Cancer mortality and morbidity among workers at the Sellafield plant of British Nuclear Fuels

Cancer mortality in workers at risk of occupational exposure to ionizing radiation in a company in the nuclear sector headquarters in São Paulo

OBJECTIVE

To compare cancer mortality among workers exposed to gamma and X radiation and the general population of the city of São Paulo, as well as that of the subgroup monitored with those not monitored for gamma and X radiation in a work unit with ionizing radiation based in the city of São Paulo.

METHODS

Between 2016 and 2021, a retrospective open cohort study was carried out with workers who were employed from 08/31/1956 to 12/31/2016 based on data collected at the company and in official institutions. Standardized mortality ratios (SMR) were calculated by sex, age and calendar period of cancers grouped according to type, risk factor and organ system in two analyses: in the external analysis, the mortality of the study population was compared with that of the general population of the city of São Paulo; In the internal analysis, the mortality of the monitored subgroup was compared with that of the subgroup not monitored for gamma and X radiation.

RESULTS

The external mortality analysis showed SMR=0.224 (95%CI 0.208-0.240) and the healthy worker effect, while the internal mortality analysis showed SMR=0.685 (95%CI 0.618-0.758).

CONCLUSION

This study showed lower cancer mortality among exposed workers when compared to mortality in the general population and the healthy worker effect. Among workers monitored for gamma and X radiation, cancer mortality was lower when compared to those not monitored.

Overview of epidemiological studies of nuclear workers: opportunities, expectations, and limitations. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2021;41:1075-1092. [PMID: 34161930 DOI: 10.1088/1361-6498/ac0df4]

Epidemiological studies of those exposed occupationally to ionising radiation offer an important opportunity to directly check the assumptions underlying the international system of radiological protection against low-level radiation exposures. Recent nuclear worker studies, notably the International Nuclear Workers Study (INWORKS) and studies of the Mayak workforce in Russia, provide powerful investigations of a wide range of cumulative photon doses received at a low dose-rate over protracted periods, and broadly confirm radiation-related excess risks of leukaemia and solid cancers at around the levels predicted by standard risk models derived mainly from the experience of the Japanese atomic-bomb survivors acutely exposed principally to gamma radiation. However, the slope of the dose-response for solid cancers expressed in terms of the excess relative risk per unit dose, ERR/Gy, differs between INWORKS and Mayak, such that when compared with the slope derived from the atomic-bomb survivors, INWORKS does not provide obvious support for the use in radiological protection of a dose and dose-rate effectiveness factor greater than one whereas the Mayak workforce apparently does. This difference could be a chance effect, but it could also point to potential problems with these worker studies. Of particular concern is the adequacy of recorded doses received in the early years of operations at older nuclear installations, such as the potential for 'missed' photon doses. A further issue is how baseline cancer rates may influence radiation-related excess risks. There is scope for a considerable increase in the statistical power of worker studies, with longer follow-up capturing more deaths and incident cases of cancer, and further workforces being included in collaborative studies, but the difficulties posed by dosimetry questions should not be ignored and need to be the subject of detailed scrutiny.

Mortality from Leukemia, Cancer and Heart Disease among U.S. Nuclear Power Plant Workers, 1957-2011

BACKGROUND

The aim of the Million Person Study (MPS) of Low Dose Health Effects is to examine the level of radiation risk for chronic exposures received gradually over time and not acutely as was the case for the Japanese atomic bomb survivors. Nuclear power plant (NPP) workers comprise nearly 15 percent of the MPS. Leukemia, selected cancers, Parkinson's disease, ischemic heart disease (IHD) and other causes of death are evaluated.

METHODS AND MATERIAL

The U.S. Nuclear Regulatory Commission's Radiation Exposure Information and Reporting System (REIRS) and the Landauer, Inc. dosimetry databases identified 135,193 NPP workers first monitored 1957-1984. Annual personal dose equivalents [Hp(10)] were available for each worker. Radiation records from all places of employment were sought. Vital status was determined through 2011. Mean absorbed doses to red bone marrow (RBM), esophagus, lung, colon, brain and heart were estimated by adjusting the recorded Hp(10) for each worker by scaling factors, accounting for exposure geometry and energy of the incident gamma radiation. Standardized mortality ratios (SMR) were calculated. Radiation risks were estimated using Cox proportional hazards models.

RESULTS

Nearly 50% of workers were employed for more than 20 years. The mean duration of follow-up was 30.2 y. Overall, 29,076 total deaths occurred, 296 from leukemia other than chronic lymphocytic leukemia (CLL), 3,382 from lung cancer, 140 from Parkinson's disease and 5,410 from IHD. The mean dose to RBM was 37.9 mGy (maximum 1.0 Gy; percent >100 mGy was 9.2%), 43.2 mGy to lung, 43.7 mGy to colon, 33.2 mGy to brain, and 43.9 mGy to heart. The SMRs (95% CI) were 1.06 (0.94;1.19) for leukemia other than CLL, 1.10 (1.07;1.14) for lung cancer, 0.90 (0.76;1.06) for Parkinson's disease, and 0.80 (0.78; 0.82) for IHD. The excess relative risk (ERR) per 100 mGy for leukemia other than CLL was 0.15 (90% CI 0.001; 0.31). For all solid cancers the ERR per 100 mGy (95% CI) was 0.01 (-0.03; 0.05), for lung cancer -0.04 (-0.11; 0.02), for Parkinson's disease 0.24 (-0.02; 0.50), and for IHD -0.01 (-0.06; 0.04).

CONCLUSION

Prolonged exposure to radiation increased the risk of leukemia other than CLL among NPP workers. There was little evidence for a radiation-association for all solid cancers, lung cancer or ischemic heart disease. Increased precision will be forthcoming as the different cohorts within the MPS are combined, such as industrial radiographers and medical radiation workers who were assembled and evaluated in like manner.

Lung Cancer Risk from Plutonium: A Pooled Analysis of the Mayak and Sellafield Worker Cohorts

In this study, lung cancer risk from occupational plutonium exposure was analyzed in a pooled cohort of Mayak and Sellafield workers, two of the most informative cohorts in the world with detailed plutonium urine monitoring programs. The pooled cohort comprised 45,817 workers: 23,443 Sellafield workers first employed during 1947-2002 with follow-up until the end of 2005 and 22,374 Mayak workers first employed during 1948-1982 with follow-up until the end of 2008. In the pooled cohort 1,195 lung cancer deaths were observed (789 Mayak, 406 Sellafield) but only 893 lung cancer incidences (509 Mayak, 384 Sellafield, due to truncated follow-up in the incidence analysis). Analyses were performed using Poisson regression models, and were based on doses derived from individual radiation monitoring data using an updated dose assessment methodology developed in the study. There was clear evidence of a linear association between cumulative internal plutonium lung dose and risk of both lung cancer mortality and incidence in the pooled cohort. The pooled point estimates of the excess relative risk (ERR) from plutonium exposure for both lung cancer mortality and incidence were within the range of 5-8 per Gy for males at age 60. The ERR estimates in relationship to external gamma radiation were also significantly raised and in the range 0.2-0.4 per Gy of cumulative gamma dose to the lung. The point estimates of risk, for both external and plutonium exposure, were comparable between the cohorts, which suggests that the pooling of these data was valid. The results support point estimates of relative biological effectiveness (RBE) in the range of 10-25, which is in broad agreement with the value of 20 currently adopted in radiological protection as the radiation weighting factor for alpha particles, however, the uncertainty on this value (RBE = 21; 95% CI: 9-178) is large. The results provide direct evidence that the plutonium risks in each cohort are of the same order of magnitude but the uncertainty on the Sellafield cohort plutonium risk estimates is large, with observed risks consistent with no plutonium risk, and risks five times larger than those observed in the Mayak cohort.

