Workplace exposure to diesel and gasoline engine exhausts and the risk of colorectal cancer in Canadian men

Our plain-English summary of Workplace exposure to diesel and gasoline engine exhausts and the risk of colorectal cancer in Canadian men, by L. Kachuri, P.J. Villeneuve, M.É. Parent, et al (Environmental Health, 2016).

The study

• Authors: L. Kachuri, P.J. Villeneuve, M.É. Parent, K.C. Johnson, Canadian Cancer Registries Epidemiology Research Group, S.A. Harris
• Journal: Environmental Health
• Published: 2016;15:4
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The International Agency for Research on Cancer (IARC) classified diesel exhaust as carcinogenic to humans (Group 1) and gasoline exhaust as a possible carcinogen (Group 2B) based studies of lung cancer, however the evidence for other sites is limited. We addressed this question by investigating exposure to diesel and gasoline emissions with respect to risk of colorectal cancer in men.

Methods: We used data from a population-based case-control study with incident cases of colon (n = 931) and rectal (n = 840) cancer and 1360 controls from 7 Canadian provinces conducted in 1994-1997. Lifetime occupational history and information on other risk factors was collected. Occupational hygienists, blinded to case-control status, assigned exposures to each job for 3 dimensions: concentration, frequency, and reliability. Logistic regression was used to estimate odds ratios (OR) and their 95 % confidence intervals (CI), adjusted for age, province, use of proxy respondents, smoking, body-mass index, physical activity, intake of alcohol, processed meats, and occupational exposure to asbestos and aromatic amines.

Results: Among CRC cases, 638 (36 %) were exposed to diesel and 814 (46 %) were exposed to gasoline emissions. Relative to the unexposed, elevated risks were observed among subjects ever exposed to high concentration levels of diesel emissions for colorectal cancer (OR = 1.65, 95 % CI = 0.98-2.80) and rectal cancer (OR = 1.98, 95 % CI = 1.09-3.60), but not colon cancer. Prolonged (>10 years) exposure at high concentrations was also associated with high risks of rectal cancer (OR = 2.33 95 % CI = 0.94-5.78; p-trend = 0.02). No statistically significant associations were observed for gasoline emissions.

Conclusions: Our findings suggest that sustained high-level exposure diesel emissions may increase the risk of rectal cancer.

In plain English

This population-based case–control study used data from the Canadian National Enhanced Cancer Surveillance System. It asked whether men's workplace exposure to diesel and gasoline engine exhaust was linked to colon and rectal cancer. It included 931 men with colon cancer, 840 with rectal cancer and 1360 controls without cancer, all aged 40 or older, from 7 provinces, studied in 1994–1997. Chemists and industrial hygienists who did not know which men had cancer rated each job for exhaust, asbestos and other agents. Ever having been exposed to diesel or gasoline exhaust was not linked to a statistically significant rise in risk. Men whose highest diesel exposure was rated high had an odds ratio of 1.98 (95% CI 1.09–3.60) for rectal cancer, but not for colon cancer. For more than 10 years at high diesel levels, the rectal cancer odds ratio was 2.33 (95% CI 0.94–5.78). Gasoline showed no marked increase. Men ever exposed to asbestos at work had an odds ratio of 1.43 (95% CI 1.15–1.78) for colon and rectal cancer combined. The authors concluded that their findings suggest a modest association between high diesel exposure and rectal cancer, and urged caution because some associations may be due to chance.

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: Population-based case–control study (analysis of the colon and rectal cancer components of the Canadian National Enhanced Cancer Surveillance System, NECSS), with expert-based occupational exposure assessment
• Who was studied: Men aged 40 or older who had worked at least one year, from 7 Canadian provinces (no colon or rectal data from Ontario), 1994–1997: 931 colon cancer cases, 840 rectal cancer cases and 1360 population controls. Questionnaires were returned by 71% of rectal and 70% of colon cases contacted and 64.0% of controls contacted.
• Exposure: Workplace exposure to diesel and gasoline engine emissions, rated job by job for concentration, frequency and reliability by blinded chemists and industrial hygienists. Asbestos, aromatic amines and crystalline silica were also assessed, and asbestos and aromatic amines were adjusted for as possible confounders.
• Main results:
  • Ever exposure to diesel emissions (OR 0.88, 95% CI 0.74–1.06) or gasoline emissions (OR 1.10, 95% CI 0.93–1.31) was not associated with a statistically significant increase in the odds of colorectal cancer.
  • Men whose highest attained diesel exposure concentration was high, compared with unexposed men, had an OR of 1.65 (95% CI 0.98–2.80) for colorectal cancer combined.
  • For high highest-attained diesel concentration, the OR was 1.98 (95% CI 1.09–3.60) for rectal cancer (29 cases, 25 controls) and 1.35 (95% CI 0.72–2.54) for colon cancer.
  • Men with more than 10 years of diesel exposure at high concentrations, compared with unexposed men, had an OR of 1.90 (95% CI 0.85–4.23) for colorectal cancer and 2.33 (95% CI 0.94–5.78) for rectal cancer (12 rectal cases, 11 controls). The authors described the positive trends as statistically significant (p-trend 0.02).
  • Gasoline emissions were not associated with a marked increase in colorectal, colon or rectal cancer for any exposure measure. Cumulative exposure to diesel or gasoline was not associated with an appreciable increase.
  • Among men with colon or rectal cancer combined, ever occupational exposure to asbestos had an OR of 1.43 (95% CI 1.15–1.78). Asbestos exposure was found in 150 colon cases, 121 rectal cases and 151 controls.
• The authors' conclusion: The authors concluded that their findings suggest a modest association between workplace exposure to high concentrations of diesel emissions and rectal cancer. They said the increases should be viewed with caution and that some associations may be due to chance.
• Limitations the authors state:
  • Response rates were modest for cases and controls, raising possible selection bias. The authors did not believe this bias was large enough to seriously distort the results.
  • Job histories were self-reported, so recall errors could reduce statistical power and weaken the associations.
  • Exposure misclassification likely occurred. The authors expected it to be non-differential, which would weaken the associations.
  • There were no direct exposure measurements, so the semi-quantitative indices cannot be used for quantitative risk assessment.
  • Workplace exposures of study subjects may have been too low to produce a detectable increase in cancer risk.
  • Overall results were inconsistent across exposure measures, and some associations may be due to chance.

Topics

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

Medical terms in this study, explained in our Lexicon: Colorectal Cancer, IARC, Carcinogenic, Lung Cancer, Case-Control Study, Occupational History, Odds Ratio, confidence interval.

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• Occupational exposure to diesel and gasoline emissions and lung cancer in Canadian men — P.J. Villeneuve, M.É. Parent, et al. (2011)
• Occupational exposure to diesel motor exhaust and risk of lung cancer by histological subtype: a population-based case-control study in Swedish men — A. Ilar, N. Plato, et al. (2017)
• Absence of multiplicative interactions between occupational lung carcinogens and tobacco smoking: a systematic review involving asbestos, crystalline silica and diesel engine exhaust emissions — M. El Zoghbi, P. Salameh, et al. (2017)
• The diesel exhaust in miners study: I. Overview of the exposure assessment process — P.A. Stewart, J.B. Coble, et al. (2010)
• Diesel exhaust and coal mine dust: lung cancer risk in occupational settings — B. Hoffmann, K.H. Jöckel (2006)
• Workplace exposure to asbestos and the risk of kidney cancer in Canadian men — C.E. Peters, M.É. Parent, et al. (2018)

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