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CHAPTER VI
The Risk/Benefit Equation
in Chemistry
Gasoline is a mixture of hydrocarbons, mainly alkanes and alkenes, but with
aromatics or tetraethy! lead added to improve combustibility. It is toxic to drink,
the aromatics are carcinogenic, the tetraethy! lead can cause lead poisoning, the
mixture is extremely flammable, and, when burned, it produces the noxious and
toxic substances nitric oxide and carbon monoxide. Gasoline is probably the most
dangerous compound that the average person will ever encounter on a daily basis.
Yet this same average person stores 5 to 10 gallons at home (in the car's gas tank),
and he or she might purchase some 500 gallons of this perilous liquid every year,
and then combust it to release into the atmosphere 250,000 cu.ft. of oxides of
nitrogen and carbon. Every city has dozens of repositories for this fluid, gasoline
stations, each storing perhaps 10,000 gallons, always in a crowded neighborhood.
These supplies must be regularly replenished by trucks that carry 20,000 gallons
each through the city amongst the normal traffic.
This is risky business! But evidently the public (that's you and me) believes that
the benefits are important enough to justify the risks. Every time you start your car,
you are implicitly stating that the r~skJbenefit equation in our reckless use of
gasoline comes down on the side of benefit.
Dichiorodipheny} trichioroethane is an insecticide that has saved over 50
million human lives and prevented untold suffering. It did so by almost
eliminating malaria. In 1959, at the height of its use, over 156 million pounds of
this chemical, commonly called DDT, were produced in the United States alone.
Many thousands of people were dusted with DDT, literally from head to toe,
without apparent harm. Such programs reduced the number of malaria victims in
India alone from 75 million in 1952 to less than 100 thousand by 1964. In Sri
Lanka, the number of malaria cases dropped from about 3 million, with 12,000
deaths per year, to less than 100, with no deaths at all. But production of this
lifesaving chemical has been sharply cut back, and in the United States it has
almost gone out of use. The reason is that DDT has been judged to be potentially
dangerous because of its persistence in the environment and because of its
accumulation in the tissues of living organisms.
This is a dilemma. There is no doubt that human lives could be saved, but that
ecological disturbances will accompany continued use of DDT. The ban against its
use indicates that the public has decided that the risks exceed the benefits.
203
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THE RISKIBENEFIT EQUATION IN CHEMISTRY
Gasoline and DDT are only 2 of the 70,000 or so chemicals that have come into
widespread use. These chemicals range from aspirin to Vitamin C, flea powder to
household detergents, Dacron shirts to Teflon-coated frying pans. Our quadity of
~ . ~ . ~ , . ~ . . ~ . . ~ . , ~ . ...
lute Is determined, sustained, and constantly Improved by our ability to control
chemical reactions and to make chemical compounds that are useful in everyday
life. But gasoline and DDT are excellent examples because they point out vividly
the fact that handling all of these chemicals must involve some risks. We have only
recently realized that minimizing risks must be considered to be as important a
dimension of progress as maximizing benefits from technological change. We must
learn to deal wisely with the risk/benefit equation.
FEARS OF THE MODERN AGE
In a recent, highly publicized incident, the compound trichioroethylene, TCE,
was found at several parts per million in the Unnking water from 35 private wells
near Palo Alto, California. A lawsuit caused these wells to be closed. Yet the
available evidence implies that these wells are probably quite safe if that is so,
then why are they closed?
Part of the answer is that there is a growing alarm in this country over chemicals
and their possible effects on individuals. The populace is concerned about chemical
pollutants, additives, waste, by-products, residues in short, any chemical that is
the direct result of technological change. Some of this current fear stems from a
general lack of information a fear of the unknown; some is triggered by sensa-
tional or overzealous reporting in newspapers and on television. Many people fee!
a sense of helplessness, a feeling they have no say in the control of these new
substances entering the environment. There is also a vague feeling of mistrust of the
priorities and interests of those with a vested financial stake in producing,
distributing, and utilizing these substances.
Yet aD of these chemicads came into being to establish and maintain our high
quality of life. For decades, we have been blithely enjoying the fruits of our
technological success without thought of the possible incumbent hazards and
undesired ejects. Now, suddenly, our society has become "chemically aware";
we have become hypersensitive about all chemicals, no matter what the source,
amount, degree of hazard, or intended purpose.
~ . . . .
, , ,
untortunate~v such fear can lead us to overreact. so that situations presenting
minimal danger can divert attention and resources from real dangers that must be
corrected and eliminated. We must alleviate this chemical insecurity so that we can
find the optimum balance in the risk/benefit equation. Then we can continue to
enjoy the growing benefits of the chemical age while guaranteeing that we protect
the health and well-being of our planet and its occupants.
WHAT IS TOXIC?
"Everything is poisonous. The dose alone determines the poison." Paracelsus,
the sixteenth century chemist, physician, and healer, made this assertion, one that
comes to mind when we read that a healthy diet should not contain too much salt,
sugar, or butterfat. Nitrogen is 80 percent of the air we breathe, but too much
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THE RlSKlBENEFIT EQUATION IN CHEMISTRY
nitrogen acts as an anesthetic, and it can give deep sea divers a dangerous feeling
of euphoria called "rapture of the depths." Selenium is essential to human and
animal health, but in excess can cause a variety of ailments. And if too much salt,
sugar, butterfat, and nitrogen is unhealthy, perhaps we should believe Paracelsus-
everything is poisonous if taken in too large amounts. This news can be a bit
unnerving since everything around us and in us is chemical, including everything
we eat and drink. But it is reassuring, too, because we, and all other life forms,
evolved and thrived in the presence of these chemicals. Perhaps the persistence of
life is evidence that the corollary to Paracelsus's remark is true as well things that
are poisonous in too large doses are not necessarily poisonous in small enough
doses.
With that premise, we are faced with two fundamental questions. First, we must
find out what hazard levels we face risk assessment- and then we must decide
what to do about them—risk management. The Environmental Protection Agency
wisely recognizes these as separate dimensions of their responsibility. Risk
assessment is mainly connected with the known scientific facts about a given
possible hazard. Risk management requires choices among options, as well as
consideration of costs and social consequences. We will discuss them in turn.
