in closer vicinity to a NPP can be externally exposed to radionuclides present in a radioactive cloud or deposited on the ground. They can also be externally contaminated by radioactive particles deposited on skin or clothes. Internal exposure may take place if radionuclides are inhaled, ingested, or enter an open wound.
The general population is not likely to be exposed to doses high enough to cause acute effects, but they may be exposed to low doses which could result in increased risk of long-term effects like cancer. Consumption of contaminated food and/or water contributes to overall radiation exposure.
If radioactive iodine is released into the environment and enters the body through inhalation or ingestion, it will concentrate in the thyroid gland increasing the risk of thyroid cancer. The risk of thyroid cancer is higher in children than adults, particularly those under 5 years, and those whose diets are generally deficient in iodine.
Protective health actions in nuclear emergencies
During nuclear emergencies, public health protective actions may be implemented to limit radiation exposure and associated health risks.
In the early phase of an emergency (within the first few hours/days), urgent protective actions should be implemented to prevent radiation exposure, taking into account projected doses that people may received in the short-term (e.g. effective dose within 2-7 days, thyroid dose within one week). Decisions are based on NPP conditions, amount of radioactivity actually or potentially released into the atmosphere, prevailing meteorological conditions (e.g. wind speed and direction, precipitation), and other factors. Local authorities may announce urgent actions including evacuation, sheltering indoors, and the administration of non-radioactive iodine.
Evacuation is most effective when used as a precautionary action before an airborne release takes place. Sheltering indoors (e.g. homes, schools, and office buildings) can also significantly reduce exposure to the radioactive material released and dispersed.
The administration of non-radioactive iodine can prevent the uptake of radioactive iodine by the thyroid gland. When potassium iodide (KI) pills are taken before or shortly after exposure, they saturate the thyroid gland to reduce the dose and risk of thyroid cancer. KI pills do not protect against external radiation, or against any other radioactive substances apart from radioactive iodine.
Potassium iodide pills should be taken only when instructed by competent authorities. It is important to follow dosage recommendations, especially for children. Pregnant women should take KI pills when instructed by competent authorities to protect their thyroid and the thyroid of the fetus. When instructed, breastfeeding women should also take KI pills to protect themselves, and give KI to the breastfed baby following recommended dosages.
Food, water and agricultural countermeasures may be implemented to reduce radiation exposure during the early phase of an emergency (e.g. restricting consumption of water, and locally produced food and dairy products).
Mental health support to manage acute stress after a nuclear event can speed recovery and prevent long-term consequences such as post-traumatic stress disorder or other persistent mental health disorders. Reactions may be intense and prolonged with profound emotional impact, particularly in children.
As environmental and human monitoring data increase, other protective actions may be implemented, including relocation of people to temporary housing or in some cases, permanent resettlement. These protective actions are implemented taking into account the doses that a population may receive over the long-term (e.g. effective dose during one year). Food and water monitoring programmes should be established to inform longer-term decisions on food restriction, water consumption, and the control of internationally traded foodstuffs.
The recovery phase may last for a considerable period. Cessation of protective measures should be linked to environmental, food and human health monitoring and based on a risk-benefit analysis. Appropriate long-term follow-up programmes should be established to assess public health consequences and the need for any subsequent actions.