Highlights of recent reports on the consequences of the Chernobyl accident on thyroid cancer, leukaemia, effects on children health and birth defects (updated version)

Higlights selected by GreenFacts of two recent publications:

1.     the summary of  the UNSCEAR’s assessments of the radiation effects;

http://www.unscear.org/unscear/en/chernobyl.html

2     The summary report on Recent scientific findings and publications on the health effects of ChernobylWorking Party on Research Implications on Health. RADIATION PROTECTION NO 170 Directorate-General for Energy Directorate D — Nuclear Energy Unit D.4 — Radiation Protection 2011

http://ec.europa.eu/energy/nuclear/radiation_protection/doc/publication/170.pdf

Short summary . The global conclusions of the UNSCEAR report are that besides the most highly exposed individuals, the great majority of the population, according to the UNSCEAR report, is not likely to experience serious health consequences as a result of radiation from the Chernobyl accident. Many other health problems have been noted in the populations that are not related to radiation exposure.

1.  Consequences for the persons directly exposed Among the 106 patients surviving radiation sickness, complete normalization of health took several years. Many of those patients developed clinically significant radiation-induced cataracts in the first few years after the accident. Over the period 1987-2006, 19 survivors died for various reasons; however, some of these deaths were due to causes not associated with radiation exposure.

2. Thyroïd cancer Among the residents of Belarus, the Russian Federation and Ukraine, there had been up to the year 2005 more than 6,000 cases of thyroid cancer reported in children and adolescents who were exposed at the time of the accident, and more cases can be expected during the next decades. Notwithstanding the influence of enhanced screening regimes, many of those cancers were, according to UNSCEAR, most likely caused by radiation exposures shortly after the accident.

3. No scientific evidence of other major health impact on the population  Apart from this increase, there is no evidence of a major public health impact attributable to radiation exposure two decades after the accident. There is also no scientific evidence of increases in overall cancer incidence or mortality rates or in rates of non-malignant disorders that could be related to radiation exposure.

4. No evidenced increase of leukemia cases related to the accident.The incidence of leukaemia in the general population, one of the main concerns owing to the shorter time expected between exposure and its occurrence compared with solid cancers, does not appear to be elevated.

The EU report in 9 questions and answers

1 Which populations exposed to the radiations after the Chernobyl accident ?

According to the Directorate-General for Energy of the EU report three major groups of people were exposed to and, to a variable extent, are still being exposed to radioactive contamination:

a. approximately 600 000 Workers (liquidators, or emergency and recovery operations workers) involved in emergency response, containment, clean-up and associated  activities at theChernobylsite and in the contaminated areas. Among which about 240 000 worked in 1986 and 1987, when doses were highest, at the reactor site and the surrounding 30 km zone. The average effective dose received by the recovery operation workers between 1986 and 1990, mainly due to external irradiation, is now estimated at about 120 mSv. The recorded worker doses varied from less than 10 mGy to more than 1,000 mGy, although about 85% of the recorded doses were in the range 20–500 mGy.

b. about 116 000 inhabitants who were evacuated or relocated from contaminated areas and in the months following the accident a further 220 000 people were relocated after 1986.  The effective dose estimates for individuals in the general population accumulated over the 20 years following the accident (1986–2005) range from a few mSv to some hundred mSv depending on location, age and lifestyle factors, such as diet, or time spent outdoors. These doses are mainly due to external exposure from a mixture of deposited radionuclides, as well as to internal exposure from intake of 134Cs and  137Cs (UNSCEAR 2000 quotrd in the report)

c. About 5 million inhabitants of contaminated areas who were not evacuated.

2.  What was the main health  impact of Chernobyl ?  

To date, thyroid cancer has been the main direct consequence of exposure to fallout in the population in Belarus, northern Ukraine, and the oblasts of the Russian Federation closest to Chernobyl.

According to the EU report, the highest organ-specific dose was to the thyroid gland, primarily from ingestion of milk contaminated with radioactive iodines, particularly 131I. The highest individual thyroid doses among the subjects were 10.2 Gy in Belarus and 5.3 Gy in Russia. 131I intake was the main pathway for thyroid exposure.

The UNSCEAR (2011) document mentions that a number of 6848 cases of thyroid cancer were observed 1991 and 2005 in the three affected republics (the whole of Belarus and Ukraine and the four most affected regions of the Russian Federation) amongst those under age 18 years in 1986. There is no doubt that a substantial fraction of this excess incidence of thyroid cancer can be attributed to exposure to radioiodine due to the Chernobyl accident.

It is confirmed that there was a large rise in the incidence of confirmed cases of thyroid carcinoma in children exposed to fallout from the Chernobyl nuclear accident;  was also confirmed the correlation of incidence and the extent of fallout; the rapid drop in incidence to near normal figures in children born more than a few months after the accident, all correlations which, combined, show a causal relation between exposure and thyroïd cancer  induction.

There is no doubt, says the report, that young children exposed to external radiation are at a greater risk of developing thyroid cancer than older children, and that adults exposed to external radiation have much lower risk.

3. Are the cases of cancer of the thyroïd still expected to increase ?

The report quotes indeed studies showing that the substantial increase in thyroid cancer incidence seen amongst those exposed as children or adolescents in Belarus, the Russian Federation and Ukraine since the Chernobyl accident shows no signs of diminishing up to 25 years after exposure.

But one of these studies also shows that long term supplementary iodide intake after the accident lowered the risk in both the higher and lower iodide levels

The report also highlights a recent study that suggests that in utero exposure to radioiodines may have increased the risk of thyroid carcinoma approximately 20 years after the Chernobyl accident, but the epidemiological evidence to date is not sufficient to accurately quantify a difference in risk between prenatal and early postnatal exposure.  One of the factors relevant to the risk of developing thyroid carcinoma after radiation exposure is indeed genetic susceptibility.

