Wednesday, 1 May 2019

Chernobyl cancer rates revised upwards

The impacts of the Chernobyl nuclear disaster in 1986 included thyroid cancers in those who were children at the time. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) produced a report in 2008 which found that, among those exposed who had been under 14 years of age in 1986, there were 5,127 reported cases of thyroid cancer between 1991 and 2005, while, for those who had been under the age of 18 in 1986, there were 6,848 cases. The main exposure route is assumed to be from drinking milk  contaminated with radioactive fallout.


Thyroid cancer can be treated e.g. by surgical removal of the thyroid (with patients then having to take compensatory pills for rest of their lives), but even so, fifteen cases had proved fatal by 2005. More are possible later. Thyroid cancer can occur naturally, but UNCEAR accepted that the observed pattern of dramatically increased thyroid cancer in the initial period 1991-1995 was associated with the accident. The typical minimum latency period for thyroid cancers is around 5 years, so it might be hoped that, sometime after that, cases would gradually tail off, but, worryingly, UNCEAR found no evidence for a decrease in the annual excess incidence of thyroid cancer up to 2005- the end of the observation period for the report. However, for those born after 1986, there was no evidence for an increase in the annual incidence of thyroid cancer. On that basis it might be assumed that new exposures or effects were not occurring, but that the latency period for cancers amongst those exposed in 1986 was extending. That cohort might also be joined by those who were in utero at the time.                                                 


There have been follow up studies and reviews and they have produced some worrying conclusions, outlined in a new UNSCEAR report. It notes that ‘the total number of cases of thyroid cancer registered in the period 1991−2015 in males and females, who were under 18 in 1986 (for the whole of Belarus and Ukraine, and for the four most contaminated oblasts of the Russian Federation), approached 20,000. This number is almost three times higher than the number of thyroid cancer cases registered in the same cohort in the period 1991−2005’.


So it’s going up significantly- with females especially at risk. UNSCEAR says ‘on average, the registered numbers of thyroid cancer for females were about four times higher than for males’. Not all of these cases will have been due to radiation exposure. UNSCEAR says other factors include an increased spontaneous incidence rate with adulthood…and improvement in diagnostic methods’.  So they claim that ‘the fraction of the thyroid cancer cases in the period 2001-2008 attributable to the radiation exposure caused by the accident is assessed to be about 0.6 and 0.25 for the evacuated and non-evacuated children and adolescents, respectively’. Even so, that’s nearly 12,000 cases for those in the zone, 1 in 4 for the rest. Although UNSCEAR note that ‘the uncertainty range of the estimated attributable fraction extends at least from 0.07 to 0.5’. They call for more research.

Full report:

Thyroid cancer was only one the impacts of the radiation release at Chernobyl, and children were not the only victims. As well as the rest of the population, many thousands of clean up workers were also exposed, some to high levels, and, although many have died, death was not the only outcome- for them or the others, there were also illnesses later in life that may not always have been linked back to radiation exposure, including immune system degradation:
However, the likely long-term health impacts of what happened at Chernobyl (and Fukushima) are still debated: It’s a contentious area. But the new UNSCEAR study may dent some of the more complacent/official views, for example see:   

Certainly more research is needed, as UNSCEAR says. Its selection of 0.6 and 0.25 as the radiation-related proportion seems debatable- why so low? Also it’s not clear exactly what is happening to the post-Chernobyl population.  Is the rise in cancers due to new exposures? The half life of Caesium 137 is around 30 years, so the activity level of any that remains in the ecosystem should be about 50% less by now and continually falling – so the cancer rate should be falling too, not increasing. More likely is a delayed onset effect from the initial exposures.

The administration of iodide pills, to block radioactive Iodine-131 uptake in the thyroid, would have limited the risk, but evidently did not happen much or in time. So now we await the long term results. Fortunately, 25 years later, most children in the Fukushima area seem to have escaped these problems: iodate pills were distributed – though they have to be taken very promptly, and that may not have always happened in the post-accident chaos there. Tragically, once more, we will have to wait to see- although some increases have already been claimed: 

It will take time to know for certain. Some say that you can worry too much about radiation exposure: we are already exposed to natural background radiation and to X-rays used for medical purposes.  Major nuclear accidents expose some people, usually reactor staff and firefighters, to massive doses of radiation, which can kill outright-  30 or more people died soon after Chernobyl.  However, it’s the longer-term risk of absorbing/ingesting/breathing in radio-nuclides that’s the key worry- including isotopes that don’t exist in nature. Once internalized, and if lodged somewhere in your body, the active particles can continue to irradiate cells intensively for very long periods. That’s not the same as exposure to low level background external radiation, or to short exposures from external sources like X-rays, or even to ‘prompt’ radiation fluxes from reactor accidents (or nuclear explosions), if you are some way away. The extra exposures from nuclear plants, including routine and accidental releases, averaged across the wider public over time, can seem small in some cases, but it does all add up, and we need to minimise total exposures, and certainly any internalisation. Especially since it’s not always averaged out: leaks and accidents at nuclear plants can expose many local people to large extra doses, with, as we have seen, uncertain long term results. It is, arguably, not a risk worth taking.  So, it could be argued that the best protection in future is not iodate pills, masks or evacuation. It’s to avoid the use of these plants- and to go for renewables instead. A small local start:

All technologies have health and safety risks, but those associated with the renewables (large hydro dam failures apart) are generally small and local (e.g. a total so far of around 180 wind turbine-related occupational fatalities, mostly from installation accidents) compared with those of nuclear and (especially) the burning of fossil fuels due to air pollution and climate change. Whatever we do now, there will be long-terms impacts from our past use of fossil and nuclear fuel, but, in both cases, we can avoid further use. These days we tend to focus on avoiding climate change and fossil fuel, but those tempted to see nuclear as an answer need to be reminded of what can go wrong- it can have wide ranging human costs and leave a long lived, brutal legacy:
New books on Chernobyl:
A movie:

The next post in this series will be on nuclear fusion- maybe not whole lot better.  


  1. Greetings David!
    Typo alert in your statement "The administration of iodide pills, to block Caesium uptake in the thyroid, would have limited the risk".
    Iodide pills are taken to block the uptake of radio-isotope Iodine-131, which concentrates in the thyroid, not Caesium-137, which spreads throughout the body. Iodine-131 has a half life of 8 days.
    Best regards,

  2. Corrected in text! Note also that background radon gas exposure, although low level, can be lengthy and internalised in some locations.