The developing crisis at the Fukushima Daiichi nuclear power plant in the wake of the March 11 earthquake and tsunami has raised concerns over the health effects of radiation exposure: What is a "dangerous" level of radiation? How does radiation damage health? What are the consequences of acute and long-term low-dose radiation?
Though radioactive steam has been released to reduce pressure within the wrecked complex's reactors and there has been additional radiation leakage from the three explosions there, the resulting spikes in radiation levels have not been sustained. The highest radiation level reported thus far was a pulse of 400 millisieverts per hour at reactor No. 3, measured at 10:22 A.M. local time March 15. (A sievert is a unit of ionizing radiation equal to 100 rems; a rem is a dosage unit of x-ray and gamma-ray radiation exposure.) The level of radiation decreases dramatically as distance from the site increases. Radiation levels in Tokyo, about 220 kilometers to the southwest, have been reported to be only slightly above normal.
"We are nowhere near levels where people should be worried," says Susan M. Langhorst, a health physicist and the radiation safety officer at Washington University in Saint Louis.
According to Abel Gonzalez, vice chairman of the International Commission on Radiological Protection who studied the 1986 Chernobyl disaster, current information coming from Japan about levels of radiation leakage are incomplete at best and speculations about "worst-case scenarios" are as of yet irrelevant.
The health effects caused by radiation exposure depend on its level, type and duration.
The average person is exposed to 2 to 3 millisieverts of background radiation per year from a combination of cosmic radiation and emissions from building materials and natural radioactive substances in the environment.
The U.S. Nuclear Regulatory Commission recommends that beyond this background level, the public limit their exposure to less than an additional one millisievert per year. The U.S. limit for radiation workers is 50 millisieverts annually, although few workers are exposed to anything approaching that amount. For patients undergoing medical radiation there is no strict exposure limit—it is the responsibility of medical professionals to weigh the risks and benefits of radiation used in diagnostics and treatment, according to Langhorst. A single CT scan, for example, can expose a patient to more than one millisievert.
Radiation sickness (or acute radiation syndrome) usually sets in after a whole-body dose of three sieverts—3,000 times the recommended public dose limit per year, Langhorst says. The first symptoms of radiation sickness—nausea, vomiting, and diarrhea— can appear within minutes or in days, according to the U.S. Centers for Disease Control and Prevention. A period of serious illness, including appetite loss, fatigue, fever, gastrointestinal problems, and possible seizures or coma, may follow and last from hours to months.
Of concern in the current situation is ionizing radiation, which is produced by spontaneously decaying heavy isotopes, such as iodine 131 and cesium 137. (Isotopes are species of the same element, albeit with different numbers of neutrons and hence different atomic masses.) This type of radiation has sufficient energy to ionize atoms (usually creating a positive charge by knocking out electrons), thereby giving them the chemical potential to react deleteriously with the atoms and molecules of living tissues.
Ionizing radiation takes different forms: In gamma and x-ray radiation atoms release energetic light particles that are powerful enough to penetrate the body. Alpha and beta particle radiation is lower energy and can often be blocked by just a sheet of paper. If radioactive material is ingested or inhaled into the body, however, it is actually the lower energy alpha and beta radiation that becomes the more dangerous. That's because a large portion of gamma and x-ray radiation will pass directly through the body without interacting with the tissue (considering that at the atomic level, the body is mostly empty space), whereas alpha and beta radiation, unable to penetrate tissue, will expend all their energy by colliding with the atoms in the body and likely cause more damage.
In the Fukushima situation, the radioactive isotopes detected, iodine 131 and cesium 137, emit both gamma and beta radiation. These radioactive elements are by-products of the fission reaction that generates power in the nuclear plants.
The Japanese government has evacuated 180,000 people from within a 20-kilometer radius of the Fukushima Daiichi complex. They are urging people within 30 kilometers of the plant to remain indoors, close all windows, and to change clothes and wash exposed skin after going outside. These measures are mainly aimed at reducing the potential for inhaling or ingesting beta-emitting radioactive material.
A very high single dose of radiation (acquired within minutes can be more harmful than the same dosage accumulated over time. According to the World Nuclear Association, a single one-sievert dose is likely to cause temporary radiation sickness and lower white blood cell count, but is not fatal. One five-sievert dose would likely kill half of those exposed within a month. At 10 sieverts, death occurs within a few weeks.
The effects of long-term, low-dose radiation are much more difficult to gauge. DNA damage from ionizing radiation can cause mutations that lead to cancer, especially in tissues with high rates of cell division, such as the gastrointestinal tract, reproductive cells and bone marrow. But the increase in cancer risk is so small as to be difficult to determine without studying a very large exposed population of people. As an example, according to Langhorst, 10,000 people exposed to a 0.01-sievert whole-body dose of radiation would potentially increase the total number of cancers in that population by eight. The normal prevalence of cancer, however, would predict 2,000 to 3,300 cancer cases in a population of 10,000, so "how do you see eight excess cancers?" Langhorst asks.
