Natural radiation is all around us and comes mostly from the sun. In recent years artificial sources of radiation have increased dramatically. In the workplace and at home new technologies expose us more and more to various kinds of radiation.
Most radiation is unseen and unfelt. But we do sense some radiation. We see by the visible rays from the sun and feel the warmth of its infra-red rays. We are aware of ultraviolet rays by the way they tan our skin.
Our radiation exposures are broadly classed as either ionising or non-ionising according to how they effect body tissues. X-rays and the rays emitted by radioactive materials are ionising.
The electromagnetic radiations (EMR) associated with electricity and electronic equipment used for telecommunications are non-ionising. At least since the 1930s ionising radiation has been known to damage human health, even at extremely low exposures. Knowledge of damage of non-ionising EMR, at low exposures is more recent. Here we deal only with the ionising radiations.
Ionising Radiation Exposure | |
Naturally Occurring |
Dose (milliSv1/year) |
| cosmic rays | 0.32 |
| internal (from air, food, and water) | 1.30 |
| external (from soil and rocks) | 0.35 |
Total |
1.97 |
Artificially Created |
|
| medical exposure | 0.50 |
| fallout from nuclear testing | 0.04 |
Total |
0.54 |
| 1 - A unit of radiation. | |
As radioactive materials decay they emit alpha, beta and gamma rays. Alpha and beta rays behave as streams of particles; gamma rays are electromagnetic like X-rays though more penetrating.
Only ten out of the 92 natural elements have atoms which are radioactive. Uranium and thorium are two of these. Many more radioactive atoms would have been present when the earth was formed but most had decayed long before life evolved on earth. Today we live with a weak background of ionising radiation from natural sources (see table above).
The Nature Of Ionising Radiation
Ionising radiations are powerful enough to knock electrons out of atoms forming the molecules from which our body tissues are built.
When an atom loses an electron the molecule to which it belongs is left with an electrical charge. Electrically charged atoms and molecules are called ions hence ionising radiation. Ions react chemically with molecules in living cells causing mutations which result in cancer and immune deficiencies.
- Alpha particles carry a positive charge and travel no
more than 40 millimetres through air. They penetrate the body to just below
the dead skin. When released inside our bodies from material we breathe
or swallow, alpha rays are able to transfer their energy at short range
to damage body cells.
- Beta particles carry a negative charge; they travel about one metre through air and penetrate the skin, to reach internal tissue. Beta rays are especially dangerous when emitted inside the body.
- Gamma rays behave like X-rays in the body; having no electrical charge and being weightless they penetrate deeply into the body, or pass through it, creating ions as they collide with atoms along their path.
- Beta particles carry a negative charge; they travel about one metre through air and penetrate the skin, to reach internal tissue. Beta rays are especially dangerous when emitted inside the body.
Early History
Evidence of harm from radioactivity came soon after Marie and Pierre Curie discovered radium in 1898. They found radium reddened their skin as if from a burn. The burns were recognised as identical with those received by radiologists using X-rays. Radium began to be used to destroy cancer cells in the same way as X-rays.
Despite the dangers, doctors injected radium into patients as a cure for almost every ailment from rheumatism to heart disease to cancer. Filters were sold, through which water was passed, to make a radioactive tonic.
Doctors using radium and X-rays often suffered ulcerated hands which turned malignant and sometimes had to be amputated. Hundreds of radiologists had their lives shortened. However, while skin ulceration and other acute effects became painfully evident the latent effects of low-level radiation exposures, in the form of cancer, were to show up only decades later.
In the 1920s, women who painted watch dials with radium to make them luminous, suffered a high incidence of bone cancer.
A doctor who had been treating the women and connected their disease with their work environment found that radium was being absorbed into their bones. Here its powerful alpha rays irradiated bone marrow cells. Yet the quantity of radium in an individual's bones was found to be less than one-millionth of a gram.
A study in 1957 by Dr Alice Stewart showed that twice as many children born of mothers who were X-rayed during pregnancy, died of cancer as those children whose mothers had not been X-rayed. In 1970 Stewart showed that even one X-ray during pregnancy increased the chance of cancer in the child.
In the 1940s patients suffering from tuberculosis were administered radiation as a cure. As a result many died of leukemia.
When ringworm on childrens' scalps was treated with x-rays it resulted, in later years, in a high incidence of thyroid cancer and brain tumour. Unfortunately, x-rays are still over-used today.
A Legacy Of Radioactive Fallout
The atomic bombings of Hiroshima and Nagasaki in August 1945 brought great human suffering from exposure to high levels of gamma rays. People suffered nausea, vomiting, loss of hair, haemorrhage and destruction of the digestive system leading to loss of body fluids.
