A mortality cohort study among workers in a graphite electrode production plant in Italy

Our plain-English summary of A mortality cohort study among workers in a graphite electrode production plant in Italy, by D.F. Merlo, S. Garattini, U. Gelatti, et al (Occupational and Environmental Medicine, 2004).

The study

• Authors: D.F. Merlo, S. Garattini, U. Gelatti, C. Simonati, L. Covolo, M. Ceppi, F. Donato
• Journal: Occupational and Environmental Medicine
• Published: 2004;61(2):e9
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Graphite electrode manufacturing workers are exposed to coal tar and its volatiles containing a variety of polycyclic aromatic hydrocarbons (PAH), silica and graphite dusts, and asbestos.

Aims: To investigate mortality from cancer and other diseases among workers in a graphite electrode production plant in Italy.

Methods: A total of 1291 males actively employed between 1 January 1950 and 31 December 1989 who had worked at the plant for at least one year were studied. The follow up extended from 1950 to 1997. Standardised mortality ratios (SMR) and their 95% confidence intervals (CI) were computed using mortality rates for the Italian and regional male population.

Results: Excess mortality was observed for all causes (SMR 1.44, CI 1.32 to 1.56), all cancers (SMR 1.27, CI 1.07 to 1.50), liver cancer (SMR 4.19, CI 2.68 to 6.23), silicosis (SMR 66.39, CI 52.56 to 82.7), and cirrhosis and other chronic diseases of the liver (SMR 1.87, CI 1.31 to 2.59) in comparison with the national male population. When regional rates were used to calculate the number of expected deaths, SMRs remained higher for silicosis (SMR 57.32, 42.11 to 76.22), and liver cancer (SMR 2.57, 1.57 to 3.97). Mortality from silicosis was increased in workers hired at young ages (<25 years, SMR 81.79; 25-34 years, SMR 82.73), and in workers aged <45 at death (SMR 333.3, CI 159.8 to 613). Mortality from liver cancer increased threefold (SMR 3.11, CI 1.78 to 5.05) in workers with more than 10 years of employment at the plant during the manufacture of Karbate products.

Conclusions: Results support the association between excess mortality from silicosis and occupational exposure to siliceous sands experienced during graphite electrode manufacturing. The observed excess mortality from liver cancer is compatible, to some extent, with exposures that may have occurred during the manufacture of phenolic and furfuryl resins treated products, although a role of lifestyle factors and viral infections cannot be excluded.

In plain English

This historical cohort study followed 1291 male production workers, employed at least one year between 1950 and 1989 at a graphite electrode plant in northern Italy, tracking deaths to 1997. Lacking individual exposure data, all workers were treated as equally exposed to polycyclic aromatic hydrocarbons, silica dusts and resin chemicals. Asbestos, named in the background for this industry, was not assessed. Standardised mortality ratios (SMRs) above 1 mean more deaths than expected. Compared with Italian men, SMRs were raised for all causes (1.44, CI 1.32 to 1.56), all cancers (1.27, CI 1.07 to 1.50), liver cancer (24 deaths; 4.19, CI 2.68 to 6.23) and silicosis (79 deaths; 66.39, CI 52.56 to 82.74). Lung and bladder cancer were close to expected; no deaths from cancer of the pleura occurred (0.63 expected). Against regional rates, liver cancer and silicosis stayed raised; all cancers did not. The authors concluded the silicosis excess is compatible with silica exposure at the plant before 1967. They also concluded that Karbate production chemicals may partly explain liver cancer, though lifestyle, viral infections and chance may have played a role.

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: Historical (retrospective) mortality cohort study comparing observed deaths with those expected from Italian national and regional male death rates (standardised mortality ratios)
• Who was studied: 1291 male production workers at a graphite electrode plant in the province of Brescia, Lombardy, northern Italy, employed for at least one year between 1 January 1950 and 31 December 1989; office workers excluded; follow-up 1950 to 1997
• Exposure: Work in graphite electrode manufacturing. With no job-specific or measured exposure data, all workers were treated as equally exposed to PAHs, silica dusts and silicates, and chemicals from phenolic and furfuryl resin treated (Karbate) products. The article's background names asbestos as an exposure in graphite electrode manufacturing generally. The study does not establish asbestos exposure at this plant and did not assess it.
• Main results:
  • Of the 1291 workers, 747 were alive at end of follow-up and 541 had died
  • Compared with Italian men, the whole cohort had excess mortality from all causes (541 deaths, SMR 1.44, CI 1.32 to 1.56) and from all cancers (141 deaths, SMR 1.27, CI 1.07 to 1.50)
  • Whole cohort, liver cancer compared with Italian men: 24 deaths, SMR 4.19, CI 2.68 to 6.23
  • Whole cohort, silicosis compared with Italian men: 79 deaths, SMR 66.39, CI 52.56 to 82.74
  • All 79 silicosis deaths were in workers hired before 1967, when rice husks replaced siliceous sand
  • Silicosis in workers aged under 45 at death: 10 deaths, SMR 333.3, CI 159.8 to 613
  • Whole cohort, no increase for lung cancer (32 deaths, SMR 0.97, CI 0.67 to 1.37) or for bladder cancer (5 deaths, SMR 1.08, CI 0.35 to 2.53)
  • Cancer of the pleura (ICD-9 163), whole cohort: no deaths observed against 0.63 expected, SMR 0.00, CI 0.00 to 4.73
  • Whole cohort, cirrhosis and other chronic liver diseases compared with Italian men: 36 deaths, SMR 1.87, CI 1.31 to 2.59
  • Compared with regional rates (1970 to 1997), all cancers were not in excess (126 deaths, SMR 0.99, CI 0.83 to 1.18). Liver cancer (20 deaths, SMR 2.57, CI 1.57 to 3.97) and silicosis (47 deaths, SMR 57.32, CI 42.11 to 76.22) remained raised.
  • Liver cancer in workers employed more than 19 years: 18 deaths, SMR 5.83, CI 3.46 to 9.22 (compared with Italian men)
  • In the subcohort employed at least one year during Karbate production (1959 to 1976), 23 of the 24 liver cancer deaths occurred. Workers in this subcohort with more than 10 years of employment had liver cancer SMR 3.11 (1.78 to 5.05) compared with regional rates.
• The authors' conclusion: The authors concluded that the large excess of silicosis deaths is compatible with silica dust exposure at the plant before 1967. They found high liver cancer mortality and said it may be due to lifestyle factors. Because liver cancer mortality was higher than in the local general population, they suggested a possible role for chemical exposures during Karbate production between 1959 and 1976.
• Limitations the authors state:
  • There were no historical data on job titles, activities or industrial hygiene, so workers could not be classified by exposure. Non-differential misclassification may have diluted the risks.
  • No information on smoking or drinking habits
  • Cancer risk may have been underestimated because of competing mortality and the healthy worker effect
  • Lifestyle factors, viral infections and chance may have contributed to the liver cancer excess

Topics

Medical terms in this study, explained in our Lexicon: Cohort Study, confidence interval, Silicosis, Occupational Exposure.

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