By publishing the estimate of risks from Fukushima accident, in its report titled “Health risk Assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami” released on February 28,2013 the WHO has violated an important principle recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation(UNSCEAR).
Some explanation is due in this context. The estimates of health risks from Fukushima accident published by the WHO are based on the Linear-No-Threshold(LNT)hypothesis. This hypothesis was introduced as a simple basis in radiation protection. Specialists knew it’s limitations.
During May 2012, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has submitted a report to the UN General Assembly. In this report, the UNSCEAR clearly stated that it “does not recommend multiplying very low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or lower than natural background levels”.
The UNSCEAR has the remit to make appropriate radiation protection related recommendations to the United Nations.
To be fair to the authors of the WHO report, we may also recognize the fact that the draft WHO report must have been prepared before the UNSCEAR gave its report to the United Nations. However it is difficult to imagine that the authors were not aware of the recommendation.
Chances are that this estimate will be the last one of its kind.
The UNSCEAR recommendation is not anything new. The US Health Physics Society has published a position paper on the topic as early as 1996. It published the same in revised form in 2004.
” In accordance with current knowledge of radiation health risks, the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 rem in one year or a lifetime dose of 10 rem above that received from natural sources. Doses from natural background radiation in the United States average about 0.3 rem per year. A dose of 5 rem will be accumulated in the first 17 years of life and about 25 rem in a lifetime of 80 years. Estimation of health risk associated with radiation doses that are of similar magnitude as those received from natural sources should be strictly qualitative and encompass a range of hypothetical health outcomes, including the possibility of no adverse health effects at such low levels.
There is substantial and convincing scientific evidence for health risks following high-dose exposures. However, below 5–10 rem (which includes occupational and environmental exposures) risks of health effects are either too small to be observed or are nonexistent.”
The UNSCEAR report has logically presented its recommendation and the context in which it was made. It is ironic that while Green Peace argued that the WHO underestimated the risks, the Japanese Government protested saying that the WHO report overestimated the risk stroking fears among the exposed people. It is impossible to have a deterministic answer to a probabilistic question.
The WHO report also should have stated that at the low doses the probability of the risk being zero cannot be overruled. Either way it will be very difficult for the public to understand the nuances of the issue.
The contribution from natural radiation at different places vary significantly. For instance, in Maharashtra it is as low as 0.4 mSv, Andhra Pradesh 1 mSv; in the high background radiation areas of Kerala and Tamil Nadu it may very well be 10 to 15 times higher. In parts of Iran it is 100 times higher.
The increase in radiation levels due to the accident at Fukushima is of the same order or even less than these values. Those who are knowledgeable will not lose sleep on possible additional risk due to these dose levels. Calculating risk based on the assumption that risk is linearly proportional to dose ignores the repair of radiation damage at low doses. Some mavericks (they are no more a minority!) may argue that exposure to low doses of ionizing radiation may lead to reduction in cancer rates. It will be practically impossible to prove or disprove any of these statements so long as we do not have some unique biomarker which indicates those cancer caused by radiation.