By far, the biggest danger from the disaster at Japan's Fukushima Daiichi power plant is to the workers who are trying to control a still-volatile situation. But with the crisis likely to play out for months, people are beginning to wonder what the release of radioactive material actually means.

Very low levels of radioactive material have been found in the water supply in Tokyo, for example, and those same particles are being carried by the wind elsewhere in the world.

Workers at the plant are being exposed to radiation coming directly from the core and spent-fuel cooling pools. For people living far from the source of the radiation, exposure can come from the radioactive material that entered the air or water during efforts to stabilize the cooling systems.

Radioactive versions of elements such as cesium, iodine, and strontium can enter the body either through the lungs or by eating and drinking affected food. A standard precaution is to prevent people, particularly growing children, from drinking milk in the area of a nuclear accident, since cows can eat grass with radioactive iodine and pass it on to people.

The Environmental Protection Agency is monitoring and publishing data on the radioactivity in water and milk from Japan in the U.S. and the levels are "far below levels of public-health concern." But some argue that being exposed to even a small dose of the radioactive materials already released--iodine-131 and cesium-137 are the most prevalent--can be significant. If ingested, radioactive iodine can be absorbed by the thyroid gland, with children at the most risk. Cesium-137, which can also lead to cancer by affecting many types of cells, is more worrisome because it has a half-life of 30 years, versus 8 days for iodine-131. Radioactive strontium, which also has a long half-life, is linked to bone cancer and leukemia.

If there is a large-scale release of radioactive isotopes from the Fukushima Daiichi reactor or spent-fuel pools, then the risks will rise substantially.

But in the current situation, how should people evaluate the health risk How do academics and scientists view this problem Are sufficient safeguards being put in place

To get a better understanding of these questions, CNET spoke to two experts in the field to get their views the same week that the Fukushima Daiichi was raised to the highest level possible for a nuclear power accident.

Below is an edited transcript of a discussion with David Brenner from Columbia University's Center for Radiological Research. My CNET colleague Elinor Mills conducted an interview with Ira Helfand, the former president of Physicians for Social Responsibility, a group firmly opposed to nuclear power, which it says poses unacceptable risks. That Q&A can be found here.

In a nutshell, the view of Brenner, who recently testified to Congress on radiation from backscatter X-rays at airports, is that the individual risks are extremely low for people outside the exclusion zone around the Fukushima Daiichi power plant. At the same time, a large number of people will be exposed, which means that over the long term, that minute risk becomes more significant.

Q: What is the difference between what workers are exposed to and the rest of the population Brenner: It's simply a matter of the radiation dose. It's relatively low for people away from the plant. While we don't know what the doses are, the workers are clearly getting relatively high doses.

There have been traces of radioactive material detected in food and milk here in the U.S. Should people be concerned Brenner: In the U.S., the levels of radioactivity in the water and milk both on the West Coast and the East Coast have been exceedingly low. I don't think there are any significant health issues with the level of radioactivity in this country.

It was inevitable that once radioactivity was released in Japan, that some of it would be blown here. What was fortunate is that most of the radioactivity released into the air was blown into the sea but it was inevitable that it would end up in this country...Very little indeed has gotten here because it got heavily distributed. The fact that you can measure it here doesn't mean that it's a high health risk, at least in the short term. That's the situation in the U.S.

In Japan, the doses are still pretty low outside the exclusion zone. Again, the further away people are from reactors, the lower the dose, such as the folks in, say, Tokyo. In Kyoto, it's even lower.

What about the longer-term effects Brenner: The health consequences are actually very small for any individual. That being said, there are longer-term issues. The two main isotopes that were released are iodine-131 and cesium-137. The half-life for half the radioactive material in iodine to decay is eight days, so by a month or two later, it's essentially all gone. There's no long-term effect.

Whatever cesium was released will get into the food chain, into the ecosystem, and it will gradually get dispersed. So there will be some in the food and water for generations to come. It will be at some level but it will be at a very low level. What we really have will be a prolonged exposure to very low levels of radioactive from the Fukushima event. That's really what we're stuck with. But the risk for any individual will be tiny.

Although individual risk is low, an awful lot of people exposed to it. Think of the lottery. An awful lot of people will [be involved] because somebody's going to win...[In this case] one would expect some extra cancers in the long run but everybody's individual risk is low.

Some people say that even a tiny bit of exposure should be avoided because it could cause a specific type of cancer, such as thyroid cancer in children. Brenner: You can think about risk in two different ways. There's the risk of an individual and certainly the risk is very small. You can also think about the lottery analogy. How many tiny individual risks affect a population It's two complementary ways of looking at it.

From an individual's point of view, one doesn't have to worry. When you're starting to think about what is significant from the point of view of the population and how do we proceed with nuclear power, we need to think about the population.

