Dictionary Thesaurus Word Dynamo Quotes Reference Translator Spanish

Radiation poisoning

Radiation poisoning, also called "radiation sickness" or a "creeping dose", is a form of damage to organ tissue due to excessive exposure to ionizing radiation. The term is generally used to refer to acute problems caused by a large dosage of radiation in a short period, though this also has occurred with long term exposure to low level radiation. Many of the symptoms of radiation poisoning occur as ionizing radiation interferes with cell division. This interference allows for treatment of cancer cells; such cells are among the fastest-dividing in the body, and may be destroyed by a radiation dose that adjacent normal cells are likely to survive.

The clinical name for "radiation sickness" is acute radiation syndrome as described by the CDC. A chronic radiation syndrome does exist but is very uncommon; this has been observed among workers in early radium source production sites and in the early days of the Soviet nuclear program. A short exposure can result in acute radiation syndrome; chronic radiation syndrome requires a prolonged high level of exposure.

The use of radionuclides in science and industry is strictly regulated in most countries (in the U.S. by the Nuclear Regulatory Commission). In the event of an accidental or deliberate release of radioactive material, either evacuation or sheltering in place will be the recommended measures.

Measuring radiation dosage

The rad is a unit of absorbed radiation dose defined in terms of the energy actually deposited in the tissue. One rad is an absorbed dose of 0.01 joules of energy per kilogram of tissue. The more recent SI unit is the gray (Gy), which is defined as 1 joule of deposited energy per kilogram of tissue. Thus one gray is equal to 100 rad.

To accurately assess the risk of radiation, the absorbed dose energy in rad is multiplied by the relative biological effectiveness (RBE) of the radiation to get the biological dose equivalent in rems. Rem stands for "Röntgen equivalent in man." In SI units, the absorbed dose energy in grays is multiplied by the same RBE to get a biological dose equivalent in sieverts (Sv). The sievert is equal to 100 rem.

The RBE is a "quality factor," often denoted by the letter Q, which assesses the damage to tissue caused by a particular type and energy of radiation. For alpha particles Q may be as high as 20, so that one rad of alpha radiation is equivalent to 20 rem. The Q of neutron radiation depends on their energy. However, for beta particles, x-rays, and gamma rays, Q is taken as one, so that the rad and rem are equivalent for those radiation sources, as are the gray and sievert. See the sievert article for a more complete list of Q values.

Acute (short-term) vs chronic (long-term) effects

Radiation sickness is generally associated with acute exposure and has a characteristic set of symptoms that appear in an orderly fashion. The symptoms of radiation sickness become more serious (and the chance of survival decreases) as the dosage of radiation increases. These effects are described as the deterministic effects of radiation.

Longer term exposure to radiation, at doses less than that which produces serious radiation sickness, can induce cancer as cell-cycle genes are mutated. If a cancer is radiation-induced, then the disease, the speed at which the condition advances, the prognosis, the degree of pain, and every other feature of the disease are not functions of the radiation dose to which the sufferer is exposed.

Since tumors grow by abnormally rapid cell division, the ability of radiation to disturb cell division is also used to treat cancer (see radiotherapy), and low levels of ionizing radiation have been claimed to lower one's risk of cancer (see hormesis).

Exposure

External vs internal exposure

External

External exposure is exposure which occurs when the radioactive source (or other radiation source) is outside (and remains outside) the organism which is exposed. Below are a series of three examples of external exposure.

A person who places a sealed radioactive source in their pocket
A space traveller who is irradiated by cosmic rays
A person who is treated for cancer by either teletherapy or brachytherapy. While in brachytherapy the source is inside the person it is still external exposure because the active part of the source never comes into direct contact with the biological tissues of the person.

One of the key points is that external exposure is often relatively easy to estimate, and if the irradiated objects do not become radioactive (except for a case where the radiation is an intense neutron beam which causes activation of the object). It is possible for an object to be contaminated on the outer surfaces, assuming that no radioactivity enters the object it is still a case of external exposure and it is normally the case that decontamination is easy (wash the surface).

Internal

Internal exposure is when the radioactive material enters the organism, and the radioactive atoms become incorporated into the organism. Below are a series of examples of internal exposure.

