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updated 3/31/2011 9:30:30 PM ET 2011-04-01T01:30:30

Here are some commonly asked questions about the earthquake and nuclear disaster in Japan. Submit your questions using the form below.

  1. Japan earthquake
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    2. Another setback in effort to control Japan reactor
    3. Most nuclear plans on track outside Japan, Germany
    4. After Japan quake, victims still await aid
    5. Superheroes cheer children in Japan's disaster zone
    6. Snowden to New Zealanders: NSA Is Spying on You
    7. Time-lapse of  aftershocks
    8. Images of chaos, destruction

Question: I've read that food and water in Japan has been contaminated by radiation. Should I be concerned that produce or fish from Japan will end up on my dinner table?

Answer: Some produce and meat products from Japan have been found to have radiation levels in excess of the allowable level. But experts say that at current levels, the contamination holds no risk for American consumers and only a minor, manageable risk for people living near the damaged nuclear complex. And fish are less likely to be hit by unsafe levels of radiation than land-dwelling species, they say.

Question: I’ve heard that plutonium has been found outside the Fukushima plant? What is the significance of that?

Answer: The Tokyo Electric Power Co., which operates the plant, said it found three radioactive isotopes of plutonium — plutonium 238, 239 and 240 — in five locations outside the plant in soil tests on March 21-22. It said two samples out of the five may be the direct result of the accident at the plant following the tsunami. It said the detected levels were minute — almost the same as those from the fallout detected in Japan following past nuclear tests by the United States and Russia, which ended in 1980 — and do not pose a major risk to human health

The reason plutonium is such a concern is that it is the most toxic of the isotopes that can be released from a nuclear reactor or explosion. Plutonium does not exist in nature. It can only be created by nuclear fission. Plutonium is fatal to human in very tiny doses. It accumulates in the bones and it has very long half lives. Plutonium 238 has a half-life (half of it will be gone) of 88 years and Plutonium 239 a half-life of 24,100 years.

That's scary stuff, but some experts say that plutonium may not pose as much of a risk to public health as radioactive iodine, which is being produced in far greater quantities. You can read more about that here. And you can learn more about plutonium in this fact sheet from the U.S. Argonne National Laboratory.

Disaster at a glance

Question: What are the health risks of radiation?

Answer: Radiation can kill at high levels. For example, 50 percent of people given whole body exposures of 4 sieverts for an hour would be expected to die within 60 days without medical attention, mostly from infections. Duration of exposure also plays a role in determining the health risks.

Acute Radiation Sickness often appears with exposure to between 0.5 and 1 sievert per hour. Symptoms include fatigue, hair loss, nausea, vomiting and diarrhea as well as skin changes such as swelling, redness, itching and radiation burns.

Exposures of less than 0.5 sieverts typically produce changes in blood chemistry, but no symptoms, according to the U.S. Environmental Protection Agency.

Experts say exposure to lower levels of radiation has the potential to cause various kinds of cancers, with higher levels of radiation seen as more dangerous.

The highest radiation reading recorded so far outside the Fukushima plant was 1,000 millisieverts per hour — or 1 sievert — in contaminated water in an overflow tunnel outside the plant’s Reactor No. 2 on March 27. The highest reading in the air so far was 400 millisieverts, or 0.4 sieverts, per hour on March 14, according to Japanese authorities.

You can learn much more about radiation risks and effects here.

Question: Is fallout from a nuclear bomb the same as fallout from a nuclear plant accident?

Answer: No. Due to differences in nuclear fuels and the resultant reactions that take place when a reactor accident occurs, the radioactive elements of the fallout (called isotopes) from a nuclear power plant accident are not the same as those found in fallout from the detonation of a nuclear device. Read more in this U.S. State Department fact sheet.

Question: What happens if the fuel rods or spent fuel at the Fukushima plant completely melt down?

Answer: That's a matter of some debate in the scientific community, but both sides agree that the worst case would be a powerful explosion that would distribute radiation over a wide area.

Click here to read more about the meltdown scenario, or here for a March 24 article on what's going on at the nuclear complex.

Question: Why not entomb the plant, as the Russians did with Chernobyl?

Answer: Authorities in Japan aren't yet thinking about a permanent entombment. But they are looking into the idea of covering up the "hot" fuel rods being stored at the site with piles of sand and soil, laced with lead and neutron-absorbing boron. You can read more about this option here.

