Mortality from multiple sclerosis and exposure to residential and occupational solar radiation: a case-control study based on death certificates

OBJECTIVES—To explore whether mortality from multiple sclerosis is negatively associated with exposure to sunlight.
METHODS—Two case-control studies based on death certificates were conducted for mortality from multiple sclerosis and non-melanoma skin cancer (as a positive control) to examine associations with residential and occupational exposure to sunlight. Cases were all deaths from multiple sclerosis between 1984 and 1995 in 24 states of the United States. Controls, which were age frequency matched to a series of cases, excluded cancer and certain neurological deaths. The effects of occupational exposure to sunlight were assessed among subjects with usual occupations requiring substantial activity, so as to exclude those whose indoor jobs resulted from disabilities subsequent to the onset of the disease. Multiple logistic regression analyses were applied, with adjustment for age, sex, race, and socioeconomic status.
RESULTS—Unlike mortality from skin cancer, mortality from multiple sclerosis was negatively associated with residential exposure to sunlight (odds ratio (OR)=0.53 (multiple sclerosis) and OR=1.24 (skin cancer)). Odds ratios for the highest occupational exposure to sunlight were 0.74 (95% confidence interval (95% CI) 0.61 to 0.89) for mortality from multiple sclerosis, compared with 1.21 (1.09 to 1.34) for mortality from non-melanoma skin cancer. The OR was 0.24 for the combined effect of the highest levels of residential and occupational exposure to sunlight on multiple sclerosis, compared with an OR of 1.38 for skin cancer.
CONCLUSIONS—In this exploratory study, mortality from multiple sclerosis, unlike mortality from skin cancer, was negatively associated with both residential and occupational exposure to sunlight.


Keywords: multiple sclerosis; aetiology; latitude; ultraviolet radiation; sunlight; occupation; residence; skin cancer     

Updated mortality among diverse operating segments of a petroleum company

OBJECTIVES—To update mortality for 34 560 employees from diverse operating segments of a Canadian petroleum company; and to investigate potential relations with occupational factors.
METHODS—Employees from 1964-83 were linked to the Canadian mortality data base to provide 11 years additional follow up. There were 6760 deaths and 750 683 person-years of follow up compared with 3909 and 428 190, respectively, in the earlier study. Analyses used standardised mortality ratios (SMRs) to compare worker cause specific mortality with the Canadian general population. Duration of employment and latency analyses were performed for causes previously found to be increased in this and other petroleum cohorts, as well as any findings of interest.
RESULTS—For the period 1964-94, employees experienced significantly low overall mortality (SMR=0.86 men, SMR=0.80 women). Kidney cancer, which has been increased in some studies of petroleum workers, was not increased. Acute non-lymphocytic leukaemia in exposed operating segments was consistent with the expected or only slightly, non-significantly increased. The most notable finding was increased deaths from mesothelioma among refinery and petrochemical workers (SMR 8.68; 95% confidence interval (95% CI) 5.51 to 13.03), most of whom were long term employees in jobs with presumed exposure to asbestos (mechanical and pipefitters). Deaths from multiple myeloma among marketing and distribution workers, which were previously increased, remained increased (SMR 2.08; 95% CI 0.95 to 3.95) in the update period 1984-94; however, there was no clear pattern by duration of employment or latency. Aortic aneurysms, which also were previously significantly increased among marketing and distribution workers approached the expected in the update period (SMR 1.18; 95% CI 0.65-1.98). Analyses by duration of employment showed suggestive trends for aortic aneurysms, but earlier studies of this cohort have not found a relation between aortic aneurysms and exposure to hydrocarbons.
CONCLUSION—The additional 2851 deaths and 322 493 person-years of follow up strengthened the assessment of mortality patterns relative to occupational factors. With the exception of mesothelioma, no clear work related increases in disease were identified.


