Ischaemic heart and cerebrovascular disease mortality in uranium enrichment workers.

OBJECTIVE: Linear and non-linear dose-response relationships between radiation absorbed dose to the lung from internally deposited uranium and external sources and circulatory system disease (CSD) mortality were examined in a cohort of 23 731 male and 5552 female US uranium enrichment workers. METHODS: Rate ratios (RRs) for categories of lung dose and linear excess relative rates (ERRs) per unit lung dose were estimated to evaluate the associations between lung absorbed dose and death from ischaemic heart disease (IHD) and cerebrovascular disease. RESULTS: There was a suggestion of modestly increased IHD risk in workers with internal uranium lung dose above 1 milligray (mGy) (RR=1.4, 95% CI 0.76 to 2.3) and a statistically significantly increased IHD risk with external dose exceeding 150 mGy (RR=1.3, 95% CI 1.1 to 1.6) compared with the lowest exposed groups. ERRs per milligray were positive for IHD and uranium internal dose and for both outcomes per gray external dose, although the CIs generally included the null. CONCLUSIONS: Non-linear dose-response models using restricted cubic splines revealed sublinear responses at lower internal doses, suggesting that linear models that are common in radioepidemiological cancer studies may poorly describe the association between uranium internal dose and CSD mortality.

Dose-response relationships between internally-deposited uranium and select health outcomes in gaseous diffusion plant workers, 1948-2011.

OBJECTIVE: To examine dose-response relationships between internal uranium exposures and select outcomes among a cohort of uranium enrichment workers. METHODS: Cox regression was conducted to examine associations between selected health outcomes and cumulative internal uranium with consideration for external ionizing radiation, work-related medical X-rays and contaminant radionuclides technetium (99 Tc) and plutonium (239 Pu) as potential confounders. RESULTS: Elevated and monotonically increasing mortality risks were observed for kidney cancer, chronic renal diseases, and multiple myeloma, and the association with internal uranium absorbed organ dose was statistically significant for multiple myeloma. Adjustment for potential confounders had minimal impact on the risk estimates. CONCLUSION: Kidney cancer, chronic renal disease, and multiple myeloma mortality risks were elevated with increasing internal uranium absorbed organ dose. The findings add to evidence of an association between internal exposure to uranium and cancer. Future investigation includes a study of cancer incidence in this cohort.

Melanoma, thyroid cancer, and gynecologic cancers in a cohort of female flight attendants.

BACKGROUND: Flight attendants may have an increased risk of some cancers from occupational exposure to cosmic radiation and circadian disruption. METHODS: The incidence of thyroid, ovarian, and uterine cancer among ∼6000 female flight attendants compared to the US population was evaluated via life table analyses. Associations of these cancers, melanoma, and cervical cancer with cumulative cosmic radiation dose and metrics of circadian disruption were evaluated using Cox regression. RESULTS: Incidence of thyroid, ovarian, and uterine cancer was not elevated. No significant, positive exposure-response relations were observed. Weak, non-significant, positive relations were observed for thyroid cancer with cosmic radiation and time zones crossed and for melanoma with another metric of circadian disruption. CONCLUSIONS: We found little evidence of increased risk of these cancers from occupational cosmic radiation or circadian disruption in female flight attendants. Limitations include few observed cases of some cancers, limited data on risk factors, and misclassification of exposures.

Mortality in a combined cohort of uranium enrichment workers.

OBJECTIVE: To examine the patterns of cause-specific mortality and relationship between internal exposure to uranium and specific causes in a pooled cohort of 29,303 workers employed at three former uranium enrichment facilities in the United States with follow-up through 2011. METHODS: Cause-specific standardized mortality ratios (SMRs) for the full cohort were calculated with the U.S. population as referent. Internal comparison of the dose-response relation between selected outcomes and estimated organ doses was evaluated using regression models. RESULTS: External comparison with the U.S. population showed significantly lower SMRs in most diseases in the pooled cohort. Internal comparison showed positive associations of absorbed organ doses with multiple myeloma, and to a lesser degree with kidney cancer. CONCLUSION: In general, these gaseous diffusion plant workers had significantly lower SMRs than the U.S. POPULATION: The internal comparison however, showed associations between internal organ doses and diseases associated with uranium exposure in previous studies. Am. J. Ind. Med. 60:96-108, 2017. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Miscarriage among flight attendants.

