A new study concludes that exposure to diesel exhaust may increase the risk of rectal cancer.
Diesel exhaust is a known carcinogen, having been classified as such by the World Health Organization (WHO) in 2012, more than 25 years after it was placed in the category of “probably carcinogenic to humans.”
But the specific connection between colorectal cancers and diesel exhaust has so far been undetermined. Colorectal cancer (cancer of the colon or rectum) is the third most common cancer worldwide and the second most likely cause of cancer death in Canadian men. According to the Colorectal Cancer Association of Canada, one in 14 men and one in 16 women will be diagnosed with colorectal cancer in their lifetime.
Researchers analyzed survey data covering over 21,000 cancer cases in 8 Canadian provinces between the years 1994 and 1997 and looked for evidence of associations between occupational exposure to diesel or gasoline exhaust and diagnoses for colorectal cancer. They found that while there were no determinate associations between high exposure to gasoline fumes and elevated colorectal cancer risks, there was a connection between diesel exhaust and rectal cancer, particularly when the occupational concentration of diesel fumes was high.
“Our results point to concentration as a key dimension of exposure influencing the association with cancer risk,” say the study’s authors.
According to the survey results, an estimated 781,000 workers (4.6% of the working Canadian population) are exposed to diesel exhaust on the job, with occupations such as truck driver, heavy equipment operator and underground miner being at the top of the list for exposure.
Diesel and gasoline emissions contain a complex mix of chemicals, including polycyclic aromatic hydrocarbons and nitroarenes, carbon monoxide and volatile organic compounds like benzene and formaldehyde. The reason why diesel exhaust is thought to be the more harmful is that while both diesel and gasoline contain similar particles, the surface properties of diesel particles are different, leading to unique interactions with the body’s tissues and cells. At present, the WHO lists gasoline exhaust as “potentially carcinogenic.”
Colorectal cancer has already been linked to other so-called modifiable lifestyle factors such as obesity, physical inactivity, consumption of red and processed meat and smoking. Just last month, a study from Stony Brook University in New York suggested that contrary to common belief, up to 90 per cent of cancers are caused by environmental and lifestyle factors, rather than being a direct result of genetics and heredity. The authors reported that almost 75 per cent of colorectal cancer is now thought to be linked to diet.
The Colorectal Cancer Association of Canada recommends that colorectal cancer screening should be a part of routine healthcare for those age 50 and up, with people at a higher risk getting screened earlier. The relative survival rates for colorectal cancer range between 60% and 67%.
The study was led by Dr. Linda Kachuri of the Dalla Lana School of Public Health, University of Toronto, and is published online in the journal Environmental Health.