According to Gonzalez, some of the emergency workers at Chernobyl received several sieverts of radiation, and many were working "basically naked" due to the heat, allowing contaminated powder to be absorbed through their skin. In comparison, the Japanese workers are most likely very well-equipped and protected at least from direct skin doses.
The Tokyo Electric Power Co. (TEPCO), the plant's owners, has evacuated most of its workers, but 50 remain at the site to pump cooling seawater into the reactors and prevent more explosions. These workers are likely exposing themselves to high levels of radiation and braving significant health risks. "As a matter of precaution, I would limit the workers' exposure to 0.1 sievert and I would rotate them," Gonzalez says. The workers should be wearing personal detectors that calculate both the rate and total dose of radiation and that set off alarms when maximum doses are reached. "If the dose of the workers start to approach one sievert then the situation is serious," he says.
The thousands of children who became sick in the aftermath of the Chernobyl disaster were not harmed from direct radiation or even from inhalation of radioactive particles, but from drinking milk contaminated with iodine 131. The isotope, released by the Chernobyl explosion, had contaminated the grass on which cows fed, and the radioactive substance accumulated in cows' milk. Parents, unaware of the danger, served contaminated milk to their children. "Certainly this will not happen in Japan," Gonzalez says.
When it comes to radiation exposure, professionals who frequently work with radioactive materials, whether in a hospital or a nuclear power plant, abide by the ALARA principle: "as low as reasonably achievable". Radiation exposure limits are conservatively set well below the levels known to induce radiation sickness or suspected of causing long-term health effects. Temporary exposure to dosages many times these limits, however, is not necessarily dangerous.
News of the U.S. Navy repositioning its warships upwind of the reactor site, the distribution of potassium iodide pills by the Japanese government, and images of officials in hazmat suits using Geiger counters to measure radiation levels among babies may stoke the public's fears—but, for now, these measures are ALARA in action, or "good extra precautions," Gonzalez says. The idea here is to always err on the side of caution.
Ionizing radiation happens when the atomic nucleus of an unstable atom decays and starts releasing ionizing particles.
When these particles come into contact with organic material, such as human tissue, they will damage them if levels are high enough, in a short period of time. This can lead to burns, problems with the blood, gastrointestinal system, cardiovascular and central nervous system, cancer, and sometimes death.
Radiation is normally managed safely, but its use also entails a risk.
If an accident happens, for example, the earthquake in Fukushima, Japan, in 2011, or the explosion at Chernobyl, Ukraine in 1986, radiation can become dangerous.
Here are some key points about radiation poisoning. More detail is in the main article.
- Radiation is all around us and it is used safely in many applications.
- Nuclear accidents, the work environment, and some medical treatment can all be sources of radiation poisoning.
- Depending on the dose, the effects of radiation can be mild or life-threatening.
- There is no cure, but barriers can prevent exposure and some medications may remove some radiation from the body.
- Anyone who believes they have been exposed to radiation should seek medical attention as soon as possible.
What is radiation poisoning?
Radiation has many uses, but it can be dangerous if it is not managed correctly.
Radiation poisoning happens when a radioactive substance gives off particles that get into a person's body and cause harm. Different radioactive substances have different characteristics. They can harm and help people in different ways, and some are more dangerous than others.
Normally, radiation occurs in a safe environment. Whether or not it becomes dangerous depends on:
- how it is used
- how strong it is
- how often a person is exposed
- what type of exposure occurs
- how long exposure lasts
A dose of radiation from a single x-ray is not normally harmful. Nevertheless, the parts of the body that are not being x-rayed will be shielded with a lead apron to prevent unnecessary exposure.
The technician, meanwhile, will leave the room when taking the image. While one small dose is not dangerous, repeated small doses could be.
A sudden, short, low dose of radiation is unlikely to cause a problem, but extended, intense, or repeated doses can be. When radiation damages cells, it is irreversible. The more often a person is exposed, the greater their risk of health problems.
How much radiation is dangerous?
Radiation dosage can measured in various ways. Some of the units used are Grays, Sieverts, rems, and rads. They are used in a similarway, but 0.1 rad is equivalent to 100 Gray.
- Below 30 rads: Mild symptoms will occur in the blood
- From 30 to 200 rads: The person may become ill.
- From 200 to 1,000 rads: The person may become seriously ill.
- Over 1,000 rads: This will be fatal.
According to the Centers for Disease Control and Prevention (CDC), radiation sickness, or acute radiation syndrome (ARS) is diagnosed when:
- A person receives over 70 rads from a source outside their body
- The dose affects the whole body, or most of it, and is able to penetrate to the internal organs
- The dose is received in a short time, usually within minutes
A person who experiences an atomic explosion will receive two doses of radiation, one during the explosion, and another from fallout, when radioactive particles float down after the explosion.
Radiation sickness can be acute, happening soon after exposure, or chronic, where symptoms appear over time or after some time, possibly years later.
The signs and symptoms of acute radiation poisoning are:
- vomiting, diarrhea, and nausea
- loss of appetite
- malaise, or feeling unwell
- rapid heartbeat
Symptoms depend on the dose, and whether it is a single dose or repeated.