RISK ASSESSMENT
· . . .
To begin with, there are two kinds of toxicity to worry about. A toxic chemical
can cause illness soon after exposure, which is called acute toxicity. Another
chemical can have no immediate effect, but it may be injurious much later, after
continuous, long-term exposure; this is called chronic toxicity. For example,
phosgene, (2, iS an acutely toxic gas that is accidentally produced by use of a
carbon tetrachIoride fire extinguisher to put out an electncal fire. A concentration
of 5 parts per million (ppm) will cause eye irritation in a few minutes, whereas
greater than 50 ppm would probably be fatal. On the other hand, benzene, C6H6, is
chronically toxic its vapor inhaled at the same level, 50 ppm, would cause no
immediate effect, but if inhaled every day for many months or years, benzene can
cause decreases in red blood cell count, hemoglobin level, and the number of
leukocytes in the blood.
Unfortunately, it isn't easy to get such detailed information. The most definitive
way, the hard way, is to have enough people exposed to a given chemical to show
that it is safe or to show the exposure at which toxicity begins to appear. Plainly,
it is hardest to learn about chronic toxicity. Very large populations must be exposed
for long periods to give a statistical chance of establishing something useful. That
is what epidemiology is all about.
What Is Epidemiology?
Historically, epidemiology is the study of epidemics, contagious diseases that
spread rapidly. But today, epidemiology is also used in a statistical way to try to
detect acute or chronic toxicity even when the ejects on health are quite small. For
example, vinyl chIonde, CH2CHCI, is known to be carcinogenic (a cause of
cancer). The reason is that a very rare form of liver cancer, angiosarcoma, is found
205
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206
THE RISK/BENEFIT EQUATION IN CHEMISTRY
statistically to be concentrated in a small number of workers who have been
continuously exposed over long periods to high levels of viny! chloride, in the
hundreds of ppm. Here we can reach the confident epidemiological conclusions
that this chemical has a toxic effect and that the degree of hazard to the general
public is extremely small.
What Causes What?
Unfortunately, epidemiological data can be misinterpreted, even when the
statistics are firm. It is one thing to show (1) that colon cancer is much more
prevalent in the United States than it is in India, and (2) that Americans eat more
dairy products than people in India do. Before jumping to the conclusion that dairy
products cause colon cancer, we must remember that colon cancer appears in older
people and that U.S. citizens live a lot longer (on the average) than citizens of India.
Thus, the opposite conclusion might be reached—that eating dairy products allows
one to grow old enough for colon cancer to show up (from other causes).
Epidemiology can show "association" but not necessarily "causality." The
epidemiologists' joke is that the twentieth century growth of population in Western
Europe has decreased at about the same rate as the decrease in the number of
storks. Few of us would conclude that the human birth rate is going down because
there aren't enough storks for the deliveries.
Animal Tests
These difficulties have driven us to the use of laboratory test animals as
substitutes for humans. Without debating the ethics of such practice, we observe
that among the animals so used are mice, rats, guinea pigs, monkeys, hamsters,
dogs, cats, pigs, and even fish. Mice and rats are used most, probably because they
are inexpensive, they breed rapidly, and their use is generally accepted.
In a typical study, groups of a few thousand mice might be exposed to two or
three different doses of a particular chemical every day for 2 years (including a zero
dose for a control group). Then these mice are killed ("sacnficed" is the term used)
and every mouse is autopsied to search for tumors. The statistical differences
between the control group (zero dose) and the exposed groups are taken as a
measure of hazard. Such an experiment might show that one milligram of chemical
X eaten every day by a half-pound mouse causes a 14 percent increase in stomach
cancer. To decide what this means for us, we usually assume that a human weighing
about 150 pounds, 300 times more than the average mouse, will need to eat about
300 milligrams per day of chemical X to have about the same 14 percent cancer
probability. Thus, toxic doses are expressed in terms of milligrams per kilogram of
body weight (mg/kg).
For acute toxicity, a substance legally earns the title "poison" if 50 percent of a
test group of animals dies from a dose of 50 mg/kg or less. This dose the one that
causes a 50 percent death rate is called the LD50 dose (lethal dose, 50 percent
death rate). Thus, strychnine is a poison it takes only 1.2 mg/kg body weight to
kill 50 percent of a rat population. On the other hand, tnchioroethylene (TCE)
(recently found in water wells at ppm concentrations) is not called a poison since
a rat has to eat 7,200 mg/kg of body weight to reach the LDso level. Transferred to
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THE RlSKlBENEFIT EQUATION IN CHEMISTRY
humans, this means that a 150-pound adult would have to eat about 3 pounds of
TCE per day to receive this same dose, based on body weight. A 50-pound child
would have to drink 4,000 gallons per day of well water containing 25 ppm of TCE
to receive this dose.
Since we cannot deliberately use human populations to test poisons and possible
cancer-causing chemicals (carcinogens), this use of animal subjects is at least a
rational approach. Even then, it raises the difficult question of whether animal
responses provide a reliable estimate of human responses. After all, we aren't
really trying to protect mice with this testing we have in mind the health of human
beings, who come from an entirely different rung on the evolutionary ladder. The
uncertainty comes when we have to rely only on this method to make decisions.
As an example, the compound 2,3,7,8-tetrachiorobenzo-p-dioxin (popularly
called "dioxin") is extremely poisonous to guinea pigs. For these little fellows, the
LD50 is only 0.6 milligrams per kg body weight. In astonishing contrast, it takes
10,000 times larger doses to reach the LD50 level for hamsters! From species to
species, we find enormous variation in toxic responses to dioxin. For this
substance, we have had many documented human exposures. Among 400 severe-
exposure cases that occurred 20 to 35
years ago, painful skin lesions were the
only definite injury that appeared, and no
deaths attributable to the exposures have
yet occurred. In this case, we can't even
predict usefully the lethal dose of dioxin
to a 50-gram hamster from measurements
on a 200-gram guinea pig, let alone a
150-pound human. This type of uncer-
tainty is part of every regulatory decision
in which tolerance limits must be estab-
lished for humans with only animal tests
as a guide.
Is There a Dose-Time Relationship?
