Cancer mortality in a Swedish cohort of pulp and paper mill workers

Purpose  

To study cancer mortality among Swedish pulp and paper mill workers by main mill pulping process and department, and to present the Swedish part of an international exposure measurements database.     

Cardiovascular mortality among Swedish pulp and paper mill workers

BACKGROUND: Malignant diseases but also cardiovascular and respiratory disorders and diabetes mellitus have been associated with work in pulp and paper production. The present cohort focuses on cardiovascular mortality in relation to various exposures in this industry. METHODS: The cohort, followed-up for mortality, includes 7,107 workers, 6,350 men and 757 women, from three major old mills in the middle of Sweden. RESULTS: Instead of a healthy-worker effect, a slightly increased risk for death in diseases of the circulatory system was found for male workers. Notably, work with sulfate digestion, steam and power generation and maintenance was associated with significantly increased risks. Cerebrovascular diseases showed non-significantly increased risks for maintenance and paper and paperboard production and manufacture. CONCLUSIONS: The differences in risk among various parts of the production are striking although it is hard to pinpoint any specific exposures. Dust and small particles along with sulfur compounds might be suspected.     

Mortality among production workers in pulp and paper mills

A cohort of 3,572 pulp and paper mill workers employed for at least one year between 1945 and 1955 was followed through 31 March 1977. Vital status was determined for 99% of the cohort. The 915 deaths observed were 79% of the number expected on the basis of comparable United States mortality rates. Statistically nonsignificant excesses of deaths due to lymphosarcoma and reticulosarcoma and to stomach cancer were observed. These findings tend to corroborate reports based on state vital statistics, and preliminary case-referent and population-based studies of workers in the pulp or paper industries. No deaths due to nasal cancer were observed, but only 0.6 were expected. When process-specific analyses were conducted, the excess risk of lymphosarcoma and reticulosarcoma was increased only for men who worked in sulfate mills. The excess risk of stomach cancer was limited to men who worked in sulfite mills. Process-specific standardized mortality ratios for these causes were highest after 20 years since first employment in the mills.     

Cohort cancer incidence among pulp and paper mill workers in British Columbia.

OBJECTIVES: A study was conducted to investigate cancer risks in a cohort of pulp and paper workers. METHODS: All male workers with > or =1 years of employment in 14 pulp and paper mills in 1950-1992 were studied. Standardized incidence ratios (SIR) were used to compare the cancer incidence of the cohort with that of the Canadian male population. Record linkage with the National Cancer Registry was performed using the generalized iterative record linkage method. RESULTS: Altogether 1756 cancer cases were observed in the entire cohort. For > or =15 years of work, the entire cohort had significantly increased SIR values for pleural and prostate cancer and skin melanoma; there was also a significantly increased risk for skin melanoma among workers in the kraft process only, rectal cancer among workers in the sulfite process only, and stomach and prostate cancer and all leukemias combined among workers in both the kraft and sulfite processes. A separate analysis comparing workers in pulping and papermaking with those in the pulping process only did not reveal any difference in cancer risk and hence did not modify the results. The SIR values for skin melanoma were not significantly increased in a comparison using the British Columbia male population. Nine of 10 pleural cancers were mesotheliomas, which likely reflect past asbestos exposure. CONCLUSIONS: The results suggest that long-term work in the pulp and paper industry is associated with excess risks of prostate and stomach cancers and all leukemias for work in both kraft and sulfite processes and of rectal cancer for work in the sulfite process only.     

Testicular cancer among Swedish pulp and paper workers

BACKGROUND: The incidence of testicular cancer has increased in recent decades. The aims of the present study were to elucidate whether Swedish paper and pulp mill workers had an increased incidence of testicular cancer, and to investigate whether certain occupational groups within the pulp and paper mill workforce were at increased risk. METHODS: The study was based on the Swedish Cancer Environment Register, which links the incidence of cancer for the period 1971-1990 with 1960 and 1970 National Census data on specific industries and occupations for all employed subjects in Sweden. RESULTS: Among maintenance workers employed both in 1960 and in 1970 in paper mills there was an increased risk for testicular cancer (standardized incidence ratio (SIR) 7.4, 95% confidence intervals (CI) 1.5-22), especially for seminomas (SIR 10.1, 95% CI 2.1-29). Maintenance workers were also at increased risk when analyzing workers employed in 1960, 1970, or both years. CONCLUSIONS: This study indicates an increased risk for testicular cancer, especially seminomas, among maintenance workers, but not among process workers, in Swedish paper mills.     

