Incidence of cancer and mortality among workers exposed to mercury vapour in the Norwegian chloralkali industry

Our plain-English summary of Incidence of cancer and mortality among workers exposed to mercury vapour in the Norwegian chloralkali industry, by D.G. Ellingsen, A. Andersen, H.P. Nordhagen, et al (British Journal of Industrial Medicine, 1993).

The study

• Authors: D.G. Ellingsen, A. Andersen, H.P. Nordhagen, J. Efskind, H. Kjuus
• Journal: British Journal of Industrial Medicine
• Published: 1993;50(10):875-80
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Incidence of cancer and mortality were studied among 674 men exposed to mercury vapour for more than one year at two chloralkali plants. Mercury excretion in urine had been monitored among the workers at the two plants since 1948 and 1949. An individual cumulative urinary mercury dose was calculated, based on about 20,000 urinary mercury measurements. The incidence of cancer and the mortality were followed up from 1953 to 1989 and 1953 to 1988 respectively. The general Norwegian male population served as a reference population. There was a lung cancer excess of borderline significance (standardised incidence ratio = 1.66, 95% confidence interval = 1.00-2.59). The introduction of a 10 year latent period before developing lung cancer did not increase the incidence ratio. The excess may be partly explained by the smoking habits in the cohort or possibly by exposure to asbestos. No excess of cancer was found in the target organs for mercury toxicity--namely, the kidney and the nervous system. No significant excess mortality was found for nephritis and nephrosis or nonmalignant diseases of the nervous system.

In plain English

This study followed 674 men who started work before 1980, and worked more than one year, at two Norwegian chloralkali plants, where they were exposed to mercury vapour that was monitored through urine tests. Cancer cases (1953 to 1989) and deaths (1953 to 1988) were compared with rates expected from the general Norwegian male population. Overall, 89 cancers were found against 85.02 expected. Lung cancer showed what the authors called a borderline significant excess: 19 cases against 11.47 expected (standardised incidence ratio 1.66, 95% confidence interval 1.00 to 2.59). Kidney and nervous system cancers were not in excess. One pleural mesothelioma occurred, in a bricklayer who before 1940 had repaired asbestos-insulated furnaces at another plant. No cause of death differed significantly from expected. The authors suggested that a higher share of smokers in the cohort, and possibly asbestos exposure, may partly explain the lung cancer excess. They found no relation between mercury exposure and cancer, but cautioned that the numbers were small.

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 cohort study comparing cancer incidence (standardised incidence ratios) and mortality (standardised mortality ratios) with national rates
• Who was studied: Men employed for more than one year at two mercury-cell chloralkali plants in southeast Norway (plant A started 1947, plant B 1949). 799 men were identified; analyses were restricted to 674 first employed before 1980. Cancer follow-up 1953 to 1989, mortality follow-up 1953 to 1988.
• Exposure: Mercury vapour, estimated as an individual cumulative urinary mercury dose from about 20,000 urine measurements. The mean cumulative dose was 3700 nmol/l and the mean employment was 9.6 years. Asbestos was not extensively used at the plants, but some was used for maintenance, and workers may also have been exposed to it at other workplaces.
• Main results:
  • All cancers in the cohort: 89 observed against 85.02 expected (standardised incidence ratio 1.05, 95% CI 0.84 to 1.29, per Table 1).
  • Lung cancer in the cohort: 19 observed against 11.47 expected, standardised incidence ratio 1.66 (95% CI 1.00 to 2.59), described as borderline significant.
  • Lung cancer occurring more than 10 years after first employment: 17 observed against 10.13 expected, standardised incidence ratio 1.68 (95% CI 0.98 to 2.69).
  • Cancers of the nervous system: 2 observed against 2.45 expected. Kidney cancers: 3 observed against 3.17 expected.
  • One pleural mesothelioma (not tabulated) was diagnosed in the 1980s in a bricklayer who before 1940 had repaired furnaces insulated with asbestos at another plant.
  • Mortality in the cohort: 204 deaths observed against 210.67 expected (standardised mortality ratio 0.97, 95% CI 0.84 to 1.11). None of the cause-specific mortality ratios differed significantly from expected.
  • Deaths from nephritis and nephrosis: 2 observed against an estimated 1.20 expected (standardised mortality ratio 1.67, 95% CI 0.17 to 6.00). Deaths from diseases of the nervous system and sense organs: 4 observed against an estimated 3.08 expected (standardised mortality ratio 1.30, 95% CI 0.36 to 2.86).
  • Smoking data, available since the 1970s, suggested that smoking prevalence in the cohort was 15% to 20% higher than in the reference population.
• The authors' conclusion: The authors concluded that they found no relation between mercury vapour exposure and cancer, or between mercury exposure and the causes of death studied. They suggested that more smoking and possibly more asbestos exposure in the cohort may, at least in part, explain the slight lung cancer excess.
• Limitations the authors state:
  • The study was based on small numbers, and the authors said the results should be interpreted with caution.
  • Smoking information was available for only 59% of the total cohort.
  • Death may not be an appropriate measure of kidney disease outcome because of renal dialysis and transplantation.
  • Health selection: people with known lung diseases had difficulty getting jobs at the plants, so mortality ratios for non-malignant lung disease must be interpreted with caution.
  • Expected numbers of deaths for nephritis and nephrosis and for nervous system diseases were estimated for 1953 to 1961 rather than calculated exactly, because of technical difficulties.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Standardized Incidence Ratio (SIR), confidence interval, Habit.

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