Keywords: epidemiology; occupational exposures; petroleum     

Update of a study of crude oil production workers 1946-94

OBJECTIVE—To update information on workers in the petroleum industry engaged in the production of crude oil to determine whether the patterns of mortality have changed with 14 additional years of follow up.
METHODS—All workers were employed at company production and pipeline locations sometime during 1946-94. The cohort now consists of 24 124 employees with an average of 22 years of follow up.
RESULTS—The overall mortality, and most cause specific mortalities were lower than or similar to those for the general United States population. For white men (81% of the cohort), there were 4361 observed deaths and 5945 expected, resulting in a significantly lower standardised mortality ratio (SMR) of 73. There were significant deficits for all the leading causes of death in the United States including all cancers, cancer of the lung, stroke, heart disease, respiratory disease, and accidents. Slightly increased mortality was found for cancer of the prostate, cancer of the brain and central nervous system, and cancer of other lymphatic tissue. For benign and unspecified neoplasms, the SMR was 152 (95% confidence interval (95% CI) 95 to 230). There was a significant increase for acute myelogenous leukaemia that was restricted to people who were first employed before 1940 and who were employed in production and pipeline jobs for >30 years. Overall mortality patterns for non-white men and women were similar to those for white men. Mortality patterns for white men were also examined by duration of employment, time first employed, and by job group.
CONCLUSIONS—The results of the updated study showed a favourable mortality experience for crude oil production workers compared with the United States population.


Keywords: petroleum industry; occupational cancer; mortality; crude oil     

Exposures and cancer incidence near oil fields in the Amazon basin of Ecuador

OBJECTIVES—To examine environmental exposure and incidence and mortality of cancer in the village of San Carlos surrounded by oil fields in the Amazon basin of Ecuador.
METHODS—Water samples of the local streams were analyzed for total petroleum hydrocarbons (TPHs). A preliminary list of potential cancer cases from 1989 to 1998 was prepared. Cases were compared with expected numbers of cancer morbidity and mortality registrations from a Quito reference population.
RESULTS—Water analysis showed severe exposure to TPHs by the residents. Ten patients with cancer were diagnosed while resident in the village of San Carlos. An overall excess for all types of cancer was found in the male population (8 observed v 3.5 expected) with a risk 2.26 times higher than expected (95% confidence interval (95% CI) 0.97 to 4.46). There was an overall excess of deaths for all types of cancer (6 v 1.6 expected) among the male population 3.6 times higher than the reference population (95% CI 1.31 to 7.81).
CONCLUSIONS—The observed excess of cancer might be associated with the pollution of the environment by toxic contaminants coming from the oil production.


Keywords: cancer; oil; Amazon; Ecuador     

Future trends in mortality of French men from mesothelioma

OBJECTIVES—Previous projections of mortality from mesothelioma among French men have used the age-generation method, based on the Poisson regression model. In this study an alternative method to model mortality from mesothelioma was used to predict its future trend: this method was based on the risk function that links this mortality to past exposure to asbestos, combined with population exposure data.
METHOD—Data on past French asbestos imports were used to model the overall past exposure to asbestos in men and assess two extreme scenarios (optimistic and pessimistic) for its future trends. The number of male deaths occurring between the ages of 50 and 79, from 1997-2050, was then calculated with the risk function for mesothelioma.
RESULTS—The results showed that mortality from mesothelioma among French men aged 50-79 will continue to increase, reaching a peak averaging between 1140 (optimistic scenario) and 1300 deaths (pessimistic scenario) annually around the years 2030 and 2040, respectively. No preventive measures applied now will affect this trend before then. These results are similar to those of two other predictions of mortality from mesothelioma among French men: a peak around 2030 of 800-1600 deaths annually among men aged 25-89 years, and a peak around 2020 of 1550 deaths annually among men aged 40-84.
CONCLUSIONS—Our results indicate that between 1997 and 2050, the most optimistic and pessimistic trends of future exposure will lead to the deaths from mesothelioma of between 44 480 and 57 020 men, with a corresponding loss of from 877 200 to 1 171 500 person-years of life.