TABLE VI-1 Dioxin's Lethal Dose
Varies from Species to Species
Animal
Guinea pig (male)
Rat (male)
Rat (female)
Mouse
Rabbit
Dog
Bullfrog
Hamster
LD50 (mg/kg)
0.6
22
45
114
115
>300
>500
5,000
There remains one further question to complicate this perplexing but crucial
issue of risk assessment. It is natural to wonder, if a large dose of something is
poisonous in a short time, whether a small dose of the stuff is also poisonous, but
over a longer time? For example, suppose we want to eliminate disease-spreading
rats with the fumigant ethylene dibromide, C2H4Br2. Lab experiments show that
rats are killed by breathing 3,000 ppm of this gas after 6 minutes of exposure. If that
is so, how long would it take to have a lethal dose at 300 ppm? The simplest guess
we can make is that at one-tenth the concentration, it takes just 10 times as Tong,
60 minutes, one hour. Actually, this linear assumption with its one-hour estimate
is pretty close to what is found in lab tests. Does this, then, let us predict the lethal
concentration for a 6-month exposure? Six months is 4,320 hours, so our linear
model predicts lethality at the very low concentration of 0.07 ppm (300/4,3201. This
time, however, experiment shows that the 6-month LD50 exposure for rats is 50
ppm. For prolonged exposure, the rats can tolerate much more ethylene dibro-
207
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208
THE RlSKlBENEFIT EQUATION IN CHEMISTRY
mice 700 times more than we estimated. In this case, the linear assumption has
failed.
This is not an isolated case. We have already mentioned selenium, which, at low
concentrations, is essential for both human and animal health. At higher concen-
trations, selenium produces serious health effects. Evidently, this contradicts the
linear model, which gives no clue to the beneficial effects of selenium but, instead,
would lead us to expect selenium to be toxic at any level if exposure is long enough.
Carbon monoxide, a treacherous poison, provides another clear example. In the
blood, CO bonds to hemoglobin and renders it useless as an oxygen carrier. If about
one third of the hemoglobin is so tied up, the victim dies. This would happen to the
average person after one hour of exposure to 4,000 ppm of CO (a partial pressure
of 3 torr). From this evidence, the linear mode] would predict that 1 ppm would be
lethal in about 4,000 hours, i.e., in about 6 months. However, the natural
atmosphere we breathe all of our lives always contains about 1 ppm of CO and is
clearly not lethal.
There are examples in the opposite direction as well. Liquid mercury has a rather
low vapor pressure, about one millito~T, and breathing it continuously has no
immediate effect on health. However, the body cannot efficiently eliminate
mercury, once ingested, so it accumulates over time. After many years of
continuous exposure, venous undesirable symptoms begin to appear, including
unsteadiness, inflammation of the gums, general fatigue, and headaches. In this
case, the absence of short-term effects gives no warning about the chronic,
fong-term danger of continuous exposure to the vapor of liquid mercury.
All of these examples suggest that we must be very careful when trying to
extrapolate data concerning potentially harmful substances. It is not possible to
predict with confidence the long-term, low-exposure toxicity of a given chemical
just from evidence about toxicity at high exposures for short times.
Summary
We see that risk assessment is a difficult business. Nevertheless, it is an essential
part of maintaining a healthy environment. We want to enjoy the benefits of
technological advances, so we must learn to evaluate possible undesired side
effects. We cannot afford to ignore the possibility that something might be
hazardous, but at the same time, we cannot be paralyzed by indecision or fear.
RISK MANAGEMENT
Our everyday lives are full of risks, but this is not a new situation. We evolved
in a threatening environment. Nature provides many risks free of charge: tornados,
hurricanes, avalanches, earthquakes, floods, fires, volcanic eruptions. But many of
the risks were "invented" by the human race from catching one of the plagues
which were spawned in the Middle Ages by the growth of cities, to falling off your
horse while riding off to war. Our modern list is getting longer and longer it
includes automobile accidents, airplane crashes, ferryboats sinking, muggings in
Central Park, smoggy air, and catching colds in the subway. Some risks we choose
to take, like risking skin cancer while getting a suntan; others we may choose to
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THE RISKIBENEFIT EQUATION IN CHEMISTRY
avoid, like smoking cigarettes. Some risks we prefer not to take, but cannot find a
way to avoid, like living under the ominous threat of nuclear war.
Thus, the sheer volume of risks we face seems to be steadily increasing with
time. Yet a look at one particular measure, life expectancy, reassures us that we are
not only holding our own in this battle, but perhaps actually winning. In the United
States, life expectancy has
steadily risen throughout this
century, and it continues to
rise at a rate of 3 years of
additional age per decade. This
impressive statistic can ease
some of the anxiety about
modern, technological nsks,
and steady our resolve to deal
with them in an attentive, pru-
dent, and rational way. Dealing
with them begins with thinking
about what is an "acceptable
risk."
Acceptable Risk
Notice that we propose to
"think about," not to "de-
cide," what is an acceptable
risk. That is because risk ac-
ceDtance is a highly personal
O()
1:
Llle Expectancy
at Age 4 5
_ 50t
209
-
_o~
~ Late Expectancy
at Blrth
~0
I , ~ I ,
1 900 1 920
94(3 YEAR 960 1980
LIFE EXPECTANCY IN THE UNITED STATES
TIlREE YEA RS 1 NCREASE EV ERY DECA DE
~ _ .
and subjective thing. It can be arbitrary and even contradictory. An individual can
decide to avoid the dangers of hang gliding but regularly Unve an automobile at 60
mph with seat belt unfastened. Another individual may smoke cigarettes but
vigorously shun marijuana—or vice versa. Some risks we take unthinkingly
because they are familiar. Californians are used to earthquakes, Nebraskans to
tornados, and Floridians to hurricanes. Everyone who can adore it goes from here
to there in airplanes equipped with life rafts but not parachutes. What factors are
at work as each of us decides what to worry about?
While the answer to this question varies enormously from person to person,
there seems to be one factor that is generally important. Most people are highly
sensitive about taking a risk involuntarily; they like to have a choice in the matter.