The exposure due to ⁴⁰K present within a normal person.
The exposure to the ingestion of a soluble radioactive substance, such as ⁹⁰Sr in cow’s milk.
A person who is being treated for cancer by means of an open source radiotherapy method where a radioisotope is used as a drug. A review of this topic was published in 1999. Because the radioactive material becomes intimately mixed with the affected object it is often difficult to decontaminate the object or person in a case where internal exposure is occurring. While some very insoluble materials such as fission products within a uranium dioxide matrix might never be able to truly become part of an organism, it is normal to consider such particles in the lungs as a form of internal contamination which results in internal exposure. The reasoning is that the particles have entered via an orifice and can not be removed with ease from what the lay person (non biologist) would regard as within the animal. It is important to note that strictly speaking the contents of the digestive tract and the air within the lungs are outside the body of a mammal.

Nuclear warfare

Nuclear warfare is more complex because a person can be irradiated by at least three processes. The first (the major cause of burns) is not caused by ionizing radiation.

Thermal burns from infrared heat radiation.
Beta burns from shallow ionizing radiation (this would be from fallout particles; the largest particles in local fallout would be likely to have very high activities because they would be deposited so soon after detonation and it is likely that one such particle upon the skin would be able to cause a localised burn); however, these particles are very weakly penetrating and have a short range.
Gamma burns from highly penetrating radiation. This would likely cause deep gamma penetration within the body, which would result in uniform whole body irradiation rather than only a surface burn. In cases of whole body gamma irradiation (circa 10 Gy) due to accidents involving medical product irradiators, some of the human subjects have developed injuries to their skin between the time of irradiation and death.

In the picture on the right, the normal clothing that the woman was wearing would have been unable to attenuate the gamma radiation and it is likely that any such effect was evenly applied to her entire body. Beta burns would be likely all over the body due to contact with fallout, but thermal burns are often on one side of the body as heat radiation does not penetrate the human body. In addition, the pattern on her clothing has been burnt into the skin. This is because white fabric reflects more infra-red light than dark fabric. As a result, the skin close to dark fabric is burned more than the skin covered by white clothing.

There is also the risk of internal radiation poisoning by ingestion of fallout particles.

Nuclear reactor accidents

Radiation poisoning was a major concern after the Chernobyl reactor accident. It is important to note that in humans the acute effects were largely confined to the accident site . Thirty-one people died as an immediate result .

Of the 100 million curies (4 exabecquerels) of radioactive material, the short lived radioactive isotopes such as ¹³¹I Chernobyl released were initially the most dangerous. Due to their short half-lives of 5 and 8 days they have now decayed, leaving the more long-lived ¹³⁷Cs (with a half-life of 30.07 years) and ⁹⁰Sr (with a half-life of 28.78 years) as main dangers.

Other accidents

Improper handling of radioactive and nuclear materials lead to radiation release and radiation poisoning. The most serious of these, due to improper disposal of a medical device containing a radioactive source (teletherapy), occurred in Goiânia, Brazil in 1987.

Ingestion and inhalation

When radioactive compounds enter the human body, the effects are different from those resulting from exposure to an external radiation source. Especially in the case of alpha radiation, which normally does not penetrate the skin, the exposure can be much more damaging after ingestion or inhalation. The radiation exposure is normally expressed as a committed effective dose equivalent (CEDE).

Deliberate poisoning

On November 23, 2006, Alexander Litvinenko died due to suspected deliberate poisoning with polonium-210. . His is the first case of confirmed death due to such a cause, although it is also known that there have been other cases of attempted assassination such as in the cases of KGB defector Nikolay Khokhlov and journalist Yuri Shchekochikhin where radioactive thallium was used. In addition, an incident occurred in 1990 at Point Lepreau Nuclear Generating Station where several employees acquired small doses of radiation due to the contamination of water in the office watercooler with tritium contaminated heavy water

Prevention

The best prevention for radiation sickness is to minimize the dose suffered by the human, or to reduce the dose rate.

Time

The longer that humans are subjected to radiation the larger the dose will be. The advice in the nuclear war manual entitled "Nuclear War Survival Skills" published by Cresson Kearny in the U.S. was that if one needed to leave the shelter then this should be done as rapidly as possible to minimize exposure.