BACKGROUND: Cosmic radiation and circadian disruption are potential reproductive hazards for flight attendants. METHODS: Flight attendants from 3 US airlines in 3 cities were interviewed for pregnancy histories and lifestyle, medical, and occupational covariates. We assessed cosmic radiation and circadian disruption from company records of 2 million individual flights. Using Cox regression models, we compared respondents (1) by levels of flight exposures and (2) to teachers from the same cities, to evaluate whether these exposures were associated with miscarriage. RESULTS: Of 2654 women interviewed (2273 flight attendants and 381 teachers), 958 pregnancies among 764 women met study criteria. A hypothetical pregnant flight attendant with median first-trimester exposures flew 130 hours in 53 flight segments, crossed 34 time zones, and flew 15 hours during her home-base sleep hours (10 pm-8 am), incurring 0.13 mGy absorbed dose (0.36 mSv effective dose) of cosmic radiation. About 2% of flight attendant pregnancies were likely exposed to a solar particle event, but doses varied widely. Analyses suggested that cosmic radiation exposure of 0.1 mGy or more may be associated with increased risk of miscarriage in weeks 9-13 (odds ratio = 1.7 [95% confidence interval = 0.95-3.2]). Risk of a first-trimester miscarriage with 15 hours or more of flying during home-base sleep hours was increased (1.5 [1.1-2.2]), as was risk with high physical job demands (2.5 [1.5-4.2]). Miscarriage risk was not increased among flight attendants compared with teachers. CONCLUSIONS: Miscarriage was associated with flight attendant work during sleep hours and high physical job demands and may be associated with cosmic radiation exposure.

Breast cancer incidence in a cohort of U.S. flight attendants.

BACKGROUND: Flight attendants may have elevated breast cancer incidence (BCI). We evaluated BCI's association with cosmic radiation dose and circadian rhythm disruption among 6,093 female former U.S. flight attendants. METHODS: We collected questionnaire data on BCI and risk factors for breast cancer from 2002-2005. We conducted analyses to evaluate (i) BCI in the cohort compared to the U.S. population; and (ii) exposure-response relations. We applied an indirect adjustment to estimate whether parity and age at first birth (AFB) differences between the cohort and U.S. population could explain BCI that differed from expectation. RESULTS: BCI was elevated but may be explained by lower parity and older AFB in the cohort than among U.S. women. BCI was not associated with exposure metrics in the cohort overall. Significant positive associations with both were observed only among women with parity of three or more. CONCLUSIONS: Future cohort analyses may be informative on the role of these occupational exposures and non-occupational risk factors.

Mortality among a cohort of U.S. commercial airline cockpit crew.

BACKGROUND: We evaluated mortality among 5,964 former U.S. commercial cockpit crew (pilots and flight engineers). The outcomes of a priori interest were non-chronic lymphocytic leukemia, central nervous system (CNS) cancer (including brain), and malignant melanoma. METHODS: Vital status was ascertained through 2008. Life table and Cox regression analyses were conducted. Cumulative exposure to cosmic radiation was estimated from work history data. RESULTS: Compared to the U.S. general population, mortality from all causes, all cancer, and cardiovascular diseases was decreased, but mortality from aircraft accidents was highly elevated. Mortality was elevated for malignant melanoma but not for non-chronic lymphocytic leukemia. CNS cancer mortality increased with an increase in cumulative radiation dose. CONCLUSIONS: Cockpit crew had a low all-cause, all-cancer, and cardiovascular disease mortality but elevated aircraft accident mortality. Further studies are needed to clarify the risk of CNS and other radiation-associated cancers in relation to cosmic radiation and other workplace exposures.

Flight attendant radiation dose from solar particle events.

