Objectives This study investigated the possibility of occupational exposure to ozone increasing the risk of obstructive airway disease among bleachery workers.

Methods Bleachery workers (N=129) from two Swedish pulp mills using ozone for bleaching were studied together with referents (N=80) from adjacent paper mills. The pulp mills had previously used chlorine dioxide as the bleaching agent. Testings included spirometry, methacholine challenge testing, and questionnaires. Area samplings showed sporadic ozone levels exceeding 0.9 ppm.

Results There was a greater prevalence of wheezing (25%) among the bleachery workers with a history of gassings (from ozone, chlorine, or sulfur dioxide) than among those without gassings (18%) and among the referents (13%). Among the current smokers the fraction with a slightly increased bronchial responsiveness to methacholine was greater among the bleachery workers reporting gassings than among those that had not been gassed. For the period from 1992 to 1996, when the mills were using ozone, there was an increased incidence rate of wheezing among the workers in the bleachery (incidence rate ratio 2.3, 95% confidence interval 1.6-5.8).

Conclusions Repeated exposure to irritants increases the risk of asthma-like symptoms. This finding reinforces the view that repeated peak exposures to irritants must be prevented in pulp mills.

Key terms asthma; bleachery worker; chlorine dioxide; irritant; occupational exposure; ozone; pulpmill worker; respiratory health