In chapter 12 he states that "Quickly putting or dumping wastes outside is not hazardous once fallout is no longer being deposited. For example, assume the shelter is in an area of heavy fallout and the dose rate outside is 400 R/hr enough to give a potentially fatal dose in about an hour to a person exposed in the open. If a person needs to be exposed for only 10 seconds to dump a bucket, in this 1/360th of an hour he will receive a dose of only about 1 R. Under war conditions, an additional 1-R dose is of little concern."

In peacetime radiation workers are taught to work as quickly as possible when performing a task which exposes them to irradiation. For instance, the recovery of a lost radiography source should be done as quickly as possible.

text{Dose} propto t

Shielding

By placing a layer of a material which will absorb the radiation between the source and the human, the dose and dose rate can be reduced. For instance, in the event of a nuclear war, it would be a good idea to shelter within a building with thick stone walls (Fallout shelter). During the height of the cold war, fallout shelters were identified in many urban areas. It is interesting to note that, under some conditions, shielding can increase the dose rate. For instance, if the electrons from a high energy beta source (such as ³²P) strike a lead surface, X-ray photons will be generated (radiation produced in this way is known as bremsstrahlung). It is best for this reason to cover any high Z materials (such as lead or tungsten) with a low Z material such as aluminium, wood, plastic. This effect can be significant if a person wearing lead-containing gloves picks up a strong beta source. Also, gamma photons can induce the emission of electrons from very dense materials by the photoelectric effect; again, by covering the high Z material with a low Z material, this potential additional source of exposure to humans can be avoided. Furthermore, gamma rays can scatter off a dense object; this enables gamma rays to "go around corners" to a small degree. Hence, to obtain a very high protection factor, the path in/out of the shielded enclosure should have several 90 degree turns rather than just one.

Reduction of incorporation into the human body

Potassium iodide (KI), administered orally immediately after exposure, may be used to protect the thyroid from ingested radioactive iodine in the event of an accident or terrorist attack at a nuclear power plant, or the detonation of a nuclear explosive. KI would not be effective against a dirty bomb unless the bomb happened to contain radioactive iodine, and even then it would only help to prevent thyroid cancer.

Fractionation of dose

While Devair Alves Ferreira received a large dose during the Goiânia accident of 7.0 Gy, he lived while his wife received a dose of 5.7 Gy and died. The most likely explanation is that his dose was fractionated into many smaller doses which were absorbed over a length of time, while his wife stayed in the house more and was subjected to continuous irradiation without a break, giving her body less time to repair some of the damage done by the radiation. In the same way, some of the people who worked in the basement of the wrecked Chernobyl plant received doses of 10 Gy, but in small fractions, so the acute effects were avoided.

It has been found in radiation biology experiments that if a group of cells are irradiated, then as the dose increases, the number of cells which survive decreases. It has also been found that if a population of cells is given a dose before being set aside (without being irradiated) for a length of time before being irradiated again, then the radiation causes less cell death. The human body contains many types of cells and the human can be killed by the loss of a single type of cells in a vital organ. For many short term radiation deaths (3 days to 30 days), the loss of cells forming blood cells (bone marrow) and the cells in the digestive system (microvilli which form part of the wall of the intestines are constantly being regenerated in a healthy human) causes death.

In the graph below, dose/survival curves for a hypothetical group of cells have been drawn, with and without a rest time for the cells to recover. Other than the recovery time partway through the irradiation, the cells would have been treated identically.

Treatment

Treatment reversing the effects of irradiation is currently not possible. Anaesthetics and antiemetics are administered to counter the symptoms of exposure, as well as antibiotics for countering secondary infections due to the resulting immune system deficiency.

There are also a number of substances used to mitigate the prolonged effects of radiation poisoning, by eliminating the remaining radioactive materials, post exposure.

Whole body vs. part of body exposure

In the case of a person who has had only part of their body irradiated then the treatment is easier, as the human body can tolerate very large exposures to the non-vital parts such as hands and feet, without having a global effect on the entire body. For instance, if the hands get a 100 Sv dose which results in the body receiving a dose (averaged over your entire body of 5 Sv) then the hands may be lost but Radiation poisoning would not occur. The resulting injury would be described as localized radiation burn.