Keywords: mesothelioma; risk function; mortality trends; prediction; France     

Study of two cohorts of workers exposed to methyl methacrylate in acrylic sheet production

OBJECTIVES—To study mortality among 4324 workers at two United Kingdom factories, Darwen, Lancashire and Wilton, Cleveland, producing polymethyl methacrylate (PMMA) sheet. The Darwen factory is still active, but the Wilton one was closed in 1970. Also, to investigate patterns of mortality after exposure to methyl methacrylate; in particular, mortality from colon and rectal cancer.
METHODS—All male employees at the Darwen factory with a record of employment in 1949-88 and all men ever employed at the Wilton factory (1949-70) were investigated. The vital status of both cohorts was ascertained on 31 December 1995. The exposure of 1526 subjects at the Darwen plant who were engaged from 1949 onwards could be characterised. The mean duration of exposure was 7.6 years at 13.2 ppm (8 hour time weighted average), although exposures in some work groups were as high as 100 ppm. It was not possible to calculate the cumulative exposure of workers first employed at the Darwen plant before 1949 or workers at the Wilton factory.
RESULTS—In the Darwen cohort, 622 deaths were identified and a further 700 deaths in the Wilton cohort. Mortalities for the cohort were compared with national and local rates and expressed as standardised mortality ratios (SMRs). In the subcohort of Darwen workers with more than minimal exposure to MMA, reduced mortalities compared with national and local rates, were found for all causes (SMR 94), and colorectal cancer (SMR 92), but mortality from all cancers was slightly increased (SMR 104). No relations were found with cumulative exposure to MMA. In the subcohort of Wilton workers, mortality from all causes of death was significantly reduced (SMR 89), but mortality from all cancers (SMR 103) and colorectal cancer (SMR 124) were increased. The excess of colorectal cancer was confined to employees with less than 1 year of employment.
CONCLUSION—The study provided no clear evidence that employment at the factories or exposure to MMA had adversely affected the mortalities of workers.


Keywords: methyl methacrylate; mortality     

Historical cohort study of 10 109 men in the North American vinyl chloride industry, 1942-72: update of cancer mortality to 31 December 1995

OBJECTIVES—To update and assess mortality from neoplasms to 31 December 1995 among 10 109 men employed in a job exposed to vinyl chloride for at least 1 year between 1942 and 1972 at any of 37 North American factories. Previous analyses indicated associations between employment in vinyl production and increased mortality risk from cancers of the liver and biliary tract, due to increased mortality from angiosarcoma of the liver, and brain cancer.
METHODS—Standardised mortality ratio (SMR) analyses, overall and stratified by several work related variables, were conducted with United States and state reference rates. Cox's proportional hazards models and stratified log rank tests were used to further assess occupational factors.
RESULTS—895 of 3191 deaths (28%) were from malignant neoplasms, 505 since the previous update to the end of 1982. Mortality from all causes showed a deficit (SMR 83, 95% confidence interval (95% CI) 80 to 86), whereas mortality from all cancers combined was similar to state referent rates. Mortality from cancers of the liver and biliary tract was clearly increased (SMR 359, 95% CI 284 to 446). Modest excesses of brain cancer (SMR 142, 95% CI 100 to 197) and cancer of connective and soft tissue (SMR 270, 95% CI 139 to 472) were found. Stratified SMR and Cox's proportional hazard analyses supported associations with age at first exposure, duration of exposure, and year of first exposure for cancers of the liver and soft tissues, but not the brain.
CONCLUSIONS—Excess mortality risk from cancer of the liver and biliary tract, largely due to angiosarcoma, continues. Risk of mortality from brain cancer has attenuated, but its relation with exposure to vinyl chloride remains unclear. A potentially work related excess of deaths from cancer of connective and soft tissue was found for the first time, but was based on few cancers of assorted histology.


Keywords: vinyl chloride; angiosarcoma; liver; brain; connective tissue; soft tissue; neoplasms     

Mortality and cancer incidence among Swedish lumberjacks exposed to phenoxy herbicides

OBJECTIVES—To determine mortality and cancer incidence relative to exposure to phenoxy herbicides.
METHODS—A cohort of Swedish lumberjacks of which 261 were exposed to phenoxy herbicides, and 250 were unexposed, was followed up for mortality from 1954 to 1994, and for cancer incidence from 1958 to 1992. The number of days of exposure to phenoxy herbicides was determined from pay slips. With the county population as a reference, standardised mortality ratios and cancer incidence ratios (SMR and SIR) were calculated.
RESULTS—Mortality and cancer incidence were low with two exceptions; a small but highly exposed group of foremen showed an increased cancer incidence (SIR 274, 95% confidence interval (95% CI) 100 to 596), and over all mortality (SMR 141, 95% CI 68 to 260). Of three cases of non-Hodgkin's lymphoma, two were found among the most exposed workers.
CONCLUSIONS—The results provide some support to claims of previous studies that exposure to phenoxy herbicides might be related to non-Hodgkin's lymphoma and to an increased overall cancer risk.


