How nuclear radiation affects health

What is a "dangerous" radiation level? How is radiation harmful to health? What are the immediate and long-term consequences of low-dose radiation exposure?

Before the Scientific American article, a few updates as of Friday evening.

The Japanese government has raised the rating of the disaster in Fukushima from level 4 to level 5 on the seven-level international scale. Level 4 means an accident with local consequences, while level 5 is about consequences over a wide area. A hazard level of 5 was recorded in 1979 on Three Mile Island in Pennsylvania where the reactor core melted. In Chernobyl, the fault was defined as level 7.

The engineers of the Tokyo Electric Company managed to connect power lines to the cooling system, which made it possible to renew the cooling in one of the reactors. The kilometer-long cable connected the local electricity grid to reactor number 2. The electricity will also be turned on after the seawater spraying on reactor number 3 is finished. According to the company, once the electricity is connected, it will activate several pumps that will flow water to the reactors and the ponds where the nuclear fuel is located, thus reducing the heat inside the reactor .
The International Atomic Energy Commission said that the reactors are now stable, although there is still a danger that things will get worse.

By Nina Bai, Scientific American website.

The developing crisis surrounding the Fukushima Daiichi power plant in Japan After being severely damaged by the earthquake that occurred on March 11, 2011 and the tsunami that followed it raises alarming questions regarding the health effects of exposure to radioactive radiation: What is a "dangerous" level of radiation? How is radiation harmful to health? What are the immediate and long-term consequences of low-dose radiation exposure?

Even though radioactive steam was released from the reactors to reduce the pressure inside them and despite the leakage of radiation following the explosions that occurred at the station, the sharp increases in the level of radiation were not prolonged. The highest level of radiation reported so far was in a burst of radiation emitted from Reactor 3 on March 15 at 10:22 Japan time, and its level reached 400 millisieverts (a unit of radioactive absorption in the body). The radiation level drops sharply when you move away from the damaged facilities. According to reports, radiation levels in Tokyo, about 220 kilometers southwest of the power plant, did not rise much above normal.

"We are not approaching alarming levels of radiation," says Susan M. Langhorst, a health physicist and radiation safety officer at Washington University in St. Louis, US.

According to Abel Gonzalez, the vice president of the International Commission on Radiological Protection, which investigated the Chernobyl disaster that happened in 1986, the information now coming from Japan about the levels of the leaking radiation is missing information at best, so the wild speculations regarding "horror scenarios" are still not relevant.

The health effects of radiation depend on its level, the type of radiation and the duration of exposure.

Radiation level:

An average person absorbs an average of 0.2 to 0.3 millisieverts of background radiation each year. The background radiation results from a combination of cosmic radiation coming from space and emissions from building materials and natural radioactive materials in the environment.

The American Nuclear Regulatory Commission recommends that the public avoid exposure to more than 1 millisievert per year beyond the background radiation. The United States limits personnel working near radioactive radiation to 50 millisieverts per year, although very few even come close to that level. There is no absolute upper limit applicable to patients receiving radiation therapy. The responsibility for determining the pros and cons of using radiation in such treatment falls on the medical staff depending on the diagnosis of the disease and the type of treatment, says Langhorst. A single CT scan, for example, may expose the subject to more than 1 millisievert of radiation.

Radiation sickness (or acute radiation syndrome) is caused when the whole body is exposed to a dose at the level of 3 sieverts, that is, 3,000 times the recommended limit for the public per year, says Langhorst. The US Centers for Disease Control states that the symptoms of radiation sickness, nausea, vomiting and diarrhea, can arise a few minutes to a few days after exposure to radiation. The period of severe illness, which causes, among other things, loss of appetite, fatigue, fever, stomach and intestinal problems and even coma attacks, may last from hours to months.

Type of radiation:

The radiation that is now worrying in Japan is ionizing radiation that is created by the spontaneous decay of heavy atoms such as iodine 131 and cesium 137. The radiation is called ionizing because it has enough energy to ionize atoms (that is, to change their charge, usually by removing electrons). Such ionization of atoms and molecules in living tissues can be dangerous.

