Journal of APPLIED BIOMEDICINE
ISSN 1214-0287 (on-line)
ISSN 1214-021X (printed)
Volume 8 (2010), No 2, p 67-72
DOI 10.2478/v10136-0010-z
Childhood leukaemia in the vicinity of German nuclear power plants - some missing links
Friedo Zolzer
Address: Friedo Zolzer, Department of Radiology and Toxicology, Faculty of Health and Social Studies, University of South Bohemia, Matice skolske 17, 370 01 Ceske Budejovice, Czech Republic
zoelzer@zsf.jcu.cz
Received 10th December 2009.
Revised 20th January 2010.
Published online 25th January 2010.
Full text article (pdf)
Abstract in xml format
Summary
Key words
Introduction
Some general facts about childhood leukaemia
The main findings of the so-called KiKK study
Comparison with other studies
The possible radiation doses involved
The question of age
Other possible explanations
Conclusion
References
SUMMARY
A recent epidemiological study in Germany, the so-called KiKK study, came to the conclusion that there was a relationship between a child's risk of contracting leukaemia in the first 5 years of life and the distance of its residence from the nearest nuclear power plant. The risk of children inside a 5 km radius was found to be 2.19 times that of children outside, with a lower 95% confidence limit of 1.51. The study seems to be epidemiologically sound and solid, and its results agree with earlier evidence about childhood leukaemia in the vicinity of nuclear installations. It does not show, however, nor does it at all claim to show, that the phenomenon was due to radiation exposure. The measured doses in the area around German nuclear power plants are at least a factor 1000 smaller than what would be needed to explain the number of leukaemia cases observed. Additional evidence suggests that the main effect was a shift of the age distribution towards younger ages, with the overall incidence for all age groups not affected, which would be rather unexpected as a radiation effect. Still other studies have shown that elevated risks can even be observed around so-called "planning sites", where no nuclear facility has ever been built. It thus seems justified to speak of "missing links" between the elevated risk of childhood leukaemia around nuclear power plants on the one hand, and the radiation exposure caused by their normal operation on the other.
KEY WORDS
KiKK; radiation; risk; leukaemia; health
INTRODUCTION
In December 2007, the German Federal Office for
Radiation Protection (Bundesamt fur Strahlenschutz)
presented to the public "An Epidemiological Study of
Childhood Leukaemia in the vicinity of Nuclear
Power Plants" ("Epidemiologische Studie zu
Kinderkrebs in der Umgebung von Kernkraftwerken",
in the German public often referred to as
"KiKK-Studie"; Kaatsch et al. 2007). The main
results were published in English shortly afterwards
(Kaatsch et al. 2008, Spix et al. 2008). This study
aroused extraordinary public interest, because it
showed a relationship between a child's risk of
contracting leukaemia in the first 5 years of life and
the distance of its residence from the nearest nuclear
power plant. Although the study summary cautioned
against hasty conclusions, emphasizing that "no
statement can be made about the biological risk
factors that might explain this relationship", the
findings seemed to imply that radioactivity released
from or radiation emitted by the nuclear plants must
be the cause of the increased leukaemia risk. There
was an uproar in the media, press releases from
supporters and opponents of nuclear energy,
statements of real and self-styled experts, and finally
a request by the Federal Ministry of the Environment
to its Radiation Protection Commission
(Strahlenschutzkommission) for an independent
review of the study. The final report of this review
was released in October 2008. It serves as the main,
but not the only basis of the following commentary.
SOME GENERAL FACTS ABOUT CHILDHOOD LEUKAEMIA
Leukaemia is a cancer of the blood-forming tissues
and is characterized by an abnormal proliferation of
white blood cells (leukocytes). The most frequently
occurring morphological types are acute
lymphoblastic leukaemia and acute myeloblastic
leukaemia (ALL and AML) much less frequent are
their chronic counterparts (CLL and CML).
Leukaemias account for about a third of all childhood
cancers, the proportion decreasing with age (Lightfoot
and Roman 2004). More than 80% of all cases are
ALL and about 15% AML, which leaves less than 5%
for the other types (Kaatsch and Mergenthaler 2008).
