A cohort mortality study of U.K. carbon black workers, 1951-1996

BACKGROUND: Carbon black, a powdered form of elemental carbon is used in the manufacture of rubber products, paints, plastics, and inks. In 1974, the Health and Safety Executive initiated a cohort mortality study on possible carcinogenic effects on carbon black workers. METHODS: The mortality of a cohort of 1,147 male manual workers from five U.K. factories manufacturing carbon black was investigated for the period 1951-1996. All subjects were employed in the carbon black industry for 12 months or more, and all were first employed before 1975. Limited work histories were used to calculate estimates of individual cumulative exposure to carbon black, using a job-exposure matrix derived by the study team. RESULTS: Based on serial rates for the general population of England and Wales, significantly elevated mortality was observed in the main study cohort for all causes (Obs 372, Exp 328.7, SMR 113, P < 0.05) and for lung cancer (Obs 61, Exp 35.3, SMR 173, P < 0.001). There were highly elevated lung cancer SMRs at two of the factories, and unexceptional SMRs at the remaining three factories. There was no indication of lung cancer SMRs increasing with period from first employment. Poisson regression analyses failed to find significant trends of lung cancer risks increasing either with cumulative exposure to carbon black (4 levels) or with duration of employment at the participating factories (4 levels). CONCLUSIONS: Confident interpretation of the elevated SMRs found for lung cancer in two of the factory subcohorts is not possible but the study has been unable to link cumulative exposure to carbon black with elevated risks of lung cancer.     

Mortality of UK oil refinery and petroleum distribution workers, 1951-2003

BACKGROUND: The health of UK petroleum industry workers has been monitored for many years. AIM: To identify any long-term adverse health outcomes from occupational exposures in this industry. METHODS: The mortality (1951-2003) and cancer morbidity (1971-2003) experienced by cohorts of 28,555 oil refinery workers and 16,477 petroleum distribution workers has been investigated. Study subjects were all those males first employed in the period 1946-74 at one of eight UK oil refineries or 476 UK petroleum distribution centres; all subjects had a minimum of 12 months employment with some employment after 1 January 1951. Observed numbers of cause-specific deaths and site-specific cancer registrations were compared with expectations based on national mortality and cancer incidence rates. RESULTS: Standardized mortality ratios (SMRs) were significantly <100 for all causes both in oil refinery workers (Obs 11,156, SMR 89) and in petroleum distribution workers (Obs 7320, SMR 96). Significantly elevated SMRs were shown in oil refinery workers for cancer of the pleura (mesothelioma) (Obs 64, SMR 261) and melanoma (Obs 48, SMR 168). Significantly elevated SMRs were not found in petroleum distribution workers for any site of cancer. Significantly elevated standardized registration ratios (SRRs) were only shown in oil refinery workers and for cancer of the pleura (mesothelioma) (Obs 115, SMR 274), melanoma (Obs 85, SMR 129) and other skin cancer (Obs 983, SRR 117). CONCLUSIONS: The only findings that showed clear evidence of an occupational cancer hazard were those for mesothelioma in oil refinery workers.     

Mortality of workers at a nickel carbonyl refinery, 1958-2000

Background: Excess risks of respiratory cancer have been shown in some groups of nickel exposed workers. It is clear, however, that not all forms of nickel exposure are implicated in these excess risks.

Aim: To determine whether occupational exposures received in a modern nickel carbonyl refinery lead to increased risks of cancer, in particular nasal cancer and lung cancer.

Methods: The mortality experienced by a cohort of 812 workers employed at a nickel refinery was investigated. Study subjects were all male workforce employees first employed in the period 1953–92 who had at least five years' employment with the company. Observed numbers of cause specific deaths were compared with expectations based on national mortality rates; SMRs were also calculated by period from commencing employment, year of commencing employment, and type of work.