The cancer mortality and incidence experience of workers at British Nuclear Fuels plc, 1946-2005

The aim of this study was to estimate cancer mortality and incidence risk associated with external radiation exposure in the BNFL cohort of nuclear workers and to determine if these risks are modified by potential for internal exposure. The cohort comprised 64,956 individuals who were employed at the four study sites between 1946 and 2002, followed up to 2005. External radiation exposures as measured by personal dosimeters (generally 'film badges') were available for 42,431 individuals classified as 'radiation workers'. Poisson regression models were used to investigate cancer mortality and incidence in relation to cumulative external radiation exposure using relative risk models. The cohort showed the expected 'healthy worker' effect. This analysis found an increased risk of all cancers associated with external occupational radiation exposure (ERR/Gy = 0.34 90% CI: 0.07; 0.64), with significant excess risks observed for all solid cancers (ERR/Gy = 0.29 90% CI: 0.02; 0.59) and leukaemia excluding CLL (ERR/Gy = 2.60 90% CI: 0.28; 7.01). The overall cancer risk estimates are consistent with values used by national and international bodies in setting radiation protection standards. The slopes of the dose response relationships for all cancer mortality and incidence were found to be significantly less steep for workers exposed to both external radiation and potentially to internal radiation (ERR/Gy = 0.09 90% CI: -0.17; 0.39) when compared to those workers only exposed to external radiation (ERR/Gy = 1.14 90% CI: 0.49; 1.89). Analyses of individual cancer types indicate that this overall result is mainly driven by that for digestive cancers and in particular cancers of the oesophagus. Categorical analyses also revealed that the difference in the dose response relationship between the two groups is only apparent for those exposed to cumulative external doses in excess of 200 mGy. Such differences have also been observed for non-cancer mortality outcomes in this cohort. Further work is required to explain these differences; for example, whether they may result from confounding by internal organ dose or lifestyle factors associated with socio-economic status.

Occupation and thyroid cancer

Numerous occupational and environmental exposures have been shown to disrupt thyroid hormones, but much less is known about their relationships with thyroid cancer. Here we review the epidemiology studies of occupations and occupational exposures and thyroid cancer incidence to provide insight into preventable risk factors for thyroid cancer. The published literature was searched using the Web of Knowledge database for all articles through August 2013 that had in their text 'occupation' 'job' 'employment' or 'work' and 'thyroid cancer'. After excluding 10 mortality studies and 4 studies with less than 5 exposed incident cases, we summarised the findings of 30 articles that examined thyroid cancer incidence in relation to occupations or occupational exposure. The studies were grouped by exposure/occupation category, study design and exposure assessment approach. Where available, gender-stratified results are reported. The most studied (19 of 30 studies) and the most consistent associations were observed for radiation-exposed workers and healthcare occupations. Suggestive, but inconsistent, associations were observed in studies of pesticide-exposed workers and agricultural occupations. Findings for other exposures and occupation groups were largely null. The majority of studies had few exposed cases and assessed exposure based on occupation or industry category, self-report, or generic (population-based) job exposure matrices. The suggestive, but inconsistent findings for many of the occupational exposures reviewed here indicate that more studies with larger numbers of cases and better exposure assessment are necessary, particularly for exposures known to disrupt thyroid homeostasis.

Mortality and cancer registration experience of the Sellafield workers known to have been involved in the 1957 Windscale accident: 50 year follow-up

This paper studies the mortality and cancer morbidity of the 470 male workers involved in tackling the 1957 Sellafield Windscale fire or its subsequent clean-up. Workers were followed up for 50 years to 2007, extending the follow-up of a previously published cohort study on the Windscale fire by 10 years. The size of the study population is small, but the cohort is of interest because of the involvement of the workers in the accident. Significant excesses of deaths from diseases of the circulatory system (standardised mortality ratio (SMR) = 120, 95% CI = 103-138; 194 deaths) driven by ischaemic heart disease (IHD) (SMR = 133, 95% CI = 112-157, 141 deaths) were found when compared with the population of England and Wales but not when compared with the population of Northwest England (SMR = 105, 95% CI = 90-120 and SMR = 115, 95% CI = 97-136 respectively). When compared with those workers in post at the time of the fire but not directly involved in the fire the mortality rate from IHD among those involved in tackling the fire was raised but not statistically significantly (rate ratio (RR) = 1.11, 95% CI = 0.92-1.33). A RR of 1.11 is consistent with an excess relative risk of 0.65 Sv(-1) as reported in an earlier study of non-cancer mortality in the British Nuclear Fuels plc cohort of which these workers are a small but significant part. There was a statistically significant difference in lung cancer mortality (RR = 2.18, 95% CI = 1.05-4.52) rates between workers who had received higher recorded external doses during the fire and those who had received lower external doses. Comparison of the mortality rates of workers directly involved in the accident with workers in post, but not so involved, showed no significant differences overall. On the basis of the use of a propensity score the average effect of involvement in the Windscale fire on all causes of death was - 2.13% (se = 3.64%, p = 0.56) though this difference is not statistically significant. The average effect of involvement in the Windscale fire was - 5.53% (se = 3.81, p = 0.15) for all cancers mortality and 6.60% (se = 4.03%, p = 0.10) for IHD mortality though neither figure was statistically significant. This analysis of the mortality and cancer morbidity experience of those Sellafield workers involved in the 1957 Windscale fire does not reveal any measurable effect of the fire upon their health. Although this study has low statistical power for detecting small adverse effects, due to the relatively small number of workers, it does provide reassurance that no significant health effects are associated with the 1957 Windscale fire even after 50 years of follow-up.

Testicular cancer risk associated with occupational radiation exposure: a systematic literature review

Testicular cancer is a rare disease, affecting mainly young men aged 15-49. There have been some recent reports that it might be associated with radiation exposure. We have systematically reviewed this topic. English-language articles published between 1990 and 2008 studying the relationship between occupational radiation exposure and testicular cancer were included. Risk of bias was assessed using a modified version of the EPHPP checklist. For ionising radiation we subdivided study populations into occupational groups. No pooled analysis was performed due to the heterogeneity of studies. Seven case-control and 30 cohort studies were included in the review. For radiation workers, one incidence study showed a significant increase and four showed no effect. Eight mortality studies did not indicate an effect while four showed a non-significant increase. Incidence among persons with military exposure was not increased in two studies and non-significantly increased in another two. Among aircrew studies, one showed no effect against five with slight increases. Medical exposure studies showed no increases. For EMF exposure, three studies showed no effect, two reported a significant and four a non-significant increase in incidence. Overall, there was very limited evidence for associations between occupational ionising radiation and testicular cancer, while there were some positive associations for EMF. Testicular cancer mortality is generally low and was not associated with radiation. New incidence studies are recommended to investigate the association between radiation exposure and testicular cancer where exposure is better specified and individually estimated.

Relationship between monoclonal gammopathy of undetermined significance and radiation exposure in Nagasaki atomic bomb survivors

Radiation exposure is a possible predisposing factor for monoclonal gammopathy of undetermined significance (MGUS), but the association has been uncertain. We investigated the relationship between radiation exposure and MGUS prevalence by using data from the M-protein screening for Nagasaki atomic bomb survivors between 1988 and 2004. Radiation exposure was assessed by exposure distance from the hypocenter and exposure radiation dose. We computed prevalence ratios (PRs) and the 95% confidence intervals (CIs) adjusting for exposure age and sex. A total of 1082 cases of MGUS were identified from 52 525 participants. MGUS prevalence was significantly higher in people exposed at distance within 1.5 km than beyond 3.0 km (PR, 1.4; 95% CI, 1.1-1.9) among those exposed at age 20 years or younger, but it was not found among those exposed at age 20 years or older. MGUS prevalence was also significantly higher in people exposed to more than 0.1 Gy than those exposed to less than 0.01 Gy (PR, 1.7; 95% CI, 1.0-2.8) among those exposed at age 20 years or younger. Thus, people exposed at younger age exhibited a significantly high risk of MGUS when exposed to a high radiation dose. There was no clear association between radiation exposure and the malignant progression of MGUS. Further detailed analysis is needed.

