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Toxicology
Toxicology
Fig. 11-3
p. 230
• Toxicology is the
science that examines
the effects of poisonous
substances on humans and other organisms
• Any chemical substance may cause negative effects
if ingested in great enough quantities
– A toxicant in a minute enough quantity may pose no
health risks
Synthetic chemicals in the
environment
• Synthetic chemicals are made by humans and
there are thousands in our soil, water, and air
– 80% of US streams contain at least 82 chemicals
• Not all synthetic chemicals pose health risks,
and most are only found in minute amounts
Silent Spring
• In 1962, Rachel Carson
published the novel Silent
Spring
• This novel brought the perils of
DDT and other pesticides into
public consciousness
– It was written at a time when
chemicals were prayed over
residential neighborhoods on the
assumption that they could do no
harm to people
• The book helped to generate
significant social change, and
resulted in the subsequent ban
of DDT in the US in 1973
– DDT is still used in many
countries
Types of Toxicants
• Carcinogens—chemicals or types of radiation
that cause cancer
– Ex) the chemicals in cigarette smoke
• Mutagens—chemicals that cause mutations in
the DNA of organisms
• Teratogens—affect the development of
human embryos
– Ex) thalidomide: was used as a sleeping pill but
turned out to cause birth defects in single doses
Practice Question!
___________ cause birth defects while the
human embryo is growing and developing
during pregnancy
1) Mutagens
2) Carcinogens
3) Teratogens
4) Biogens
5) Hanta viruses
Types of Toxicants
• Allergens—overactivate the immune system
and cause an immune response when not
necessary
• Neurotoxins—assault the nervous system
– Ex) mercury, lead, and some chemical weapons
• Endocrine disruptors—interfere with the
endocrine system (makes hormones)
Endocrine Disruptors
• Hormones stimulate growth, development,
and sexual maturity, as well as regulating brain
function, appetite, sexual drive, etc
• Some toxicants disrupt an animal’s system by
blocking the hormones or accelerating their
breakdown
– Others mimic the hormone and block receptors
Endocrine Disruptors
• Ex) some chemicals cause feminization of
male animals by mimicking estrogen
– Many people think this is occurring in humans due
to chemicals found in our water and in plastic
products
Toxicants in surface water and
groundwater
• Runoff often carries
toxicants from large
areas of land
• Many chemicals leach
down into
groundwater and
contaminate drinking
water supplies
Airborne Toxicants
• Pesticide drift occurs when pesticides
are transported through the air and
may cause effects far from the site of
direct chemical use
Toxicants may accumulate in the food
chain
• Some toxicants are not easily broken down in
the body and build up in the body
– Some substances are stored in fat or muscle tissue
• Bioaccumulation refers to the process where
toxicants build up in an organisms
Toxicants may accumulate in the food
chain
• Biomagnification occurs when
the concentration of toxicants
increases each step up the food
chain
– Ex) the most famous example of
this occurred with DDT into birds;
this caused many species of birds
in the US to decline
Practice Question
In order for biomagnification to occur, a pollutant
must be
I.
Concentrated by producers
II.
Soluble in water
III. Long-lived
1) I only
2) I and III only
3) I and II only
4) II and III only
5) I, II, and III
Germ Resistance to
Antibiotics
 Bacteria’s high reproductive rate allows
these organisms to become genetically
resistant to an increasing number of
antibiotics
 The overuse of pesticides and antibiotics
has fostered this resistance
 Every major disease-causing bacteria
now has at least one strain that resist
common antibiotics
Case study on pesticides:
Bhopal, India
 On December 3, 1984 the
world’s worst industrial
accident occurred at a
Union Carbide pesticide
plant
 An underground storage
tank exploded and
released a large quantity
of toxic gas used to
produce pesticides
 600,000 people were
exposed and at least
22,000 died
 The company was found
to be at fault
Case Study: DDT
 DDT (dichloro-diphenyl-trichloroethane) was
discovered in 1874
 In 1939 it was developed as an insecticide
 In 1948 the inventor won a Nobel Prize
 DDT is a broad-spectrum insecticide, meaning
that it is toxic to many species
Case Study: DDT
DDT is extremely effective in killing mosquitoes
and stemming the spread of malaria
Case Study: DDT
 DDT has a long persistence time and
thus will stay in the environment for
extended periods (up to 15 years)—it
will be biomagnified
 In birds, DDT decreases the
reproductive rate by causing
eggshell thinning and embryo deaths
 In aquatic animals, DDT is highly
toxic
 In humans, DDT is a probable
human carcinogen, damages the
liver, temporarily damages the
nervous system, and damages
reproductive system
 Currently, DDT cannot be used in the
US, but it can be manufactured and
sold to other companies
Types of exposure affect responses
• Acute exposure occurs when a person
experiences high exposure for short periods of
time
• Chronic exposure occurs with lower exposure
over long periods of time
– This is harder to recognize as the effects show up
gradually
– Ex) alcohol abuse can cause liver damage,
pesticide residues on food can build up in your
body
Synergistic effects of toxicants
• Synergistic effects are the interactive impacts
that occur when toxicants are mixed together
– These may be more than or different than the
simple sum of their separate effects
• Ex) wild wood frogs will suffer deformities in
their limbs due to parasitic infection
– The infections are exacerbated when the frogs are
exposed to pesticides that weaken their immune
responses
Regulating toxicants
• The Food and Drug Administration (FDA) regulates
foods, food additives, cosmetics, and drugs and
medical devices
– Formed under the Food, Drug, and Cosmetic Act of 1938
• The Environmental Protection Agency (EPA) regulates
pesticides under the Federal Insecticide, Fungicide,
and Rodenticide Act (FIFRA) of 1947
– They also regulate chemicals not covered by other laws,
under the 1976 Toxic Substances Control Act (TSCA)
• The Occupational Safety and Health Administration
(OSHA) regulates workplace hazards
More details on the EPA
• The FIFRA was intended not to protect public
health and the environment but to assure
consumers that products actually worked as
their manufacturers claimed
– Later amendments changed the focus to
protecting health and charged the EPA with
registering each new pesticide
• TSCA directed the EPA to monitor around
75000 chemicals and requires screening of
substances