Chernobyl's Stressful After-Effects

The first clear scientific findings are more surprising than is generally appriciated, and their meaning is more obscure

Photo: Sake Elzinga/IPD
View of Chernobyl Unit 4 was taken days after the accident of April 26, 1986. The force of the explosions that ripped the top off the reactor can be gauged from the bent-outward girders near the center.

Defining terms

Becquerel: one nuclear disintegration per second, equal to 2.7 X 10-11 curie.

Gray (Gy): 1 J/kg, equal to 100 rad.

Rad: 100 erg/g, equal to 0.01 Gy.

Rem (radiation-equivalent man):
a rad (radiation-absorbed dose) adjusted for a quality factor (q) reflecting the biological "effectiveness" (that is, destructiveness) of the radiation and situation. That is, q is a function of radiation type, its energy, and the material affected.

Sievert: 100 rem.

Person.sievert (or person.gray): a unit of population exposure obtained by summing dose-equivalent values for all exposed persons.

The explosions and fires that wrecked the Chernobyl nuclear reactor 10 years ago last April brought on what is universally recognized as a catastrophe. Besides the immediate fatalities and human upheaval, which left hundreds of thousands disoriented, anxious about their own health, and bitterly concerned about their children, the accident inflicted incalculable material losses. In economic terms alone (though not in terms of casualties), Chernobyl was the greatest peacetime industrial disaster of all time. Its 10th anniversary was a fitting occasion for stocktaking--for determining what has been and has yet to be learned about the event, and for improving efforts to help the victims.

The one salvageable benefit is vital new information on how ionizing radiation affects human health. Already, to be sure, that relationship is better understood than the effects of most industrial pollutants, in both qualitative and quantitative terms. Further, unlike other contaminants, radiation doses are easy to reconstruct from the trails left by radioactive decay. But until now, the most important data on radiation health effects have come from the ongoing studies of survivors of the Hiroshima and Nagasaki atomic bombings. And inferences drawn from those intense exposures to radiation have not always meshed well with the results found when less radiation over a longer time is involved. Chernobyl is the first instance of huge populations being exposed to mostly low doses for many months and years.

As the 10th anniversary of the April 26, 1986, nuclear accident drew near, three major international conferences on its health effects were mounted. The culmination was a large gathering of experts in early April at the Austria Centre in Vienna, which IEEE Spectrum attended. It was sponsored by the International Atomic Energy Agency (IAEA), the World Health Organization (WHO), and the European Commission (EC). Concurrently, the Nuclear Energy Agency, based in Paris, issued an appraisal of the accident's radiological and health consequences. As for the two earlier conferences, one was sponsored by the WHO in Geneva, in November 1995, and the other was sponsored by the EC, Belarus, Russia, and the Ukraine in March 1996 in Minsk, Russia.

The scale of the reevaluations and the large overlap among the specialists taking part encouraged a fair degree of consensus about the accident's health effects so far. Still, first findings are tentative. One U.S. expert at the IAEA conference, radiologist F. A. Mettler, frowned on the Vienna meeting's billing: "Summing Up the Consequences of the Accident." Mettler, a member of the University of New Mexico's School of Medicine, Albuquerque, observed that full comprehension would take not 10 but 50 years.

Vastly complicating analysis is the crisis afflicting the former Soviets since the breakup of the USSR. In Russia, where national output is thought to have dropped by 50 percent and industrial production by nearly 75 percent, life expectancy for men has plummeted about seven years (to 58!) since 1986.

Often, too, those responsible for the welfare of victims are tempted to exaggerate, desperate as they are for funds. Belarus, the Ukraine, and Russia each have had at one time or another a ministry just for Chernobyl relief and monitoring. In Belarus, home to the worst-affected districts, 20­-25 percent of the state budget goes to remedying Chernobyl's effects. Small wonder that Angela Merkel, Germany's environmental minister and the president and keynote speaker of the Vienna conference, agreed with Mettler that Chernobyl's consequences "cannot be summarized conclusively even today, 10 years after the accident."

