某艦船修理事業場における石綿曝露労働者の歴史的コホート研究

Abstract

To investigate the risks of developing asbestos-related diseases, we con- ducted a historical cohort study on 249 ship repair workers (90 laggers and 159 boiler repairers) in a single refitting shipyard in Yokosuka city, Japan. We successfully identified the vital status of 87 (96.7%) laggers and 150 (94.3%) boiler repairers, and, of these, 49 (56.3%) and 65 (43.3%) died, respectively, during the follow-up period from 1947 till the end of 1996. Our in-person interviews with some of the subjects clarified that asbestos exposure was considered to be substantially high in the 1950-60s, decreased thereafter gradually but remained till the end of 1979 in the shipyard. The laggers, who had handled asbestos materials directly, showed a significantly elevated SMR (Standardized Mortality Ratio) of 2.8 [95 % C.I. (Confidence Interval) : 1.1-6.5] for lung cancer. The magnitude of the risk developing the cancer was greater after considering a 20-year latency (SMR= 3.4). Pancreatic cancer also yielded a greater SMR than unity (5.2, 90% C.I. : 1.4-16.9) in the 20-year latency group. Four laggers died from asbestosis. The boiler repairers, who had many chances for secondary exposure to asbestos and a few for direct exposure, showed no elevation of the SMR of lung cancer in either the overall group or the group after a 20-year latency. One boiler repairer died from mesothelioma and four from asbestosis. We were able to interview 71 among 85 living retired workers. Forty-three (60.6%) of them had been diagnosed to have asbestosis by physicians. The prevalence of the subjects having asbestosis and working for 180 months and more was significantly higher than that among those working for a shorter period after adjusting the different distributions of ages and smoking habits. These results suggested that asbestos exposure in the refitting shipyard causally related to some types of malignant neoplasms among the deceased and to respiratory symptoms among the living retired workers.