There are different types of ionizing radiation. Gamma radiation and X-rays (X-rays) is electromagnetic radiation, or invisible light, capable of penetrating the body. Alpha radiation and beta radiation, consists of particles whose permeability is low and sometimes it is possible to block them even with a cardboard board. However, if radioactive material is inhaled into the lungs or swallowed inside the body, it is precisely the alpha particles and these cells, whose energy is less, that are more dangerous. The reason for this is that most gamma and X-rays simply pass through the body without affecting the tissues (because at the subatomic level most of the body is actually empty space). Conversely, alpha and cell particles that are unable to penetrate through the tissues will lose their energy by colliding with the atoms in the body, and will therefore cause more damage.

In Fukushima, the radioactive materials detected, iodine 131 and cesium 137 emit both gamma radiation and beta radiation. These radioactive atoms are the products of the fission reactions used to generate electricity in the reactor.

The Japanese government evacuated 180,000 people from their homes within a 20 kilometer radius of the Fukushima Daiichi power plant. She recommends that people within a 30-kilometer radius stay at home or in a closed place, close the windows, change clothes and wash exposed skin when they come in from outside. These measures are designed to reduce the risk of inhaling and swallowing radioactive material that emits radiation in the cell.

Duration of exposure:

A short and very high dose of radiation (which affects for a few minutes) may be more harmful than the same amount of radiation absorbed by the body over time. According to the World Nuclear Association, a single exposure to radiation at a level of 1 Sievert can cause transient radiation sickness and lower white blood cell counts, but not death. A single dose at the level of 5 sieverts will kill half of those exposed to it within one month. A level of 10 sievert kills within weeks.

It is much more difficult to estimate the effects of prolonged exposure to a low level of radiation. Damage to DNA may cause mutations that may lead to cancer, especially in tissues where cell division is vigorous, such as in the digestive system, the reproductive system and the bone marrow. But because the increase in the cancer rate is small, it is very difficult to estimate without a study of a very large population exposed to radiation. According to Langhorst, exposure of 10,000 people to radiation of 10 millisieverts (0.01 Sievert) in their whole body, will increase the cancer rate in this entire population by 8 cases. However, the normal rate of cancer cases in a population of this size is 2,000 to 3,300 cases, so it is impossible to detect a real increase of 8 cases, she says.

Lessons from Chernobyl:

Gonzalez says that some of the emergency workers at Chernobyl were exposed to radiation levels of several zivrets, and many of them worked "almost naked" due to the intense heat. This caused a fine, radiation-contaminated powder to be absorbed and penetrate their skin. In comparison, the Japanese workers are well equipped and at least protected from direct skin contact.

TEPCO, which owns the reactor in Japan, evacuated most of the workers. 50 workers remained to pump seawater to cool the reactors to prevent further explosions. These workers are probably exposed to high levels of radiation and greatly endanger their health. "As a precaution, I would limit the level of radiation that the workers are exposed to to 0.1 Sievert, and change them in shifts," says Gonzalez. Employees must carry personal radiation meters that calculate both the rate of exposure to radiation at each moment, and the total level of radiation, and sound an alarm when the exposure limit is reached. "If the workers are exposed to a level close to 1 Sievert, the situation is dangerous," he says.

The thousands of children who fell ill after the Chernobyl disaster were not harmed by direct radiation, not even by inhalation of radioactive particles, but by drinking milk contaminated with radioactive substances. Cesium 137 released in the Chernobyl explosion penetrated the grass the cows ate, and the radioactive contamination accumulated in their milk. Unaware parents thus gave their children contaminated milk. "There is no doubt that this will not happen in Japan," says Gonzalez.

Professionals who often work with radioactive materials, in hospitals or nuclear power plants, obey the principle: "the lowest exposure that can reasonably be achieved". Exposure regulations are set with deliberate conservatism well below levels known to cause radiation sickness or suspected of causing long-term health damage. Even a short exposure to radiation several times higher than these limits is not necessarily dangerous.

News reports of a US Navy ship passing through a radioactive cloud, the distribution of potassium iodide pills by the Japanese government, and images of experts in protective suits pointing Geiger counters at the heads of babies may inspire fear in the public, but these are means of achieving reasonably low exposure, meaning these are precautionary measures are increased, says Gonzalez. The idea is always to be overly cautious.