Cancer mortality among workers exposed to amphibole-free chrysotile asbestos

Our plain-English summary of Cancer mortality among workers exposed to amphibole-free chrysotile asbestos, by E. Yano, Z.M. Wang, X.R. Wang, et al (American Journal of Epidemiology, 2001).

The study

• Authors: E. Yano, Z.M. Wang, X.R. Wang, M.Z. Wang, Y.J. Lan
• Journal: American Journal of Epidemiology
• Published: 2001;154(6):538-43
• Cited by: 73 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The issue of whether exposure to chrysotile asbestos alone, without contamination from amphibole asbestos, causes lung cancer and mesothelioma was investigated in a 25-year longitudinal study (1972-1996) in Chongqin, China. The study cohort comprised 515 male asbestos plant workers exposed to chrysotile only; the control cohort included 650 non-dust-exposed workers. The results of analysis in which the proportional hazards model was used indicated that mortality due to all causes, all cancers, and lung cancer was related to asbestos exposure; the relative risks, adjusted for age and smoking, were 2.9, 4.3, and 6.6, respectively. Fiber concentrations in the raw material section and the textile section of the plant were 7.6 and 4.5 fibers/ml, respectively. Because of differences between the study and control plants, the authors also compared various sections of the asbestos plant that had different levels of dust exposure. The adjusted relative risk of lung cancer was 8.1 for workers exposed to high versus low levels of asbestos. Two cases of malignant mesothelioma, one pleural and the other peritoneal, were found in the asbestos cohort. These results suggest that heavy exposure to pure chrysotile asbestos alone, with negligible amphibole contamination, can cause lung cancer and malignant mesothelioma in exposed workers.