Results: Overall, standardised mortality ratios (SMRs) were close to 100 for all causes (Obs 191, SMR 96, 95% CI 83 to 111), all neoplasms (Obs 63, SMR 104, 95% CI 80 to 133), non-malignant diseases of the respiratory system (Obs 18, SMR 97, 95% CI 57 to 153), and diseases of the circulatory system (Obs 85, SMR 94, 95% CI 75 to 116). There were no significantly increased SMRs for any site of cancer. There was a non-significant excess for lung cancer (Obs 28, Exp 20.17, SMR 139, 95% CI 92 to 201), and in subgroup analyses a significantly increased SMR of 231 (Obs 9) was found for those 142 workers with at least five years' employment in the feed handling and nickel extraction departments. In the total cohort there was a single death from nasal cancer (Exp 0.10).

Conclusions: The non-significant excess of lung cancer deaths may well be a chance finding, but in light of previous studies some role for nickel exposures cannot be excluded.

     

Mortality of UK electricity generation and transmission workers, 1973-2002

OBJECTIVE: To examine mortality from cancer and non-malignant causes among a large cohort of UK electricity generation and transmission workers. METHODS: The mortality experienced by a cohort of 83,923 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-2002. All employees had worked for at least 6 months with some employment between 1973 and 1982. Standardized mortality ratios (SMRs) were used to assess mortality in the total cohort and in three sub-cohorts: power station workers, substation and transmission workers and workers at non-operational locations. These classifications were based on the place of work of the first known job. RESULTS: Overall mortality was significantly below that expected, based on national rates [males: observed (Obs) 18,773, expected (Exp) 22,497.9, SMR 83; females: Obs 1122, Exp 1424.9, SMR 79]. Statistically significant deficits of deaths were also found for most of the major disease groupings. However, significant excesses of deaths were found in male power station workers for cancer of the pleura (Obs 129, Exp 30.3, SMR 426) and in male workers from non-operational locations for cancer of the brain (Obs 55, Exp 36.0, SMR 153). There was also a non-significant excess of deaths from cancer of the breast in male power station workers (Obs 10, Exp 5.3, SMR 190). CONCLUSIONS: Mortality was exceptionally low for most causes of death but late health effects from earlier asbestos exposure were still in evidence.     

Lung cancer mortality in UK nickel-cadmium battery workers, 1947-2000

Aims: To investigate mortality from lung cancer in nickel-cadmium battery workers in relation to cumulative exposure to cadmium hydroxide.

Methods: The mortality of a cohort of 926 male workers from a factory engaged in the manufacture of nickel-cadmium batteries in the West Midlands of England was investigated for the period 1947–2000. All subjects were first employed at the plant in the period 1947–75 and employed for a minimum period of 12 months. Work histories were available for the period 1947–86; the factory closed down in 1992. Two analytical approaches were used, indirect standardisation and Poisson regression.

Results: Based on serial mortality rates for the general population of England and Wales, significantly increased mortality was shown for cancers of the pharynx (observed (Obs) 4, expected (Exp) 0.7, standardised mortality ratio (SMR) 559, p<0.05), non-malignant diseases of the respiratory system (Obs 61, Exp 43.0, SMR 142, p<0.05), and non-malignant diseases of the genitourinary system (Obs 10, Exp 4.1, SMR 243, p<0.05). Non-significantly increased SMRs were shown for lung cancer (Obs 45, Exp 40.7, SMR 111) and cancer of the prostate (Obs 9, Exp 7.5, SMR 116). Estimated cumulative cadmium exposures were not related to risks of lung cancer or risks of chronic obstructive pulmonary diseases, even when exposure histories were lagged first by 10, then by 20 years.

Conclusions: The study findings do not support the hypotheses that cadmium compounds are human lung carcinogens.

     

Lung cancer risk among refractory brick workers exposed to crystalline silica: a retrospective cohort study.

We conducted a retrospective cohort study among 1,022 refractory brick workers exposed to crystalline silica. Mortality from lung cancer (SMR = 1.77) and respiratory diseases (SMR = 3.15) was elevated in workers first employed less than or equal to 1957 who are likely to have shared the highest exposure to crystalline silica. Workers with at least 19 years of cumulative employment in the plant experienced particularly increased risks for lung cancer (SMR = 2.01) and respiratory diseases (SMR = 3.89). Relative mortality from these specific causes increased with years since first employment (that is, first exposure) and decreased with age at first employment. Indirect adjustment for smoking habits and the lack of excess mortality from cardiovascular diseases and emphysema indicated little effect of smoking on the increased risks for lung cancer and respiratory diseases.     