A dose of as low as 30 rads can lead to:
- loss of white blood cells
- nausea and vomiting
A dose of 300 rads dose may result in:
- temporary hair loss
- damage to nerve cells
- damage to the cells that line the digestive tract
Stages of radiation sickness
Symptoms of severe radiation poisoning will normally go through four stages.
Prodomal stage: Nausea, vomiting, and diarrhea, lasting from a few minutes to several days
Latent stage: Symptoms seem to disappear, and the person appears to recover
Overt stage: Depending on the type of exposure, this can involve problems with the cardiovascular, gastrointestinal, hematopoietic, and central nervous system (CNS)
Recovery or death: There may be a slow recovery, or the poisoning will be fatal.
Hematopoietic stem cells, or bone marrow cells, are the cells that all other blood cells derive from.
Different doses, different effects
The risk of illness depends on the dose. Very low doses of radiation are all around us all the time, and they do not have any effect. It also depends on the area of the body that is exposed.
If the whole body is exposed to, say, 1,000 rads within a short time, this could be fatal. However, far higher doses can be applied to a small area of the body with less risk.
After a mild dose, the person may experience symptoms for just a few hours or days. However, a repeated or even a single, relatively low dose that produces few or no visible symptoms around the time of exposure may cause problems later on.
A person who is exposed to 3,000 rads will experience nausea and vomiting, and they may experience confusion and a loss of consciousness within a few hours. Tremors and convulsions will occur 5 to 6 hours after exposure. Within 3 days, there will be coma and death.
People who experience repeated doses, or who appear to recover, may have long-term effects.
- a loss of white blood cells, making it harder for the body to fight infection
- reduction in platelets, increasing the risk of internal or external bleeding
- fertility problems, including loss of menstruation and reduced libido
- changes in kidney function, which can lead to anemia, high blood pressure, and other problems within a few months
There may also be skin redness, cataracts, and heart problems.
Localized exposure may lead to changes in the skin, loss of hair, and possibly skin cancer.
Exposure to certain parts of the body is more dangerous than others, for example, the intestines.
The effects of radiation are cumulative. Damage to cells is irreversible.
Exposure to radiation can result from workplace exposure or an industrial accident, radiation therapy, or even deliberate poisoning, as in the case of the former Russian spy, Alexander Litvinenko, who was murdered in London by polonium 210 placed in his tea. However, this is extremely rare.
CT scans should only be carried out when necessary, as they expose a person to more radiation than is usual in everyday life.
Most people are exposed to an average of around 0.62 rads, or 620 Gray each year.
Half of this comes from radon in the air, from the Earth, and from cosmic rays. The other half comes from medical, commercial, and industrial sources. Spread over a year, this is not significant in terms of health.
Levels of radiation from an x-ray are not high, but they occur at one moment.
- A chest x-ray gives the equivalent of 10 days' exposure to radiation
- Mammogram gives the equivalent of 7 weeks' normal exposure
- PET or CT used as part of nuclear medicine exposes a person to the equivalent of 8 years of radiation
- A CT scan of the abdomen and pelvis gives the equivalent of 3 years' normal exposure
Nuclear medicine is used to target the thyroid in people with a thyroid disorder. Other types of medical treatment include radiation therapy for cancer.
Living at a higher altitude, for example, in the plateau of New Mexico and Colorado, increase exposure, as does traveling in an airplane. Radon gas in homes also contributes.
Food, too, contains small amounts of radiation. The food and water we drink is responsible for exposure to around 0.03 rads in a year.
The many activities that can expose people to sources of radiation include:
- watching television
- flying in an airplane
- passing through a security scanner
- using a microwave or cell phone
Smokers have a higher exposure than non-smokers, as tobacco contains a substance that can decay to become polonium 210.
Astronauts have the highest exposure of anyone. They may be exposed to 25 rads in one Space Shuttle mission.
Damage by radiation is irreversible. Once the cells are damaged, they do not repair themselves. Until now, there is no way for medicine to do this, so it is important for someone who has been exposed to seek medical help as soon as possible.
Possible treatments include:
- Removing all clothing,
- Rinsing with water and soap.
- Use of potassium iodide (KI) to block thyroid uptake if a person inhales or swallows too much radioiodine
- Prussian blue, given in capsules, can trap cesium and thallium in the intestines and prevent them from being absorbed. This allows them to move through the digestive system and leave he body in bowel movements.
- Filgrastim, or Neupogen, stimulates the growth of white blood cells. This can help if radiation has affected the bone marrow.
Depending on exposure, radiation can affect the whole body. For cardiovascular, intestinal, and other problems, treatment will target the symptoms.
Reducing exposure to radiation
Tips for reducing unnecessary exposure to radiation include:
- keeping out of the sun around midday and using a sunscreen or wearing clothes that cover the skin
- making sure any CT scans and x-rays are necessary, especially for children
- letting the doctor know if you are or may be pregnant before having an x-ray, PET, or CT scan
It is not possible or necessary to avoid all exposure to radiation, and the risk posed to health by most sources is extremely small.