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 (contd)

• 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 lt45)
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 be interpreted 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 contd

• 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 SCZs
• Careful studies needed to study the real effect