That said, three early results stand out:

  • The incidence of thyroid cancer has risen far more than expected among infants and even children still in the womb who were in the most contaminated zones right after the accident.
  • There is as yet no significant rise in leukemia among the inhabitants of those same zones or among the emergency workers and evacuees hit by the highest initial doses of radiation.
  • Perhaps most widespread are psychosomatic illnesses--even in not-too-contaminated areas, there has been a large upswing in stress-related physical ailments, notably stomach and autoimmune disorders. In fact, morbidity and mortality due to such disorders may well in the end exceed sicknesses and deaths caused by radiation.

Photo: Pacific Northwest Laboratory
Figure 2: The Ukrainian woman is living in the small village of Opachi, in the "forbidden zone" that people are still not supposed to inhabit. Studies have shown that, especially for old people, the stress of permanently leaving the ancestral home can outweigh the benefits of avoiding residual radiation.

Scope of accident
The amount of radioactive materials released in the Chernobyl accident totaled about 10 exabecquerels (EBq, or 1018 Bq), which resulted in a global dose of about 600 000 person.sievert [see Defining Terms, above]. About six tons of the reactor fuel, or roughly 3.5 percent of the reactor's initial fuel mass, is thought to have been ejected: first, when fuel fragmented during the initial explosion(s), and a week to 10 days later, when temperatures climbed again, maybe as graphite continued to burn and the remaining core reconfigured itself and melted down more radically. While the releases contained numerous fission products [Table 1], the iodide and cesium components were the most deleterious. Releases of Cs137 are put at 85 petabecquerels (1015 Bq) and of I131, at 1760 PBq (20­40 and 50­60 percent respectively of initial inventory).

A comparison with the effects of atmospheric tests of nuclear weapons was made by B.G. Bennett, secretary of the United Nations Scientific Committee on the Effects of Atomic Radiation (Unscear), Vienna. At the summing-up, he said that the amount of Cs137 released at Chernobyl was about one-tenth the total from the weapons tests, but that the amount deposited in Central Europe in April through December 1986 was equivalent to the total deposited over all the years in which weapons testing took place. Thus, "the greatest global release of radionuclides from a man-made source was atmospheric testing of nuclear weapons. The greatest local impact of man-made releases was, however, the Chernobyl accident."

table_1
Click on image to see the complete graphic.

Of the total dose of 600 000 person sievert from Chernobyl, about 40 percent fell on the former Soviet states, 50 percent on Europe, and the rest elsewhere in the Northern Hemisphere. At least a third of the dose was delivered to people by the first anniversary of the accident.

Persons nearest the blast
The health record is clearest for plant employees and emergency workers identified right after the accident as suffering from acute radiation sickness: 134, out of the 237 immediately hospitalized with clinical syndromes attributable to radiation. Out of the 134 acute cases, 28 died. In addition, two workers died at the site from injuries unrelated to radiation, and 14 more of the 237 have died in the 10 years since, not necessarily of causes related to radiation.

Most of the 28 who died early on were exposed to more than 6 gray, according to a report presented at Vienna and coauthored by one the world's leading experts on acute radiation sickness, Angelina K. Guskova of the Institute of Biophysics, Moscow. "In almost all of these cases, there was combined injury due to beta exposure resulting in skin radiation injury," the report said. Other major damage was to bone marrow and to mucous membranes in the digestive and respiratory tracts.

Those diagnosed as acute cases tended to suffer impaired fertility for rather long after the accident. Besides being at greater risk of contracting cancer, they may be more prone to cataracts and cardiovascular and gastrointestinal problems many years hence. Nevertheless, "to date, a detailed and scientifically sound overall account of clinical signs and symptoms of the surviving patients in the population of 237 is lacking in general," the Vienna report said. "Also, confounding factors have not always been dissociated from possible radiation effects."

In terms of treatment, Chernobyl's unequivocal lesson is that bone marrow treatment did not work. It was done at the time by the physician Robert Peter Gale of the Medical Center of the University of California at Los Angeles (UCLA). But most of those given transplants, as directed by Gale in collaboration with Guskova, died. So, as Gerard Wagemaker drily noted in Vienna, the focus needs to be on therapies that "don't do more harm than good." Wagemaker, a radiobiologist at Erasmus University, Rotterdam, the Netherlands, was principal author of the report on acute radiation sickness.

figure2
Photo: Sake Elzinga/IPD
Ukrainian administrator [right] checks dosimetry records. The reliability of dosimetry for the absorption of radio-active iodine and cesium is an important issue--and may have a bearing on what otherwise seem puzzling results.