Keywords: phenoxy herbicides; lumberjacks; cancer     

Crystalline silica exposure and lung cancer mortality in diatomaceous earth industry workers: a quantitative risk assessment

OBJECTIVE—To use various exposure-response models to estimate the risk of mortality from lung cancer due to occupational exposure to respirable crystalline silica dust.
METHODS—Data from a cohort mortality study of 2342 white male California diatomaceous earth mining and processing workers exposed to crystalline silica dust (mainly cristobalite) were reanalyzed with Poisson regression and Cox's proportional hazards models. Internal and external adjustments were used to control for potential confounding from the effects of time since first observation, calendar time, age, and Hispanic ethnicity. Cubic smoothing spline models were used to assess the fit of the models. Exposures were lagged by 10 years. Evaluations of the fit of the models were performed by comparing their deviances. Lifetime risks of lung cancer were estimated up to age 85 with an actuarial approach that accounted for competing causes of death.
RESULTS—Exposure to respirable crystalline silica dust was a significant predictor (p<0.05) in nearly all of the models evaluated and the linear relative rate model with a 10 year exposure lag seemed to give the best fit in the Poisson regression analysis. For those who died of lung cancer the linear relative rate model predicted rate ratios for mortality from lung cancer of about 1.6 for the mean cumulative exposure to respirable silica compared with no exposure. The excess lifetime risk (to age 85) of mortality from lung cancer for white men exposed for 45 years and with a 10 year lag period at the current Occupational Safety and Health Administration (OSHA) standard of about 0.05 mg/m³ for respirable cristobalite dust is 19/1000 (95% confidence interval (95% CI) 5/1000 to 46/1000).
CONCLUSIONS—There was a significant risk of mortality from lung cancer that increased with cumulative exposure to respirable crystalline silica dust. The predicted number of deaths from lung cancer suggests that current occupational health standards may not be adequately protecting workers from the risk of lung cancer.


Keywords: crystalline silica; cristobalite; lung cancer     

Mortality from cancer and chronic respiratory diseases among workers who manufacture carbon electrodes

OBJECTIVES—To investigate the risk of cancer and non-neoplastic respiratory diseases among workers who manufacture carbon electrodes, as this industry entails exposure to mixtures of polycyclic aromatic hydrocarbons.
METHODS—A historical cohort study was carried out of 1006 male workers employed for at least 1 year between 1945 and 1971 in a carbon (graphite) electrode production plant in central Italy, who were followed up for mortality between 1955 and 1996. The ratio of observed to expected deaths (standardised mortality ratios, SMRs) was computed from both national and (for the period 1964-96) regional age and period specific mortalities. A multivariate Poisson regression analysis was performed to investigate the relative risk (RR) of death according to duration of employment and time since first employment in the factory.
RESULTS—A total of 424 workers had died, 538 were still alive, and 44 were lost to follow up. Mortalities from all causes, all cancers, and respiratory tract cancer were in line with the regional figure. An excess was found over the expected deaths from skin cancer including melanoma (SMR 3.16, 95% confidence interval (95% CI) 0.65 to 9.23) and from non-neoplastic respiratory diseases (SMR 1.58, 95% CI 1.16 to 2.11). Poisson regression analysis including age as a covariate showed an increased risk of dying from gastric cancer with increasing duration of employment, and an increase in the RR of dying from lung cancer and from non-neoplastic respiratory diseases with increasing time since first employment, although the linear trend was not significant.
CONCLUSION—This study supports previous findings that working in the carbon electrode manufacturing industry may not increase the risk of dying from respiratory cancer. However, a possible association with non-malignant respiratory diseases cannot be excluded.