INTRODUCTION: Research has suggested that work as a flight attendant may be related to increased risk for reproductive health effects. Air cabin exposures that may influence reproductive health include radiation dose from galactic cosmic radiation and solar particle events. This paper describes the assessment of radiation dose accrued during solar particle events as part of a reproductive health study of flight attendants. METHODS: Solar storm data were obtained from the National Oceanic and Atmospheric Administration Space Weather Prediction Center list of solar proton events affecting the Earth environment to ascertain storms relevant to the two study periods (1992-1996 and 1999-2001). Radiation dose from exposure to solar energetic particles was estimated using the NAIRAS model in conjunction with galactic cosmic radiation dose calculated using the CARI-6P computer program. RESULTS: Seven solar particle events were determined to have potential for significant radiation exposure, two in the first study period and five in the second study period, and over-lapped with 24,807 flight segments. Absorbed (and effective) flight segment doses averaged 6.5 µGy (18 µSv) and 3.1 µGy (8.3 µSv) for the first and second study periods, respectively. Maximum doses were as high as 440 µGy (1.2 mSv) and 20 flight segments had doses greater than 190 µGy (0.5 mSv). DISCUSSION: During solar particle events, a pregnant flight attendant could potentially exceed the equivalent dose limit to the conceptus of 0.5 mSv in a month recommended by the National Council on Radiation Protection and Measurements.

Mortality and ionising radiation exposures among workers employed at the Fernald Feed Materials Production Center (1951-1985).

OBJECTIVES: To examine mortality patterns and dose-response relations between ionising radiation and mortality outcomes of a priori interest in 6409 uranium workers employed for at least 30 days (1951-1985), and followed through 2004. METHODS: Cohort mortality was evaluated through standardised mortality ratios (SMR). Linear excess relative risk (ERR) regression models examined associations between cause-specific mortality and exposures to internal ionising radiation from uranium deposition, external gamma and x-ray radiation, and radon decay products, while adjusting for non-radiologic covariates. RESULTS: Person-years at risk totalled 236 568 (mean follow-up 37 years), and 43% of the cohort had died. All-cause mortality was below expectation only in salaried workers. Cancer mortality was significantly elevated in hourly males, primarily from excess lung cancer (SMR=1.25, 95% CI 1.09 to 1.42). Cancer mortality in salaried males was near expectation, but lymphohaematopoietic malignancies were significantly elevated (SMR=1.52, 95% CI 1.06 to 2.12). A positive dose-response relation was observed for intestinal cancer, with a significant elevation in the highest internal organ dose category and a significant dose-response with organ dose from internal uranium deposition (ERR=1.5 per 100 µGy, 95% CI 0.12 to 4.1). CONCLUSIONS: A healthy worker effect was observed only in salaried workers. Hourly workers had excess cancer mortality compared with the US population, although there was little evidence of a dose-response trend for any cancer evaluated except intestinal cancer. The association between non-malignant respiratory disease and radiation dose observed in previous studies was not apparent, possibly due to improved exposure assessment, different outcome groupings, and extended follow-up.

Assessment of occupational cosmic radiation exposure of flight attendants using questionnaire data.

INTRODUCTION: Female flight attendants may have a higher risk of breast and other cancers than the general population because of routine exposure to cosmic radiation. As part of a forthcoming study of breast and other cancer incidence, occupational cosmic radiation exposure of a cohort of female flight attendants was estimated. METHODS: Questionnaire data were collected from living female cohort members who were formerly employed as flight attendants with Pan American World Airways. These data included airline at which the flight attendant was employed, assigned domicile, start and end dates for employment at domicile, and number of block hours and commuter segments flown per month. Questionnaire respondents were assigned daily absorbed and effective doses using a time-weighted dose rate specific to the domicile and/or work history era combined with self-reported work history information. RESULTS: Completed work history questionnaires were received from 5898 living cohort members. Mean employment time as a flight attendant was 7.4 yr at Pan Am and 12 yr in total. Estimated mean annual effective dose from all sources of occupational cosmic radiation exposure was 2.5 +/- 1.0 mSv, with a mean career dose of 30 mSv. DISCUSSION: Annual effective doses were similar to doses assessed for other flight attendant cohorts; however, questionnaire-based cumulative doses assessed in this study were on average higher than those assessed for other flight attendant cohorts using company-based records. The difference is attributed to the inclusion of dose from work at other airlines and commuter flights, which was made possible by using questionnaire data.

