Objective: To investigate the association
between childhood leukaemia and established risk factors or other
factors related to La Hague nuclear waste reprocessing plant.
Design: Case-control study.
Setting: Area within a 35 km radius of La Hague,
Normandy, France.
Subjects: Twenty seven cases of leukaemia diagnosed
during the period 1978-93 in people aged under 25 years and 192
controls matched for sex, age, place of birth, and residence at time of
diagnosis.
Main outcome measures: Antenatal and postnatal
exposure to x rays and viral infections, occupational
exposure of parents (particularly ionising radiation), living
conditions, lifestyle of parents and children.
Results: Increased trends were found for use of local
beaches by mothers and children (P=0.01 or less); relative risks 2.87 (95%
confidence intervals 1.05 to 8.72) and 4.49 (1.52 to 15.23) when
categories were aggregated in two levels (more or less than once a
month). Consumption of local fish and shellfish also showed an
increased trend (P 0.01); relative risk 2.66 (0.91 to 9.51) when
categories were grouped in two levels (more or less than once a week).
A relative risk of 1.18 a year (1.03 to 1.42) was observed for length
of residence in a granite-built house or in a granitic area. No
association was shown with occupational radiation exposure in parents.
Conclusions: There is some convincing evidence in
childhood leukaemia of a causal role for environmental radiation
exposure from recreational activities on beaches. New methods for
identifying the environmental pathways, focusing on marine ecosystems,
are warranted.
Introduction
La Hague (France) is one of the three nuclear reprocessing
plants operating in the world on an industrial scale (the other two are
Sellafield, England, and Dounreay, Scotland). In recent years there has
been considerable scientific and public interest in clusters of
leukaemia in children in the vicinity of the British plants, which are
still considered as being a matter of concern.(1-8)
Subsequently, Gardner et al reported that occupational
exposure to ionising radiation in fathers before conception of the
child yields an eightfold increase in risk of childhood leukaemia and
could explain the cluster observed around Seascale.(9) These
results have been much debated, however, and more recently Doll
et al concluded that this association is "largely or
wholly a chance finding."(10) Hence, the reasons for the
increased incidence of childhood leukaemia around the nuclear
reprocessing plants are still largely unknown.
In this respect, La Hague, whose mode of operations and nature of
discharges are more similar to those at Sellafield and Dounreay than at
other nuclear plants, offers an independent opportunity to shed some
light on this issue. Two preliminary studies were inconclusive, but in
a recent paper we highlighted a small but increased risk of childhood
leukaemia in the electoral ward in which the plant is
situated.(11-13) The aim of our case-control study, which is
the first to be carried out in France although heavy investment in
nuclear energy has been made there, was to examine whether childhood
leukaemia among young people near the La Hague reprocessing plant is
associated with established risk factors or with factors related to the
plant.
Subjects and methods
The La Hague facility is situated in Normandy (France) in the
rural "Nord-Cotentin" area. The study was undertaken within a 35 km
radius of the nuclear plant, hence including the usual places of
residence of its workforce. Three other nuclear establishments are
located nearby, making this study area one of the most densely
nuclearised in the world: a contiguous low level radioactive waste
depository; a nuclear power station, 16 km away; and the navy
dockyards, 19 km away, where submarine nuclear fuel is handled.
The process for the identification of cases has been fully described
elsewhere.(13) Briefly, a list of cases of leukaemia
diagnosed (and histologically confirmed) from January 1978 to December
1993 among people aged under 25 years with a residential address in the
study area has been retrospectively compiled from local and regional
hospitals and pathology laboratories. Doctors' permission to approach
the parents was obtained for all 27 cases.
