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.

Mortality experience of male workers at a UK tin smelter.

BACKGROUND: Between 1937 and 1991, Capper Pass and Sons Limited operated a tin smelter complex in North Humberside, UK, at which employees were potentially exposed to a number of substances, including lead, arsenic, cadmium and natural series radionuclides. Decommissioning and site clearance continued until 1995. Between 1967 and 1995 the company was a subsidiary of Rio Tinto plc. AIMS: The aim was to identify any significant excess, or deficits, in mortality among former employees that might be attributable to factors associated with occupation. METHODS: We defined a cohort of 1462 males who had been employed for at least 12 months between 1/11/1967 and 28/7/1995, followed-up through to 31/12/2001. The mortality of the cohort was compared against that expected for both national and regional populations. RESULTS: Mortality from all causes and all cancers did not differ from that expected. Mortality from ischaemic heart disease showed a deficit and mortality from lung cancer showed a statistically significant excess. Mortality from smoking related diseases other than lung cancer showed a non-significant deficit. CONCLUSIONS: The pattern of lung cancer mortality is consistent with the hypothesis that the risk of lung cancer has been enhanced by occupational exposure to one or more carcinogens, the effect of which diminishes with time since exposure. The deficit in ischaemic heart disease may be attributed to a protective effect from manual labour. The results provide no evidence for attribution of other excess or deficits in mortality to factors associated with employment.

Occupational exposure to ionizing radiation has no effect on T- and B-cell total counts or percentages of helper, cytotoxic and activated T-cell subsets in the peripheral circulation of male radiation workers.

PURPOSE: To investigate changes in immune cell subsets in the peripheral circulation of a male population occupationally exposed to ionizing radiation. MATERIALS AND METHODS: Peripheral blood samples were taken from 194 male workers with cumulative exposures of >200 mSv (mean exposure 331.5 mSv, mean age 51 years) and from a reference population of 131 male workers with cumulative exposures of <27.5 mSv (mean exposure 13.9 mSv, mean age 47 years). Samples were analysed by flow cytometry for T- and B-cell total counts and for the T-cell subset percentages of CD4+ (helper T-cells), CD8+ (cytotoxic T-cells) and CD3+/HLA-DR+ (activated T-cells). RESULTS: Comparison of the >200 and <27.5 mSv exposure groups using linear regression analysis showed no statistically significant differences between the two groups for T-cell total count, B-cell total count or for percentages of the T-cell subsets CD4+, CD8+ or CD3+/HLA-DR+ and CD4+:CD8+. However, statistically significant increases in both T- and B-cell total counts were observed within the two exposure groups and data pooled from both groups when non-smokers (never and ex-smokers) were compared with current smokers. For pooled data T-cell total count increased in smokers by 35% (p=0.0001) and B-cell total count increased by 37% (p=0.0004). CONCLUSIONS: No significant immunological effects were observed in male radiation workers with cumulative exposures of >200 mSv when compared with a reference population with cumulative exposures of <27.5 mSv, although highly significant increases in both T- and B-cell total counts were observed in smokers compared with non-smokers.

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.

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.

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 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.

Additive isotonic regression models in epidemiology.

Stone's method for assessing disease risk around a point source through isotonic regression is routinely used in spatial epidemiology. It is useful in situations where the relationship of risk with exposure (distance being commonly used as a surrogate variable) is assumed monotonic but otherwise of unknown form. This paper extends this method to non-spatial epidemiology, where typically two or more risk factors are present. The methodology described is based on the additive isotonic model approach of Bacchetti; versions appropriate to count (Poisson) data and case-control (binomial) data are described. In both cases, adjustment for covariates is incorporated, and a Monte Carlo method of hypothesis testing and interval estimation is presented. The methodology is illustrated through a case-control example concerning the analysis of the possible effect of preconceptional external ionizing radiation doses on the sex ratio at birth among children of fathers working at the Sellafield nuclear installation, Cumbria, U.K.

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.

The sex ratio of children in relation to paternal preconceptional radiation dose: a study in Cumbria, northern England.