Mortality and cancer morbidity of production workers in the UK flexible polyurethane foam industry: updated findings, 1958-98

Aims: To describe cause specific mortality and site specific cancer morbidity among workers employed in factories that produce polyurethane foams, and to determine if any part of the experience may be caused by occupation, in particular to investigate any association between respiratory disease (malignant and non-malignant) and exposure to diisocyanates.

Methods: The mortality (1958–98) and cancer morbidity (1971–94) experienced by a cohort of 8288 male and female employees from 11 factories in England and Wales engaged in the manufacture of flexible polyurethane foams were investigated. All employees were employed for at least six months with some period of employment in the period 1958–79. Two analytical approaches were used, indirect standardisation and Poisson regression.

Results: Compared with the general population of England and Wales, mortality from lung cancer in female employees was significantly increased (observed (Obs) 35, expected (Exp) 19.4, standardised mortality ratio (SMR) 181). A similar excess was not found for male employees (Obs 134, Exp 125.0, SMR 107). There were no significantly increased cause specific SMRs among the subcohort (n = 1782) with some period of isocyanate exposed employment. No significant positive trends were found between risks of lung cancer or risks of non-malignant diseases of the respiratory system and durations of "lower" or "higher" exposures to diisocyanates.

Conclusions: The study has been unable to link isocyanate exposed employment either with risks of lung cancer or with risks of non-malignant diseases of the respiratory system. The increased SMR for female lung cancer is most likely caused by factors unrelated to the industry under study.

     

Mortality of workers at a plant manufacturing nickel alloys, 1958-2000

BACKGROUND: Excess risks of respiratory cancer have been demonstrated in some groups of nickel-exposed workers. It is clear, however, that not all forms of nickel exposure are implicated in these excess risks. Aim To determine whether occupational exposures received in the manufacture of nickel alloys lead to increased risks of cancer, in particular nasal cancer and lung cancer. METHODS: The mortality experienced by a cohort of 1999 workers employed at a plant manufacturing nickel alloys has been investigated. Study subjects were all those male workforce employees first employed in the period 1953-1992 who had at least 5 years employment with the company. Observed numbers of cause-specific deaths were compared with expectations based on national mortality rates. Standardized mortality ratios (SMRs) were calculated by period from commencing employment and by operating area of first job. In addition, rate ratios derived from Poisson regression and based on an internal standard were calculated by levels of duration of employment. RESULTS: SMRs were significantly below 100 for all causes (observed 557, expected 704.3, SMR 79), all neoplasms (observed 169, expected 209.4, SMR 81) non-malignant diseases of the respiratory system (observed 50, expected 73.0, SMR 69) and diseases of the circulatory system (observed 261, expected 335.5, SMR 78). Significantly elevated SMRs were not shown for any cause of death and mortality was below expectation for stomach cancer (observed 8, expected 16.0, SMR 50), lung cancer (observed 64, expected 73.6, SMR 87) and bladder cancer (observed 3, expected 8.0, SMR 38). There were no deaths from nasal cancer (expected 0.33). More detailed findings were unexceptional. CONCLUSIONS: The analyses did not suggest the presence of an occupational cancer hazard in the mortality experience of the cohort.     

Cancer incidence and cancer mortality in a cohort of UK semiconductor workers, 1970-2002