The same individual who may choose to try skydiving, smoke cigarettes, consume
caffeine, take birth control pills, or just cross a busy street in the middle of the block
is likely to object strongly to the news that a pesticide might be found on his or her
fresh fruit. People just fee! better making their own choices. The current nervous-
ness about chemicals probably stems largely from the feeling that chemical risks
are being taken involuntanly and that they are increasing.
On the other hand, it is difficult for most people to deal with the magnitude of a
risk. How does one evaluate the news that eating peanut butter might involve a risk
of one in 500,000 that its 2 parts per billion (ppb) aflatoxin content might result in
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210
THE RISKIBENEPIT EQUATION IN CHEMISTRY
cancer? The numbers tend to blur in the face of the news that a dreaded disease
may be involved. But there is one way to evaluate risks that most people can
appreciate and use as a guide in decision making. It is to compare the risk for an
unfamiliar hazard with another risk that is usual and similar in kind. That type of
comparison calibrates for each of us what is an acceptable risk.
.
Comparable Risks
Let us begin by examining quantitatively the magnitude of a risk almost everyone
takes voluntarily and daily: riding in an automobile. Ample statistics indicate that
the chance of being killed while driving 3 miles is about one in a million. That means
that a city dweller who travels that much every day for a year takes an annual risk
of about 4 in 10,000. Over such an individual's 60-year lifetime, the chances of a
fatal accident in an automobile are about one percent. This single example says that
we regularly expose ourselves to an "acute risk" of one in a million and probably
without realizing it, a "chronic risk" of one in a hundred.
Now let's look at some comparisons between similar risks. For example, 10
years ago, careful estimates were made of the possible effect of spray can
propellants and refrigerator fluids on the stratospheric ozone. The outcome at that
time was that the ozone would be lowered in the next few decades by at most 20
percent if chIorofluorocarbon use were continued. Since stratospheric ozone
shields us from ultraviolet radiation, this depletion, if it were to occur, would cause
a predictable increase in the number of nonfatal skin cancers in the U.S.
population. To what could this new risk be compared? Is it large or small? Here we
have a firm basis for an answer. The increased probability that an individual might
end up with such a skin cancer is about the same as the increased probability of skin
cancer associated with moving from San Francisco to the more sunny Los Angeles
or from Baltimore to Miami.
That comparison does not decicle the question of whether the chiorofluorocar-
bons should or should not be used. That depends upon the benefits to be lost as
well. But it gives a person with a nonscientific background a tangible measure of
what is at stake.
The Palo Alto water wells contaminated with trichIoroethylene provide a second
example. These wells, used for drinking water, were found to contain up to 3 ppm
of tnchloroethylene (TCE). At this concentration level, TCE is known to be a weak
carcinogen through laboratory animal tests. Is there a comparison risk we can use
to guide us? Tests show that the TCE contaminant is 1,000 times less hazardous
than drinking an equal volume of cola, beer, or wine, each of which also contain
weak carcinogens. Cola and beer, for example, both contain the carcinogen
formaldehyde, cola at ~ ppm and beer at 0.7 ppm. These can be compared, in turn,
to human blood, which also contains fo~-~naIdehyde at about 3 ppm from normal
metabolism. These contrasts allow a lay person to compare, in everyday terms, just
how big (or small) the TCE risk is in those water wells.
What about pesticides? Man-made pesticide residues are found in our food at
about 0.1 ppm, and most of them are classified as noncarcinogenic. Here, a useful
comparison can be made to the presence of natural pesticides that are also present
in our foods, but at 10,000 times higher concentrations than the man-made
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THE RISKIBENEFIT EQUATION IN CHEMISTRY
pesticides. These natural pesticides, present in every plant, are toxic chemicals that
Nature evolved to protect the plant from fungus, insect, and animal predators.
Some of these have been tested on rats or mice and found to be carcinogenic at
sufficiently high dosages: estragole in basil, safrole in various herbs, psoralins in
parsley and celery, hydrazines in mushrooms, and ally! isocyanate in mustard. That
is useful and relevant evidence to be considered when we are considering the
current hazard posed by agncultural pesticides.
We see that comparable risks provide us with an easily understood measuring
stick that can help us decide which potential hazards are serious enough to warrant
corrective or restraining action. This kind of evidence can help us sort out those
hazards small enough to be ignored so that we can concentrate our efforts (and
resources) on the hazards that deserve and require attention.
Who Is at Risk?
Risk management is connected with getting general agreement on the balance
between risks and benefits. But sometimes the people who see themselves at risk
are different people than the ones who benefit. Thus, the society at large wishes to
dispose of radioactive waste by storing it safely in some remote area. Unfortu-
nately, it is necessary to transport it there on trucks that pass through many small
towns on the way. The people who live in these towns are the ones at risk that a
truck might overturn right downtown at the intersection of 1st and Main. They are
likely to agree with Los Angeles that the wastes should be stored in some desert,
but not be ready to endorse carrying that dangerous material through the town. As
another example, lots of people in Logan, Utah, depend for their livelihood on their
jobs in the smelters, and people all over benefit from the useful materials that come
from these smelters. However, the smelters make their contribution to the air
pollutants that generate acid rain a thousand miles away in the Northeast and in
Canada. The neonIe in the regions suffenne from acid rain see the issue entirely
~ - r -a _ _ _
~ . _ .. . .. · .. · ~ ~ ~ .' . _ 1 ._ _ ~
dluerently than those in the region whose economy Depends upon Ine vl~allly OI
those industries.
There is no easy answer to such dilemmas except to say that the interests of both
groups must be considered in shaping public policy. Recognizing the nature of the
problem helps, though, in see-
ing why diametncally opposed
positions might be persua-
sively argued by reasonable
and sincere people on each
side.
