Environmental and Health Consequences of the Chernobyl accident

1. Environmental and Health Consequences of the Chernobyl accident Cancer effects of radiation exposure from the Chernobyl accident E. Cardis, IARC, Lyon

2. Composition of EGH 1 and 2

3. The WHO Expert Groups on Health • Many reports on health effects in 20 years • Expert groups reviewed • UNSCEAR 2000 report • More recent peer-reviewed scientific literature and scientific meeting presentations • Reports and statistics prepared by National authorities • Outcome • Scientific consensus on health impact from radiation to date • Identification of research gaps • Recommendations for health care programmes

4. Assessing the health impact of the accident • Requirements for studies to provide information about radiation risks • Large populations • Follow-up: non-differential, complete, accurate diagnosis • Dose-estimates: individual, accurate, precise … particularly important when relatively small doses and hence, a priori relatively small impact on global burden of diseases • The situation • Very large exposed populations • Difficulties in conducting complete follow-up • Decreases in lifespan in affected countries (both contaminated and non-contaminated areas) • Individual dose estimates not available for most exposed persons

5. Reports/studies reviewed • Many – insufficient numbers of subjects to allow conclusion • Some – insufficient methodological information to allow conclusion • Most – no information on other potentially much more important risk factors for the diseases such as tobacco and alcohol … many reports reviewed – few are informative to assess the health impact of the accident

6. The exposed population

7. Distribution of thyroid dose from I131

8. Increase in thyroid cancer incidence in young people Courtesy Yu. E. Demidchik

9. Thyroid cancer in young people after Chernobyl • Major increase in risk : • 4000 cases among those who were below 18 at the time of the accident (1992-2002) • 3000 among those who were below 15 ! • Many epidemiological studies • Confirm increased risk • Provide estimates of risk per Gy • Most cases attributable to radiation from the accident • Prognosis very good • 9 deaths to date among those exposed in childhood

10. Thyroid cancer risk • Uncertainties • Pattern over time – no information … increased risk likely to continue for many more years • Effect of large scale screening efforts in contaminated areas … important implications for public health and risk estimation • Stable iodine status • Iodine deficiency appears to increase risk per Gy • Dietary iodine supplements appear to reduce radiation related risk … potentially important implications – need confirmation • Effect of exposure as an adult - unclear

11. Leukaemia • Associated with radiation exposure in a-bomb survivors and other exposed populations • Appears early (2-5 years after exposure) • Risk per Gy is high in those exposed as children • “Marker” of radiation effect • Exposure in utero and in children • ECLIS, Belarus, Russia, Sweden, Finland, Germany, Greece • No consistent increase • Limited statistical power of studies

12. Leukaemia (cont’d) • Exposure as an adult • Liquidators • Large-scale studies: two-fold increase in most highly exposed group • Dose estimates uncertain • More precise risk estimates expected from on-going studies • General population • Increases in incidence reported, but not related to contamination levels • Methodological limitations /little power • Difficult to conclude

13. Cancers other than thyroid • Ionising radiation associated with risk of cancer at many sites in a-bomb survivors and other populations • Chernobyl – risk for all solid cancers combined • Liquidators (Russia, Belarus, Ukraine) • No consistent increase overall in the incidence of all cancers • Slight non-significant increase per Gy • Population in contaminated regions • Incidence of all cancers not significantly different from general population • Unclear trend over time

14. Standardized incidence ratios for all solid cancers in Russian liquidators compared to the general Russian population 1990-2001. (Ivanov et al) Dynamics of SIR for all solid cancer among residents of 5 rayons of Bryansk oblast (Ivanov et al).

15. Incidence of specific types of cancer • Increases in incidence of specific cancer types reported periodically • No information about dose level … difficult to conclude about radiation effects • Breast cancer incidence: • Increases in Belarus and Ukraine • Ecological study (Belarus and Ukraine) • Describe spatial and temporal trends • Evaluate whether the reported increases correlate with radiation exposure

16. Breast cancer incidence (Pukkala et al, submitted)

17. Breast cancer incidence (Pukkala et al, submitted) Time trend in breast cancer RR by average cumulative dose category in territories of Belarus and Ukraine most contaminated by the Chernobyl accident (doses lagged by 5 years; age at exposure <45)

18. Conclusions - solid cancers other than thyroid • Lack of evidence of any clearly demonstrated effect of Chernobyl radiation exposures on leukaemia or solid cancers (except thyroid cancer) • But: • Studies of these effects are few and methodologically limited • Doses to most organs (except thyroid) tended to be low • Minimum latent period is likely to be much higher than that for leukaemia or thyroid cancer – of the order of 10 to 15 years or more – and it may therefore be too early … Need careful epidemiological studies with individual dose reconstruction to evaluate, in particular: • leukaemia/cancer risk among liquidators • breast cancer in young women in most contaminated areas

19. What is the cancer burden from Chernobyl today? • no clearly demonstrated increased cancer risk … does not imply that no increase in risk has occurred. • it is expected that the low to moderate doses received will have led to a small increase in the relative risk of cancer … a small increase in the relative risk could mean many cancer cases, given the large number of individuals exposed

20. What will be the cancer burden from Chernobyl? • At present, must rely on experience of other exposed populations to predict cancer risk • But many uncertainties • Transfer of risk across populations • Projection over time • Effect of low dose rate chronic exposures • Effect of mixture of external and internal exposures … Any prediction must beinterpreted with caution and only gives an order of magnitude estimation

21. Predictions of background and excess deaths from leukaemia About 700 extra leukaemia deaths over life among 5.6 million people- about 300 among the 600 000 most exposed - From Cardis et al., 1996

22. Predictions of background and excess deaths from solid cancers About 8 250 extra cancer deaths over life among 5.6 million people- about 3650 among the 600 000 most exposed - From Cardis et al., 1996

23. Conclusions – 20 years after • No clearly demonstrated increase in the incidence of cancers (other than thyroid) that can be attributed to radiation from the accident • Increases in incidence of cancers have been reported, but no association with radiation dose … much of the increase appears to be due to other factors, including improvements in diagnosis, reporting and registration • Recent findings indicate a possible doubling of leukaemia risk among Chernobyl liquidators above 100 mGy and an increase in the incidence of pre-menopausal breast cancer in the very most contaminated districts, which appear to be related to radiation dose. These need to be further investigated

24. Conclusions – cont’d • No demonstrated increase does not mean no risk! • Based on experience of other populations, a small increase in relative risk is expected … • Power of existing studies is low and methodological limitations • Predictions based on other populations are very uncertain but provide an estimate of the order of magnitude of the risk • About 9 000 deaths from all cancers and leukaemia expected in the main exposed populations • About 4 000 of these among the most exposed: liquidators, evacuees and residents of SCZ’s … Careful studies needed to study the real effect