Today's treatment of choice involves the pharmaceutical use of blood growth factors--circulating proteins, sensed by growth factor receptors on the blood cell surface, which control function and cell division or growth. But in 1986, they were only just becoming available, and their use was not well understood.

Thyroid cancer epidemic
By far the gravest health effect to have turned up so far has been the hugely elevated incidence of thyroid cancers among children [Fig. 5]. It has been much greater than most mainstream radiation health experts would have predicted on the basis of Unscear's 1988 and 1994 reports, the U.S. National Academy of Sciences' 1990 survey, or the latest studies from the Radiation Effects Research Foundation in Hiroshima [see To Probe Further, bottom].

E. D. Williams, a physician at Cambridge University's Addenbrooke's Hospital and president of the European Thyroid Association, reported that among children in the province of Gomel in Belarus--the most irradiated region anywhere--the thyroid cancer rate was more than seven times as high as in Belarus as a whole: 92 cases per million children per year, versus 14.6. Similarly, he said, in the most affected northern regions (oblasts) of Ukraine, the rate was 10.6 cases per million children per year, versus 1.5 in all of Ukraine. The normal rate of childhood thyroid cancer in Ukraine and Belarus, as well as in England and Wales, is 0.5 per million per year.

table 2
Click on image to see the complete graphic.

The rarity of the disease makes the Belarus and the Ukrainian results quite startling. Extrapolating from Japanese data, only five excess cases would have been expected in Gomel during the last decade. In fact, there were about 200.

Doses of I131 were to be sure large. In the Gomel oblast, children aged 0­-7 got an average dose of about 1 Sv, and nearly 300 of them got 10­40 Sv. In total, close to 800 children in the three countries have contracted thyroid cancer to date [Table 2]. Clinical experience indicates that 5­10 percent of them will die of the cancer, though only a handful have so far.

At first sight, since thyroid cancer can be treated if detected promptly, and since its increase is to date the accident's only documentable long-term effect from radiation, the situation may seem less serious than it is. But everyone who lived as a child in the worst-hit districts right after the accident will forever be at greater risk of thyroid cancer. For the tens of thousands of parents and grandparents of those children, it is small consolation that even if a cancer appears, the risk of death is "only" 10 percent. Even when the thyroid gland is successfully removed, recurrence is likely, and at best the individual faces a lifetime of regulating thyroid levels--a tricky business, with fatigue and malaise often the punishment for misdosage.

Searching for explanations
Until the latest data from Chernobyl, medical researchers generally held that the risk of cancer due to internal irradiation of the thyroid by inhaled or ingested iodine was about four times smaller than cancer risks from comparable external radiation, such as X-rays. Some physicists and biologists argued, to the contrary, that iodine was as dangerous as X-rays, so that the same linear model of dose response applied to both. While this position was favored by health physicists and adopted by the U.S. Food and Drug Administration, it was widely viewed as very pessimistic.

table 3
Click on image to see the complete graphic.

Lynn Anspaugh, a dose reconstruction expert and biophysicist at the Lawrence Livermore National Laboratory, California, told Spectrum that he guesses the incidence of thyroid cancers resulting from Chernobyl is higher than the best accepted models would have predicted by a factor of at least three or four. That pretty much squares with the views of Arthur Upton, a former director of the National Cancer Institute, Bethesda, Md., and chairman of the National Academy's 1990 survey. The fifth major study of low-level radiation effects on health (BEIR V), it was the first in many years to achieve a consensus among its authors. Upton and his colleagues recently prepared estimates of the relationships of dose to effect for the Centers for Disease Control and Prevention, Atlanta, Ga. Based on several studies, the relationships vary quite widely, but those implied by the Chernobyl data appear much higher [Table 3].