TABLE VI-2 Media Treatment of Three
Chemical Spills
Incident
10,000 gallons of toluene
leaked into bay
Newspaper Headline
Chemical Scare Blocks Estuary
Toluene—the ``T'' in TNT
__.
White solid substance Giant Traffic Jam
spilled on roadway Scare Closes Bay Bndge
MEDIA TREATMENTS OF ''Mystenous white Chemical Scare on Gate Bndge
CHEMICAL SPILLS substance" found in
roadway
Table VI-2 lists three inci-
dents that occurred during 1983 in the San Francisco Bay Area. In the first of these,
both the television and the local newspapers opened their reports with the
misleading remark: "Toluene—that's the T in TNT.'' What the press did not report
211
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212
THE RISKIBENEFIT EQUATION IN CHEMISTRY
was what all this toluene was doing in the area. Toluene is widely used as a solvent
for many useful products such as paints and lacquers. Because of its wide use, large
volumes of toluene are regularly transported over large distances. It has come into
use as a substitute for benzene because toluene is safer: it is less flammable than
benzene, it has a lower vapor pressure, and benzene is considered to be carcino-
genic. These facts and the outcome- that no one was injured- add perspective to
this undesirable accident, but they were not effectively communicated to the
public.
The second incident caused the closure of the Bay Bridge during the peak commute
hours, trapping 20,000 autos and disrupting the plans of their 40,000 occupants heading
to work, to the airport, to the hospital, or to visit the San Francisco Art Museum. The
spired white substance proved to be lime, used in making concrete, handed daily by
construction workers. The third incident in Table VI-2 was reason for closing the
Golden Gate Bridge for 3 hours. This "chemical scare" was associated with a big bag
of cornstarch that must have dropped off the back of a truck. These are two of the five
closures of these bridges due to "chemical spins" since 1980. As in the three examples
in Table VI-2, the other three closures were reported in the press and on television with
emphasis on the worst-case scenano. These three chemicals were iron oxide (used as
a pigment; it has the composition of rust), calcium phosphate (a fertilizer and
component of detergents), and talcum powder. The talcum powder case closed the
bndge for 10 hours! In none of the five bridge closures was there a newspaper
foDow-up article reassuring the public that not one individual had been harmed and,
indeed, that no one was ever In danger.
What do we learn from these examples? The first lesson to be learned is that
reporters rushed to the scene of an accident cannot be expected to be chemists.
They will be reporting information received from other individuals, such as police,
who are also unlikely to be chemists but whose responsibility is to act in the public
interest in the face of the limited information they have. These latter officials can do
nothing other than assume the worst possible situation. Consequently, media
reports of chemical spills will usually overestimate the danger.
We might hope, though, that the reporters would feel enough responsibility to
avoid unjustifiable, fear-laden expressions (the " 'T' in TINTS. We might expect
them to tell us what the chemicals are used for (once identified) and to let the public
know, in retrospect, that this incident, at least, did not pose any real public hazard.
As for the officials, they did what they had to do. In our social climate, they must
act as though every white powder is as lethal as, say, sodium cyanide. What we can
do to help them is to look ahead to avoidance of repeats. How might these spills
have been handled after the first example? First, a plastic sheet held down over the
spill would reduce wind-blowI1 distribution. Then, bridge personnel wearing
fine-pore dust masks could sweep the solid material into a pile for later removal by
a cleanup truck equipped with a vacuum cleaner.
Turning from bndges to the larger context, it win be, more often than not, fire
personnel and police who will deal with the immediate consequences of a chemical
spin. Such personnel must (and many already do) have specific training in how to deal
with chemical spills. There should be particular emphasis on the industnal feedstocks
and chemical products in local use. A college chemistry course with a laboratory
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THE RISKIBENEFIT EQUATION IN CHEMISTRY
would be of immeasurable value and should be a normal criterion for advancement in
a fire department.
LARGE-SCALE USES OF CHEMICALS
Any large-scale human activity carries with it a special consideration. While an
unexpected and undesired outcome may have a quite low probability, the fact that
very large numbers of people may be affected must influence our thinking. This
special consideration is obviously applicable to nuclear war, reactor meltdowns,
and genetic engineenng; it also is awakened by large-scale uses of particular
chemical substances. We have already discussed in Chapter I! the possible global
impact of the widespread use of chiorofluoromethanes as spray-can propellants and
air-conditioner refngerants. The worldwide use of DDT provides a second,
informative case history and will be discussed here. Large-scale industnal acci-
dents fall in this category as well.
Most chemical spills are well-handled and contained, but there have been, and
will continue to be, rare but serious industnal accidents in which there is the
possibility of catastrophe. While the potential dangers do not approach the
centur~es-Iong and worldwide impact of a Chernobyl reactor meltdown, we are
reminded by Bhopal and the recent chemical spills into the Rhine River that
large-scale industrial operations pose real public risks. Two large-scale accidents
occurred within the last 10 years in which large populations were put at risk. One
of these took place at Seveso, Italy, in 1976, and the other at Bhopal, India, in 1984.
These two catastrophic events deserve review.
Seveso and Dioxin
A Swiss-Italian chemical firm, Industrie Chemiche Meda Societa, Anonima
(ICME-SA), manufactured the effective herbicide 2,3,5-trichIorophenoxyacetic
acid (2,4,5-T) in large quantities at its plant in northern Italy, near the town of
Seveso. The herbicide, used worldwide to increase food supply, is made from the
simpler compound 2,4,5-trichIorophenol (TCP). In manufacturing TCP, an unde-
sired impurity is formed in small quantity. The impurity, 2,3,7,8-tetrachIorodi-
benzo-p-dioxin, popularly called "dioxin," has been discussed earlier in this
section because of its extreme toxicity for certain small animals and the strong
species dependence of its toxicity (see Table VIM.
This large-scale accident at the ICME-SA plant began in July 1976, when cooling
water was turned off to a chemical reactor making TOP. The temperature and
pressure rose until a safety valve opened, releasing the reactor contents into the
atmosphere over a densely populated area. The reactor was estimated to contain
several pounds of the dioxin impurity.
Among the toxic chemicals that have received notoriety during the last 20 years,
dioxin may well be the one for which there exists the largest amount of and most
systematic epidemiological data. Since 1949, there have been eight large industrial
accidents, two of them involving U.S. companies. Table VI-3 shows that 823
workers were exposed, two thirds of whom suffered chIoracne, a very unpleasant
skin lesion, as a result. Much smaller numbers suffered liver dysfunction, elevated
213
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214
THE RISKIBENEFIT EQUATION lN CHEMISTRY
TABLE VI-3 Industrial Accidents Causing Dioxin Exposurea
Number of Number of Deaths
Workers Chloracne Number Expected Number
Date Exposed Location Cases without Exposure Observed
1949 250 Nitro, West Virginia 132 46.4 32
1953 75 Ludwigshaften, West 55 ~18 l7b.c
Germany
1963 106 Amsterdam, The 44 13 8c
Netherlands
1964 61 Midland, Michigan 49 7.8 4
1965-1969 78 Prague, Czechoslovakia 78 ? 5a,b,~
1966 7 Grenoble, Prance 21 ? ?
