Cohort mortality study of rock salt workers in Italy

Our plain-English summary of Cohort mortality study of rock salt workers in Italy, by M. Tarchi, D. Orsi, P. Comba, et al (American Journal of Industrial Medicine, 1994).

The study

• Authors: M. Tarchi, D. Orsi, P. Comba, M. De Santis, R. Pirastu, G. Battista, M. Valiani
• Journal: American Journal of Industrial Medicine
• Published: 1994;25(2):251-6
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A cohort mortality study of rock salt workers was carried out in Volterra, Italy. The occupational risk factors identified during environmental hygiene surveys were high noise levels and exposure to dusts and to chrysotile asbestos. The cohort consists of 487 subjects (367 males and 120 females) employed in the mine between 1/1/1965 and 12/31/1989. At the end of follow-up, 387 individuals were alive (295 males and 92 females), and 100 were decreased (72 males and 28 females). For two decedents, the cause of death was unknown. Regional rates were used for the computation of standardized mortality ratios (SMRs). In the entire cohort, observed mortality for all causes was similar to expected (SMR = 98, 100 obs); SMR for all cancer was 127 (41 obs); for lung cancer, the SMR was 146 (10 obs). Two cases of pleural mesothelioma, both in males, resulted in a statistically significant elevation of this cause (SMR = 741, 90% confidence interval (CI) 131-2,332). Two malignant brain tumors were detected (SMR 328, 90% CI 58-1,032); one of these was identified as a secondary neoplasm with consideration of additional clinical information. Among males, mortality for all cancers was significantly increased (SMR = 140, 90% CI 106-192). The observed mortality for malignant tumors of the digestive and the respiratory systems was higher than expected. In women, two cases of malignant ovarian cancer were observed vs. 0.42 expected on the basis of the regional rates. Increased mortality from lung and pleural tumors was consistent with the exposure to asbestos, which has also been shown to play a role in the development of ovarian tumors. The main limitations of this study were the small number of subjects and the definition of exposure solely in terms of duration of employment. Further studies of rock salt workers are needed to elucidate our findings.

In plain English

This retrospective cohort study tracked deaths among all 487 people (367 men and 120 women) who worked for any length of time from 1965 through 1989 at the state-owned rock salt mine in Volterra, Italy. Workplace surveys had found high noise, dust, and chrysotile asbestos in the boiler and piping system. Deaths were compared with Tuscany regional rates, using 90% confidence intervals chosen in advance. By the end of 1989, 100 workers had died. Deaths from all causes were close to expected (SMR 98). Two deaths from pleural cancer, both in men, were a statistically significant excess (SMR 741, 90% CI 131 to 2,332). There were 10 lung cancer deaths (SMR 146), which did not reach statistical significance. Men had a significant excess of all cancers (SMR 140, 90% CI 106 to 192). Two women died of malignant ovarian cancer versus 0.42 expected. The authors concluded that the pleural excess and suggested lung cancer increase were consistent with past asbestos exposure. They noted the small cohort, and that exposure was measured only by length of employment.

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: retrospective cohort mortality study using standardized mortality ratios (SMRs) with 90% confidence intervals, compared with Tuscany regional death rates
• Who was studied: All 487 persons (367 males, 120 females) employed for any length of time at the state-owned 'Salina di Stato' rock salt mine in Volterra, Italy, between January 1, 1965 and December 31, 1989; follow-up to December 31, 1989
• Exposure: Work in the rock salt mine. Surveys identified high noise levels, elevated dust exposure, and chrysotile asbestos in the boiler and vapor piping system. Exposure was defined only by duration of employment and time since hire.
• Main results:
  • At the end of follow-up, 387 cohort members were alive (295 males, 92 females) and 100 had died (72 males, 28 females)
  • Whole cohort, all causes of death: similar to expected (SMR 98, 90% CI 82 to 116, 100 observed)
  • Whole cohort, all cancers: SMR 127 (41 observed)
  • Whole cohort, lung cancer: SMR 146 (10 observed)
  • Whole cohort, tumors of the pleura and other parts of the respiratory system: two cases, both cancers of the pleura (in males; described in the abstract as pleural mesothelioma), a statistically significant increase (SMR 741, 90% CI 131 to 2,332)
  • In the whole cohort, no other cause of death reached statistical significance
  • Males, all tumors: significantly increased (SMR 140, 90% CI 106 to 192, 33 observed)
  • Males, tumors of the pleura and other parts of the respiratory system: statistically significant at the 90% confidence level (SMR 952, 90% CI 169 to 2,998)
  • Whole cohort, malignant brain tumors: two observed (SMR 328, 90% CI 58 to 1,032). Additional clinical information showed one was a secondary tumor.
  • Females: two deaths from malignant ovarian cancer versus 0.42 expected from regional rates; one benign ovarian tumor was also detected
  • Females, lung cancer: observed exceeded expected (SMR 414, 90% CI 74 to 1,036)
  • Workers with 20 or more years since hire had significantly increased all-cancer mortality (SMR 145, 90% CI 107 to 193). Those with less than 20 years had an SMR of 90 (90% CI 45 to 163).
  • 10 of 11 respiratory system tumors occurred more than 20 years after first employment
• The authors' conclusion: The authors concluded that the increased pleural tumor mortality and the suggested increase in lung cancer were consistent with past asbestos exposure. Citing other studies, they noted that asbestos has also been shown to play a role in ovarian tumors. They also concluded that further studies of rock salt workers are needed.
• Limitations the authors state:
  • Small number of subjects, and a low proportion (35%) of person-years with more than 20 years since hire
  • Exposure was categorized only by duration of employment in the mine
  • Too few deaths from specific cancer sites for more detailed analysis
  • For brain tumors, exposure of cohort members to other suspected factors (chlorinated solvents, pesticides, laboratory work) could not be ruled out
  • Stomach cancer findings may partly reflect high regional rates linked to diet
  • No previous studies of rock salt workers existed against which to check consistency

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, standardized mortality ratio (SMR), Lung Cancer, Pleural Mesothelioma, confidence interval, Neoplasm, Ovarian Cancer.

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