The world watches as Japanese officials struggle to gain control of the Fukushima Daiichi nuclear power plant, and the short- and long-term health of people living in the area has become an overriding priority and topic of conversation around the world.
ABC News contacted a dozen experts on radiation and, while most said that it is unlikely that the radioactive material will have severe health repercussions on those in Fukushima for now, doctors also agreed that it is too early to tell what will happen as the situation continues.
The Japanese government has evacuated nearly 200,000 residents living in the 20-kilometer exclusion zone and urged others within 30 kilometers of the plant to stay indoors and keep their homes airtight.
Jacky Williams, director and core leader of the Center for Biophysical Assessment and Risk Management Following Irradiation at the University of Rochester Medical Center, called the 20-kilometer evacuation radius an "extremely conservative safety zone to protect against fallout."
On Monday, the World Health Organization's spokesman, Gregory Hartl, tried to ease concerns: "From what we know at the moment on the radiation levels, the public health risk is minimal for Japan."
"That means that if someone is affected, there is no great risk," Hartl said.
But many people remained concerned after Japan's Prime Minister Naoto Kan said the damaged nuclear reactors may spew further radiation.
"The leaked radiation level is now rather high and there is high chance for further leakage of radiation from now on," Kan told residents on Tuesday.
"These are figures that potentially affect health," Chief Cabinet Secretary Yukio Edano told residents. "There is no mistake about that."
Experts agree that simple measures like creating a sealed containment in one's home and washing one's body and clothing has a direct impact on long-term and short-term effects of potential radiation exposure. Experts also agree that it is too early to tell the short-term and long-term damage.
"Until the type and quantity of the radioactive materials released into the atmosphere can be determined, it is impossible to estimate," said Jeff Clanton, director of radiopharmacy services at Vanderbilt University Medical Center.
The Japanese government has dispensed more than 200,000 units of potassium iodide, a drug commonly used to treat low-level radiation exposure, which would block radioactive iodine to prevent thyroid cancers.
Experts Can't Be Sure of Risks
"Biologically, our cells have mechanisms to repair the kind of small amounts of damage that occur daily due to background radiation and other causes, so it is quite possible, even likely, that doses below a certain point do not have the effect of causing increased cancer risk," said David Rocke, distinguished professor of biostatistics at the University of California, Davis.
"As far as risk to the Japanese population…it is all a matter of dose, and if there is any question, people can wear dosimeters," he said.
While there is no minimizing the potential threat of residents living near Fukushima, Clanton said that he'd feel safe staying in Tokyo and other parts of Japan at this time.
"If I had a trip planned for tomorrow, I would get on the plane with no reservation," said Clanton.
But John Williams, director of the Nuclear Reactor Laboratory and professor of nuclear energy engineering at University of Arizona, was more cautious.
"Unless needed there, I would be making immediate arrangements to leave [Tokyo]," said Williams. "Later developments are likely to make it more hazardous to leave the area [right outside the evacuation limit]."
Radiation Dosage and its Effects
People who receive a single large dose of 1,000 millisieverts of radiation to the total body can expect to experience acute radiation syndrome, characterized by changes in blood count, nausea, vomiting and diarrhea.
Three nuclear plant workers have suffered from acute radiation syndrome, the New York Times reported.
The sievert is a unit of dosage that is used to evaluate the biological effects of radiation.
To put radiation in perspective, a mammogram gives off about .30 millisieverts of radiation and a chest X-ray gives off .04 millisieverts, according to the Environmental Protection Agency. The World Nuclear Association says the lowest level of radiation that is clearly at a carcinogenic level is 100 millisieverts per year. The average American's total radiation exposure equals about nine millisieverts per year.
But even with the potential increased dose of radiation for residents of Fukushima, most doctors said they do not think that the reported levels will lead to a substantial increase in future cancers or other long-term health problems.
They warned, though, that things could change quickly if workers cannot cool the exposed fuel rods.
"Remember that the normal incidence rate of cancer in the U.S., for example, is about 43 percent," said Jerrold Bushberg, director of health physics programs and clinical professor of radiology and radiation oncology. "Even if we assume the linear dose-response is correct and the exposure results in a radiation dose that is 40 [or more] times the normal annual radiation dose from background radiation that we all receive, the increased cancer risk of developing cancer from that exposure would be less than one percent."
Differences and Similarities between Fukushima and Chernobyl
Most nuclear power experts have said that Fukushima's plant will not cause as severe of disaster to health as the Chernobyl Nuclear Power Plant accident, which is considered to be the worst nuclear power plant accident in history. The accident caused radioactive fallout that spread throughout the western part of the Soviet Union, and parts of Eastern, Western and Northern Europe, and the area continues to be uninhabited today.
Several studies have shown a significant spike in thyroid cancer in children who lived close to the Chernobyl plant. Other long-range effects associated with the Chernobyl blast included a peak in babies born with Down syndrome and birth and neural tube defects caused during the fetal development in the mother's womb.
"I would agree in general that this is well below Chernobyl in overall exposure risk to the public," said Edward Morse, a nuclear engineer at the University of California, Berkeley. "Chernobyl had nuclear propulsion of its entire core contents shot into the atmosphere after being supercritical... And most importantly, they are receiving the best possible type of human intervention to minimize radiation leakage and exposure to the public."
But Williams said Japan's public health outcomes could be just as bad as Chernobyl's, and perhaps worse.
"This disaster is different from Chernobyl, but the consequences will be very severe," said Williams. "Because of the high population density, the local effects may be as bad or worse. Disruption and displacement of the population are likely to produce the greatest health impacts, as was the case with Chernobyl."
And Dr. Janette D. Sherman, who published a book on Chernobyl, agreed.
"It appears that a Chernobyl-style disaster is underway," said Sherman. "It took but 10 days for radionuclides from Chernobyl to spread through the northern hemisphere… Chernobyl shows clearly that there is no barrier to spread of radioactivity."
Henry Spitz, professor of nuclear and radiological engineering at the University of Cincinnati, had a more optimistic outlook, though he said things could change.
"It is unlikely that any elevated health effects will be observed resulting from the radioactive emissions that have occurred to date," said Spitz. "Unfortunately, the event at the Fukushima reactor site continues to evolve."