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Myths of Chernobyl
The following news release has been posted on the Australasian Radiation
Protection Society web-site http://www.arps.org.au/.
THE MYTHS OF CHERNOBYL
One of the most widespread myths of recent times is that the Chernobyl
nuclear reactor accident in 1986 caused many thousands of extra cancer
deaths in neighbouring regions, and that public health has been severely
affected by exposure to radiation.
According to the latest report of the United Nation Scientific Committee on
the Effects of Atomic Radiation (UNSCEAR) neither of these beliefs is true.
UNSCEAR recently approved its UNSCEAR 2000 report and a review of its
contents was presented at the International Radiation Protection
Association Congress in Hiroshima in May. The report is expected to be
published shortly.
Apart from the early fatalities in rescue workers who responded to the
accident, the main health effect is an increased risk of non-fatal thyroid
cancer in children. About 1800 cases of thyroid cancer have been diagnosed
in those who were children at the time of the accident. This increased
risk is linked to exposure to iodine-131, a radionuclide with a half-life
of 8 days, which was a major component of the fission products released
from the reactor. However, UNSCEAR reports no evidence of any other health
effects attributable to radiation exposures. In particular, there has been
no evidence of increases in cancer incidence or mortality. The risk of
leukaemia, one of the main concerns due to its short latency period (5-10
years after radiation exposure in adults), is also not elevated in the
exposed groups, including the recovery workers who received some of the
highest exposures.
The accident on April 26 1986 in reactor 4 of the Chernobyl nuclear power
plant caused the deaths of 30 power plant employees and firemen within a
few days or weeks (including 28 deaths that were due to acute radiation
exposure). Later on, during 1986-87, about 240 000 recovery workers were
called on to take part in clean-up activities at the plant and within the
30-km exclusion zone established around the reactor. The remediation
activities continued until 1990 and ultimately involved about 600 000
people.
In addition, about 116 000 people were evacuated from areas surrounding the
reactor in 1986, because of large-scale radioactive releases of radioactive
materials into the atmosphere. After 1986, about 220 000 people were
relocated in what are now the three independent republics of the former
Soviet Union: Belarus, the Russian Federation, and Ukraine. Wide areas of
the three republics were contaminated and trace levels of released
radionuclides were measurable in all countries of the Northern Hemisphere.
The radiation exposures arising from the accident were due initially to
iodine-131 and short-lived radionuclides, and subsequently to radiocaesiums
from both external radiation and the consumption of foods.
The highest radiation doses arising from the accident were received by
approximately 600 emergency workers and plant operators who were on the
plant site during the night of the accident. Acute radiation sickness was
experienced by 134 of these workers. The recovery operation workers,
subsequently called upon to decontaminate the reactor site and roads, and
to build the sarcophagus and a town for reactor personnel, received
generally much lower doses. The average recorded doses decreased from
about 170 millisievert (mSv) for those employed in 1986, to 130 mSv in
1987, and much lower values in subsequent years. (A lifetime dose from
natural background radiation is typically 100 to 200 mSv, but is
significantly greater in some parts of the world.)
Within a few weeks of the accident more than 100 000 persons were evacuated
from the most contaminated areas of Ukraine and Belarus. While the thyroid
doses, largely from ingestion of iodine-131, were significant, particularly
in infants, doses to organs other than the thyroid were much smaller with
effective doses (excluding the thyroid) of about 40 mSv in Belarus and 30
mSv in Ukraine. The thyroid cancer cases which arose were, regrettably,
largely avoidable. No significant measures were taken at the time to
reduce exposures by distributing stable iodine or by restricting the
consumption of milk and fresh leafy vegetables in the vicinity of
Chernobyl. If such countermeasures had been instituted, as in Poland, it
is likely that the incidence of thyroid cancer would have been much
reduced.
Many of the persons evacuated from the more contaminated areas after 1986
would, if they had remained, have received doses of not more than about 2
mSv per year, and in many cases the relocation of these people was
unnecessary on radiological grounds. These relocations served mainly to
heighten anxiety, and concerns and misconceptions about the dangers of
radiation. Natural background radiation dose rates are normally in the
range 2-10 mSv/y. The International Commission on Radiological Protection
has issued new guidance on dose levels at which intervention should be
considered and has proposed 10 mSv/y as a generic reference level below
which intervention is not likely to be justifiable.
Apart from the radiation-associated thyroid cancers among those exposed in
childhood, the only group that received doses high enough to possibly incur
statistically detectable risks is the recovery operation workers. Among
the emergency response workers there is a particular group of about 100
individuals who survived relatively high doses of radiation in the
immediate, acute, phase of the accident and are currently experiencing
health impairments as a consequence of their original injuries. Studies of
this group will probably contribute to scientific knowledge on late effects
of ionising radiation.
The UNSCEAR report notes that, of papers available to date regarding the
estimation of health effects resulting from the Chernobyl accident, many
suffer from methodological weaknesses such as inadequate diagnoses and
classification of diseases, selection of inadequate control groups, or
inadequate estimation of radiation doses. It concludes that, apart from
the substantial increase in thyroid cancer after childhood exposure -
· there is no evidence, 14 years after the Chernobyl accident, of any
other major public health impact caused by exposure to ionising radiation;
· no other increases in overall cancer incidence or mortality have been
observed that could be associated with radiation exposure,
· there was no increase in the incidence of birth defects as a result of
the accident.
The risk of leukaemia, one of the most sensitive indicators of radiation
exposure, has not been found to be elevated even in the recovery operation
workers or in children. In spite of claims of cancers, genetic effects and
many other disorders, including statements by health and other officials in
the countries concerned, there is no scientific proof of an increase in
malignant or non-malignant disorders, somatic or mental, that is related to
ionising radiation (except for thyroid cancers in children). The additional
annual doses to residents in the contaminated zones are generally well
within the normal range of variation of natural background radiation doses.
It must be concluded that reports of health effects caused by radiation
have been greatly exaggerated. A particular example is that of the groups
of children from around Chernobyl who visited other countries after the
accident or who were filmed in hospitals following chemotherapy. These
were widely reported to have been suffering sickness due to radiation.
Many of the children appeared to be in poor health. However, with the
possible exception of any thyroid cancer cases among them there is no
evidence that their illnesses were caused by radioactive emissions from the
damaged reactor.
________________________________
Andrew C McEwan PhD
National Radiation Laboratory
PO Box 25-099
Christchurch, New Zealand
Ph 64 3 366 5059
Fax 64 3 366 1156
Andrew_McEwan@nrl.moh.govt.nz
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