The age distribution shows a maximum around
2-3 years for lymphoblastic leukaemia and around
1 year for myeloblastic leukaemia. In Europe,
leukaemia occurs with an incidence rate of 4-5 per
100 000 children. This incidence rate has been
increasing by about half a percent per year over the
last few decades (Kaatsch and Mergenthaler 2008).
There are also considerable geographical
variations. In Germany, for instance, some counties
(Landkreise) have an incidence rate of less than half
the average, while in others the incidence rate is more
than double the average (Kaatsch and Mergenthaler
2008). Although many factors have been identified
which play a role in the aetiology of childhood
leukaemia, such as genetic predisposition, nutrition,
allergies, and environmental factors, it is not clear
how exactly they influence incidence rates or their
temporal and spatial variations (Lightfoot and Roman
2004). One particular fact is that rural areas tend to
have a higher than average incidence, which may be
related to population mixing as discussed below.
THE MAIN FINDINGS OF THE SO-CALLED KIKK STUDY
The latest study of childhood leukaemia around
German nuclear power plants was designed to test the
hypothesis that children living close to these
installations have an increased risk of contracting
leukaemia before their 5th birthday. The distance from
the nuclear power plant was supposed to serve as a
proxy for the radiation exposure of the children; no
attempt was made to actually measure radiation
doses.
The authors of the study chose a case-control
design, analyzing data for all 1592 children in the
study regions who were diagnosed with cancer of any
type between 1980 and 2003. These cases were
matched with 4735 controls, i.e. children of the same
age, sex and year of residence in the study region.
Each study region was defined as the county in which
one of the 16 German nuclear power plants was
situated, the closest neighbouring county and the
closest county to the east. The study period began in
the year after the start of the power plant's operation,
and ended 5 years after its decommissioning.
Although all types of cancer were included in the
study, only the results for leukaemia are discussed
here, because none of the other types yielded any
significant results.
For leukaemia, 593 cases were matched with
1766 controls. The statistical evaluation of the data
showed a significant trend towards a higher
leukaemia risk for children living closer to a nuclear
power plant. When the Odds Ratio (which for small
probabilities are the same as the Relative Risk) was
described as OR = 1 + beta/x, where x is the distance in
km from the next power plant, the factor beta came out
as 1.75 km, with a lower 95% confidence limit of
0.46 km. For instance, a child living at a distance of
3.5 km would have a Relative Risk of 1.5 (50% above
normal), whereas a child living at 17.5 km would
have a Relative Risk of just 1.1 (10% above normal).
When the data were evaluated not continuously (as a
trend with the distance from the power plant), but in
two categories (either closer to or further away from
the power plant than a certain distance), it was found
that the risk of children inside the 5 km radius was
2.19 times that of children outside, with a lower 95%
confidence limit of 1.51.
It should be noted that the absolute number of
cases was comparatively small. There were altogether
37 cases of leukaemia within the 5 km radius, where
statistically 17 cases would have been expected. The
20 additional cases occurred over a period of
23 years, which means less than 1 additional case per
year. That, of course, is no comfort to the affected
children and their families, but it shows how
extremely thin the statistical basis of the study is.
Nevertheless, the review of the Radiation Protection
Commission states that the statistical methods used
were adequate and "according to good
epidemiological practice". Some details are criticized,
but the main findings are confirmed.
COMPARISON WITH OTHER STUDIES
This study was not the first to analyse data of children
living close to nuclear installations. An excess of
childhood leukaemia was first observed in the vicinity
of the fuel reprocessing plant Sellafield near Seascale
in West Cumbria, England (COMARE 1986). Later,
similar findings were reported around the Dounreay
Nuclear Establishment in Scotland (COMARE 1988)
and around the fuel reprocessing plant at La Hague in
France (Guizard et al. 2001), to name just two further
examples. A leukaemia cluster was also found to exist
in the community of Elbmarsch in northern Germany,
within a distance of 5 km from the Krummel nuclear
power plant (Schmitz-Feuerhake et al. 1993). In this
latter case, 9 cases of childhood leukaemia were
observed between 1990 and 1996, which is a more
than threefold increase over the expected number
(Laurier et al. 2002).