Question: What is the risk of the released radiation to the U.S.?

Traces of radiation from the damaged Fukushima plant have reached the United States and traveled

as far east as Massachusetts

, but

pose no health threat

, public health experts say.  

Question: Then why are people snapping up potassium iodide tablets?

Answer: May people are frightened and are acting out of an overabundance of concern. Potassium iodide is used to "block" the thyroid's intake of iodine-131, a radioactive isotope released during nuclear fission that can cause thyroid cancer. Experts and public health authorities are not recommending that Americans take any precautions at this juncture.

Question: How do we know how much radiation is reaching the U.S.?

Answer: The U.S. cannot monitor sparse concentrations of radiation from space. However, the Departments of  Defense and Energy and the Environmental Protection Agency and the Pentagon are capable of monitoring radiation in the air. Click here to learn more about U.S. radiation monitoring.

Question: I've heard Americans are being evacuated from Japan. What are the details?

Answer: The State Department in mid-March authorized the voluntary departure of up to 600 family members and diplomats who wish to leave Japan. The department also said it would assist Americans wishing to leave the country. Here are some details on that. It also set up an e-mail address — japanemergencyusc@state.gov — for Americans seeking help leaving the country. The Pentagon also has signed the order authorizing a voluntary departure for eligible families members on the entire island of Honshu. It is unknown how many people would be eligible, but a spokesman confirmed that the number is in the "thousands."

Question: I’ve been planning a trip to Tokyo, but the earthquake, tsunami and nuclear crisis has me worried. Should I go?

Answer: The U.S. State Department is advising Americans to defer travel to Japan if possible. The government also is offering to evacuate Americans in Japan.

Question: Are any Americans confirmed to have died in the quake or tsunami?

Answer: A single death of a U.S. citizen — 24-year-old teacher Taylor Anderson of Richmond, Va. — has been confirmed.  State Department officials say "several" other Americans remain unaccounted for. The department has a web page with more information.

Question: Could a similar nuclear disaster happen here?

Answer: The Nuclear Regulatory Commission says the odds of an earthquake causing catastrophic failure at a U.S. nuclear plant are astronomical — assessing the risk on average as a 1 in 74,176 chance that a plant's nuclear core could be damaged by an earthquake, potentially exposing the public to radiation. The NRC says that "operating nuclear power plants are safe," but it also recently revised its risk assessments based on new seismic data and acknowledges that, for some plants, the margin of safety has been reduced. You can read more about the risk assessments here.

Question: Are coastal U.S. plants also safe if they are swamped by a tsunami?

Answer: Operators of California's two nuclear plants say they are well prepared for a possible tsunami strike. Some experts, however, want new risk assessments in light of the catastrophe in Japan. Learn more here.

Question: How much will the twin disaster in Japan cost?

Answer: It’s early in the assessment process, so any estimate is just that. But the Japanese government is forecasting the damage at $309 billion, which would make it the costliest natural disaster ever. For purposes of comparison, Hurricane Katrina left $125 billion in damage in its wake. Read more about estimating the damage.

Question: Will some products be difficult to find as a result of the disruption to the Japanese economy?

Answer: Experts say the auto industry will be affected by the shutdown of manufacturing centers in Japan, with the subsequent parts shortage also hurting foreign automakers. Some market watchers see price hikes coming as the impact of the disruption to supply chains is felt. Prices and availability of electronic goods also may be affected, with Toshiba, Sony, Panasonic, Fujitsu and Mitsubishi all reporting disruptions to their production lines.

Question: What can I do to help?

Answer: Click here for a list of relief organizations assisting in Japan.

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Video: Setbacks mount at Japanese nuke plant

  1. Closed captioning of: Setbacks mount at Japanese nuke plant

    >> radiation levels are on the rise in the evacuation zone near the troubled nuclear facility may not be enough. lee cowan has more from tokyo. lee, good morning.

    >> reporter: good morning, tamron. the latest news comes from the iaea who says there have been high radiation levels found far outside the current evacuation zone prompting fears that perhaps the crisis may widen. foukushima is already a waste land . deserted streets and empty shops that some 70,000 residents may never return to again. new tests done by the international atomic energy commission found dangerous levels of radiation in a vielg 25 miles outside that seclusion zone suggesting that the no-go area for humans may have to be doubled.

