INGESTED ARSENIC AND INTERNAL CANCER - A HISTORICAL COHORT STUDY FOLLOWED FOR 33 YEARS

A historical cohort study was conducted to investigate the long-term e ffect of exposure to ingested arsenic. The 454 residents who had been identified in a list made in 1959 were followed until 1992. They lived in an arsenic-polluted area, called Namiki-cho, Nakajo-machi, in Niig ata Prefecture, Japan, and used well water containing inorganic arseni c. The exposure period was estimated to be about 5 years (1955-1959). Death certificates for the people who died between 1959 and 1992 were examined, and a total of 113 of the 454 residents were estimated to ha ve drunk well water containing a high dose of arsenic (greater than or equal to 1 ppm). The standardized mortality rate ratios of these 113 residents were 15.69 for lung cancer (observed/expected = 8/0.51; 95% confidence interval (CI) 7.38-31.02) and 31.18 for urinary tract cance r (observed/expected = 3/0.10; 95% CI 8.62-91.75). Cox's proportional hazard analyses demonstrated that the hazard ratios of the highest exp osure level group (greater than or equal to 1 ppm) versus the backgrou nd exposure level group (0.001 ppm) were 1.74 (95% CI 1.10-2.74) for a il deaths and 4.82 (95% CI 2.09-11.14) for all cancers. The analysis a ccording to the skin signs of chronic arsenicism in 1959 showed that t hey were useful risk indicators for subsequent cancer development. In the development of lung cancer, there was evidence of synergism betwee n arsenic intake and smoking habit.