Keywords: carbon electrode manufacturing; polycyclic aromatic hydrocarbons; historical cohort study     

Lung cancer mortality in a site producing hard metals

OBJECTIVES—To study the mortality from lung cancer from exposures to hard metal dust at an industrial site producing hard metals—pseudoalloys of cobalt and tungsten carbide—and other metallurgical products many of which contain cobalt.
METHODS—A historical cohort was set up of all subjects who had worked for at least 3 months on the site since its opening date in the late 1940s. A full job history could be obtained for 95% of the subjects. The cohort was followed up from January 1968 to December 1992. The exposure was assessed by an industry specific job exposure matrix (JEM) characterising exposure to hard metal dust from 1 to 9 and other possibly carcinogenic exposures as present or absent. Smoking information was obtained by interview of former workers. Standard lifetable methods and Poisson regression were used for the statistical analysis of the data.
RESULTS—Mortality from all causes was close to the expected (standardised mortality ratio (SMR) 1.02, 399 deaths) whereas mortality from lung cancer was significantly increased among men (SMR 1.70; 46 deaths, 95% confidence interval (95% CI) 1.24 to 2.26). By workshop, lung cancer mortality was significantly higher than expected in hard metal production before sintering (SMR 2.42; nine deaths; 95%CI 1.10 to 4.59) and among maintenance workers (SMR 2.56; 11 deaths; 95%CI 1.28 to 4.59), whereas after sintering the SMR was lower (SMR 1.28; five deaths; 95%CI 0.41 to 2.98). The SMR for all exposures to hard metal dust at a level >1 in the JEM was in significant excess (SMR 2.02; 26 deaths; 95%CI 1.32 to 2.96). The risks increased with exposure scores, duration of exposure, and cumulative dose reaching significance for duration of exposure to hard metal dust before sintering, after adjustment for smoking and known or suspected carcinogens.
CONCLUSION—Excess mortality from lung cancer was found among hard metal production workers which cannot be attributed to smoking alone. This excess occurred mostly in subjects exposed to unsintered hard metal dust.


Keywords: lung cancer; hard metals     

Occupational exposure to magnetic fields relative to mortality from brain tumours: updated and revised findings from a study of United Kingdom electricity generation and transmission workers, 1973-97

OBJECTIVE—To investigate whether risk of brain tumour is related to occupational exposure to magnetic fields.
METHODS—The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All workers were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calculations had been performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardisation (n=83 997) and Poisson regression (n=79 972).
RESULTS—Based on serial mortalities for England and Wales, deaths from brain cancer were close to expectation (observed 158, expected 146.4). No significant positive trends were shown for risks of brain tumours either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years.
CONCLUSIONS—There are no discernible excess risks of brain tumours as a consequence of occupational exposure to magnetic fields in United Kingdom electricity generation and transmission workers.


Keywords: magnetic fields; brain tumours; electricity generation and transmission; cohort mortality study     

Mortality from all cancers of asbestos factory workers in east London 1933-80

OBJECTIVE—To give the observed and expected deaths due to cancer at all separate sites in asbestos workers in east London, and to analyse these for overall effect and exposure-response trend.
METHODS—The mortality experience of a cohort of over 5000 men and women followed up for over 30 years since first exposure to asbestos has been extracted.
RESULTS—There was a large excess of deaths due to cancer (537 observed, 222 expected). Most of these were due to cancer of the lung (232 observed, 77 expected) and pleural (52) and peritoneal (48) mesothelioma. The exposure-response trend for all these three causes was highly significant. There was also an excess of cancer of the colon (27 observed, 15 expected) which was significantly related to exposure. There were significant excesses of cancer of the ovary, of the liver, and of the oesophagus but with no consistent relation to exposure.
CONCLUSIONS—The excess risk of cancer after exposure to asbestos was mainly due to cancer of the lung and mesothelioma. An exposure related excess of cancer of the colon was also detected but the possibility that some of these deaths may have been peritoneal mesotheliomas could not be excluded. There was no consistent evidence of exposure related excesses at any other site.