To circumvent the absence
of sampling lists (register of live births, National Health Service
central register, family practitioner committee registration, etc) and
the French tough regulation constraints (access to nominal data from
the population census is strictly forbidden), we have relied on the
general practitioners of the area who had delivered care to children
with leukaemia. No one had computerised patient records, which could
have represented a database for sampling. So general practitioners
prospectively identified all adult patients who had a child fulfilling
the matching criteria with the index case - that is, sex, age (within
2 years), place of birth (inside the current study area or
outside), and place of residence (the same electoral ward or a
contiguous one) at time of diagnosis of leukaemia of the corresponding
case. If so, doctors filled in a brief descriptive form, whatever the
final decision regarding the family participation in the study, and
sent it immediately to the research team. To avoid a selection bias
quality control procedures were applied. Firstly, doctors were asked to
check at the end of each week if they had missed some potential parents
of controls among their outpatients and if so to get in touch with
them. Secondly, when the identification forms were received, their
accuracy was checked by the research team, which declared the control
eligible or not. Finally, the research team stopped the recruitment for
a given general practitioner when the 10th eligible control was
included; but because of tight matching criteria and time constraints
on the control identification phase (which ended in October 1995), 235
families were asked to participate in the study. Two refusals, one lost
to follow up, five absences of answer despite repeated requests, and 35
ineligible controls who did not meet the matching criteria left 192
eligible controls.
Data were collected from parents by way of face to face interviews at
home between November 1993 and January 1996. Parents were asked to sign
an informed consent form, and those employed at nuclear establishments
were also asked for signed permissions for access to their occupational
records. Two trained interviewers administered a detailed structured
questionnaire that included information on sociodemographic data,
medical history, residential history, lifestyle (recreational
activities on beaches, consumption of local fruit and vegetables,
drinking of raw milk, drinking well water, exposure to electromagnetic
fields), and occupational exposure of parents before the child's
conception, during pregnancy, and after the birth. Specific data about
antenatal exposures (x rays, viral infections, drug
treatments during pregnancy with the index child) were collected.
Regarding children, places of residence, lifestyle, viral infections,
and x ray exposure up to the date of diagnosis were also
recorded.
Radiation dosimetry data for parents ever employed in a nuclear
facility were obtained from occupational medical officers who were
unaware of the children's status. Radiation details were available in
the form of external whole body ionising radiation dosimetry in
millisieverts (mSv). We assessed lifetime levels before conception
and radiation doses in the three and six months before conception,
during pregnancy, and from birth to date of diagnosis of leukaemia.
Because of the available data format, these period doses were estimated
proportionally from the cumulative doses up to 1982, from yearly doses
between 1983 and 1987, and from monthly doses later. The father of one
affected child (who had been employed at La Hague only after the birth
of his child) and the father of one control refused access to their
dosimetries. For a further man hired by a subcontracting company, no
information on ionising radiation could be
retrieved.
To compare general characteristics between cases and controls, exact
Mann-Whitney and chi2 tests were performed with
StatXact-3.(14) Risk factors analyses were carried out
within the sets of cases and controls and findings are represented as
relative risks (95% confidence intervals). The results were calculated
with the exact conditional logistic regression module of the LogXact
computer package.(15) Linear trends in the relative risks
for ordinal variables were tested by regularly scoring the categories
and using these scores as continuous variables. Only univariate
analyses were performed, the small numbers eligible for inclusion in
the study precluding any powerful multivariate analysis. All the
statistical tests were two sided and P values of 0.05 or less were considered
significant. For the sake of clarity among the 173 items analysed, only
variables associated with a P value of 0.20 or less are detailed except for
fathers' dosimetries.
Results
A total of 27 parents of cases and 192 parents of controls were
investigated, the median and modal number of controls being 9 and 10
per case, respectively. Table 1 shows the characteristics of cases by
subtypes of leukaemia, sex, year of birth, and age at diagnosis. The
distribution of various characteristics of parents and children (at
time of birth and interview) were similar in case and control groups
(table 2).
| Table 1 - Numbers (percentages) of cases by subtypes of
leukaemia, sex, year of birth, and age at diagnosis around La Hague,
France, 1978-93 |
| Group | No (%) |
| Leukaemia
subtypes: |
| Acute lymphatic
leukaemia* | 20 (74.1) |
| Acute
myeloid leukaemia | 5 (18.5) |
| Chronic myeloid
leukaemia | 2 (7.4)
|
| Sex: |
| Female | 11 (40.7)
|
| Male | 16 (59.3) |
| Year of
birth: |
| 1956-69 | 7 (26.0)
|
| 1970-80 | 10 (37.0) |
| 1981-90 | 10
(37.0) |
| Age at diagnosis
(years): |
| 0-4 | 10 (37.0)
|
| 5-14 | 11 (40.7) |
| 15-24 | 6
(22.3) |
| *One child had Down's syndrome. |
Neither parents' medical history nor characteristics of pregnancy or
birth revealed significant associations (P>0.20, results not shown but
available on request to authors). Regarding viral infections during
childhood we found a relative risk (95% confidence interval) of 17.95
(0.93 to 1060.49) for glandular fever (two cases and one control).
