Ground deposition of radionuclides in French Polynesia resulting from atmospheric nuclear weapons tests at Mururoa and Fangataufa atolls

Genetic factors for differentiated thyroid cancer in French Polynesia: new candidate loci

Background

Populations of French Polynesia (FP), where France performed atmospheric tests between 1966 and 1974, experience a high incidence of differentiated thyroid cancer (DTC). However, up to now, no sufficiently large study of DTC genetic factors in this population has been performed to reach definitive conclusion. This research aimed to analyze the genetic factors of DTC risk among the native FP populations.

Methods

We analyzed more than 300 000 single nucleotide polymorphisms (SNPs) genotyped in 283 DTC cases and 418 matched controls born in FP, most being younger than 15 years old at the time of the first nuclear tests. We analyzed the genetic profile of our cohort to identify population subgroups. We then completed a genome-wide analysis study on the whole population.

Results

We identified a specific genetic structure in the FP population reflecting admixture from Asian and European populations. We identified three regions associated with increased DTC risk at 6q24.3, 10p12.2, and 17q21.32. The lead SNPs at these loci showed respective p-values of 1.66 × 10^-7, 2.39 × 10^-7, and 7.19 × 10^-7 and corresponding odds ratios of 2.02, 1.89, and 2.37.

Conclusion

Our study results suggest a role of the loci 6q24.3, 10p12.2 and 17q21.32 in DTC risk. However, a whole genome sequencing approach would be better suited to characterize these factors than genotyping with microarray chip designed for the Caucasian population. Moreover, the functional impact of these three new loci needs to be further explored and validated.

Assessment of Differentiated Thyroid Carcinomas in French Polynesia After Atmospheric Nuclear Tests Performed by France

Importance

Due to the amount of iodine 131 released in nuclear tests and its active uptake by the thyroid, differentiated thyroid carcinoma (DTC) is the most serious health risk for the population living near sites of nuclear tests. Whether low doses to the thyroid from nuclear fallout are associated with increased risk of thyroid cancer remains a controversial issue in medicine and public health, and a misunderstanding of this issue may be associated with overdiagnosis of DTCs.

Design, Setting, and Participants

This case-control study was conducted by extending a case-control study published in 2010 that included DTCs diagnosed between 1984 and 2003 by adding DTCs diagnosed between 2004 and 2016 and improving the dose assessment methodology. Data on 41 atmospheric nuclear tests conducted by France between 1966 and 1974 in French Polynesia (FP) were assessed from original internal radiation-protection reports, which the French military declassified in 2013 and which included measurements in soil, air, water, milk, and food in all FP archipelagos. These original reports led to an upward reassessment of the nuclear fallout from the tests and a doubling of estimates of the mean thyroid radiation dose received by inhabitants from 2 mGy to nearly 5 mGy. Included patients were diagnosed from 1984 to 2016 with DTC at age 55 years or younger and were born in and resided in FP at diagnosis; 395 of 457 eligible cases were included, and up to 2 controls per case nearest by birthdate and matched on sex were identified from the FP birth registry. Data were analyzed from March 2019 through October 2021.

Exposure

The radiation dose to the thyroid gland was estimated using recently declassified original radiation-protection service reports, meteorological reports, self-reported lifestyle information, and group interviews of key informants and female individuals who had children at the time of these tests.

Main Outcomes and Measures

The lifetime risk of DTC based on Biological Effects of Ionizing Radiation (BEIR) VII models was estimated.

Results

A total of 395 DTC cases (336 females [85.1%]; mean [SD] age at end of follow-up, 43.6 [12.9] years) and 555 controls (473 females [85.2%]; mean [SD] age at end of follow-up, 42.3 [12.5] years) were included. No association was found between thyroid radiation dose received before age 15 years and risk of DTC (excess relative risk [ERR] per milligray, 0.04; 95% CI, -0.09 to 0.17; P = .27). When excluding unifocal noninvasive microcarcinomas, the dose response was significant (ERR per milligray, 0.09; 95% CI, -0.03 to 0.02; P = .02), but several incoherencies with the results of the initial study reduce the credibility of this result. The lifetime risk for the entire FP population was 29 cases of DTC (95% CI, 8-97 cases), or 2.3% (95% CI, 0.6%-7.7%) of 1524 sporadic DTC cases in this population.

Conclusions and Relevance

This case-control study found that French nuclear tests were associated with an increase in lifetime risk of PTC in FP residents of 29 cases of PTC. This finding suggests that the number of thyroid cancer cases and the true order of magnitude of health outcomes associated with these nuclear tests were small, which may reassure populations of this Pacific territory.

Contribution of close-in fallout from the French atmospheric tests in inventories of 137Cs, 241Am and plutonium (238, 239, 240) in Gambier Islands (French Polynesia) - Signatures of stratospheric fallout in the Southern Hemisphere

