Environmental Engineering Reference
In-Depth Information
Some scientists challenge the validity of extrapo-
lating data from test animals to humans because hu-
man physiology and metabolism often differ from
those of the test animals. Other scientists say that such
tests and models work fairly well (especially for re-
vealing cancer risks) when the correct experimental
animal is chosen or when a chemical is toxic or harm-
ful to several different test-animal species.
The problem of estimating toxicities gets worse. In
real life, each of us is exposed to a variety of chemicals,
some of which can interact in ways that decrease or
enhance their individual effects over the short and
long term.
Toxicologists have great difficulty in estimating
the toxicity of a single substance. But adding the prob-
lem of evaluating mixtures of potentially toxic sub-
stances, separating out which ones are the culprits,
and determining how they can interact with one an-
other is overwhelming from a scientific and economic
standpoint. For example, just studying the interactions
of three of the 500 most widely used industrial chemi-
cals would take 20.7 million experiments—a physical
and financial impossibility.
they are all we have. To take this uncertainty into ac-
count and minimize harm, scientists and regulators
typically set allowed exposure levels to toxic sub-
stances and ionizing radiation at 1/100 or even 1/1,000
of the estimated harmful levels.
According to risk assessment expert Joseph V.
Rodricks, “Toxicologists know a great deal about a few
chemicals, a little about many, and next to nothing
about most.” The U.S. National Academy of Sciences
estimates that only 10% of at least 80,000 chemicals in
commercial use have been thoroughly screened for
toxicity, and only 2% have been adequately tested to
determine whether they are carcinogens, teratogens,
or mutagens. Hardly any of the chemicals in commer-
cial use have been screened for possible damage to hu-
mans' nervous, endocrine, and immune systems.
Currently, federal and state governments do not
regulate about 99.5% of the commercially used chemi-
cals in the United States. Several reasons explain this
lack of regulation. For example, under existing U.S.
laws, most chemicals are considered innocent until proven
guilty. Some analysts think this is the opposite of the
way it should be. Why, they ask, should chemicals have
the same legal rights as people? Critical thinking: should
chemicals be considered guilty until proven innocent?
In addition, there are not enough funds, person-
nel, facilities, and test animals available to provide
such information for more than a small fraction of
the many individual chemicals we encounter in our
daily lives. It is also too difficult and expensive to
analyze the combined effects of multiple exposures to
various chemicals and their possible interactions.
Solutions: Protecting Children
from Toxic Chemicals
Children tend to be much more vulnerable than adults
to toxic chemicals.
Children are usually much more susceptible to the ef-
fects of toxic substances than are adults for three major
reasons. First, children breathe more air, drink more
water, and eat more food per unit of body weight than
do adults. Second, they are exposed to toxins in dust or
soil when they put their fingers, toys, or other objects
in their mouths (as they frequently do). Third, immune
systems and bodily processes for degrading or excret-
ing toxins and repairing damage are usually less well
developed in children than in adults.
In 2003, the U.S. Environmental Protection Agency
(EPA) proposed that in determining risk, regulators
should assume children have 10 times the exposure
risk of adults to cancer-causing chemicals. Some health
scientists contend that these guidelines are too weak.
They suggest that, to be on the safe side, we should as-
sume that the risk of harm from toxins for children is
100 times that of adults.
Science and Economics: Pollution Prevention
and the Precautionary Principle
Preliminary but not conclusive evidence that a
chemical causes significant harm should spur
preventive action, some say.
So where does this leave us? We do not know a lot about
the potentially toxic chemicals around us and inside of
us, and estimating their effects is very difficult, time-
consuming, and expensive. Is there a way out of this
dilemma?
Some scientists and health officials, especially
those in European Union countries, are pushing for
much greater emphasis on pollution prevention. They
say we should not release into the environment chemi-
cals that we know or suspect can cause significant
harm. This means looking for harmless or less harmful
substitutes for toxic and hazardous chemicals or recy-
cling them within production processes so they do not
reach the environment.
This prevention approach is based on the precau-
tionary principle: When there is plausible but incom-
plete scientific evidence (frontier science evidence) of
significant harm to humans or the environment from a
Science, Politics, and Economics: Why Do
We Know So Little about the Harmful
Effects of Chemicals?
Under existing laws, most chemicals are considered
innocent until proven guilty, and estimating their
toxicity to establish guilt is difficult, uncertain, and
expensive.
As discussed previously, all methods for estimating
toxicity levels and risks have serious limitations. But
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