The non-cancer mortality experience of male workers at British Nuclear Fuels plc, 1946-2005

BACKGROUND

Recent studies of the Hiroshima and Nagasaki A-bomb survivors, together with some (but not all) cohorts exposed occupationally or medically to ionizing radiation, have found an increasing trend in mortality from non-malignant disease with increasing radiation dose. The aim of this study was to establish whether such a trend could be found in a large cohort of employees in the UK nuclear industry.

METHODS

The cohort comprised 64 937 individuals ever employed at the study sites between 1946 and 2002, followed up to 2005; radiation exposures as measured by personal dosimeters ('film badges') were available for 42 426 individuals classified as 'radiation workers'. Poisson regression models were used to investigate the relationship between excess mortality rates and cumulative radiation exposure, using both relative and additive risk models.

RESULTS

The cohort shows a pronounced 'healthy worker' effect. Overall, socio-economic status as indicated by employment status has a greater influence on mortality than does radiation exposure status. For male radiation workers, there is an apparent dose response for mortality from circulatory system disease [P < 0.001, ERR = 0.65 (90% CI 0.36-0.98) Sv(-1)]. However there is evidence for inhomogeneity in the apparent dose response (P = 0.016), arising principally at cumulative doses in excess of 300 mSv, when the four categories of employment and radiation exposure status are examined separately.

CONCLUSIONS

We have found evidence for an association between mortality from non-cancer causes of death, particularly circulatory system disease, and external exposure to ionizing radiation in this cohort. However, the tentative nature of biological mechanisms that might explain such an effect at low chronic doses and the above inhomogeneities in apparent dose-response, mean that the results of our analysis are not consistent with any simple causal interpretation. Further work is required to explain these inhomogeneities, and on the possible role of factors associated with socio-economic status and shift working, before any further conclusions can be drawn.

Cancer risk in nuclear workers occupationally exposed to uranium-emphasis on internal exposure

Workers involved in the nuclear fuel cycle have a potential for internal exposure to uranium. The present review of epidemiological studies of these workers aims to elucidate the relationship between occupational internal uranium exposure and cancer risk. Eighteen cohort and 5 nested case-control studies published since 1980 are reviewed. Workers occupationally exposed to uranium appear to be at increased risk of mortality from neoplasms of the lung, larynx, and lymphatic and haematopoietic tissue. Currently available evidence for a positive association between internal exposure to uranium and the risk of cancer is limited. The common weaknesses in reviewed studies include low statistical power and inaccurate assessment of internal exposure to uranium. Further investigations should focus on precise assessment of occupational exposure and address the issue of potential confounders.

The non-Hodgkin lymphomas: a review of the epidemiologic literature

The non-Hodgkin lymphomas (NHL) are a heterogeneous group of B-cell and T-cell neoplasms that arise primarily in the lymph nodes. NHL incidence rates in the US doubled between about 1970 and 1990, and stabilized during the 1990s. NHL accounts for approximately 3.4% of cancer deaths in the US. Although some of the observed patterns in NHL have been related to HIV/AIDS, these conditions cannot fully explain the magnitude of the changes; neither do changes in classification systems nor improved diagnostic capabilities. Studies of occupational and environmental exposures (e.g., pesticides, solvents) have produced no consistent pattern of significant positive associations. Inverse associations with ultraviolet radiation exposure and alcohol and fish intake, and positive associations with meat and saturated fat intake have been reported in several studies; additional studies are needed to confirm or refute these associations. Family history of NHL or other hematolympho-proliferative cancers and personal history of several autoimmune disorders are associated with increased risk of NHL, but are not likely to account for a large proportion of cases. HIV and other infectious agents, such as human herpesvirus 8 and Epstein-Barr, appear to be associated with differing types of NHL, such as some B-cell lymphomas. Future epidemiologic studies should evaluate associations by NHL type, enhance exposure information collected, and elucidate factors that may identify susceptible (or resistant) subpopulations because of genetic, immunologic or other characteristics. The extent to which the etiology of NHL types may differ is important to resolve in ongoing and future studies.

Cancer incidence among Australian nuclear industry workers

To assess whether workers at Lucas Heights Science and Technology Centre (LHSTC) had different levels of cancer incidence from the New South Wales (NSW) population in Australia. A retrospective cohort study was undertaken at LHSTC. Data on 7,076 workers employed between 1957-98 were abstracted from personnel, dosimetry, and medical files. An inception cohort was defined which included 4,523 workers in employment between 1972-96 to examine cancer incidence. Cancer registrations in the inception cohort were identified to 1996 through electronic linkage of records with the NSW and the Australian national registers of cancer incidence. All-cancer incidence in workers at LHSTC was 15% below the NSW rates [SIR=0.85; 95% CI=(0.75, 0.95)]. Of 37 specific cancers and groups of cancers examined, statistically significant excesses relative to NSW rates were observed only for pleural cancer incidence [SIR=17.71; 95%=(7.96, 39.43)], and for incidence of cancer of the small intestine [SIR=4.34; 95% CI=(1.40, 13.46)]. This study gives little evidence of an increased risk of cancers associated with radiation exposure in a cohort of nuclear workers in Australia. The observed increase in the risk of cancer of the pleura was probably due to unmeasured exposures, given the lack of an established association with radiation exposure, and the strong link to asbestos exposure. Findings for cancers of the small intestine were based on small numbers and were likely to be due to chance.

Multiple myeloma: A review of the epidemiologic literature

Multiple myeloma, a neoplasm of plasma cells, accounts for approximately approximately 15% of lymphatohematopoietic cancers (LHC) and 2% of all cancers in the US. Incidence rates increase with age, particularly after age 40, and are higher in men, particularly African American men. The etiology is unknown with no established lifestyle, occupational or environmental risk factors. Although several factors have been implicated as potentially etiologic, findings are inconsistent. We reviewed epidemiologic studies that evaluated lifestyle, dietary, occupational and environmental factors; immune function, family history and genetic factors; and the hypothesized precursor, monoclonal gammopathies of undetermined significance (MGUS). Because multiple myeloma is an uncommon disease, etiologic assessments can be difficult because of small numbers of cases in occupational cohort studies, and few subjects reporting exposure to specific agents in case-control studies. Elevated risks have been reported consistently among persons with a positive family history of LHC. A few studies have reported a relationship between obesity and multiple myeloma, and this may be a promising area of research. Factors underlying higher incidence rates of multiple myeloma in African Americans are not understood. The progression from MGUS to multiple myeloma has been reported in several studies; however, there are no established risk factors for MGUS. To improve our understanding of the causes of multiple myeloma, future research efforts should seek the causes of MGUS. More research is also needed on the genetic factors of multiple myeloma, given the strong familial clustering of the disease.

