An updated historical cohort mortality study of workers exposed to asbestos in a refitting shipyard, 1947–2007

Abstract

To evaluate the long-term health effects of occupational asbestos exposure, an updated historical cohort mortality study of workers at a refitting shipyard was undertaken. The cohort consisted of 249 male ship repair workers (90 laggers, 159 boiler repairers). To determine relative excess mortality, standardized mortality ratios (SMRs) were calculated using mortality rates among the Japanese male population. Mortality follow-up of study subjects was performed for the period from 1947 till the end of 2007. We identified the vital status of 87 (96.7%) laggers and 150 (94.3%) boiler repairers. Of these, 63 (72.4%) and 95 (63.3%), respectively, died. Laggers, who had handled asbestos materials directly, showed a significantly elevated SMR of 2.64 (95% confidence interval [CI]: 1.06-5.44) for lung cancer and 2.49 (95% CI: 1.36-4.18) for nonmalignant respiratory diseases. Boiler repairers, who had many opportunities for secondary exposure to asbestos and a few for direct exposure, showed no significant elevation in SMR for lung cancer but a significantly elevated SMR of 1.78 (95% CI: 1.06-2.81) for nonmalignant respiratory diseases. In an analysis according to duration of employment, there was a significantly elevated SMR of nonmalignant respiratory diseases in the longer working years group. Among workers from both jobs, no deaths caused by mesothelioma in addition to those in the original study were found and no subject died from larynx cancer. This updated study confirmed a significant excess of asbestos-related mortality from diseases such as lung cancer and nonmalignant respiratory diseases among workers in a refitting shipyard in Japan.