03/30/2011 08:26 am ET | Updated May 30, 2011

Three Weeks After Japan's Disaster, What Are the Real Risks in the U.S.?

Three weeks after the onset of the nuclear power plant disaster in Fukushima, Japan, many residents of the U.S. are fearful about the possible health effects of radiation traveling across the Pacific.

The Union of Concerned Scientists (UCS), an independent scientific research-based environmental advocacy group, has been monitoring the crisis closely. Below is a condensed version of some of the information the UCS has placed on its website regarding the health consequences of the Fukushima disaster, as well as information shared at news briefings by David Lochbaum and Edwin Lyman, nuclear safety experts with the UCS:

What are radioactive isotopes, and which ones are of most concern in a nuclear power accident?

UCS: Radioactive materials decay, releasing particles that can damage living tissue and lead to cancer. Some elements have different forms, called isotopes, that differ in the number of neutrons in the nucleus.

The radioactive isotopes of greatest concern in a nuclear power accident are iodine-131 and cesium-137. Iodine-131 has a half-life of 8 days, meaning half of it will have decayed after 8 days, and half of that in another 8 days, etc. Therefore, it is of greatest concern in the days and weeks following an accident. It is also volatile so it will spread easily.

In the human body, iodine is taken up by the thyroid, and becomes concentrated there, where it can lead to thyroid cancer later in life. Children who are exposed to iodine-131 are more likely than adults to get cancer later in life.

To guard against the absorption of iodione-131, people can proactively take potassium iodine pills so the thyroid becomes saturated with non-radioactive iodine and is not able to absorb any iodine-131.

Cesium-137 has a half-life of about 30 years, so will take more than a century to decay by a significant amount. Living organisms treat cesium-137 as if it were potassium, and it becomes part of the fluid electrolytes and is eventually excreted. It can cause many different types of cancer.

Is there a threat to Americans in Hawaii, Alaska, or the U.S. West Coast? Should residents of these areas take potassium iodide pills to protect against thyroid cancer?

UCS: No. While wind patterns will likely carry the radioactive plume eastward, since Japan is thousands of miles from the United States, radioactive material in the air will be so diffuse by the time it reaches Hawaii, Alaska, or the mainland United States that it is highly unlikely to create significant health concerns.

As a result, people in those locations will not have to worry about direct inhalation of a radiation plume, which is the kind of exposure potassium iodide (KI) pills are most effective against.

Americans could also be exposed to radioactive iodine if agricultural products were contaminated. Radioactive iodine could be ingested by dairy cows, for example, and then would be concentrated in milk. Potassium iodide, however, would not be effective in that situation. Moreover, federal and state health authorities would test for such contamination and could take products off the market if necessary.

The people of Japan should be given priority access to KI pills. Indeed, if there is a run on medication in the United States, or elsewhere, there might not be enough left for Japanese residents who truly need it.

Radioactive Iodine has been found in water supplies as far away as the East Coast of the United States. Should U.S. residents be concerned about the safety of their drinking water supply?

Dr. Lyman: In my judgment, at this point, no. We have to use a disclaimer that no level of radiation is safe, because the scientific consensus is that there's no threshold to the carcinogenic effect of radiation, but the risk is proportional to dose, and the dilution that's experienced as a plume travels many thousands of miles is highly significant.

Also, the quantity of iodine that's available for release is decreasing rapidly in time because of the short half-life of iodine 131. So, provided the reactors don't go critical again, which they take measures to prevent, the total amount of iodine will decrease steadily.

Can you be exposed to dangerous levels of radiation if you fly in a plane across the United States due to the radiation released in Japan?

UCS: No. As noted in the previous question, since Japan is thousands of miles from the United States, radioactive material carried by the wind to Hawaii, Alaska, or the mainland United States will be so diffuse that it is highly unlikely to create significant health concerns. This is true whether you are on the ground or in an airplane.

Can plants in the United States withstand disasters such as the earthquake and tsunami that crippled nuclear reactors in Japan?

UCS: Some U.S. reactors are sister plants to the Fukushima Unit 1 reactor, which is a boiling water reactor (BWR) of General Electric design, and they are operating under similar regulations. If confronted with a similar challenge, it's folly to assume the outcome would not also be similar.