When epidemiological studies were carried out
including all nuclear power plants in Germany, partly
contradictory conclusions were reached. A paper in
1992, by authors from the same institution as the
KiKK study, claimed that there was an increased
relative risk of acute leukaemia before five years of
age for children living within a 5 km radius around
German nuclear installations. This seemed to be
mainly due, however, to an unusually low incidence
in the control regions chosen for the study (Michaelis
et al. 1992). A later report in 1998 did not confirm the
earlier findings, although it said that the relative risk
for the children in question was 1.39, but this figure
was not significantly different from 1.00 (Kaatsch et
al. 1998). The fact is that the KiKK study, which
shared two thirds of its data with its predecessor, now
produced a much clearer result (RR = 2.19), which
can probably be attributed to its case-control design.
It may be interesting to note that exclusion of the
cases from the cluster around the Krümmel nuclear
power plant would not have changed the overall result
of the KiKK study dramatically (RR = 1.96, Kaatsch
et al. 2008).
A recent meta-analysis of 17 studies from
8 countries (Baker and Hoel 2007) looked at data for
children of different age groups living in the
proximity of nuclear facilities, where "proximity" in
some cases meant "closer than 10 km", in other cases
"in the same county". These reports were greatly at
variance with each other, some showing increased
risks, some reduced risks, but significance was hardly
ever reached. Nevertheless, pooling the data in the
meta-analysis gave a clear result, namely that
standardized incidence ratios were between 1.07 and
1.25 for children living near nuclear facilities, with
confidence intervals not containing 1.00 for most age
groups and geographic zones. It should be mentioned
that the meta-analysis was based on a selection of
17 out of 37 individual studies and that the selection
criteria have been criticised (Spix and Blettner 2009).
It is unclear, however, if that really created an undue
bias.
While most studies in the past did not pay special
attention to the age group below 5 and a distance less
than 5 km, two recent studies from France and Great
Britain were designed to match the German study as
closely as possible. The French study showed a
standard incidence ratio for the children in question of
0.96, but that was based on the difference between
5 observed cases and 5.2 expected (Laurier et al.
2008). The British study reported 18 observed cases
against 14.6 expected, which looked like an increase,
but did not reach significance either (Bithell et al.
2008). For the time being, the KiKK study remains
the largest and statistically strongest of such analyses,
and it seems reasonable to accept , for now, that there
is indeed an elevated risk for childhood leukaemia in
the vicinity of nuclear power plants.
THE POSSIBLE RADIATION DOSES INVOLVED
As to the possible reasons for such an excess of
leukaemia cases, the authors of the study said that "no
statement can be made about the possible biological
risk factors which may explain this relationship". This
was due to the fact that the radiation doses to which
children living close to the German nuclear power
plants could have been exposed, to the best of
everybody's knowledge, were far too small to explain
the observed increase in risk.
The 2008 review by the German Radiation
Protection Commission also addressed this point. It
stated that releases of radioactivity from German
nuclear power plants are monitored by a combined
system of emission and immission control, which
ensures the detection of external and internal
exposures to radiation in the vicinity of the
installations. The review specifically states that "the
experience with the atmospheric nuclear weapons
tests and with the Chernobyl accident leads to the
conclusion that an additional radioactivity causing
radiation exposures to more than 0.01 mSv annually
would leave such distinct traces in the environment
that they could be reliably measured". The stated dose
of 0.01 mSv is more than 200 times smaller than the
annual background exposure in Germany. The real
radiation exposure of people living close to the
nuclear power plants, of course, most probably
differed from the natural background exposure by
even less than the detectable 0.01 mSv annually.