Could the Chernobyl results be spurious? After all, a Chicago study has found that with increased publicity and screening the observed incidence of thyroid cancer increased sevenfold. But the European Thyroid Association's Williams, speaking in Vienna, felt that this "ascertainment effect" played little part in the Chernobyl results. He pointed to the multitude of cases, the aggressiveness of the cancers, their dominant types (papillary or solid follicular, consistent with radiation induction), and above all the age distribution of the victims--skewed to children very young at the time of the accident.

The probability of radiation induction does not exclude, of course, the synergistic action of other factors, such as genetics and diet. Jews may be three times as susceptible as others to thyroid cancer, and among the thyroid cancer victims, about 15 percent are said to be of Jewish ancestry. The local diet may have been short on iodides, so that radioactive iodine would be eagerly taken up by the thyroid, and long on items that can damage the thyroid. [One way to prevent thyroid cancer is to distribute potassium iodide, which is concentrated in the thyroid. See, "Stockpiling potassium iodide: A U.S. policy issue. "]

Absence of leukemias
The one thing that members of the informed public tended to expect after the Chernobyl catastrophe is the one thing that has not been spotted--the kind of "leukemia epidemic" (Upton's phrase ) that followed the Hiroshima and Nagasaki bombings. Cases there began to increase within a few years of 1945, peaking about six years later, particularly among those exposed as children.

Note, however, that even among the populations most heavily irradiated at Chernobyl, the numbers of excess leukemia cases expected are near the outer limits of detectability. That is, the numbers of normally expected cancers are so large, any excess would be buried in the noise. The same goes for the excess of solid cancers expected to be diagnosed with time lags mostly longer than 10 years.

Because radiation from Chernobyl has been more diffuse than from the bombings, experts have generally believed that most cellular damage would be repaired by the body without causing malignancies. Nonetheless, within the best-defined populations of concern, some excess leukemias should in principle be identifiable by now. The facts were laid out by Elisabeth Cardis, a leading epidemiologist, head of the program on radiation and cancer at the International Agency for Research on Cancer, Lyon, France, and the principal author of the Vienna report on long-term health consequences of the nuclear accident.

Cardis said that 600 000-­800 000 people took part in clean-up operations, about 200 000 of them in 1986­87. In the most heavily exposed group of these so-called liquidators, the average dose was in the region of 100 mSv.

table 4
Click on image to see the complete graphic.

Besides the emergency workers, about 135 000 individuals were evacuated soon after the accident from a 30-km zone around the reactor. Then about 270 000 lived within a few hundred kilometers of the plant in areas classified as strict control zones, where deposition of Cs137 in 1986 was more than 555 kBq/m2. Finally some 6.8 million people live in areas classified as contaminated.

Among members of those groups, just over 5000 excess deaths from leukemia and solid cancers would be expected among residents of the widely defined contaminated areas, as against 827 000 such cancer deaths otherwise occurring; 1500 among residents of the strict control zones, as compared with 43 500 background cancer deaths; 150 among the evacuees, versus about 21 500; and--among the liquidators--2000 as against 41 500 [Table 4].

Most of those excess cancers would be "difficult to detect epidemiologically," Cardis reported, with a degree of understatement. But among the liquidators, about 150 excess would have been expected in the first decade, against 40 normally occurring, and in strict control zones, perhaps 170 against 60. In other words, incidence ought to be three to four times the norm.

Other leukemia findings
Cardis reported a nonsignificant doubling in the incidence of leukemia among Belarussian liquidators in 1993­94, and a threefold increase among Ukrainian emergency workers. But she said these results had to be treated cautiously because of differences in follow-up between exposed and nonexposed populations.

Evidence for a doubling of leukemia cases among liquidators was produced at Vienna by A.F. Tsyb, director of medical radiological research, Russian Academy of Medical Sciences, Obninsk. But the epidemiological basis of those results appears little accepted, and in any event, twofold increases are suspect because of the ascertainment effect--because closer scrutiny and improved health care for the affected populations would raise observed rates.

Epidemiologists are skeptical as well about a report of a post-Chernobyl increase in infant leukemia cases in Greece, according to Gilbert Beebe of the National Cancer Institute. Greece was one of the more highly irradiated countries outside the former Soviet Union. The report said that "infants exposed in utero to ionizing radiation from the Chernobyl accident had 2.6 times the incidence of leukemia compared to unexposed children" and that "those born to mothers residing in regions with high radioactive fallout were at higher risk of developing infant leukemia."

