su-etc
rationality in cancer risk estimation
Bruce Ames, the discoverer of the Ames test that estimates carcinogenicity
of substances by whether they cause mutations in bacteria, is trying
to inject a little rationality.  I will be surprised if he wins, given
the political advantages of making cancer an issue.

a230  1304  16 Apr 87
AM-Cancer Risk, Bjt,0708
Cancer-Risk Scale Emphasizes Importance of Exposure
For release at 6:30 p.m. EDT
By WARREN E. LEARY
AP Science Writer
    WASHINGTON (AP) - Scientists have developed a scale for ranking the
potential hazard to humans of natural and man-made chemicals that
cause cancer in animals, a measure they say takes into account
real-life exposure to the substances.
    Researchers at the University of California, in Berkeley, said
Thursday that their system - which, for example, rates a daily glass
of beer as a greater cancer hazard than some pesticide pollution - is
designed to help people assess the dangers of the many carcinogens
they hear about.
    ''Our purpose is not to scare people about an occasional raw
mushroom or beer, but to help them make sense of the many reports
they see about this or that causing cancer in animals,'' Dr. Bruce N.
Ames, the principal researcher, said in a telephone interview.
    Ames, with Renae MaGaw and Lois Swirsky Gold of the university's
Lawrence Berkeley Laboratory, said their scale rates possible cancer
hazards to people based upon the known potency of a substance in
animals and the likely human exposure over a lifetime.
    The researchers describe their HERP scale, for ''Human Exposure
dose-Rodent Potency,'' in the April 17 issue of the journal Science,
a special issue focusing on assessing risks.
    Ames said the work is an extension of a much-discussed report he
published in 1983. That study concluded that the most-common
carcinogens to which people are exposed are natural substances, such
as by-products of mold and fungus contamination of grains and other
foods, and not man-made compounds such as pesticides and industrial
chemicals.
    The new report said half of all chemicals tested, whether natural or
man-made, have been identified as potential cancer-causing agents in
rats or mice. The researchers questioned the validity of making
inferences about human risks based upon high-dose rodent tests.
    The scientists said most things that cause cancer in animals in high
doses may pose little real danger to humans in low doses,
particularly if most people have little or no exposure to them.
    Simply identifying a substance as a potential cancer agent is not
very useful for making health decisions without considering amount
and likelihood of exposure, as well as other hazards with which
people come in contact, they said.
    For example, plants have evolved effective chemical defenses against
their natural pests, the scientists said. By eating plants, people
ingest 10,000 times, by weight, more natural toxic pesticides than
the man-made variety.
    Ames bases his HERP rating on a ratio between the dose rate that
induces cancer in half of the animals tested, called TD-50, and
lifetime human daily exposure to the chemical per unit of body
weight.
    Using this scale, chlorinated tap water had a low HERP rating that
still was several times higher than the potential hazard of pesticide
residues, the researchers said.
    Chlorine in the water kills many disease-causing bacteria and
viruses, they noted, making its potential cancer hazard insignificant
compared with the sickness and death it prevented.
    By contrast, the potential hazard from breathing formaldehyde from
building materials in the air of a mobile home is 1,000 times greater
than the risk of chlorinated tap water, according to the scale.
    The alcohol in a glass of beer poses a possible cancer hazard 3,000
times that of tap water, said the report, and dried herbs, raw
mushrooms, peanuts and other natural foods can have higher scores in
the amounts generally consumed than trace pollutants.
    There aren't enough human data to determine whether any of these
potential hazards warrant a change of eating habits, the researchers
said, but the numbers serve to point out that there isn't enough
information to do low-dose risk assessment on many potential
carcinogens.
    ''Again, we are not trying to scare people,'' Ames said. ''But I
think the public has been scared stiff about small amounts of
man-made chemicals without a way of comparing the risks.
    ''If people start worrying about all the things that give cancer,
then they can't concentrate on the important things, such as
cigarette smoking and the buildup of radon gas in buildings,'' he
said.
    
 
 
AP-NY-04-16-87 1604EDT
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