Exposure to Radon and Progeny in a Tourist Cavern.

ABSTRACT: The primary objective of this work was to characterize employee exposure to radon and progeny while performing guide/interpretation and concessions duties in a tourist cavern. Radon gas and progeny concentrations, fraction of unattached progeny, and other environmental parameters were evaluated in a popular tourist cavern in Southeastern New Mexico. Alpha-track detectors were used to measure radon gas in several cavern locations during a 9-mo period. Additionally, radon gas and attached and unattached fractions of radon progeny were measured at three primary cavern work locations during a 1-d period using a SARAD EQF 3220. Radon gas concentrations in the cavern were elevated due to extremely low air exchange rates with substantial seasonal variation. Mean measured radon concentrations ranged from 970 to 2,600 Bq m-3 in the main cavern and from 5,400 to 6,000 Bq m-3 in a smaller cave associated with the regional cave system. Measurements of unattached fractions (0.40-0.60) were higher than those commonly found in mines and other workplaces, leading to the potential for relatively high worker dose. Although radon gas concentrations were below the Occupational Safety and Health Administration Permissible Exposure Limit, employees working in the cavern have the potential to accrue ionizing radiation dose in excess of the annual effective dose limit recommended by the National Council on Radiation Protection and Measurements due to a high unattached fraction of radon progeny. There was a strong negative correlation between unattached fractions and equilibrium factors, but these parameters should be further evaluated for seasonal variation. Introduction of engineering controls such as ventilation could damage the cavern environment, so administrative controls, such as time management, are preferred to reduce employee dose.

Cohort profile: four early uranium processing facilities in the US and Canada.

PURPOSE: Pooling of individual-level data for workers involved in uranium refining and processing (excluding enrichment) may provide valuable insights into risks from occupational uranium and external ionizing radiation exposures. METHODS: Data were pooled for workers from four uranium processing facilities (Fernald, Mallinckrodt and Middlesex from the U.S.; and Port Hope, Canada). Employment began as early as the 1930s and follow-up was as late as 2017. Workers were exposed to high concentrations of uranium, radium, and their decay products, as well as gamma radiation and ambient radon decay products. Exposure and outcome data were harmonized using similar definitions and dose reconstruction methods. Standardized mortality ratios (SMR) were estimated. RESULTS: In total, 560 deaths from lung cancer, 503 non-malignant respiratory diseases, 67 renal diseases, 1,596 ischemic heart diseases, and 101 dementia and Alzheimer's disease (AD) were detected in the pooled cohort of over 12,400 workers (∼1,300 females). Mean cumulative doses were 45 millisievert for whole-body external ionizing radiation exposure and 172 milligray for lung dose from radon decay products. Only SMR for dementia and AD among males was statistically significant (SMR=1.29; 95% confidence interval: 1.04, 1.54). CONCLUSIONS: This is the largest study to date to examine long-term health risks of uranium processing workers.

A nested case-control study of multiple myeloma risk and uranium exposure among workers at the Oak Ridge Gaseous Diffusion Plant.

The primary risk factors of multiple myeloma are age, race and sex, but several studies have found an association between radiological hazards and multiple myeloma. The purpose of this nested case-control study was to investigate whether workers with chronic low-level exposure to internally deposited uranium at the Oak Ridge Gaseous Diffusion Plant in eastern Tennessee were at higher risk of dying of multiple myeloma than those without occupational exposure to uranium, with the consideration of potential confounders of external ionizing radiation and occupational chemical hazards such as mercury, nickel and trichloroethylene. The main analyses were carried out using conditional logistic regression on 98 cases and 490 controls (five controls matched to each case on gender, race and age at risk). Our study showed a weak association between internal uranium dose estimated from urinalysis results and multiple myeloma risk: OR = 1.04 (95% CI 1.00-1.09) at 10 microGy with the inclusion of other risk factors. The parameter estimates and the corresponding odds ratios were very similar when internal doses were imputed for subjects without urine samples. Further studies that include updating this cohort and combining with workers from other gaseous diffusion plants are needed to investigate the relationship between multiple myeloma risk and radiation or other chemical exposures.

