© 2006 Nature Publishing Group

Vol. 440|20 April 2006

COMMENTARY

993

Too soon for a final diagnosisTwenty years ago, the nuclear accident at Chernobyl exposed hundreds of thousands of people to radioactivefallout. We still have much to learn about its consequences, argue Dillwyn Williams and Keith Baverstock.

Why should we still be concerned about theChernobyl accident after 20 years, some 3,000papers and many conferences? One reason isthat the consequences of the world’s worstpeacetime nuclear accident are relevant tonational debates about building new nuclearpower stations. Another is that at this point wecannot predict the future health consequencesof Chernobyl with any certainty.

The radiation exposure from the Chernobylaccident differed greatly from that created by the atomic bombs in Japan, yet only frag-mented studies have tracked the human con-sequences of Chernobyl, in contrast to thecoordinated approach of Japan’s Atomic BombCasualty Commission (now the RadiationEffects Research Foundation). Without a simi-lar approach, speculation about Chernobyl’shuman cost will be unconstrained by hard evi-dence, and interested parties will be able toexaggerate or underplay the consequences.

This month, UN agencies will mark 20 yearssince Chernobyl by publishing an international

assessment of the accident’s health, environ-mental and economic effects. A draft1 issuedlast year detailed the health consequences andpredictions for the future, but the accompany-ing press release downplayed the predictednumber of cancers, emphasizing reassurancerather than the uncertainties.

Misplaced confidenceFor example, simply by citing a specific num-ber — up to 4,000 predicted deaths from radi-ation exposure — the press release suggested acertainty unwarranted by the underlying stud-ies (see Special Report, page 982). The figuresquoted in the body of the report suggested thatthere may be an additional 5,000 radiation-related deaths in heavily contaminated regions.Yet these predictions ignore the large numberof Europeans who received very low radiationdoses. The dose–response relationship at lowdoses remains uncertain; it could be linear, butalso higher or lower2,3. If it is linear, there maybe tens of thousands more attributable deaths.

In 1965, 20 years after the atomic bombingsin Japan, the Atomic Bomb Casualty Com-mission reported significant increases in the incidence of just two cancers — thyroidcancer and leukaemia. It was another decadebefore a significant increase in other cancerswas reported. Almost 45 years after thebombs, unexpected and significant increasesin a range of non-cancer diseases, includingheart disease, were found4. And nearly 50years after exposure, significant increaseswere reported for ten different cancers, withrisks approximately doubled for colon, lung,breast, ovary and bladder tumours5. Giventhat about one in four people anywhere devel-ops cancer, detecting these and more modestincreases in other cancers would have beenimpossible without the long-term, large-scalestudies conducted on some 80,000 Japanesebomb survivors.

In Chernobyl, the type of radiation exposurewas different from that in Nagasaki and Hiro-shima, and the aftermath will take a different

Check up: a Russian womanliving near Chernobyl isexamined for signs of thyroid cancer.

L. T

CH

ALE

NKO

/CA

MER

A P

RESS

20.4 Commentary NS 18/4/06 10:22 AM Page 993

Nature Publishing Group ©2006

© 2006 Nature Publishing Group

COMMENTARY CHERNOBYL AND THE FUTURE NATURE|Vol 440|20 April 2006

994

form. The atomic bombs resulted largely inwhole-body radiation from �-rays and neu-trons, exposing all tissues uniformly. Exposurefrom Chernobyl was, apart from in those work-ing near the reactor, largely internal, fromradioactive isotopes in fallout — so differenttissues initially received different doses.

The large increase in childhood thyroidcancer so soon after the Chernobyl accident6,7

— the first cases appeared after just fouryears — took experts by surprise. Experts’expectations were based on known adultexposure risks (mini-mal) and assumptionsabout latency times (tenyears or more). Theywere wrong, and thereis every reason toexpect more surprisesover the next 20 years.The high incidence ofthyroid cancers hasbeen linked to the hugeamount of 131-iodinein fallout, and to con-suming local milk in particular. But the thyroid is not the only tissue to concentrateradioiodine: the salivary glands, breast andstomach also take it up to a lesser extent,potentially increasing their risk of malignancy.Any female who was lactating or pubescent atthe time of the accident could be particularlyat risk of breast cancer. The future is uncertain,although there is recent evidence for anapproximate doubling in breast-cancer inci-dence in Gomel, Belarus, and other heavilycontaminated areas of Belarus and Ukraine8.Studies of the atomic bomb show that 20 yearsis far too early to assume, as some have, thatradioactive fallout causes only thyroid cancer.

The most detailed studies since Chernobyl,of the thyroid-cancer epidemic, yielded muchvaluable information9. We have learnt that therisk of developing thyroid cancers dependsheavily on the age of exposure to fallout, withchildren under one being the most susceptible.Several thousand excess cases of thyroid cancerhave occurred so far in the three most exposedcountries, allowing researchersto link the speed of tumourdevelopment with molecularchanges and with differenttumour types (see figure). Theearly tumours were clinicallyaggressive and pathologicallyunusual. Later ones were moretypical and less aggressive, witha changing pattern of oncogene mutation. Butthe future epidemiology even for thyroidtumours is unpredictable. Other types of thyroid tumour may emerge, and an increase inthe lethality of these usually curable tumourscannot be ruled out. Continuous medical surveillance is necessary.