Mortality among Radiation Workers at Rocketdyne (Atomics International), 1948–1999

A retrospective cohort mortality study was conducted of workers engaged in nuclear technology development and employed for at least 6 months at Rocketdyne (Atomics International) facilities in California, 1948-1999. Lifetime occupational doses were derived from company records and linkages with national dosimetry data sets. International Commission on Radiation Protection (ICRP) biokinetic models were used to estimate radiation doses to 16 organs or tissues after the intake of radionuclides. Standardized mortality ratios (SMRs) compared the observed numbers of deaths with those expected in the general population of California. Cox proportional hazards models were used to evaluate dose-response trends over categories of cumulative radiation dose, combining external and internal organ-specific doses. There were 5,801 radiation workers, including 2,232 monitored for radionuclide intakes. The mean dose from external radiation was 13.5 mSv (maximum 1 Sv); the mean lung dose from external and internal radiation combined was 19.0 mSv (maximum 3.6 Sv). Vital status was determined for 97.6% of the workers of whom 25.3% (n = 1,468) had died. The average period of observation was 27.9 years. All cancers taken together (SMR 0.93; 95% CI 0.84-1.02) and all leukemia excluding chronic lymphocytic leukemia (CLL) (SMR 1.21; 95% CI 0.69-1.97) were not significantly elevated. No SMR was significantly increased for any cancer or for any other cause of death. The Cox regression analyses revealed no significant dose-response trends for any cancer. For all cancers excluding leukemia, the RR at 100 mSv was estimated as 1.00 (95% CI 0.81-1.24), and for all leukemia excluding CLL it was 1.34 (95% CI 0.73-2.45). The nonsignificant increase in leukemia (excluding CLL) was in accord with expectation from other radiation studies, but a similar nonsignificant increase in CLL (a malignancy not found to be associated with radiation) tempers a causal interpretation. Radiation exposure has not caused a detectable increase in cancer deaths in this population, but results are limited by small numbers and relatively low career doses.

A comprehensive dose reconstruction methodology for former rocketdyne/atomics international radiation workers

Incomplete radiation exposure histories, inadequate treatment of internally deposited radionuclides, and failure to account for neutron exposures can be important uncertainties in epidemiologic studies of radiation workers. Organ-specific doses from lifetime occupational exposures and radionuclide intakes were estimated for an epidemiologic study of 5,801 Rocketdyne/Atomics International (AI) radiation workers engaged in nuclear technologies between 1948 and 1999. The entire workforce of 46,970 Rocketdyne/AI employees was identified from 35,042 Kardex work histories cards, 26,136 electronic personnel listings, and 14,189 radiation folders containing individual exposure histories. To obtain prior and subsequent occupational exposure information, the roster of all workers was matched against nationwide dosimetry files from the Department of Energy, the Nuclear Regulatory Commission, the Landauer dosimetry company, the U.S. Army, and the U.S. Air Force. Dosimetry files of other worker studies were also accessed. Computation of organ doses from radionuclide intakes was complicated by the diversity of bioassay data collected over a 40-y period (urine and fecal samples, lung counts, whole-body counts, nasal smears, and wound and incident reports) and the variety of radionuclides with documented intake including isotopes of uranium, plutonium, americium, calcium, cesium, cerium, zirconium, thorium, polonium, promethium, iodine, zinc, strontium, and hydrogen (tritium). Over 30,000 individual bioassay measurements, recorded on 11 different bioassay forms, were abstracted. The bioassay data were evaluated using ICRP biokinetic models recommended in current or upcoming ICRP documents (modified for one inhaled material to reflect site-specific information) to estimate annual doses for 16 organs or tissues taking into account time of exposure, type of radionuclide, and excretion patterns. Detailed internal exposure scenarios were developed and annual internal doses were derived on a case-by-case basis for workers with committed equivalent doses indicated by screening criteria to be greater than 10 mSv to the organ with the highest internal dose. Overall, 5,801 workers were monitored for radiation at Rocketdyne/AI: 5,743 for external exposure and 2,232 for internal intakes of radionuclides; 41,169 workers were not monitored for radiation. The mean cumulative external dose based on Rocketdyne/AI records alone was 10.0 mSv, and the dose distribution was highly skewed with most workers experiencing low cumulative doses and only a few with high doses (maximum 500 mSv). Only 45 workers received greater than 200 mSv while employed at Rocketdyne/AI. However, nearly 32% (or 1,833) of the Rocketdyne/AI workers had been monitored for radiation at other nuclear facilities and incorporation of these doses increased the mean dose to 13.5 mSv (maximum 1,005 mSv) and the number of workers with >200 mSv to 69. For a small number of workers (n=292), lung doses from internal radionuclide intakes were relatively high (mean 106 mSv; maximum 3,560 mSv) and increased the overall population mean dose to 19.0 mSv and the number of workers with lung dose>200 mSv to 109. Nearly 10% of the radiation workers (584) were monitored for neutron exposures (mean 1.2 mSv) at Rocketdyne/AI, and another 2% were monitored for neutron exposures elsewhere. Interestingly, 1,477 workers not monitored for radiation at Rocketdyne/AI (3.6%) were found to have worn dosimeters at other nuclear facilities (mean external dose of 2.6 mSv, maximum 188 mSv). Without considering all sources of occupational exposure, an incorrect characterization of worker exposure would have occurred with the potential to bias epidemiologic results. For these pioneering workers in the nuclear industry, 26.5% of their total occupational dose (collective dose) was received at other facilities both prior to and after employment at Rocketdyne/AI. In addition, a small number of workers monitored for internal radionuclides contributed disproportionately to the number of workers with high lung doses. Although nearly 12% of radiation workers had been monitored for neutron exposures during their career, the cumulative dose levels were small in comparison with other external and internal exposure. Risk estimates based on nuclear worker data must be interpreted cautiously if internally deposited radionuclides and occupational doses received elsewhere are not considered.

A nested case-control study of leukemia mortality and ionizing radiation at the Portsmouth Naval Shipyard

A nested case-control study using conditional logistic regression was conducted to evaluate the exposure-response relationship between external ionizing radiation exposure and leukemia mortality among civilian workers at the Portsmouth Naval Shipyard (PNS), Kittery, Maine. The PNS civilian workers received occupational radiation exposure while performing construction, overhaul, repair and refueling activities on nuclear-powered submarines. The study age-matched 115 leukemia deaths with 460 controls selected from a cohort of 37,853 civilian workers employed at PNS between 1952 and 1992. In addition to radiation doses received in the workplace, a secondary analysis incorporating doses from work-related medical X rays and other occupational radiation exposures was conducted. A significant positive association was found between leukemia mortality and external radiation exposure, adjusting for gender, radiation worker status, and solvent exposure duration (OR = 1.08 at 10 mSv of exposure; 95% CI = 1.01, 1.16). Solvent exposure (including benzene and carbon tetrachloride) was also significantly associated with leukemia mortality adjusting for radiation dose, radiation worker status, and gender. Incorporating doses from work-related medical X rays did not change the estimated leukemia risk per unit of dose.

Mortality rates among nuclear industry workers at Lucas Heights Science and Technology Centre

OBJECTIVES

To assess whether workers at Lucas Heights Science and Technology Centre (LHSTC) have different levels of mortality from the New South Wales (NSW) and Australian populations.

METHODS

A retrospective cohort study was undertaken at LHSTC. Data on 7,076 workers employed between 1957-98 were abstracted from personnel, dosimetry, and medical files. Deaths registrations in the cohort were identified to 1998 through electronic linkage of records with NSW and national registers of cancer incidence and mortality. Two inception cohorts were defined as including 4,717 and 3,543 workers in employment between 1972-98 and 1980-98, to examine cancer mortality and all-cause mortality respectively.

RESULTS

All-cause mortality was 31% lower than the national rates; all-cancer mortality was 19% below the NSW rate. Of 37 specific cancers and groups of cancers examined, statistically significant excesses relative to NSW rates were observed only for pleural cancer mortality (SMR = 21.11; 95% Cl 8.79-50.72).

CONCLUSIONS

The observed increase in the risk of cancer of the pleura was probably due to unmeasured exposures, given the lack of an established association with radiation exposure and the strong link to asbestos exposure.

