R A D I A T I O N
strikes fear into the stoutest heart
By Stephen Pincock
As the crisis mounted at the Fukushima Daiichi and Daini power plants, the UN’s atomic watchdog said 230,000 units of stable iodine — or potassium iodide — had been sent to nearby evacuation centres. “The iodine has not yet been administered to residents; the distribution is a precautionary measure in the event that this is determined to be necessary,” the International Atomic Energy Agency said. Iodine tablets get a lot of attention in any online discussion of radiation, where they are regularly described as “anti-radiation pills.” In reality, their benefits are much more limited than that name might suggest. The idea behind taking potassium iodide (KI) is to prevent the thyroid from absorbing radioactive iodine, one of radioactive substances that likely to be present in the plume from a nuclear accident. In the wake of the 1986 Chernobyl accident, for example, when the entire reactor blew up and vaporised its radioactive fuel, there was an epidemic of thyroid cancer. “If taken within the appropriate time and at the appropriate dosage, KI blocks the radioactive iodine from being absorbed by the thyroid gland and reduces the risk of thyroid cancers and other diseases,” says the US Nuclear Regulatory Commission. “KI does not protect against any other inhaled radioactive materials, nor will it offer protection from external exposure to radiation.” Experts recommend limiting the use of KI to people inside a 16km radius around a disaster — the area where people are most likely to be exposed to radiation by inhalation. Outside that zone, where the most likely exposure to radiation is via eating or drinking contaminated substances, KI is considered not worth using. “There has been a lot of controversy over the years about iodine — its effectiveness and when it should be administered,” says Associate Professor Gerald Laurence, an expert in radiation safety from the University of Adelaide. “It’s probably going to help some people [in the case of a nuclear disaster] but it’s uncertain how many.” So if iodine is of only minor protective value, can modern medicine offer any other assistance to those exposed to radiation? Little Boy’s legacy The atomic bombs dropped by the US on Nagasaki and Hiroshima in August 1945 provided the first opportunity for the world to witness the health impacts of exposure to large amounts of radiation. More than 150,000 people died in those two cities within four months of the bombings, about half of them in the first day. The following year, the US Strategic Bombing Survey (Atomic attacks) estimated that 15-20% of the deaths resulted from exposure to the gamma radiation emitted by the bombs. Exactly why the radiation was harmful wasn’t clear at that point. Since those early days, researchers at the Radiation Effects Research Foundation (RERF) — a joint Japan-US endeavour — have conducted some of the most impressive and important epidemiological studies of their kind, revealing much more about the short- and long-term effects of exposure. Their research on survivors of the bombings show that the constellation of illnesses we call radiation sickness, or acute radiation syndrome, develop only in people exposed to doses of radiation that are high enough to kill cells — generally considered to be in excess of 1-2Sv of radiation. The main signs and symptoms of acute radiation syndrome include vomiting within a few hours, followed within days to weeks by diarrhoea, reduced blood cell counts, bleeding, hair loss, and temporary male sterility. According to the RERF researchers, diarrhoea results from damage to the intestinal lining, reduction in blood cells is caused by the death of hematopoietic stem cells in bone marrow, and bleeding is the consequence of declining blood platelets generated from stem cells. Hair is lost due to damage to hair-root cells. In the long term, other effects of radiation exposure — such as an increased risk of solid cancers and leukaemia — reflect an increased rate of mutations in living cells, triggered by the radiation. Exactly how many people in Hiroshima and Nagasaki have developed these conditions after radiation exposure isn’t clear, but it may be fewer than we think. RERF researchers estimate that about 1900 cases of cancer were attributable to radiation exposure in the two cities over the course of the 45 years following the bombs. Unwarranted fear Of course, civilian nuclear disasters so far have been nowhere near as catastrophic as the atomic bombs dropped during the war. Even the most infamous disaster of all — the explosion of the Chernobyl reactor in the Ukraine, 25 years ago — was less catastrophic in health terms than the general perception would suggest. Following the accident — which caused the largest uncontrolled radioactive release into the environment ever outside war — a total of 134 plant staff and emergency workers suffered acute radiation syndrome, all of whom breathed in huge amounts of radioactive smoke. Twenty-eight of those people died. Several hundred thousand people were exposed to smaller doses of radiation, but, “there were no cases of acute radiation syndrome among the general public”, according to a UN report published this month. In fact, other than an increase in thyroid cancers among those who were children or adolescents at the time, 20 years of research have revealed no persuasive evidence of any other health effect in the general population that can be attributed to radiation exposure, the report says. “The vast majority of the population need not live in fear of serious health consequences from the Chernobyl accident,” say the UN authors. Less-severe accidents, such as the disaster at Pennsylvania’s Three Mile Island reactor in 1978, are thought to have resulted in at most one or two additional cancer deaths in the 16km around the reactor. According to the American Nuclear Society, “the average radiation dose to people living within 10 miles of the plant was eight millirem … about equal to a chest X-ray”. (Radiation units are confusing: a millirem is equal to 0.00001Sv, so the exposure was about eight ten-thousandths that required to cause radiation sickness). If nuclear accidents are less harmful than we think, why are they attended by such widespread panic? Associate Professor Laurence from the University of Adelaide thinks it has to do with the “Big C” — cancer. “When you have an agent whose primary effect is to increase the risk of cancer, it generates fear,” he says. “I suspect that if radiation caused heart attacks people wouldn’t be so worried.” As Dr Jim Smith says: “A key risk at present is public panic in response to this incident. It is important to focus on the radiation risk, but experience from past nuclear incidents has shown that the stress and panic caused by these events can be as bad as, or worse than, the direct threat from radiation. “Even after Chernobyl, although there were some severe health effects at the population level, the risk to individuals, except within the immediate vicinity of the plant, was very low,” says Smith, from the School of Earth and Environmental Sciences at the University of Portsmouth, UK. “So, for people outside the immediate vicinity of the plant, even in meltdown on the scale of Chernobyl, the individual risk is likely to still be very low.” Big dose, little hope If the news is good for many of those outside the vicinity of a nuclear catastrophe, there is less hope for those who do find themselves exposed to large doses of radiation. Despite much research over the past 55 years, there has been no remedy developed that can help those with acute radiation syndrome, says Associate Professor Laurence. “All sorts of interventions have been proposed but none of them that gone as far as a clinical trial,” he says. Proposals have included plant extracts, fruits, hormones and antioxidants, some of which have proven effective in cell culture — but none in the real world. “The reactions happen so quickly at the cellular level when radiation exposure occurs, that I find it difficult to imagine a mechanism by which taking a lot of antioxidants could benefit you,” he says. The challenges of treating people who suffer enormous radiation exposures were illustrated during another Japanese nuclear catastrophe in 1999. During the so-called Tokaimura Criticality Accident, three workers received high doses of radiation in a small Japanese plant preparing fuel for an experimental reactor. The three workers each received radiation doses of between five and 20Sv. The men were hospitalised, and despite the best efforts of Japanese experts, one died 12 weeks later and the other seven months later. The third man survived.
“Heroic efforts were made to save them, and the full weight of technological medicine was employed, but in the end with that massive dose, nothing could be done,” says Associate Professor Laurence.