OBJECTIVE: To examine cancer risks in a cohort of workers employed in the manufacture of semiconductors. METHODS: The mortality (1970-2002) and cancer morbidity (1971-2001) experienced by a cohort of 1807 male and female workforce employees from a semiconductor factory in the West Midlands (UK) have been investigated. Standardized mortality ratios (SMRs) and standardized registration ratios (SRRs) were used to assess mortality and morbidity, respectively. RESULTS: Overall mortality was close to expectation in males [SMR 99, 95% (confidence interval) CI 79-122] and significantly below expectation in females (SMR 74, 95% CI 65-85). Incidence of all sites of cancer was somewhat elevated in males (SRR 130, 95% CI 95-173) but close to expectation in females (SRR 94, 95% CI 82-109). There were significant deficits of deaths from cancer of the oesophagus in males and females combined and from cancer of the breast in females. Significantly elevated SRRs were found in males for cancer of the rectum [Observed (Obs) 6, SRR 284, 95% CI 104-619], in females for cancer of the pancreas (Obs 10, SRR 226, 95% CI 108-415) and malignant melanoma (Obs 11, SRR 221, 95% CI 110-396) and in males and females combined for cancer of the rectum (Obs 19, SRR 199, 95% CI 120-310) and malignant melanoma (Obs 12, SRR 217, 95% CI 112-379). Detailed work history data were unavailable for analysis. The finding of excess morbidity was not mirrored in the corresponding mortality findings. CONCLUSIONS: The study found elevated morbidity for a number of cancer sites that may be unconnected with occupation. Elimination of all possible occupational causes will, however, require more detailed analyses of cancer risks in relation to exposure histories.     

Follow-up study of chrysotile asbestos textile workers: Cohort mortality and case-control analyses

Previous studies of mortality among white males employed in a Charleston, South Carolina asbestos textile plant using chrysotile demonstrated significant excess mortality due to asbestos-related disease and a steep exposure-response relationship for lung cancer. This cohort was further studied by adding 15 years of follow-up and including mortality among white female and black male workers. Nested case-control analyses were undertaken to further explore possible differences in lung cancer risk by textile operation as well as possible confounding by mineral oil exposures. Preliminary data for white males have been previously published. White males experienced statistically significant excess mortality due to lung cancer (standardized mortality ratio [SMR] = 2.30; confidence interval [CI] = 1.88–2.79), all causes (SMR = 1.48; CI = 1.38–1.58), all cancers (SMR = 1.50; CI = 1.29–1.72), diabetes mellitus (SMR = 2.05; CI = 1.18–3.33), heart disease (SMR = 1.41; CI = 1.26–1.58), cerebrovascular disease (SMR = 1.50; CI = 1.08–2.02), pneumoconiosis and other respiratory diseases (SMR = 4.10; CI = 3.10–5.31), and accidents (SMR = 1.49; CI = 1.15–1.91). Among white females, statistically significant excesses occurred for lung cancer (SMR = 2.75; CI = 2.06–3.61), all causes (SMR = 1.21; CI = 1.11–1.32), pneumoconiosis and other respiratory diseases (SMR = 2.40; CI = 1.53–3.60), and other respiratory cancers (SMR = 14.98; CI = 4.08–38.7). Among the total cohort of black males, the only statistically significant excess observed was for pneumoconiosis (SMR = 2.19; CI = 1.23–3.62). Based on historical exposure measurements at the plant, there was a positive exposure-response relationship for both lung cancer and pneumoconiosis. Data for the entire cohort demonstrate an increase in the lung cancer relative risk of 2–3% for each fiber/cc-year of cumulative chrysotile exposure. This relationship was more consistent for the white male workers. The excess risk for lung cancer among white males and females appeared to occur at cumulative exposures lower than those for black males. Possible reasons for the lesser lung cancer risk among black males include less smoking and differences in airborne fiber characteristics experienced by black males as a result of plant job placement patterns. The case-control analysis found employment in preparation and carding operations (where most of the black males worked) to be associated with a slightly reduced lung cancer risk, although not statistically significant, whereas spinning and twisting employment was associated with a statistically significant increased lung cancer risk compared to other plant operations. Airborne fiber size data, determined by transmission electron microscopy, demonstrated slightly longer fibers in spinning and twisting compared to other textile operations. Case-control analyses demonstrated little effect of mineral oil exposures on the lung cancer exposure-response estimates. Two deaths due to mesothelioma were observed among this cohort.     