1968 90 Derbyshire, United 79 ? 1
Kingdom
1976 156 Seveso, Italy 134 ? Normalab'~
Total 823 592
aAll at plants manufacturing TCP; dioxin was an undesired impunty.
bImpaired mobility; fatigue, neurological symptoms.
CLiver damage.
Elevated blood cholesterol levels.
lipid and cholesterol levels in the blood, and neurological damage. All of these
conditions gradually recover. Astonishingly, for the 492 workers exposed before 1964
(22 years ago), the number of individuals who have died (61) is 30 percent lower than
expected from normal causes. No one concludes, of course, that dioxin increases
longevity, but it is difficult to conclude that it has a lethal effect on humans.
To summarize the outcome of the widely reported Seveso accident, hundreds of
townspeople and ICME-SA workers were evacuated, many of these having
received severe exposure to the chemicals released. An estimated 37,000 people
received minor exposure. The health of 500 people who received the largest
exposures is being carefully monitored. To date, there have been no known deaths,
involuntary abortions, or birth defects attributable to the exposure. Many small
animals and rodents were killed in the town of Seveso. The disposal of 41 drums of
toxic waste from the cleanup was in the European news for the next few weeks. A
French waste disposal company contracted to move the drums from Italy to an
authonzed waste disposal site in West Germany. Then began a strange odyssey for
the 41 drums occasioned by the fact that everyone wanted to get rid of the wastes
but no one wanted to have them pass through their town, let alone be stored
nearby.
Dioxin has received much attention, both in the courts and in the press.
Certainly, a factor has been the extreme and well-documented toxicity for guinea
pigs and mice, coupled with the fact that there are some well-established, though
most often temporary, human ailments caused by severe exposure. It does help to
show that the '~chronic risk" to any individual, even those living near TCP
chemical plants, is negligible compared with the chronic risks involved in driving a
car, smoking cigarettes, eating peanut butter sandwiches, or drinking beer or wine.
However, these are familiar and voluntary risks. As we have said before, the public
is extraordinarily sensitive to any risks to which it is exposed involuntanly.
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THE RISKIBENEPI T EQUA T10N IN CHEMISTR Y
Bhopal and Methyl Isocyanate
Near midnight on Sunday, December 2, 1984, the impoverished residents of
the squatter community called J.P. Nagar slept, unaware of the tragedy about to
strike them. They occupied huts and hovels in a crowded shantytown built in the
safety zone surrounding the Union Carbide plant just outside of Bhopal. Bhopal
is a city of 800,000 and the capital of the agricultural State of Madhya Pradesh,
the largest State in India. The plant was sited near Bhopal to manufacture
pesticides, an essential element of the "green revolution" in a country trying to
come to grips with its most cntical national problems, starvation and maInour-
ishment.
This plant had three large, underground storage tanks containing the volatile and
toxic liquid methyl isocyanate, which is an immediate precursor to several effective
herbicides. Late in the evening of December 2, the weekend plant personnel found
that the pressure in one of these tanks, number 610, was abnormally low. Then, the
temperature and pressure in 610 began to nse, this dangerous development being
accentuated by the fact that the protective refrigeration unit may have been
switched off. The plant personnel panicked as the temperature began to rise
precipitously. The vapor pressure of the volatile liquid soared upward until it
ruptured first a safety disk and then a relief valve designed to alleviate such an
emergency. However, the vent line to the flare tower, where such releases are
burned to harmless products, was closed off for repairs. The torrent of gas passed
into, and overwhelmed, chemical scrubbers intended to neutralize any methyl
isocyanate release not handled by the (inoperative) flare tower. Pressurized
sprinklers designed to form a "water curtain" over such a release did not function
because the water pressure was too low.
In an accelerating calamity, tank 610 discharged 41 tons of lung-searing methyl
isocyanate gas on the people of I.P. Nagar. The wind carried the lethal cloud
south toward the Railway Station, which had its own shanty community. Before
that terrible night ended, about 14,000 of the 800,000 inhabitants of Bhopal had
been seriously exposed. Perhaps 1,500 men, women, and children died within the
first few hours. Without question, the world had seen the worst mass exposure
to toxic chemicals since the deliberate chemical warfare of World War I. The
repercussions of this tragic event are still with us, as both societies and chemical
industries around the world work to ensure that it will not happen again.
The Chemistry Behind Bhopal
Methyl isocyanate (MIC) is a volatile, reactive, toxic, and flammable liquid. It
boils at 39°C, and its vapor pressure is almost half an atmosphere at 20°C. It is
shipped only in stainless steel or glass-lined containers under a slight ove~pressure
of dry nitrogen to prevent the entry of atmospheric moisture. In bulk storage, it
should be cooled, preferably to 0°C.
It is toxic to rats with an LD50 of 21 ppm for 2 hours of exposure and 5 ppm for
4 hours of exposure. In 1965 (when it was still permitted), four human volunteers
in West Germany were exposed to low levels of MIC. At 0.4 ppm, none of the
subjects detected it, but at 2 ppm, there was nasal irritation and their eyes watered.
215
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216
METHYL ISOCYANATE
tWHAT IT S FOR |
N= C~ ~ + ROH -
CH3
WHAT IT S NOT FOR|
THE RISKIBENEFIT EQUATION IN CHEMISTRY
At 21 ppm, the irritation became extreme and the test was terminated. There were
no lasting aftereffects.
