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Chemistry for Changing Times
12th Edition
Hill and Kolb
Chapter 22
Poisons:
Chemical Toxicology
John Singer
Jackson Community College, Jackson, MI
© 2010 Pearson Prentice Hall, Inc.
Chemical Toxicology
Poison
A poison is a substance that causes injury,
illness, or death of a living organism.
“The dose makes the poison.” All substances
are poisonous, depending on the amount.
Toxicology is the study of poisons, their effects,
detection, identification, and antidotes.
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Natural Poisons
Many natural substances are acutely toxic.
Socrates was put to death by drinking a cup of
hemlock. Hemlock contains coniine, which is
an alkaloid.
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Natural Poisons
Poisons in the Garden and on the Farm
Many of the berries, flowers, and leaves found in a
common garden are toxic. Farmers and ranchers have to
deal with plants that poison their livestock. Locoweek is
one such plant.
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Corrosive Poisons: A Closer
Look
Acids and bases can catalyze the hydrolysis
of amides. The peptide bond of proteins is an
amide linkage. Exposure to acids and bases
can denature proteins by hydrolyzing the
peptide bonds. If the protein is an enzyme, it
can be deactivated by hydrolysis.
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Corrosive Poisons: A Closer
Look
Oxidizing Agents
Many airborne pollutants are damaging to living
tissue. Ozone, peroxyacetyl nitrate (PAN), and
other oxidizing agents found in photochemical
smog can cause the deactivation of enzymes.
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Poisons Affecting Oxygen
Transport and Oxidative
Processes
Blood Agents
Carbon monoxide (CO) binds tightly to the iron
in hemoglobin preventing the transport of oxygen.
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Poisons Affecting Oxygen
Transport and Oxidative
Processes
Blood Agents
Nitrate ions (NO3-) found in some foods and in drinking
water in some areas are converted to nitrite ions (NO2-).
Nitrite ions oxidize Fe2+ in hemoglobin to Fe3+, forming
methemoglobin, which is incapable of carrying oxygen.
The result is a condition known as methemoglobinemia or
“blue-baby syndrome”.
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Poisons Affecting Oxygen
Transport and Oxidative
Processes
Blood Agents
Cyanide ions (CN-) bind to the iron(III) ions in
oxidative enzymes known as cytochrome
oxidases. This puts an end to cellular
respiration and brings near immediate death.
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Make Your Own Poison:
Fluoroacetic Acid
When fluoroacetic acid is
ingested, it is converted to citric
acid. Citric acid is normally
broken down in the citric acid
cycle, releasing energy.
Fluoroacetic acid effectively shuts
down the citric acid cycle making it
an effective poison. Natives in
South Africa used a plant
containing fluoroacetic acid from
the giftblaar plant to poison the
tips of their arrows.
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Heavy Metal Poisons
Many metals are toxic. Heavy
metals with densities at least five
times greater than water are
especially so.
Most heavy metals display their
toxicity by reacting with sulfhydryl
groups (-SH) deactivating
enzymes.
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Heavy Metal Poisons
Mercury
Mercury is used in many places. Many people
have dental amalgams containing mercury. It is
used in thermometers and thermostatic switches
in homes. It is used as fungicide on seeds used
in farming. Mercury vapor is toxic when inhaled.
The body converts the mercury to Hg2+.
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Heavy Metal Poisons
Lead
Lead too has many uses and is found in the
environment. It was once widely used in
household paints and in gasoline. Lead can
cause brain, liver, and kidney damage.
Treatment for lead and mercury poisoning can
involve the use of chelating agents.
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Heavy Metal Poisons
Cadmium
Cadmium is used in alloys, electronics, and
rechargeable batteries. Cd2+ ions lead to the
loss of Ca2+ ions in bones. They also cause
severe abdominal pain, vomiting, and diarrhea.
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More Chemistry of the Nervous
System
Acetylcholine (ACh) is a neurotransmitter. ACh
carries a nerve impulse across a synapse. It is
then hydrolyzed to acetic acid and choline by the
enzyme acetylcholinesterase. The receptor
releases these products, which are then converted
back to ACh by other enzymes.
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More Chemistry of the Nervous
System
Nerve Poisons and the ACh Cycle
The following nerve poisons affect the ACh cycle:
Botulin is a powerful ACh antagonist. It blocks
the synthesis of ACh.
Curare, atropine, and some local anesthetics act
by blocking receptor sites.