The report, by E. Petridou of the Harvard Center for Cancer Prevention, Boston, and colleagues, appeared in the July 25 issue of Nature, the esteemed British science weekly. In its favor is the fact that Greece has kept a national register of every case of childhood leukemia since 1980. But as Ron Shore, a thyroid epidemiology expert at New York University, New York City, noted, the excess cancers were few, the implied radiation doses were tiny, and no other study has found a similar effect (pronounced only in the first year of life and arising in the first three months of pregnancy).

Pieces of the puzzle
The failure to clearly identify excess cases of leukemia squares poorly with the evidence for thyroid cancers in children. To be sure, estimated bone marrow doses were rarely more than a few milligrays to a few centigrays, whereas thyroid doses were not uncommonly 1­10 Gy. Still, if dose estimates are systematically wrong, then the errors should affect both cancer types. Moreover, if an ascertainment effect has exaggerated the thyroid cancer rates, then the observed rates should be higher for leukemias, too--not lower than expected.

Estimates of the radiation released in the accident have in fact been revised drastically upwards since the Soviet experts' first presentation at the IAEA in 1986. The total is now thought to be double or triple the initial estimate, Spectrum learned from Lennart Devell of Studsvik Eco & Safety AB, Nyköping, Sweden, who was responsible for the radionuclide estimates reproduced in the Nuclear Energy Agency's 1996 summary report [Table 1].

But Devell emphasized that most of the increase was deposited outside the former USSR and that the original Soviet estimates--based on local dosimetry--still largely hold for within the former USSR. What's more, he said, the standard estimate for I131 used in the summary reports at Vienna, 2 EBq, was "an overestimate by almost 100 percent because some iodine decayed in the core before release."

figure 4
Photo: Pacific Northwest Laboratory
Aerial close-up of the reactor soon after the accident shows the upper biological shield [top], which after being tossed into the air landed on its side. The gaping hole just in front of it may have exposed radioactive materials to the atmosphere. "Elephant's foot" [bottom], consisting of molten fuel that solidified in the sarcophagus, suggests the extent of the meltdown.

Alexander Sich, a nuclear engineer who trained at the Massachusetts Institute of Technology, Cambridge, has published a theory about the course of the accident that may throw some light on the iodine dosimetry question. In the week after the April 28 accident, despite heroic efforts by helicopters to dump reactivity-damping materials on the burning reactor, most of the core remained uncovered, in Sich's opinion. He thinks this is plain from a comparison of the current disposition of equipment and materials at the reactor with photographs taken at the time from above [Figs. 1 and 2]. If the reactor was in fact exposed, it would have been spewing fission products into the environment all week long.

Sich, currently at the Department of Energy's Pacific Northwest Laboratory, Richland, Wash., can claim to have spent more time at Chernobyl studying physical evidence than has any other outside expert. He is inclined to see a good deal of uncertainty in the dosimetry [Fig. 3]. "People from Pripyat [Chernobyl's immediate home village] were standing there the next morning watching the reactor burn--what was their dose burden, and where are they now?"

But Lawrence Livermore's Anspaugh, a top dose reconstruction expert, expresses a lot of confidence in the standard estimates. He said that several hundred thousand direct thyroid measurements were made right after the accident in the heavily contaminated areas, and that the collective dose was largely constructed out of those known individual doses. Moreover, he said, that estimate agrees quite closely with a speculative reconstruction from environmental models.

As for the nonappearance of excess cases of leukemia, Anspaugh believes that when better studies are done over longer periods of time, the expected rates will materialize. It is generally agreed that identification and tracking of liquidators has not been what it might be.

Stress-related health effects
In the days right after the accident, the top Soviet authorities not only failed to level with the world and their own people, but also were in a kind of denial about the almost unthinkable occurrence. But as they came to terms with it, they kicked in with the kind of top-down, take-no-hostages campaign that made them both respected and hated. A second round of evacuations, in 1990-­91, aggravated stress without materially protecting anybody from further irradiation.

