(April 25, 2014) The never-ending debate over the Chernobyl cancer death toll turns on the broader debate over the health effects of low-level radiation exposure. The overwhelming weight of scientific opinion holds that there is no threshold below which ionising radiation poses no risk. Uncertainties will always persist. In circumstances where people are exposed to low-level radiation, public health (epidemiological) studies are unlikely to be able to demonstrate a statistically-significant increase in cancer rates. Cancers are common diseases and most are multi-causal. Other complications include the long latency period for some cancers; and limited or uneven data on cancer incidence and mortality. The upshot is that cancer incidence and mortality statistics are being pushed up and down by a myriad of factors at any point in time and it becomes impossible or near-impossible to isolate any one factor.
While the overwhelming weight of scientific opinion holds that there is no threshold below which radiation exposure is harmless, there is less scientific confidence about how to quantify the risks. Risk estimates for low-level radiation exposure are typically based on a linear extrapolation of better-understood risks from higher levels of exposure.
This 'Linear No Threshold' (LNT) model has some heavy-hitting scientific support. For example a report in the Proceedings of the National Academy of Sciences states: "Given that it is supported by experimentally grounded, quantifiable, biophysical arguments, a linear extrapolation of cancer risks from intermediate to very low doses currently appears to be the most appropriate methodology."
Likewise, the 2006 report of the US National Academy of Sciences' Committee on the Biological Effects of Ionising Radiation (BEIR) states that "the 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."
Nonetheless, there is uncertainty with the LNT model at low doses and dose rates. The BEIR report makes the important point that the true risks may be lower or higher than predicted by LNT − a point that needs emphasis and constant repetition because nuclear apologists routinely conflate uncertainty with zero risk. That conflation is never explained or justified; it is simply dishonest.
The UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the International Commission on Radiological Protection recommend against using collective dose figures and risk estimates to estimate total deaths. The problem with that recommendation is that there is simply no other way to arrive at an estimate of the death toll from Chernobyl (or Fukushima, or routine emissions from the nuclear fuel cycle, or weapons tests, or background radiation, etc).
Indeed UNSCEAR itself (PDF) co-authored a report which cites an estimate from an international expert group − based on collective dose figures and risk estimates − of around 4,000 long-term cancer deaths among the people who received the highest radiation doses from Chernobyl. And UNSCEAR doesn't claim that low-level radiation exposure is harmless − its 2010 report (PDF) states that "the current balance of available evidence tends to favour a non-threshold response for the mutational component of radiation-associated cancer induction at low doses and low dose rates."
The view that low-level radiation is harmless is restricted to a small number of scientists whose voice is greatly amplified by the nuclear industry (in much the same way as corporate greenhouse polluters and their politicians amplify the voices of climate science sceptics). In Australia, for example, uranium mining and exploration companies such as Cameco, Toro Energy, Uranium One and Heathgate Resources have sponsored speaking tours by Canadian junk scientist Doug Boreham, who claims that low-level radiation exposure is beneficial to human health. Medical doctors have registered opposition to this dangerous quackery and collusion.
About 50 people died in the immediate aftermath of the Chernobyl accident. Beyond that, studies generally don't indicate a 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 low doses of radiation from Chernobyl fallout.
For a few fringe scientists and nuclear industry insiders and apologists, that's the end of the matter - the statistical evidence is lacking and thus the death toll from Chernobyl was just 50. (If they were being honest, they would note an additional, unknown death toll from cancer and from other radiation-linked diseases including cardiovascular disease.) 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 an appropriate risk estimate.
The International Atomic Energy Agency estimates a total collective dose of 600,000 person-Sieverts over 50 years from Chernobyl fallout. Applying the LNT risk estimate of 0.10 fatal cancers per Sievert gives an estimate of 60,000 deaths. Sometimes a risk estimate of 0.05 is used to account for the possibility of decreased risks at low doses and/or dose rates (in other words, 0.05 is the risk estimate when applying a 'dose and dose rate effectiveness factor' or DDREF of two). That gives an estimate of 30,000 deaths.