| Table 2 - Characteristics of parents and children by
case-control group in study of leukaemia among young people around
La Hague, France, 1978-93. Values are numbers (percentages) of
cases and controls unless stated otherwise |
| Variables | Cases | Controls | P
value |
| Mothers |
| Mean (SD) age at
interview (years) | 44.9
(11.4) | 43.9 (10.7) | 0.65 |
| Smoking habits
at interview: |
| Non-smoker | 20
(76.9) | 149 (78.4) | 1.00
|
| Smoker | 6 (23.1) | 41
(21.6) |
|
| Educational level
(years)*: |
| 10 and under | 19
(70.4) | 141 (73.4) | 0.82
|
| 11 and over | 8 (29.6) | 51
(26.6) |
|
| Social
class**: |
| 1/2/6/8/9/10 | 21
(77.8) | 160 (83.3) | 0.55
|
| 7 | 2 (7.4) | 16
(8.3) |
|
| 3/4/5 | 4 (14.8) | 16
(8.3) |
|
| Mean (SD) No of children | 2.8
(1.3) | 2.9 (1.6) | 0.66
|
| Fathers |
| Mean (SD) age at interview
(years) | 47.4 (11.5) | 46.3
(10.6) | 0.39 |
| Smoking habits at
interview: |
| Non-smoker | 13
(54.2) | 112 (62.6) | 0.28
|
| Smoker | 11 (45.8) | 67
(37.4) |
|
| Educational level
(years)*: |
| 10 and under | 20
(74.1) | 160 (83.3) | 0.24
|
| 11 and over | 7 (25.9) | 32
(16.7) |
|
| Social
class**: |
| 1/2/6/8/9/10 |
5
(18.5) | 42 (21.9) | 0.21
|
| 7 | 14 (51.9) | 119
(62.0) |
|
| 3/4/5 | 8 (29.6) | 31
(16.1) |
|
| Children |
| Place of
birth: |
| Hospital | 25
(92.6) | 184 (95.8) | 0.52
|
| Home | 2 (7.4) | 8
(4.2) |
|
| Admission to a special care baby
unit: |
| No | 22
(84.6) | 171 (89.1) | 0.62
|
| Yes | 4 (15.4) | 21
(10.9) |
|
| Congenital
abnormality: |
| No | 25
(96.2) | 182 (94.8) | 1.00
|
| Yes | 1 (3.8) | 10
(5.2) |
|
*At time of child's birth.
**According to INSEE (French National Statistical Institute for
Economical Studies) classification widely used in France for
administrative and research purposes: 1/2/6/8/9/10 - farmers/farm
workers/non-manual employees/domestics and service workers/artists,
clerical staff, army, and police/non-active people; 7 - blue collar;
3/4/5 - proprietors, self employed people/directors, managers,
professionals, upper white collar workers/technical staff, lower white
collar workers. |
Table 3 presents some details about maternal lifestyle during
pregnancy. The analyses were restricted to the 23 mothers who lived
during their pregnancy and gave birth in the study area. Analysis by
recreational activities on local beaches indicated a significant
increased trend (P<0.01) and a relative risk of 4.49 (1.52 to 15.23)
if categories were grouped in two levels (cut off point of once a
month). Analyses by eating habits, use of seaweed as fertiliser,
exposure to electromagnetic fields, or characteristics of residences
did not indicate any associated risk (P>0.20, results not shown).
