Predicting the global health consequences of the Chernobyl accident
Methodology of the European Committee on Radiation Risk
University of Ulster
European Committee on Radiation Risk
April 24th 2011
There have been a number of calculations and predictions of the health consequences of the Chernobyl accident exposures. These range from virtually none (The UN Chernobyl Forum) through 60,000 excess cancer deaths (Fairlie and Sumner 2006) to 1.8 million cancers (Rosalie Bertell 2006) and include the prediction of between 900,000 and 1.4 million cancers in the last 25 years made recently by Alexey Yablokov (Yablokov 2011) in Berlin and widely covered in the media. In view of the recent local and ongoing global contamination being produced by the Fukushima nuclear power station meltdown in Japan and the 25th anniversary of the 1986 Chernobyl accident it would seem of interest to revisit the various calculations and to employ the ECRR2010 approach to predicting the cancer yield and other ill health, and at the same time, check the results against other epidemiological approaches to obtaining the correct result for exposures to the radionuclides emitted from an accident involving a nuclear reactor.
Some predictions are given in Table 1 including the results of the present analysis.
Table 1. Predictions of the health outcome of exposures to radioactive contamination for the Chernobyl accident.
|Gofman J. W 1990||970,500||Excess Fatal cancers, calculated from Cs-137 deposition doses and Gofmans risk factor of 0.28/Sv; worldwide|
|IAEA/WHO 2005||9000||Excess All cancers using ICRP risk factor 0.05/Sv; worldwide|
|Fairlie Sumner TORCH report 2006||30,000-60,000||Excess All fatal cancers worldwide; ICRP model assumptions and collective doses|
|Bertell Rosalie (ECRR2006)||899600 to 1,787,000||Excess Fatal cancers worldwide; not clear of method|
|Yablokov 2011||900,000 to 1.4 million||Excess Cancer in 25 years only. Comparing increases in cancer in differentially contaminated populations of Europe.|
|This analysis based on contamination||489,500||Excess Cancer incidence in 10 years following the exposure based on Tondel epidemiology|
|This analysis based on dose||Between 740,000 and 1.48 million||Cancer incidence in 50 years; global; based on ECRR 2010 absolute risk model and assumptions of internal fraction|
|This analysis based on contamination||2.45 million||Cancer incidence in 50 years based on Tondel epidemiology|
2. The data and assumptions
There are several sources of data for the contamination available but many of them disagree slightly with each other. In general, the percentage of the Chernobyl reactor contents which was released has been increased from the first estimates of 5% to between 50% and even 95%. Gofman’s calculation was based upon total Cs-137 releases of 1,990,000 Curies i.e. 7.3 x 1016 Bq (73 PBq) and this is not very different from the value given in the latest UNSCEAR 2008 report (published 2011) of 85PBq. Early assessments were of less. Sumner et al 1987 gave 38PBq Cs-137. I do not propose to employ a source term for the calculations but base them on two kinds of input. The first is the effective first year dose to an individual in a defined national population. The second is the mean area contamination by Caesium-137. I obtain these data from the following sources:
- UNESCO 1995
- UNSCEAR 2011
The UNESCO (Savchenko) data are given as average first year committee effective doses from the Chernobyl accident to populations of different countries (Fig 1). Where Savchenko has not listed a country I have gone to UNSCEAR 2011. By employing maps of contamination given in IAEA, UN and many other publications, I have adjusted the contamination levels in one or two countries where the UNSCEAR 2011 data seems incorrect, notably Poland. I have used the Handbook of Radiological Protection and the USA EPA FGR12 Part 2 tables and graphs to convert between Cs-137 contamination on the ground and dose rate. I have assumed that internal dose is 1/3rd of external dose from this source, where the absolute ECRR 2010 method requires this. This is based on ratios of internal and external doses given in UNSCEAR 2008. I have taken the first year dose as the effective dose from Chernobyl exposure. I have used the mean ECRR2010 hazard factor of 300 for internal exposures.
I calculate the cancer yield in two ways. First I employ the ECRR2010 method. Then second, as a check, I employ the results of the epidemiological study of cancer in Northern Sweden by Tondel et al 2004 who found a 11% increase in cancer for each 100kBq/m2 Cs-137 contamination. It should be noted in all these calculations that they do not assume that the cancer is caused by the Cs-137 exposure but that the latter is a flag for a range of harmful radionuclides. The ECRR hazard factor 300 for this range of harmful radionuclides is based upon the regression analysis of cumulative committed effective dose from Strontium-90 on increases in cancer in populations differentially exposed to global weapons fallout (Busby 1994, 1995, ECRR2003, ECRR2010). One such correlation is shown in Fig 2.
