February 28, 2013

expert reaction to the WHO Fukushima health risk report

The World Health Organisation (WHO) released a report on health risks associated with the Fukushima Daiichi nuclear power plant (NPP) disaster in Japan, concluding that for the general population the predicted risks are low and no observable increases in cancer rates  are anticipated, but estimated risk for specific cancers in certain subsets of the population in Fukushima Prefecture has increased. 

Prof Jim Smith, Professor of Environmental Science at the University of Portsmouth, said:

“The WHO report is a major step forward in our understanding of the likely health consequences of the Fukushima accident.  Apart from the emergency workers, the most affected people were those who remained in some highly contaminated towns and villages to the northwest of the power station for up to four months before evacuation. The report found that these people received a lifetime radiation dose of up to 50 milli-Sieverts (mSv) and therefore have a significant, but relatively small, additional risk of contracting cancer in later life.

“Whilst serious, this additional radiation exposure is not high compared to exposures received by all people worldwide from natural background radiation and diagnostic medical procedures.  For example, the average British person receives over 150 mSv during their lifetime from background radiation, and in some areas natural radiation exposures are much higher.  Around 200 emergency workers at Fukushima received an average radiation dose of about 200 mSv.

“The report does not yet present data on numbers of people who received particular radiation doses, so it is not as yet possible to estimate overall health consequences.  However, the report’s findings imply that, as expected, the health consequences of Fukushima (in particular the incidence of thyroid cancer) will be much less than those of the Chernobyl accident.  The report highlights the importance of potential social and psychological impacts of the accident on the affected populations as well as the direct health effects.”

Jim Thurston, medical radiation expert at the Institute of Physics and Engineering in Medicine, said:

“The report appears to be a very well-considered assessment, showing that as a result of the radiation doses received by the most-exposed group of the general population living near the plant (12-25mSv), any increases in the cancer incidence rate in the general population local to the plant will be very small and barely detectable (overall a 1% increase on the ~30% normal lifetime incidence rate for all solid cancers together), and will be hidden within the normal random fluctuations in a population.  Furthermore, the increases in cancer due to the doses received by other populations will be extremely small and certainly won’t be detectable. 

“It is important to emphasise the normal incidence rates for solid tumour type cancers – near 1 in 3 of the population will get cancer in their lifetime, and that the terrible events at Fukushima have led to only a very small incremental increase in that normal incidence rate.  Even for the worst-case scenario in terms of a specific cancer – thyroid cancer in females, for which the survival rate is very high – the increases implies that the lifetime incidence rate will only rise from approximately 0.75% to 1.25%.

“These predictions are based on a standard radiation dose–risk model, called the ‘linear-quadratic’ model.  This model predicts that at the low doses received as a result of the incident the response is roughly linear – i.e. double the radiation dose received means double the risk, and no lower level below which radiation can’t cause harm.  It is a compromise between a lot of data gathered over the decades since Hiroshima and Nagasaki – a compromise between data that might suggest that radiation is more harmful at lower dose then the model predicts, and other data that shows the exact opposite.  Overall, the linear-quadratic model remains the best model for predicting the risk of harm from radiation exposure to a population from both external irradiation and the ingestion of radioactive contamination.

“The executive summary and press release go on to state that of course these predictions will be followed up with continued long-term monitoring of the population to look at the actual cancer incidence rates over the future years and decades.  Experience of previous incidents and accidents would suggest that this report’s predictions will, if anything, overestimate the subsequent excess cancer incidence rates measured.”

Prof Richard Wakeford, Visiting Professor at Dalton Nuclear Institute at the University of Manchester and contributor to the WHO report, said:

“The release of radioactive materials into the environment during the Fukushima nuclear accident was substantial; but based on measurement data, the radiation doses received by the surrounding population are small, even for the most exposed communities.

“These doses produce an extra risk of cancer over a lifetime of about 1% at most, in addition to background lifetime cancer risks from all other causes of, on average, 40% for men and 29% for women.  The extra cancer risk is much lower than this outside the most exposed communities.  Radiation exposure from the Fukushima accident has had only a small impact on the overall health of the nearby population, and much less outside the most affected areas.”

WHO Fukushima health risk report:
http://www.who.int/ionizing_radiation/pub_meet/fukushima_report/en/index.html