The danger of radiation leaks from Tokyo Electric Power Co.’s Fukushima Dai-Ichi nuclear plant is rising after explosions at the site caused by Japan’s earthquake and tsunami, Prime Minister Naoto Kan said today.
As of 10:22 a.m. local time, radiation as high as 400 millisieverts was detected at the plant’s No. 3 reactor, Chief Cabinet Secretary Yukio Edano said at a briefing. That’s 20 times the annual limit for nuclear industry employees and uranium miners, according to the World Nuclear Association, a London-based advocate for the nuclear energy industry. A radiation dose of 100 millisieverts a year is the lowest level at which any increase in cancer is evident, the London-based WNA said on its website.
“This is a level that could harm people,” Edano said. The station is about 220 kilometers (135 miles) north of Tokyo.
Here are answers to some frequently asked questions about radiation poisoning. The information is drawn from the World Nuclear Association, the Science Media Centres of Japan and Australia, the World Health Organization in Geneva, the U.S. Centers for Disease Control and Prevention in Atlanta, and the U.S. Environmental Protection Agency in Washington.
Q: How does the situation at Fukushima compare with the 1986 disaster in Chernobyl, Ukraine, and 1979 Three Mile Island accident in Pennsylvania? A: The International Atomic Energy Agency has rated the seriousness of the nuclear situation at the Fukushima reactors as 4 on a scale of 7. Three Mile Island was rated as 5/7 while Chernobyl was rated 7/7. Each additional point on this scale represents a factor of ten, so the situation at Fukushima is 1/10th as serious as that at Three Mile Island, and 1/1000 that at Chernobyl.
Q: What level of radiation is dangerous to human health? A: One hundred millisieverts a year is the lowest level at which any increase in cancer is clearly evident. Above this, the probability of cancer occurrence increases with higher doses.
A cumulative dose of 1,000 millisieverts would increase the incidence of fatal cancer by about 5 percent. A single dose of 1,000 millisieverts causes temporary radiation sickness and decreased white blood cell count, but not death. A single dose of 5,000 millisieverts would kill about half those receiving it within a month.
Air crew on flights over the North Pole between New York and Tokyo are exposed to about 9 millisieverts of radiation a year, and a chest x-ray radiates about 0.1 millisieverts. Humans are exposed to about 2 millisieverts a year from naturally occurring radiation in soil and cosmic rays.
Q: What are the health consequences of radiation? A: Exposure to high levels of radiation can cause acute radiation syndrome, or radiation poisoning, resulting in substantial damage to human body tissues, premature aging and possibly death. Prolonged exposure to lower levels is also associated with increased risk of ill health.
Q: How is radioactive contamination spread? A: People who are externally contaminated with radioactive material can contaminate other people or surfaces that they touch. For example, people who have radioactive dust on their clothing may spread the radioactive dust when they sit in chairs or hug other people.
People who are internally contaminated can expose people near them to radiation from the radioactive material inside their bodies. The body fluids (blood, sweat, urine) of an internally contaminated person can contain radioactive materials. Coming in contact with these body fluids can result in contamination and/or exposure.
Q: What are the symptoms of radiation poisoning? A: The first symptoms of acute radiation syndrome are typically nausea, vomiting and diarrhea. These symptoms can start within minutes to days of exposure and can last for days. After that, a person with acute radiation syndrome may look and feel healthy for a short time, then become sick again with loss of appetite, fatigue, fever and possibly seizures and coma. This stage may last a few hours or several months. Radiation poisoning also typically causes skin damage.
Q: How is radiation poisoning treated? A: Potassium iodide can be used to block radioactive iodine from being taken into the thyroid gland, protecting it from injury. It cannot protect other parts of the body or reverse damage to the thyroid once it has occurred. Prussian blue, a dye used by artists and manufacturers since 1704, can also be used to remove certain radioactive materials from the body. It should only be used under medical supervision.
Q: What is being done to protect human health? A: Japan has distributed 230,000 units of stable iodine to evacuation centers from the area around Fukushima Daiichi and Fukushima Daini nuclear power plants. The iodine has not yet been administered to residents; the distribution is a precautionary measure in the event that this is determined to be necessary.
Q: What is the worst-case scenario? A: It depends on how much radiation leaks and the prevailing weather conditions. Radioactive iodine, or I-131, is heavier than air and won’t spread far in mild wind. Iodine 131 has a half-life of eight days, meaning it takes eight days of decay to decrease by half.
Q: How do radioactive materials contaminate food? A: Atomic bomb tests in Nevada during the 1950s and 1960s released I-131 into the atmosphere that was blown thousands of miles away. Animals grazing on pastures contaminated with I-131 had the radioactive material in their milk, which poisoned some children. People exposed to I-131 may have an increased risk of thyroid cancer.
Q: What is ionizing radiation? A: Ionizing radiation is the energy or particles produced by unstable atoms of radioactive materials. Humans are exposed to low levels of radiation naturally from the Earth and the sun.
Q: What risk does Cesium-137 pose? A: External exposure to large amounts of Cs-137 can cause burns, acute radiation sickness and even death. Exposure to Cs-137 can increase the risk for cancer because of exposure to high-energy gamma radiation. Internal exposure to Cs-137, through ingestion or inhalation, allows the radioactive material to be distributed in the soft tissues, especially muscle tissue, exposing these tissues to the beta particles and gamma radiation and increasing cancer risk.