The 25th anniversary of the accident at the Chernobyl nuclear power station was on April 26, this year. The accident caused large scale releases of radioactive materials into the environment. Design deficiencies and operator errors caused the accident.
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) confirmed that 134 plant staff suffered acute radiation syndrome (ARS). Many of them had skin injuries caused by intense beta radiation ( UNSCEAR 2008, April 2011 ). Twenty eight of these staff died. Among the persons who suffered ARS, 19 died before 2006. They died because of various reasons, not related to radiation exposure.
New findings
Among the ARS survivors, there is clear evidence of skin injuries and radiation induced cataracts. Among several hundred thousand persons who participated in recovery operations, there are indications that those who received higher doses had increases in the incidence of leukaemia and cataracts. There is no evidence of other radiation exposure related health effects.
UNSCEAR found that the threshold dose of induction of cataract is lower than previously thought. There are indications of an increase in the incidence of cardiovascular and cerebro-vascular diseases among the recovery operation workers that correlate with the estimated doses; the Committee conceded that the influence of confounding factors and potential study biases remain.
The thyroid doses to some members of the public were high. By 2006, the number of thyroid cancers rose to 6000. This was avoidable if the authorities initiated prompt measures against consumption of milk contaminated with iodine-131. Substantial fraction of thyroid cancers was found among those who were children or adolescents in 1986. Thyroid cancers are curable. However, by 2005, 15 of them died.
No other effects
UNSCEAR 2008 confirmed its earlier assertion that to date, there has been no persuasive evidence of any other health effect in the general population.
Most of the workers and members of the public were exposed to low level radiation comparable to or, at most, a few times higher than the annual natural background levels; these exposures will continue to decrease as the deposited radioactivity decays or is further dispersed in the environment.
Since UNSCEAR published the last report, researchers estimated the thyroid doses to an additional 150,000 emergency and recovery operation workers. Researchers also extended the data on the estimated thyroid doses and effective doses from five million to about 100 million inhabitants of Belarus, the Russian Federation and Ukraine; they updated similar data on 500 million residents of most other European countries.
UNSCEAR noted that several studies have now been conducted that provide rather consistent estimates of the radiation risk factors for thyroid cancer.
Controversies
Quantitative estimates of the health effects due the Chernobyl accident are mired in controversy. Different interest groups have arrived at different estimates.
Virtually none but the most scientific groups cautioned against estimating the projected health consequences such as deaths from very low doses to large sections of the populations. Such estimates are not scientifically supportable.
The total number of deaths due to the accident is 62 — 47 plant staff and 15 persons due to thyroid cancer. Except in areas very close to the stricken Chernobyl reactor, increases in doses were low, often within the changes in the natural background radiation present every where.
In April 2006, Greenpeace International estimated that from 1986 to 2056, over 93,000 persons will die due to cancer arising out of radiation exposure from the accident.
According to another compilation “Chernobyl: Consequences of the Catastrophe for People and Environment” published in December 2009, 985,000 persons worldwide died due to Chernobyl fallout from 1984 to 2004!
Since the authors used the publication services of the New York Academy of Sciences, the estimate got wide publicity. Soon after its publication, the Academy distanced itself from the book stating that the expressed views are those of the authors or by advocacy groups or individuals with specific opinions about the Chernobyl volume. The Academy asserted that it is not a work commissioned by it.
Interestingly, Rod Adams who is himself an atomic energy activist listed several reasons to argue that the book is not a legitimate academy report. ( Atomic Insights, Sept 13, 2010 ).He noted that the preface of the report states that the writing of the report was undertaken with the initiative of Greenpeace International!
Let us hope that UNSCEAR will be able to throw more light on the health effects of radiation in its future reports.
( Raja Ramanna Fellow, Department of Atomic Energy ) ksparth@yahoo.co.uk