Risk of Lung Cancer and Leukemia from Exposure to Ionizing Radiation and Potential Confounders among Workers at the Portsmouth Naval Shipyard

Significantly elevated lung cancer deaths and statistically significantly positive linear trends between leukemia mortality and radiation exposure were reported in a previous analysis of Portsmouth Naval Shipyard workers. The purpose of this study was to conduct a modeling-based analysis that incorporates previously unanalyzed confounders in exploring the exposure-response relationship between cumulative external ionizing radiation exposure and mortality from these cancers among radiation-monitored workers in this cohort. The main analyses were carried out with Poisson regression fitted with maximum likelihood in linear excess relative risk models. Sensitivity analyses varying model components and using other regression models were conducted. The positive association between lung cancer risk and ionizing radiation observed previously was no longer present after adjusting for socioeconomic status (smoking surrogate) and welding fume and asbestos exposures. Excesses of leukemia were found to be positively, though not significantly, associated with external ionizing radiation, with or without including potential confounders. The estimated excess relative risk was 10.88% (95% CI -0.90%, 38.77%) per 10 mSv of radiation exposure, which was within the ranges of risk estimates in previous epidemiological studies (-4.1 to 19.0%). These results are limited by many factors and are subject to uncertainties of the exposure and confounder estimates.

Analysis of the Mortality Experience amongst U.S. Nuclear Power Industry Workers after Chronic Low-Dose Exposure to Ionizing Radiation

Workers employed in 15 utilities that generate nuclear power in the United States have been followed for up to 18 years between 1979 and 1997. Their cumulative dose from whole body ionizing radiation has been determined from the dose records maintained by the facilities themselves and the REIRS and REMS systems maintained by the Nuclear Regulatory Commission and the Department of Energy, respectively. Mortality in the cohort from a number of causes has been analyzed with respect to individual radiation doses. The cohort displays a very substantial healthy worker effect, i.e. considerably lower cancer and noncancer mortality than the general population. Based on 26 and 368 deaths, respectively, positive though statistically nonsignificant associations were seen for mortality from leukemia (excluding chronic lymphocytic leukemia) and all solid cancers combined, with excess relative risks per sievert of 5.67 [95% confidence interval (CI) -2.56, 30.4] and 0.506 (95% CI -2.01, 4.64), respectively. These estimates are very similar to those from the atomic bomb survivors study, though the wide confidence intervals are also consistent with lower or higher risk estimates. A strong positive and statistically significant association between radiation dose and deaths from arteriosclerotic heart disease including coronary heart disease was also observed in the cohort, with an ERR of 8.78 (95% CI 2.10, 20.0). While associations with heart disease have been reported in some other occupational studies, the magnitude of the present association is not consistent with them and therefore needs cautious interpretation and merits further attention. At present, the relatively small number of deaths and the young age of the cohort (mean age at end of follow-up is 45 years) limit the power of the study, but further follow-up and the inclusion of the present data in an ongoing IARC combined analysis of nuclear workers from 15 countries will have greater power for testing the main hypotheses of interest.

Solid cancer incidence among the Chernobyl emergency workers residing in Russia: estimation of radiation risks

An analysis is presented of solid cancer incidence during 11 years of follow-up (1991-2001) of Chernobyl emergency workers residing in Russia. The analysis is based on data from the cohort of male emergency workers from 6 regions in Russia including 55718 persons with documented external radiation doses in the range of 0.001-0.3 Gy who worked within the 30 -km zone in 1986-1987. The mean age at exposure for these persons was 34.8 years and the mean external radiation dose 0.13 Gy. In the cohort 1370 cases of solid cancer were diagnosed and 3 follow-up periods were considered: 1991-1995, 1996-2001 and 1991-2001. The second follow-up period was chosen to allow for a minimum latency period of 10 years being characteristic of solid cancers. For risk assessment two control groups have been introduced, the first 'external' one representing incidence rates for corresponding ages in Russia in general, the second 'internal' one consisting of emergency workers. The risk estimates were based on spontaneous incidence rates of solid cancer. The estimated standardized incidence ratio (SIR) is in good agreement (95% CI) with that of the control. The values of excess relative risk per unit dose (ERR/Gy) for solid malignant neoplasms have been estimated to be 0.33 (95% CI: -0.39, 1.22) (internal control) for the follow-up period 1991-2001 and 0.19 (95% CI: -0.66, 1.27) for 1996-2001.

Mortality and cancer morbidity experience of female workers at the British Nuclear Fuels Sellafield plant, 1946-1998

BACKGROUND

Studies of nuclear workers have focused mainly on the experience of male workers. To date, little has been published specifically on the experience of female workers in the nuclear industry.

METHODS

We report on the mortality, cancer morbidity, and tracing experience of the 6,376 females ever employed at the British Nuclear Fuels Ltd. plant at Sellafield to the end of 1998. These workers have accumulated 142,337 person-years of experience.

RESULTS

Radiation workers were exposed to low doses of radiation. No statistically significant associations were noted between mortality or cancer morbidity and cumulative assessed organ-specific internal plutonium dose or cumulative external whole body radiation dose overall, or for any of the individual disease groupings examined. The power of the study was insufficient to detect the risks indicated in other radiation studies.

CONCLUSION

This study offers reassurance that there is no detrimental effect on the health of the female workers from occupational exposures at Sellafield. Am. J. Ind. Med. 44:653-663, 2003.

Second analysis of mortality of nuclear industry workers in Japan, 1986-1997

IA cohort study of nuclear industry workers was initiated in 1990 to determine the possible health effects of low-level radiation. A total of 5,527 deaths were ascertained among 176,000 male workers who had been retrospectively and/or prospectively followed for an average of 7.9 years during the observation period 1986-1997. Statistical analyses were made mainly on the prospective follow-up outcome of 120,000 workers followed for an average of 4.5 years. The standardized mortality ratio (and its 95% confidence interval) was 0.94 (0.90, 0.97) for 2,934 cases of all causes combined and 0.86 (0.82, 0.91) for 1,305 cases of non-malignant diseases combined, which suggested a healthy worker effect. For 1,191 cases of all cancers combined, it was 0.98 (0.93, 1.04), indicating no difference in mortality from that of the general population. In tests for trend of death rate with increasing radiation dose, no significant correlation was found for all cancers combined. For site-specific cancers, most cancers including leukemia showed no positive correlation with dose, except for cancers of the esophagus, stomach and rectum and multiple myeloma. External causes showed a significant correlation with dose. A separate questionnaire study indicated that these positive findings could be ascribed in part to lifestyle characteristics of the workers. For leukemia only, we attempted to estimate the excess relative risk per unit dose of radiation, which, with reservations because of its wide confidence interval, was within the range of variation of the risks reported in other radiation epidemiological studies. This population must be studied for a longer time and with a consideration of the possible effects of confounding factors.

Epidemiology and primary prevention of thyroid cancer

The purpose of this review is to provide an account of our present knowledge about the epidemiology of nonmedullary thyroid carcinoma, to discuss the effects of environment, lifestyle and radiation on the risk of developing thyroid cancer, and to discuss aspects on primary prevention of the disease. In areas not associated with nuclear fallout, the annual incidence of thyroid cancer ranges between 2.0-3.8 cases per 100,000 in women and 1.2-2.6 per 100,000 in men, women of childbearing age being at highest risk. Low figures are found in some European countries (Denmark, Holland, Slovakia) and high figures are found in Iceland and Hawaii. Differences in iodine intake may be one factor explaining the geographic variation, high iodine intake being associated with a slightly increased risk of developing thyroid cancer. In general, lifestyle factors have only a small effect on the risk of thyroid cancer, a possible protective effect of tobacco smoking has been recently reported. Because of the (small) increase in risk of thyroid cancer associated with iodination programs, these should be supervised, so that the population does not receive excess iodine. The thyroid gland is highly sensitive to radiation-induced oncogenesis. This is verified by numerous reports from survivors after Hiroshima and Nagasaki, the Nevada, Novaja Semlja and Marshal Island atmospheric tests, and the Chernobyl plant accident, as well as by investigations of earlier medical use of radiation for benign diseases in childhood. These reports are summarized in the review. There appears to be a dose-response relation for the risk of developing cancer after exposure to radioactive radioiodine. The thyroid gland of children is especially vulnerable to the carcinogenic action of ionizing radiation. Thus, the incidence of thyroid cancer in children in the Belarus area was less than 1 case per million per year before the Chernobyl accident, increasing to a peak exceeding 100 per million per year in certain areas after the accident. It is a social obligation of scientists to inform the public and politicians of these risks. All nuclear power plants should have a program in operation for stockpiling potassium iodide for distribution within 1-2 days after an accident.

