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Most people would be surprised to learn that the list
of proven human carcinogens is pretty small. The
International Agency for Research on Cancer (IARC) lists
under 70 agents and groups of agents as known human
carcinogens. Some of these are viruses and radioisotopes.
Asbestos, aflatoxins and benzene and some derivatives head
the list of known chemical carcinogens.Thereare certainly

many other substances out there which can cause cancer in
human beings but ethical considerations forbid scientific
testing of these on people. There is a much longer list of
suspected carcinogens. These substances are generally
suspected because they either gave a positive reaction in an
Ames test or have been shown capable of inducing cancer in
laboratory animals. The Ames test is a screening test for
the ability of a substance to produce mutations in bacteria.
Since bacteria are single celled organisms, cancer, which is
a disease of multicellular organisms, can not be induced in
them. While not all carcinogens are mutagens, some mutagens
are carcinogens and a positive mutagenic Ames test is an
indication that a substance has the potential to be a human
carcinogen and merits further study. Animal laboratory
testing is often performed on rats. Because of biochemical
differences between rats and people, the ability of a
substance to cause cancer in rats, while certainly worrisome,
does not constitute proof that the substance can cause cancer
in humans. There have been many cases of both false negatives
and positives in animals, when extrapolating a substance's
carcinogenicity to humans. Individual studies must be
judged on their own merits, but a series of studies
indicating possible carcinogenicity should not be taken
lightly.
How then should suspected carcinogens be treated
with, by individuals and society as a whole? At one end of
the spectrum lies chlorination of municipal water supplies.
This act produces small amounts of chloroform (a suspected
human carcinogen) and other chlorinated hydrocarbons. Since
the risks of not chlorinating public water supplies are
likely much greater, this source of potential carcinogens is
allowed to remain. At the other end of the spectrum is Red
Dye #2, formerly used as a food additive. Since its only
possible benefit was in the appearance of treated foods, it
was (eventually) banned as a food additive. Most suspected
carcinogens lie somewhere between these two extremes. Since
this is a public health issue and we're really dealing from
a position of ignorance, you have to draw the line somewhere
on the side of safety. Potential carcinogens should be
avoided whenever possible and replaced with safer
alternatives. Individuals though, should realize that
they'll never be able to totally avoid them. If you feel
that those who should be protecting you from exposure to
these substances may not be doing their job, your best
defense is to keep informed and make your own risk
assessment.

Learn more about this author, Neil Wagner.
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