STUDY OBJECTIVE: To investigate whether the occupational exposure to external ionising radiation of men employed at the Sellafield nuclear installation, West Cumbria, affects the sex of the children they subsequently father. DESIGN: A retrospective cohort study using logistic regression to analyse the sex ratio, in particular in relation to paternal preconceptional irradiation. SETTING AND PARTICIPANTS: The 260,060 singleton births between 1950 and 1989 to mothers resident in Cumbria, north west England. RESULTS: The sex ratio among children of men employed at any time at Sellafield was 1.094 (95% CI: 1.060, 1.128), significantly higher than that among other Cumbrian children, 1.055 (95% CI: 1.046, 1.063). There was an increased sex ratio of 1.396 (95% CI: 1.127, 1.729) in the 345 children whose fathers were estimated from annual dose summaries to have received more than 10 mSv of external radiation in the 90 days preceding conception, but no significant linear trend between sex ratio and 90 day paternal preconceptional dose was found. There was no significant association between sex ratio and the external dose accumulated before the 90 day period preceding conception. CONCLUSIONS: Men employed at Sellafield fathered a greater proportion of boys than would be expected for a Cumbrian population, which may be partly explained by their younger age distribution. A greater effect was observed in the fathers with recorded doses exceeding 10 mSv in the 90 days before conception. While this may reflect a true statistical association, it is also possible that it may be a chance finding due to imprecision in the dose estimates and consequent misclassification.

Shiftwork and mortality from ischaemic heart disease.

OBJECTIVES: To investigate the relation between shift work and death from ischaemic heart disease (IHD). METHODS: A nested case-control approach was used. The cohort comprised male manual workers who joined an industrial company aged 50 years or under between 1 January 1950 and 31 December 1992 and worked there for at least one month. Cases were 467 cohort members who died during the same period aged 75 years or under, with ischaemic heart disease (IHD) (international classification of diseases (ICD) 410-414) coded from the death certificate. For each case a control worker was chosen, who joined the company at the same age and in the same period but who survived the case. Work status (shift work or day work) was assigned to cases for their entire employment and to controls for that part of their employment which preceded the matching case's death. The main source of information was historical personnel records containing pay codes which differed for day work and shift work. Information on weight, height, blood pressure, and smoking from a pre-employment medical was available. RESULTS: Two thirds of subjects had been employed for at least one month as shift workers and there was evidence that they had slightly better health at recruitment than day workers. The odds ratio for shift workers during the period starting 10 years after shift work began, and after adjustment for height, body mass index, blood pressure, smoking, duration of employment, and job status (skilled or unskilled) was 0.90 (90% confidence interval (90% CI): 0.68-1.21). There was no relation between risk of IHD death, and duration of shift work, but there was evidence of a reduced risk when actively employed as a shift worker, together with an increased risk in the first five years after leaving shift work to do day work. CONCLUSIONS: Shift work did not increase the risk of death from ischaemic heart disease in this study. Those workers with poorer cardiovascular health may be under represented in groups with longer shift work experience because of health related selection out of shift work.

Geographical distribution of preconceptional radiation doses to fathers employed at the Sellafield nuclear installation, West Cumbria.

OBJECTIVE: To examine whether the geographical distribution of births associated with preconceptional exposure of fathers to radiation at the Sellafield nuclear installation is consistent with the suggestion that this exposure explains the excess of childhood lymphoid malignancy in the adjacent village of Seascale. DESIGN: Retrospective birth cohort study. SETTING: Cumbria, West Cumbria health district, and Seascale civil parish. SUBJECTS: The 10,363 children born in Cumbria during 1950-89 to fathers employed at Sellafield. MAIN OUTCOME MEASURES: The doses of external whole body ionising radiation received by fathers at Sellafield in the total time and in the six months before conception of their children; the proportions of the collective doses associated with Seascale and the rest of West Cumbria. RESULTS: 9256 children were born to fathers who had been exposed to radiation before the child's conception. Of these, 7318 had fathers who were exposed in the six months before conception. Overall 7% (38 person-Sv) of the collective total preconceptional dose and 7% (3 person-Sv) of the collective dose for the six months before conception were associated with children born in Seascale. Of all the children whose fathers worked at Sellafield, 842 (8%) were born in Seascale. The mean individual doses before conception were consistently lower in Seascale than in the rest of West Cumbria. CONCLUSIONS: The distribution of the paternal preconceptional radiation dose is statistically incompatible with this exposure providing a causal explanation for the cluster of childhood leukaemias in Seascale.