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Risk of Mesothelioma from Exposure to Crocidolite Asbestos: a 1995 Update of a South African Mortality Study

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Risk of Mesothelioma from Exposure to Crocidolite Asbestos: a 1995 Update of a South African Mortality Study Occup Environ Med 2000;57:563–567 563 Occup Environ Med: first published as 10.1136/oem.57.8.563 on 1 August 2000. Downloaded from Risk of mesothelioma from exposure to crocidolite asbestos: a 1995 update of a South African mortality study Danuta Kielkowski, Gillian Nelson, David Rees Abstract Prieska is a small, remote town in South Africa, Objective—To find the risk of developing close to a crocidolite asbestos mining area that mesothelioma in a cohort born in 1916–36 was productive from 1893 to the late 1960s. in Prieska, Northern Cape Province, Twenty four crocidolite rich deposits had been South Africa. identified in the Prieska magisterial district by Methods—A birth cohort mortality study 1930.1 These were mined at various times from was carried out in a small town in the 1919–43 by the Cape Asbestos Company and Northern Cape Province, South Africa, from 1929 by smaller companies. A crushing with a history of crocidolite asbestos min- mill was built in Prieska town in 1930, and ing and milling. The cohort comprised all residents were exposed to asbestos fibre white births registered in the magisterial emissions from the mill which was close to both district of Prieska from 1916 to 1936, the residential and business areas,2 until at least inclusive (2390). Causes of death due to 1964. Local residents, however, remember the mesothelioma and other cancers as re- mill working in the late 1970s. Other sources of corded on medical certificates of cause of exposure were the asbestos dumps (on which death were investigated. Person-years children played); spillage of fibres during analysis was used to calculate mortalities transport; and tailings which were used for, due to mesothelioma, other respiratory among other things, surfacing roads and mak- cancers, and other non-respiratory can- ing bricks.3 The last major store of asbestos was cers. Proportional cancer mortalities removed from the town in 1982. Homes are were also calculated for mesothelioma and still polluted through years of wind blown other specific neoplasms. fibres accumulating in the ceilings. Results—The follow up rate for the cohort Several studies have shown an increased risk was 74.3% in 1995, and 683 traced mem- of developing mesothelioma or respiratory bers (38.6%) had died. Cause of death was cancer after occupational and environmental unknown for 6.4% of deaths. There were exposure to crocidolite.4–7 118 cases of cancer, 28 of them from mes- Botha et al6 reported an annual death rate othelioma, giving a cause specific mor- due to asbestosis or mesothelioma for white http://oem.bmj.com/ tality for mesothelioma of 277 (170–384) people of 542 per million for a high exposure 6 per 10 person-years. The rates for men crocidolite area (which included Prieska), 87 6 and women were 366 and 172 per 10 for a low exposure crocidolite area, and 24 in a person-years, respectively. The mortality control area. By comparison the rates for the for lung cancer (29 deaths) was 287 coloured (mixed race) population were 573 per 6 (135–436) per 10 person-years, and that million and 215 per million in the high and low for other non-respiratory cancers (60 exposure areas respectively. The standardised deaths) was 593 (442–745). Two cases of mortality ratio (SMR) was increased for all on September 29, 2021 by guest. Protected copyright. laryngeal and four of colon cancer were cancers in both population groups and sexes. Epidemiology and observed. All cancer mortality, mesothe- This was significant except for white women. Surveillance Section, lioma, and lung cancer proportional can- The lung cancer SMR was moderately in- National Centre for cer mortality ratios were increased. creased at 1.73 for white men, 1.87 for white Occupational Health, Conclusion—The mortality for mesothe- women, and 1.28 and 2.47 for coloured men PO Box 4788, lioma in men was twice that in women, and women respectively. Significance was Johannesburg 2000, probably because men were more likely to South Africa reached for white men and coloured women. D Kielkowski have had both occupational and environ- An interesting result was the increase in the G Nelson mental exposure to asbestos. SMRs for stomach cancer and neoplasms of D Rees Nevertheless, the mortality in women was the digestive organs and peritoneum for both still high and is probably indicative of the men and coloured women. Department of environmental exposure as white women Sluis-Cremer et al showed a mesothelioma Community Health, were rarely employed in the asbestos University of the rate of 446 per million person-years for white Witwatersrand, 7 York industry in the Prieska area. Due to the men employed in crocidolite mining.7 Rd, Parktown 2193, long latency from first exposure to diag- Cases of mesothelioma