When water comes into contact with MIC, it reacts rapidly to form methyl amine
and carbon dioxide. The reaction releases heat, so if there is no cooling, the
temperature rises and the reaction speeds up. As the temperature rises (or in the
presence of catalysts such as
Fe, Cu. Sn, or Zn), MIC reacts
with itself to form a tnmer,
again liberating heat so that the
temperature rises still more and
reactions accelerate. These un-
desired reactions have the po-
tential for a thermal "run-
awav.'' so safe handling of MIC
N_C O ~ H20
CH3
~2 N= C—O
CH3
o
11
RO—C—NH—CH3
CARBONATE
PESTICIDES
+ CO2
aH =-231ccal
o
11
H3C_ SCOW ACHE
I I An=-54lccal
in ~
requires careful temperature
control, avoidance of moisture,
and meticulously clean contain-
ers (to avoid catalysts).
With all of these hazardous
~B=-54]ccal properties, why does anyone
O^' ANN to use MIC, let alone store 40
H TRIMETHTt tons in a single storage tank?
3 I SOCIANURATE The value of MIC is that it
readily reacts with alcohols to
form carbamates, which are extremely effective pesticides. It is used by Union
Carbide to make the pesticide Levine (1-naphthyI-N-methy! carbamate), by Shell to
make Nun (methonyI), by DuPont to make Lennate@, and by FMC to make
Furudon~ (carbofuran).
Union Carbide has its biggest MIC production plant at Institute, West Virginia
(10 times bigger than the Bhopal plant). Because of the importance of pesticides
in raising the food supply for the 700 million population of India, Union Carbide
established near Bhopal the most advanced Research and Development Center
for pesticides in all of Asia. In addition, Union Carbide built the plant at Bhopal
so that pesticides for use in India could be manufactured in India by Indian
personnel.
~ ~ ,
w. ~3 T ROCYANURATE
The Victims
One year after the Bhopal accident, the official government cleath toll was
placed at about 1,800, although it is possible that this estimate is too low by as
much as 500 to 1,000. Among the most exposed victims, lung damage was
persisting, eye damage was generally recovering, and liver dysfunctions were
prevalent (due, in part, to complications caused by the drugs administered). In
the exposed population, with a normal death rate of 250 per month, deaths were
being registered at 265 per month. No birth defects had been associated with the
exposure.
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THE RISKIBENEFIT EQUATION IN CHEMISTRY
lessons To Be [earned
Governments in developing countries are generally enthusiastic, sometimes
insistent, that manufacturing of essential products be conducted within the
country's borders. Some countries require majority local ownership, local
engineering and construction, and local operating and maintenance staff. These
requirements can affect safety adversely because of cultural differences in work
attitudes, understanding of industrial concepts, and response to training. Some of
these factors may have contributed to the magnitude of the Bhopal disaster.
Whether that is so or not, these are real problems that must be recognized and
handled effectively while giving proper attention to national sensitivities.
More generally, this catastrophe draws acute attention to the importance of
safety in chemical operations. There should be an enforced safety zone around a
chemical plant, and care should be exercised in the placement of chemical plants.
There is now an increased awareness in communities near chemical plants, and in
this country, many chemical industries have responded to this awareness with
active communication programs that directly involve the local citizenry. These
efforts are leading to improved readiness plans for various emergency situations
that might develop.
Perhaps the most important single lesson of Bhopal is, however, that particularly
dangerous intermediate chemicals should not be stored in unnecessarily large
quantities. Processes must be designed to manufacture these intermediates at the
time of use and only in the quantity needed. This is a time-honored principle in any
chemistry research laboratory, and it is even more important when the lives and
health of many people are involved.
The DDT Story
It all began in 1939 when a Swiss chemist, Paul Muller, synthesized dichIoro-
dipheny! trichIoroethane (DDT) during a systematic exploration for new insec-
ticides. At the outset DDT appeared to be a miracle compound; it was extremely
potent against a wide range of insect pests, and it did not have the acute human
toxicity problems associated with the lead and arsenic compounds widely used at
the time.
The Benefits
The United States first used DDT extensively in 1944 dunng World War I] to
counter a growing typhus epidemic among troops and the civilian population in
Italy. Typhus is cawed by body lice, and thousands of people were liberally dusted
from head to toe with DDT to eliminate these pests. The epidemic was stopped,
preventing a potentially devastating loss of human life.
In the light of this massive success, DDT was put into service against the
Anopheles mosquito, which spreads malaria across many parts of the globe. Before
the use of DDT, malaria was responsible worldwide for 2 m~lion-3 million deaths
per year and recurrent, periodic suffering for a much larger number. After a decade
of use, malana has been removed as the primary scourge of human existence in
several countnes. In India, the number of malana cases was lowered from 75
217
OCR for page 218
ago
~ -I E0~ ~ ~~y
mUbonin1932lolOO,OOO in 1964. In 1be Soviet Union, 1be number of cases dropped
Mom 33 mUbon in 1936 to 13~000 in 1966. In Sh Lanka over 1bb same time period,
1be meads toU went Mom 12~000 deaths per year 10 zero! The Wodd BeaRb
O~ganizabon of the Onited Nabons teas credited this wonder cbemica1 Bob saving
possibly 30 miDion Eves ham mama alone. For big accompliAbments, Dr. Paul
MOHer was amazed the 1948 global Faze in Medicine.
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THE RISKIBENEFlT EQUATION IN CHEMISTRY
addition, some insects and pests became resistant to DDT after its prolonged use,
and some beneficial insects were locally exterminated unintentionally.
The Risk/Benefit Equation
Here we see the evolution of a classic risk/benefit case. At the outset, it is clear
that short-term benefits are great (in this case, the saving of human lives), and there
are no known costs to be weighed against these benefits. But, despite the
realization of the anticipated benefits, vigilant monitoring revealed environmental
disturbances that were too pervasive to be ignored. Even though no human ailment
has ever been connected with exposure to DDT, it is plain that some of its
properties are incompatible with our desire to protect the world around us DDT's
incredible stability, its mobility, and its amenity for living systems. However, at the
same time that these special problems worked against its continued use, they
defined the properties needed for a substitute. These now exist insecticides that
are much more species specific, that are also nontoxic for human exposure, and
that degrade in the environment after a few days or a few weeks. While DDT was
saving millions of human lives, it was also guiding us to better solutions to the
risk/benefit equation.
CONCLUSION
The most resounding message that emerges is that risk assessment is a difficult
business. Paracelsus told us: "Everything is poisonous. The dose alone deter-
mines the poison." Yet it is extremely difficult to determine the dose. Tests with
humans are not permitted, and animal tests have questionable applicability to
humans. Epidemiology shows association but not necessarily causality.