Athough the long-term magnitude of risk cannot yet be quantified, it is expected  from many decades of follow-up of studies of populations exposed to external radiation, that Chernobyl-related thyroid cancers will continue to occur for many more years.

Moreover, if  current risk models are right, says a study quoted in the EC report, we have seen up to now only the tip of the iceberg and many thousands of cases of thyroid cancer are still to come among those heavily exposed to radioiodine in childhood.

4. What about the impact of Chernobyl on leukemia and breast cancer ?

Recentstudies mentioned in the report found significantly increased incidence of leukemia on Chernobyl liquidators from Ukraine and from Belarus, Russia and the Baltic countries,

There are currently few other clear evidence of increase in the incidence of cancers in the most affected populations, with the possible exception of breast cancer. The report mentions a study showing that the increase was highest among women who were younger at the time of the exposure and the authors concluded that it is unlikely that this excess could be entirely due to the increased diagnostic activity in these areas.

5. Were genetic effects identified in the populations affected by the Chernobyl accident ?

Studies in exposed families from rural areas of Ukraine and Belarussia also mentioned in the report are indicative of a statistically significant elevated paternal mutation rate in the exposed families (1.6 fold increase). However, studies conducted in families of Chernobyl cleanup workers globally failed to show increases in DNA damage such as  minisatellite mutation rates or slight to modest  increase above 200 mSv; , not statistically significant. The only clearly positive study has been criticised for the methodology used, says the report.

6. Were birth defects observed as a consequence of the Chernobyl accident ?

The results of a current research on environmental pollution and congenital anomalies in Belarus mentioned in the EU report show a clear excess of congenital anomalies (polydactyly, reduction defects of limbs, multiple  congenital malformations) was observed in the highly contaminated districts during the three first years after the accident.  Another study mentioned shows that, among about 100.000 births in Rivne between 2000 and 2006, the overall rate of neural tube defects (including spina bifida) is among the highest in Europe (22.2 vs 9 per 10 000 live births). The rates of conjoined twins and teratomas also seem to be elevated and in Polissia, the overall rates of neural tube defects are even higher while the rates of microcephaly and microphthalmia may also be elevated.

7. What were the major routes to radiation exposure ?

Wild foods, especially mushrooms and berries, and locally produced foods, especially milk related, were major radiation exposure routes. The authors concluded that, twenty four years after the Chernobyl accident, women continue to be chronically exposed to low-dose radiation at levels exceeding current recommendations and this might contribute (especially synergistically with alcohol consumption and micronutrient deficiencies) to higher prevalence of birth defects in areas with high levels of radiation contamination compared to uncontaminated areas.

8. Were other health effects observed as a consequence of the Chernobyl accident ?

Regarding children morbidity (cardiovascular symptoms in children such as arterial hypertension, and neurobehavioral and cognitive performances), as it was the case with birth defects, the currently available data do not allow drawing firm conclusions but are important enough to ask for further good quality research on morbidity in children living in contaminated territories. Series of studies are announced.

As for children living in contaminated territories, numerous studies have been published concerning non cancer diseases in liquidators, but, underlines the report, many of them also not published in English, and often being controversial due to a number of biases and confounding risk factors such as excessive weight, hypercholesterolemia, smoking, alcohol consumption, and others.

9. What were the radionuclides released from the Chernobyl reactor ?

According to the UNSCEAR report, the radionuclides released from the reactor that caused exposure of individuals were mainly 131iodine, 134caesium-and 137cesium-. 131 Iodine has a short radioactive half-life (eight days), but it can be transferred to humans relatively rapidly from the air and through consumption of contaminated milk and leafy vegetables. Iodine becomes localized in the thyroid gland. For reasons related to the intake of milk and dairy products by infants and children, as well as the size of their thyroid glands and their metabolism, the radiation doses are usually higher for them than for adults.

The isotopes of caesium have relatively longer half-lives (134cesium has a half-life of 2 years while that of 137caesium is 30 years). These radionuclides cause longer-term exposures through the ingestion pathway and through external exposure from their deposition on the ground. Many other radionuclides were associated with the accident, which were also considered in the exposure assessments.

Reference documents  

- Recent scientific findings and publications on the health effects of Chernobyl  -  Working Party on Research Implications on Health.  RADIATION PROTECTION NO 170  Directorate-General for Energy Directorate D — Nuclear Energy Unit D.4 — Radiation Protection 2011

This report was prepared by the Working Party on Research Implications on Health and Safety Standards of the Article 31 Group of Experts with the following members: A. Friedl, R. Huiskamp, L. Lebaron-Jacobs, P. Olko, S. Risica, P. Smeesters (Chairman), R. Wakeford, S. Mundigl (Scientific Secretary).

-Complete report of the UNSCEAR’s assessments of the radiation effects;

http://www.unscear.org/docs/reports/2008/11-80076_Report_2008_Annex_D.pdf

UNSCEAR (United Nations Scientific Committee on the Health effects of Atomic Radiations) was established by the General Assembly of the United Nations in 1955. Its mandate in the United Nations system is to assess and report levels and effects of exposure to ionizing radiation.

Other references : Strategic research agenda: the health consequences of the Chernobyl accident. 2011. International Agency for Research on Cancer (IARC) . FP 7 Project ARCH (Agenda for Research Agenda on the Health consequences ogf the Chernobyl Accident).

To make the best use of this unique opportunity to increase  understanding of radiation effects,the ARCH project has developed a long-term strategic plan for research into the health effects of the Chernobylaccident and the specific individual project proposals set out in this document. see:  http://arch.iarc.fr

note: the Report’s Highlights of GreenFacts are not verified by its Scientific Board

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