[cdn-nucl-l] Chernobyl: An Overlooked Aspect?

["Adam McLean" <adam.mclean@utoronto.ca>]

Posted in Science Magazine Volume 299, Number 5603, Issue of 3 Jan 2003, p.
44 and at:
http://www.sciencemag.org/cgi/content/full/299/5603/44b?etoc

Adam

-------------------------

Chernobyl: An Overlooked Aspect?

The dramatic rise in the incidence of thyroid cancer in those exposed as
children to fallout from the Chernobyl accident (1-3) has led to other
possible health consequences being largely ignored. Recent data highlight
the uncertainty in whole-body dose assessment, raise the possibility that
organs other than the thyroid may have received significant doses, and
suggest that a wide range of possible health effects urgently need to be
addressed.

For example, on the basis of recent reports (4, 5), the average effective
dose of radiation to adults evacuated from the 30-km zone in Ukraine can be
estimated at about 0.045 Sv (6). This is in contrast to an estimated average
whole-body dose of 0.4 Gy (equivalent to an effective dose of 0.4 Sv), based
on chromosome aberration counts in children evacuated from the Belarussian
exclusion zone (7). This study represents the average dose to 60 individuals
from six settlements; the technique, but not the original observations, was
revalidated. The studies quoted differ in age, country, and methodology and,
as for any reconstructed dosimetry, confidence limits are wide. However,
taking this together with a number of other studies of evacuees and others
living close to the exclusion zone (8-10) suggests that this population
received whole-body doses in the range of 0.1 to 0.5 Gy.

Average population doses can, of course, conceal wide variations in
individual doses; estimates suggesting an average effective dose for
Ukrainian evacuees of 0.045 Sv also show that the dose in some settlements
ranged up to nearly 0.5 Sv. There were about 25,000 evacuees from the
Belarussian zone (3), and if the average whole-body dose was indeed 0.4 Gy
(7), some could have received whole-body doses well in excess of 1 Gy.

Radiation to the thyroid from isotopes of iodine made by far the greatest
contribution to the effective dose (4, 5). If the whole-body dose estimates
(7) based on chromosome spreads are correct, the thyroid doses in many
evacuees could easily have exceeded the threshold for deterministic effects,
particularly in those exposed as young children. A survey of evacuees for
hypothyroidism should be a high priority. This would bring needed medical
assistance to this group and further validate the uncertain estimates of
dose to evacuees.

However, tissue doses to other organs are also potentially important in this
group. From one of the recent studies (4), it can be deduced that in some
Ukrainian settlements, average tissue doses to the lung were as high as 0.6
Gy in adults. Average doses to infants could be considerably higher. These
doses largely derive from inhalation of isotopes of barium, ruthenium, and
cerium, which occur as insoluble oxides and together formed about 35% of the
inhaled contribution to the effective dose (4). Organs adjacent to the lung,
such as breast and heart, would have received radiation from isotopes
retained in the lung; breast epithelium would also have received some
radiation from isotopes of iodine.

It is therefore important for the international community to initiate and
provide long-term support for collaborative studies of all possible
consequences of the Chernobyl accident. These recent studies suggest that
organs other than thyroid could have received doses comparable to those of
the atomic bomb survivors, who showed significant increases in a wide range
of cancers and nonmalignant diseases. The UN (11) recently proposed the
creation of an independent "Chernobyl Research Board"; this board could take
the lead in initiating studies to examine the type of issue raised here and
provide assistance or reassurance based on internationally verified
evidence.

Keith Baverstock*
World Health Organization (WHO) Regional Office for Europe,
Bonn Office,
Görresstrasse 15, D-53113, Bonn,
Germany.

Dillwyn Williams
Strangeways Research Laboratory,
Wort's Causeway,
Cambridge, CB1 4RN,
United Kingdom.

*The views expressed are those of the author and should not necessarily be
taken to be those of the WHO.

References and Notes


V. S. Kazakov, E. P. Demidchik, L. N. Astakhova, Nature 359, 21 (1992). 
K. Baverstock et al., Nature 359, 21 (1992). 
UN Scientific Committee on the Effects of Atomic Radiation, Sources and
Effects of Ionising Radiation (United Nations, New York, 2000), vol. II,
Annex J. 
K. Mück et al., Health Phys. 82, 157 (2002). 
G. Pröhl et al., Health Phys. 82, 173 (2002). 
Effective dose (unit = Sv) is derived from the absorbed tissue or whole-body
dose in Gy by multiplying by a tissue-weighting factor to reflect the
overall risk to health of radiation absorbed by that tissue. The weighting
factors recommended by the International Commission on Radiological
Protection include the following: whole body, 1.0; thyroid, 0.05; and lung,
bone marrow, stomach, and colon, 0.12. The value of 0.045 Sv is derived from
the estimates given for ingestion (5) of 0.005 Sv, inhalation (4) of 0.025
Sv, and 0.015 Sv for external exposure (12). 
L. S. Mikhalevitch, D. C. Lloyd, A. A. Edwards, G. A. Perepetskaya, N. A.
Kartel, Radiat. Prot. Dosim. 87, 109 (2000). 
N. A. Maznik et al., Radiat. Prot. Dosim. 74, 5 (1997). 
F. Darroudi, A. T. Natarajan, in The Radiological Consequences of the
Chernobyl Accident (European Commission, Minsk, Belarus, 1996), pp.
1067-1072. 
S. Salomaa et al., in Proceedings of 8th IRPA Congress (International
Radiation Protection Association, Montreal, Canada, 1992), pp. 801-804. 
UN, The Human Consequences of the Chernobyl Accident: A Strategy for
Recovery (United Nations, New York, 2002) (available at
www.reliefweb.int/library/documents/2002/undp_rus_25jan.pdf). 
I. A. Likhtarev, V. V. Chumack, V. S. Repin, Health Phys. 66, 643 (1994).