Ira Helfand, board member and past president of Physicians for Social Responsibility.

The news out of Japan has not been good this week. Officials there raised the severity rating of the nuclear disaster at the Fukushima Daiichi power plant to the highest level, while the plant continues to dump radiation into the air and water and radiation is found in milk and drinking water in U.S. cities and elsewhere. What does this mean for you and me

To help make sense of the health and environmental consequences of this crisis, CNET spoke to two experts in the nuclear field. My colleague Martin LaMonica spoke with David Brenner from Columbia University's Center for Radiological Research. Brenner says that while the individual risks are currently low for people outside the area around the Fukushima Daiichi power plant, radioactive particles have entered the food chain and will be there for generations, which will likely cause at least some cases of cancer. That Q&A can be found here.

Ira Helfand, board member and former president of the medical and public health group Physicians for Social Responsibility, says there is no "safe" level of radiation and that while levels reaching the U.S. now are relatively low, they could get much worse if things deteriorate at the Japanese plant. But for now, he advises caution, not panic.

What health risks for people in the United States does the nuclear crisis in Japan pose I think the health risk right now in the U.S. is relatively low. There is no safe dose of radiation, so any exposure is not good for you and does increase your chance of getting cancer. The concern is how much radiation is ultimately going to come out of this plant. At the moment, the amount is said to be about 10 percent of the amount released at Chernobyl. The amount that is potentially releasable there is much, much larger than Chernobyl, and the situation remains completely out of control at this point. There's still a substantial risk that there will be large amounts of radiation from Fukushima, and in that case we could see a significant exposure here in the United States. Following Chernobyl, people in large numbers developed cancers as a result of their exposure to that radiation, and that is the potential risk here, although we're not at that point yet.

There are indications that Fukushima has more than 20 times the amount of nuclear fuel than Chernobyl had. Does this mean that the potential threat from Fukushima could exceed that of Chernobyl Absolutely there is much more radioactive material in play here. There are some important differences. There was a huge fire at Chernobyl and it was hard to disperse the radioactivity, and there has not been that kind of fire so far at Fukushima. But there's an enormous amount of radioactive material there, which is not under control at this point and which could enter the environment and potentially travel large distances.

Did comparable levels of air, water, and milk contamination show up in the United States after the Chernobyl disaster in 1986 I don't know the exact levels that showed up in the United States after Chernobyl. There certainly was contamination and large contaminations across a big swath of Europe. The issue for us with Fukushima is that the predominant winds tend to blow from west to east so that, although there has been some radiation blowing towards mainlands Japan and Korea, there is a real possibility that if there is a large release that it would blow the other direction toward the United States.

What's the difference between the radiation that plant workers are exposed to and air-borne radioactivity For the most part workers are being exposed to a very intense Gamma Field. They're wearing protective suits and filters so the radioactive particles aren't getting into their lungs and on their skin. They're still getting gamma rays, which are like X-rays, they pass right through those radiation suits. So they're getting a one-time radiation dose and they're at risk of radiation sickness and at risk of cancer down the road. The airborne particles pose a slightly different problem. They get into food and water and get inhaled by people as well. They then become what are called "internal emitters" and get incorporated into our tissues and continue to irradiate us on an ongoing basis for, in some cases, decades of time. In that way they deliver a much higher dose of radiation over time.

You've said hundreds of thousands of cancer cases that occurred in the former Soviet Union because of the Chernobyl catastrophe were due to people eating radioactively contaminated food. Is that the biggest risk to people outside Japan Probably. It depends how much radiation is released. But probably the main way this would get into our systems is if we eat contaminated food. And that could be food imported from Japan or grown here in the U.S. if there is a large amount of radioactive material here. There's an area in the United Kingdom where people are still not allowed to raise sheep for consumption because of intensely radioactive contamination there from Chernobyl 25 years ago.

How far do radioactive particles travel It's basically a worldwide distribution. Radioactive material from Fukushima is probably detected at any place on the planet at this point. Obviously, the closer you are, the more downwind you are, the greater exposure you are going to see. When you release this much radioactivity it ultimately disperses everywhere.

Do you think that the levels of iodine 131 and cesium 137 showing up in air, water, and milk in the U.S. are safe U.S. officials say they are at low levels and that we shouldn't be worried. The word "safe" is kind of charged here. I would say that there is no safe exposure to radiation and the Bier VII report (PDF) from the National Academies agrees with that. Any dose of radiation you are exposed to increases your risk of getting cancer. Having said that, the doses we are seeing right now are extremely low. The increased risk of cancer an individual person gets from drinking that water is extremely low. On the other hand, if very large numbers of people are exposed to a very low risk, some of those people are going to get cancer and they are going to die from it. That's the problem with using a word like "safe." What you can say is the risk is so low that people should feel that they can drink the water, but it's not the same as saying there is no risk at all.