| Table 3 - Numbers of cases and controls with relative
risks by mothers' lifestyle factors during pregnancy in study of
leukaemia among young people around La Hague, France, 1978-93
|
| Recreational activities on local beaches | No (%)
of cases | No (%) of controls | Relative
risk (95% confidence interval) | P value | No
of discordant sets | No of subjects
|
| Never | 4
(17.4) | 56 (30.1) | 1.00 | <0.01* | 22 | 207 |
| Holidays
only | 1 (4.3) | 39 (21.0) | 0.60
(0.01 to 8.06) |
|
|
|
| Less than once
a month | 2 (8.7) | 19
(10.2) | 2.10
(0.16 to 20.74) |
|
|
|
| Once
a month to less than once a week | 9 (39.1) | 21
(11.3) | 6.69
(1.46 to 42.44) |
|
|
|
| Once
a week to less than every day | 4 (17.4) | 45
(24.2) | 1.99
(0.29 to 16.21) |
|
|
|
| Almost
every day | 3 (13.0) | 6
(3.2) | 11.84
(0.98 to 157.36) |
|
|
|
| *P value for trend across six categories. |
Table 4 summarises some aspects of the children's lifestyle. Results
for recreational activities on local beaches showed a significant
increased trend (P 0.01) and a relative risk of 2.87 (1.05 to 8.72)
when categories were aggregated in two classes (cut off point once a
month). Consumption of local fish and shellfish yielded similar
findings with a significant increased trend (P 0.01) and a borderline
significant increased relative risk of 2.66 (0.91 to 9.51) if
categories were grouped in two levels (cut off point once a week).
Restriction of analyses to the 209 children born in the study area gave
quite similar results with significant increased trends (P 0.04 for
both factors) and relative risks of 2.34 (0.82 to 7.30) and 2.31 (0.71
to 9.89) for use of local beaches and consumption of fish and shellfish
(same cut off points as above), respectively. There was no evidence of
any relation with drinking local raw milk or use of seaweed as
fertiliser (P>0.20, results not shown). We found an increased relative
risk of 1.18 (1.03 to 1.42) a year for homes made of granite materials
or built on granite ground. Relative risks around unity were observed
for various surrogates of exposure to electromagnetic fields or for
time lived in homes with double glazing (P>0.20, results not shown).
| Table 4 - Numbers of cases and controls with relative
risks by child's lifestyle factors in study of leukaemia among young
people around La Hague, France, 1978-93 |
| Lifestyle factor | No (%) of cases | No
(%) of controls | Relative risk (95% confidence
interval) | P value | No of discordant
sets | No of subjects |
| Recreational activities on
local
beaches: |
|
|
|
|
|
|
| Never | 2
(7.4) | 28
(14.6) | 1.00 | 0.01** | 26 | 217
|
| Holidays only | 6 (22.2) | 64
(33.3) | 1.49
(0.20 to 18.30) |
|
|
|
| Less than once
a month | 2 (7.4) | 18 (9.4) | 1.21
(0.08 to 18.89) |
|
|
|
| Once
a month to less than once a week | 4 (14.8) | 28
(14.6) | 2.28
(0.26 to 30.76) |
|
|
|
| Once
a week to less than every day | 11 (40.7) | 47
(24.5) | 4.99
(0.84 to 56.74) |
|
|
|
| Almost
every day | 2 (7.4) | 7
(3.6) | 6.59
(0.31 to 147.82) |
|
|
|
| Eating
local fish and
shellfish: |
|
|
|
|
|
|
| Never | 0 | 24
(12.5) | 1.00 | 0.01** | 25 | 211
|
| Holidays only | 0 | 3
(1.6) | * |
|
|
|
| Less than once
a month | 1 (3.7) | 13 (6.8) | 1.41
(0.04 to infinity) |
|
|
|
| Once
a month to less than once a week | 4 (14.8) | 26
(13.5) | 5.49
(0.60 to infinity) |
|
|
|
| Once
a week to less than every day | 22 (81.5) | 123
(64.1) | 7.62
(1.16 to infinity) |
|
|
|
| Almost
every day | 0 | 3
(1.6) | * |
|
|
|
| Usual
local vegetable or fruit
consumption: |
|
|
|
|
|
|
| No | 13
(48.1) | 54
(28.1) | 1.00 | 0.20 | 22 | 192
|
| Yes | 14 (51.9) | 138
(71.9) | 0.50
(0.18 to 1.38) |
|
|
|
| Drinking
well
water: |
|
|
|
|
|
|
| Never | 23
(85.2) | 179
(93.2) | 1.00 | 0.13 | 12 | 124
|
| Ever | 4 (14.8) | 13
(6.8) | 3.45
(0.71 to 13.77) |
|
|
|
| Use
of electric hair
dryer: |
|
|
|
|
|
|
| Never | 16
(59.3) | 152
(79.2) | 1.00 | 0.13 | 20 | 161
|
| Ever | 11 (40.7) | 40
(20.8) | 2.28
(0.81 to 6.45) |
|
|
|
| Length
of residence (No of
years): |
|
|
|
|
|
|
| On
ground floor |
|
| 0.92
(0.83 to 1.03) | 0.15 | 22 | 190
|
| In a granite built house or granitic
area |
|
| 1.18
(1.03 to 1.42) | 0.01 | 12 | 109 |
*Not calculated.