The review continues to say that a relative risk of
2.19 for leukaemia, as was found for children under
the age of 5 living within a 5 km radius around
nuclear power plants, would be indicative of an
exposure to at least 10 mSv in utero. This estimate is
based on the results of the Oxford Survey of
Childhood Cancers and similar studies, which looked
at the leukaemia risk of children exposed to
diagnostic X-rays mainly during the third trimester of
pregnancy. These studies pointed to an excess relative
risk of about 50 per Sv, which is more than 10 times
that of adults (Wakeford 2008). A comparison with
the risk from in utero exposure is clearly the most
appropriate here, because leukaemia is induced by
radiation with a latency period of a few years and thus
a major proportion of the cases appearing before the
5th birthday would be induced during pregnancy. A
dose of 10 mSv, however, is more than 1000 times
higher than what could reliably have been detected by
the monitoring system around the German nuclear
power plants.
THE QUESTION OF AGE
In the meta-analysis of Baker and Hoel (2007),
standardized incidence ratios were always higher for
children under the age of 9 than for children and
youth under the age of 25. This is an interesting fact
not addressed in the German study of 2007, which
was limited to children under the age of 5. However,
one of the earlier German reports mentioned above
(Kaatsch et al. 1998), which also pointed towards an
increased risk for these younger children, even though
the results were not statistically significant, found no
evidence of an increase when all children under the
age of 15 living within a 15 km radius around nuclear
power plants were included. Similarly, a re-analysis
of data from Great Britain (COMARE 2005) did not
show a general excess of leukaemia cases around
nuclear installations, but a higher risk for children
under the age of 5 than for those between the ages of
5 and 14.
All this supports the notion that the children's age
is of critical importance in this context. It has even
been proposed (Grosche 2008) that what we are
dealing with here is not a general increase in the
incidence rate for leukaemia, but rather a shift in the
age distribution towards younger ages, where the
higher risk for children under 5 would be
compensated by a lower risk for children between
5 and 14.
Such a shift, however, would be rather unexpected
as a radiation effect. The data from the survivors of
Hiroshima and Nagasaki, for instance, do not suggest
an elevated incidence in some age groups which is
compensated by a reduction in others, although
admittedly few of the survivors were exposed in utero
and no firm conclusion can be drawn for the age
groups of primary interest here (Preston et al. 1994).
Also, the exposures from the atomic bomb explosions
were acute, while those around nuclear power plants,
if they occurred, would presumably be protracted, so
that the two cases are not fully comparable. Further
investigation is clearly needed in this area.
OTHER POSSIBLE EXPLANATIONS
Perhaps the most surprising facts in this whole
context relate to the question of leukaemias around
so-called "planning sites", which unfortunately is not
addressed at all in the study discussed here and is
only mentioned in passing in the later review by the
Radiation Protection Commission. Excess mortality
was observed in regions which had once been
considered for the building of a nuclear facility, but in
which nothing of the kind was ever built
(Cook-Mozaffari et al. 1989, Michaelis et al. 1992).
Similarly, when incidence rates were compared
before and after the start-up of a facility, they
remained unchanged; where incidence rates were
elevated, they had been already elevated before any
radiation was ever produced (Baron 1984, further
quotes in Baker and Hoel 2007).
What the explanation of such increased incidence
without radiation is, nobody seems to know. One
hypothesis, or rather speculation, suggests that
leukaemia can be caused by an as yet unknown
infectious agent, which is shared between different
people when population mixing occurs (Kinlen 1988).
The influx of new workers and their families into the
rural areas in which nuclear installations are built
could create such a situation. That population mixing
is indeed associated with an elevated incidence of
childhood leukaemia, has been shown in a number of
studies (Kinlen et al. 1995, further quotes in Boutou
et al. 2002). The effect seems to at least in part
explain the above mentioned observations around the
reprocessing plants Sellafield (Dickinson and Parker
1999) and La Hague (Boutou et al. 2002). The most
important draw-back of the population mixing
hypothesis, however, is that the infectious agent
which presumably causes all those leukaemias more
than 20 years after the creation of the hypothesis has
not yet been identified.
There is another problem with the population
mixing hypothesis: it cannot easily account for the
observations around "planning sites", as the influx of
new people would probably not have started there.