As described below, one of the primary dangers of whole-body exposure is immunodeficiency due to the destruction of bone marrow and consequent shortage of white blood cells. It is treated by maintaining a sterile environment, bone marrow transplants, and blood transfusions.

Chelation therapy can be useful to an extent if radiation poisoning is caused by the presence of heavy fissionable materials (e.g. radium or plutonium) in the bloodstream.

Experimental treatments designed to mitigate the effect on bone marrow

Neumune, an androstenediol, was introduced as a radiation countermeasure by the US Armed Forces Radiobiology Research Institute, and was under joint development with Hollis-Eden Pharmaceuticals until March, 2007. Neumune is in Investigational New Drug (IND) status and Phase I trials have been performed.

Some work has been published in which Cordyceps sinensis, a Chinese Herbal Medicine has been used to protect the bone marrow and digestive systems of mice from whole body irradation.

Table of exposure levels and symptoms

Dose-equivalents are presently stated in sieverts:

0.05–0.2 Sv (5–20 REM)

No symptoms. Potential for cancer and mutation of genetic material, according to the LNT model: this is disputed (Note: see hormesis). A few researchers contend that low dose radiation may be beneficial. 50 mSv is the yearly federal limit for radiation workers in the United States. In the UK the yearly limit for a classified radiation worker is 20 mSv. In Canada and Brazil, the single-year maximum is 50 mSv, but the maximum 5-year dose is only 100 mSv. Company limits are usually stricter so as not to violate federal limits.

0.2–0.5 Sv (20–50 REM)

No noticeable symptoms. Red blood cell count decreases temporarily.

0.5–1 Sv (50–100 REM)

Mild radiation sickness with headache and increased risk of infection due to disruption of immunity cells. Temporary male sterility is possible.

1–2 Sv (100–200 REM)

Light radiation poisoning, 10% fatality after 30 days (LD 10/30). Typical symptoms include mild to moderate nausea (50% probability at 2 Sv), with occasional vomiting, beginning 3 to 6 hours after irradiation and lasting for up to one day. This is followed by a 10 to 14 day latent phase, after which light symptoms like general illness and fatigue appear (50% probability at 2 Sv). The immune system is depressed, with convalescence extended and increased risk of infection. Temporary male sterility is common. Spontaneous abortion or stillbirth will occur in pregnant women.

2–3 Sv (200–300 REM)

Moderate radiation poisoning, 35% fatality after 30 days (LD 35/30). Nausea is common (100% at 3 Sv), with 50% risk of vomiting at 2.8 Sv. Symptoms onset at 1 to 6 hours after irradiation and last for 1 to 2 days. After that, there is a 7 to 14 day latent phase, after which the following symptoms appear: loss of hair all over the body (50% probability at 3 Sv), fatigue and general illness. There is a massive loss of leukocytes (white blood cells), greatly increasing the risk of infection. Permanent female sterility is possible. Convalescence takes one to several months.

3–4 Sv (300–400 REM)

Severe radiation poisoning, 50% fatality after 30 days (LD 50/30). Other symptoms are similar to the 2–3 Sv dose, with uncontrollable bleeding in the mouth, under the skin and in the kidneys (50% probability at 4 Sv) after the latent phase.

4–6 Sv (400–600 REM)

Acute radiation poisoning, 60% fatality after 30 days (LD 60/30). Fatality increases from 60% at 4.5 Sv to 90% at 6 Sv (unless there is intense medical care). Symptoms start half an hour to two hours after irradiation and last for up to 2 days. After that, there is a 7 to 14 day latent phase, after which generally the same symptoms appear as with 3-4 Sv irradiation, with increased intensity. Female sterility is common at this point. Convalescence takes several months to a year. The primary causes of death (in general 2 to 12 weeks after irradiation) are infections and internal bleeding.