**P value for trend. |
There was no evidence of any association with mothers' types of
occupational exposures in any period (various chemical products, wood
dust, radioactive materials, ionising radiations) (P>0.20, results not
shown). A few mothers claimed to have been exposed to radiation, but
this led to non-significant relative risks whatever the period
considered (P>0.20, results not shown). Fathers' types of
occupational exposures were also not related to leukaemia in any period
(P>0.20, results not shown). A few fathers claimed to have been
exposed to radiation, but no trend seemed to be significant whatever
the period considered (P>0.20, results not shown).
According to employment and radiation records none of the fathers of
children with leukaemia had detectable lifetime doses before the
conception of the child, whereas doses for fathers of controls ranged
from 0.15 mSv to 79.00 mSv for the whole period, from 0.03 mSv to
9.10 mSv during the six months before conception, and from 0.02 mSv
to 4.62 mSv during the three months before conception. During the
gestational period, doses ranged from 0.40 mSv to 1.97 mSv for cases
and from 0.06 mSv to 13.29 mSv for controls, and during the postnatal
period from 0.20 mSv to 26.10 mSv and from 0.30 mSv to 162.45 mSv,
respectively. Table 5 presents corresponding relative risks. We found
no significant trend whatever the period of
exposure.
| Table 5 - Numbers of cases and controls with relative
risks by fathers' estimated radiation doses according to time of
exposure in a study of leukaemia among young people around La Hague,
France, 1978-93 |
| Fathers' exposures (mSv)* | No (%)
of
cases | No (%) of controls | Relative risk
(95% confidence interval) | No of discordant
sets | No of subjects |
| Before
conception**: |
| 0 | 27
(100.0) | 169
(89.9) | 1 | 10 | 89
|
| 0.1-0.99 | 0 | 5
(2.6) | *** |
|
|
| 1-34.99 | 0 | 7
(3.7) | *** |
|
|
|
35 and over | 0 | 7
(3.7) | *** |
|
|
| In 6 months
(182 days) before
conception**: |
| 0 | 27
(100.0) | 172
(91.5) | 1 | 9 | 86
|
| 0.1-0.49 | 0 | 5
(2.6) | *** |
|
|
| 0.50-2.99 | 0 | 5
(2.6) | *** |
|
|
|
3 and over | 0 | 6
(3.2) | *** |
|
|
| In 3 months
(91 days) before
conception**: |
| 0 | 27
(100.0) | 173
(92.0) | 1 | 9 | 86
|
| 0.1-0.19 | 0 | 4
(2.1) | *** |
|
|
| 0.2-1.49 | 0 | 6
(3.2) | *** |
|
|
|
1.5 and over | 0 | 5
(2.6) | *** |
|
|
| From
conception** to
birth: |
| 0 | 25
(92.6) | 171
(90.9) | 1 | 11 | 99
|
| 0.1-0.99 | 1 (3.7) | 5
(2.6) | 1.13 (0.02 to
11.09) |
|
|
| 1-3.99 | 1
(3.7) | 7 (3.7) | 1.19 (0.03 to
11.09) |
|
|
|
4 and over | 0 | 5
(2.6) | *** |
|
|
| From birth to
diagnosis****: |
| 0 | 21
(80.8) | 169
(89.9) | 1 | 12 | 96
|
| 0.1-1.99 | 4 (5.4) | 5
(2.6) | 2.99 (0.36 to
25.03) |
|
|
| 2-9.99 | 0 | 7
( 3.7) | *** |
|
|
|
10 and over | 1 (3.8) | 7 (3.7) | 1.97 (0.03
to 29.21) |
|
|
*Exposure categories: no exposure and thirds among controls.
**Conception was taken to be 38 weeks before date of birth.
***Not calculated.
****From birth to diagnosis date for cases or corresponding date
for controls. |
Discussion
Our main finding was that some lifestyle factors are associated
with the development of leukaemia among young people, suggesting
contamination with radiation through an environmental route.
