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Chemistry for Changing Times
11th Edition
Hill and Kolb
Chapter 20
Poisons
John Singer
Jackson Community College, Jackson, MI
© 2007 Prentice Hall
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.
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.
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 which poison their livestock.
Locoweed is one such plant.
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.
Acids are particularly damaging to the lungs,
where they can lead to the breakdown of lung
tissue.
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.
Poisons Affecting Oxygen
Transport and Oxidative Processes
Blood Agents
Carbon Monoxide (CO) binds tightly to the iron
in hemoglobin, preventing the transport of
oxygen.
Nitrate ions (NO3-), found in some foods and in
drinking water in some areas, is 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.”
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.
Make Your Own Poison:
Fluororacetic 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.
Heavy Metals Poisons
Many metals are toxic.
Heavy metals with densities
at least 5x greater than
water are especially so.
Most heavy metals display
their toxicity by reacting with
sulfhydryl groups (-SH),
deactivating enzymes.
Heavy Metals 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+.
Heavy Metals 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.
Heavy Metals Poisons
Cadmium
Cadmium is used in alloys, electronics,
and rechargeable batteries. Cd2+ ions
lead to loss of Ca2+ ions in bones. They
also cause severe abdominal pain,
vomiting, and diarrhea.
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.
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.
More Chemistry of the Nervous System
Organophosphorus
insecticides inhibit the
enzyme
acetylcholinesterase.
ACh builds up, causing
overstimulation of
muscles, glands, and
organs.
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.
The Lethal Dose
The toxicity of substances is often quantified by the LD50.
LD50 stands for lethal dose for 50% of a population
exposed.
The Lethal Dose
The larger the LD50, the less toxic the substance.
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
are actually more toxic than the reactants.
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.
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.
Chemical Carcinogens: Slow Poisons
What Causes Cancer?
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.
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.
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, E. Diets
rich in cruciferous vegetables (cabbage,
broccoli, Brussels sprouts, kale, and
cauliflower) have been shown to reduce
the risk of cancer.
Three Ways to Test for Carcinogens
The Ames test assumes
that most carcinogens are
also mutagens. It uses a
special strain of bacteria
that require 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.
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.
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.
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, an anti-acne
medication), and ethyl alcohol. Ethyl
alcohol is by far the most hazardous
teratogen in terms of the number of
children affected.
Hazardous Wastes
Hazardous wastes are substances that cause or
contribute to death or illness or environmental damage
when improperly managed.
Hazardous Wastes
Hazardous wastes can be divided into 4
categories:
Reactive wastes
Flammable wastes
Toxic wastes
Corrosive wastes
Hazardous Wastes
Hazardous wastes can be dealt with by
recycling, treatment to render less hazardous,
incineration, or storage in a landfill.
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.