Increased incidences of radiation-related health effects among those exposed from the March 2011 accident at Japan's Fukushima Daiichi nuclear power plant are unlikely to be discernible, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) said in a new report  on 9 March. The report's major findings and conclusions broadly confirm those of UNSCEAR's 2013 report on the accident.

Workers decontaminate the roof of a house in Tamura City (Image: Fukushima prefectural government)

In May 2011, UNSCEAR began a two-year assessment of the levels and effects of radiation exposure from the accident. The Committee's 2013 report was published in April 2014, along with the supporting scientific data and evaluation. That report set out the Committee's assessment of the levels of exposure of defined groups of the general public in Japan, including those evacuated and different age groups, and of workers. The committee concluded that health risks resulting from the Fukushima accident were far lower than those for Chernobyl, due to the substantially lower doses received by the public and workers, and did not expect discernible increased incidences of radiation-related health effects among those exposed.

In 2018, UNSCEAR decided to update the 2013 report - which was limited to information published or disclosed by the end of October 2012 - to reflect the latest cumulative scientific findings and developments. The UNSCEAR 2020 Report, published on 9 March, summarises all of the relevant scientific information available (up to the end of 2019) relating to the levels and effects of radiation exposure due to the accident at Fukushima Daiichi. UNSCEAR said the aim of its latest report is to provide a summary of all scientific information and an appraisal of the implications of this information for its 2013 report.

"In the last decade, a significant amount of new information has emerged with regard to exposure estimates," UNSCEAR said. "This new information has enabled the Scientific Committee to perform an improved and more robust evaluation of the levels and effects of radiation due to exposure from the accident."

Titled Levels and effects of radiation exposure due to the accident at the Fukushima Daiichi Nuclear Power Station: Implications of information published since the UNSCEAR 2013 Report, the new document broadly confirms the major findings and conclusions of the 2013 report.

"The improved models, based on additional monitoring data and more comprehensive information about people's actual diet and behaviour in Japan, led to the committee reviewing and updating its dose estimates," UNSCEAR said. "The updated dose estimates to members of the public have either decreased or are comparable with the Scientific Committee's previous estimates. The committee therefore continues to consider that future health effects directly related to radiation exposure are unlikely to be discernible."

UNSCEAR also assessed the incidence of thyroid cancer that could be inferred from the estimated radiation exposure and concluded that this is not likely to be discernible, in any of the age groups considered, including to children and those exposed in utero to radiation. The Committee said it believes the large increase (relative to that expected) in the number of thyroid cancers detected among exposed children is not the result of radiation exposure. Rather, they are the result of ultrasensitive screening procedures that have revealed the prevalence of thyroid abnormalities in the population not previously detected. In addition, in the general public, USCEAR found there has been no credible evidence of excess congenital anomalies, stillbirths, preterm deliveries or low birthweights related to radiation exposure.

"Since the UNSCEAR 2013 Report, no adverse health effects among Fukushima residents have been documented that could be directly attributed to radiation exposure from the accident," said UNSCEAR Chair Gillian Hirth.

An increase in the incidence of cancers is also unlikely to be discernible in workers at the Fukushima Daiichi site, UNSCEAR concluded.

The committee also evaluated the information on the transfers of released radioactive material through the terrestrial, freshwater and marine environments. UNSCEAR said it continues to consider regional impacts on wildlife populations with a clear causal link to radiation exposure resulting from the accident to be unlikely. However, it said some detrimental effects in some plants and animals have been observed in areas of enhanced radiation levels.

Researched and written by World Nuclear News