Potential limitations of our survey, as of any case-control study,
should be noted. The possibility that a selection bias in the
prospective identification of controls has strongly influenced the
results does not seem likely for several reasons. Firstly, a two step
quality control procedure (internal and external) was used. Secondly,
parents and not children were recruited when they visited their general
practitioner to avoid the selection of a population having complaints
and calling for medical consultations. Thirdly, the high motivation of
the general practitioners resulted in a high participation rate (96%)
among potential eligible families. Fourthly, cases and controls were
comparable for sociodemographic characteristics and perinatal
conditions. Although we chose our methods to bypass legal constraints
and to cope with restrictive matching criteria, matching controls on
general practitioner's catchment area led (more or less) to matching
on socioeconomic status and neighbourhood, hence potentially decreasing
confounding effects.(16)
Recall bias can be ruled out, in our opinion, at least for our main
findings. Firstly, in contrast with Great Britain, neither public
debate nor media coverage on leukaemia clusters around nuclear
facilities occurred in France before December 1995 because of previous
negative results.(11)(12) A cluster around La Hague was
suggested at that time,(13) but marine contamination had
never been considered.(13) although an aerial route was
hypothesised. Secondly, the data collection from cases was completed in
March 1995. Hence parents of children with leukaemia would probably not
link such exposure as a possible cause of their child's disease.
Thirdly, nuclear occupational results are not prone to recall bias
because they are derived from dosimetry files. Fourthly, the French
public does not yet seem concerned about radon exposure. As a
precautionary measure, we did not use the word "radon" in our
survey.
Non-significant findings are difficult to interpret because of the wide
confidence intervals on many of the relative risks given in relation to
the small number of cases included. By performing exact conditional
statistical analyses, however, we have used the most powerful
statistical tool available. When some data cells are empty, maximum
likelihood estimates do not exist whereas the exact method can yield
median unbiased estimates, exact confidence intervals, and exact P
values. Some chance findings, however are likely because of the number
of variables under study.
Marine pathway
Our main finding was that the use of local beaches by children and
mothers was associated with the development of leukaemia among the
children. If ionising radiations are involved, this suggests a totally
different pathway to occupational exposure, putting the environmental
hypothesis in the limelight again. Supporting evidence for a causal
effect comes from various factors. Firstly, a dose-response effect is
highlighted. Secondly, a chance finding is unlikely because of the low
P value (0.01) and the fact that another significant variable
(consumption of local shellfish and fish) also points to a potential
marine pathway. Thirdly, confounding by geographical distribution of
places of residence (residence closer to the sea could increase the
likelihood of a child visiting a beach to play) is not plausible
because of the matching of control on general practitioner (and then on
neighbourhood). Fourthly, this result does not stand in isolation,
being in agreement with the study conducted by Urquhart et
al around Dounreay.(17) The use of local beaches
before diagnosis also appeared as a significant risk factor in this
area (P 0.04).
An earlier study has found an excess of childhood leukaemia in the
electoral ward containing the reprocessing plant.(13) A
pertinent question is to what extent this excess may be explained by
the demonstrated association with use of beaches. All four children
with leukaemia who lived in this ward played on the beach at least once
a month compared with 13 out of the 23 similarly affected children who
lived in the remaining area (exact P trend on six categories 0.14).
Hence, the observed geographical excess can be explained by the
association of playing on the beach with leukaemia.
At La Hague most routine releases of radionuclides have been discharged
through chimneys. Liquid releases occurred by direct piping below the
surface of the Channel. Besides, leaks from the contiguous low level
radioactive waste depository to groundwater pathways and releases from
the two other nuclear establishments of the study area (both on the
coastline) may have contributed to marine radioactive exposure.
Nevertheless, in a comparison of the amounts of liquid releases (15
times lower than gaseous releases) the evidence would rather lie in the
environmental pathways by which radiation reaches the body rather than
in the quantitive aspect of releases. Individual lifestyle (bathing and
playing on the beach) can extend the contact with radionuclides in the
environment and result in possible uptake of high levels of
contamination.(18) Besides, larger particles of insoluble
materials can settle out near the discharge point. Radionuclides in
particulate form are especially subject to concentration by filter
feeding organisms and then by the whole aquatic food chain. As a
result, intake of radionuclides such as strontium-90, which tends to
concentrate in bones, is probably higher for consumers of small fish.