By relocating tens of thousands of people, often with little or no explanation, the authorities may have saved many from potentially lethal exposure to cesium. But their high-handedness created a whole other category of long-term health problems, which may prove more significant than all the excess cancers combined.

Early medical reports from the Soviet Union noted extensive "asthenia"--an archaic clinical term for lassitude, apathy, and inertia. The word is no longer used in the West and is perhaps best remembered as the working title of Woody Allen's film Annie Hall. At the time the symptoms might have seemed a temporary disorientation or mere worrying. But as Terence Lee, a psychologist at the University of St. Andrews, Fife, Scotland, reported at the Vienna conference, the lingering aftermath of Chernobyl is depression, anxiety, pessimism, and poor physical health far beyond what can be justified in terms of lifetime doses or thyroid conditions.

"Stress is not, contrary to wide opinion, a residual [a statistical catch-all category] where you dump everything that you can't explain," Lee said, "[but] a well-defined condition which, in association with alcoholism, smoking, and so on, can and does lead to measurable physical effects." Stomach disorders are the most sensitive indicators of stress, he said, and the main physical agents are the endocrine system and the autonomic nervous system, which malfunctions under prolonged or intense emotional arousal.

The kind of disorder common in the populations affected by Chernobyl is different from post-traumatic stress disorder in terms of both causation and characteristic symptoms, so Lee has coined a new term: "chronic environmental stress disorder." He emphasizes that studies of comparable nonirradiated populations have proved the syndrome is caused by Chernobyl as such, not just the upsetting conditions of life in the former Soviet states.

figure5
Photo: Gamma Liaison
Figure 5: Alexei Ruban, aged 14, has the very rare disease of thyroid cancer, which has shown up in large numbers of children living near Chernobyl. Ruban was seven at the time of the accident and believes that his deceased father also was a victim.

Rebuilding trust
The IAEA's 1990 Chernobyl Project was the first major study by outside experts of the health of people living in the less contaminated zones. According to the study, Lee noted, 45 percent of those in the contaminated areas versus 30 percent in the clean ones believed they had maladies attributable to radiation exposure. The boundaries were not sharp because, as Lee said, "people are aware of the great irregularity in the pattern of deposition; of the arbitrary nature of the threshold values; of the fact that averages are computed from fairly sparse measurements; and that areas identified by different authorities do not precisely coincide. In any case, they deeply distrust the authorities, are convinced that they have reason to underplay the seriousness of the situation and, indeed, believe that there was a cover-up during the early days."

Mona Dreicer, an environmental consultant based in Washington, D.C., and the coordinator of the 1990 Chernobyl project, said that when outside physicians arrived in the affected areas in the late 1980s, the commonest question they were asked was, "Does the outside world know about Chernobyl?" Commented Lee: "It's a baleful situation when external authorities are trusted more than local."

Lee reported that fatalism, together with attitudes toward the failing economy, was more indicative of stress in the Chernobyl populations than exposure as such. Moreover, fatalism tends to be self-propagating: fatalistic people are less careful about their diet, eat more cesium, so are more likely to get sick, and so on. Dreicer reported, for example, that people who eat wild mushrooms raw--contrary to public health advisories--will absorb three times as much cesium. Stigmatizing evacuees with nicknames like "glow worms" does not help.

To restore morale, Unesco has set up so-called trust centers among relocated people and in contaminated areas. The centers provide consultations and training for adults and play centers for children, foster creation of support groups, and organize social events to start reknitting a social fabric. Since opening several years ago, an estimated 10 000-­15 000 therapy groups have been started at the centers.

Fatalistic attitudes, besides compounding radiation effects, also complicate their evaluation. For one thing, with the establishment of compensation programs for special groups such as evacuees and liquidators, the claimed membership of these groups has soared. At Vienna, at least two physicians reported from the floor that at summer camps set up in countries like Sweden and the Netherlands for kids with early leukemia, the children have all been found to be in good health, despite certificates to the contrary from local doctors. One of the physicians said flatly that if she were a mother living near Chernobyl under the present conditions in the former Soviet states, she would move heaven and earth to get a small child of hers out of the country for any length of time she could manage [Fig. 5].