Should we be restricting food imports Brenner: Most of radioactivity being seen in food, water, and fish is almost certainly from iodine. I would expect in a month or two months, those restrictions will probably go away. But what will be left will be much lower levels of cesium in food [in part because less cesium than iodine was released]. It's more than appropriate that Japan and the U.S. and any other country should be monitoring the food. It's not hard to do. I don't expect this will be long-term except in a broader sense.

How do people in your profession decide what's an acceptable risk Brenner: We try to think about risk and benefits. Having a CT scan, there's a small radiation risk, but there's a benefit to hopefully getting an accurate diagnosis. It's another story whether we get that balance right since there are alternatives to CT scanners.

You could argue, one should be doing the same estimations for nuclear power. The risk, unfortunately, is the scenario like what we have in Fukushima. What are the benefits of power without oil or use of fossil fuels It's up to society to make the risk-benefit analysis as best they can. You need to understand risks as well as you can and different folks will come up with different conclusions.

One thing that's pretty clear is that we have in this country and Japan a pretty aging fleet of nuclear reactors. The Fukushima plant was built in the 1970s and there are plenty of similar reactors also built at the same time in the U.S.

It seems to me we're at that point where we have to make decisions about replacing older reactors with more modern reactors that have more defense mechanisms built into them. We can never say anything is 100 percent safe, but they can be a lot more safe.

Are you pro nuclear power Brenner: My job is to try to understand the risks. It's for society in general to determine how to balance risks. I'm all in favor of safe nuclear if it can be achieved. Some risks do always exist. The question is do they counter-balance the benefits.

The two extremes around nuclear power are either that it's extremely unsafe and it should be abolished, but that is not true. The other extreme is that it's entirely safe. That's not true either. The reality is in the middle.

It seems that there isn't agreement on the ultimate health impact from the Chernobyl disaster in 1986. Does that disaster provide much guidance Brenner: Most of the epidemiological studies that should have been done haven't been done for political and economic reasons. The Soviet Union broke up shortly after so was difficult to have Belarus, Ukraine, and Russia work together on it.

The studies that have been done are the low-hanging fruit--studies about thyroid cancer and leukemia which you would expect to see first. There's no question there was a tremendous increase in thyroid cancers and it's pretty clear for [an increase in] leukemia too.

Studies on the more common cancers like lung cancer and breast cancer have not been done. And that's a shame, to put it mildly. Lacking those, people are having to estimate what consequences were because we don't know enough about the effects of very low levels or radiation.

It's still not appropriate to compare Fukushima to Chernobyl, where the containment blew up entirely and large amounts of the core were emitted high into the atmosphere. There was no ocean. I heard a statement that Fukushima was one tenth as hazardous as Chernobyl but I think it is far less.

You testified in Congress about backscatter X-rays at airports. For most people, this is the day-to-day question: how much low-level radiation is OK. Do we know Brenner: The argument's a little bit the same [as Fukushima]. The individual risk is miniscule. I didn't hesitate to go through [security] on my flight home. The concern is the population risk because an awful lot of people fly, about 700 million a year in the U.S.

If the TSA wants to scan every passenger, you got a scenario where you have a tiny risk and you take that tiny risk [and multiply it], you do get significant population risk. You could argue that there's risk but it's OK as there is a benefit. But there are alternative technologies, such as millimeter scanners that don't have this X-ray risk.

An individual who lives in Tokyo doesn't have that choice and there are no individual benefits. Fortunately, for an individual the risks are extremely low.

You readers may or may not know this but 40 percent of them are going to get cancer, so the sorts of increases we're talking about are miniscule. It's a tiny addition to a very large problem.

You've been working on a system where people can do individual testing with a blood test (called the RABIT, for rapid automated biodosimetry tool for radiological triage). Is the goal to get away from statistical estimates for whole populations Brenner: Yes. The motivation is [a response to] a large-scale radiological terrorist event [from a dirty bomb]. In many senses, that scenario is quite like the scenario in Japan with a very small number of people exposed to high doses. And a very large number of people exposed to very small doses and not believing what they are being told. There is a great deal of skepticism in Japan and I'm sure that would be true in this country too. The goal is to have some very high-throughput way of estimating one's dose. So you can try to find the folks who did get high doses who need to be treated. The other part is to reassure people.

We're developing a finger stick approach where you take a drop of blood, something that can be done by nonexperts. You'd have many centers, such as hospitals and railway stations, where you can go have your finger sticked, give a drop of blood, and it would get transported to more centralized machines. An individual estimate will mean that you won't clog up the emergency services.

What sorts of precautions should someone in the U.S. and Japan take right now Brenner: You don't need to be doing anything. The EPA is testing the water and milk and the levels are all pretty low and will get a lot lower as iodine decays. There's no reason to avoid any food or drink. The same goes for Japan. Yes, there will be some contaminated food [and they are being monitored with spot checks] for the moment. That's what the government is and should be doing [to watch that] it is going to be at reasonable levels.