Mortality of United Kingdom oil refinery and petroleum distribution workers, 1951-1998

The mortality experienced by cohorts of 28 630 oil refinery workers and 16 480 petroleum distribution workers has been investigated. Study subjects were all those male employees first employed in the period 1946-1974 at one of eight UK oil refineries or at one of 476 UK petroleum distribution centres; all subjects had a minimum of 12 months employment with some employment after 1 January 1951. The observed numbers of cause-specific deaths were compared with expectations based on national mortality rates. The resultant standardized mortality ratios (SMRs) were significantly below 100 for all causes, in both oil refinery workers (observed, 9341; expected, 10 649.7; SMR = 88) and petroleum distribution workers (observed, 6083; expected, 6460.3; SMR = 94). Significantly elevated SMRs were shown in oil refinery workers for cancer of the gall bladder (observed, 24; expected, 14.0; SMR = 172), cancer of the pleura (observed, 38; expected, 15.0; SMR = 254) and melanoma (observed, 36; expected, 22.2; SMR = 162). Significantly elevated SMRs were not found in petroleum distribution workers for any site of cancer. SMRs for selected causes of death were calculated by period from commencing employment, by year of hire and by job type. The only findings that suggested the presence of an occupational cancer hazard were an excess of mesothelioma in oil refinery workers and an excess of leukaemia in petroleum distribution workers, both excesses occurring in long-term follow-up for workers first employed >30 years ago.     

Carbon black and lung cancer: Testing a new exposure metric in a German cohort

BACKGROUND: A cohort mortality study of a large carbon black production plant in Germany showed an elevation in lung cancer mortality (SMR 1.81 (95% CI: 1.34-2.39)), although the elevation could not be linked to exposure to carbon black. METHODS: In follow up to a British study of carbon black production workers [Sorahan et al., 2007] in which risk of lung cancer progressively declined after cessation of employment-in contrast to an expected upward trend-we evaluated the German cohort with a similar methodology, that is, by focusing on the first 15 years after leaving employment in terms of lung cancer SMR. RESULTS: In our SMR analysis of the German cohort of 1,528 men and an inception cohort of 1,271 men, distinctly different results from the British cohort were observed. We observed a rising trend in lung cancer SMR, in contrast to the declining SMR trend noted in the British cohort. In fact, Cox models for lung cancer mortality with attained age as the basic time variable showed negative coefficients for the full and inception cohorts. CONCLUSIONS: Our analysis of a large German cohort of carbon black workers does not support the concept of a declining risk of lung cancer following cessation of employment.     

Cancer mortality in German carbon black workers 1976-98

Background

Few studies have investigated cancer risks in carbon black workers and the findings were inconclusive.

Methods

The current study explores the mortality of a cohort of 1535 male German blue‐collar workers employed at a carbon black manufacturing plant for at least one year between 1960 and 1998. Vital status and causes of death were assessed for the period 1976–98. Occupational histories and information on smoking were abstracted from company records. Standardised mortality ratios (SMR) and Poisson regression models were calculated.

Results

The SMRs for all cause mortality (observed deaths (obs) 332, SMR 120, 95% CI 108 to 134), and mortality from lung cancer (obs 50, SMR 218, 95% CI 161 to 287) were increased using national rates as reference. Comparisons to regional rates from the federal state gave SMRs of 120 (95% CI 107 to 133) and 183 (95% CI 136 to 241), respectively. However, there was no apparent dose response relationship between lung cancer mortality and several indicators of occupational exposure, including years of employment and carbon black exposure.

Conclusions

The mortality from lung cancer among German carbon black workers was increased. The high lung cancer SMR can not fully be explained by selection, smoking, or other occupational risk factors, but the results also provide little evidence for an effect of carbon black exposure.     