Anticholinesterase poisons inhibit the enzyme
cholinesterase. © 2010 Pearson Prentice Hall,
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Inc.
More Chemistry of the Nervous
System
Organophosphorus
insecticides inhibit the
enzyme
acetylcholinsterase.
ACh builds up, causing
overstimulation of
muscles, glands and
organs.
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More Chemistry of the Nervous
System
Research on
organophosphorus
insecticides has allowed for
the development of powerful
chemical warfare nerve
poisons, such as tabun,
sarin, and soman.
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The Lethal Dose
The toxicity of substances is often quantified by
the LD50. LD50 stands for lethal dose for 50% of
a population exposed.
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The Liver as a Detox Facility
Through the use of enzymes, the liver is able to
detoxify many compounds through oxidation,
reduction, or coupling.
Sometimes the products of these reactions is
actually more toxic than the reactants.
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Chemical Carcinogens: Slow
Poisons
A carcinogen is a substance that causes the
growth of tumors. Tumors can be either benign
or malignant. Benign tumors grow slowly and
do not invade surrounding tissue. Malignant
tumors (cancers) grow rapidly and invade and
destroy neighboring tissue.
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Chemical Carcinogens: Slow
Poisons
What Causes Cancer?
The U.S. Occupational Safety and Health
Administration (OSHA) has a National
Toxicology Program (NTP). NTP lists
carcinogens into two categories: known human
carcinogens and reasonably anticipated to be
human carcinogens. The latter compounds are
structurally similar to known carcinogens. The
vast majority of carcinogens are naturally
occurring substances.
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Chemical Carcinogens: Slow
Poisons
What Causes Cancer?
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Chemical Carcinogens: Slow
Poisons
How Do Cancers Develop?
Genetics play a role.
Some carcinogens modify DNA, scrambling the
code for replication and protein synthesis.
Oncogenes seem to cause certain normal cells
to become cancerous cells.
Suppressor genes prevent the development of
cancers.
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Chemical Carcinogens: Slow
Poisons
Chemical Carcinogens
A variety of natural and synthetic chemical
substances are carcinogenic, including polycyclic
aromatic compounds, aromatic amines,
nitrosoamines, vinyl chlorides, heterocyclic
compounds, and epoxides.
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Chemical Carcinogens: Slow
Poisons
Anticarcinogens
Some substances in our food appear to act as
anticarcinogens including: the food additive
butylated hydroxytoluene (BHT) and antioxidant
vitamins A, C, and E. Diets rich in cruciferous
vegetables (cabbage, broccoli, Brussels sprouts,
kale, and cauliflower) have been shown to
reduce the risk of cancer.
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Three Ways to Test for
Carcinogens
The Ames test assumes
that most carcinogens are
also mutagens. It uses a
special strain of bacteria
that requires histidine. The
bacteria are incubated in a
medium with the suspected
carcinogen and without
histidine. If they mutate
and grow, the substance is
likely a carcinogen.
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Three Ways to Test for
Carcinogens
Animal testing
Suspected carcinogens can be tested on animal
populations such as rats or mice. Such tests are
expensive, and there may not be a strong
correlation to humans.
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Three Ways to Test for
Carcinogens
Epidemiological Studies
Epidemiological studies involve studying a
population of humans that show more than a
normal rate of cancer. The population is studied
to see if there are common factors that could
lead to cancers. Epidemiological studies have
concluded that cigarette smoking, asbestos
exposure, and exposure to vinyl chloride cause
cancer.
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Birth Defects: Teratogens
Teratogens are substances that cause birth defects.
Epidemiological studies have shown that a number of
substances are teratogens, including thalidomide,
isotretinoin (Accutane and anti-acne medication), and
ethyl alcohol. Ethyl alcohol is by far the most hazardous
teratogen in terms of the number of children affected.
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Hazardous Wastes
Hazardous wastes are substances that cause or
contribute to death or illness or environmental damage
when improperly managed.
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Hazardous Wastes
Hazardous wastes can be divided into four
categories:
1. Reactive wastes
2. Flammable wastes
3. Toxic wastes
4. Corrosive wastes
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Hazardous Wastes
Hazardous wastes can be dealt with by:
recycling, treatments to render them less
hazardous, incineration, or storage in a landfill.
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What Price Poisons?
The use of any substance includes potential
risks and benefits. Generally, it is the misuse of
chemical substances that leads to tragedy.
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