Long-term expected effects
Roughly 85 percent of all radioactivity released in the Chernobyl accident consisted of radionuclides with half-lives of less than a month. Now, 10 years later, the amount of radioactivity in the environment is about 1 percent of the initial release. While transfer rates of cesium from water to fish and from soil to plants have been rather high, Dreicer reported, "about 60 percent of the total external doses and over 90 percent of the total internal doses have already been received by now." Most excess cancer cases expected in the future, then, will be caused by past exposures.

Given that general picture, and extrapolating from the Hiroshima-Nagasaki figures, using age- and sex-specific estimates of risk per unit dose, the data presented by Cardis in Vienna suggest a death toll of about 7000 in the worst-affected populations due to Chernobyl-induced leukemias and solid cancers [Table 4]. And assuming about a million children received a thyroid dose of 500 mGy and using the incidence rate of 0.8 percent per sievert, Williams estimated that a further 4000 diagnoses of thyroid cancer would be expected over that population's lifetime. So, given a death rate of 5­10 percent among those diagnosed with the cancer, the total expected number of deaths from all excess cancers would come to around 7300.

The evolution of these estimates is not uninteresting, A month after the accident, physicists Frank von Hippel of Princeton University's Center for Energy and Environmental Studies and Thomas Cochran of the Natural Resources Defense Council, Washington, D.C., predicted 3500­-70 000 excess cancers caused by exposure to cesium and 2000-­40 000 excess thyroid tumors among the 100 million people living in the western Soviet Union, eastern Europe, and Scandinavia. As summarized in The New York Times, which had solicited the estimates, 500 excess deaths from thyroid cancers and 2000 excess leukemia and solid cancer deaths were to be expected among those 100 million people.

figure5
Photo: Sake Elzinga/IPD
Figure 6: These refugee children from Pripyat, the village where most of the Chernobyl workers lived, now go to school in Kiev. The best news is that a higher-than-normal incidence of leukemia has not appeared in such groups.

In 1988, radiobiologist Marvin Goldman of the University of California, Davis, health physicist Robert Catlin of the Electric Power Research Institute, Palo Alto, and Anspaugh reported an estimate for total excess cancer deaths, worldwide, of 17 400. Cardis's current estimate is, according to Upton, consistent with an estimate for total excess cancer incidence of 30 000--roughly 12 000 within the old East Bloc, the rest elsewhere in the Northern Hemisphere.

Those forecasts would inspire more confidence if the rate of leukemia among the evacuees and liquidators in the first 10 years after the accident had been as predicted, and if better sense could be made of the thyroid/leukemia paradox. Lacking an identifiable surplus of leukemias even in the worst-affected group, it will remain a nagging question whether the presumed cancers in the much larger groups are to be viewed as real or dubious.

Research imperatives
All specialists on Chernobyl health effects agree that more and better studies are needed, despite the prodigious efforts already made. The first major study, the IAEA's 1990 Chernobyl project, dealt with 825 000 people living in 2225 settlements. Requested by Soviet authorities to reassure their own people about the adequacy of remedial measures, its objective was to assess the safety of those living in a 25 000-km2 area with surface cesium contamination of over 185 kBq/m2. The more endangered groups (liquidators and evacuees) were therefore excluded. This was not well understood by the public, however, and so when the project's report gave the people in the less contaminated areas a clean bill of health, a lot of people did not believe it. The investigation was complicated, Mettler pointed out in Vienna, by the fact that thyroid cancer and leukemia rates were rising throughout the USSR before and after the accident.

In 1991, the World Health Organization launched its International Programme on the Health Effects of the Chernobyl Accident (Ipheca), aided by ¥ 2.6 billion from the Japanese government. Japan's Sasakawa Memorial Health Foundation also has sponsored some large research projects, and Japanese radiation health experts have participated prominently in most of the more ambitious programs. Besides the IAEA, WHO, and Unesco, Unicef and the Food and Agriculture Organization also have been active.

The European Union has committed US $40 million to $45 million to a long-term research program, with some matching money from Belarus, Russia, and Ukraine. The work embraces the assessment and mitigation of environmental contamination; evaluation and treatment of health effects; and off-site emergency management. While commitments from the U.S. government have been smaller, the National Cancer Institute, the Nuclear Regulatory Commission, and the Department of Energy have promoted some significant work.