The inventories of ¹³⁷Cs (503 ± 34 Bq.m^-2), ²⁴¹Am (11.3 ± 1.2 Bq.m^-2), ²⁴¹Pu (33.7 ± 3.4 Bq.m^-2), ²³⁸Pu (6.82 ± 0.87 Bq.m^-2) and ^239+240Pu (113.0 ± 5.9 Bq.m^-2), sum of ²³⁹Pu (100 ± 11 Bq.m^-2) and ²⁴⁰Pu (14.5 ± 1.7 Bq.m^-2), in the Gambier archipelago (23°S) of the French Polynesia, are well higher the global fallout at this latitude, in unequal proportions for the different radionuclides. (²⁴⁰Pu/²³⁹Pu)_AR (AR: atomic ratio) of 0.0394 ± 0.0062, and (²⁴¹Pu/²³⁹Pu)_AR of (2.03 ± 0.39)10^-4, confirm that the overwhelmingly dominant source of these radionuclides comes from local fallout during the 1970s of the French atmospheric tests of Moruroa and Fangataufa located nearly 400 km from Gambier. The signatures of the local fallout were deduced from the excess of its inventory in ¹³⁷Cs and from the mixing lines established from the signatures of the global fallout, some of the test sites and the isotopic ratios measured in Gambier. Signatures obtained are 2.0 ± 0.4 for ¹³⁷Cs/^239+240Pu, 0.045 ± 0.008 for ²³⁸Pu/^239+240Pu, 0.031 ± 0.009 for ²⁴¹Am/^239+240Pu, 0.092 ± 0.027 for ²⁴¹Pu/^239+240Pu, 0.0163 ± 0.0049 for (²⁴⁰Pu/²³⁹Pu)_AR, (0.78 ± 0.23)10^-4 for (²⁴¹Pu/²³⁹Pu)_AR. The concordance of the mixing lines of the [(²⁴⁰Pu/²³⁹Pu)_AR, (²⁴¹Pu/²³⁹Pu)_AR] and the linear regression of these ratios measured in the stratosphere (40°S) during the 1970s, indicates that the signatures of the close-in deposition are also those of the stratospheric injections of the French tests. The signatures of stratospheric fallout in the Southern Hemisphere were evaluated by considering that the fission energy of these injections represents 11% and that of the Northern Hemisphere represents 89% and that the isotopic ratios of stratospheric injections remained the same over the period 1970-1974. The activity ratios deducted are 21.9 ± 0.1 in ¹³⁷Cs/^239+240Pu, 0.11 ± 0.05 in ²³⁸Pu/^239+240Pu, 1.03 ± 0.12 in ²⁴¹Pu/^239+240Pu and 0.35 ± 0.04 in ²⁴¹Am/^239+240Pu. The associated atom ratios are 0.157 ± 0.011 for (²⁴⁰Pu/²³⁹Pu)_AR and (8.33 ± 0.48)10^-4 for (²⁴¹Pu/²³⁹Pu)_AR. These signatures appear to be consistent with the results of the inventories at Hiva Oa, located more than 1,000 km north of both French test sites, and with those found in the Australian continent, in regions not impacted by UK-test debris. The proportions of close-in tropospheric fallout from the French tests are about 90% in Gambier. They represent a proportion in the inventories of 40% for the ¹³⁷Cs, 60% for ²⁴¹Am and in the range between 80 and 90% for Pu isotopes.

Radiological Impact of Atmospheric Nuclear Weapons Tests at Mururoa and Fangataufa Atolls to Populations in Oceania, South America and Africa: Comparison with French Polynesia

Objective:

To evaluate the potential radiological impact of atmospheric nuclear weapons tests conducted in 1966-1974 at Mururoa and Fangataufa atolls on populations in Oceania, South America and Africa.

Methods:

Results of measurements of total beta(β)-concentrations in filtered air and ¹³¹I activity concentrations in locally produced cow’s milk in Oceania, South America and Africa after the tests were compared with those in French Polynesia. Radiation doses due to external irradiation and thyroid doses due to ¹³¹I intake with milk by local populations were also compared.

Results:

Higher total β-concentrations in filtered air, ¹³¹I activity concentrations in locally produced milk and radiation doses to local population were, in general, observed in French Polynesia than in other countries in the southern hemisphere. However, for specific years during the testing period, the radiological impact to South America was found to be similar or slightly higher than that to Tahiti. The resulting thyroid doses in the considered countries were lower than those in French Polynesia with two exceptions: thyroid doses due to ¹³¹I intake with cow’s milk for 1-y old child in 1968 were higher in Peru (0.35 mGy) and in Madagascar (0.30 mGy) than in Tahiti (0.25 mGy). However, the populations outside French Polynesia received doses lower than those from the natural sources of radiation.

Conclusion:

According to the current knowledge in radiation epidemiology, it is very unlikely that nuclear fallout due to French nuclear tests had a measurable radiological and health impact outside French Polynesia.

Thyroid Doses to French Polynesians Resulting from Atmospheric Nuclear Weapons Tests: Estimates Based on Radiation Measurements and Population Lifestyle Data

Thyroid doses were estimated for the subjects of a population-based case-control study of thyroid cancer in a population exposed to fallout after atmospheric nuclear weapons tests conducted in French Polynesia between 1966 and 1974. Thyroid doses due to (1) intake of I and of short-lived radioiodine isotopes (I, I, I) and Te, (2) external irradiation from gamma-emitting radionuclides deposited on the ground, and (3) ingestion of long-lived Cs with foodstuffs were reconstructed for each study subject. The dosimetry model that had been used in 2008 in Phase I of the study was substantially improved with (1) results of radiation monitoring of the environment and foodstuffs, which became available in 2013 for public access, and (2) historical data on population lifestyle related to the period of the tests, which were collected in 2016-2017 using focus-group discussions and key informant interviews. The mean thyroid dose among the study subjects was found to be around 5 mGy while the highest dose was estimated to be around 36 mGy. Doses from I intake ranged up to 27 mGy, while those from intake of short-lived iodine isotopes (I, I, I) and Te ranged up to 14 mGy. Thyroid doses from external exposure ranged up to 6 mGy, and those from internal exposure due to Cs ingestion did not exceed 1 mGy. Intake of I was found to be the main pathway for thyroid exposure accounting for 72% of the total dose. Results of this study are being used to evaluate the risk of thyroid cancer among the subjects of the epidemiologic study of thyroid cancer among French Polynesians.