    >> the situation remains very serious.

    >> reporter: officials say the levels aren't high enough for acute radiation illness but they far exceed the standards for the general public designed to cut the risk of cancer. japan's government spokesman said they are taking the findings under advisement but had no plans to widen the evacuation zone. tamron, we should point out that in the u.s. the epa did find some radioactive iodine in milk products in the u.s. after doing tests in washington state . they say the levels were minute. there is no threat to human health , even children and infants.

Interactive: Japan before and after the disaster

These aerial photos show locations in Japan before and after the 9.0-magnitude earthquake and tsunami that struck March 11. Use the slider below the images to reveal the changes in the landscape.

  1. Above: Interactive Japan before and after the disaster
  2. Image: The wave from a tsunami crashes over a street in Miyako City, Iwate Prefecture in northeastern Japan
    Ho / Reuters
    Timeline Crisis in Japan

Explainer: The 10 deadliest earthquakes in recorded history

  • A look at the worst earthquakes in recorded history, in loss of human life. (The March 11, 2011, earthquake and tsumani that affected eastern Japan is not included because the fatalities caused, about 15,000, are fewer than those resulting from the temblors listed below.) Sources: United States Geological Survey, Encyclopedia Britannica

  • 1: Shensi, China, Jan. 23, 1556

    Magnitude about 8, about 830,000 deaths.

    This earthquake occurred in the Shaanxi province (formerly Shensi), China, about 50 miles east-northeast of Xi'an, the capital of Shaanxi. More than 830,000 people are estimated to have been killed. Damage extended as far away as about 270 miles northeast of the epicenter, with reports as far as Liuyang in Hunan, more than 500 miles away. Geological effects reported with this earthquake included ground fissures, uplift, subsidence, liquefaction and landslides. Most towns in the damage area reported city walls collapsed, most to all houses collapsed and many of the towns reported ground fissures with water gushing out.

  • 2: Tangshan, China, July 27, 1976

    Chinese Earthquake
    Keystone  /  Getty Images
    1976: Workers start rebuilding work following earthquake damage in the Chinese city of Tangshan, 100 miles east of Pekin, with a wrecked train carriage behind them. (Photo by Keystone/Getty Images)
    Magnitude 7.5. Official casualty figure is 255,000 deaths. Estimated death toll as high as 655,000.

    Damage extended as far as Beijing. This is probably the greatest death toll from an earthquake in the last four centuries, and the second greatest in recorded history.

  • 3: Aleppo, Syria, Aug. 9, 1138

    Magnitude not known, about 230,000 deaths.

    Contemporary accounts said the walls of Syria’s second-largest city crumbled and rocks cascaded into the streets. Aleppo’s citadel collapsed, killing hundreds of residents. Although Aleppo was the largest community affected by the earthquake, it likely did not suffer the worst of the damage. European Crusaders had constructed a citadel at nearby Harim, which was leveled by the quake. A Muslim fort at Al-Atarib was destroyed as well, and several smaller towns and manned forts were reduced to rubble. The quake was said to have been felt as far away as Damascus, about 220 miles to the south. The Aleppo earthquake was the first of several occurring between 1138 and 1139 that devastated areas in northern Syria and western Turkey.

  • 4: Sumatra, Indonesia, Dec. 26, 2004

    Aerial images show the extent of the devastation in Meulaboh
    Getty Images  /  Getty Images
    MEULABOH, INDONESIA - DECEMBER 29: In this handout photo taken from a print via the Indonesian Air Force, the scene of devastation in Meulaboh, the town closest to the Sunday's earthquake epicentre, is pictured from the air on December 29, 2004, Meulaboh, Aceh Province, Sumatra, Indonesia. The western coastal town in Aceh Province, only 60 kilometres north-east of the epicentre, has been the hardest hit by sunday's underwater earthquake in the Indian Ocean. Officials expected to find at least 10,000 killed which would amount to a quarter of Meulaboh's population. Three-quarters of Sumatra's western coast was destroyed and some towns were totally wiped out after the tsunamis that followed the earthquake. (Photo by Indonesian Air Force via Getty Images)

    Magnitude 9.1, 227,898 deaths.