Keywords: asbestos; cancer; exposure-response     

Mortality surveillance and occupational hazards: the Solutia mortality experience 1980-94

OBJECTIVES—Several investigators argue that company wide mortalities for recent workers allow early identification of potential workplace hazards. Mortalities for recent workers were compared with published studies of workers with specific exposures in the same company to find whether mortality surveillance results could be used to identify previously unknown health effects from workplace hazards.
METHODS—Relative risks for causes of death in published substance specific studies at the plants were compared with the relative risks in the mortality surveillance of workers 20 or more years after first being employed.
RESULTS—As reported by other companies, low mortalities were found among workers in the mortality surveillance. The mortality surveillance reports often found no increased risk of disease at plants in which substance specific studies had found no effects. However, disease specific relative risks were not found by the mortality surveillance predictions of relative risks in the substance specific studies with increased risk.
CONCLUSION—Mortality surveillance is of limited use for identifying health effects from past workplace exposures to specific materials. The healthy worker and survivor effects, the failure to identify subsets of workers exposed to potentially toxic substances, the typically long induction period between exposure and disease, and the inability of recent mortality levels to reflect historical conditions all may make it difficult to use mortality surveillance to identify workplace hazards. Combining mortality surveillance with studies of workers with potentially toxic exposures helps identify occupational hazards.


Keywords: mortality surveillance; occupational cancer; bladder cancer; leukaemia     

A further cohort study of workers employed at a factory manufacturing chemicals for the rubber industry, with special reference to the chemicals 2-mercaptobenzothiazole (MBT), aniline, phenyl-beta-naphthylamine and o-toluidine

OBJECTIVES—To investigate mortality and cancer morbidity in workers from a factory manufacturing chemicals for the rubber industry.
METHODS—The mortality (1955-96) and cancer morbidity experience (1971-92) of a cohort of 2160 male production workers from a chemical factory in north Wales were investigated. All subjects had at least 6 months employment at the factory and some employment in the period 1955-84. Detailed job histories were abstracted from company computerised records and estimates of individual cumulative exposure to 2-mercaptobenzothiazole (MBT) and its derivatives were obtained, with a job exposure matrix derived by a former factory hygienist. Durations of employment in the aniline, phenyl-β-naphthylamine (PBN) and o-toluidine departments were also calculated. Two analytical approaches were used, indirect standardisation and Poisson regression.
RESULTS—Based on serial rates for the general population of England and Wales, observed mortality for the total cohort was close to expectation for all causes (observed (obs) deaths 1131, expected (exp) deaths 1114.5, standardised mortality ratio (SMR) 101), and for all cancers (obs 305, exp 300.2, SMR 102). There was a significant (p<0.05) excess mortality from cancer of the bladder in the 605 study subjects potentially exposed to one or more of the four chemicals being investigated (obs 9, exp 3.25, SMR 277, 95% confidence interval (95% CI) 127 to 526). This excess was dependent primarily on deaths occurring >20 years after first exposure in those who started employment before 1955 (obs 7, exp 1.25, SMR 560, 95% CI 225 to 1154, p<0.001). There were 30 subjects in the total study cohort who, on the basis of death certificates or cancer registration particulars, had had malignant bladder cancer. In separate analyses of the four exposure history variables (after adjustment for age), Poisson regression showed significant positive trends for risk of notification of bladder cancer increasing with cumulative duration of employment in the PBN (p<0.001) and o-toluidine departments (p<0.01); similar findings were not obtained for cumulative exposure to MBT or for duration of employment in the aniline department. In a simultaneous analysis of all four chemical exposure variables, a significant positive trend remained for duration of employment with exposure to PBN (p<0.05). Further analyses of all cases of bladder cancer (malignant and benign diagnoses) used employment histories lagged by 15 years; similar findings were obtained.
CONCLUSIONS—It seems likely that some members of this cohort have had occupational bladder cancer. Confident interpretation is difficult because of small numbers in the exposed subcohorts, relatively crude measures of exposure assessment for the four chemicals under study, and presence of unconsidered potential chemical confounders. The simplest interpretation of the findings about bladder cancer may be that PBN (or a chemical reagent or chemical intermediate associated with its production at this factory in the 1930s and 1940s) is a bladder carcinogen. Priority should be given, however, to obtaining information on the cancer experience of other working populations exposed to PBN or to o-toluidine.


