Low radiation risk in Fukushima

AN international team assembled by the World Health Organisation (WHO) looked at a number of communities in Fukushima prefecture and estimated their health risk from their exposure to radiation as a result of the accident in March 2011. The results were released in a report entitled “Health risk assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami”.

For the general population in the wider Fukushima prefecture, across Japan and beyond, “the predicted risks are low and no observable increases in cancer rates above baseline rates are anticipated”, said the WHO. A programme of continued monitoring and screening was recommended.

“The primary concern,” said Maria Neira of the WHO, “is related to specific cancer risks linked to specific locations and demographic factors.” Of note is the population of Namie, outside the evacuation zone to the north-west of the plant, where radioactive materials were carried by the wind. Those among its 22,000 or so inhabitants who remained at home for four months after the accident were considered as the most exposed group and the WHO estimated that a certain marginal increase in cancer risk could result. The second-most exposed group were those who spent four months in Iitate, with risks to its population, about 7,000, raised by about half the amount of Namie.

The WHO also addressed the fear that the accident could badly affect fertility or the health of unborn children. It said the effects of the accident “are not expected to cause an increase in the incidence of miscarriages, stillbirths and other physical and mental conditions that can affect babies born after the accident”.

The WHO’s use of the linear, no-threshold method of gauging health risks will have resulted in a cautious overestimate of health impact. But the WHO noted that it was being “prudent” in adopting the method, “[in] attempting not to underestimate the risks”.

Clear cases of health damage from radiation generally only occur following exposures of 1,000 mSv (millisievert, a unit of radiation measurement), far more than the 10-50 mSv that the WHO said was received by people in Namie and Iitate. Across Fukushima, the doses were generally in the range 1-10 mSv.