U.S. plants have the same key vulnerability that led to the crisis in Japan. The basic problem is that the Japanese reactors lost both their normal and back-up power supplies, which are used to cool fuel rods and the reactor core. The reactors had batteries that could supply power for eight hours until the back-up system or normal power supply was restored. But officials were unable to fully restore either.

Most U.S. reactors are designed to cope with station power outages (where both primary and back-up power supplies are out) lasting only four hours. Measures that increase the chance of restoring power within the four-hour time period, and provide better cooling options if that time runs out, would make U.S. reactors less vulnerable.

In addition, we know that earthquakes can cause fires at nuclear reactors, and U.S. reactor safety studies conclude that fire can be a dominant risk for reactor core damage by disabling primary and backup emergency systems. Yet dozens of nuclear reactors in the United States have operated for years in violation of federal fire protection regulations, with no plans to address these safety risks any time soon.

Finally, reactor emergency plans in the U.S. assume that a reactor accident would be the only demand on emergency response resources. The accident in Japan is another reminder of the need to revisit emergency plans to ensure that emergency responders are able to respond to both the problem at the power plant and the nearby community's needs.

Since 9/11, the U.S. nuclear industry has implemented additional power plant safeguards. Are we better equipped than the Japanese to cope with such a situation?

Mr. Lochbaum: Well, I think with the situation they have, they have to grasp at straws to try to explain why what happened there can't happen here. They're basically similar reactor designs operating under similar regulations, so if our reactors were faced with a similar challenge, the outcome would be similar.

There are certain things that were done since 9/11 that help, but I don't think that's a panacea that makes any of our reactors invulnerable to the type of problem that Japan faced.

Dr. Lyman: First of all, the plans are secret. So, no member of the public actually knows what those plans involve. Second, what we do know is that because those were addressing what (the Nuclear Regulatory Commission) considers to be a beyond design basis event, mainly an aircraft attack on a currently operating plant, we do know that the equipment, any equipment that would be staged or designated for that post-accident management would not meet the highest nuclear safety standards that are required for protecting its design basis events.

So, for instance, (the) Nuclear Energy Institute (an industry group) already admitted that that equipment is not safety-related and would not be seismically qualified. So, if you have an event other than an aircraft crash, let's say a large earthquake, it's not clear that those plans and that equipment would actually survive to be available, and putting U.S. reactors in the same spot that they were in Japan.

Will washing Japanese produce make it safe? Can Japanese produce be decontaminated?

Dr. Lyman: With regard to iodine, that is a limited problem, and will be cleared in a few months. To the extent there's contamination with cesium, and other longer lived isotopes, frankly, I don't think there are any good answers about how affected produce can be decontaminated. There are both national limits in Japan, international limits for destruction of contaminated produce, and I think those will have to be followed.

The problem is going to be when the contamination is within limits that the authorities say is safe. I think people need to understand more. I think I've said before, understand the potential doses associated with those levels and make their own decisions whether they should consume the produce or not.

But I would think whether or not it can be washed off, because I've been watching NHK and seeing what people are saying, I would be very wary of any unverified information about how to make produce safe at this point.

There have been concerns about radioactive water from the plant entering the ocean. Is seafood safe to eat?

Dr. Lyman: There is the potential, when you're talking about certain types of seafood, that you can have reconcentration. So, even dilute levels of contamination can be enhanced in certain marine life, just like mercury concentrates in large fish, like tuna. Also, plants like seaweed are known to concentrate certain isotopes, and so are certain types of shell fish.

But I would think certainly in the fishing industry in the region, they're most likely going to have to take measures to inspect their catches, and I guess the primary responsibility for that will have to be with the Japanese to inspect and interdict any contaminated seafood. So, it certainly could be an issue.

I would think (dangerous levels of radiation are) unlikely for seafood that is not caught relatively close to the Japanese shore, but, you know, we haven't done any analysis on this, so we can't really speculate.

The FDA has banned the import of milk and fresh produce from the Fukushima region. Should the U.S. ban all Japanese food products?

Dr. Lyman: Obviously it's not just the real risk, but it's also public perception and it's the same, whether it's Mad Cow Disease or melamine or lead. Unfortunately, one of the economic outcomes of this type of event ... is the perception of contamination which can be as damaging as the actual, or more damaging than the actual health risk, and that will have an economic impact whether or not there's actually a significant health risk.

So, unfortunately, it's going to take a long time for Japan to restore confidence in the safety of its exports.

A similar version of this article originally appeared on the website of New America Media.