External γ-radiation exposure
has been shown to be associated with mortality risk due to leukemia, solid
cancer, and, possibly, circulatory diseases (CSD). By contrast, little
information is available on health risks following the internal contamination,
especially the inhalation of uranium compounds with respect to their
physicochemical properties (PCP), such as solubility, isotopic composition and
others.
The aim of this PhD thesis was
to estimate mortality risk of cancer and non-cancer diseases in French nuclear
fuel cycle workers and comprises three objectives: (1) evaluation of the impact
of uranium on mortality through a critical literature review, (2) analysis of
cancer and non-cancer mortality in a cohort of uranium enrichment workers, (3)
analysis of the relationship between CSD mortality and internal uranium dose in
AREVA NC Pierrelatte workers.
Existing epidemiological data
on uranium PCP and associated health outcomes are scarce. Studies of nuclear
fuel cycle workers by sub-groups within the specific stage of the cycle (e.g.,
uranium enrichment and fuel fabrication) are considered the most promising to
shed light on the possible associations, given that such sub-groups present the
advantage of a more homogenous uranium exposure.
To study the mortality risk
associated with exposure to rapidly soluble uranium compounds, we set up a
cohort of 4,688 uranium enrichment workers with follow-up between 1968 and
2008. Individual annual exposure to uranium, external γ-radiation, and other non-radiological
hazards (trichloroethylene, heat, and noise) were reconstructed from
job-exposure matrixes (JEM) and dosimetry records. Over the follow-up period,
131,161 person-years at risk were accrued and 21% of the subjects had die.
Analysis of Standardized Mortality Ratios (SMR) showed a strong healthy worker
effect (SMR all deaths 0.69, 95% confidence intervals (CI) 0.65 to 0.74;
n=1,010). Exposures to uranium and external γ-radiation were not significantly
associated with any cause of mortality in log-linear and linear excess relative
risk models. A monotonic decreasing trend was observed for lung and
lymphohematopoietic cancers across uranium exposure categories.
Previous analysis of a cohort
of AREVA NC Pierrelatte uranium processing workers suggested that exposure to
uranium may increase CSD mortality. A nested case-control study was set up to
analyze the dose-response relationship and adjust for major CSD risk factors
(smoking, blood pressure, body mass index, total cholesterol, and glycemia)
collected from medical files. The study included 102 CSD cases and 416 controls
matched on attained age, gender, birth cohort, and socio-professional status.
Absorbed dose was calculated taking into account the solubility of uranium
compounds extracted from the JEM. CSD risk was analyzed by conditional logistic
regression. A positive but imprecise association was observed (excess odds
ratio per mGy 0.2, 95% CI 0.004 to 0.5). None of the considered CSD risk factor
confounded this association.
Compared to previous studies,
our work provided important methodological improvements: consideration of
specific uranium PCP, calculation of uranium organ doses, and adjustment on
potential confounding factors (non-radiological exposures and CSD risk
factors). The absence of association between exposure to rapidly soluble
uranium compounds and mortality in the cohort of uranium enrichment workers may
be indicative of the effective elimination of uranium from the human body.
Analysis within the nested case-control study confirmed an association between
uranium exposure and CSD mortality, not confounded by CSD risk factors. Our
results should be confirmed in further studies. Future work should focus on
uncertainties associated with internal uranium dose estimation, on nature of association
with CSD mortality, and on temporal relationships between radiation and CSD
risk factors.