The numbers of cancers generated by the Tondel method assumed that the all person all cancer rate per year was 450/100,000 (various sources including CIFC, SEER and national cancer registries).
Results are given in Table 2. It should be noted that the assumptions of 1/3 of the internal exposure carrying a weighting of 300 is based on nuclear atmospheric test fallout in the 1960s and other similar spectra of contamination radionuclides. In addition, the factor is base on exposure to Sr-90. The ratio of Sr-90 to Cs-137 in fallout is far greater in weapons fallout than in the distant Chernobyl contamination. The Chernobyl exposures generally had a greater particulate and uranium contamination and therefore are likely to carry a greater hazard weighting. A factor of about 400 is necessary to explain the infant leukemias after Chernobyl (Busby 2009)
Fig 1 Mean doses from Chernobyl fallout to some countries (from Savchenko/ UNESCO 1995).
Fig 2 Cumulative dose from Strontium 90 1954 to 1974 plotted against age standardised excess all cancers in Wales 20 years later (Busby 2006)
Table 2. Absolute cancer (incidence, numbers) yield following exposures from the Chernobyl accident contamination in countries of the world with data on immediate area contamination, population and committed dose (from UNESCO 1995, UNSCEAR 2011)
|50yr cancer yield
The results obtained by the two methods I have used compare well with each other. The ECRR 50 year cancer yield is about three times the value for the 10 year excess found by Tondel et al 2004 in Sweden, based on Cs-137 contamination. However, the cancers caused by the Chernobyl accident are likely to show in the first ten or 15 years and then reduce in number. The yield of about 1.4 million cancers worldwide also agrees quite well with the calculations of John Gofman, with Rosalie Bertell and also with Alexey Yablokov. The ECRR method used was developed in 2003, before Tondel et al published the results of their study of cancer in Sweden. Yet the ECRR 2003 method predicted what they found with a fair degree of accuracy. It should be noted that Tondel et al found an 11% increase in cancer at contamination levels of 100kBqm-2 and at this level the annual external doses from the Caesium are about 3mSv, around natural background and should not have cause any increase in cancer. It was not, of course, these external doses that caused the damage, but internal exposures to radioactive substances that were also there at the time, substances which carried enhanced hazard from a number of biophysical and biochemical sources discussed in ECRR2003 and ECRR2010.
It should be noted that this study has focused only on cancer. ECRR2010 also predicts significant harm from a wide range of conditions and causes of death, including heart disease, strokes, diabetes, congenital illness in children, infant mortality and loss of fertility as a result of damage to sperm and ova. In general it is now clear that radiation causes a general loss of lifespan through premature ageing and therefore, as in the areas heavily contaminated from Chernobyl, the overall increases in cancer predicted here on a linear basis may be truncated at higher doses by competing causes of early death.
Two separate methods have been employed to calculate the global cancer yield of the Chernobyl accident. The results show between approximately 469,000 and 1.4 million incident cancers in the 10 years and 50 years following exposure. These results agree rather well with earlier estimates by Gofman (1990), Bertell (2006) and epidemiological approaches using real data by Yablokov (2011) but are much greater than those published by the World Health Organisation and the International Atomic Energy Agency or by Fairlie and Sumner 2006.
The agreement between the ECRR2003 method employed and real data on cancer from ex Soviet Union areas contaminated by Chernobyl, from weapons fallout and Sweden after Chernobyl suggests that the current approach to modelling radiation risk based on the ICRP dependence on the external exposures of the Japan A-Bomb survivor cohorts is erroneous (Lesvos Declaration 2009). The matter has significant implications for policy in the case of Fukushima.
Busby, C. (1994), `Increase in Cancer in Wales Unexplained’, British Medical Journal, 308: 268
Busby, C. C. (1995), Wings of Death: Nuclear Pollution and Human Health (Aberystwyth: Green Audit)
Busby C.C. (2009) Very Low Dose Fetal Exposure to Chernobyl Contamination Resulted in Increases in Infant Leukemia in Europe and Raises Questions about Current Radiation Risk Models. International Journal of Environmental Research and Public Health.; 6(12):3105-3114. http://www.mdpi.com/1660-4601/6/12/3105
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