As well as radioactive iodine, Chernobylexposed millions of people to much lowerdoses to the whole body from 134- and

137-caesium. The dose range overlaps withthat received by survivors 1 to 2 kilometresfrom the hypocentre of the atomic bombs. Inaddition, the 90-strontium released is a poten-tial source of bone cancers.

The UN report acknowledges the need forfurther epidemiological studies to assess theeffects of low-dose exposure after Chernobyl;such studies must include verification of theprimary data. But existing patchy and uncoor-dinated studies will not answer all the ques-tions. We believe that, even now, a coordinated

approach to monitoring exposed populationswould at least provide an upper limit to thelong-term health risks from fallout.

Fortunately, very few of those who con-tracted thyroid cancer have died from the dis-ease (15 children so far), but it is too early toconclude that present or future cases will showa similarly low death rate. Other cancers arenot so easily treatable. The need for an inter-national effort to monitor all possible healthconsequences, using the studies of Japanesebomb survivors as a model, cannot be over-stressed. At the very least, comprehensivestudies should be conducted on the hundredsof thousands in the most affected areas ofBelarus, Ukraine and Russia.

A loss of trustWho should fund such studies? The 2005 bud-get for the Radiation Effects Research Founda-tion was US$40 million. Currently, the UnitedStates and the European Union are committedto providing more than a billion dollars to

make the Chernobyl sarcopha-gus safe, in addition to themany millions they havealready contributed to human-itarian assistance and otherstudies. We do not suggestdiverting funds from theseworthwhile efforts, but com-prehensive studies of the health

consequences of Chernobyl would cost only atiny fraction of the amount spent annually bythe nuclear industry on energy production.

In terms of public health, the psychologicalconsequences of exposure to the accident areprobably more important than the physicalconsequences. Millions were exposed to fallout; all must have some concern for themselves and their children. For hundreds of thousands, fear of the unknown was

compounded by forced evacuation and loss oftrust in government, caused by poor risk com-munication. Those living near the 30-kilo-metre exclusion zone were troubled by rulingsthat it was dangerous to live just inside theboundary, but perfectly safe to live just outside.

Public mistrust of the authorities was height-ened by mismanaged responses to the accident.At the time, the Soviet nuclear industry andgovernment failed to alert the public to takesafety precautions. Later, various national andinternational organizations downplayed the

effects, while othersexaggerated them togain financial support,often contrary to thebest evidence. Environ-mental organizationsand the media havebeen important whistle-blowers, but have alsoused unsubstantiatedfigures, selective quota-tions and horrificimages to paint the

worst possible picture of the consequences. Thenuclear industry has been equally selective inits use of figures and quotations, often equatinga lack of evidence for an effect with evidence ofits absence. As a result, rational public debate isvery difficult.

The importance of Chernobyl lies thereforenot only in numbers of cancers or deaths, or theeconomic costs, but also in its effect on people’sattitudes. Villagers meeting a team from theInternational Atomic Energy Agency in 1990voiced their fear of radiation, fear for their chil-dren, and mistrust of officialdom10: “Whatchance do the inhabitants of strict controlregions have to raise normal children?” “Peoplehave been deceiving us for five years — will youtell us the truth?”

If a full, independent study of the conse-quences of the world’s worst nuclear accidentis not established, and its results published forall to assess, wildly differing claims will con-tinue, and public mistrust of the nuclearindustry will grow further. ■

Dillwyn Williams is in the Thyroid CarcinogenesisResearch Group, Strangeways ResearchLaboratories, Worts Causeway, Cambridge CB1 8RN, UK.Keith Baverstock is in the Department ofEnvironmental Science, University of Kuopio,70211 Kuopio, Finland.

1. International Atomic Energy Authority, Viennawww.iaea.org/NewsCenter/Focus/Chernobyl/index.shtml

2. Brenner, D. J. et al. Proc. Natl Acad. Sci. USA 100,13761–13766 (2003).

3. Brenner, D. J. & Sachs, R. K. Radiat. Environ. Biophys. 44,253–256 (2006).

4. Shimizu, Y. et al. Radiat. Res. 130, 249–266 (1992).5. Thompson, D. E. et al. Radiat. Res. S17–S67 (1994).6. Kazakov, V. S. et al. Nature 359, 21 (1992).7. Baverstock, K. et al. Nature 359, 21–22 (1992).8. Pukkala, E. et al. Int. J. Cancer doi: 10.1002/ijc.21885 (2006). 9. Williams, D. Nature Rev. Cancer 2, 543–549 (2002).10. The International Chernobyl Project Tech. Rep.

(International Atomic Energy Agency, Vienna, 1991).

0 years 20 years 40 years

Unusually aggressive tumours

Radiationexposure

More typical tumours Future tumours?

“Studying the effectsof Chernobyl wouldcost a tiny fraction ofthe amount spent bythe nuclear industry.”

Early cases of thyroid tumours after Chernobyl differed from later ones in unexpected ways.

20.4 Commentary NS 18/4/06 10:22 AM Page 994

Nature Publishing Group ©2006