As Japan struggles to repair nuclear power plants damaged in the March 11 disaster, questions linger over the long- and short-term health risks of radiation exposure in the region and beyond.
Norman J. Kleiman, PhD, a faculty member in the Mailman School's Department of Environmental Health Sciences, is an expert on the health effects of radiation, who has been repeatedly tapped by the media in recent weeks to discuss this issue. He cautions against overstating the dangers. Dr. Kleiman offers a historical perspective on how this catastrophe compares to nuclear plant incidents at Three Mile Island in 1979 and Chernobyl in 1986. He also offers some surprising insights into the real public health impact of the current disaster.
How does this compare to Three Mile Island or Chernobyl?
These are two ends of the spectrum. Three Mile Island was a partial meltdown of a nuclear reactor that was completely contained by the structure of the reactor. The only release was a small amount of gas that was vented by the operators in order to reduce pressure in the structure. There has been no epidemiological evidence of any increased health risks to those living near Three Mile Island.
Chernobyl was at the opposite end. It involved the release of several hundred tons of material that were ejected into the atmosphere due to a steam and possibly hydrogen explosion within the reactor core itself. Unlike U.S. and Japanese designs, the reactor was not protected by a concrete and steel primary containment vessel. The explosion contaminated a large amount of air, water, and soil over thousands of square kilometers and exposed a relatively large number of people to low amounts of radiation.
The explosions in Japan were of hydrogen gas in the secondary containment above the reactors. But the reactors and their primary containment are essentially intact as far as we know – although there may be small cracks with some radioactive material escaping. The entire containment vessel has not been compromised, whereas in Chernobyl the reactor itself exploded and was not contained. At this time, with the information we have so far, the situation in Japan appears to be much closer to a Three Mile Island kind of incident.
How was the population affected by the Chernobyl explosion?
Those who worked in the first 24-48 hours in the immediate aftermath were exposed to potentially lethal doses of radiation with 30-40 of the several hundred plant employees and emergency workers dying from the acute effects of radiation exposure over the ensuing months and years.
Beyond that about 600,000 young Russian army recruits worked for 2 years to clean up the debris and soil around the plant and were exposed to significantly lower doses [than the initial workers] but much higher than background levels of radiation.
Researchers, including former Mailman faculty members Lydia B. Zablotska and the late Geoff Howe, have followed those workers–but we’re not seeing a large increase in cancer cases so far although a small elevation in absolute risk for leukemia was noted. In addition, work initiated by the late Basil Worgul at Columbia University, including my ongoing studies at the Mailman School, indicates there is an increased risk for radiation cataracts in these individuals at exposure levels previously thought to be below the threshold for such non-cancer effects.
In the general population, the only direct radiation-related health outcome we can definitively point to is in children and adolescents who consumed milk contaminated with radioactive iodine in the first two months after the explosion. Dr. Zablotska and her collaborators here at Columbia University's Medical Center and at the National Cancer Institute have reported that to date, there have been about 5-6,000 excess thyroid cancer cases, including 50 deaths attributed to that exposure. But there is no definitive epidemiological evidence of any other dose-related cancer outcomes in the exposed general population and no statistical increase in birth defects or non-cancer effects of radiation.
Why weren’t the health impacts of Chernobyl more severe?
As compared to Hiroshima, where radiation exposure was perhaps hundreds fold lower but instantaneous, the Chernobyl radioisotope composition and ratios, dose, and dose rates were very different. Low dose exposure for some individuals may continue for years to come yet these continued exposures needs to be counterbalanced by the body’s natural ability to repair radiation-induced DNA damage.
Keep in mind, the DNA in each cell in our body is damaged tens of thousands or more times each day from a variety of environmental and endogenous sources. This is natural – human beings have evolved in background of DNA damaging insults including natural ionizing radiation – found in rocks, radon gas, and cosmic rays from the sun and other stars. Human activity like diagnostic X-Ray, CT, and PET procedures, flying, smoking cigarettes or burning coal also contribute to our background radiation exposure such that we’re exposed to ~6 millisieverts a year from natural and man-made sources. Estimates from large scale epidemiological studies of the A-bomb survivors and multi-country studies of nuclear plant workers suggest an additional cancer mortality risk of ~0.005% per mSv (or 1/20,000 per mSv).
As it stands, our risk of developing cancer during our lifetime from all sources is about 44%; our lifetime risk of dying from cancer is roughly 1 out of 4. The relatively small increased risk from radiation exposures such as those found at Chernobyl needs to be seen within that context.
In recent days, the Japanese government has detected high levels of radiation in foods like milk and spinach produced in areas far from the affected nuclear plants. What does this food contamination tell us about the zone of exposure?
I think that it’s important to define "high" – not just looking at it as higher than background levels or in some cases higher than regulated limits – but in terms of risk to human health. I’ve seen reports that at the levels detected so far you’d have to consume spinach every day to reach the level of one CT scan. We need to remember that although the levels are significantly higher than background and the government is taking the right steps to take that food off the shelves– the actual effect of consumption of small quantities is quite low.
What lessons are there from previous events that would help the current situation in Japan?
The take-home message from Chernobyl is that in these situations, public health concerns relate more to access to food and clean water, appropriate nutrition, alleviating anxiety and psychological distress, the effects of displacement, mental health concerns, and excess smoking and alcohol consumption-all of which are often side effects of any large natural and/or man-made disaster (similar to what is happening in Japan) that cause disruptions in people’s lives.
Had the Russian authorities stopped consumption of milk and dairy products, they would have prevented many of those thyroid cancer cases and deaths. Rapid public health response from officials, including rapid dissemination of accurate information and guidance, relocation and providing shelter and medical care for potentially exposed populations, and where appropriate, interrupting contaminated food and water supplies are the public health priorities in these situations.
More than two weeks after the disaster, plutonium has been detected in soil samples surrounding the Fukishima nuclear plant. What are the public health implications of this?
The source of this contamination and the actual amounts are a bit unclear but, according to most reports, the amounts appear to be relatively low and are likely to pose minimal risk to public health, although there is no absolutely safe level of such contamination.
It has been suggested that some of the soil contamination resulted from decades earlier above-ground nuclear testing in the Pacific although some fraction may indeed have come from the damaged fuel rods. At present, the overall human health risks from exposure to lighter radioactive contaminants such as iodine and caesium (which may travel further distances) are of somewhat greater public health concern, although levels of these radionuclides also seem to be declining in recent days.
What about the reports indicating that the levels of radioactive iodine in drinking water in Tokyo and other regions have, on occasion, exceeded regulatory limits?
At present, it appears that the levels of iodine have fallen back to “safe” levels in the water supply. It is important to remember that these “action levels” are set several orders of magnitude below that which might result in significant human health risks, in part to protect the most vulnerable segments of the population, i.e. infants, children and those particularly radiosensitive individuals.
While the crisis is yet far from over and levels may continue to fluctuate, at present, the risks from contaminated water seems to be lower in comparison to a few days ago. The government is continuing its efforts to measure radioactive contamination in a wide variety of food products and water sources to ensure that any contaminated food is removed from the supply chain and that water levels continue to be at safe levels. At the same time the government is advising the population, particularly parents of young children, to use bottled water as a precaution.
Posted March 22, 2011
Updated March 30, 2011