Keywords: 2-mercaptobenzothiazole; phenyl-β-naphthylamine; o-toluidine; aniline     

Exposure to high concentrations of nitrosamines and cancer mortality among a cohort of rubber workers

OBJECTIVES—To examine if the occurrence of different cancers was increased among rubber workers, as the highest known exposures of humans to nitrosamines have occurred in the rubber industry.
METHODS—A cohort of 8933 rubber workers (hired after 1 January 1950, still active or retired on 1 January 1981 and employed for at least 1 year in one of five study factories) was followed up for mortality from 1 January 1981 to 31 December 1991. Work histories were reconstructed with routinely documented cost centre codes, which allowed identification by employment in specific work areas. For each cost centre code time and factory specific, semi-quantitative exposures to nitrosamines (three levels: low, medium, high) and other compounds were estimated by industrial hygienists. Rate ratios for medium (RR_m) and high (RR_h) exposures and 95% confidence intervals (95% CIs) were calculated with Cox's proportional hazards models with the low exposure as reference.
RESULTS—Exposure to nitrosamines was significantly associated with an increased mortality from cancers of the oesophagus (13 deaths: RR_m 1.7, 95% CI 0.3 to 10.3; RR_h 7.3, 95% CI 1.9 to 27.8) and of the oral cavity and pharynx (17 deaths: RR_m 0.8, 95% CI 0.2 to 4.1; RR_h 3.9, 95% CI 1.4 to 11.1). A non-significant trend of increasing mortality with exposure to higher concentrations of nitrosamines was found for mortality from cancer of the prostate (26 deaths: RR_m 1.4, 95% CI 0.5 to 3.8; RR_h 2.2, 95% CI 0.9 to 5.6), and the brain (six deaths: RR_m 3.9, 95% CI 0.3 to 42.6; RR_h 6.0, 95% CI 0.6 to 57.6). No association was found between exposure to nitrosamines and cancer of the stomach (RR_m 0.8, 95% CI 0.4 to 1.8; RR_h 1.2, 95% CI 0.5 to 2.5) or lung (RR_m 1.0, 95% CI 0.6 to 1.5; RR_h 1.0, 95% CI 0.7 to 1.6).
CONCLUSIONS—Exposure to high concentrations of nitrosamines is associated with increased mortality from cancers of the oesophagus, oral cavity, and pharynx, but not with increased mortality from cancers of the stomach or lung.


Keywords: nitrosamines; cancer mortality; rubber industry     

Daily deaths are associated with combustion particles rather than SO(2) in Philadelphia

OBJECTIVES—To assess whether the association between SO₂ and daily deaths in Philadelphia during the years 1974-88 is due to its correlation with airborne particles, and vice versa.
METHODS— There is a significant variation in the relation between total suspended particulate (TSP) and SO₂ in Philadelphia by year and season. Firstly, 30 separate regressions were fitted for each pollutant in the warm and cold season of each year. These regressions controlled for weather, long term temporal patterns, and day of the week. Then a meta-regression was performed to find whether the effect of SO₂ was due to TSP, or vice versa.
RESULTS—Controlling for TSP, there was no significant association between SO₂ and daily deaths. By contrast, in periods when TSP was less correlated with SO₂, its association with daily deaths was higher. However, all of the association between TSP and daily deaths was explained by its correlation with extinction coefficient, a measurement of the scattering of light by fine particles, which has been shown to be highly correlated with fine combustion particles in Philadelphia.
CONCLUSIONS—The association between air pollution and daily deaths in Philadelphia is due to fine combustion particles, and not to SO₂.


Keywords: air pollution; mortality; hierarchical models     

A case-referent study of cancer mortality among sulfate mill workers in Sweden

OBJECTIVES—To investigate whether workers in Swedish sulfate mills have an increased risk of death from certain malignancies that have previously been linked to the pulping process.
METHODS—Subjects of the study (n=2480) were men aged 40-75 at death during 1960-89 in the parishes surrounding four sulfate mills. Exposure assessment was based on information from the personnel files in the mills— 35% of the subjects were recognised there, and work categories were created.
RESULTS—Among all sulfate mill workers, the odds ratio (OR) (90% confidence interval (90% CI)) for death from lung cancer was 1.6 (1.1 to 2.3), pleural mesotheliomas 9.5 (1.9 to 48), brain tumours 2.6 (1.2 to 5.3), and liver or biliary tract cancer 2.3 (1.0 to 5.2). There was an increased mortality from leukaemia among workers in the soda recovery plant (5.9 (2.6 to 13)) and bleaching plant and digester house (2.8 (1.0 to 7.5)).
CONCLUSIONS—Sulfate mill workers were at increased risk of dying from lung cancer and pleural mesotheliomas, probably due to exposure to asbestos. Increased risks of brain tumours and cancers of the liver or biliary tract were also found but the aetiology is not obvious.


