PERSPECTIVES ON RISK
Challenge of Quantitation
Heptachlor and chlordane
Animal Testing Models
Linear (genotoxic carcinogens)
Human Exposure/Rodent Potency index
We are unavoidably exposed to hazardous chemicals, usually at low levels.
A variety of
attitudes toward such exposures are prevalent in the population.
On the one hand, we see a pessimistic
or fatalistic view expressed by some that this menace, fueled by population increases, will inevitably
destroy the ecosystem and us with it.
Alternately, some observers present an optimistic viewpoint that
the consequences will be minimal; they may even glorify risk in general as a challenge with selective
For example, a publication by Dow Chemical entitled Life Is In The Balance: Weighing the
Questions of Risk and Benefit in Today’s World
starts with a quotation by Helen Keller (1902).
is mostly a superstition.
It does not exist in nature, nor do the children of men as a whole experience it.
Avoidance of danger is no safer in the long run than outright exposure.
Life is a daring adventure, or
An issue inherent in the regulatory process is how to estimate the magnitude of risk so that we
can decide rationally how much to spend to alleviate it.
It is illuminating to examine the basis for some
early regulatory decisions and to analyze how this process has changed with experience.
line is that regulations are based on estimates of risk.
But results of risk calculations are acknowledged
to have very large uncertainties, limiting the effectiveness of the regulatory system.
To reduce these
uncertainties, better methods to extrapolate among species and, ultimately, better understanding of
toxic mechanisms are needed.
In 1975, the EPA banned for general use the chlorinated hydrocarbons chlordane and
heptachlor on the grounds these pesticides presented an "imminent hazard".
To fulfill its mandate to
protect the environment from "unreasonable" effects, the agency based its decision on three elements.
First, it was found at that time that these agents are rodent carcinogens and thus likely human
Since virtually all known human carcinogens are animal carcinogens, it was concluded
the reverse relationship also holds.
Some observers, including the company manufacturing these
pesticides, objected because rodent metabolism of the chemicals and thus our internal defenses
against them are "totally different", thus invalidating the extrapolation.
(This argument in various forms
persists for many agents in risk estimation.) Second, an extrapolation to humans was made.
agents are highly persistent in the environment, and were widely distributed, being found in soil, animal
feed, and human food (crops, meat).
They were detectable in the adipose tissue of over 90% of the
population, so exposure clearly occurred.
Third, the burden of proof for safety is on the manufacturer.
danger exists, the manufacturer must show safe and effective substitutes are not available.