There are strong subjective elements, too. One person's negligible risk is
another's unacceptable hazard. Worse yet, often the group at risk is different from
the group that benefits. Finally, everyone is sensitive about any risk to which the
exposure is involuntary.
Despite these difficult and sometimes perplexing aspects, nskJbenefit trade-offs
have become a common element of countless decisions that affect us all. Some
of these are decided for us by our elected officials in our state capitols and in
Washington, D.C. Some of them we decide for ourselves in voting booths.
Wherever these decisions are made, they should reflect both the common good
and the common will. To make this possible, we need to improve scientific
literacy throughout our population. Plainly, this must begin early in our schools;
science education must receive more attention.
In conclusion, we should be reminded that our quality of life and steadily
increasing longevity are directly attributable to our technological advances in
chemistry. An approach to chemical hazards based on unreasonable fear can
deprive us of health-restoring drugs, essential sources of energy, increased food
supplies, useful commodities, and industrial productivity. To avoid paralysis and
the loss of these benefits, we need calm, wise, and rational decisions in deciding
when and how much regulation is needed. We can achieve this by dealing wisely
with the risk/benefit equation.
219
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220
THE RISKIBENEFIT EQUATION IN CHEMISTRY
SUPPLEMENTARY READING
Chemical & Engineering News
"BhopaI" by W. Lepkowski (C.&E.N. staff),
vol. 63, pp. 18-32, Dec. 2, 1985.
"Stringfellow Cleanup Mishaps Show Need
to Alter Superfund Law" by L.R. Ember
(C.& E.N. staff), vol. 63, pp. 11-21, May
27, 1985.
"Bhopal, A C. and E.N. Special Issue" (C.&
E.N. staff), vol. 63, pp. 1~63, Feb. 11, 1985.
"Dioxin, A C. and E.N. Special Issue" (C.&
E.N. staff), vol. 61, pp. 20-64, June 6, 1983.
"Acid Pollutants: Hitchhikers Ride the
Wind" by L.R. Ember (C.& E.N. staid,
vol. 59, pp. 20-31, Sept. 14, 1981.
"William Lowrance: Probing Societal
Risks," Interview, W. Lowrance, vol. 59,
pp. 13-20, July 6, 1981.
Science
"Risk Assessment and Comparisons: An In-
troduction" by R. Wilson and E.A.C.
Crouch, vol. 236, pp. 267-270, April 17,
1987.
'`Ranking Possible Carcinogenic Hazards'
by B.N. Ames, R. Magow, and L.S. Gold
vol. 236, pp. 271-289, April 17, 1987.
"Perception of Risk" by P. Slovic, vol. 236,
pp. 280-285, April 17, 1987.
"Risk Assessment in Environmental Policy-
Making" by M. Russell and M. Gruber,
vol. 236, pp. 28~290, April 17, 1987.
"Health and Safety Risk Analysis: Informa-
tion for Better Decisions" by L.B. Lave,
vol. 236, pp. 291-295, April 17, 1987.
OCR for page 221
CHAPTER VII
Career Opportunities and
Education in Chemistry
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Library into Space
Unbelievable though it sounds, we may have to place whole libraries in a space-like
environment over the next decade! This strange proposal is not made because our
orbiting astronauts need more reading maters, but because if we don't do that or
something' similar, most of our books won't be around very long for the rest of us to
read. An Warming and little know problem faces mankind today the vast majority of
books, those printed since the 1850s, are relentlessly yellowing and crumbling to dust.
The library at the University of California at Berkeley alone stands to lose 60,000 books
and periodicals per year to decomposition. This is not because of air pollution; the
source of the destruction lies in the very paper on which the books are pnnted. Now,
some clever chemists have discovered that, surpnsingly, a trip into an environment
similar to space provides at least one solution to this vexing problem.
Papennaking processes used since the 1850s universally employ an alumrosin sizing
to keep irk from "feathenng" or spreading on the paper. Slowly, this papermaker's
alu~aluminum suIfate~ombines with moisture in the pages and in the air to form
sulfuric acid. This aggressive substance, in turn, facilitates attack on the cellulose fibers
in the paper, breaking them into smaller arid smaller fragments and, ultimately, to dust.
Between 75 and 95 percent of the deterioration in ``modern'' paper is caused by such
acid attack.
In recent years, chemists have developed a number of acid-neutralizing processes for
books. One of these, developed in the Library of Congress research laboratory,
suggests that the chemical diethyl zinc may be ideal for the job. Diethy} zinc is a gas,
so its molecules can easily permeate even a closed book. Once inside, the substance
deacidifies each book and then looks ahead to the future by leaving an alkaline residue
of zinc oxy-carbonate. This residue, uniformly distributed throughout the paper fibers,
protects the book Tom any future acid attack.
Iron~caBy,- this life-sav~ng agent, diethy} zinc, bursts into flame on contact with air
and explodes when it touches water. How does a chemist work with a compound that
cannot be exposed to am or water? In a deep space environment, of course. A suitable
location was fourth at NASA's Goddard Flight Center, where 5,000 books from the
Library of Congress took a simulated flight, not on a rocket into space, but in a
laboratory space-simulating vacuum chamber.
First, the books were thoroughly dried by wing under vacuum for about 3
days. Then, with all oxygen removed from the chamber, gaseous diethyl zinc
was introduced and allowed to defuse into the books. As the neutralizing
~ '7 Jo reaction proceeds, harmless ethane gas is produced and pumped away.
,~ (I >~~ Then the protective zinc oxy-carbonate is fanned. The results have
_ \~ been extremely promising, and, as the technology Is perfected,
Em, ~ libraries across the nation will be looking to instaI1 huge deacidifi-
` ~ ~ cation facilities. These countermeasures, coupled with the new
,,_ "alkaline reserve" papers now used in modern printing, promise
that the precious heritage of the worId's libraries, including the
A, ~ enormous Library of Congress, will be preserved for future genera-
~ tions to enjoy, and profit from, just as we do today.
222
Representative terms from entire chapter:
chemical spills