Rural areas in general, even those with low
population mixing, tend to have an increased
incidence rate, but the increase is less dramatic
(Alexander et al. 1990, Boutou et al. 2002). The
KiKK study, although not addressing the question of
"planning sites", suggests that other factors must play
a role. A re-evaluation of its data for the review of the
Radiation Protection Commission showed that the
leukaemia risk for children under the age of five
living inside the 5 km radius was significantly
increased both in rural and in mixed or urban areas. It
is therefore probably better to say that we simply do
not know what is happening.
CONCLUSION
In summary, we can state that the 2007 study initiated
by the German Federal Office for Radiation
Protection is epidemiologically sound and solid, and
gives clear evidence that children under the age of
5 have an increased incidence of leukaemia if they
live within a 5 km radius around a nuclear power
plant. The absolute number of additional cases is in
the order of 1 per year for the whole of Germany,
although the relative risk is more than 2.
A number of observations, however, would seem
to make it highly improbable that this phenomenon is
due to radiation exposure. The measured doses in the
area are far too small, the shift in age distribution is
rather unexpected as a radiation effect, and similarly
elevated risks can be observed around so-called
"planning sites". Obviously, there are some "missing
links" between childhood leukaemia around nuclear
power plants and the radiation exposure caused by
their normal operation.
The option of nuclear energy may have to be
rejected on other grounds, such as the remaining risk
of a core meltdown or the unresolved problems of
permanent waste disposal, but with any such problem
we have to seek the best evidence available instead of
proceeding from preconceived ideas. And our best
evidence currently suggests that the operation of
nuclear power plants in itself does not pose a threat to
human health - whatever may be going on in the
regions where they tend to be built.
REFERENCES
Alexander FE, Ricketts TJ, McKinney PA, Cartwright RA: Community lifestyle characteristics and risk of acute lymphoblastic leukaemia in children. Lancet 336:1461-1465, 1990.
Baker PJ, Hoel DG: Meta-analysis of standardized incidence and mortality rates of childhood leukaemia in proximity to nuclear facilities. Eur J Cancer Care (Engl) 16:355-363, 2007.
Baron JA: Cancer mortality in small areas around nuclear facilities in England and Wales. Br J Cancer 50:815-824, 1984.
Bithell JF, Keegan TJ, Kroll ME, Murphy MF, Vincent TJ: Childhood leukaemia near British nuclear installations: methodological issues and recent results. Radiat Prot Dosim 132:191-197, 2008.
Boutou O, Guizard AV, Slama R, Pottier D, Spira A: Population mixing and leukaemia in young people around the La Hague nuclear waste reprocessing plant. Br J Cancer 87:740-745, 2002.
Committee on Medical Aspects of Radiation in the Environment (COMARE): First Report. The implications of the new data on the releases from Sellafield in the 1950s for the conclusions of the Report on the Investigation of the Possible Increased Incidence of Cancer in West Cumbria. HMSO, London 1986.
Committee on Medical Aspects of Radiation in the Environment (COMARE): Second Report. Investigation of the possible increased incidence of leukaemia in young people near the Dounreay Nuclear Establishment, Caithness, Scotland. HMSO, London 1988.
Committee on Medical Aspects of Radiation in the Environment (COMARE): Tenth Report. The incidence of childhood cancer around nuclear installations in Great Britain. Health Protection Agency, London 2005.
Cook-Mozaffari P, Darby S, Doll R: Cancer near potential sites of nuclear installations. Lancet 11:1145-1147, 1989.
Dickinson HO, Parker L: Quantifying the effect of population mixing on childhood leukaemia risk: the Seascale cluster. Br J Cancer 81:144-151, 1999.
Grosche B: The risk of childhood leukaemia in the vicinity of nuclear installations: a review. Radioprotection 43:60-61, 2008.
Guizard AV, Boutou O, Pottier D, Troussard X, Pheby D, Launoy G, Slama R, Spira A: The incidence of childhood leukaemia around the La Hague nuclear waste reprocessing plant (France): A survey for the years 1978-1998. J Epidemiol Community Health 55:469-474, 2001.