Radiation Exposure of Workers and Volunteers in Shelters and Community Reception Centers in the Aftermath of a Nuclear Detonation.

After a nuclear detonation, workers and volunteers providing first aid, decontamination, and population monitoring in public shelters and community reception centers will potentially be exposed to radiation from people they are assisting who may be contaminated with radioactive fallout. A state-of-the-art computer-aided design program and radiation transport modeling software were used to estimate external radiation dose to workers in three different exposure scenarios: performing radiation surveys/decontamination, first aid, and triage duties. Calculated dose rates were highest for workers performing radiation surveys due to the relative proximity to the contaminated individual. Estimated cumulative doses were nontrivial but below the occupational dose limit established for normal operations by the Occupational Safety and Health Administration.

Chronic lymphocytic leukaemia and radiation: findings among workers at five US nuclear facilities and a review of the recent literature.

The aetiology of chronic lymphocytic leukaemia (CLL) is largely unknown. Despite compelling evidence for ionising radiation as a cause of most forms of leukaemia, CLL was not found to be radiogenic in early studies. Herein we describe the recent evidence for causation of CLL by ionising and non-ionising radiation, including a nested case-control study conducted within a cohort of 94 517 US workers at four nuclear weapons facilities and a nuclear naval shipyard. Forty-three cases of CLL deaths and 172 age-matched controls were identified with follow-up up to between 1990 and 1996. Radiation exposure from external sources and plutonium (lagged 10 years) was assessed for each worker, based on monitoring records. The excess relative rate (ERR) was estimated for workers receiving elevated doses compared to unexposed workers, controlling for possible risk factors. The ERR per 10 mSv was -0.020 (95% confidence interval: <0, 0.14) based on all exposed workers. However, for workers receiving <100 mSv, the ERR per 10 mSv was 0.20 (-0.035, 0.96). Recent studies of uranium miners and other populations have shown elevations of CLL possibly associated with ionising and non-ionising radiation. New studies should use incident cases and sufficient latency to account for the expected lengthy induction period for CLL.

Risk of chronic myeloid and acute leukemia mortality after exposure to ionizing radiation among workers at four U.S. nuclear weapons facilities and a nuclear naval shipyard.

A nested case-control study was conducted among workers at five U.S. nuclear facilities to evaluate leukemia mortality risk (excluding chronic lymphocytic) from ionizing radiation using worksite doses and adjusting for potential confounding. Conditional logistic regression was used to estimate the relative risk (RR) of exposed workers and the excess relative risk (ERR) per unit of radiation among 206 cases and 823 age-matched controls. Adjusting for sex and benzene, the RR of leukemia for workers receiving more than 10 mSv was higher compared to those receiving lower or no dose; however, the risk increase was attenuated in the highest dose group. The ERR per 10 mSv was 1.44% (95% CI: < -1.03%, 7.59%) but was higher for workers born after 1921 compared to workers born earlier or when excluding leukemias of uncertain type. Excluding the 7% who were high-dose workers (> 100 mSv), the sex- and benzene-adjusted ERR per 10 mSv was 6.82% (95% CI: -2.87%, 24.1%). The results suggest that risks among these nuclear workers are comparable to those observed in high-dose populations, although no evidence was observed of a positive quadratic dose-response term in this study. This large study is among the first to jointly evaluate benzene and ionizing radiation risk.

Method for analyzing left-censored bioassay data in large cohort studies.

