Asthma and cancer among pulp and paper mill workers

Abstract

There were two main aims of this thesis. One was to study if repeated high exposures to irritant gases give rise to new-onset asthma, and the other was to study if exposure in pulp and paper mills were associated with cancer.Two studies were case-referent studies of male mortality in parishes surrounding three sulfite (N=780) and four sulfate mills (N=2480). An increased mortality from asthma was found among workers in sulfite mills, possibly as a result of accidental exposure to sulfur dioxide. Brain tumor mortality was two to three times higher than expected among both sulfite and sulfate mill workers. In sulfate mills, the excess mortality was seen among workers from maintenance departments, wood rooms and saw mills. The workers from the sulfate mills had an increased mortality from lung cancer and pleural mesotheliomas, probably caused by asbestos exposure. Stomach cancer mortality was not increased in any of the studies.One study investigated glioma incidence between 1971 and 1990 among men in different occupations in Swedish pulp and paper mills from census and cancer incidence data in the Cancer Environment Register 6070. All gainfully employed Swedish men were used as a reference group. Standardized incidence ratios were calculated using 5-year birth cohorts stratified by calendar period and region. A 50% excess incidence of gliomas was found among maintenance workers in the pulp and paper industry and among process workers in pulp mills. Process workers in paper mills showed a lower incidence than expected. The reasons for these findings are not obvious.In a historical cohort study, 101 bleachery workers and 314 paper department workers were investigated by questionnaires with items on airway symptoms and exposure to irritant gases. About 50% of the irritant gas-exposed workers had experienced high exposures giving respiratory symptoms (gassings). Incidence rates of adult-onset physician-diagnosed asthma and adult-onset wheeze were calculated and Cox regression analyses were performed. The incidence of asthma was significantly increased among bleachery workers during mill working years compared to paper workers (5.4 and 1.0 cases per 1000 person-years, respectively), especially among workers who reported gassings. The incidence of new-onset wheeze was also increased among the workers with gassings. Both for asthma and wheeze, the risk estimate was five times higher for those reporting gassings, stratified for sex, and controlled for hay fever and smoking.It was shown that repeated high exposure to irritant gases gave rise to new-onset asthma among bleachery workers. Such exposure should be prevented. It was also found that glioma incidence was increased in some occupations in pulp and paper mills. Mortality from lung cancer and pleural mesotheliomas was increased, probably caused by asbestos exposure.