Chernobyl's Stressful After-Effects

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.

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."

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.

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.

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.

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.

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."