Gavin Atkins, former media officer with the Australian Nuclear Science and Technology Organisation, takes me to task in Asian Correspondent for articles I have written concerning the death toll from Chernobyl.
Atkins thinks I must find George Monbiot’s critique of Helen Caldicott’s estimate of the Chernobyl death toll to be “most disturbing”. But I have repeatedly noted that Caldicott relies on a single Russian study, which uses a loose methodology to arrive at an unlikely conclusion of a death toll nearing one million.
The debate over the Chernobyl death toll turns on the broader debate over the health effects of low-level ionising radiation — and in particular the cancer risk it poses. The weight of scientific opinion holds that there is no threshold below which ionising radiation poses no risk and that the risk is proportional to the dose: the “linear no-threshold” (LNT) model.
Uncertainties will always persist. In circumstances where people are exposed to low-level radiation, epidemiological studies are unlikely to be able to demonstrate a statistically significant increase in cancer rates. This is because of the “statistical noise” in the form of widespread cancer incidence from many causes, the long latency period for some cancers, limited data on disease incidence, and various other data gaps and methodological difficulties.
Notwithstanding the difficulties, there is growing scientific confidence in the LNT model. An important study in this regard is the 2006 report of the Committee on the Biological Effects of Ionising Radiation (BEIR) of the US National Academy of Sciences.
The BEIR report comprehensively reviewed available data and concluded that: “The balance of evidence from epidemiologic, animal and mechanistic studies tend to favor a simple proportionate relationship at low doses between radiation dose and cancer risk. … [T]he risk of cancer proceeds in a linear fashion at lower doses without a threshold and … the smallest dose has the potential to cause a small increase in risk to humans.”
The report notes that uncertainty remains because of the unavoidable methodological difficulties: “Even with the increased sensitivity the combined analyses are compatible with a range of possibilities, from a reduction of risk at low doses to risks twice those upon which current radiation protection recommendations are based.”
There is general agreement that 30 to 60 people died in the immediate aftermath of the Chernobyl accident. Beyond that, epidemiological studies generally don’t indicate a statistically significant increase in cancer incidence in populations exposed to Chernobyl fallout. Nor would anyone expect them to because of the data gaps and methodological problems mentioned above, and because the main part of the problem concerns the exposure of millions of people to very low doses of radiation from Chernobyl fallout.
For a few marginal scientists and nuclear industry spruikers, that’s the end of the matter − the epidemiological evidence is lacking and thus the death toll from Chernobyl was just 30-60. Full stop. But for those of us who prefer mainstream science, we can still arrive at a scientifically defensible estimate of the Chernobyl death toll by using estimates of the total radiation exposure, and multiplying by a standard risk estimate.
The International Atomic Energy Agency estimates a total collective dose of 600,000 person-Sieverts over 50 years from Chernobyl fallout (see the IAEA Bulletin, Vol.38, No.1, 1996). A standard risk estimate from the International Commission on Radiological Protection is 0.05 fatal cancers per Sievert. Multiply those figures and we get an estimated 30,000 fatal cancers. Now let’s recall that, according to the BEIR report, the LNT model may overstate risks or understate them by a factor of two. Thus the estimated death toll ranges from something less than 30,000 — up to 60,000.
A number of studies apply that basic methodology — based on collective radiation doses and risk estimates — and come up with results varying from 9,000 to 93,000 deaths. While that tenfold difference seems significant, it is explained by the differing approaches and assumptions used in the various studies − for example, whether or not they consider radiation exposure across Europe or just in the most heavily contaminated countries of Eastern Europe. (And of course that tenfold difference is peanuts compared to the many orders of magnitude separating Monbiot’s estimate of 43 deaths and Caldicott’s 985,000.)
To briefly note some of the reports:
Reports by the UN Chernobyl Forum and the World Health Organisation in 2005-06 estimated up to 4000 eventual deaths among the higher-exposed Chernobyl populations and an additional 5,000 deaths among populations exposed in Belarus, the Russian Federation and Ukraine.
A study by Cardis et al. published in the International Journal of Cancer estimates 16,000 deaths.
UK radiation scientists Dr Ian Fairlie and Dr David Sumner estimate 30,000 to 60,000 deaths.
A 2006 report, commissioned by Greenpeace and involving 52 scientists, estimates a death toll of about 93,000.
In contrast, the most strident nuclear advocates want us to believe that the death toll was just 30-60. To that end they are very keen to focus our attention on a recent report by the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).
But the UNSCEAR report made no effort to assess the effects of widespread low-level radiation exposure. Specifically, the report states: “The Committee has decided not to use models to project absolute numbers of effects in populations exposed to low radiation doses from the Chernobyl accident, because of unacceptable uncertainties in the predictions. It should be stressed that the approach outlined in no way contradicts the application of the LNT model for the purposes of radiation protection, where a cautious approach is conventionally and consciously applied.”
So UNSCEAR cites “unacceptable uncertainties in the predictions” as its reason for shying away from an assessment of the impacts of widespread radiation exposure. The rest of us needn’t be so shy − we can draw on the rigorous scientific research underpinning the estimates of 9000 deaths (in relatively highly contaminated areas) to 93,000 (across Europe).
Last, the broader significance of this debate. The Chernobyl debate feeds into studies comparing the hazards of difference energy sources. These studies generally attempt to quantify the hazards, expressing them in deaths per gigawatt-year of electricity.
A recent paper by the Australian ‘Choose Nuclear Free’ partner groups summarises the comparative assessments. It reaches three main conclusions.
First, the greatest hazards − the link between fossil fuels and global warming, and the link between nuclear power and nuclear weapons − cannot be meaningfully quantified.
Second, it is also difficult to accurately quantify hazards such as particulate emissions from coal plants, and routine radiation emissions across the nuclear fuel cycle (which are responsible for far more radiation exposure than the Chernobyl accident).
Third, notwithstanding the above, coal and nuclear power are clearly far more hazardous than renewables − even without considering global warming and nuclear weapons proliferation.
Factor in global warming and nuclear proliferation, and coal and nuclear are extremely hazardous indeed.
Jim Green is the national nuclear campaigner with Friends of the Earth, Australia (www.foe.org.au).