Occupational risk factors for mortality from stomach and lung cancer among rubber workers: an analysis using internal controls and refined exposure assessment

OBJECTIVES: To determine occupational risk factors for stomach and lung cancer among workers in the German rubber industry. METHODS: A cohort of all male German rubber workers (n = 11,633) who had been employed for at least one year in one of five study plants and who were alive and actively employed or retired on 1 January 1981 was followed for mortality from 1 January 1981 through December 1991. A subcohort of n = 8,933 workers who were hired after 1 January 1950 was defined to focus on working conditions in the more recent rubber industry. Work histories were reconstructed using routinely documented 'cost centre codes' and classified into six work areas as well as subgroups of some work areas. The work areas are: 1. preparation of materials, 2. production of technical rubber goods, 3. production of tyres, 4. storage and dispatch, 5. maintenance, 6. others. Standardized mortality ratios (SMR) and Cox proportional hazards models were calculated for each of the work areas (>1 year of employment in the respective work area). Hazard rate ratios were adjusted for age (time marker) and stratified for year of hire (1950-1959, > or =1960) and years of employment in the respective work area (1-9 years, > or =10 years); years of employment were lagged 10 years to account for latency. RESULTS: Compared to the national reference population mortality from cancer of stomach (observed 44, SMR = 117; 95% CI: 85-157) and lung (observed 154, SMR = 123; 95% CI: 104-144) was slightly increased. Using internal controls we observed excess deaths from stomach cancer in work area 1 (relative risk [RR] = 2.3; 95% CI: 1.2-4.2) and from lung cancer in work areas 1 (RR = 1.7; 95% CI: 1.2-2.3), 2 (RR = 1.5; 95% CI: 1.1-2.1), and 3 (RR = 1.3; 95% CI: 0.9-1.8). On the basis of cumulative years of employment an exposure response relationship was observed for mortality from both cancer sites among a subcategory of work area 1: weighing and mixing. Increased risks were also seen for lung cancer among workers employed in production of technical rubber goods. CONCLUSION: Our results support an association between an excess mortality from stomach and lung cancer and employment in early production stages of rubber manufacturing, especially weighing and mixing. This may point to an aetiologic role of asbestos or carbon black. For stomach cancer additional risk factors, e.g. exposure to dust and talc, deserve further investigation. The results of the present study do not support a causal role of nitrosamines for stomach or lung cancer.     

A cohort mortality and cancer incidence survey of recent entrants (1982-91) to the UK rubber industry: findings for 1983-2004

AIM: To monitor the occurrence of cancer in a recently defined cohort of UK rubber workers. METHODS: A cohort of 8651 male and female workers from 41 UK 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 and cancer incidence data for the period 1983-2004 were compared with expected values based on appropriate national rates. RESULTS: Mortality from lung cancer was close to expectation for males [observed 22, standardized mortality ratio (SMR) 93] and females (observed 2, SMR 70). Mortality from stomach cancer was also unexceptional in males (observed 4, SMR 86) and females (observed 0, SMR 0). Although based on small numbers, significantly elevated mortality was shown for multiple myeloma in males (observed 5, SMR 385) and females (observed 2, SMR 952). All seven of these latter deaths occurred in workers from the general rubber goods (GRG) sector. CONCLUSIONS: The findings should be treated with caution as they relate to a relatively early period of follow-up. Nevertheless, they hold out the prospect that the elevated SMRs for stomach and lung cancers reported for historical cohorts of UK rubber workers will not be present in more recent cohorts. The elevated occurrence of multiple myeloma may represent no more than a chance finding. Alternatively, these findings may reflect the presence of an unrecognized occupational cancer hazard in parts of the GRG sector of the UK rubber industry.     

A cohort study of art glass workers in the Empoli area

The investigation aimed at studying cause-specific mortality of art glass workers employed in 17 industrial facilities in Tuscany, Italy. A cohort of 3390 workers employed for at least 1 year was obtained from company payrolls. Follow-up was between the year each factory started operations, mostly in the mid-fifties, and the end of 1993. The cause specific expected mortality was computed relative to Tuscany rates, specified for gender, 5-year age groups and calendar year. Separate analyses were carried out for the job titles of makers, batch mixers and grinders. For males, 3180 individuals, the observed mortality for cancer causes was above the expected for the lung [standardized mortality ratio (SMR) 123, 10 observed (Obs)], larynx (SMR 166, 10 Obs), stomach (SMR 105, 30 Obs) and brain (SMR 150, 7 Obs). For non-cancer causes observed mortality was above expected for hypertensive diseases (SMR 178, 10 Obs) and diseases of the genitourinary system (SMR 169, 11 Obs). Increases for the above listed causes were shown also among makers. Mortality for larynx and lung cancer increased with time since first exposure and significantly increased SMRs were observed for 21 or more years since first exposure: this pattern was still present with smoking adjustment. The results showed consistently increased mortality for lung and larynx cancer in the overall cohort and among makers. Stomach cancer, brain cancer, hypertensive diseases and diseases of the genitourinary system were also increased in the overall cohort and among makers.     