Death occurred over weeks in great agony. At lower exposures victims suffered vomiting, loss of appetite, chromosome damage, cataracts and loss of hair.
Children born of mothers pregnant at the time of the bombing suffered a high rate of microencephaly a reduction in the size of head and brain.
People in the outer areas of the two cities received low radiation exposures. In the years since the bombings the survivors' health has been closely followed. The number of deaths from cancer has been plotted against the radiation dose to individual survivors. The results of this study are used to estimate the risk of cancer from radiation exposures and for setting safety standards .
When leaders of the major powers began testing nuclear weapons they knew the fallout would damage the health of their own, and other, citizens. By the time of the signing of the Comprehensive Test Ban Treaty in 1996 the six major nuclear-weapons nations had tested around 2000 nuclear weapons. Of these 518 have been in the atmosphere, under water or in space.
The Australian government agreed, without consulting the Australian people, to the British government testing at Monte Bello Islands, Emu fields and Maralinga.
Nuclear test sites became mock radioactive battlefields to train 'atomic' soldiers for nuclear war. Some nuclear veterans developed cancer later as a result of their radiation exposures.
In 1963 the Partial Test Ban Treaty banning open-air tests came into force. Since then 1400 tests have been conducted underground around the world.
A study of the health and environmental effects of radioactive fallout by the International Physicians for the Prevention of Nuclear War has found that:
- atmospheric testing will cause 430,000 cancer deaths by year 2000 and eventually over 2 million cancer deaths.
- thousands of people downwind of the test nuclear explosions were dangerously exposed to high levels of radioactivity.
- underground testing creates large quantities of waste in highly fractured underground caverns which could one day contaminate water supplies.
Communities In Danger
In the early hours of the morning on 26 April 1986 a reactor at the Chernobyl nuclear power station, in the Ukraine, exploded. Radioactive material was blasted high into the sky. Fallout descended on Soviet farmlands and cities for hundreds of kilometres. Finer radioactive dust covered vast areas of Europe. The finest dust reached the stratosphere and descended during rain on North America.
Soviet citizen groups are preparing a Black Book compiling the human cost of the disaster.
According to Ukrainian physicist, Vladimir Chernousenko by 1990 the Black Book held 7000 names of people who had died from leukemia and birth defects. Depression of the immune system called 'Chernobyl AIDS' has reduced resistance to disease especially among children.
Ten years after the accident three million people remain exposed to dangerous radiation emanating from the long-lived strontium-90 and cesium-137 in the fallout.
In 1945 nuclear reactors at Hanford, in the United States, produced the first plutonium for nuclear weapons. Today small farming communities close to the plant are paying a high price for their country's nuclear weaponry.
Clouds of strontium-90, cesium-137 and plutonium issuing from the plant's stacks have concentrated in 'hotspots' where radiation levels can be as high as those from the Chernobyl fallout.
Of 28 families along a 'death mile', in 27 of them there has been cancer, thyroid abnormalities, a handicapped child, stillbirth or general bad health.
Far away in Rajasthan, in India, villagers living near a nuclear power station tell a similar story of woe to the Hanford community.
Since 1989 village midwives have seen a doubling of the number of miscarriages and deformed children born with no fingers, joined toes, missing genital organs and abnormal heads.
Visitors witnessed villagers suffering a rare skin disease which causes large blue lumps to grow on their bodies.
The British nuclear reprocessing plant at Sellafield isolates plutonium from radioactive wastes discharged from nuclear reactors. Millions of litres of radioactive effluent pour daily into the Irish Sea. Ocean currents have carried radioactive effluent as far as the Scandinavian coast.
Seascale village lies three kilometres from Sellafield. The village children suffer an excess of leukemia and multiple myeloma six times the national rate.
The villagers saw an obvious link with the plant but the management denied any link. Then in 1990 a research team, headed by Dr Martin Gardner, found that children of male workers at the plant had six times greater chance of developing cancer than other children.
After the release of the report worried workers were told by the plant's health officer: "Don't have a family".
The Pathways
Once released into the environment radionuclides the radioactive atoms of elements find their way into food along innumerable pathways.
In the sea small marine creatures concentrate radionuclides which have been absorbed on to seabed sediments. As predators eat their prey the radionuclides pass, in turn, from shrimps to crabs to fish, many varieties of which are eaten by humans.
Seaweeds and other algae have a remarkable capacity to concentrate radionuclides. Welsh people have been warned not to eat their traditional lava bread made from a local seaweed because it is badly contaminated by ruthenium-106.