The mortality and cancer morbidity experience of employees at the Chapelcross plant of British Nuclear Fuels plc, 1955-95

The results presented here are from the follow-up of the cohort of workers ever employed at the Chapelcross site of British Nuclear Fuels plc (BNFL) between 1955 and 1995. The study cohort consists of 2628 workers, 2249 of whom were male, who were first employed at the plant before 1 January 1996, and who have 63967 person-years of follow-up. The mean follow-up period is 24.3 years. The 2209 members of the cohort (84%) classified as radiation workers accumulated 185.1 person-sieverts of external radiation; their median cumulative dose was 39.1 mSv, and 95% of their cumulative doses were less than 339.3 mSv. The Chapelcross workers show the usual 'healthy worker' effect. To the end of 1995, there were 528 deaths among the total cohort (20%), including 449 (20%) amongst the radiation workers. When the dose was unlagged, a statistically significant association was noted between cancer registrations of the buccal cavity and pharynx and dose, based on five cases. When the dose was lagged by 10 years, a statistically significant excess relative risk was noted between all cancer morbidity and dose, 1.80 Sv(-1) (0.03 to 4.45), based on 162 cases. This result is driven by the non-significant, but high excess relative risk estimates from the 12 prostatic cancer registrations. A statistically significant association is noted between the eight deaths amongst radiation workers who had prostatic cancer as the underlying cause of mortality and cumulative external radiation dose when the dose was lagged by 0, 2 and 10 years. The association is unlikely to be causal. The finding has little biological plausibility as the strength of the association weakened as the dose lagging increased; it was strongest when the dose was unlagged and disappeared when the dose was lagged by 20 years. None of the workers who was registered for or died from prostatic cancer had ever been monitored for exposure to tritium or to 51Cr, 59Fe, 60Co or 65Zn. There is no evidence to date amongst the Chapelcross cohort of increased risk for cancers considered to be radiogenic based on studies of populations exposed to high levels of radiation.

Radiation risk estimates in the beginning of the 21st century

In the early years of the 21st century, results from a number of epidemiologic studies of populations with specific ionizing radiation exposures will become available. These include populations with accidental exposures in the former Soviet Union and elsewhere and populations with occupational exposures from routine operations of nuclear power plants. The strengths and limitations of these studies are reviewed together with the radiation protection questions they may answer. Many of these studies will provide specific information to complement the atomic-bomb survivor studies, particularly the effects of dose-rate and exposure protraction, modifiers of radiation risks (both environmental and host factors), and different types of radiation. These studies will therefore be important as a test of the adequacy of the current scientific bases for the radiation protection of workers and the general public. An example is thyroid cancer risk in young children following the Chernobyl accident, which has brought attention to a very high sensitivity of very young children that was difficult to assess on the basis of atomic-bomb data alone. Radiation protection will also benefit from formal comparisons and combined analyses of data from populations with different exposure patterns and exposures. Finally, future epidemiological studies will be most valuable if they are well focused, designed specifically to answer outstanding radiation protection questions. An integrated approach based on epidemiology and mechanistic studies, in which epidemiologic studies are designed to test specific mechanistic hypotheses and realistic mechanistic models are used for the analysis of epidemiological data, will probably be the most fruitful for radiation protection.

The mortality and cancer morbidity experience of workers at the Capenhurst uranium enrichment facility 1946-95

The results presented here contain the follow-up of the cohort of workers ever employed at the Capenhurst site of British Nuclear Fuels plc or its predecessors between 1946 and 1995. The main activity of the plant is isotopic, 235U, enrichment of uranium. The study cohort consists of 12,540 employees and contains 334,473 person-years of follow up. This is a relatively mature cohort, with a mean follow-up period of 26.7 years, that has been exposed to low levels of radiation. The collective external radiation dose received by the 3244 radiation workers was 31.95 person-sieverts, with mean cumulative dose 9.85 mSv. To the end of 1995 there have been 3841 deaths recorded for this cohort, 585 of which were amongst radiation workers. The standardised mortality ratios (SMRs) for all causes were significantly low, 83 and 91 respectively, for radiation and non-radiation workers, indicating the usual 'healthy worker' effect. The cancer mortality was less than that expected, though not significantly so, with SMRs for all cancers of 88 and 97, for radiation and non-radiation workers respectively. The cancer registration rates were significantly low, with standardised registration ratios (SRRs) for all cancers of 82 and 88, for radiation and non-radiation workers respectively. An association between bladder cancer registrations and cumulative external radiation exposure was noted when the cumulative external dose was lagged by 20 years.

Mortality and cancer registration experience of the Sellafield employees known to have been involved in the 1957 Windscale accident

The mortality and cancer morbidity experience of the 470 male Sellafield employees known to be involved in the 1957 Windscale accident is reported. All these employees are known to have been involved in dealing with the fire itself, or in the clean-up operation afterwards. The size of the study population is small, leading to predicted low power to reveal any effects, but the cohort is of interest because of the involvement of the workers in the accident. For 1957-97, using rates for England and Wales to calculate the expected numbers, the all causes standardised mortality ratio (SMR) is 100 (observed = 258, expected = 258.80), and the all malignant neoplasms SMR is 79 (observed = 58, expected = 73.12) which is not significantly different from 100. For 1971-91, the all malignant neoplasms standardised registration ratio (SRR) of 85 (observed = 59, expected = 69.23) is not significantly different from 100. Significant excesses of deaths from diseases of the circulatory system (SMR = 121) and from ischaemic heart disease (SMR = 128), and a significant deficit of deaths from cancer of the genito-urinary organs (SMR = 31), were found. There were no significant differences in mortality rates between workers who had received high recorded external doses during the fire and those who had received low doses, though the power of this comparison was low. Comparison of the mortality rates of workers directly involved in the accident with workers in post, but not so involved, showed no significant differences. This study has been unable to detect any effect of the 1957 fire upon the mortality and cancer morbidity experience of those workers involved in it.

The assessment of organ doses from plutonium for an epidemiological study of the Sellafield workforce

An epidemiological study of mortality and cancer rates in plutonium workers at the Sellafield nuclear installation has been carried out by researchers at the London School of Hygiene and Tropical Medicine. The study required the assessment of organ-specific doses from plutonium for more than 5000 workers over a period of 40 years. This was a major undertaking as it involved the reconstruction of annual received doses from the results of some 223,000 urine samples that had been provided by the workers in the study. This paper outlines the techniques and strategies adopted in order to generate best estimates of dose from the available data, and presents summaries of these doses.