In plain English

This prospective cohort study followed 515 men at a chrysotile asbestos plant in Chongqin, China, from 1972 to 1996, plus male electronics workers without dust exposure. The plant used only chrysotile; four samples contained under 0.001 percent tremolite. Adjusted for age and smoking, asbestos workers' relative risk of lung cancer death versus controls was 6.6 (95% CI 1.92 to 23.0). It was 2.87 (95% CI 2.00 to 4.12) for all deaths and 4.29 (95% CI 2.17 to 8.46) for cancer deaths. Within the plant, raw material and textile workers had a lung cancer relative risk of 8.1 (95% CI 1.8 to 36.1) versus office and asbestos cement workers. Two mesotheliomas occurred among asbestos workers, one pleural and one peritoneal. Using only pathologically confirmed cancers, the all-cancer result stayed significant, but lung cancer estimates fell to 1.9 versus controls and 1.1 (95% CI 0.9 to 1.4) for high versus low exposure, both with intervals including 1. The authors concluded that uncontaminated chrysotile alone may be related to increased lung cancer risk comparable to mixed-type asbestos, and suggested it can also cause mesothelioma.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Prospective, fixed cohort study with 25 years of follow-up (1972 to 1996). It compared asbestos plant workers with an external control cohort and also compared exposure levels within the plant, using the Cox proportional hazards model.
• Who was studied: 515 male workers at an asbestos plant in Chongqin, China, who were actively working in January 1972 and had worked there at least 1 year. All 130 females and 109 males with less than 1 year were excluded. The control cohort was 650 male workers at an electronics plant in suburban Chongqin with no workplace dust exposure. Five of them were lost to follow-up and excluded, so 645 were analysed.
• Exposure: Chrysotile asbestos only, from two mines in Sichuan. Four commercial samples contained less than 0.001 percent tremolite fiber. Products included textiles, asbestos cement, friction materials, rubber products and heat-resistant materials. Personal sampling in June 1999 gave geometric mean fiber levels of 12.6 fibers/ml in raw material bagging, 6.5 in raw material opening, 4.5 in textile, 2.8 in rubber plate and 0.1 in asbestos cement, where one worker was monitored.
• Main results:
  • After adjustment for age and smoking, asbestos plant employment was associated with a relative risk of lung cancer death of 6.6 compared with the control cohort. Table 3 gives 6.64 (95% CI 1.92 to 23.0).
  • Adjusted relative risks for asbestos plant employment were 2.87 (95% CI 2.00 to 4.12) for death from all causes and 4.29 (95% CI 2.17 to 8.46) for all cancer deaths.
  • Of the asbestos workers, 132 of 515 died (25.6%), compared with 42 of 645 control workers (6.5%). Fifty asbestos workers developed malignant tumors, 22 of them lung cancer. Control workers had 11 cancers, 3 of them lung cancer.
  • When only pathologically confirmed cancers were analysed, the association with all cancer deaths remained significant. The lung cancer relative risk for asbestos versus control workers was 1.9. Table 3 appears to give 1.94 (95% CI 0.48 to 7.79), an interval that includes 1.
  • Compared with the control plant, adjusted lung cancer relative risks were 17.6 (95% CI 4.5 to 69.3) for the raw material section, 9.8 (95% CI 2.1 to 44.4) for the textile section and 7.3 (95% CI 1.6 to 33.5) for maintenance. Relative risks for the asbestos cement section (2.5, 95% CI 0.4 to 15.5) and the rubber plate section (5.3, 95% CI 0.5 to 51.2) were not statistically significant. Office workers had no lung cancer cases.
  • Within the asbestos cohort, the high-exposure group (raw material and textile sections) had 13 lung cancers among 150 workers (8.7%). The low-exposure group (office and asbestos cement) had 2 among 162 (1.2%). The age- and smoking-adjusted relative risk was 8.1 (95% CI 1.8 to 36.1). The intermediate group (maintenance, rear service, rubber plate) had 7 among 203, with a relative risk of 3.6 (95% CI 0.7 to 17.5).
  • Restricted to pathologically confirmed lung cancer, the high-versus-low relative risk was 1.1 (95% CI 0.9 to 1.4). This rested on five cases in the high-exposure group and one in the low-exposure group.
  • Two pathologically confirmed mesotheliomas occurred in the asbestos cohort and none in the control cohort. One was pleural, in the raw material section, with 13.8 years from first exposure to death. One was peritoneal, in the textile section, with 21.8 years. Together they made up 1.5 percent of deaths in the asbestos cohort.
  • After adjustment for age, the relative risks of lung cancer were 1.5 for smoking, 3.4 for asbestos exposure and 12.6 for both together. Only the combined figure was statistically significant, which the authors took to suggest an interaction between asbestos and smoking.
  • During follow-up, 139 workers in the asbestos cohort were found to have asbestosis.
• The authors' conclusion: The authors concluded that exposure to uncontaminated chrysotile alone may be related to an increased risk of lung cancer comparable to that caused by mixed-type asbestos. They also said the study suggests pure chrysotile can cause mesothelioma.
• Limitations the authors state:
  • Fiber levels were measured only in 1999. Past levels were probably much higher, which the authors say could lead to overestimating the effect.
  • Only a small proportion of tumors were confirmed by pathology, which could have caused misclassification.
  • Excluding the five control workers lost to follow-up might have introduced selection bias.
  • There may have been unrecognized differences between workers at the asbestos plant and at the control plant.
  • Smoking was recorded only as yes or no, so smoking differences may not have been well controlled.
  • The asbestosis count may be an underestimate, because ILO category 1/0 is not diagnosed as pneumoconiosis under the Chinese standard.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Amphibole Group, Chrysotile, Amphibole Asbestos, Lung Cancer, Mesothelioma, Asbestos Exposure, Relative Risk, Malignant Mesothelioma.

Related studies

• Cancer mortality among Chinese chrysotile asbestos textile workers — X.R. Wang, I.T. Yu, et al. (2012)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• A case control study of lung cancer and exposure to chrysotile and amphibole at a slovenian asbestos-cement plant — M. Dodic Fikfak, D. Kriebel, et al. (2007)
• Cancer mortality and asbestosis among workers in an asbestos plant in Chongqing, China — F. Zhong, E. Yano, et al. (2008)
• Mesothelioma in a worker who spun chrysotile asbestos at home during childhood — E. Yano, Z.M. Wang, et al. (2009)
• The mortality of amphibole miners in South Africa, 1946-80 — G.K. Sluis-Cremer, F.D. Liddell, et al. (1992)

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