An epidemiological study of workers exposed to vinyl chloride in the plants of Ferrara, Rosignano and Ravenna

The aim of the present study is to investigate cause-specific mortality among male workers employed in vinyl chloride manufacture and polymerization in three Italian plants located in Ferrara, Rosignano and Ravenna. The cohorts include all workers hired between start of operation and, respectively 1985, 1978 and 1985, amounting to 418, 206 and 635 subjects followed up for mortality until 1996 (Ferrara and Rosignano) and 1997 (Ravenna). Cause specific SMRs (Standardized mortality ratios) were computed. Expected figures were obtained from mortality rates for the population resident in the region where the plant was located, for each SMR value a 90% confidence interval (CI) was calculated on the assumption of a Poisson distribution. The study detected an increased mortality for primary liver cancer in all three plants; SMR values were 444 in Ferrara (4 Obs. 90% CI 160-1069), 200 in Rosignano (1 Obs. 90% CI 10-869) and 375 in Ravenna (3 Obs. 90% CI 110-1038). In the pooled cohort liver cancer SMR was equal to 364 (8 Obs. 90% CI 108-390). In one plant, Ferrara, observed mortality was above the expected for lung cancer, SMR = 146 (14 Obs. 90% CI 89-229) and for larynx cancer, SMR = 500 (4 Obs. 90% CI 174-1167). One death from pleural cancer was observed in Rosignano (SMR = 1000 90% CI 47-4331). A non significant increase was detected for liver cirrhosis, in Ferrara (SMR 108, 6 Obs. 90% CI 73-332) and Rosignano (SMR 129, 3 Obs. 90% CI 35-332). The study results are confirming the carcinogenic action of vinyl chloride on the liver, they are pointing to its possible role in lung cancer development, as already shown for workers employed in Porto Marghera; an increased risk for larynx cancer is also shown.     

Mortality among workers in the diatomaceous earth industry.

A cohort mortality study was conducted among workers from two plants in the diatomaceous earth mining and processing industry in California. Diatomaceous earth consists of the skeletal remains of diatoms. Exposure to amorphous (non-crystalline) and crystalline silica in the form of quartz results from open pit mining and exposure to crystalline silica (principally cristobalite) occurs in the processing of the material. Lung cancer and non-malignant respiratory diseases have been the health outcomes of greatest concern. The main study cohort included 2570 white men (533 Hispanic and 2017 non-Hispanic workers) who were employed for at least 12 months cumulative service in the industry and who had worked for at least one day during the follow up period, 1942-87. Vital status was ascertained for 91% of the cohort and death certificate information was retrieved for 591 of 628 (94%) identified deaths. The all causes combined standardised mortality ratio (SMR) was slightly increased (SMR = 1.12; 628 observed) compared with rates among US white males. The principal contributors to this excess were increased risks from lung cancer (SMR = 1.43; 59 observed) and non-malignant respiratory disease (NMRD) excluding infectious diseases and pneumonia (SMR = 2.59; 56 observed). The excess of lung cancer persisted when local county rates were used for comparison (SMR = 1.59). Internal rate comparisons by Poisson regression analysis were conducted to assess potential dose-response relations for lung cancer and NMRDs. Mortality trends were examined in relation to duration of employment in dust exposed jobs and with respect to an index of cumulative exposure to crystalline silica. The crystalline silica index was a semiquantitative measure that combined information on duration of exposure, differences in exposure intensity between jobs and calendar periods, the crystalline content of the various product mixes, and the use of respiratory protection devices. Increasing gradients of risk were detected for lung cancer and NMRD with both exposure indices. The relative risk trends for lung cancer and NMRD with crystalline silica exposure lagged 15 years were respectively: 1.00, 1.19, 1.37, and 2.74, and 1.00, 1.13, 1.58, and 2.71. Based on a review of available but limited data on cigarette smoking in the cohort and from application of indirect methods for assessing confounding variables, it seems unlikely that smoking habits could account for all of the association between exposure to dust and lung cancer. The intense and poorly controlled dust exposures encountered before the 1950s were probably the most aetiologically significant contributors to risks from lung cancer and NMRDs. The absence of an excess of lung cancer among workers hired since 1960, and the finding of no deaths attributed to pneumoconiosis as an underlying cause of death among workers hired since 1950 indicate that exposure reductions in the industry during the past 40 years have been successful in reducing excess risks to workers. Further mortality follow up of the cohort and the analysis of radiographic data will be needed to determine conclusively the long term patterns of disease risks in this industry.     

