Mortality studies of machining fluid exposure in the automobile industry. III: A case-control study of larynx cancer

Our plain-English summary of Mortality studies of machining fluid exposure in the automobile industry. III: A case-control study of larynx cancer, by E.A. Eisen, P.E. Tolbert, M.F. Hallock, et al (American Journal of Industrial Medicine, 1994).

The study

• Authors: E.A. Eisen, P.E. Tolbert, M.F. Hallock, R.R. Monson, T.J. Smith, S.R. Woskie
• Journal: American Journal of Industrial Medicine
• Published: 1994;26(2):185-202
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A case-control study of larynx cancer was conducted within a cohort of automobile workers exposed to metal working fluids, commonly referred to as machining fluids (MF). Results are based on 108 cases of larynx cancer and 5:1 matched controls. Risks associated with specific types of MF, as well as specific components of the fluids were evaluated. Based on a retrospective exposure assessment, lifetime exposures to straight and soluble fluids, grinding particulate, biocides, selected metals, sulfur, and chlorine were examined. Exposure to asbestos and acid mists at two of the three study sites was also characterized. Results suggest that straight mineral oils are associated with almost a two-fold excess in larynx cancer risk. There was also evidence of an association with elemental sulfur, commonly added to straight MF to improve the integrity of the materials under extreme pressure and heat. It is not clear whether sulfur is causally related to an excess relative risk of larynx cancer or whether the observed association is the result of unmeasured confounding by another contaminant or process feature. For example, the high stress operations that require MF enriched with sulfur are also more likely to produce polycyclic aromatic hydrocarbons (PAHs) during the process. Thus, the observed association with sulfur may be due to an association with PAH. The finding of excess risk of laryngeal cancer associated with MF is consistent with several previous reports in the literature. This is the first study, however, to distinguish straight mineral oils from other types of MF. Based on these findings, a general reduction in concentrations of straight mineral oil particulate in occupational environments would be prudent.

In plain English

This nested case-control study looked at larynx (voice box) cancer among hourly workers exposed to machining fluids, the oils and coolants used in metalworking, at three Michigan auto parts plants. From a cohort of 46,384 workers, it compared 108 people with larynx cancer to 538 matched controls. Past exposures were estimated from air samples, company records and interviews. Workers with the highest exposure to straight (mineral oil) fluids had an odds ratio of 2.23 (95% CI 1.25-3.98) versus unexposed workers. No evidence of an association was found for soluble fluids. Versus no sulfur exposure, more than 3 years of sulfur, a fluid additive, had an odds ratio of 2.06 (95% CI 1.00-4.24). Asbestos was assessed only at two plants, as years in jobs such as brake, axle and transmission assembly. The odds ratio per year of asbestos exposure was 0.98 (95% CI 0.93-1.02), and the authors found asbestos did not confound the straight-fluid result. Smoking and alcohol were not measured directly. The authors concluded that larynx cancer was associated with straight fluids and suggested reducing these exposures.

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: Nested case-control study within a cohort of autoworkers. Each case had five matched controls, and the analysis used conditional logistic regression.
• Who was studied: Hourly employees who had worked at least 3 years before January 1, 1985 at three auto parts plants in Michigan (cohort of 46,384). Cases were larynx cancers detected before January 1, 1990. The analysis included 108 cases and 538 controls.
• Exposure: Machining fluids: straight and soluble fluids and grinding particulate, plus components (biocides, steel, iron, aluminum, sulfur, chlorine). Asbestos and acid mist were assessed qualitatively at Plants I and II only. Asbestos exposure occurred in brake and axle assembly (Plant I) and transmission assembly (Plant II). No fiber type is named.
• Main results:
  • Straight machining fluids: the odds ratio rose with exposure, reaching 2.23 (95% CI 1.25-3.98) among those with more than 0.5 mg/m3-years, compared with no exposure.
  • No evidence of an association was observed for soluble machining fluids, and no consistent pattern was seen for grinding particulate.
  • Sulfur (10-year lag), compared with no sulfur exposure: the odds ratio for more than 3 years of exposure was 2.06, with a 95% CI printed in Table V as 1.00-4.24. The text describes this CI as excluding 1.00.
  • With straight fluids and sulfur in the same model, the highest-category odds ratios fell. For straight fluids the odds ratio went from 2.23 to 1.91, and it remained statistically significant. For sulfur it went from 2.50 to 1.69.
  • Asbestos (Plants I and II only): the odds ratio per year of exposure was 0.98 (95% CI 0.93-1.02).
  • In Plants I and II, the odds ratio for straight fluids was 1.25 (95% CI 1.04-1.52) and did not change when asbestos or acid mist was added to the model.
  • In the full cohort, there was no evidence that lung cancer or cirrhosis risk increased with exposure to straight fluids. The authors used these as indirect checks for smoking and alcohol.
• The authors' conclusion: The authors concluded that larynx cancer was associated with exposure to straight machining fluids and suggested these exposures be reduced. They added that further work was needed to identify the causal agent.
• Limitations the authors state:
  • Smoking and alcohol were not measured; a pilot study found relatives of long-dead subjects could not feasibly be located.
  • The sulfur association may reflect unmeasured confounding by another contaminant or process feature, such as PAHs.
  • Changes over time in the PAH or long-chain aliphatic content of the oils were not assessed.
  • Plant-specific analyses had lower statistical power.
  • The test of sulfur as a tumor promoter had limited statistical power, because it could only use subjects diagnosed or deceased before 1985.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Auto mechanics and brake work, Throat and laryngeal cancer.

Medical terms in this study, explained in our Lexicon: Case-Control Study, Laryngeal Cancer, Relative Risk, Confounding.

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