The mortality and cancer morbidity experience of workers at the Springfields uranium production facility, 1946-95

The results presented here are from the follow-up of the cohort of workers ever employed at the Springfields site of British Nuclear Fuels plc (BNFL) between 1946 and 1995. The main activity of the site is uranium fuel fabrication and uranium hexafluoride production. The study cohort consists of 19454 current and former employees, 13 960 of which were classified as radiation workers, and contains 479146 person-years of follow-up. The mean follow-up period is 24.6 years. To the end of 1995 there have been 4832 deaths recorded for this cohort, 3476 of which were amongst radiation workers and 1356 were amongst non-radiation workers. The standardised mortality ratios (SMRs) for all causes were 84 and 98 for radiation workers and non-radiation workers respectively. For all cancers the SMRs were 86 and 96 respectively. For cancer morbidity the standardised registration ratios (SRRs) for all cancers were 81 and 81 respectively. Significant associations were noted for both mortality and morbidity due to Hodgkin's disease and cumulative external dose. A strong association was also noted for morbidity, but not mortality, due to non-Hodgkin's lymphoma. These associations, however, are unlikely to be causal. The excess relative risk estimates for cancer other than leukaemia and for leukaemia excluding chronic lymphatic leukaemia are consistent with other occupationally exposed cohorts and estimates from the high-dose studies.

A case control study of multiple myeloma at four nuclear facilities

PURPOSE

Reported elevations of multiple myeloma among nuclear workers exposed to external penetrating ionizing radiation, based on small numbers of cases, prompted this multi-facility study of workers at US Department of Energy facilities.

METHODS

Ninety-eight multiple myeloma deaths and 391 age-matched controls were selected from the combined roster of 115,143 workers hired before 1979 at Hanford, Los Alamos National Laboratory, Oak Ridge National Laboratory, and the Savannah River site. These workers were followed for vital status through 1990 (1986 for Hanford). Demographic, work history, and occupational exposure data were derived from personnel, occupational medicine, industrial hygiene, and health physics records. Exposure-disease associations were evaluated using conditional logistic regression.

RESULTS

Cases were disproportionately African American, male, and hired prior to 1948. Lifetime cumulative whole body ionizing radiation dose was not associated with multiple myeloma, however, there was a significant effect of age at exposure, with positive associations between multiple myeloma and doses received at older ages. Dose response associations increased in magnitude with exposure age (from 40 to 50) and lag assumption (from 5 to 15 years), while a likelihood ratio goodness of fit test reached the highest value for cumulative doses received at ages above 45 with a 5-year lag (X2=5.43,1 df; relative risk = 6.9% per 10 mSv). Dose response associations persisted with adjustment for potential confounders.

CONCLUSIONS

Multiple myeloma was associated with low level whole body penetrating ionizing radiation doses at older ages. The exposure age effect is at odds with interpretations of A-bomb survivor studies but in agreement with several studies of cancer among nuclear workers.

Nuclear industry family study:methods and description of a United Kingdom study linking occupational information held by employers to reproduction and child health

OBJECTIVE

To describe the methods used in the nuclear industry family study for which a comprehensive database has been assembled that links employment in the nuclear industry and dosimetry records to information on employees' reproductive health and the health of their children. To discuss the response rates and characteristics of the study population.

METHODS

Occupational cohort design leading to a retrospective cohort study of reproductive outcomes reported by 46 396 current and former employees of both sexes in the nuclear industry. Employees of nuclear establishments in the United Kingdom operated by the Atomic Energy Authority, the Atomic Weapons Establishment, and British Nuclear Fuels were surveyed with postal questionnaires ot collect information on pregnancies, children,and periods of infertility. Information on employment and monitoring for ionising radiation was supplied by the employing nuclear authority and was linked to pregnancies and periods of infertility with unique personal identification numbers.

RESULTS

The design and completion of this study resulted in high quality data on a representative population of the Atomic Energy Authority, Atomic Weapons Establishment, and British Nuclear Fuels workforces. The response to the survey was extremely good (82% for male workers and 88% for female workers, excluding undelivered questionnaires), and a unique relational database has been created which will enable infertility, pregnancy, and child health outcomes to be examined with respect to the employment and radiation monitoring characteristics of parents.

CONCLUSION

This is the first United Kingdom study to link detailed reproductive history data to occupational information held by employers. The methods developed for the study were found to be feasible and successful. The design can be adapted for other investigations of reproductive hazards to men and women in the workplace and is currently in use to survey over 100 000 armed forces personnel in an investigation of reproductive outcome among veterans of the Gulf war.

Cancer in children of nuclear industry employees: report on children aged under 25 years from nuclear industry family study

OBJECTIVE

To determine whether children of men and women occupationally exposed to ionising radiation are at increased risk of developing leukaemia or other cancers before their 25th birthday.

DESIGN

Cohort study of children of nuclear industry employees.

SETTING

Nuclear establishments operated by the Atomic Energy Authority, Atomic Weapons Establishment, and British Nuclear Fuels.

SUBJECTS

39 557 children of male employees and 8883 children of female employees.

MAIN OUTCOME MEASURES

Cancer incidence in offspring reported by parents. Employment and radiation monitoring data (including annual external dose) supplied by the nuclear authorities.

RESULTS

111 cancers were reported, of which 28 were leukaemia. The estimated standardised incidence ratios for children of male and female employees who were born in 1965 or later were 98 (95% confidence interval 73 to 129) and 96 (50 to 168) for all malignancies and 109 (61 to 180) and 95 (20 to 277) for leukaemia. The leukaemia rate in children whose fathers had accumulated a preconceptual dose of >/=100 mSv was 5.8 times that in children conceived before their fathers' employment in the nuclear industry (95% confidence interval 1.3 to 24.8) but this was based on only three exposed cases. Two of these cases were included in the west Cumbrian ("Gardner") case-control study. No significant trends were found between increasing dose and leukaemia.

CONCLUSIONS

Cancer in young people is rare, and our results are based on small numbers of events. Overall, the findings suggest that the incidence of cancer and leukaemia among children of nuclear industry employees is similar to that in the general population. The possibility that exposure of fathers to relatively high doses of ionising radiation before their child's conception might be related to an increased risk of leukaemia in their offspring could not be disproved, but this result was based on only three cases, two of which have been previously reported. High conceptual doses are rare, and even if the occupational association were causal, the number of leukaemias involved would be small; in this study of over 46 000 children, fewer than three leukaemias could potentially be attributed to such an exposure.

Cancer mortality and morbidity among plutonium workers at the Sellafield plant of British Nuclear Fuels

The mortality of all 14 319 workers employed at the Sellafield plant of British Nuclear Fuels between 1947 and 1975 was studied up to the end of 1992, and cancer incidence was examined from 1971 to 1986, in relation to their exposures to plutonium and to external radiation. The cancer mortality rate was 5% lower than that of England and Wales and 3% less than that of Cumbria. The significant excesses of deaths from cancer of the pleura and thyroid found in an earlier study persist with further follow-up (14 observed, 4.0 expected for pleura; 6 observed, 2.2 expected for thyroid). All of the deaths from pleural cancer were among radiation workers. For neither site was there a significant association between the risk of the cancer and accumulated radiation dose. There were significant deficits of deaths from cancers of mouth and pharynx, liver and gall bladder, and larynx and leukaemia when compared with the national rates. Among all radiation workers, there was a significant positive association between accumulated external radiation dose and mortality from cancers of ill-defined and secondary sites (10-year lag, P = 0.04), leukaemia (no lag, P = 0.03; 2-year lag, P = 0.05), multiple myeloma (20-year lag, P = 0.02), all lymphatic and haematopoietic cancers (20-year lag, P= 0.03) and all causes of death combined (20-year lag, P= 0.008). Among plutonium workers, there were significant excesses of deaths from cancer of the breast (6 observed, 2.6 expected) and ill-defined and secondary cancers (29 observed, 20.1 expected). No significant positive trends were observed between the risk of deaths from cancers of any specific site, or all cancers combined, and cumulative plutonium and external radiation doses. For no cancer site was there a significant excess of cancer registrations compared with rates for England and Wales. Analysis of trends in cancer incidence showed significant increases in risk with cumulative plutonium plus external radiation doses for all lymphatic and haematopoietic neoplasms for 0-, 10- and 20-year lag periods. Taken as a whole, our findings do not suggest that workers at Sellafield who have been exposed to plutonium are at an overall significantly increased risk of cancer compared with other radiation workers.