Kaatsch P, Mergenthaler A: Incidence, time trends and regional variation of childhood leukaemia in Germany and Europe. Radiat Prot Dosimetry 132:107-113, 2008.
Kaatsch P, Kaletsch U, Meinert R, Michaelis J: An extended study on childhood malignancies in the vicinity of German nuclear power plants. Cancer Causes Control 9:529-533, 1998.
Kaatsch P, Spix C, Schmiedel S, Schulze-Rath R, Mergenthaler A, Blettner M: Epidemiologische Studie zu Kinderkrebs in der Umgebung von Kernkraftwerken, Bundesamt fur Strahlenschutz, Salzgitter, 2007 (available on-line at http://www.bfs.de/de/bfs/druck/Ufoplan/4334_KiKK_Gesamt_T.pdf).
Kaatsch P, Spix C, Schulze-Rath R, Schmiedel S, Blettner M: Leukaemia in young children living in the vicinity of German nuclear power plants. Int J Cancer 15:721-726, 2008.
Kinlen L: Evidence for an infective cause of childhood leukaemia: Comparison of a Scottish new town with nuclear reprocessing sites in Britain. Lancet 10:1323-1327, 1988.
Kinlen LJ, Dickson M, Stiller CA: Childhood leukaemia and non-Hodgkin's lymphoma near large rural construction sites, with a comparison with Sellafield nuclear site. Brit Med J 310:763-768, 1995.
Laurier D, Grosche B, Hall P: Risk of childhood leukaemia in the vicinity of nuclear installations-findings and recent controversies. Acta Oncol 41:14-24, 2002.
Laurier D, Jacob S, Bernier MO, Leuraud K, Metz C, Samson E, Laloi P: Epidemiological studies of leukaemia in children and young adults around nuclear facilities: A critical review. Radiat Prot Dosimetry 132:182-190, 2008.
Lightfoot TJ, Roman E: Causes of childhood leukaemia and lymphoma. Toxicol Appl Pharmacol 199:104-117, 2004.
Michaelis J, Keller B, Haaf G, Kaatsch P: Incidence of childhood malignancies in the vicinity of west German nuclear power plants. Cancer Causes Control 3:255-263, 1992.
Preston DL, Kusumi S, Tomonaga M, Izumi S, Ron E, Kuramoto A, Kamada N, Dohy H, Matsuo T, Nonaka H, Thompson DE, Soda M, Mabuchi K: Cancer incidence in atomic bomb survivors. Part III: Leukemia, lymphoma and multiple myeloma, 1950-1987. Radiat Res 137S:68-97, 1994.
Schmitz-Feuerhake I, Schroder H, Dannheim B, Grell-Buchtmann I, Heimers A, Hoffmann W, Nahrmann A, Tomalik P: Leukaemia near water nuclear reactor. Lancet 342:1484, 1993.
Spix C, Blettner M: Re: Baker PJ & Hoel DG (2007) European Journal of Cancer Care 16, 355-363. Meta-analysis of standardized incidence and mortality rates of childhood leukaemia in proximity to nuclear facilities. Eur J Cancer Care (Engl) 18:429-430, 2009.
Spix C, Schmiedel S, Kaatsch P, Schulze-Rath R, Blettner M: Case-control study on childhood cancer in the vicinity of nuclear power plants in Germany 1980-2003. Eur J Cancer 44:275-284, 2008.
Strahlenschutzkommission: Bewertung der epidemiologischen Studie zu Kinderkrebs in der Umgebung von Kernkraftwerken (KiKK-Studie). Berichte der Strahlenschutzkommission (SSK), Heft 57, 2008 (available on-line at http://www.ssk.de/de/werke/2008/volltext/ssk0815.pdf).
Wakeford R: Childhood leukaemia following medical diagnostic exposure to ionizing radiation in utero or after birth. Radiat Prot Dosimetry 132:166-174, 2008.
|
BACK
|
