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                                                                                SCIENCE, Page  61

The Danger In Doomsaying


Just how hazardous are dioxin, Alar and other chemicals? Skeptics
call for a better method of measuring risk.

By DICK THOMPSON/WASHINGTON


    Marilyn Leistner doesn't believe scientists anymore -- at
least not the ones who once denounced dioxin but now downplay
its dangers. Leistner was the last mayor of Times Beach, Mo.,
the town of 2,400 that the U.S. government evacuated and closed
down in 1982 because it was contaminated with dioxin,
considered by many to be one of the most fearsome of chemicals.
The mayor saw dioxin's toxic effects all too clearly: the
elderly forced out of their homes and into retirement centers,
people so paranoid that every common illness was assumed to be
dioxin poisoning, neighbors quarreling and even threatening to
kill one another. "This chemical uprooted 801 families," she
says. "The frustration, the divorces, the stress, the deaths can
all be blamed on this chemical."

    Well, no. It was not so much the chemical that caused the
chaos as it was a questionable government judgment about the
risks of dioxin. Now that some scientists are asserting -- 10
years too late -- that the concentrations of dioxin present at
Times Beach were not harmful, the dispossessed residents, and
the public in general, have every right to be confused.

    There was a similar pattern of uncertainty in judgments
about Alar, radon and even some forms of PCBs and asbestos.
Citing government studies, environmentalists sounded the alarm
about toxicity and cancer. The public fretted. Officials issued
warnings and regulations. But then skeptical scientists
re-evaluated the threat and began to argue that the risks had
been exaggerated. After this series of debates, people are
wondering if they have been unduly frightened by overzealous,
if well-meaning, regulators.

    At issue is risk assessment, the method of evaluating how
dangerous a substance is to humans. In the U.S. officials have
been quick to ban chemicals that according to lab tests are
carcinogenic. But skeptics contend the system is so sensitive
that if standard tests were applied to all chemicals, both
natural and synthetic, fully half of them would appear to cause
cancer. "It's a bit like the search for witches. You can always
find them," says Colin Berry, chairman of the British
government's pesticide advisory board and a critic of the way
American scientists have evaluated risk. Now that U.S. system
of risk assessment is itself being reassessed. Just last month,
for example, the Environmental Protection Agency reversed an
earlier decision and eased restrictions on the use of a class
of pesticides known as EBDCs.

    Proving that a chemical causes cancer is difficult, since
the disease may not strike until years after exposure. Unable
to wait that long, scientists have tried to speed up the
process by feeding huge amounts of suspect chemicals to
laboratory animals such as mice. Typically they are given what
is known as the maximum tolerated dose, an amount just below the
lethal level. In the case of the artificial sweetener saccharin,
mice were given the equivalent of hundreds of cans of diet soda
a day; similarly, a person would have had to eat thousands of
apples a day to get the maximum tolerated dose of Alar, a
fruit-ripening chemical used by growers until it was withdrawn
from the market because of a cancer scare. If as few as five
mice out of 200 given these megadoses develop tumors over two
years, the substance is usually labeled a carcinogen.

    Such a conclusion is based on a host of conservative
assumptions, among them that the effect on mice is generally the
same as on humans and that it makes no difference whether the
chemical is swallowed, inhaled or rubbed on the skin. Another
questionable premise is that there is no safe dose of a
carcinogen. In fact, the body may have evolved methods of coping
with small amounts of such chemicals. But when lab mice are
given a megadose of a chemical, it could overwhelm their natural
repair systems. Such a dose may also stimulate cells to divide
rapidly, which magnifies normal genetic errors and produces
cancer.

    If traces of chemicals can cause cancer, then the peril is
inescapable. Most fruits and vegetables contain natural
pesticides -- chemicals that plants themselves have manufactured
to ward off bugs and blights -- and about half these compounds
have tested positive as carcinogens. "Just because something is
natural doesn't make it good, and just because something is
man-made doesn't make it bad," says Ronald Hart, director of the
National Center for Toxicological Research.

    A recent survey of the causes of cancer, published in
Science, concluded that "the perception that environmental
pollution is a major cancer hazard is incorrect." While
estimates vary, many experts agree that pesticides and other
environmental contaminants are responsible for no more than 1%
of cancers and 5,000 deaths a year. The potential cost of
erroneous risk assessments is enormous: America's bill for
complying with environmental regulations could top $100 billion
this year.

    Congress is considering whether to loosen the Delaney
clause, a 1958 law that bans any amount of any carcinogen from
the food supply. In the 33 years since Delaney was written,
science has developed an ability to identify substances at
levels unimaginable to politicians who originally voted for the
measure. Today one part per quintillion can be detected -- the
same as a tablespoon of liquid in all the Great Lakes combined.
As scientists become more sophisticated in detecting potential
carcinogens and analyzing test results, lawmakers and consumers
will have to become more sophisticated in deciding how to
balance the risks against the benefits.