6–10 Sv (600–1,000 REM)

Acute radiation poisoning, near 100% fatality after 14 days (LD 100/14). Survival depends on intense medical care. Bone marrow is nearly or completely destroyed, so a bone marrow transplant is required. Gastric and intestinal tissue are severely damaged. Symptoms start 15 to 30 minutes after irradiation and last for up to 2 days. Subsequently, there is a 5 to 10 day latent phase, after which the person dies of infection or internal bleeding. Recovery would take several years and probably would never be complete.

Devair Alves Ferreira received a dose of approximately 7.0 Sv (700 REM) during the Goiânia accident and survived, partially due to his fractionated exposure.

10–50 Sv (1,000–5,000 REM)

Acute radiation poisoning, 100% fatality after 7 days (LD 100/7). An exposure this high leads to spontaneous symptoms after 5 to 30 minutes. After powerful fatigue and immediate nausea caused by direct activation of chemical receptors in the brain by the irradiation, there is a period of several days of comparative well-being, called the latent (or "walking ghost") phase. After that, cell death in the gastric and intestinal tissue, causing massive diarrhea, intestinal bleeding and loss of water, leads to water-electrolyte imbalance. Death sets in with delirium and coma due to breakdown of circulation. Death is currently inevitable; the only treatment that can be offered is pain therapy.

Louis Slotin was exposed to approximately 21 Sv in a criticality accident on 21 May 1946, and died nine days later on 30 May.

More than 50 Sv (>5,000 REM)

A worker receiving 100 Sv (10,000 REM) in an accident at Wood River, Rhode Island, USA on 24 July 1964 survived for 49 hours after exposure, and an operator receiving between 60 and 180 Sv (18,000 REM) to his upper body in an accident at Los Alamos, New Mexico, USA on 30 December 1958 survived for 36 hours; details of this accident can be found in the journal "Los Alamos Science", Number 23 (1995).

History

What may be the earliest confirmed cases of acute radiation poisoning occurred in 1879 in Barry County, Missouri, where three men were fatally poisoned and a fourth permanently injured under mysterious circumstances. After chasing an animal they were hunting to the mouth of a cave, they discovered what the cave appeared to be several large veins of silver. They returned the next day to begin prospecting, but fled when they began to fall ill; by the time they had left, one of them was so ill that he was paralyzed and had to be carried to aid. In 1912, after the discovery of radium was announced, a local entrepreneur who had recalled the story investigated the cave to find that the metal was in fact radium, the first isolated veins of the metal ever found (previously, radium was only known from samples extracted from uranium-bearing pitchblende ore). The mine would be the first in the world to be excavated specifically for radium.

Although radiation was discovered in late 19th century, the dangers of radioactivity and of radiation were not immediately recognized. Acute effects of radiation were first observed in the use of X-rays when the Serbo-Croatian-American electric engineer Nikola Tesla intentionally subjected his fingers to X-rays in 1896. He published his observations concerning the burns that developed, though he attributed them to ozone rather than to X-rays. His injuries healed later.

The genetic effects of radiation, including the effects on cancer risk, were recognized much later. In 1927 Hermann Joseph Muller published research showing genetic effects, and in 1946 was awarded the Nobel prize for his findings.

Before the biological effects of radiation were known, many physicians and corporations had begun marketing radioactive substances as patent medicine and radioactive quackery. Examples were radium enema treatments, and radium-containing waters to be drunk as tonics. Marie Curie spoke out against this sort of treatment, warning that the effects of radiation on the human body were not well understood (Curie later died from aplastic anemia assumed due to her work with radium, but later examination of her bones showed that she had been a careful laboratory worker and had a low burden of radium. A more likely cause was her exposure to unshielded X-ray tubes while a volunteer medical worker in WWI). Eben Byers, a famous American socialite, died in 1932 after consuming large quantities of radium over several years; his death drew public attention to dangers of radiation. By the 1930s, after a number of cases of bone necrosis and death in enthusiasts, radium-containing medical products had nearly vanished from the market.

Nevertheless, dangers of radiation weren't fully appreciated by scientists until later. In 1945 and 1946, two U.S. scientists died from acute radiation exposure in separate criticality accidents. In both cases, victims were working with large quantities of fissile materials without any shielding or protection.

Atomic bombings of Hiroshima and Nagasaki resulted in a large number of incidents of radiation poisoning, allowing for greater insight into its symptoms and dangers.