Beyond the devastation caused by the Earthquake and Tsunami, Japan faces an even longer-term problem in the lingering effects of radiation emitted by the Fukushima nuclear power plant. Officials have detected greater-than-acceptable amounts of radioactive elements in tap water, milk and spinach, and readings from seawater near the plant set off alarms at 15 to 120 times government standards.
So how safe is the Japanese food supply? Officials say that despite exceeding government thresholds, the amounts of radioactive material that have infiltrated water and crops are relatively small--you would have to eat pounds of the spinach to receive the amount of radiation in one CT scan of your head, for example--and do not pose health risks. Children who drank contaminated milk in the Chernobyl region after that area's nuclear-plant meltdown have developed above-average rates of thyroid cancer, but according to the International Atomic Energy Agency, the radiation released in Fukushima is far below the levels measured in the 1986 Ukrainian disaster.
Still, Dr. James Cox, a radiation expert at M.D. Anderson Cancer Center, notes that doctors have very little information about the effects of radiation ingested with food. Some of the material emitted in Japan has a long radioactive half-life, which means it could persist in soil and water and possibly emerge in crops and livestock for years, if not decades, and continue to pose a cancer hazard. To be safe, Japanese authorities have banned distribution of milk and vegetables grown in the regions adjoining Fukushima, and it's not clear how long those restrictions will remain. Contemporary Japanese may take solace, however, from the lesson of Hiroshima and Nagasaki. Decades after being destroyed by an atomic bomb dropped by the U.S., Hiroshima now boasts off its coast Japan's most prized beds of oysters, which people enjoy without fear.
We absorb radiation every day, but how much is too much?
[The following text appears within a chart. Please see hardcopy or PDF for actual chart.]
Up to 6.2 mSv
This yearly level of radiation exposure can cause relatively benign changes in blood chemistry
Up to 30 mSv
Symptoms are still limited to changes in the blood
Nausea, fatigue and vomiting can start within hours of exposure at this level
Hair loss, hemorrhage and internal bleeding could develop over two months, followed by death
Average U.S. adult
Daily sources of exposure include cosmic rays and minerals as well as medical X-rays
Many of the evacuees were exposed to low levels of radiation
Emergency workers at Fukushima
Such levels are close to those allowed for nuclear-plant workers over an entire year
Measured in millisieverts, a common unit of radiation dosing
PEOPLE AT RISK
Assessing The Threat