    This was the third largest earthquake in the world since 1900 and the largest since the 1964 Prince William Sound, Alaska temblor. In total, 227,898 people were killed or were missing and presumed dead and about 1.7 million people were displaced by the earthquake and subsequent tsunami in 14 countries in South Asia and East Africa. (In January 2005, the death toll was 286,000. In April 2005, Indonesia reduced its estimate for the number missing by over 50,000.)

  • 5: Haiti, Jan 12, 2010

    Haitians walk through collapsed building
    Jean-philippe Ksiazek  /  AFP/Getty Images
    Haitians walk through collapsed buildings near the iron market in Port-au-Prince on January 31, 2010. Quake-hit Haiti will need at least a decade of painstaking reconstruction, aid chiefs and donor nations warned, as homeless, scarred survivors struggled today to rebuild their lives. AFP PHOTO / JEAN-PHILIPPE KSIAZEK (Photo credit should read JEAN-PHILIPPE KSIAZEK/AFP/Getty Images)

    Magnitude 7.0. According to official estimates, 222,570 people killed.

    According to official estimates, 300,000 were also injured, 1.3 million displaced, 97,294 houses destroyed and 188,383 damaged in the Port-au-Prince area and in much of southern Haiti. This includes at least 4 people killed by a local tsunami in the Petit Paradis area near Leogane. Tsunami waves were also reported at Jacmel, Les Cayes, Petit Goave, Leogane, Luly and Anse a Galets.

  • 6: Damghan, Iran, Dec. 22, 856

    Magnitude not known, about 200,000 deaths.

    This earthquake struck a 200-mile stretch of northeast Iran, with the epicenter directly below the city of Demghan, which was at that point the capital city. Most of the city was destroyed as well as the neighboring areas. Approximately 200,000 people were killed.

  • 7: Haiyuan, Ningxia , China, Dec. 16, 1920

    7.8 magnitude, about 200,000 deaths.

    This earthquake brought total destruction to the Lijunbu-Haiyuan-Ganyanchi area. Over 73,000 people were killed in Haiyuan County. A landslide buried the village of Sujiahe in Xiji County. More than 30,000 people were killed in Guyuan County. Nearly all the houses collapsed in the cities of Longde and Huining. About 125 miles of surface faulting was seen from Lijunbu through Ganyanchi to Jingtai. There were large numbers of landslides and ground cracks throughout the epicentral area. Some rivers were dammed, others changed course.

  • 8: Ardabil, Iran, March. 23, 893

    Magnitude not known, about 150,000 deaths

    The memories of the massive Damghan earthquake (see above) had barely faded when only 37 years later, Iran was again hit by a huge earthquake. This time it cost 150,000 lives and destroyed the largest city in the northwestern section of the country. The area was again hit by a fatal earthquake in 1997.

  • 9: Kanto, Japan, Sept. 1, 1923

    Kanto Damage
    Hulton Archive  /  Getty Images
    1923: High-angle view of earthquake and fire damage on Hongokucho Street and the Kanda District, taken from the Yamaguchi Bank building after the Kanto earthquake, Tokyo, Japan. (Photo by Hulton Archive/Getty Images)
    7.9 magnitude, 142,800 deaths.

    This earthquake brought extreme destruction in the Tokyo-Yokohama area, both from the temblor and subsequent firestorms, which burned about 381,000 of the more than 694,000 houses that were partially or completely destroyed. Although often known as the Great Tokyo Earthquake (or the Great Tokyo Fire), the damage was most severe in Yokohama. Nearly 6 feet of permanent uplift was observed on the north shore of Sagami Bay and horizontal displacements of as much as 15 feet were measured on the Boso Peninsula.

  • 10: Ashgabat, Turkmenistan, Oct. 5, 1948

    7.3 magnitude, 110,000 deaths.

    This quake brought extreme damage in Ashgabat (Ashkhabad) and nearby villages, where almost all the brick buildings collapsed, concrete structures were heavily damaged and freight trains were derailed. Damage and casualties also occurred in the Darreh Gaz area in neighboring Iran. Surface rupture was observed both northwest and southeast of Ashgabat. Many sources list the casualty total at 10,000, but a news release from the newly independent government on Dec. 9, 1988, advised that the correct death toll was 110,000. (Turkmenistan had been part of the Soviet Union, which tended to downplay the death tolls from man-made and natural disasters.)

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