In retrospective epidemiological studies of large cohorts of workers exposed to radioactive materials, it is often necessary to analyze large numbers of bioassay data sets containing censored values, or values recorded as less than a detection limit. Censored bioassay data create problems for all bioassay analysis methods, including analytical techniques based on least-squares regression to estimate intakes. A method is presented here that uses a simple empirically-derived equation for imputing replacement values for urine uranium concentration results reported as zero or less than a detection limit, that produces minimal bias in intakes estimated using least-square regression methods with the assumption of lognormally distributed measurement errors.

Exposure to Recycled Uranium Contaminants in Gaseous Diffusion Plants.

As part of an ongoing study of health effects in a pooled cohort of gaseous diffusion plant workers, organ dose from internal exposure to uranium was evaluated. Due to the introduction of recycled uranium into the plants, there was also potential for exposure to radiologically significant levels of 99Tc, 237Np and 238,239Pu. In the evaluation of dose response, these radionuclide exposures could confound the effect of internal uranium. Using urine bioassay data for study subjects reported in facility records, intakes and absorbed dose to bone surface, red bone marrow and kidneys were estimated as these organs were associated with a priori outcomes of interest. Additionally, 99Tc intakes and doses were calculated using a new systemic model for technetium and compared to intakes and doses calculated using the current model recommended by the International Commission on Radiological Protection. Organ absorbed doses for the transuranics were significant compared to uranium doses; however, 99Tc doses calculated using the new systemic model were significant as well. Use of the new model resulted in an increase in 99Tc-related absorbed organ dose of a factor of 8 (red bone marrow) to 30 (bone surface).

Bone marrow dose estimates from work-related medical x-ray examinations given between 1943 and 1966 for personnel from five U.S. nuclear facilities.

Inclusion of dose from work-related medical x-ray examinations with occupational external dose in an epidemiological study may reduce misclassification of exposures and provide more accurate assessment of leukemia risk from occupational exposure to ionizing radiation. In a multi-site leukemia case-control study, annual bone marrow doses due to work-related x-ray examinations given between 1943 and 1966 were estimated for cases and controls employed at five nuclear facilities. Only active bone marrow dose from photofluorographic chest and routine lumbar spine x rays were included. Bone marrow dose assigned for a single exposure ranged from 1.0 to 1.4 mGy. Mean and median cumulative bone marrow doses for each of the five sites from work-related x-ray examinations ranged from 2.0 to 14 mGy and 2.1 to 8.8 mGy, respectively. Results suggest that bone marrow dose from work-related photofluorographic and lumbar spine x-ray examinations given during the time period of this study may be significant compared to occupational bone marrow dose.

Breast cancer incidence among female flight attendants: exposure-response analyses.

OBJECTIVE: The aim of this study was to examine the association of breast cancer incidence with cosmic radiation dose and circadian rhythm disruption in a cohort of 6093 US female flight attendants. METHODS: The association of breast cancer risk with cumulative cosmic radiation dose, time spent working during the standard sleep interval, and time zones crossed (all lagged by ten years), adjusted for non-occupational breast cancer risk factors, was evaluated using Cox regression. Individual exposure estimates were derived from work history data and domicile- and era-specific exposure estimates. Breast cancers were identified from telephone interviews and state cancer registries, and covariate data were obtained from telephone interviews. RESULTS: Breast cancer incidence in the overall cohort was not associated with exposure. Positive associations in breast cancer incidence were observed with all three exposures only among the 884 women with parity of ≥3. Adjusted excess relative risks for women with parity of ≥3 were 1.6 [95% confidence interval (95% CI) 0.14-6.6], 0.99 (95% CI -0.04-4.3), and 1.5 (95% CI 0.14-6.2) per 10 mGy, per 2000 hours spent working in the standard sleep interval, and per 4600 time zones crossed (the approximate means of the fourth exposure quintiles among breast cancer cases), respectively. CONCLUSIONS: Positive exposure-response relations, although observed only in a small subset of the cohort, were robust. Future studies of breast cancer incidence among other workers with circadian rhythm disruption should assess interaction with parity to see if our findings are confirmed.