Most scientists are relying on much the same general databases, which need improvement. Only Belarus had a central cancer registry before 1986; Russia and Ukraine are only now setting up registries. The Chernobyl Registries established by each state compile information on liquidators, evacuees, those living in the contaminated areas, and all children born to members of these groups.

There is still no world-class study on genetic effects of the accident, as Academician Tsyb pointed out in Vienna. A better job needs to be done of identifying and tracking the liquidators. And especially desirable, said Cardis at the IAEA's summation conference, are studies of well-defined sample populations and diseases of interest.

At the same time, the various types of specialists studying the accident need to spend more time comparing notes. The ramifications of Chernobyl have involved nuclear safety engineers, dose reconstruction specialists, physicians and epidemiologists, social scientists like Lee, and environmental scientists like Dreicer--to name just the most obvious groups. Any marked change in a group's consensus view can affect calculations done in the other groups. Thus, for example, a revision of the basic accident scenario could impinge on assessment of doses and dose distribution.

Wider health and safety issues
Summing up what is known to date by no means exhausts the health and safety issues raised by the accident. The sarcophagus entombing the disabled reactor is in poor shape and deteriorating, yet two of the three adjacent units continue to operate. Ukraine has promised to turn them off by the year 2000 but is bargaining hard with the European Union about the terms, to extract as much financial aid as possible.

Another concern is the upgrades done on the Chernobyl-type reactors throughout the former USSR. While reports on their adequacy at Vienna were fairly reassuring, it is a labyrinthine subject.

Last and not necessarily least, there are lingering concerns about the food produced in contaminated areas, and about long-term ecological changes. Here, too, reports were reassuring, but still need to be fully substantiated and ultimately credited by the general public.

To Probe Further

The most authoritative general statements of the health effects of radioactivity are: United Nations Scientific Committee on the Effects of Atomic Radiation Sources and Effects of Ionizing Radiation (1994) and Sources, Effects and Risks of Ionizing Radiation (1988), from the United Nations, New York City; and Health Effects of Exposure to Low Levels of Ionizing Radiation (BEIR V), from the National Research Council's Committee on the Biological Effects of Ionizing Radiations (National Academy Press, Washington, D.C., 1990).

For Chernobyl, the latest consensual scientific view is Chernobyl Ten Years On: Radiological and Health Impact, from the Nuclear Energy Agency (Organization for Economic Cooperation and Development, Paris, 1996). For Greenpeace's view of the health consequences, see its Chernobyl l0 Years After: The Consequences (Amsterdam, the Netherlands, March 1996). Greenpeace has circulated an estimate, based on comparative mortality statistics and not generally accepted by cancer epidemiologists, that 30 000 people already have died as a result of Chernobyl in the former Soviet states.

Conference proceedings are to be expected but are not yet available from the IAEA's April conference in Vienna and WHO's November 1995 meeting in Geneva. Proceedings from the Minsk conference, The Radiological Consequences of the Chernobyl Accident (EUR 16544 EN), edited by A. Karaoglou and others., are available from the European Union's Office for Official Publications in Luxembourg, fax, (352) 488 573.

Retrospectives on the accident appeared last spring in the May-­June Bulletin of the Atomic Scientists, pp. 22­-59; Science, April 19, pp. 352­-360; and Nature, April 25, pp. 653, 665-­666, 683-­686, and 707­-708. The Nature issue included reports from two research groups of abnormally high mutation rates in certain kinds of genetic material in one group of humans and two types of rodents, suggesting that congenital health defects, including a greater propensity to cancers, may result from the accident.

Perhaps the most important recent paper on thyroid cancers and Chernobyl is by V. Beral and appeared in the Proceedings of the 92nd Annual Meeting of the NCRP, "Implications of New Data on Radiation Cancer Risk" (1996), from the National Council on Radiation Protection and Measurements, Bethesda, Md.

An excellent summary of Poland's experience with potassium iodide distribution is Janusz Nauman's and Jan Wolff's "Iodide Prophylaxis in Poland after the Chernobyl Reactor Accident: Benefits and Risks," The American Journal of Medicine, May 1993, pp. 524­-32.

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