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Le mésothéliome malin pleural en Nouvelle-Calédonie : analyse spatiale et déterminants environnementaux - facteurs de risque d'exposition à l'amiante naturel

Abstract : Background: Asbestos groups mainly two families of fibrous silicate minerals: serpentines and amphiboles, of which 6 minerals are used for industry and diagnosed by agrees laboratories. Inhalation of asbestos fibres is responsible for lung cancers and malignant pleural mesothelioma. In natural environment, asbestos is commonly found in serpentinites. In 1980, mineralogical analysis showed the presence of asbestos in nickel ore specimens from NC. However, a study established in 1995 a relationship between excess cases of pleural cancer in NC and a traditional whitewash of houses, called “Pö”. Four successive steps set up our study: we first studied the spacial distribution of cancer incidences in NC to check the over incidence of mesothelioma and lung cancer, then we lead a case-control study of mesothelioma in order to identify high risk areas and main risk factors, third we carried out epidemiological, geological and mineralogical investigations in high incidence areas, finally we analysed the clusters of the disease and we performed an ecological study to assess the associations with environmental factors. Objectives: Main objectives were to highlight high risk populations, to study the spatial and temporal variation of mesothelioma in NC and to analyse its association with environmental factors. Methods: From the Cancer Registry of NC, we calculated world age standardized incidences (ASR) of cancers by sex, age group, ethnic group and site, and analysed their trends for the past 30 years. Then we compared malignant pleural mesothelioma diagnosed between 1984 and 2002 with controls selected from the cancer registry. Pö, mining activity and serpentinite in surface soil were analyzed using a qualitative method comparing communes of residence with and without mesothelioma cases, and a quantitative linear regression. In the third step we rebuilt the residential and occupational history of cases living in the highest risk areas, we looked for the asbestos sources in the geological environment, and we checked the presence of fibres by using mineralogical analysis of samples. Then all the 109 mesothelioma cases recorded in the Cancer Registry of New Caledonia for the 1984-2008 period were investigated. We conducted an ecological study in the 100 tribes of a large study area including the highest incidence communes. Spatial, temporal and space-time cluster analyses were performed. Associations with environmental factors were assessed using logistic and Poisson regressions analyses. Confidence intervals of incidence rates, odds ratios (OR) and incidence rate ratios (IRR) are given at 95% level, under the assumption that observed distribution follows a Poisson distribution. Results:Analysis of cancer incidence in NC for the past 30 years showed an over incidence of lung cancers and mesothelioma in both sexes, particularly in Melanesians of Northern Province. Sixty-eight mesothelioma cases were included in the case-control study. Melanesians had the highest risk (OR = 16.18; 95% CI = [5.68; 49.64]) compared to Europeans. The sex ratio close to 1 and the number of young cases were consistent with environmental exposure in this group. Two high risk areas were highlighted: Houailou-Bourail (35% of cases) and Koné-Touho-Poindimié (20% of cases). Mining activity and Pö were not significant risk factors. The existence of a significant relationship between soil containing serpentinite and mesothelioma was demonstrated (p = 0.017). We noticed the presence of numerous serpentinite quarries in the highest risk areas, whose main fibrous mineral was antigorite. Our investigations showed also that Pöwas not always made of tremolite. It could be made of coral, clay or silica. This use was given up since the 1960’s in Houaïlou area while it was present until the last 1990’s in some tribes of Hienghène and Poya. The highest mesothelioma incidence was observed in the Houaïlou area (ASR=128.7 per 100,000 person-years; 95%CI: 70.41–137.84). A significant spatial cluster grouped 18 tribes (31 observed cases vs 8.12 expected cases,p=0.001), but no significant temporal clusters were identified. The ecological analyses identified serpentinite on roads as the greatest environmental risk factor: OR = 495.0, 95%CI: 46.2–4679.7; multivariate IRR=13.0, 95%CI: 10.2-16.6. The risk increased with serpentinite surface, proximity to serpentinite quarries and distance to the peridotite massif. The association with serpentines, particularly antigorite, was stronger than for amphiboles. Living on a slope and close to dense vegetation appeared protective. The use of whitewash was not associated with mesothelioma incidence. Conclusions: This study demonstrated that the use of serpentinite to cover roads is a major environmental risk factor for mesothelioma in NC. It is urgent to finish the census of serpentinite quarries, to ban their use, to neutralize them and the roads covered with this material. Our work shows also that antigorite may release fibers which are dangerous for human health. This mineral should be added on the list of asbestos fibers to diagnose in the analysis of natural environment samples.
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Francine Baumann. Le mésothéliome malin pleural en Nouvelle-Calédonie : analyse spatiale et déterminants environnementaux - facteurs de risque d'exposition à l'amiante naturel. Santé publique et épidémiologie. Université de la Nouvelle-Calédonie, 2010. Français. ⟨NNT : 2010NCAL0031⟩. ⟨tel-02973274⟩

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