Risk of mesothelioma from exposure to crocidolite asbestos: a 1995 update of a South African mortality study

Objective-To find the risk of developing mesothelioma in a cohort born in 1 916-36 in Prieska, Northern Cape Province, South Africa. Methods-A birth cohort mortality study was carried out in a small town in t he Northern Cape Province, South Africa, with a history of crocidolite asbe stos mining and milling. The cohort comprised all white births registered i n the magisterial district of Prieska from 1916 to 1936, inclusive (2390). Causes of death due to mesothelioma and other cancers as recorded on medica l certificates of cause of death were investigated. Person-years analysis w as used to calculate mortalities due to mesothelioma, other respiratory can cers, and other non-respiratory cancers. Proportional cancer mortalities we re also calculated for mesothelioma and other specific neoplasms. Results-The follow up rate for the cohort was 74.3% in 1995, and 683 traced members (38.6%) had died. Cause of death was unknown for 6.4% of deaths. T here were 118 cases of cancer, 28 of them from mesothelioma, giving a cause specific mortality for mesothelioma of 277 (170-384) per 10(6) person-year s. The rates for men and women were 366 and 172 per 10(6) person-years, res pectively. The mortality for lung cancer (29 deaths) was 287 (135-436) per 10(6) person-years, and that for other non-respiratory cancers (60 deaths) was 593 (442-745). Two cases of laryngeal and four of colon cancer were obs erved. All cancer mortality, mesothelioma, and lung cancer proportional can cer mortality ratios were increased. Conclusion-The mortality for mesothelioma in men was twice that in women, p robably because men were more Likely to have had both occupational and envi ronmental exposure to asbestos. Nevertheless, the mortality in women was st ill high and is probably indicative of the environmental exposure as white women were rarely employed in the asbestos industry in the Prieska area. Du e to the long latency from first exposure to diagnosis of the neoplasm, the cause specific mortality in this cohort could be expected to increase rapi dly over the next 10 years.