On the other hand, LNT may underestimate risks. The BEIR report states that "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." Likewise the BEIR report states: "The committee recognizes that its risk estimates become more uncertain when applied to very low doses. Departures from a linear model at low doses, however, could either increase or decrease the risk per unit dose." So the true death toll could be lower or higher than the LNT-derived estimate of 60,000 deaths.
A number of studies apply that basic method − based on collective radiation doses and risk estimates − and come up with estimates of the Chernobyl cancer death toll varying from 9,000 (in the most contaminated parts of the former Soviet Union) to 93,000 deaths (across Europe).
UN reports in 2005 (PDF) and 2006 estimated up to 4,000 eventual deaths among the higher-exposed Chernobyl populations (emergency workers from 1986−1987, evacuees and residents of the most contaminated areas) and an additional 5,000 deaths among populations exposed to lower doses in Belarus, the Russian Federation and Ukraine.
The estimated death toll rises further when populations beyond those three countries are included. For example, a study (PDF) by Cardis et al reported in the International Journal of Cancer estimates 16,000 deaths.
Dr Elisabeth Cardis, head of the Radiation Group at the World Health Organization's International Agency for Research on Cancer, said: "By 2065 (i.e. in the eighty years following the accident), predictions based on these models indicate that about 16,000 cases of thyroid cancer and 25,000 cases of other cancers may be expected due to radiation from the accident and that about 16,000 deaths from these cancers may occur. About two-thirds of the thyroid cancer cases and at least one half of the other cancers are expected to occur in Belarus, Ukraine and the most contaminated territories of the Russian Federation."
UK radiation scientists Dr Ian Fairlie and Dr David Sumner estimate 30,000 to 60,000 deaths. Dr Fairlie notes that recent statements by UNSCEAR indicate that it believes the whole body collective dose across Europe from Chernobyl was 320,000 to 480,000 person-Sieverts, from which an estimate of 32,000 to 48,000 fatal cancers can be deduced (using the LNT risk estimate of 0.10).
According to physicist Dr. Lisbeth Gronlund: "53,000 and 27,000 are reasonable estimates of the number of excess cancers and cancer deaths that will be attributable to the accident, excluding thyroid cancers. (The 95% confidence levels are 27,000 to 108,000 cancers and 12,000 to 57,000 deaths.) In addition, as of 2005, some 6,000 thyroid cancers and 15 thyroid cancer deaths have been attributed to Chernobyl. That number will grow with time. Much lower numbers of cancers and deaths are often cited, but these are misleading because they only apply to those populations with the highest radiation exposures, and don't take into account the larger numbers of people who were exposed to less radiation."
A 2006 report commissioned by Greenpeace estimates a cancer death toll of about 93,000. According to Greenpeace: "Our report involved 52 respected scientists and includes information never before published in English. It challenges the UN International Atomic Energy Agency Chernobyl Forum report, which predicted 4,000 additional deaths attributable to the accident as a gross simplification of the real breadth of human suffering. The new data, based on Belarus national cancer statistics, predicts approximately 270,000 cancers and 93,000 fatal cancer cases caused by Chernobyl. The report also concludes that on the basis of demographic data, during the last 15 years, 60,000 people have additionally died in Russia because of the Chernobyl accident, and estimates of the total death toll for the Ukraine and Belarus could reach another 140,000."
Those are the credible estimates of the eventual death toll from Chernobyl. Another defensible position (or non-position) is that the long-term cancer death toll is unknown and unknowable because of the uncertainties associated with the science. The third of the two defensible positions, unqualified claims that the death toll was just 50, should be rejected as dishonest or uninformed spin from the nuclear industry and some of its scientifically-illiterate supporters ... and from every last one of the self-proclaimed pro-nuclear environmentalists − James Hansen, Patrick Moore, Mark Lynas, George Monbiot, James Lovelock, etc.
This article was written by Jim Green − Nuclear Monitor editor - and is published in the Nuclear Monitor #785, April 24, 2014