Would you consider the low or moderate levels of cesium-137 contamination that we are all now experiencing worth the risk They're not safe. The added risk of cancer is very low for any one individual, but that's not the same as saying people aren't going to get cancer from this because large numbers of people are potentially going to get exposed to it. Unlike iodine, which has a half life of eight days (every eight days the radiation is halved), cesium's half life is 30 years, so this is a long-lived contaminant and long-lived threat to the people exposed to it. They are reporting cesium in milk in the U.S. and how low the dose is I don't know at this point. I'm not sure we do know what the doses are. One of the things that was very troubling for those of us who gave the Japanese the benefit of the doubt was to discover that they knew for several weeks that this accident was much worse than they were letting on. There are real concerns about the quality of the data we are getting. This certainly was a huge issue after Chenobyl.

But there are suggestions by government officials and others that low levels of radiation cause no health problems. There is no safe level of radiation. It's wrong to say that they are safe. What you can say is the risk is extremely low, so low that for any one individual it is reasonable to continue to drink the water or milk. But if enough people drink it some of them are going to get cancer.

Is it reasonable for any one person to assume that risk People have to decide how much risk they are willing to live with. When you get into a car and drive to work there a certain risk that you are going to have an accident. Some people aren't willing to drive to work, or fly in airplanes. There are a lot of things we have to do that have some risk associated with it. The key point for me is even if the risk is one that an individual might be willing to assume, it's not necessarily a risk that society should assume. Even if we don't need to take individual action to protect our health, we shouldn't be letting this happen in the first place.

The U.S. FDA has stopped food imports from Japan. Is this likely to be temporary How is this sort of thing determined It's not clear how long this will be a problem. It depends on how much radiation continues to come out of the plant. If the radiation stops, most of it has been iodine 131, and that will decay quickly. But if it continues to leak iodine 131 or we get a bigger leak of cesium 137, this could be longer term problem.

What about the radiation risk to seafood, and seaweed, which is commonly used in sushi Would you consider them safe to consume Not necessarily. It depends on where they are gathered from. They're dumping an enormous amount of radioactivity into the ocean right now. They're going to have to monitor the fish and the seaweed very closely to see if they've incorporated significant amounts of this radioactive material. The problem is that the fish move around, so fish that have swum through that area could get caught somewhere else. We're going to have to be careful.

Should the government be testing seafood from any international waters at this point They probably do need to do some surveillance testing, at least. Tuna migrates and some ends up off the coast of the U.S. and Canada. We'll have to make sure this stuff isn't carrying high levels of radioactivity, particularly cesium.

What else should the U.S. government do I think the main thing they need to do is to review policy around our own nuclear power plants. It's very disturbing that the reaction of the U.S. government from Obama on down is this knee-jerk reaffirmation of our continued intention to use nuclear power. In the face of this accident a little bit of examination would seem to be appropriate. The U.S. government just said that people shouldn't be within 50 miles of the Fukushima plant. If you draw 50-mile circles around all the power plants in the United States there are 110 million people who live within those circles. There are individual power plants whose evacuation zone would be 17 million people. That's in New York. It is very wrong to just say we are going to go full speed ahead, damn the torpedoes, when we have this number of people in harm's way.

What should people in Japan do to protect themselves And how about people in the U.S. Here in U.S. at the moment we don't need to take any specific measures to protect ourselves, except monitor the situation closely so if there are significant further releases we are prepared to act then. In Japan there are people who should and probably are taking potassium iodide to protect themselves in the event of iodine 131 exposures. They have be very careful about their food supply. The produce grown in Fukushima won't be safe for human consumption.

Will they ever be able to grow food there again If there is a lot of cesium in the soil, it's going to be a very long time before they grow anything safely there. There are areas around Chernobyl where people still aren't supposed to be growing food.

There is a perception that low radiation levels are just more incremental noise in an environment already filled with background contamination from cosmic rays, radon gas, and X-rays. Do people die from that contamination we get on a daily basis Why is this different People do die from that. One of the things that causes cancer in the world is radiation. People get melanoma from solar radiation. They get lung cancer from breathing radon particles, particularly in areas of construction done with granite. And a certain amount of natural instance of cancer is caused by natural background radiation. The point is, the fact that we already have radiation in the environment isn't reason to expose people to more of it and cause more of that effect.

Anything else that you would like to add I would like to point out the role that nuclear power plays in the proliferation of nuclear weapons. We've got this weird situation where we identify the proliferation of nuclear weapons as the No. 1 security threat to the United States. At the same time it is our formal government policy to promote the export of nuclear power to countries all around the world. Any country that has a nuclear power industry can build nuclear weapons, and we just can't have it both ways.