Keywords: epidemiology; pulp and paper industry; brain neoplasm     

Cohort mortality and cancer incidence survey of recent entrants (1982-91) to the United Kingdom rubber industry: preliminary findings

OBJECTIVES—To monitor the occurrence of stomach and lung cancer in a newly defined cohort of United Kingdom rubber workers and to report findings for other cancers in an early period of follow up.
METHODS—A prospective cohort of 9031 male and female workers from 42 United Kingdom rubber factories has been enumerated. All employees had a minimum of 12 months employment and were first employed at one of the participating factories in the period 1982-91. Mortality data were available for the period 1983-98 and cancer registration data for the period 1983-94. The mortality and cancer incidence experienced by the cohort were compared with expected values based on national rates defined by period, age, and sex.
RESULTS—Mortality from lung cancer was close to expectation (men: observed (obs) 11, expected (exp) 12.70, standardised mortality ratio (SMR) 87, 95% confidence interval (95% CI) 43 to 155; women: obs 0, exp 1.34, SMR 0, 95% CI 0 to 275). Mortality from stomach cancer was unexceptional (men: obs 1, exp 2.69, SMR 37, 95% CI 1 to 207; women: obs 0, exp 0.24, SMR 0, 95% CI 0 to 1537). Many statistical comparisons were made both for mortality data and for cancer registration data; only one difference between observed and expected numbers was significant (mortality from cancer of the testis: obs 3 exp 0.51, SMR 589, 95% CI 122 to 1722). Corresponding findings for incident cancers of the testis were unexceptional (obs 5, exp 5.13, standardised registration ratio (SRR) 97, 95% CI 32 to 227).
CONCLUSION—The findings should be treated with caution as they relate to an early period of follow up. Nevertheless, they hold out the prospect that the increased SMRs for stomach and lung cancers reported for historical cohorts of United Kingdom rubber workers may not be apparent in more recent cohorts.


Keywords: rubber workers; lung cancer; stomach cancer; cohort study     

Risk of mesothelioma from exposure to crocidolite asbestos: a 1995 update of a South African mortality study

OBJECTIVE—To find the risk of developing mesothelioma in a cohort born in 1916-36 in Prieska, Northern Cape Province, South Africa.
METHODS—A birth cohort mortality study was carried out in a small town in the Northern Cape Province, South Africa, with a history of crocidolite asbestos mining and milling. The cohort comprised all white births registered in the magisterial district of Prieska from 1916 to 1936, inclusive (2390). Causes of death due to mesothelioma and other cancers as recorded on medical certificates of cause of death were investigated. Person-years analysis was used to calculate mortalities due to mesothelioma, other respiratory cancers, and other non-respiratory cancers. Proportional cancer mortalities were also calculated for mesothelioma and other specific neoplasms.
RESULTS—The follow up rate for the cohort was 74.3% in 1995, and 683 traced members (38.6%) had died. Cause of death was unknown for 6.4% of deaths. There were 118 cases of cancer, 28 of them from mesothelioma, giving a cause specific mortality for mesothelioma of 277 (170-384) per 10⁶ person-years. The rates for men and women were 366 and 172 per 10⁶ person-years, respectively. The mortality for lung cancer (29 deaths) was 287 (135-436) per 10⁶ person-years, and that for other non-respiratory cancers (60 deaths) was 593 (442-745). Two cases of laryngeal and four of colon cancer were observed. All cancer mortality, mesothelioma, and lung cancer proportional cancer mortality ratios were increased.
CONCLUSION—The mortality for mesothelioma in men was twice that in women, probably because men were more likely to have had both occupational and environmental exposure to asbestos. Nevertheless, the mortality in women was still high and is probably indicative of the environmental exposure as white women were rarely employed in the asbestos industry in the Prieska area. Due to the long latency from first exposure to diagnosis of the neoplasm, the cause specific mortality in this cohort could be expected to increase rapidly over the next 10 years.


Keywords: South Africa; asbestos; environmental exposure; occupational exposure; cohort; mesothelioma; lung cancer