As workers hurry to cool the exposed fuel rods at the Daiichi nuclear plant in Japan's quake-battered Fukushima prefecture, health officials are screening evacuees from the 12-mile danger zone surrounding the plant for radiation.
Nineteen people have shown signs of radiation exposure following the two hydrogen blasts at the plant's No.1 and No. 3 reactor buildings. And 141 more are feared to have been exposed while waiting for evacuation, including a group of 60 people removed by helicopter from a high school, according to Japan's Nuclear and Industrial Safety Agency.
Although the health impact of radiation at low doses is controversial, the National Research Council maintains that no level of above what occurs naturally is safe. Prior to the latest emergency at the Daiichi plant, radiation levels at the plant reached 3,130 microsieverts per hour -- roughly half the average annual dose in the U.S.
Jacky Williams, director of the Center for Biophysical Assessment and Risk Management Following Irradiation at the University of Rochester Medical Center, called the 12-mile evacuation radius an "extremely conservative safety zone to protect against fallout."
But even if a meltdown is avoided, the possibility of low-level radiation circulating in the air and contaminating the soil following the two steam-releasing explosions is very real, according to Dr. Janette Sherman, author and specialist in internal medicine and toxicology from Alexandria, Va.
"To assume that steam containing radioisotopes found in nuclear reactors is not going to have health effects, I think, is wishful thinking," Sherman said.
Those radioisotopes, such as iodine-131, strontium-90 and cesium-137, get taken up by the body. As they decay, they give off energy in the form of gamma rays, beta rays that penetrate deep through tissues, and alpha rays that damage DNA. Sherman likens them to harmful chemicals that settle in various tissues of the body.
"We know that radioactive iodine, which goes to the thyroid, can cause cancer and stunt children's growth," said Sherman, adding that exposure during pregnancy can damage the fetal brain. "We know strontium 90 goes to bones and teeth and is linked to leukemia and immune dysfunction. And we know cesium goes to soft tissues, like muscle and breast tissue."
For pregnant women, the risk of birth defects and miscarriages may also rise, Sherman said.
Is the Evacuation Zone Big Enough?
The Japanese government has evacuated 184,670 residents from 10 towns in the 20-kilometer exclusion zone surrounding the plant -- a distance that Sherman said might not be sufficient.
"We know nuclear radiation [from Chernobyl] drifted as far as North America," Sherman said.
Drifting fallout could also contaminate food and water beyond the evacuation zone.
"They shouldn't eat or drink anything contaminated by cesium," Sherman said. "All food and drink have to come from outside the area."
The Japanese government has distributed 230,000 units of potassium iodide to evacuation centers bordering the danger zone as a precaution, in case radiation levels surge. Potassium iodide can block radioactive iodine from entering the thyroid -- a butterfly-shaped gland in the neck that produces hormones that regulate metabolism.
"One of the things after Chernobyl, you saw massive numbers of cancers in children. The radioactive iodine got into the grass, the cows ate the grass, it got into the milk," said Dr. Richard Besser, ABC News chief medical editor.
In addition to dozens exposed to low-dose radiation, three plant workers suffered from acute radiation sickness, the New York Times reported.
"When people receive a very high dose of radiation to the total body, like the workers did, they develop nausea, vomiting and diarrhea," said Dr. Ritsuko Komaki, professor of radiation oncology at M.D. Anderson Cancer Center in Houston.
Komaki, a native of Hiroshima, was en route to Tokyo for a scientific meeting when the earthquake hit. Her plane was rerouted from Narita airport to Nagoya.
"I've never seen such a disaster in my life," said Komaki, who was 2 years old when the atomic bomb hit, ultimately killing a dozen of her relatives in Hiroshima. Komaki was moved to become an oncologist because of her childhood friend Sadako Sasaki, who died from leukemia at age 12.
Radiation affects the body's cells by damaging DNA inside the nucleus. Because DNA is copied each time a cell divides, cells that divide frequently like those that line the respiratory and gastrointestinal tracts, as well as the infection-fighting white blood cells of the immune system produced in the bone marrow are most affected.
"After a few days, they may have nosebleeds and infections and become anemic," Komaki said. "They usually recover, but sometimes people die from that."
Treating High-Dose Radiation Exposure
Prussian blue, a dye that binds to radioactive cesium and thallium, can speed the elimination of radiactive particles from the body and reduce the amount of radiation absorbed by cells. Potassium iodide will also help protect the thyroid from acute exposure to high levels of radioactive iodine.
While the immune system is down, high-dose antibiotics can help stave off infection. And if white blood cell levels don't climb back to normal levels, Neupagen -- a drug often used during chemotherapy -- can help boost white cell production by the bone marrow.
Red blood cells live longer than their white counterparts, so their level drops later, causing anemia. This can be treated using Procrit -- a drug similar to that used by Lance Armstrong during his recovery from prostate cancer.
Komaki's grandmother was exposed to high dose radiation at age 45 when the bomb hit Hiroshima. She had bone marrow suppression, gastrointestinal toxicity and lost her hair. Later, she developed anemia, osteoporosis, thyroid dysfunction and heart disease, but never cancer. She died at age 72.
"If the workers survive, they'll have long-term health concerns," Komaki said.