Studies on silicosis as reported in migrant workers. (Report 3)-- Mortality among migrant workers in tunnelling works

Abstract

The eastern part of Toyama prefecture is well known as being one of the areas where many migrant workers* live who have been exposed to dust and suffer from silicosis. The purpose of this study is to investigate the mortality rates of migrant workers exposed to dust through jobs such as tunnelling. Questionaires on occupational careers were sent to all male inhabitants aged 30 or over in the selected area between 1977 and 1978. Two thousand and seventy-seven of the respondents were followed-up until the end of 1983. For those who died, the causes and dates of death were confirmed by death certificates. The mean person-years of observation per a person was 5.9. The subjects were divided into three groups. One group included 644 migrant workers who had worked in jobs with exposure to dust, 275 migrant workers whose jobs did not expose them to dust and 1158 persons who were not migrant workers and whose jobs did not also expose them to dust. Mortality rates compared among the three groups. The mortality rate per 1, 000 person-years of migrant workers who had worked in jobs with exposure to dust was 22.3. The mortality rate was significantly higher than that of migrant workers who had not worked in jobs with exposure to dust (11.4) and those who were not migrant workers (9.1). Especially significant is the excess mortality rates of migrant workers whose jobs exposed them to dust in ages 40 to 69. There was no significant difference in mortalities between non-migrant workers and migrant workers who had not worked in jobs with exposure to dust. Among migrant workers who had worked in jobs with exposure to dust, the highest mortality rates per 1, 000 person-years were found in malignant neoplasms (4.3) and also in pulmonary tuberculosis (4.3) followed by heart diseases (3.8), pneumonia & bronchitis (3.0), cerebrovascular diseases (2.7) and pneumoconiosis (2.1). The mortality rates for pulmonary tuberculosis, pneumonia & bronchitis and pneumoconiosis among migrant workers whose jobs exposed them to dust were higher than those among non-migrant workers. There were no significant differences among all cause-specific mortalities between migrant workers who had not worked in jobs with exposure to dust and non-migrant workers.