Occupational radiation exposure and mortality: second analysis of the National Registry for Radiation Workers

The National Registry for Radiation Workers (NRRW) is the largest epidemiological study of UK radiation workers. Following the first analysis published in 1992, a second analysis has been conducted using an enlarged cohort of 124,743 workers, updated dosimetry and personal data for some workers, and a longer follow-up. Overall levels of mortality were found to be less than those expected from national rates; the standardised mortality ratio for all causes was 82, increasing to 89 after adjusting for social class. This 'healthy worker effect' was particularly strong for lung cancer and for some smoking-related non-malignant diseases. Analysis of potential radiation effects involved testing for any trend in mortality risk with external dose, after adjusting for likely confounding factors. For leukaemia, excluding chronic lymphatic leukaemia (CLL), the central estimate of excess relative risk (ERR) per Sv was similar to that estimated for the Japanese atomic bomb survivors at low doses (without the incorporation of a dose-rate correction factor); the corresponding 90% confidence limits for this trend were tighter than in the first analysis, ranging from just under four times the risk estimated at low doses from the Japanese atomic bomb survivors to about zero. For the grouping of all malignancies other than leukaemia, the central estimate of the trend in risk with dose was closer to zero than in the first analysis; also, the 90% confidence limits were tighter than before and included zero. Since results for lung cancer and non-malignant smoking-related diseases suggested the possibility of confounding by smoking, an examination was made, as in the first analysis, of all malignancies other than leukaemia and lung cancer. In this instance the central estimate of the ERR per Sv was similar to that from the A-bomb data (without the incorporation of a dose-rate correction factor), with a 90% confidence interval ranging from about four times the A-bomb value to less than zero. For multiple myeloma there was an indication of an increasing trend in risk with external dose (p = 0.06), although the evidence for this trend disappeared after omitting workers monitored for exposure to internal emitters. The second NRRW analysis provides stronger inferences than the first on occupational radiation exposure and cancer mortality; the 90% confidence intervals for the risk per unit dose are tighter than before, and now exclude values which are greater than four times those seen among the Japanese A-bomb survivors, although they are also generally consistent with an observation of no raised risk. Furthermore, there is evidence, of borderline statistical significance, of an increasing risk for leukaemia excluding CLL, and, as with solid cancers, the data are consistent with the A-bomb findings.

Cancer mortality in relation to monitoring for radionuclide exposure in three UK nuclear industry workforces

Cancer mortality in 40,761 employees of three UK nuclear industry facilities who had been monitored for external radiation exposure was examined according to whether they had also been monitored for possible internal exposure to tritium, plutonium or other radionuclides (uranium, polonium, actinium or other unspecified). Death rates from cancer were compared both with national rates and with rates in radiation workers not monitored for exposure to any radionuclides. Among workers monitored for tritium exposure, overall cancer mortality was significantly below national rates [standardized mortality ratio (SMR) = 83, 165 deaths; 2P = 0.02] and none of the cancer-specific death rates was significantly above either the national average or rates in non-monitored workers. Although the overall death rate from cancer in workers monitored for plutonium exposure was also significantly low relative to national rates (SMR = 89, 581 deaths; 2P = 0.005), mortality from pleural cancer was significantly raised (SMR = 357, nine deaths; 2P = 0.002); none of the rates differed significantly from those of non-monitored workers. Workers monitored for radionuclides other than tritium or plutonium also had a death rate from all cancers combined that was below the national average (SMR = 86, 418 deaths; 2P = 0.002) but prostatic cancer mortality was raised both in relation to death rates in the general population (SMR = 153, 37 deaths; 2P = 0.02) and to death rates in radiation workers who had not been monitored for exposure to any radionuclide [rate ratio (RR) = 1.65; 2P = 0.03]. Mortality from cancer of the lung was also significantly increased in workers monitored for other radionuclides compared with those of radiation workers not monitored for exposure to radionuclides (RR = 1.31, 164 deaths; 2P = 0.01). For cancers of the lung, prostate and all cancers combined, death rates in monitored workers were examined according to the timing and duration of monitoring for radionuclide exposure, with rates of radiation workers not monitored for any radionuclide forming the comparison group. In tritium-monitored workers, RRs for prostatic cancer varied significantly according to the number of years in which they were monitored (2P = 0.03). In workers monitored for plutonium exposure, RRs for all cancers combined increased with the number of years in which they were monitored (2P = 0.04) and with the number of years since first monitoring (2P = 0.0003). There was little suggestion of systematic variation in RRs for workers monitored for other radionuclides in relation to the timing or duration of monitoring, nor did it appear that their raised rates of cancer of the lung and prostate were explained by external radiation dose. These analyses of cancer mortality in relation to monitoring for radionuclide exposure reported in a large cohort of nuclear industry workers suggest that certain patterns of monitoring for some radionuclides may be associated with higher death rates from cancers of the lung, pleura, prostate and all cancers combined. Some of these findings may be due to chance. Moreover, because of the paucity of related data and lack of information about other possible exposures, such as whether plutonium workers are more likely to be exposed to asbestos, firm conclusions cannot be drawn at this stage. Further investigations of the relationship between radionuclide exposure and cancer in nuclear industry workers are needed.

Occupational exposure to ionising radiation and mortality among workers of the former Spanish Nuclear Energy Board

OBJECTIVES

Firstly, to ascertain whether mortality among workers of the former Spanish Nuclear Energy Board (Junta de Energía Nuclear-JEN) was higher than that for the Spanish population overall; and secondly, if this were so, to ascertain whether this difference was associated with exposure to ionising radiation.

METHODS

A retrospective follow up of a cohort of 5657 workers was carried out for the period 1954-92. Cohort mortality was compared with that for the Spanish population overall, with standardised mortality ratios (SMRs) adjusted for sex, age, and calendar period. Also, Poisson models were used to analyse mortality from lung cancer in the cohort by level of exposure to ionising radiation.

RESULTS

Workers' median and mean cumulative exposures were 4.04 and 11.42 mSv, respectively. Mean annual exposure was 1.33 mSv. Excess mortality due to bone tumours was found for the cohort as a whole (six deaths observed; SMR 2.95; 95% confidence interval (95% CI) 1.08 to 6.43). Among miners, excess mortality was found for non-malignant respiratory diseases (SMR 2.94; 95% CI 2.27 to 3.75), and for lung cancer bordering on statistical significance (SMR 1.50; 95% CI 0.96 to 2.23; P = 0.055). Relative risks of dying of lung cancer from ionising radiation in the dose quartiles 2, 3, and 4 versus the lowest dose quartile, were 1.00, 1.64, and 0.94, respectively.

CONCLUSIONS

Excess mortality from lung cancer was found among JEN miners. Nevertheless, no clear relation was found between mortality from lung cancer and level of exposure to ionising radiation in the JEN cohort. Continued follow up of the cohort is required to confirm excess mortality from bone tumours.

Epidemiology of accidental radiation exposures

Much of the information on the health effects of radiation exposure available to date comes from long-term studies of the atomic bombings in Hiroshima and Nagasaki. Accidental exposures, such as those resulting from the Chernobyl and Kyshtym accidents, have as yet provided little information concerning health effects of ionizing radiation. This paper will present the current state of our knowledge concerning radiation effects, review major large-scale accidental radiation exposures, and discuss information that could be obtained from studies of accidental exposures and the types of studies that are needed.