On pastures strontium-90 and iodine-131 migrate from soil through the grass eaten by cows to milk. Cesium-137 accumulates in animals from farm fodder. Fungi and mosses concentrate radionuclides. Reindeer meat is the staple diet of Laplanders but since Chernobyl it has been highly contaminated with radionuclides from the fallout.
Radionuclides produced in a nuclear reactor behave chemically in the same way as nutrient elements, which are vital for keeping good health. Their chemical resemblance to the essential nutrients means they are taken up by the body; once in the body they follow the same metabolic pathways to particular organs as the nutrient elements.
Iodine-131 mimics natural iodine and so finds its way into the human thyroid. Here it can irradiate the tissue at close range with beta rays. Strontium-90 mimics calcium and so follows the same pathway into bone where it irradiates bone marrow.
Because it behaves like potassium cesium-137 has an affinity for muscle and other soft tissue where it could cause us to age more quickly. Plutonium mimics iron and finds its way into bone and reproductive organs.
| For information on the effects of radiation on human health
see:
Radiation Exposures - The Hidden Story of the Health Hazards Behind Official Safety Standards
Written by Les Dalton. A book which spells out the new radiation environment created by the telecommunications, medical and nuclear technologies and its effect on our health.
"Les Dalton...has described the manifold sources of non-nuclear and nuclear radiation in modern life and draws on a wide range of research to justify his claim for caution." - Irina Dunn, Sydney Morning Herald, 18 May 1991. "Most comprehensive, clear explanation of electromagnetic radiation I've ever seen...beautifully written." - Peter Hunt, ABC - Radio Science Unit. Published by Scribe in cooperation with Community Education Publication Association. Price: $24.95 Order from: Scribe Publications, P.O. Box 287, Carlton North, Vic. 3054 |
Mutation
Mutation change to the genes which determine our hereditary has become a commonplace word in our radiation age. Mutations caused by ionising radiations rarely show up as unique health effects; radiation-induced mutations cannot be distinguished from those of other causes.
Almost all mutations are harmful to health. When they occur in ordinary body cells the damage is limited to the person's body. It could mean cancer, leukemia or coronary failure.
When mutation occurs in sex cells the mutations may be passed on to future generations. This happens when Sellafield's male workers are irradiated.
No Safe Dose
The nuclear industry says that its activities cause only low radiation exposures that pose little risk.
When a doctor prescribes an X-ray, and you question its safety, he will assure you the dose is too low to do harm. In fact since Alice Stewart's studies on childhood cancers it has been known that no dose of ionising radiation is so low that it is without some risk.
We should be sure of the benefits of an exposure before taking the risk. In the case of X-rays the medical benefits may well justify exposure; nonetheless there is a risk not only to the patient but a mutation may be transmitted to his or her descendants perhaps several generations hence.
In the case of exposures from nuclear activities, since Chernobyl, the risks are being seen to outweigh any benefits.
How Safe Are Safety Standards ?
In Australia the limits of exposure to ionising radiations for workers and public are recommended by the National Health and Medical Research Council (NHMRC). The NHMRC has rubber-stamped the limits set by the International Commission on Radiological Protection (ICRP).
The ICRP set its first standard in 1934. As new evidence showed the dangers of radiation exposures the dose limit was reduced. However, once the nuclear power industry was established the ICRP came under its influence and has since resisted further reduction of dose limits despite overwhelming evidence of a need to do so.
The medical journal Lancet suggested that the ICRP's reluctance could be because it was concerned about "financial and practical consequences of a reduction" for the nuclear industry.
New data from studies on Japanese atomic bomb survivors, published in 1986, shows the cancer risk of ionising radiation to be at least five times greater than that on which the ICRP had based its 1956 dose limit.
The ICRP 1956 dose limit, for workers, was 50 milliSieverts (milliSv) and 1 milliSv for members of the public. However, despite acknowledging radiation to be five times more dangerous the ICRP reduced its limit to only 20 milliSv for workers a little less than half the previous limit. Public exposure was not reduced at all and was kept at 1 milliSv.
The dose limit should have been 10 milliSv for workers and 0.2 for members of the public.
The new limit means that the annual risk of death (from cancer) for a uranium miner is 1 in 1250, which is nearly ten times the risk of fatal injury in Australian industry generally, which is 1 in 20,000.
Even so the uranium industry has protested that the ICRP's new limits would be uneconomic for underground mining. In the Roxby mine underground miners have received up to 30 milliSv a year.
The dose limits which the NHMRC has adopted permit a health risk which is clearly unacceptable. Not only do uranium miners have a high risk imposed on them but also radiographers in industry and many workers in medical institutions.
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