induced by environ- South Africa nosis of the neoplasm, the cause specific mental (non-workplace) asbestos exposure are D Kielkowski mortality in this cohort could be expected D Rees well documented, with domestic exposure due to increase rapidly over the next 10 years. to relatives working with asbestos a common (Occup Environ Med 2000;57:563–567) 8–11 Correspondence to: source. A recently published study from Aus- Dr D Kielkowski tralia estimates the incidence of mesothelioma [email protected] Keywords: South Africa; asbestos; environmental expo- sure; occupational exposure; cohort; mesothelioma; due to environmental asbestos exposure in Wit- Accepted 25 February 2000 lung cancer tenoom as 270 per million person-years.12 www.occenvmed.com 564 Kielkowski, Nelson, Rees Occup Environ Med: first published as 10.1136/oem.57.8.563 on 1 August 2000. Downloaded from Not surprisingly, an unusually large number they obtained identity numbers through the of cases of mesothelioma among the residents course of the study. of Prieska have been reported over the past few decades, which was the motivation for this DATA ANALYSIS study in which the risks of developing mesothe- All deaths among white people that had been lioma or other respiratory cancers were calcu- detected by the end of 1995 are included in the lated for this community. Preliminary data analysis. Descriptive statistics include a com- were published in 19905; this paper updates the parison of number of deaths within diVerent findings to 1995. age groups for specific causes of death; cancers are of particular interest. Person-years analysis was used to calculate Methods mortalities due to mesothelioma and other res- SUBJECTS piratory cancers (lung and bronchus). Person- This cohort mortality study included all white years were the number of years from birth to people whose births were registered in the death for deceased cohort members and the magisterial district of Prieska in 1916–36. Sub- years from birth to the end of 1995 for those jects who were not white had to be excluded still living. Proportional cancer mortality ratios because of poor oYcial records. The cohort (PCMRs) for mesothelioma and other respira- was established by copying the birth register for tory cancers were also calculated, with the the Prieska district for the selected years. white South African population as The unique national identity number and comparison.13 Sex specific and total expected vital status of the 2390 cohort members was numbers were calculated from people who had sought in the computerised population registry died at >30 so the age profile of the studied of the Department of Home AVairs. The regis- population and reference population were the try contains the unique identification number, same. The 95% confidence intervals (95% surname, all names, birth date, address, and if CIs) for the specific mortalities and PCMR the person has died, the date of death and analysis were calculated from the Poisson cause of death. This registry is organised by distribution. unique identification number but it can be searched also by surname and birth date. For Results each computerised record a physical file exists In the period 1917–36 a total of 5898 births which contains original documents such as were registered in the Prieska district. Of these death registration and medical death certifi- 2390 (40.5%) were white, 2376 (40.3%) were cates. Not all cohort members were entered coloured, 909 (15.4%) were black, and 16 into the computerised registry—namely, those (0.3%) were Asian (table 1). The population who died before it was established in 1972, and group of the remaining 207 births (3.5%) was those who had not obtained an identity not stated in the registers. document. In these cases, information was By the end of 1995 a total of 2410 members obtained by a manual search of the physical of the cohort were traced (table 1), most of files. whom were white (73.7%). Of the white people http://oem.bmj.com/ The identity numbers were subsequently who were traced 38% had died. A disappoint- used to ascertain vital status throughout the ingly small proportion of cohort members who follow up period. The identity numbers were were not white could be traced, so analysis had periodically sent to the Department of Home to be restricted to white subjects. AVairs, which provided copies of the medical As figure 1 shows, the age group with the certificate of death and the death register form highest proportion of deaths (44.8%) was of cohort members who had died. mature adults, followed by infants (24.9%). If a person dies at the age of <10, the name The most common causes of death in infants, on September 29, 2021 by guest. Protected copyright. of one or both parents (or the guardian) is as stated on the death certificates, were recorded on a form along with information complications of pregnancy, childbirth, and such as place of birth and address, parents’ purpureum (33%), followed by respiratory dis- names, and places of residence.
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