While officials in Japan and elsewhere are offering assurances that the health risks posed to the general public by three nuclear reactors are low, many are still worried.
Some are surely remembering images of the 1986 Chernobyl disaster. That disaster is thought to have caused more than 30 deaths from acute radiation sickness alone, as well as thousands of cancer deaths, and birth defects.
So far, the two events seem quite different.
At Chernobyl, explosions blew the reactor apart, which vapourized its radioactive fuel, sending a toxic cloud across the Ukraine and parts of Europe. In Japan, explosions have been contained within the reactors, and only small amounts of radioactive particles are said to have been released.
The radiation release from Chernobyl was about a million times the amount released from the partial core meltdown at Three Mile Island, which itself is considered a worse disaster than the troubles underway at Japan's Fukushima facility.
Acute radiation sickness
Nevertheless, at least three Fukushima workers have already come down with acute radiation sickness. Since it's unclear how much radioactive material they were exposed to, what kind of radiation, and for how long, their prognosis is uncertain.
Officials haven't revealed what symptoms the workers are experiencing, but they likely include nausea, fatigue, vomiting, and diarrhea. More severe radiation exposures result in fever, bloody vomit and stools, and later, hair loss, infections, and poor wound healing.
What makes ionizing radiation from radioactive material so dangerous is that it interferes with the cells' ability to divide and reproduce. The effects are usually seen first in the cells that divide rapidly. These include blood cells in bone marrow and intestinal cells, as well as reproductive and hair cells.
For most with radiation sickness, the biggest risk is infection.
Though severe radiation exposure is fatal within weeks about 50 per cent of the time, many can survive milder forms of radiation sickness.
If the Fukushima workers develop more serious symptoms in the next few weeks, they would likely be offered medications that increase white blood-cell production, which can help reduce the risk of infections.
But the risk of cancer will remain for the workers for many years down the road.
Cancer risk
For the rest of the Japanese public, there is still a risk of long-term effects of radiation exposure, particularly is officials are downplaying the severity of the situation, as some suspect they might be.
The Japanese government has ordered anyone living within 20 kilometres of the Fukushima nuclear power plant to evacuate the area as a precaution. They are also handing out iodine pills in hopes of preventing thyroid cancer.
The reason for the pills is that the thyroid gland tends to absorb iodine from wherever it can. By flooding the thyroid with ordinary iodine, it will inhibit its absorption of radioactive iodine from the atmosphere.
But Dr. David J. Brenner, director of the Center for Radiological Research at Columbia University, is not convinced that's an effective strategy. He tells The New York Times that the risk from inhaling radioactive iodine is low; almost 98 per cent of people's exposure comes from ingesting contaminated milk and other dairy products.
In fact, he believes that the epidemic of thyroid cancer around Chernobyl could have been prevented if the government had immediately stopped people from drinking milk.
Leukemia is also a risk, as many of those who survived Chernobyl eventually came down with the blood-based cancer.
Cancer is the biggest long-term risk. Usually when the body's cells reach their "sell-by date" they commit suicide. Cancer results when cells lose this ability,
The body has various processes for ensuring that cells do not become cancerous, and for replacing damaged tissue.
The damage caused by exposure to radiation can disrupt the body's ability to regenerate new cells, allowing old cells to "go rogue" and continue to divide and multiply in an uncontrolled fashion, allowing tumours to grow.
Radiation can also result in mutations to the body's genetic material, which may also be potentially passed down to offspring, leading to deformities in future generations.
These can include smaller head or brain size, severe learning difficulties, and stunted growth.