Mortality pattern among pulp and paper mill workers in Sweden: a case-referent study.

The mortality pattern among Swedish pulp and paper mill workers was evaluated in a case-referent study encompassing 4,070 men decreased during the period 1950-1987. The subjects were identified from the register of deaths and burials in six parishes. A significantly increased mortality was seen for diabetes mellitus and for secondary tumors of the lung and liver among the pulp and paper mill workers. Indications of excess risks were also found for obstructive lung disorders, pulmonary emboli, accidents, and pneumonia, as well as for malignant lymphomas, leukemias, and cancer of the pancreas and stomach. In the only parish where a sulfite process was exclusively used, cancer of the digestive tract and especially of the rectum was found to be in excess. Except for this parish, the sulfate process predominated in the plants included. The mortality pattern found in this study is in reasonable agreement with findings in various studies from this type of industry.     

Industry-wide study of mortality of pulp and paper mill workers

A study of pulp and paper mill workers indicated low risks of death from all causes (standardized mortality ratio (SMR) = 0.74) and all cancers (SMR = 0.81) compared with U.S. rates. The leukemia death rate in workers was not higher than the U.S. rate but was higher than the rate in county populations surrounding mills. Workers whose last jobs were in the finishing areas of the mills had an elevated SMR for liver cancer. An internal comparison of occupational characteristics indicated that workers employed in mills using other chemical pulping operations had significantly elevated mortality from all causes, all cancers, heart disease, lymphomas, and brain cancers. Lung cancer mortality was elevated in mills using kraft pulping. The internal comparisons confirmed the association between work in finishing and the risk of liver cancer. This study was designed to investigate whether pulp and paper mill workers have any risks that would indicate the need for studies detailing exposures. Am. J. Ind. Med. 33:354–365, 1998. © 1998 Wiley-Liss, Inc.     

Cancer incidence and mortality among Swedish smelter workers

Cancer incidence was analysed in a retrospective cohort of 3710 male Swedish smelter workers between 1958 and 1982 using a record linkage with the Swedish Cancer Register. During this period 467 cancers were registered in the cohort. An excess incidence of total cancer of about 30% was shown relative to general and local populations mainly due to 120 respiratory cancers. Excess SMRs for all cancer and respiratory cancer were highly significant. Trends in the incidence of cancer were studied using moving five year calendar periods. A decreasing rate of lung cancer was found during 1976-80 for both mortality and incidence. Incidence figures for two more years show a continued decreasing trend. This is validated by an analysis of different employment cohorts, taking latency into account, showing that the later the date of first employment the lower the incidence of cancer, especially for lung cancer.     

Cohort mortality study of Swedish pulp and paper mill workers-nonmalignant diseases

OBJECTIVES: The aim of this study was to determine mortality among pulp and paper mill workers according to the main mill pulping process, department, and gender, particular reference being given to diseases of the circulatory and respiratory systems. METHODS: The cohort of 18 163 men and 2 291 women employed between 1939 and 1999 and with >1 year of employment was followed for mortality from 1952 to 2001 (acute myocardial infarction from 1969). Standardized mortality ratios (SMR) with 95% confidence intervals (95% CI) were estimated by comparing the observed number of deaths with the expected number for the entire Swedish population. Exposure was assessed from personnel files in the mills. Data from an exposure measurement database are also presented. RESULTS: There were 5898 deaths in the cohort. Total mortality had an SMR of 1.02 (95% CI 0.98-1.06) for the men in the sulfate mills and an SMR of 0.93 (95% CI 0.90-0.97) for the men in the sulfite mills. Mortality from acute myocardial infarction was increased among the men in both the sulfate and sulfite mills [SMR 1.22 (95% CI 1.12-1.32) and SMR 1.11 (95% CI 1.02-1.21), respectively] and by department in sulfate pulping (SMR 1.29, 95% CI 1.07-1.54), paper production (SMR 1.26, 95% CI 1.06-1.49), and maintenance (SMR 1.16, 95% CI 1.02-1.30). Mortality from cerebrovascular disease, diabetes mellitus, and nonmalignant respiratory diseases was not increased. CONCLUSIONS: Death from acute myocardial infarction, but not cerebrovascular diseases, was increased in this cohort and was probably related to a combination of different occupational exposures (eg, dust, sulfur compounds, shift work, and noise).     