Mortality among a cohort of United Kingdom steel foundry workers with special reference to cancers of the stomach and lung, 1946-90.

OBJECTIVE--The aim was to describe cause specific mortality among steel foundry workers and to determine if any part of the experience may be due to occupation. DESIGN--Historical prospective cohort study. SETTING--Nine steel foundries in England and one in Scotland. SUBJECTS--10,438 male production employees first employed in the period 1946-65 and with a minimum period of employment of one year. MAIN OUTCOME MEASURES--Observed and expected numbers of deaths for the period 1946-90. RESULTS--Compared with the general population of England and Wales, standardised mortality ratios (SMRs) for all causes and all neoplasms were 115 (observed deaths (Obs) 3976) and 119 (Obs 1129) respectively. Statistically significant excesses were found for cancer of the stomach (Obs 124, expected deaths (Exp) 92.5, SMR 134, 95% confidence interval (95% CI) 111-160) and cancer of the lung (Obs 551, Exp 378.3, SMR 146, 95% CI 134-158). A raised SMR (153) was also found for non-malignant diseases of the respiratory system. Classifications of jobs attracting either higher dust or higher fume exposures did not usefully predict these increased SMRs. Poisson regression was used to investigate risks of mortality from all cancers, cancer of the stomach, cancer of the lung, and non-malignant diseases of the respiratory system associated with duration of employment in the foundry area, the fettling shop, the foundry area/fettling shop, and the industry in general. Monotonic dose-response relations were not found, although there were positive trends for lung cancer and employment in the foundry area/fettling shop (1.0, 1.21, 1.44, 1.26) and for diseases of the respiratory system and employment in the fettling shop (1.0, 1.37, 1.18, 1.35). CONCLUSIONS--Confident interpretation of the causes of the raised SMRs was not possible. There was limited evidence of an occupational role in the excesses of lung cancer and diseases of the respiratory system. Smoking history was shown, in an indirect way, to be an unlikely explanation.     

A cohort mortality study of employees in the U.S. carbon black industry

OBJECTIVES: The objectives of this study are to evaluate historical mortality patterns, especially due to cancers, among employees of the U.S. carbon black industry and to address the methodological shortcomings of previous U.S. mortality studies. METHODS: We followed mortality of 5011 workers employed 1 year or more since the 1930s at 18 carbon black facilities through December 31, 2003. Age-, race-, sex-, and calendar year-adjusted standardized mortality ratios (SMRs) were calculated using state-specific mortality rates. RESULTS: Follow up was 96% complete. All-cause (SMR = 0.74, 95% confidence interval [CI] = 0.70-0.78) and all-cancer mortality (SMR = 0.83, 95% CI = 0.74-0.92) showed significant deficits. No excess was observed from lung (SMR = 0.97, 95% CI = 0.82-1.15) or bladder (SMR = 0.93, 95% CI = 0.47-1.87) cancers or from nonmalignant respiratory diseases (SMR = 0.99, 95% CI = 0.83-1.18). No trends were seen with duration of employment or time since hire for any cause of death. CONCLUSION: Employment in carbon black production in the United States seems not to be associated with increased mortality overall, cancer overall and, in particular, lung cancer. Further research, however, incorporating a detailed exposure assessment is needed to determine whether exposure to carbon black at high levels may be associated with an increased risk of cancer.