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
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.
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
“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
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