Cancer incidence in a cohort of Swedish sewage workers: extended follow up

OBJECTIVES: To study the cancer incidence in a cohort of Swedish sewage workers. An increased incidence of cancer of the stomach, the kidney and the nervous system in this cohort was previously reported. This new analysis reports on 9 more years of follow up. METHODS: The study is an analysis of a cohort of all 711 employees at 17 Swedish sewage plants employed for at least for 1 year during the years 1965-86. Assessment of exposures was performed by classification of work tasks. Standardised incidence ratios (SIRs), and 95% confidence intervals (95% CIs) were calculated. RESULTS: The total cancer incidence was not significantly increased (SIR = 1.2, 95% CI 0.92 to 1.5) but the incidence of prostate cancer was (SIR = 1.6, 95% CI 1.0 to 2.5), and based on two cases only, there seemed to be a significant increase of cancer of the nose and the nasal sinuses (SIR = 12, 95% CI 1.5 to 44). The incidence of stomach cancer was also increased (SIR = 2.3, 95% CI 0.99 to 4.5). There was no relation between cancer incidence and level of sewage exposure. CONCLUSIONS: Sewage workers did not have an increased risk of cancer, and the increased risk estimates for some specific cancer sites were not conclusive.       

Cancer incidence among pulp and paper workers exposed to organic chlorinated compounds formed during chlorine pulp bleaching

The risk of cancer of 152 male workers exposed to organic chlorine compounds formed during chlorine pulp bleaching was assessed in a retrospective cohort study. The men had worked continuously for at least one year in selected job categories between 1 January 1945 and 31 December 1961. The cohort was followed for death and cancer incidence until 31 December 1987 with the use of the data of the National Population Register and the Finnish Cancer Registry. There were 12 observed cancers against 8.1 expected [standardized incidence ratio (SIR) 1.5, 95% confidence interval (95% CI) 0.8-2.6]. Among the stock preparation workers (N = 53), a significantly elevated risk of lung cancer was found (6 observed, 1.0 expected, SIR 6.3, 95% CI 2.3-14) that was especially prominent after a latency (time since first employment) of at least 15 years and in the age group of 35 to 59 years. Although all of the cases involved smokers, a part of the increased incidence may be associated with the workplace exposure to organic chlorinated compounds.     

Cancer incidence of workers in the Finnish pulp and paper industry

The cancer incidence of 3,545 workers in the Finnish pulp and paper industry was assessed in a retrospective cohort study. The cohort included workers with continuous employment of at least one year between 1 January 1945 and 31 December 1961 and was followed until 31 December 1980. Six subcohorts were formed (sulfite mill, sulfate mill, paper mill, board mill, maintenance department, and power plant). Separate analyses were made for the 2,597 workers hired after 1 January 1945. The smoking habits were surveyed. Among the men, 196 cases of primary cancer were detected versus 203.8 expected [standardized incidence ratio (SIR) 96, 95% confidence interval (95% CI) 82-114], and there were 47 cancer cases among the women versus 57.9 expected (SIR 91, 95% CI 60-108). Lung cancer occurred in 78 men (62.6 expected, SIR 125, 95% CI 98-155), and the excess was the most prominent for the male board mill workers (40 observed, 81.1 expected, SIR 222, 95% CI 158-302), particularly after 20 year's latency (25 observed, 7.8 expected, SIR 323, 95% CI 209-476). Analogous excesses of lung cancer occurred among the men (especially the male board mill workers) who began work after 1 January 1945. The findings were not explained by smoking habits.     