Finally, for radiation exposures from external sources in the
environment, the absorbed dose to body organs increases with decreasing
body size, as with children.(18)
Paternal exposure
Our data clearly do not support a genuine association of leukaemia
with fathers' occupational exposure to radiation. Among fathers of
children with leukaemia, none had accumulated any dose before
conceptional, detracting from the conclusions of Gardner et
al,(9) and no significant trend was seen during the
subsequent periods. These results are in line with those from two
case-control studies conducted around Dounreay and in
Ontario.(17)(19) Apart from the fact that Gardner's results
could be due to chance alone,(11) two explanations for the
discrepancy between findings from Sellafield and La Hague can be put
forward. Firstly, figures for all the control fathers indicated that
radiation exposure in workers was somewhat lower in La Hague. For
cumulative preconceptional doses, 89.5 % (17/19) lay within the range
1-49 mSv at La Hague and only 60 % (45/75) at Sellafield. Secondly,
there may be differences in the occupational exposures of fathers in
the two settings (internal exposure to tritium, concomitant
exposure to toxic chemicals, etc).
We found some evidence of an increased risk of leukaemia associated
with a surrogate for radon exposure. We verified the presence of
granite in the ground or in the building materials during the home
interview, but unfortunately could not do so for the previous houses
inhabited by the families. Nevertheless, the strength of the
association reported (relative risk 1.18 a year, P 0.01) deserves
consideration. Some studies have suggested a similar connection either
with terrestrial gamma radiation or radon, but a recent one has
challenged this association.(20-23)(25)
On the whole, some convincing evidence is found of a causal role for
environmental radiation exposure operating through recreational
activities on beaches or consumption of fish and shellfish, whereas
there is no confirmatory evidence of the association represented by
Gardner et al.(9) But one explanation
probably does not account for all cases, and other exposures such as to
radon may play some part, maybe even a synergistic one. New methods for
the identification of the environmental pathways (focusing on marine
ecosystems) and their integration in the dose reconstruction process
for children are clearly warranted.
| Key messages |
| The reasons for leukaemia clusters around nuclear
installations remain unknown
La Hague in France (the other two are Sellafield and Dounreay
in Britain) is one of the three nuclear reprocessing plants operating
in the world on an industrial scale, and offers an independent
opportunity for research
Some lifestyle risk factors (use of local beaches, consumption
of fish and shellfish) were associated with the development of
leukaemia among young people
Some convincing evidence was found of a causal role for
environmental radiation exposure, whereas no association was found with
fathers' occupational exposure to radiation |
We thank Dr Carre and Mr Boceno for their efficient cooperation
in the field; the hospital physicians who identified the cases: Drs
Boutard, Danel, Malet, Barrelier, and Reman; the general practitioners,
highly motivated, who introduced the study to their patients: Drs
Aerts, Bauzon, Bienvenu, Burtin, Cau, Compagnon, Decourselle, Dejonghe,
Dolbecq, Dossmann, Etienne, Gigan, Gras, Haquet, Houly, Huet, Lebon,
Lenoel, Lepleux, Lerosier, J Letellier, J R Letellier, Levast, Lucas,
Mougenot, Navez, Olivier, Rabay, Rousseau, Servant, Sevin, Stefani,
Varin, and Vidal; the occupational medical officers who provided the
radiation dosimetries: Drs Ducousso, Fournet, and Royer; and Mrs
Tilatti, Mrs Ninucci, and Mr Vincent for their technical support.
Funding: This study received primary financial support from
Institut National de la Sante et de la Recherche Medicale (grant
931010) and supplemental support from Ligue contre le Cancer (comite
departemental du Doubs), France. Dr Pobel received grants from
Ministre de la Recherche and Ligue contre le Cancer (comite
departemental de l'Orne), France.
Conflict of interest: None.
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(Accepted 28 October 1996)
Faculty of Medicine,
Department of Public
Health,
Biostatistics and Epidemiology Unit,
25030 Besancon,
France
Dominique Pobel, research epidemiologist
Jean-Francois Viel, professor of biostatistics and
epidemiology
Correspondence to: Dr
Viel.
