Motor vehicle exhaust emissions are widespread and include a number of known and likely carcinogens. Investigating the carcinogenic potential of diesel and gasoline emissions has been identified as a high priority by the International Agency for Research on Cancer.
To investigate exposure to diesel and gasoline engine emissions with respect to colorectal cancer (CRC) risk in Canadian men.
We used data from a population-based case-control study with incident cases of colon (931) and rectal (840) cancer and 1642 controls from 7 Canadian provinces between 1994 and 1997. Lifetime occupational history and information on other risk factors was self-reported. Occupational hygienists, blinded to case-control status, assigned exposures to each job for 3 dimensions: concentration (low, medium, high); frequency (≤5%, 6-30%, >30% of time in a typical week); and reliability (possible, probable, definite). Logistic regression was used to estimate odds ratios (OR) and their associated 95% confidence intervals, adjusting for age, province, use of proxy respondents, smoking, body-mass index, physical activity, intake of alcohol, processed meat, juice, exposure to asbestos and aromatic amines.
Among CRC cases, 638 (35%) were exposed to diesel and 814 (44%) were exposed to gasoline emissions. A trend for increasing CRC risk was observed for increasing levels of concentration of diesel emissions (ORhigh=1.65, 95% CI: 0.98-2.80; p=0.008), relative to the unexposed. Examining colon and rectal cancers separately revealed that the association with diesel exposure was statistically significant for rectal (ORhigh=1.98, 95% CI: 1.09-3.60; p=0.02), but not colon cancer (ORhigh=1.35, 95% CI: 0.72-2.54; p=0.08). No statistically significant associations were observed for exposure to gasoline emissions.
Our findings suggest that occupational exposure to high concentrations of diesel emissions increases the risk rectal cancer. In contrast, our analysis does not support an increased risk of colon or rectal cancer from occupational exposure to gasoline engine emissions.