Cancer incidence and mortality among Swedish smelter workers.

Cancer incidence was analysed in a retrospective cohort of 3710 male Swedish smelter workers between 1958 and 1982 using a record linkage with the Swedish Cancer Register. During this period 467 cancers were registered in the cohort. An excess incidence of total cancer of about 30% was shown relative to general and local populations mainly due to 120 respiratory cancers. Excess SMRs for all cancer and respiratory cancer were highly significant. Trends in the incidence of cancer were studied using moving five year calendar periods. A decreasing rate of lung cancer was found during 1976-80 for both mortality and incidence. Incidence figures for two more years show a continued decreasing trend. This is validated by an analysis of different employment cohorts, taking latency into account, showing that the later the date of first employment the lower the incidence of cancer, especially for lung cancer.     

Cancer incidence among women in the Norwegian pulp and paper industry.

BACKGROUND: The aim of the present study was to investigate cancer risk among women working in the Norwegian pulp and paper industry. The cohort included a total of 4,247 workers employed for at least one year between 1920 and 1993 (108,095 person-years), 85% of them as paper or administration workers. METHODS: The follow-up period for cancer was from 1953-1993. No data of exposure measurements were available. The analyses were based on comparisons of standard incidence ratios. The expected numbers of cancer cases were calculated using the five-year age-specific incidence rates for the entire female population. RESULTS: During the follow-up period, 380 new cases of cancer were observed vs. 322 expected (SIR = 1.2, 95% CI = 1.07-1.30). An excess risk of ovarian cancer was found (SIR = 1.5, 95% CI = 1.07-2.09). The SIR was highest among those younger than 55 years, and mostly among those working in paper departments. Short-term workers showed increased risk of lung and bladder cancer. CONCLUSIONS: Based on results from the present study, the increased risk of ovarian cancer is difficult to interpret, since existing knowledge of its etiology is limited. However, these women might have been exposed to various work-related agents such as talc, microbes, and different types of paper dust.     

Cancer incidence among Danish seafarers: a population based cohort study

Aims: Seafarers aboard oil and chemical tankers may be exposed to many chemicals, including substances like benzene that are known to be carcinogenic. Other seafarers are exposed to engine exhaust, different oil products, and chemicals used aboard and some years ago asbestos was also used extensively in ships. The aim of this study was to study cancer morbidity among Danish seafarers in relation to type of ship and job title. Methods: A cohort of all Danish seafarers during 1986–1999 (33 340 men; 11 291 women) registered by the Danish Maritime Authority with an employment history was linked with the nationwide Danish Cancer Registry and followed up for cancer until the end of 2002. The number of person years at risk was 517 518. Standardised incidence ratios (SIR) were estimated by use of the corresponding national rates. Results: The SIR of all cancers combined was higher than expected: 1.26 (95% CI 1.19 to 1.32) for men and 1.07 (95% CI 0.95 to 1.20) for women. This was mainly due to an excess of cancer of the larynx, lung, tongue, mouth, pharynx, oesophagus, pancreas, kidney, urinary bladder, colon, and bone as well as skin melanomas among men (the three latter borderline significantly increased), and an excess of cancer of the lung, rectum, and cervix uteri among women. The differences in risk pattern for lung cancer between the different job categories among men ranged in terms of SIR from 1.2 (95% CI 0.9 to 1.7) (engine officers) to 2.3 (1.6 to 3.3) (engine room crew), and 4.1 (2.1 to 7.4) among maintenance crew. Non-officers had a 1.5 times higher lung cancer risk than officers. No increased occurrence of all lymphatic and haematopoietic malignancies combined was found for employees on tankers, but the number of cases was limited to a total of 7. Conclusions: Danish seafarers, especially men, face an increased overall cancer risk, in particular a risk for lung cancer and other tobacco associated cancers.     

