Three issues are particularly important when determining which chemical substances should be the focus of cancer prevention efforts. First of all, there is the matter of the existence of knowledge that the substance causes cancer in humans. Secondly, the substance must be present in the environment at levels that can impose significant cancer risk. Finally, there is the question of how large a percentage of the population is being exposed at such significant risk causing levels.

Dioxins and dioxin-like compounds (DLC) are a group of chemical compounds considered to be probable human carcinogens. The most toxic substance in this group, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has been classified as Known to Be a Human Carcinogen by the National Toxicology Program (NTP, 2005).  Dioxins and DLC persist for long periods of time in the environment. These pollutants are stored in fat tissue and reach elevated concentrations at higher levels in food chains. According to the US Environmental Protection Agency's (US EPA) dioxin reassessment, dioxins and DLC contaminate animal fat foods produced in the United States to a degree that imposes a 1 in 1000 excess cancer risk upon the average consumer of these foods (US EPA, 2003). A large fraction of the American public consumes animal fat in the quantities considered to be average. Based upon the three criteria set forth above, dioxins and DLC are clearly a group of chemicals for which reduced exposure will yield substantive cancer prevention benefit for large numbers of people.

Polycyclic aromatic hydrocarbons (PAHs) are a group of chemical compounds that include several known and suspected human carcinogens (ATSDR, 1995). The most important exposure pathways for PAHs are believed to be consumption of foods contaminated with these fat-soluble pollutants and inhalation of polluted air. Gasoline and diesel engine exhaust are major sources of PAHs. Cancer risk of PAH exposure resultant from consumption of contaminated foods has been quantified at approximately 1 in 10,000.

Benzene is a known human carcinogen present in exhaust (ATSDR, 2005). No risk quantification has been performed for background environmental exposures of the general public.

Considering the fact of widespread exposure and the presence of numerous carcinogenic substances in exhaust, it is reasonable to believe that reducing exhaust exposure would be a valuable cancer prevention measure.

References:

ATSDR.  “Toxicological Profile for Benzene - Draft”; U. S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 2005; http://www.atsdr.cdc.gov/toxprofiles/tp3.html

ATSDR.  “Toxicological Profile for Polycyclic Aromatic Hydrocarbons (PAHs)”; U. S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 1995; http://www.atsdr.cdc.gov/toxprofiles/tp69.html

NTP.  “Report on Carcinogens, Eleventh Edition”; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, 2005; http://ntp.niehs.nih.gov/ntpweb/index.cfm?objectid=035E5806-F735-FE81-FF769DFE5509AF0A

US EPA. “Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds”; United States Environmental Protection Agency, 2003; http://www.epa.gov/ncea/pdfs/dioxin/nas-review/  

The government reports contained in Part I of the following book serve as a basis for the conclusion that reducing exposure to dioxins and DLC, PAHs, and other carcinogenic substances present in gasoline and diesel engine exhaust will lower cancer risk for many Americans.

Cancer Prevention Doc 1.pdf