Cancer mortality and incidence among a cohort of benzidine and dichlorobenzidine dye manufacturing workers

BACKGROUND: Benzidine is classified as a definite human carcinogen and dichlorobenzidine as a probable human carcinogen. METHODS: A cohort study of 538 workers potentially exposed to benzidine and/or dichlorobenzidine from a single chemical manufacturing facility was conducted. Social Security records were used to identify all employees who worked at the facility from 1960 to 1977. Vital status was determined through 2001 and cancer incidence through 2002. RESULTS: A total of 22 bladder cancer cases were identified. For three individuals, bladder cancer was the underlying cause of death. Increased standardized mortality ratios (SMRs) were found for all cancer 1.54 (95% CI 1.04-2.19), bladder cancer 8.34 (95% CI 1.72-24.78), and lymphohematopoietic cancer 2.84 (95% CI 1.04-6.18). The standardized incidence ratio (SIR) for bladder cancer was 6.85 (95% CI 4.30-10.4). Only one case of bladder cancer was identified among the workers who were exposed to dichlorobenzidine only. However, an increased risk for lymphohematopoietic cancer was found among these dichlorobenzidine only workers (SMR 6.62 (95% CI 1.37-19.36)). CONCLUSIONS: This study confirms the high risk of bladder cancer among benzidine exposed workers even years after exposure has ceased, and raises suggestive evidence of increased risk to lymphohematopoietic cancer from exposure to benzidine or dichlorobenzidine.     

Mortality and incidence of cancer among sewage workers: a retrospective cohort study.

To study the incidence of and mortality from cancer among sewage workers a retrospective analysis was performed on a cohort of 656 men employed for at least one year at any one of 17 Swedish sewage plants during the years 1965-86. Assessment of exposure was done by classification of work tasks. Lower than expected total mortality (standardised mortality ratio (SMR) = 0.75, 95% confidence interval (95% CI) 0.58-0.97) and cardiovascular mortality (SMR = 0.61, 95% CI 0.39-0.91) was found. This was interpreted as a result of the healthy worker effect. For all cancers combined the mortality (SMR = 1.08, 95% CI 0.68-1.67) and morbidity (SMR = 1.02, 95% CI 0.72-1.38) were comparable with those of the general population. There were increased incidences for brain tumours (SMR = 2.19, 95% CI 0.45-6.39), gastric cancers (SMR = 2.73, 95% CI, 1.00-5.94), and renal cancers (SMR = 1.68, 95% CI = 0.35-4.90). For lung cancer the risk was reduced (SMR = 0.70, 95% CI 0.15-2.05). Allowance for a latency period of 10 years from the start of exposure did not change the pattern. Logistic modelling was used to search for exposure-response relations. In a logistic model with the confounder age forced in, renal cancer had a significant positive relation with a weighted sum of employment times, where the weights describe the classification of exposure. No exposure-response relations were found for brain tumors or gastric cancers. The increased risks are based on small numbers of cases. A future follow up will add more conclusive power to the study. Specific exposures need to be identified to allow for a better dose-response analysis.     

Mortality among a cohort of uranium mill workers: an update

Aims: To evaluate the mortality experience of 1484 men employed in seven uranium mills in the Colorado Plateau for at least one year on or after 1 January 1940.

Methods: Vital status was updated through 1998, and life table analyses were conducted.

Results: Mortality from all causes and all cancers was less than expected based on US mortality rates. A statistically significant increase in non-malignant respiratory disease mortality and non-significant increases in mortality from lymphatic and haematopoietic malignancies other than leukaemia, lung cancer, and chronic renal disease were observed. The excess in lymphatic and haematopoietic cancer mortality was due to an increase in mortality from lymphosarcoma and reticulosarcoma and Hodgkin's disease. Within the category of non-malignant respiratory disease, mortality from emphysema and pneumoconioses and other respiratory disease was increased. Mortality from lung cancer and emphysema was higher among workers hired prior to 1955 when exposures to uranium, silica, and vanadium were presumably higher. Mortality from these causes of death did not increase with employment duration.

Conclusions: Although the observed excesses were consistent with our a priori hypotheses, positive trends with employment duration were not observed. Limitations included the small cohort size and limited power to detect a moderately increased risk for some outcomes of interest, the inability to estimate individual exposures, and the lack of smoking data. Because of these limitations, firm conclusions about the relation of the observed excesses in mortality and mill exposures are not possible.